Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch

Using Magneto -Rheological Fluidin the Forearm Crutch

Innovation in Medical Devices:

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Abstract

Abbreviations

Market Trends/Challenges

Solution

Best Practices

Conclusion

Reference Reference

Author Info

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3

3

4

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Table of Contents


A forearm crutch is a mobility aid which is used to counter mobility impairment or an injury that limits one’s walking ability. It has been almost exclusively used by people with permanent or lifelong disabilities. The forearm crutch used today is obsolete. The cuff, which is used to provide steady grip to the arms of the patient, actually gives a lot of discomfort.

ThisThis paper proposes a modified design for the forearm crutch, making the steady grip provided by the cuff variable, according to the force applied while walking, to actually provide the user with a sense of support rather than causing discomfort. Magneto Rheological (MR) fluid - a unique fluid that solidifies when a magnetic field is applied, can come to the aid.

Materials and the processes to shape them are developing at a faster pace than at any time before in history. The challenges and the opportunities are therefore greater than ever before with the evolution of smart materials. This paper presents a case study to illustrate the use of one such smart material - Magneto Rheo-logical fluid - in the modification of a medical device – the forearm crutch.

Medical devices and instruments are in a constant state of evolution. Responding to these trends, the need of the hour is to build effective, accurate and precise devices that ensure the safety of human life. The use of smart materials provides a convenient solution and compels the industry to adopt such materials by which the effectiveness and precision of medical devices can be increased manifold. However, there are still concerns over the desired mechanical and rheological properties of the smart materials that can be used.

Sl.No

1

2

3

4

5

6

77

8

9

MR

g

cP

KHz

kg

V

AA

PIC

SCR

Magneto Rheological

Gram

Centipoise

KiloHertz

Kilogram

Voltage

AmpereAmpere

Peripheral Interface Controller

Silicon Control Rectifier

Full FormAcronyms

Abstract

Abbreviations

Market Trends/Challenges

Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 3


Forearm crutches are used by slipping the arm into a cuff to get a grip. The cuff, typically made of plastic or metal, can be a half-circle or a full circle with a V-type opening in the front, allowing the forearm to slip out in case of a fall. The forearm crutch used today is not too effective as it causes discomfort to the user instead of providing support with a convenient grip.

The proposed modified design of the crutch is to prevent any discomfort to the user and to give a sense of support for walking as if someone is holding the arms of the user.

This paper elucidates the following aspects of the crutch design:

Magneto Rheological (MR) fluids are a class of smart materials whose rheological properties can be rapidly controlled by an external magnetic field. MR fluids are a suspension of micron-sized, magnetically polarizable particles in oil or other liquids. Under normal conditions, MR fluids are free-flowing liquids having a consis-tency similar to that of Motor oil.

WhenWhen a magnetic field is applied, the interaction between the magnetically induced dipoles causes the parti-cles to form a columnar structure which is parallel to the applied field. This results in the restriction of flow of the fluid thereby increasing its viscosity. The degree of change in a MR fluid depends on the magnitude of the applied field.

Table 1. Composition of Magneto Rheological Fluid

Preparation of Magneto Rheological fluid to be used in a forearm crutch.

Design of the crutch with the Magneto Rheological fluid in the cuff region with a complete electrical circuit to actuate the fluid.

A basic MR fluid consists of three parts: Magnetically Polarizable Particles, Carrier Fluid, and Surfactant. Table 1 enlists the materials that are used to prepare 100 ml of the Magneto Rheological fluid in the laboratory.

Sl.No

1

2

3

Magnetically Polarizable Particles

150

55

5

Carrier Fluid

Surfactants

Ottokemi Electrolytic 99.5%Iron Powder of 300 mesh (86.4 microns approx) size

Fork Oil (Teleshocab Oil from Yamaha)

Pennzoil White Lithium Grease

Used Material Quantity (g)Component

Solutions

Preparation of MR Fluid



Figure 1. Magnetic Stirre Figure 2. Sonicator

The constituents were weighed using an electronic weighing balance as per the required quantity. White Lithium Grease and Fork Oil were mixed thoroughly for a period of 30 minutes at 50oC using a magnetic stirrer to achieve a homogeneous uniform mixture.

Iron powder was added in small amounts while the mixture was being stirred until no dry iron powder was visible and the mixture appeared uniform without any lumps of iron powder.

The fluid was allowed to mix thoroughly by sonicating it in an ultrasonic bath sonicator (at 33 KHz) The fluid was allowed to mix thoroughly by sonicating it in an ultrasonic bath sonicator (at 33 KHz) for 15 minutes to disperse all the particles uniformly.

The sample was placed in between the poles of a magnetometer to check if it displayed the Magneto Rheological effect.

The MR fluid so obtained was a dark grey, almost black color and highly viscous. Since such a highly viscous fluid cannot be used in the forearm crutch, we needed a low viscosity MR fluid, the composition of which could be estimated only by finding out the effect of the particle size, carrier fluid type and the percentage of magnetic particles on the viscosity. A Magneto Rheological fluid with viscosity comparable to that of conven-tional fork oil, i.e., close to 60 centipoises (cP) was required. Also, the settling time had to be improved so that the particulates did not settle down too soon in the forks.

TheThe viscosities of the prepared samples were measured using the Anton Paar Physica Rheometer MCR 301 series at the Indian Institute of Technology, Madras. The settling time for all the nine samples was measured. The samples were kept in vials and allowed to settle without any external disturbance. The time taken for the MR particulates to settle down was monitored using a stop clock.

Thus, a sample with 70% concentration of MR fluid, fork oil as the carrier fluid and white lithium grease as the surfactant was found to be suitable for the fore arm crutch because of its high viscosity and settling time compared to the other samples.

Procedure for preparation of Magneto Rheological Fluid:


LCD

PIC CONTROLLER

LOAD CELL

BATTERY

SCRCONTROL UNIT

ELECTROMAGNET


MR fluid so obtained can be filled near the cuff region. The force applied to the ground while walking is sensed by the pressure sensor and a signal is transmitted to the controller which controls the current to be passed to the electromagnet which is provided in the cuff region in order to produce the magnetic field. MR fluid solidi-fies according to the magnetic field produced due to this force. Thus, the grip offered to the arm varies accord-ing to the pressure applied by the user while walking. It clearly provides the sense of someone upholding the user while walking. The pressure applied is classified into three categories - high, medium and small. The con-trollertroller is programmed in a way to provide the corresponding current from the battery to the electro magnet according to the pressure applied. This actually changes the magnetic field, thereby varying the grip provided to the arm.

The pressure sensor used is the load cell. It is in the form of a wheat stone network. The pressure in the load cell is used to control the magnetic field by controlling the voltage of the lithium ion battery, using a peripheral interface controller by means of a SCR (Silicon Control Rectifier) control unit. The voltage of the battery is con-trolled according to the pressure applied there by varying the magnetic field and changing the viscosity of the MR fluid.

ELECTROMAGNET BATTERY

CONTROLLER

MR FLUID

PRESSURE SENSOR


Figure 3. Flowchart to actuate the MR Fluid

Figure 4. Setup to change the magnetic field


Finally, the controller setup to actuate the fluid is made and the voltage of the battery is controlled according to the load applied. The voltage given to the electro magnet actuates the Magneto Rheological fluid, changing the viscosity to vary the grip provided to the arm.

Figure 5. Prototype of forearm crutch

We designed a general design prototype with 12 V 1A batteries, a load cell, PIC controller and electromagnet in a forearm crutch in solid works software, as shown in Figure 5. Using a single 12 V battery, electromagnets and the PIC controller increases the weight of the prototype model. The load has to be evenly distributed along the fore arm crutch to decrease the weight. The problem with this design is that the use of the control-ler, electromagnet, and battery increases the weight and size of the stick.

By following the above three steps to modify the design of the forearm crutch, it can now be considered a for-midable new product that uses smart materials that increase its effectiveness. The modified prototype is shown in Figure 6.

Three steps have to be taken to reduce the size and weight of the crutch.

The controller setting has to be done in the chip design, to reduce the size.

The battery must be made small by using batteries of smaller voltages connected in a series to get 12V. It must be distributed along the stick.

The cuff region has to be changed as the electromagnet instead of having a separate magnet attached to it.

Load in kg

0-10

10-20

20-30

T

8

10

12

Electromagnet

Battery

PIC ControllerLoad Cell

Voltage in V

Best Practices

General Design Prototype

New Design



Figure 6. Modified Design of Prototype

This modified design is mainly targeted at the high-end customer who has a higher spending capacity, as this is an innovative new product using smart materials. Such a breakthrough is sure to attract customers around the world, mainly in developed economies, such as Europe and North America.

The new design for the fabrication of the forearm crutch, with the help of Magneto Rheological fluid, seems to offer great benefits:

A new product, providing the requisite support more effectively to the user.

It provides more comfort to the user and reduces the irritation on the arm.

Using smart materials will draw the attention of a large number of customers.

It provides a feeling of someone actually upholding the user while walking.

Electromagnet

Battery

Controller in Chip

Load Cell

Conclusion


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Author InfoKhaleelur Rahman

HCL Engineering and R&D Services

References

1. KetillHeiðarGuðmundssonDesign of a Magneto rheological Fluid for an MR Prosthetic Knee Actuator with an Optimal

Geometry

2. Henry hsu, aliso Viejo Magneto rheological fluid composition and prosthesis knee utilizing same (US) patent in 2004

3. S.Q. Abu-Ein, S.M. Fayyad, WaleedMomani -Experimental Investigation of Using MR Fluids in Automobiles Suspension Systems

.journal publishes in 2011

4. Hugh Herr and Ari WilkenfeldUser-adaptive control of a magneto rheological prosthetic knee

5. Carlson David J.What Makes a Good MR Fluid?, Journal of Intelligent Material Systems and Structures, Volume 13, 2002, 5. Carlson David J.What Makes a Good MR Fluid?, Journal of Intelligent Material Systems and Structures, Volume 13, 2002, Pages 7-8

6. ISO-2631, International Standards Organization, Guide for the Evaluation of Human Exposure to Whole-Body Vibration,

International Standard ISO 2631-1:1997(E)


Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch

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