FINAL REPORT

THREE-POINT BENDING DEVICE FOR FLEXURE TESTING OF SOFT TISSUES

TEAM 4

Michael Harman

Minh Xuan Nguyen

Eric Sirois

CLIENT CONTACT

Wei Sun, Ph.D.

Assistant Professor

UCONN BME and ME Department

Arthur B. Bronwell Building Rm. 203

Phone: (860) 486-0369

Fax: (860) 486-5088

E-mail: weisun@engr.uconn.edu

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TABLE OF CONTENTS

ABSTRACT ........................................................................................................................... 2

1.0 INTRODUCTION .................................................................................................................. 3

1.1 Background ..................................................................................................... 3

1.2 Purpose of the project ..................................................................................... 3

1.3 Previous work done by others .......................................................................... 4

1.3.1 Products ...................................................................................................... 4

1.3.2 Patent Search Results ................................................................................. 4

1.4 Purpose of the project ..................................................................................... 5

2.0 PROJECT DESIGN ................................................................................................................. 6

2.1 Optimal Design ............................................................................................. 10

2.1.1 Objective ................................................................................................... 10

2.1.2 Subunits .................................................................................................... 11

2.1.2.1 Motor System ............................................................................. 11

2.1.2.2 Mounting Bath ........................................................................... 13

2.1.2.3 Temperature Controller .............................................................. 15

2.1.2.4 Image Acquisition ....................................................................... 18

2.1.2.5 The Program, .............................................................................. 21

2.2 Prototype ...................................................................................................... 25

3.0 REALISTIC CONSTRAINTS .......................................................................................... 39

4.0 SAFETY ISSUES .......................................................................................................... 41

5.0 IMPACT OF ENGINEERING SOLUTIONS ...................................................................... 42

6.0 LIFE-LONG LEARNING ............................................................................................... 43

7.0 BUDGET ................................................................................................................... 44

8.0 TEAM MEMBERS CONTRIBUTION TO THE PROJECT ................................................... 45

9.0 CONCLUSION ............................................................................................................ 49

10.0 REFERENCES ............................................................................................................. 50

11.0 ACKNOWLEDGEMENTS ............................................................................................. 50

12.0 APPENDIX ................................................................................................................ 51

12.1 Updated Specifications .................................................................................. 51

12.2 Other Data .................................................................................................... 52

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ABSTRACT

This 3-Point Bending Device is intended to provide the user with a novel tool used to

obtain material property information for biological tissues. Specifically, the device provides the

user with the stress-strain relationship of the tested tissue in the low-strain region (<5% strain)

and provides the location of the neutral axis. The stress-strain relationship is useful because it

allows the user to predict the response of tissue to an applied load. The location of the neutral

axis is important because it allows the user to estimate the contributions of different layers in a

multi-layered tissue specimen. No patented device or device described in the literature is

capable of carrying out both of these functions.

In addition to the primary functions of the device, secondary capabilities are included to

maximize the validity and repeatability of the data provided to the user. One secondary

function is to provide a stable, physiologically appropriate environment for testing. The other

secondary function is to allow for convenient calibration of the force-measuring system.

The 3-Point Bending Device works by submerging a tissue test specimen in into a bath

containing a phosphate-buffered normal saline solution maintained at a pH of 7.3 and a

temperature of 37° ± 1° C. The temperature is maintained by circulation of water through a

separate outer bath containing a heating element. The tissue is deformed by the application of

a small force generated by rotation of a stepper motor coupled through a stage to a bending

bar. The bending bar acts upon the tissue and the actual force applied is calculated by the

bending bar’s distance from a reference bar. The reference bar is also moved by the translation

of the stepper motor rotation, but does not interact with the tissue specimen. The change in

distance between the two bars is a direct result of the force of the tissue on the bar. Because

the bending bar is a homogeneous, linearly elastic material, this displacement can be correlated

with an applied force. The correlation is experimentally derived by the device prior to each

experiment using a convenient built-in bending bar calibration feature. On the side of the

tissue opposite from the bending bar, two stationary posts are used to hold the tissue in place

such that all deformation is due to bending. The deformation of the tissue and displacement of

the bending bar are monitored using a CCD camera mounted above the testing bath. The CCD

camera is capable of resolving markers placed on the tissue as small as 10 microns in diameters.

The 3-Point Bending Device features a custom-designed LabView program capable of

controlling system hardware, interfacing with the user, and performing the complex

calculations required to provide information about tissue mechanical properties. The hardware

controlled includes output to the stepper motor for movement, output to the heating element

for heat generation, input from the CCD camera for marker tracking (both in test mode and in

calibration mode), and input from the resistance temperature detector for control of the

heating element. Through a series of calculations, the program is able to output to the user

several data items, including force vs. displacement, stress vs. strain, stress vs. strain rate,

moment of inertia vs. time, location of the specimen’s neutral axis, and test bath temperature.

Should a need be identified, the software could also be reconfigured to include any other

combination of this data either in relation to another variable, or in relation to time elapsed.

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1.0 INTRODUCTION

1.1 Background

An understanding of the mechanical properties of soft tissues can lead to better

comprehension of tissue pathologies and how the tissue reacts, mechanically, towards an

implant. Because the mechanical properties, such as stress, of soft tissues cannot be measured

directly in vivo, finite element method will be required to accurately estimate the stress

distribution and simulate the interactions between the implant and host tissue. This requires

comprehensive and accurate quantitative information on tissue material behavior.

Experimental testing is, thus, necessary to provide data for the quantification and

characterization of soft tissues. This can usually be accomplished through tensile mechanical

testing, such as uniaxial or biaxial testing. Uniaxial testing involves loading of a tissue specimen

in one direction, whereas biaxial testing is loading of the specimen in two axes. Tensile

mechanical testing, however, is limited in that it cannot provide accurate quantification of the

mechanical behavior of soft tissues in the low strain region and with different layers of fibers.

Flexure testing, on the contrary, is an effective method of evaluating the force-deformation

relationship of different layers of soft tissues. It can complement tensile mechanical testing

with its ability to measure the mechanical behavior of soft tissues experiencing very little stress

and strain.

1.2 Purpose of the Project

The client and his research team in the Biomechanics Lab are currently

conducting studies on the mechanical properties of various soft tissues, primarily heart valves.

Their lab contains a biaxial testing machine, which is frequently used to determine the stress

and strain response of tissues. Data collected via biaxial testing are fundamental in quantifying

and validating the nonlinear elastic, anisotropic nature of the tissues. Biaxial testing, however,

is limited because it treats the test specimen as a homogeneous material. Soft tissues, such as

blood vessels and heart valves, are heterogeneous and consist of multiple layers of fibers

arranged in different networks. When biaxial testing is performed on the leaflet, the collected

data is unable to indicate how the different layers of the leaflet response to the applied load

because, as previously mentioned, the leaflet is treated as homogeneous.

Thus, the client has requested for the construction of a three-point bending device

capable of performing flexure testing on soft tissues. Flexure testing is capable of rendering the

different layers of soft tissues to deformed by different amounts in different regions, which is

essential and critical in analyzing the effect of applied loads on the different layers of the tissue.

Furthermore, since soft tissues have very low bending stiffness, flexural deformation provides a

sensitive approach to evaluating the mechanical properties of the tissue, especially in the low

strain range, which is often very difficult if using tensile mechanical testing.

Therefore, the purpose of the project was to design and construct a three-point bending

device capable of flexural testing of soft tissues. This device is able to compute the flexural

rigidity, bending stiffness, transmural strain, and transverse shear stiffness of a soft tissue

specimen. It is run and controlled by a computer program that has been written specifically for

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the device. The program allows the user to apply a load to a tissue specimen submerged in

saline solution at body temperature. The deformation of the tissue is tracked by a high

resolution camera and computed, along with the amount of load applied, by the program. The

data collected is used by the program to calculate the flexure rigidity, bending stiffness,

transmural strain, and transverse shear stiffness.

1.3 Previous Work Done by Others

There are a couple of three-point bending devices that are similar to the current

project that have been built previously by others. These devices are available in university

laboratories and are usually constructed by researchers of the labs for their research needs.

For example, in the Bioengineering Lab at the University of California in San Diego, there is a

soft tissue bending device consisting of a muscle bath, a system to apply and control force, a

force-measuring system, a deformation-measuring system, and a photographic system. A force

is applied to the tissue by a thin stainless steel wire. The wire is clamped at the top and free at

the bottom, and it is deflected when a dead load is applied at the free end. The deflection of

the wire is used to measure the force acting at the tip on the tissue. In addition, at the Tissue

Mechanics Lab at the University of Miami, there is also a three-point bending device that

utilizes a thin bar of a known, homogenous material to apply force to a soft tissue in cantilever

bending. A specimen is held in place between two stationary posts an adjustable distance

apart, and the force is applied to the center of the specimen. All tests are recorded on a high-

resolution CCD camera. These two devices are similar to the current project and many features

of their design and construction have been used towards the implementation of the project.

1.3.1 Product

A product search for three-point flexure test device did not yield many

results in the market. There is a three-point flexure test device for ampoules from Zwick Roell

Co. This universal device is able to measure the predetermined breaking strength at the break

ring of pharmaceutical ampoules. It can be adjusted to the various geometries and sizes of the

ampoules with the help of distance shims and movable bending bearings. The device is

designed for a nominal force of 500 N. Although this device is capable of performing flexure

testing, it can only test on ampoules and measure the breaking strength. The design of this

device is different from the current project as the current project requires very small, precise

bending of soft tissues and also tracking of the displacement of the tissues.

1.3.2 Patent search results

A patent search on the website http://patft.uspto.gov/ for “three-point

bending device” yielded one result that is irrelevant to the current project. A search for

“bending device” on the same website yielded 1156 results ranging from bending devices use

for solid materials to devices use for wires and a variety of other materials.

Patent number 7,283,891 invented by Werner Butscher, Friedrich Riemeier, Ru Rubbert,

Thomas Weise, and Rohit Sachdeva involves a robotic bending apparatus for bending

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orthodontic archwires and other elongate, bendable medical devices. The device consists of a

robot comprised of a six-axis bending robot with gripping tools and a movable arm that can

move about three translational axes and three rotational axes. This device is suitable for use in

a precision appliance-manufacturing center.

Patent number 7,275,406 invented by Teruaki Yogo is a bending device which includes a

fixed mount having a chuck mechanism gripping workpiece and an articulated robot which

moves a bending mechanism. The workpiece is clamped between a bending die and a clamping

die. The bending and chuck mechanisms are moved by the articulated robot to bend the

workpiece at a plurality of positions.

Although there are a variety of bending devices, none of the patented devices are

similar to the current project. Thus, it can be safely concluded there are currently no patented

three-point bending device for flexure testing of soft-tissues.

1.4 Map for the Rest of the Report

The rest of the report will focus primarily on the design of the project, the

realistic constraints and safety issues, the budget, and others. In the project design, a brief

overview will be given about what the device should at least be able to do, how the device was

implemented, what subunits were used, and how the subunits and the whole device was

tested. The project design will described succinctly each of the three alternative designs

proposed for this device and the advantages and disadvantages of each in terms of complexity,

functionalities, and cost-efficiency. From the advantages and disadvantages of each alternative

design, an optimal design was proposed which makes use of the best characteristics all three

alternative designs and minimizes their disadvantages. The project design will described the

optimal design in great detail along with the parts and subunits that will be used to implement

the design. In addition, the project design will also describe the finished prototype and its

operations.

Subsequently, the report will concentrate on constraints and safety issues associated

with the device. The constraints included environmental constraints, manufacturability,

sustainability, ethics, and health and safety. The constraints section will described in depth

each of these constraints, how they affect the overall design of the device, and how they will be

resolved. Furthermore, safety is always the main concern of any product design. Thus, this

report will also address some of the safety issues associated with the device and how the

device was implemented such that these issues are minimized.

One of the most important aspects of product design is budget. This report will clearly

address the budget allowed for this project and how the budget was allocated to each subunit.

In addition, the report will also include a timeline for the project.

The rest of the report concerns with impacts of engineering solution, life-long learning,

and contributions of each team member. Impacts of engineering solution describes how some

of the engineering features associated with the device help solve, on a smaller scale, simple,

every day problems and, on a larger scale, global and societal issues. Life-long learning explains

how working on this project help enhance the team’s understanding of engineering. Finally,

the contributions of each team member are also listed in this report to show some of the work

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each team member had done towards this project and how he or she helped in improving and

making the team stronger and better.

2.0 PROJECT DESIGN

In order to simplify the construction of the device, the device is divided into multiple

systems: the mounting bath system, the force application system, the temperature controller

system, the image acquisition system, the calibration system, and the program and interface

system. The purpose of the mounting bath system is to provide an area where flexure testing

of the tissue can occur. It is used to hold the solution, the tissue specimen, and the two posts.

The purpose of the force application system is to use a bending bar to apply a force to the

tissue to make it bends. The system consists of a bending bar, a reference bar, and a motor

unit. The motor unit is attached to the bending bar, such that when the motor rotates, the

bending bar will move linearly in one axis. The temperature controller unit is used to maintain

the 37° ± 1° C temperature of the solution. It is consisted of flow loops, a power unit, a

centrifugal pump, a heater, contact plates, and a temperature recorder. The image acquisition

system is used to track markers on the tissue while flexure testing is performed. It is consisted

of a CCD video camera and a camera mount. The CCD video camera captures images of the

tissue while it is being tested and transmits the images to the computer. The calibration system

is used to calibrate the bending bar. The calibration system consists of the CCD video camera,

known weights, and the bending bar. The known weights are attached to the bending bar, and

the displacement of the bending bar for each known weight is tracked by the camera. This will

create a calibration curve for the bending bar, such that a load can be determined from a

known bending-bar displacement using the calibration curve. Finally, the program and

interface system is used to connect all the previously-mentioned systems together. The

interface provides a display where the user can control and interact with the device. And the

program controls the functioning of all the systems according to the user’s commands. In

addition, the program also performs all the necessary calculations using the data obtained from

all the systems. Table 1 below gives a summary of all the systems, their functions, and the parts

they contained.

To construct a device that is easy to use and maintain, safe, cost-effective, and has all

the required functionalities, several ideas were proposed (see Alternative Designs Report). The

first of which consists of a movable testing platform within a mounting bath, as shown in Fig. 1.

The advantages of this design are only one motor is needed to move the platform and the

bending bar and reference bar can remain stationary. On the contrary, the disadvantages are

tracks have to be placed inside the mounting bath and wheels have to be attached to the

platform. This creates unnecessary frictional forces due to the wheels rubbing against the

tracks. Moreover, this system also requires that the flow loops have to be flexible and move

with the platform in order for the solution inside the platform to move in and out (Fig. 2). This

is also a major disadvantage of the system because movable flow loops are very inefficient and

their sustainability will be limited due to fatigue at the sections that continuously move back

and forth.

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Table 1: Summary of all the systems, their functions, and associated parts.

Systems Functions Parts

Mounting Bath Provide an area for testing

Hold the solution and the tissue specimen

Mounting bath

Two posts

Force Application Apply a force to the tissue

Bending bar

Reference bar

Motor unit

Temperature Controller Maintain the 37° ± 1° C of the solution

Flow loops

Power unit

Centrifugal pump

Heater

Contact plates

Temperature recorder

Image Acquisition

Track images of the tissue and resolve

markers on the tissue while it is being

tested

CCD video camera

Camera mount

Calibration Calibration the bending bar to create a

load-displacement calibration curve

CCD video camera

Bending bar

Known weights

Program and Interface

Provide an interface for the user

Control all the functioning of the device

Perform all necessary calculations from

collected data

Computer

LabVIEW program

Matlab program

The second design idea was to have a movable bending bar while the platform

consisting of the two posts remains fixed (Fig. 3). The advantages of this design are there is no

need for the platform inside the mounting bath – thus, saving time and money – and the flow

loops can remain stationary. The primary disadvantage of this design is, unless the CCD camera

can focus on the whole test area (i.e., the area of the maximum displacement of the tissue) and

clearly resolve each markers on the tissue, the camera will have to move as the bending bar

moves to keep the markers on the tissue in view. This will tremendously complicate the design

because a second motor will be needed to move the camera, and the movement of the camera

has to be rigorously controlled in order for it to move simultaneously and exactly with the

movement of the tissue.

The third and last design idea was to move the two posts, to which the tissue specimen

is fixated, and keep the bending bar stationary. The advantage of this design is a similar version

of it has been built and shown to work by a notable research group, see [2]. Moreover, this

design also allows the measurement of the transmural strain of the tissue without the need for

complex automation controls and image-control feedback to move the camera. A notable

downside of this design, however, is that the stationary region near the bending appears to be

a stress concentration point when a mock-up of the system is analyzed using finite element

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software (Fig. 5). Such stress concentrations are known to mask the true tissue stress-strain

response.

Fig. 1 – Cross-sectional side view of mounting bath

Fig. 2 – Side view of mounting bath

Mounting

Bath

Tissue

Bending Bar

Posts

Reference Bar

Motor Fig. 3 – Cross-sectional side view of mounting bath and motor

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Fig. 4 – Sketch of three-point bending apparatus taken from [2]

Fig. 5 – Finite element analysis of the 3-point bending system. The region of peak stresses is

highlighted, which is also the region of least tissue radial movement in this design, and thus the

region used for transmural strain measurement

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After careful deliberation of all three alternative designs, it was decided that the second

alternative design offers the best design ideas in terms of least complexity, cost-effectiveness,

and functionality. Additionally, this design can use ideas proposed in the other two alternative

designs to further improve and enhance its capabilities and functioning. Figure 6 shows a

schematic of the complete system.

2.1 Optimal Design

2.1.1 Objective

The client has requested the development of a 3-point bending device

similar to two devices described in previous literature. The current device will, however, be

entirely original and take advantages of advancements in automation and image acquisition to

provide the user with the most accurate results possible. The device must be capable of

bending a tissue specimen and outputting to the user strain measurements in the low strain

region (<5%) and the location of the neutral axis. The device must also allow for accurate and

repeatable data collection by providing a closely controlled environment for the specimen

during the testing procedure.

Force Application. The device must be capable of applying an appropriate load to cause

small bending deformation of a tissue specimen. This will require extremely small magnitude

loading. Since accurate measurement of such small loads would require costly load cell

equipment, the client has requested that measurement of applied force instead be measured

by comparing the displacement of a material of known mechanical properties. In practice, this

will mean that the bar (described below in Section 2.2) applying load to the tissue be operating

within its linear stress-strain region, and the Young’s Modulus of this region determined via a

calibration procedure. The device must be equipped to carry out this calibration procedure as

well as the actual tissue bending.

Strain Measurement. The device must be capable of imaging tissue displacement and

calculating the instantaneous effective modulus for the tissue’s stress-strain response. This

modulus should be output to the user graphically and made available numerically for data

collection purposes. The time rate of change of the modulus itself should also be calculated

and output to the user.

Neutral Axis Determination. The device should have high enough resolution to image

tissue deformation in a very small region such that local tissue strain can be observed. This will

allow for the measurement of strain as a function of position through the tissue thickness. The

device should track markers as small as 2µm and output the location of the neutral axis to the

user.

Environmental Controls. The device should allow for accurate and repeatable data

collection by providing the tissue with a physiologically appropriate environment. This

environment must include chemical and thermodynamic components. Chemically, the tissue

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must remain submerged at all times in a phosphate-buffered normal saline solution with a pH

of 7.4. Thermodynamically, the bath must be maintained at 37 0C. The device should be

designed to minimize time of testing, which will minimize inaccurate data due to tissue

degradation.

Figure 6 below shows a schematic of the overall device.

CPU

Monitor

Camera Stand

Motor

Motor Thread

CCD Camera

Motion Controller

Bending Bar

Tissue

Posts

Mouting Bath

Temp. Recorder

Flow

Centrifugal PumpHeater

Contact Plates

Power Supply*Not drawn to scale

Fig. 6 – Schematic of the overall device

2.1.2 Subunits

2.1.2.1 Motor System

The motor system consists of a National Instrument (NI) NEMA 17

stepper motor, a Thomson’s Baseline WB linear drive from Danaher Motion, a NI P70360

stepper drive, a NI PCI-7332 motion controller, and SH68-to-SH68 pin cable. Table 2 below

summarizes the parts in the motor system and their functions. Basically, the motor will be

connected to the stepper drive, and the stepper drive will be connected, via the cable, to the

motion controller, which will be installed to the CPU. The motion controller receives user

commands from the computer (i.e., the LabVIEW program) and transmits the commands to the

stepper drive. The stepper drive, in turn, translates the command signals into current that

causes rotation in the motor. The motor will also be attached to the linear drive. Rotation of

the motor will cause the stage on the linear drive to move linearly in one axis. Motion of the

linear drive translates into motion of the bending bar, resulting in movement of the bending bar

back and forth. Figure 7 below shows a general schematic of the motor system.

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Table 2: Summary of the parts in the motor system and their functions

Parts Manufacturer Images Functions

NEMA 17 Stepper

Motor NI

Receive current from

stepper drive and rotate

Cause linear drive to move

WB Linear Drive Danaher

Motion

Move linearly in one-axis

Cause bending bar to move

P70360 Stepper

Drive NI

Receive signals from

motion controller

Convert signals to current

causing motors to rotate

PCI-7332 Motion

Controller NI

Receives user commands

from computer

Transmits commands to

stepper drive

SH68-SH68 Cable NI

Connect stepper drive and

motion controller

Fig. 7 – Schematic of the motor system

The NEMA 17 stepper motor has up to 80 oz-in of holding torque and 1.8 degree of

resolution. Since the motor is only used for rotating and translating the rotation to linear

movement of the linear drive, torque is not an important aspect of the motor. The resolution

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of the motor determines how many steps per revolution the motor is able to rotate. A 1.8

degree resolution means that the motor is able to move 1.8 degrees per step, resulting in 200

steps per revolution. The specification of the linear drive includes a maximum linear speed of

250/1000 mm/s or 0.25 mm/s. The linear speed of the drive in conjunction with the resolution

of the motor determines the velocity of the linear drive per revolution of the motor. Thus, one

revolution of the motor will move the linear drive 0.25 mm/s.

The PCI-7332 is a stepper motor controller which provides fully programmable motion

control for up to two independent or coordinated axes of motion. The 7332 motion controller

can be used for point-to-point and straight-line vector moves for stepper motor applications,

which is completely suitable to perform the linear movement function required in this project.

It accepts real-time commands from the user, and converts the commands into stepper pulses

to be transmitted to the stepper drive. The stepper drive, then, accepts full step pulse

commands from the controller and inserts fine micro-steps to smooth coarse low speed motion

via current flow to the motor. The P70360 provides 2.5 A of continuous current and 3.5 A peak

current output to the motor. The advantage of using the P70360 is its capability of current

reduction. This means that if the user does not require the motor’s full torque to hold a load at

rest, the user can select the right amount of current to reduce the motor heating and power

consumption. This will tremendously increases the life of the motor system.

2.1.2.2 Mounting Bath

The mounting bath system is the central testing platform of the

entire three point bending device. All the other systems are located around and function from

the mounting bath. It is a simple, yet critical aspect of the device design that could essentially

determine the success of the overall project. Without a properly designed mounting bath

everything from the tissue fixation to the testing measurements will be at risk. The mounting

bath itself is composed of two main components.

The first constituent is the inner bath. This inner bath will hold a phosphate buffered

normal saline solution and two stationary fixation posts. The fixation posts in this design are a

specific distance apart, but if possible it would be advantageous to make this distance

adjustable for different size tissue samples. One of the fixation posts will have a removable

sleeve to attach to one end of the tissue sample to create frictionless movement under loading.

The other end of the tissue will lie against the opposite fixation post during bending. The

bending bar and reference bar will move between these fixation posts during testing while the

CCD camera is above capturing the movement. The saline solution inside of the inner bath will

be heated by the water that is being pumped around it.

The second main section is the outer bath. The outer bath will include an inlet and

outlet so that temperature controlled water may be pumped through it at a desired rate. The

outer bath will be larger so that the inner bath can rest inside of it. There will be four posts

located on the base of the outer bath for the inner bath to rest on top of, thus creating more

surface area below the inner bath for heat transfer to the saline solution.

The entire bath will be machined using sheets of Lexan. Lexan is a highly durable

polycarbonate resin thermoplastic that was chosen for its extreme resistance to corrosion and

strength. Lexan is readily available and easily machineable, therefore making it an ideal choice

for material. The exact dimensions and spe

Fig. 8

strength. Lexan is readily available and easily machineable, therefore making it an ideal choice

for material. The exact dimensions and specifications of each part can be seen in Fig. 9 below.

Fig. 8 – Top view of mounting bath with labeling

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strength. Lexan is readily available and easily machineable, therefore making it an ideal choice

cifications of each part can be seen in Fig. 9 below.

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Fig. 9 – Schematic of mounting bath with dimensions

2.1.2.3 Temperature Control System

The principle function of the temperature control system is to

maintain the temperature of the test specimen within physiological bounds. Maintaining this

temperature range will minimize the variance of data collected using the device from one test

run to another. The optimal temperature band for living tissue has been determined to be

37+/-1 oC. This subsystem will be responsible for maintaining the water in the vicinity of the

test specimen within this temperature band.

The in direct contact with the test specimen is in fact in contact with excised tissue. This

fluid is thus potentially contaminated with hazardous or harmful microbial growth. To minimize

the spread of microbial growth, this fluid has been kept to as small a volume as possible.

Specifically, the device has been designed using a “bath within a bath” concept, where the

inner bath contains the test specimen and the outer bath does not. This system has the added

benefit of requiring fewer chemicals for maintenance of salinity and pH (Section 2.2) because

only the inner bath need be maintained as a constant environment for the tissue. This design

also prevents the water circulation pump from coming in contact with high salinity water, which

is corrosive and would inevitably lead to shortened pump life (or much more expensive

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corrosion-resistant materials). The two baths will from this point on be referred to as the inner

and outer baths.

One downside of the two bath system is that direct mixing of fluid would provide for

much more efficient heat transfer. In this configuration, the outer bath fluid flows against the

inner bath wall and transfers heat into the wall. The heat is transferred through the wall and

into the inner bath fluid. This system is less efficient that the direct mixing alternative, but the

potential benefits of the two bath system have been deemed more significant.

To maintain inner bath temperature, heat must be added into it. Setting up a control

volume around the inner bath, all directions of heat transfer can be seen (Fig. 10). On the five

sides of the inner bath that are in contact with the fluid of the outer bath, convective heat

transfer occurs between the moving outer bath fluid and the inner bath’s outer wall. The

convective heat transfer equation is:

�� �� � ����� ����

In the above equation, �� ��is the convective heat transfer into the control volume, h is the

convective heat transfer coefficient, A is the surface area upon which the fluid is acting, TOBF is

the temperature of the outer bath fluid, and TIBOW is the temperature of the inner bath’s outer

wall. The total energy transferred into and out of the control volume is the sum of the fluxes

across each face, or:

����� � � �� ���

���� �����

The system is assumed to be in steady state, so the net flux (�����) is equal to zero. Also

acting on the control volume of the inner bath is the outbound flux, or the radiant heat transfer

of the inner bath water into the surrounding ambient air. This form of heat transfer follows the

equation:

����� � ������ ����

In the above equation, ����� is the free convective heat transfer out of the control volume, h

and A have the same meaning but potentially different values, TIBF is the temperature of the

inner bath fluid, and Tamb is the ambient air temperature.

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Fig. 10 – Side view of the inner bath. Here the inner bath is taken as a control volume for

energy balance analysis. On each of the five faces in contact with the fluid of the outer bath

(larger blue arrows, with two sides not shown) forced convective heat transfer occurs from the

fluid of the outer bath into the wall of the inner bath. On the top surface of the inner bath, the

inner bath fluid loses heat via free convection to the ambient air. Note that other heat input

sources, such as friction from tissue movement and radiant losses, are negligible compared to

other sources and are thus not described here.

There remains one step in the transfer of heat for this particular control volume. The

heat transfer through the inner bath wall is conductive heat transfer, and follows the equation:

��� � � !��� ����" #

In the above equation, ���is the conduction heat transfer from the outer wall of the inner bath

to the inner wall of the inner bath, κ is the thermal conductivity, A is again the area of the wall

in question, TIBOW and TIBIW are the temperatures of the inner bath’s outer and inner wall

surfaces (respectively), and t is the thickness of the wall.

Combining the conduction and convection equations, it was possible to determine the

required temperature of the outer bath, as well as the flowrate in the outer bath (this goes into

the determination of h). The same process was repeated for the outer bath, taking losses to

ambient air and losses into the inner bath’s outer wall as heat sinks, and taking heat in from a

heating element as the heat source. This gave us the required capacity of the heat source,

which was determined to be (including safety margin) 1000 watts. Additionally, the required

capacity of the pump was determined from the calculated flowrate. Since it was assumed that

the pump would be at the same elevation as the bath system and the bath is open to ambient,

pump flow rates against no backpressure were used. The required pump capacity was

determined to be (including safety margin) 5 L/min.

Free Convection

Heat Transfer to air

Inner Bath

Lh

Water

Level

Forced

Convection

Forced

ConvectionForced

Convection

18

The pump has been designed to operate continuously, supplying water to the outer

bath. The pump will be powered by single phase 120v power from a standard electrical outlet.

The pump draws suction from a return line which is also connected to the outer bath. To match

pump outlet size, the inlet and outlet pipes are ½” inner diameter. The loop containing the

pump will contain three valves, including inlet and outlet pump isolation valves to allow for

pump removal or system isolation, and a drain valve to allow for efficient draining of the

system. The pump inlet and outlet lines will also be equipped with a recirculation line to allow

the pump to safely run even when the pump’s outlet valve to the outer bath is shut.

The heating element has been designed to operate intermittently. When in operation,

the heating element receives single phase 120v power from a standard electrical outlet. When

not is operation, the heating element receives no power. This operation will be carried out via

a temperature feedback loop. A resistance temperature detector (RTD) will be used to record

inner bath temperature. The output temperature from the RTD will be taken as in input into

the controlling LabView program. The program will monitor the current temperature. When

inner bath temperature falls below the acceptable operating band (36oC), the program will send

a signal to close a set of contacts, which will allow input power to reach the heating element.

When temperature reaches the high end of the operating band, the contact will be opened and

the heating element will lose power. The program will also provide high and low temperature

alarms to warn the operator that data obtained may not be reliable. A separate manual

thermometer will also monitor inner bath temperature for redundancy.

The combined temperature control system can be seen below in Fig. 11.

19

Fig. 11 – Schematic of temperature control system. Note that the walls of the inner bath have

been omitted for the sake of clarity.

2.1.2.4 Image Acquisition System

The flexibility and accuracy of the image acquisition system

represent the heart of the device’s capabilities. This system is responsible for gathering

location information for several key components: the bending bar, the reference bar, the two

fixed posts, the inner and outer edges of the specimen (for thickness), and the test specimen

itself in many specific regions. The imaging system is also responsible for bending bar

calibration, which is a crucial component in force determination (and in the subsequent stress

calculation).

A high resolution CCD camera will be used to track the positions of the desired

components in real time. The positions will be defined for the benefit of the user as marker

20

beads or ink, depending upon the application. The beads will be glued on micro-fragments of

crushed stone (Fig. 12a) and the ink will be sprayed on in microdots as small as 2 µm in

diameter (Fig. 12b). Markers will be applied to the bending bar, the reference bar, each of the

two stationary posts, and at as many points in the field of view on the test specimen surface as

possible.

Fig. 12 – Markers used for location tracking, including a) glued on micro-beads and b) sprayed

on ink microdots.

The CCD camera must be capable of resolving the smallest of microdots, which are

predicted to be 2 µm in diameter. This specification is called spatial resolution, in µm/pixel.

Additionally, the maximum previously recorded tissue displacement for this three-point

bending test was 2 mm. Allowing a safety margin, the field of view in the y-direction was thus

taken to be 4 mm. The boundary in the horizontal direction should be wide enough to

encompass the two stationary posts. If this x-direction distance was chosen to be wider, then

more representative data would be obtained using the device. As a trade-off though, a wider

view area resulted in more total pixels and thus a much more costly CCD camera. Common

pixel field values give one direction to be 2/3 of the other direction, so for the least costly

version of a CCD camera with a spatial resolution of 2 µm/pixel that would still meet device

specifications would be a 4 mm by 6 mm field. The number of pixels in each row (Nx) and

column (Ny) would thus be:

$� � % &'()*"'+, -),."�/01"'1- ()/+-2"'+,

$3 � 4 &'()*"'+, -),."�/01"'1- ()/+-2"'+,

The relationship between distance and spatial resolution can be seen below in Fig. 13. Also, the

total pixel count (PC) could be determined by the following equation:

21

PC = Nx * Ny

Fig. 13 – Visualization of field distances and spatial resolution used in pixel determination

For the above example where the x-direction was 6 mm, the y-direction 4 mm, and the spatial

resolution was 2 µm/pixel, PC was determined to be only 60 kPix. The ideal dimension for x-

direction is, however, 30 mm (giving a y-direction value of 20 mm). Using the same spatial

resolution, this would require a pixel count of 150 MPix. Clearly, the best option lies between

the two bounding scenarios. The price of the CCD camera drives the final selection though, and

exact price quotes are still pending at this time.

One additional feature of the imaging system will be its role in stress calculation. The

final objective of the device is to output the stress-strain relationship of the test specimen to

the user. The imaging system will calculate strain by tracking displacement (of markers, as

mentioned above), but it will also be largely responsible for the calculation of stress. Stress

calculation will be derived from the imaging system in two specific ways: bending bar

displacement due to the tissue’s resistance and bending bar Young’s Modulus.

The bending bar displacement will be computed by tracking the positions of the tips of

both the bending bar and the reference bar. Since their movements are coupled mechanically,

any difference in their relative distance is due solely to reactionary force of the tissue against

the bending bar. This displacement can be converted into force by using the second imaging-

force subsystem, calibration.

Before each test run (this may be extended based on the observed changes in

calibration from one run to another during pilot trials, but for now the most conservative

option is being applied) a calibration of the bending bar to be used will be carried out. The

calibration procedure consists of observing the bending bar in a zero state condition and then

applying a known load and observing bending bar displacement. By accounting for bending bar

X-direction distance

Spatial Resolution

22

cross-sectional area, the stress-strain relationship for the bar can be calculated. Since the

bending bars will be metallic, they will have a linear stress-strain relationship over the elastic

region. As long as the known load caused elastic deformation, the slope of the line drawn

between the stress-strain pairs (0,0) and (measured strain, measured stress) is the Young’s

Modulus for that specimen.

Specifically, to carry out the calibration procedure with minimal system reconfiguration,

the CCD camera will be mounted such that it can swivel 90 degrees and lock in place in either

the test position or the calibration position. The test position will be down and the calibration

position will be parallel to the table-top. The bending bar will be mounted into a clamp at a

height even with the viewing field of the CCD camera. The bar will then be loaded with the

known load, which will be a weight appropriately sized for that particular bending bar. The

weight will be tied with fishing line to the end of the bar and allowed to pull downward due to

the gravitational force. The resulting displacement will yield a Young’s Modulus as described

above. When the bending bar is loaded by the test specimen, the displacement can be

converted into strain and the strain cross-referenced to find the corresponding stress value.

This stress value can be mathematically equated back to force as long as the cross-sectional

area of the bending bar is known (and it is because it was already determined during the

calibration step).

The entire imaging system can be seen below in Fig. 14.

Fig. 14 – Schematic of camera system. Note that the walls of the inner bath have been omitted

for clarity.

2.1.2.5 The Program

A program will be specifically written to integrate all the

hardware, give the user full control over all the functioning of the hardware, and perform all

23

the necessary calculations. Writing the program will require the use of the following software:

NI LabVIEW 8.5, Measurement and Automation 4.3, Motion Assistant, Vision Assistant 8.5, and

Matlab. The Measurement and Automation (MAX) program will be used to configure all the

connected hardware. Briefly, it detects all the hardware that is connected to the computer – in

this case, the motion controller, the CCD camera, and the temperature controller. It, then,

gives each piece of hardware a unique identity which can be used by the LabVIEW program to

communicate with that specific piece of hardware. For example, the motion controller

connected to the computer will be identified by the software as having board ID number 1.

This number will be unique only to the motion controller and will not be used to identify any

other hardware. The LabVIEW program will use this board ID number 1 to communicate only

with the motion controller. MAX will be used extensively throughout this project to manage

and configure all the hardware.

National Instrument Motion Assistant is a stand-alone prototyping tool used to quickly

develop motion applications. It is used to graphically construct, preview, and test motion

applications without writing code. It can also create usable LabVIEW code that can be used to

build stand-alone applications or add to other LabVIEW applications. Motion Assistant will be

used in this project to configure, precisely, the movement of the motor such that it will move

linearly in one axis and at user-determined speed and direction.

Vision Assistant is a National Instrument image processing software. It allows the user

to quickly and easily process an image to the desired image quality and construct usable

LabVIEW code to be integrated into the LabVIEW program. Vision Assistant will be used to

process the images captured by the CCD camera in order to resolve and track the markers on

the tissue. Table 3 below shows some of the main processing functions that will be used to

process the images and track the markers on the tissue.

Table 3: Summary of processing functions

Processing Functions Purpose

Brightness Alter the brightness, contrast, and gamma of

an image

Threshold

Segment pixels in grayscale images

Isolate pixels that are of interest and set all

other pixels as background

Convert an image from grayscale to binary

Filter Smooth, sharpen, transform, and remove

noise from an image

Morphology

Prepare particles in the image for quantitative

analysis, such as finding the area, perimeter,

or position

Particle Analysis Analyze particles and display all of the

measurement results

LabVIEW is short for Laboratory Virtual Instrument Engineering Workbench. It is a

powerful and flexible graphical development environment that uses a graphical programming

24

language, known as G programming language, to create programs relying on graphical symbols

to describe programming actions. LabVIEW programs are called Virtual Instruments, or VIs.

LabVIEW consists of a front panel and block diagram of LabVIEW. The front panel window is

the interface to the VI code. The block diagram window contains program code that exists in a

graphical form. The front panel contains various types of controls and indicators, or inputs and

outputs, respectively. The block diagram contains terminals corresponding to front panel

controls and indicators, as well as constants, functions, subVIs, structures, and wires that carry

data from one object to another [6]. Figure 15 shows an example of a motion controller code

that was recently constructed in LabVIEW. The block diagram contains all the graphical symbols

and functions to execute the code; and the front panel displays the inputs for the user to enter

in and the outputs of the code after it has been executed.

Fig. 15 – Front panel and block diagram of a motion control VI

LabVIEW will be used in this project to integrate all the hardware together, perform all

necessary calculations (by implementing Matlab user-defined functions), and to provide the

user full control of the device. Codes will be written to control the movement of the motor,

process acquired images from the camera and track the positions of the markers as the tissue

deforms, and calculate the deformation of the tissue. The program will use codes generated by

Motion Assistant and Vision Assistant to simply the coding process for the motion control and

image acquisition. In order to determine the deformation of the tissue, the calculations will be

broken into two parts: 1) to identify the instantaneous effective modulus, and 2) to identify the

neutral axis location. To determine these two parts, LabVIEW will make use of the following

equations:

25

5 � 678∆

8 � �:;�<

= � |?�|·|��|·|�?|AB�|?�|C|��|C|�?|��|?�|D|��|C|�?|��|?�|C|��|D|�?|��|�?|D|?�|C|��|�E

F� � A2H�� I 1, L�)() ' � 1,2

λ� � 1 I 1� N� O� , L�)() ' � 1,2

$+(P1-'Q)& $� -+*1"'+, � �R�R

Please refer to the Proposal Report for detailed explanations of the equations. Summarily,

LabVIEW calls user-defined Matlab functions to allow its graphical programming language and

symbols to calculate the deformation of the tissue from the data collected from the image

acquisition and motion control, using all of the equations above. The overall programs consists

of nearly 100 user-defined functions, but the major functions for the flexural rigidity portion are

responsible for determination of the young’s modulus of the bending bar from the calibration

data, converting distance measurements in pixels into millimeters, calculating flexural rigidity,

and then graphically and numerically outputting flexural rigidity data to the user. The

subroutines used for the transmural strain portion include inputting point location data in the

undeformed and deformed states, correlating points from the two states such that they are in

the same order, developing a 2-D finite element triangular mesh of the undeformed points in

real time (and not requiring use of another program), using the mesh to determine finite

element strain for each of the triangles in the mesh, and then outputting the transmural strain

data both numerically and graphically to the user, including a blended multicolor gradient

display of strain in each principle direction.

2.2 Prototype

A prototype of the device has been designed to the specifications described

above, fabricated, assembled, and tested. The major subsystems of the device are the physical

components, the software to control device movement and image acquisition, and the software

to perform all necessary calculations and provide output to the user.

2.2.1 Prototype Subsystems

2.2.1.1 Physical Components

26

The three point bending device prototype carries out its principle

function of bending tissue by applying a force to the specimen via a bending bar. The actual

force applied is measured by comparing the distance between the bending bar and reference

bar at any point in time. The bending bar and reference bar mounting system can be see below

in Figure 16. During testing, the bending bar is normally attached to a linear actuator, which is

also shown in Figure 16. The bending bar mount is able to be removed though, for conducting

the calibration procedure. Additionally, the bending and reference bars may easily be removed

by loosening setscrews to allow for bars of differing diameters to be used. In this way, the user

maintains full control over bending bar stiffness and the most appropriate configuration for

each specimen can be determined.

Fig. 16 – Bending bar mount shown in the testing configuration with bending and reference

bars connected to a linear actuator (which is driven by a Stepper Motor, and controlled by the

device software)

The tissue specimen lies in a dual bath system, where the inner bath houses the tissue

along with two reinforcing posts. The inner bath is maintained in a chemically appropriate

solution for tissue testing (see above), while the outer bath is normal tap water and is used to

provide the proper thermal environment for testing. The temperature of the system is

maintained by a 1KW heater that is controlled by comparing a user-adjusted control knob value

to the reading of the capillary bulb, which is intended to be placed within the inner fluid bath.

The fluid in the outer bath is circulated by a 500 gph centrifugal pump. The components for this

bath and temperature control system can be seen below in Figure 17.

Bending Bar

Reference Bar

Linear

Actuator

Stepper Motor

Wire Harness to

Motion Controller

27

Fig. 17 – The dual bath system, shown with the individual components of the temperature

control system. Each component is labeled individually above.

The data acquisition for the device is carried out via a 5 megapixel, 12 bit monochrome

CCD camera. The camera is mounted upon a custom built stand that is capable of maneuvering

the camera either closer to or further away from the specimen via a height adjustment.

Additionally, the camera stand is capable of rotating away from the specimen by 90 degrees to

allow for imaging of the calibration procedure. Output from the camera is sent to the hardware

interface portion of the software via a USB connection to the controlling PC. The images

acquired are then processed to determine specific locations, such as marker coordinates. The

camera and camera mount can be seen below in Figure 18.

Fixation PostsOuter Bath

Mounting

Bath

Centrifugal Pump

Pump Outlet

Pump Inlet Priming Reservoir

Capillary Bulb

Thermostat Dial

Power Lead

Heater Lead

Heating Elements

Lead Housing

Heater & Power Leads

28

Fig. 18 – CCD camera and camera mount. The camera is shown in the testing configuration, but

can also be rotated 90 degrees to allow for calibration imaging.

The subunits are all mounted upon a 24”x24” table using 1/4-20 standard machine

screws. The arrangement of all subunits can be seen below in Figure 19.

CCD Camera

USB to Computer

Base

Height

Adjustment

Pin to Adjust

Camera Position

29

Fig. 19 – Assembled prototype. All component labels correspond to the descriptive table

above.

A

B

C

D

E

G

H

I

J

K

F

Label Component Features

A Thermostat SPST with dial

B Immersion Heater Copper sheath, single element

C Camera Stand Adjusts height and position of camera

D CCD Camera Image acquisition

E Linear Actuator Moves the bending bar mount

F Stepper Motor Controls the linear actuator

G Bending Bar Mount Holds the bending and reference bars

H Centrifugal Pump Regulates the temperature flow loop

I Outer Bath Used for heated water flow

J Tissue Bath Used for tissue testing, saline solution

K NI Motion Controller Integrates the stepper motor with LabVIEW

30

2.2.1.2 Hardware Interface Software

A LabVIEW program was written to provide automatic control

over all the necessary hardware. Specifically, this program was written to control the motor

and the camera. In addition, this software is the main software for the user to use. It is the

interface between the user and the device.

The program is divided into three separate individual modules. The first module

controls the motion of the motor, allowing the user to move the motor to any position. It

allows the user to move the motor away or toward the mounting bath prior to testing. Figures

20 A and B show the front panel and associated block diagram for the motor control module.

As can be seen from the front panel, there are two buttons designing the directions the motor

can go. In addition, there is a motor speed bar, which allows the user to adjust how fast the

motor moves. Finally, there is a stop motor button that stops the motor from moving when

pressed.

The second module is the image acquisition module. This module allows the user to

acquire continuous, real-time image from the camera. It allows the user to adjust the settings

on the camera such that optimal image is acquired before any testing. In addition, this module

also allows the user to process the image such that only markers of interest are tracked.

The third and final module is the testing module. Basically, this module is the

integration between the motor module and image acquisition module. The testing module

allows the user to input in all the necessary information prior to actual flexural testing, and

then presses the start button and the testing will be performed automatically through the

program. The testing module controls the movement of the motor, while simultaneously

acquires images through the camera and tracks markers on the images. In addition, while the

motor and camera are performing their functions, the testing module also output all the critical

information, such as the positions of the markers and the time. After the testing is completed,

the output data will be written into a text file. Furthermore, the output data will also be passed

a calculation subroutine that will calculate all the necessary information for the user. The

results will be outputted on the front panel of the program. Thus, to summarize, the testing

module consists of the integration between the motor, the camera, and also the calculation.

Figure 21 below shows the front panel and block diagram for the testing module.

31

Fig. 20 – A) Front panel and B) block diagram for motor control module

32

Fig. 21 – A) Front panel and B) block diagram for image acquisition module

33

Fig. 22 – A) Front panel and B) block diagram for testing module

2.2.1.3 Calculation and Output Software

To process the acquired image data and provide the desired

output to the user, a custom set of Matlab user-defined functions was developed. There are

nearly 100 of these functions, but the purpose of at least the principle subroutines will be

discussed here. First, for the flexural rigidity calculations the desired output is an effective

modulus and its relation to rate of change of the curvature. To carry out this functionality, the

34

program is capable of converting the coordinate locations from their pixel values into their

adjusted real-world equivalent values. Additionally, the modulus of the bending bar must be

determined using data provided during the calibration procedure. This modulus is then used to

determine the force applied to the tissue at any given time during testing. Also, each of the

tissue markers that were tracked by the CCD camera is used in a calculation of the current

tissue radius of curvature and location of circle center. By combining this radius of curvature

information with the force applied calculations, the effective modulus was determined at each

time instance. This information is then output to the user in real time (with a slight delay for

calculation). The LabView MathScript implementation of these Matlab functions can be seen

below in Figure 23.

Fig. 23 – LabView MathScript subVI used to call user-defined Matlab functions associated with

the flexural rigidity calculations.

In addition to the flexural rigidity calculations, a separate family of Matlab user-defined

functions was developed for processing of the transmural strain data. Based on the work by

Y.C. Fung (see references), it was determined that three independent measurements were

required to determine the transmural strain of a region. These three measurements naturally

lend themselves to building a triangular area and using the three measurements as the lengths

of the three sides of the triangle bounding the area. Turning a surface into a grid of triangles is

known as meshing. While there are many commercial programs available to perform this

meshing function, none could be performed in real time and all would require additional

(undesirable) work on the part of the user. As such, the device includes a unique real-time

meshing algorithm that converts the dataset of points into a triangular grid. Other subroutines

then calculate the transmural strain for each of these triangles, much as a commercial finite

element software package might do. The output to the user also was designed to mirror that of

35

commercial finite element displays and includes a blended color representation of strain in

each of the principle directions. The LabView Matlab Script that calls the Matlab subroutines

can be seen below in Figure 24. A Matlab Script was used vice a MathScript node to facilitate

use of higher level Matlab graphical functions, many of which are not available in LabView

alone. The downside of this approach is that the user must open Matlab prior to opening the

LabView program.

Fig. 24 – LabView Matlab Script implementation of Matlab user-defined functions associated

with the transmural strain calculations.

2.2.2 Prototype Testing

To test the functionality of the device, we carried out the calibration,

flexural rigidity, and transmural strain procedures. The calibration procedure, as mentioned

above, involved turning the camera 90 degrees and recording the deflection the bending bar

away from the reference bar as a result of the application of two different weight values. The

result was a calculated Young’s modulus for that particular bending bar, which could be used

later to correlate distance between bending and reference bars with force applied to the

bending bar. The calibration procedure can be seen below in Figure 25.

36

Fig. 25 – Calibration procedure, where a weight of known mass is hung from bending bar.

Change in distance between bending bar and reference bar is used to determine a Young’s

modulus for the bending bar.

After the calibration procedure was performed, tissue specimens were marked for both

the flexural rigidity test and the transmural strain test. The flexural rigidity marking included a

series of marking beads placed roughly along the center of the thickness of the tissue. If placed

properly, they should all lie on the perimeter of a circle as the tissue is deformed. The

Camera

Bending Bar

Calibration Force

37

transmural strain marking was performed using inked applied with a common toothbrush,

following the practice of Yu et al. Since transmural strain markings were tracked for very small

regions, the best region was chosen and imaged. The marking of both tissue specimens can be

seen below in Figure 26.

Fig. 26 – Tissue specimens marked for a) the flexural rigidity test and b) the transmural strain

test.

The tests were carried out on the specimens and the resulting image data analyzed

using the software built for the device. The Flexural rigidity data closely followed that of data

published previously. The transmural strain calculations provided numerical data as well as

graphical output to the user. The results of pilot trials both for theoretical and actual tissue

specimens can be seen below in Figure 27.

a. b.

38

Fig. 27 – Transmural strain output data for a theoretical test (left vertical panel) and for a test of

a porcine aorta (right vertical panel)

39

3.0 REALISTIC CONSTRAINTS

3.1 Engineering Standards

This device will be required to record, calculate, and output extremely small

order stresses and strains. The margin for error must then be kept appropriately small or the

data obtained with the device will have little or no value. Possible sources of error include:

• Environmental Changes – if testing is performed on the same tissue at two different

environmental conditions (temperature, for example) there will be two different

responses

• Imaging Error – The device must track the change of position of the test specimen over

time. The tissue strain calculations will be based on these measurements. The tissue

thickness and radius of curvature must also be recorded. These will be used in stress

calculations. This error occurs when the position determined by the device differs from

the actual position or when strain is measured in a non-representative region.

• Force Recording Error – The device must record the change in force applied to the tissue

over time. The tissue stress calculations will be based on this force measurement. This

error occurs when the force read by the device differs from the actual force applied. A

possible cause could be an unaccounted-for loss of force (such as friction).

• Calculation Error – This type of error could result from rounding off significant figures,

which is of particular concern for the strain values which will be of low magnitude.

To prevent excessive error, many features have been built into the device design. To

reduce environmental error, a stable, repeatable environment has been planned. This

environment will be discussed below in section 2.2. To reduce imaging error, a large number of

small markers will be used, along with a CCD camera capable of resolving very small

displacements. The displacement of the tissue will be taken as the average of the numerous

markers. Any error should be removed, or at least identifiable in the form of a standard

deviation. The force recording error has been minimized by tracking the force using

displacement of the bending bar (see mounting bath subsection of the subunits section) instead

of inputting force directly from linear actuator displacement. Using the linear actuator would

not account for any force lost to rolling friction in the wheels of the platform, or any sliding of

the test specimen. Calculation error will be reduced by carefully monitoring use of significant

digits in any calculation performed.

3.2 Environmental

For proper tissue mechanical response, the tissue must be maintained in

conditions that simulate the in vitro environment. By developing a suitable environment, the

data obtained during device operation will be closer to the in vivo response, and thus more

relevant. By creating specific bounds for the environmental conditions, the introduction of

error due to testing being conducted at different conditions is also eliminated. For example,

tissue responds differently to mechanical stimuli at higher temperatures than it does at lower

temperatures. By fixing the tissue’s environment, the device is more likely to provide

40

reproducible data. This will inevitably make the device more attractive to researchers and

industrial scientists.

It should be pointed out here that the first step in creating a stable in vitro environment

is to maintain the test specimen submerged at all times. Even short-duration exposure to open

air begins an irreversible degradation process. The next step is to select the ideal properties for

the fluid in which the tissue will be submerged. To fix the environment, we have targeted three

specific areas that will make the testing fluid closely resemble blood: salinity, pH, and

temperature. The first, salinity, will be accomplished by using a normal saline solution. Normal

saline mimics blood in many ways. The second condition, pH, will be accomplished by buffering

the normal saline solution. We have chosen to use phosphate as a buffer. Phosphates will be

added until the saline solution reaches a pH of 7.4. For the third condition, temperature, the

phosphate-buffered saline solution will be maintained at 37 ± 2°C. This will be accomplished

using a circulation system that will be described later. The resulting environment will be mildly

corrosive.

3.3 Manufacturability

Many of the parts required for system operation will be extremely small, and

thus expensive to manufacture precisely. In some cases trade-offs will have to be made to

lower manufacture costs at the expense of device accuracy. Whenever possible, parts will be

manufactured in-house (at the University of Connecticut machine shop).

3.4 Sustainability

Wherever possible, non-corrosive parts have been chosen. All potentially

corrosive parts will be periodically replaced. The method chosen for measuring tissue

displacement will be calibrated prior to each use. Any components subject to friction will be

lubricated periodically to prevent wear and unnecessary error. It is anticipated that this will

include the wheel system beneath the platform. The system will be monitored closely during

prototype development and testing to identify any additional wear surfaces. These measures

will increase the repeatability of data obtained using the system.

3.5 Ethics

The budget for this project is limited. As such, all purchased parts will be

thoroughly researched so that the most reliable, and yet most cost-effective, component is

chosen in each case. All funds spent will be used solely for the purchase of parts and services.

Whenever possible, parts will be manufactured in-house to conserve funds. Finally, the client

will be kept informed of the initially planned budget along with periodic updates and consulted

prior to any necessary deviations from the budget.

41

3.6 Health and Safety

The device will be routinely exposed to excised animal tissue. Surface materials

should be chosen such that they are smooth and capable of being sterilized after each use.

Materials chosen should also be non-toxic and non-destructive to the tested tissue. The health

and safety allowances for the device will be expanded upon in Section 3.

4.0 SAFETY ISSUES

The finished device will contain several subunits that could pose health risks if left

unchecked. Such subunits include:

• Pump – the centrifugal pump (in the temperature control loop) represents a rotating

mechanical device. If run dry, the pump could cause damage to itself, the rest of the

device, or the operator. While running, the pump also represents a hazard to the user if

skin were to come in contact with the impeller. This could result in loss of digits.

• Pump motor – the pump motor represents both an electrical and a fire hazard.

• Heating element – like the pump motor, the heating element poses both an electrical

and a fire hazard. The heating element additionally poses a burn hazard to the user.

• Motion system motor – the motion system motor also poses both an electrical and a

fire hazard. The exposed rotating shaft of the motor also poses a risk to users with long

hair or loosely worn accessories (such as necklaces).

• Fluid medium – the test fluid medium poses a potential chemical risk to the user and to

the other components.

• Test bath surface – the test bath will routinely be exposed to excised biological tissue.

This will result in a potentially biohazardous surface.

To minimize the potential negative impact of the above subunits, several measures have

been taken. For the pump, the system has been designed to have the pump hard-mounted into

the piping. This should minimize the chance of the pump impeller coming in contact with the

user. Also, the user’s manual will include warnings against running the pump in a dry tank

condition. The pump has also been selected such that the lowest allowable horsepower rating

will be used, which will minimize the potential damage caused if any adverse event were to

occur. The pump motor will be contained in an enclosed structure, and will also benefit from

the choice of a low horsepower pump. The heating element has been chosen such that it can

safely withstand being submerged in the test fluid. This should prevent any short-circuiting of

the heating element and the subsequent fire hazard that it could pose. The heating element

will also remain submerged and has been chosen to emit as little power as necessary to

maintain system temperature. These safety measures should combine to eliminate the risk of

user burn injury.

The motion system motor will be enclosed to minimize the risk of electrical shock and

fire. The motor shaft will also be enclosed to prevent personal injury due to the rotating

machinery. Users will be warned about the potential risks of operating the system with either

the motor or shaft exposed. The fluid medium has been chosen such that the chemical

composition and pH are insignificant hazards to humans. The bath remains, however, mildly

42

corrosive. A warning will be provided to the user to remind them that the use of corrosive

replacement parts should be avoided whenever possible.

The surface of the bath itself is a potential breeding ground for microbial agents. Three

measures have been taken to reduce this risk. The first is that a “bath within a bath” system

has been employed. This means that the fluid circulating through the pump and the outer bath

will never have been exposed to biological tissue. Reducing the potential surface area for

microbial growth should significantly reduce the risk to the user. The second measure taken

was the choice of material used. The bath will be fabricated from Lexan, which will form a non-

porous and sterilizable surface. The third measure, in combination with the second, is to

routinely sterilize the exposed surface. The user will be provided with instructions on sterilizing

the work surface with alcohol after each use.

5.0 IMPACT OF ENGINEERING SOLUTIONS

The chosen optimal design for the project consists of a moving bending bar with a

stationary mounting bath and image acquisition system. This design helps simplify the device

while still determining the flexural rigidity and bending stiffness of the tissue sample. By

combining techniques taken from the other alternative designs the transmural strain and

transverse stress will also be measured during testing. This device offers the capability of

measuring nearly all the mechanical properties of a given tissue sample in order to accurately

characterize the specific material behaviors of the tissue. Additionally the device will be able to

locate and quantify specific layers within the tissue that display distinct behaviors, rather than

measuring the entire sample as a single, homogenous material. This is critical to the

understanding and analysis of the soft tissue mechanical properties.

5.1 Global Impact

In general this three point bending device will assist many disciplines beyond the

field of engineering in understanding the mechanical behavior of soft tissues. It is the first

device to combine techniques for testing not only flexural rigidity and bending stiffness, but

also transmural strain and transverse stress. The comprehension of these properties is critical

to many areas of study, specifically biomechanics.

The client for this project is Dr. Wei Sun at the University of Connecticut. The focus of

much of his research is on cardiac valve replacements. In recent years there have been a

plethora of advances in the way of valve repair, but most of the cardiac valve implants have

experienced continued failure. While some valve implants are successful in the short term,

nearly all of them suffer failure within a year of implantation. This catastrophe is mainly due to

the radical difference in behavior between the valve implant and the surrounding cardiac

tissue. This three point bending device will give specific properties to the tissue so that the

valve replacements can be more precisely designed and will successfully integrate into the

functioning system.

The applications of this testing device extend beyond cardiac valve replacements and

will be optimal for studying a wide variety of soft tissues. These tests may facilitate in

furthering the significant understanding of soft tissues such as vascular, pulmonary or renal.

43

5.2 Societal Impact

As advances in medicine continue to extend the expected life span, patients are

constantly eager for further improvements in treatment. Patients will no longer accept that a

doctor is not capable of repairing, replacing or healing any disease or abnormality. The thought

of a cardiac valve replacement is no longer foreign to society and it is expected that these

advancements in technology will be readily available and completely successful. For this reason

many companies continue to develop more and more products, however many of them fail to

perform their proposed function. The further study of soft tissues using this three point

bending device will enable many products to be more accurately designed and implemented

into their environment. Not only will they perform their desired function, but they will also

remain successful once inside the anatomical setting.

6.0 LIFE-LONG LEARNING

The project has emphasized the integral objective of biomedical engineering; that is, the

improvement of health and life of mankind through the integration of research and technology.

Technology enhances, improves, and expands the capability of research, and research, in

return, expands and disseminates knowledge on how to improve the health of human. This

project was requested by Dr. Wei Sun in order to enhance his research on the biomechanical

interactions between host tissues and implants. Dr. Sun’s research area focuses on

understanding, through experimental and computational approaches, the biomechanical

interactions between percutaneous devices and surrounding body tissues for the treatment of

heart valve diseases, such as mitral regurgitation and aortic stenosis. He is currently working on

constructing finite element models of body tissues and percutaneous devices to simulate

tissue-device interactions when the device is implanted. Critical to this is a comprehensive and

accurate description of material behavior. Experimental testing is, thus, necessary to provide

data for the comprehension of the dependence of tissue stress on strain and the effect of small

deformation on the different layers of tissue. The construction of the three-point bending

device will contribute tremendously to this understanding of tissue behavior and the

improvement of implant design for optimal implant performances in vivo.

This project also underscores many important engineering principles and designing

aspects that the team will use in their future career. Such principles and aspects include taking

into consideration, during the designing process, the safety, maintainability, sustainability,

marketability, etc., of the device. These considerations can tremendously affect the success of

the device in terms of its functioning and marketability. The team has also learned that

sometimes, some designing aspects have to be sacrificed for the sake of other aspects. For

instance, in this particular project, the accuracy and repeatability of the data collected from the

device are extremely important in obtaining correct calculations. Thus, the mechanical

properties of the bending bar and the resolution of the CCD camera have to be exactly the

same as their desired specifications, even if such specifications result in having to spend more

money. Consequentially, the material chosen for the mounting bath has to be cheap at the

expense of its sustainability in order to keep the budget low for the device. The team has also

44

learned that safety should always be the primary consideration in designing any devices. Safety

should never be sacrificed for any other aspects of the design.

Additionally, the team learns that designing a device requires extensive planning,

organization, time, and cooperation in order to be successful. Planning sets the goals to be

accomplished in a designing project. Timing determines the amount of time and sets the time

required to perform and accomplish the goals. Organization makes certain that each goal is

carried out and accomplish in an orderly manner. And cooperation from each team member is

very critical in fulfilling all the objectives. Designing and constructing a device that functions

correctly requires a tremendous amount of work and contribution from each team member. If

one team member does not perform his or her duty, than the other team members have to

pick up the slack or the design will fail. Therefore, planning, organization, time, and team

cooperation are essential in design success; without them, the project will be doomed to

failure.

This project has also improved the team’s understanding of nonlinear biomechanics.

The team learned that soft tissues consist of various layers of collagen fiber and each layer

deformed differently to an applied load. Moreover, in order to characterize and quantify the

material properties of soft tissues, experimental testing to obtain material parameters is

essential. In addition, this project has also improved the team’s LabVIEW programming skill.

This project will make extensive use of the LabVIEW program, and by the completion of this

project, our knowledge of LabVIEW and programming skill will be dramatically expanded and

improved.

Furthermore, the team also learns that success is also based upon failure. In the

designing process, failure is inevitable as mistakes will be made and some goals will not be

accomplished. However, failure will not deter the team’s determination. We will accept the

failure, learn from it, and continuously try our best throughout this project to make the device

works. Ultimately, throughout this design project, we will learn valuable designing principles

which we will use and improve on through our engineering career.

7.0 BUDGET

The cost of this project was close to $3000. Our allowed budget was around $5000, but

throughout this project, we managed to keep the cost down by using materials that were

already available, recycling materials, and finding materials that are the cheapest but have all

the specifications that were needed.

The majority of the money was used to purchase the parts for the motor, the camera,

and the breadboard. The linear actuator was an expensive component of the motor system,

while the camera was the most expensive component of the whole device. The reason why we

purchased such an expensive camera was because the specifications we required for the

camera are extremely strict. We required that the camera has a large field of view while at the

same time able to resolved markers that are approximately 2 μm in size. Due to these strict

specifications, we were able to only find a few cameras that fit. These cameras, however, came

with a very expensive price tag. The camera we purchased was the cheapest of all the available

cameras.

45

Of all the components, the aluminum breadboard was a last addition. It was quite

unnecessary, actually. However, the sponsor wants the whole device to be assembled on the

breadboard such that it looks professional and organized. Thus, he allowed us to purchase the

breadboard. Without the breadboard, our expense would have been cheaper, but overall, we

were quite below our allowed budget. Table 4 shows a summary of the budget.

Table 4: Summary of Budget

ITEM / PART COST

Motor

- Linear Actuator

- NEMA 11 Motor

- MID Connector

$534

$86

$60

Camera

- Computar Lens

- Extension Tube Kit

- 5 MP 12-bit Monochrome CMOS camera

$122

$53

$749

Flow Loop

- Nylon Tube

- Pondmaster Pump

$4

$54

Heater

- Screw Plug Heater

- Thermostat

- Knob

- Housing for Thermostat

$113

$50

$5

$21

Aluminum Breadboard $537

Miscellaneous (materials, etc.) $500

TOTAL $2888

8.0 TEAM MEMBERS CONTRIBUTIONS TO THE PROJECT

Michael Harman

My responsibilities for this project were mainly focused on the mechanical

aspects of the device, while Xuan worked on the imaging and Eric processed the coding

necessary to perform the calculations for the desired mechanical properties. There were three

46

distinct areas of the project that required the majority of my time. The CCD camera, along with

the bending bar, both needed mounting systems, and the temperature control loop needed to

be constructed.

The camera mount was constructed from 3/8 inch thick aluminum plating, a 1/2

inch thick stainless steel bar and a variety of hardware. The necessary functions were that it

adequately and safely held the camera, was adjustable in height and position, could swivel from

the testing to calibration position and be cost effective in the system. The camera is supported

with a horseshoe shaped attachment to add stability. The height is adjustable using two wing

nuts in a sliding track and the entire stand can be moved using the tracks machined into the

base. The entire camera mount can swivel using a push pin system.

The bending bar mount needed to be able to attached the stage of the linear

actuator and move the bending and reference bars towards the tissue at the correct height and

location. This was again made from ¼ inch thick aluminum bars, utilizing a set screw setup to

hold the bending and reference bars. In this way the actual height of the bending bars could be

adjusted for different tissues. These bars also needed to be set on a slight angle so that the

camera could still have a good view of the testing.

For the temperature control loop I reconstructed the mounting bath several

times to accommodate new features of the device. I decided on multiple different heater

setups before I found the copper sheath immersion heater, which works perfectly in the device.

I also researched and found an appropriate centrifugal pump for a low price and constructed

the actual flow loop using ½” ID ¾” OD flexible tubing.

Minh Xuan Nguyen

My contributions to this project were primarily working on setting up the motor

system and writing the main LabVIEW program. I purchased all the necessary components for

the motor, such as the motor, the linear actuator, and the MID connector which connects the

motor to the power unit. In addition, I connected the motor to the power unit, and the linear

actuator to the motor.

The majority of my contribution was in writing the LabVIEW program. The

program was an extremely extensive program. I spent a lot of time trying to use LabVIEW to

communicate to each of the individual hardware, such as the motor and the camera. After

LabVIEW was able to communicate to the hardware, I had to try to integrate the hardware

such that they can work together and simultaneously within the program.

My other contributions included mainly administrate works. I setup the format

for the reports and maintained the team’s website. In addition, I helped updated the final

report and wrote part of the operator’s manual.

Eric Sirois

My contributions to the project include the theoretical framework for the tissue

bending process, the theoretical framework for the selection of flow loop components, the

theoretical framework for the selection of the CCD camera, the safety analysis of the device, an

analysis of the realistic constraints for the device, and implementation of the calculations

performed for both the flexural rigidity and transmural strain portions of the device.

47

The theoretical framework for the tissue bending process included a

review of the literature to determine previously employed methods and their limitations. I

determined that two groups had successfully measured tissue bending, but that neither fully

accomplished all goals for our project. I combined the methods used in the two approaches to

yield one new approach.

The theoretical framework for selection of the flow loop components

yielded a minimum heating element capacity and pump flowrate requirement. This was done

by first analyzing the heat that would be lost to ambient from the inner bath. I then calculated

the heat flux required into the inner bath from the outer bath (through the Lexan wall). This

information, combined with the heat loss of the outer bath to ambient allowed me to calculate

the amount of heat that would be required to maintain optimal system temperature.

The theoretical framework for the selection of the CCD camera involved

calculating pixel size from our required resolution and determining the number of pixels that

would be necessary to take data on the entire field (also determined from our initial

specifications). I was also responsible for the eventual purchase of the CCD camera based upon

these specifications and the wishes of the client for future flexibility in use of the camera.

Safety analysis and realistic constraint analysis are fairly self-explanatory.

I have also been responsible for implementing the software that performs the calculations and

output for both the flexural rigidity and transmural strain portions of the device. I chose to use

the Matlab programming environment for its flexibility and simplified integration with LabView,

which was used for the interface with all hardware components. The Matlab user-defined

subroutines consisted of 78 unique functions adding up to thousands of lines of custom-written

code. The major components of the software include a real-time finite element meshing

program (Fig. 28a), a real-time finite element calculation program, and a commercial equivalent

blended strain graphical output (Fig. 28b). The software is also capable of performing all

specified calculations and functionalities.

48

Figure 28 – Output from the meshing subroutine (a) and finite element strain calculation

(magnitude of strain is shown here) (b). Both subroutines are built and output to the

user in real time base on point data input from a CCD camera and processed by LabView

code.

Although I have done much work, each item represents a collaborative effort

from all team members and our client. As an example, the calculations for the flow loop

required extensive details of the dimensions of the baths and the materials to be used. Both of

these items were provided during numerous conversations with Michael Harman, who

designed the baths. The calculations to determine CCD camera requirements involved many

conversations with Xuan Nguyen about the capabilities of the automation system. I would

personally like to thank Dr. Claire Gloeckner for her insights into the flexural rigidity

calculations, Dr. Miles Li of Mightex systems for his help in selecting both a CCD camera and

lens, David Kaputa for his assistance with integration of LabView and Matlab, David Price for his

many suggestions and insights, including CCD camera selection and LabView integration, and of

course Dr. Wei Sun for his insights on finite element meshing and calculation, as well as for his

support for and direction of the project. There are many more such examples.

a.

b.

49

9.0 CONCLUSION

This 3-Point Bending Device, as designed, will be a novel tool for research scientists to

conduct mechanical analysis on soft biological tissue specimens. The device will output to the

user, in real time, the requested tissue response. The user will be able to select from an

extensive list of output variables, including stress vs. strain and location of the neutral axis. This

data will be useful because accurate stress vs. strain data in the low strain region (<5%) is not

obtainable using traditional soft testing methods such as biaxial and uniaxial mechanical

testing. Additionally, these traditional tests provide little or no insight into the contribution of

various layers of a tissue specimen to the overall response, but outputs such as the neutral axis

location provide this valuable information. The data provided by the test device will also be

accurate and repeatable due to the environmental control systems (including chemical control,

salinity control, pH control, and temperature control), calibration system, and high resolution

CCD camera.

The system functions by using metal bending bars of varying thickness and stiffness to

deform the test specimen. The force applied is measured by use of a built-in calibration and

calculation system. In this system, the effective Young’s modulus of the bending bar is

determined prior to each experiment and the displacement of the bending bar from a reference

bar is used to calculate the force that the tissue specimen exerts upon the bar (due to force

equilibrium, this is also the force that the bar exerts on the tissue).

The bar displacement and tissue displacement are tracked and reported to the

controlling software system in real time by a high-resolution CCD camera. The camera is

capable of resolving tissue markers as small as 10 microns in diameter. It also has a field of

vision large enough to encompass the undeformed test specimen, bending bar, reference bar,

both stationary posts, and the deformed test specimen.

The CCD camera gives marker position as an input to the governing LabView program.

This program uses specific marker information, such as post location, tissue thickness, tissue

edge marker location, and transmural marker location to determine the tissue dimensions and

radius of curvature. When combined with the force applied to the tissue, this information can

be used to calculate bending moment, stress, strain, strain rate, and transmural strain (for use

in determining the location of the neutral axis). The program also controls several important

hardware systems, including stepper motor rotation for bending bar movement, and heating

element operation for control of test bath temperature.

This 3-Point Bending Device represents advancement in imaging and automation

capabilities over other soft tissue bending devices that have been previously described. The

result is a device that provides the user with valuable testing information about low strain

material properties and transmural strain distribution. This combination of (relatively) large

scale measurement and micro-scale measurement was not previously possible due to the

limitations of CCD cameras and precise automation controls. The enhanced features of this

device, in combination with the secondary features added to provide reliable, repeatable data,

will make this a valuable addition to any tissue mechanics laboratory.

50

10.0 REFERENCES

1. Mirnajafi, Ali, et al. The Effects of Collagen Fiber Orientation on the Flexural

Properties of Pericardial Heterograft Biomaterials. Biomaterials 26 (2005) 795-804.

2. Yu, Qilian, et al. Neutral Axis Location in Bending and Young’s Modulus of Different

Layers of Arterial Wall. The American Physiological Society (1993) H52 –H60.

3. Gloeckner, Claire, et al. Effects of Mechanical Fatigue on the Bending Properties of

the Porcine Bioprosthetic Heart Valve. ASAIO Journal (1998).

4. Fung, Y.C., Biomechanics: Mechanical Properties of Living Tissues. 2nd ed. 1993, New

York: Springer Verlag. 568.

5. Bathe, K.J., Finite Elements Proceedures in Engineering Analysis. 1982, Englewood

Cliffs,NJ: Prentice-Hall.

6. National Instrument. [www.ni.com]

7. Danaher Motion. [www.danahermotion.com]

8. Bishop, Robert. Learning with LabVIEW 8. Pearson Education, Inc.; Upper Saddle

River, NJ, 2007.

9. Lexan. [www.polymerplastics.com/transparents_lexan.shtml]

10. Digital Camera Resolution. [http://www.howstuffworks.com/digital-camera2.htm]

11. Charge-coupled device. [http://en.wikipedia.org/wiki/Charge-coupled_device]

12. CCD Camera. [http://www.sentechamerica.com/]

13. Temperature Controller.

[http://www.omega.com/prodinfo/temperaturecontrollers.html]

14. Force Sensing Probes. [http://www.femtotools.com/force.htm]

15. Linear Actuators. [http://deltron.com/image_search/dril-down.php?g=20]

16. NEMA 11 Motor.

[http://www.linengineering.com/line/contents/stepmotors/211.aspx]

17. Micro Force Sensor. [http://sensorone.com/AE801_Home.asp]

18. FlexiForce Force Sensor. [http://www.tekscan.com/flexiforce/flexiforce.html]

19. Engineering Search Engine. [http://www.globalspec.com]

20. DL Linear Actuator. [http://deltron.com/DL_Linear_Actuators.html]

21. NEMA 11 Stepper Motor.

[http://www.linengineering.com/line/contents/stepmotors/211.aspx]

11.0 ACKNOWLEDGMENTS

The team would like to thank Dr. Wei Sun for sponsoring this project and for his

constructive feedbacks and advices.

Thanks Dr. John Enderle for guiding the team in the right direction toward engineering

design and providing very useful information.

Thanks Dave Price for providing many constructive feedbacks throughout the whole

designing process.

51

The team would also like to acknowledge the following people for their helps,

information, and suggestions: Dr. Claire Goeckner, Dave Kaputa, Thuy Pham, Dr. Miles Li

and Steve Stagon.

12.0 APPENDIX

12.1 Updated Specifications

Physical:

Tissue Mounting Size

Thickness 100-400 μm

Width 3-5 mm

Length (maximum) 30 mm

Minimum image points on tissue specimen 30

Tissue Displacement

Distance

In direction of tissue curvature 0.5 mm

Against direction of tissue curvature 2 mm

Time 5 seconds

Mounting Bath

Inner Bath

Length 85 mm

Width 85 mm

Height 20 mm

Thickness 5 mm

Outer Bath

Length 115 mm

Width 115 mm

Height 30 mm

Thickness 5 mm

Electrical:

Input voltage 1φ, 115V AC

Input current 5 A

Mechanical:

Applied Load (maximum) 10 grams

Force Measurement Accuracy 0.001 grams

Motor

Torque 0.42 lb-ft

Resolution 1.8 degree

Software:

User Interfaces Keyboard, Mouse

Hardware Interfaces Monitor, Data Acquisition,

Equipment, Camera

Resolution Capability (minimum) 640 x 480 pixels

52

Spatial Resolution 30 μm / pixel

Communication Protocols USB, PCI, PXI

Computer Requirements

Operating System XP or higher

Processor 2 GHz Intel Core 2

Memory 1 GHz

Environmental

Optimum Operating Temperature 37 ± 1°C

Optimum Operating pH 7.4

Operating Environment Indoor

12.2 Other Data

Dimensions for NEMA 11 Motor (inches)

CAD Drawings for DL 15 Linear Actuator