Fluid Needles: transforming shock waves into syringescdohl/publication/NRP Report Seow Chze...

Proceedings of 2009 Nanyang Research Programme

NRP Project Code SPMS4

Fluid Needles: transforming shock waves into syringes

SEOW CHZE KIAN ANGLO-CHINESE JUNIOR

COLLEGE

Abstract- A phenomenon named fluid focusing creates very fast liquid needle like flows from accelerated concave fluid interfaces. In this project, a shock-wave generator imposes this acceleration onto a liquid meniscus inside a capillary. Thereby, a liquid jet is generated which shoots up with more than 300km/h with a thickness of only a few micrometer. Using high-speed cameras, the motion of such liquid jets is being captured and studied upon. The idea behind this research is to use these thin liquid needles for drug delivery such as for vaccines. Yet the study is on the underlying physical principles. This paper explores the velocities and shapes of such jets and the subsequent motion of the concave fluid interfaces in order to determine more accurately the possible applications of such jets.

Keywords: Fast liquid needle, liquid jet, shock-wave, high-speed cameras, drug delivery

1 INTRODUCTION

Research has been done in the field of fast flowing fluids [1] and applications of such fluids are wide. Some of them include vaccination using air to bypass the skin instead of conventional needles [2] and in transportation technology. Lithotripsy, which is the medical procedure used to break kidney stones also employs shock waves in its operation [3]. The objective of the project is hence to understand in greater detail the conditions as to why shockwaves can achieve such feats and its possible applications when fluids are used.

Previous research by D. Martens of the University of Twente, The Netherlands [4] has shown that fluid focusing is not needed for the development of a jet. However, it plays an important role in the development of the jet. In this project, the velocity of the liquid jet arising from fluid focusing on the concave

A/P CLAUS-DIETER OHL NANYANG TECHNOLOGICAL

UNIVERSITY - SCHOOL OF PHYSICAL AND MATHEMATICAL

SCIENCES

fluid interface, the shape of the jet including the tip and the subsequent motion of the bubble is being investigated and by using the jet velocities obtained, possible applications of the fluid jets can be determined. However, this paper does not include the exact details of fluid focusing.

This paper is separated into Introduction, Research Methodology and Experiments, Results, Conclusions and discussions, Acknowledgements and References.

Definition of terms

Lithotripter (piezoelectric transducer)

A device that passes shock waves through a water-filled tub generating high pressures at its point of focus.

Bubble/bubble meniscus

The concave fluid interface which is at the bottom of the capillary tube. It is aligned to the focus of the lithotripter.

Cavitation

The formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure.

2 METHODOLOGY / MATERIALS AND

EXPERIMENTS

I EXPERIMENTAL SET-UP

The main experimental set-up consists of the lithotripter being held by a carefully designed base acrylic 30cm thick. Boards of carefully measured acrylic are being placed in 2 boxes above the base. A simple sketch of the experimental set-up and a picture of it can be found in Appendix A.



II INTERNAL WORKINGS OF THE LITHOTRIPTER

The lithotripter (piezoelectric transducer) designed by Rainer E. Riedlinger [5] is connected to an external power source that discharges voltages according to user settings. A simplified sketch of the internal make-up of the lithotripter is shown below (Figure 1). Upon initiating the external power source (Front and Back piezoceramics width1 = 10 µm), the back transducer would generate a pulse which coincides with the pulse generated by the front transducer 2.4 µs later. This superimposes a pulse with 2 times the amplitude [6]. Placed at the base (point A) of the liquid (water) container, the pulse travels through the water in the container and focuses at a point of the water surface. A jet is thus formed resembling a syringe allowing for penetration into other surfaces.

III HOW THE SET-UP WORKS

1 Width refers to the pressure of the wave generated. In this case, it is negative 10 Mpa pressure

According to the manufacturing specifications, the point of focus of the shockwave from the lithotripter is 194mm vertically above the base of the lithotripter. The focal point is where the highest pressure generated by the pulse is. By filling up the container with water and ensuring that the water level coincides with the focal point of the pulse, the highest pressure is ensured at the surface of the fluid. This results in flowing water which allows for cavitation to occur. The bubbles release contains the greatest amount of energy and this upward release of energy by the bubble greatest a water jet at the water surface.

By placing a thin capillary tube at the point of jet formation, cavitation can occur at the surface of a curved meniscus similar to a bubble [4] which allows for a much faster jet to be formed. The meniscus is formed by attaching a syringe to the capillary tube and increasing the pressure inside the tube in order to force the air out as a meniscus. A sketch of the place where the capillary tube is placed is shown (Figure. 2).

IV ADDITIONAL EQUIPMENTS

All experiments were carried out using this set-up (Design sketches of acrylic boards can be found in the Appendix B). Other than this, a Photron High-speed camera (FASTCAM SA1.1 mono/colour) controlled using the Photron FASTCAM Viewer 3

software, Pulse/Delay generator and a HBO 50, Carl Zeiss Mercury lamp were used in the experiments. The lamp provided sufficient illumination in the form of diffused light2 for the camera (the camera is tilted 90° anti-clockwise with respect to the lamp) to record at high frame rates and short exposure time. The Pulse/Delay generator coordinated all the apparatus and acts as a trigger for the

2 Kimwipes towelettes were placed in front of the lamp and acts as a light diffuser

Direction of Wave

A

Back piezoceramics

Front piezoceramics

Figure 1: Internal sketch of lithotripter (Looking from A into the plane of the paper)

Figure 2: Experimental set-up with capillary tube

Path of pulse

106mm

70mm

Lithotripter

Transparent acrylic boards

194m

Capillary tube



recording. The full experimental set-up can be found in Appendix C.

V EXPERIMENTS

Three experiments were carried out to find out:

1) The velocity of the jet originating from the bubble

2) The shape of the jet tip

3) The subsequent motion of the jet bubble

Taking maximum care to avoid possible errors, the following assumptions were made.

1) The capillary tube is at point of focus of shockwave and all energy from the shockwave is transferred to the curved meniscus

2) Velocity of the jet is constant throughout the duration of observation of the jet

EXPERIMENT 1

By varying the extent of protrusion of the bubble (0.4mm, 0.8mm, 1.2mm) from the capillary tube as shown in Figure 3, different jet velocities are obtained.

The external pulse/delay generator is attached to the lithotripter to control the width of the pulse and initiate the pulse. The settings on the generator are as follows:

1) Front and back 10 µm width

2) Front 2.4 µs delay

3) 5kV voltage

Known measurement: 1 pixel = 0.0244 mm

In calculating the velocity of the jet, two pieces of information which are

1) Displacement of the jet

2) Duration of displacement

must be known. These two values are connected by the velocity equation:

time

ntdisplacemevelocity =

The time is calculated using the frame rate of the camera. For this experiment, the frame rate is 100, 000 fps (frames per second). By inversing this value, the duration of 1 frame can be calculated to be 0.00001s. Displacement is calculated through pixels. Using the known measurement, the displacement in 1 pixel can be calculated. To obtain the known measurement beforehand, an object of known dimension is placed within the field of the camera and the number of pixels it occupies is recorded and by inversing the value, the displacement per pixel is calculated. In this case, the diameter of the capillary tube (1.95mm) acts as the object of known dimension. Knowing these 2 values, a displacement – time graph was plotted for the displacement at every frame. The velocity of the jet is then calculated from the gradient of the graph.

EXPERIMENT 2

In this experiment, the Photron high speed camera is used to capture the tip of the jet. The settings were the same as in Experiment 1.

EXPERIMENT 3

Using the Photron high speed camera, the process of the bubble stabilizing after the initial impact of the shockwave is recorded and then analyzed.

Figure 3: Different extents of protrusions of bubble meniscus (0.4, 0.8, 1.2mm)



3 RESULTS

The displacement-time graph of the jet for each of the different degrees of protrusions of bubble meniscus as its corresponding image of jet at the end-point of the observation is shown below.

I EXPERIMENT 1 – 0.4mm PROTRUSION

y = 15.74x

0

0.001

0.002

0.003

0.004

0.005

0.006

0 0.0001 0.0002 0.0003 0.0004

Time /s

Dis

pla

cem

ent

/m

Figure 4: Displacement-time graph of jet with 0.4mm protrusion

In Figure 4, due to the unclear images from t=0.00072s to t=0.0001s, no points were plotted there. The velocity of the jet was calculated to be 15.7 ms-1. In Figure 5, the splashing of the jet tip is probably due to the jet destabilizing [7] as it reaches higher levels.

EXPERIMENT 1 – 0.8mm PROTRUSION

y = 17.157x + 0.0005

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0 0.00005 0.0001 0.00015 0.0002 0.00025 0.0003 0.00035

Time /s

Dis

pla

cem

ent

/m


In Figure 6, due to the unclear images from t=0.00007s to t=0.00011s, no points were plotted there. The velocity of the jet was calculated to be 17.2 ms-1.

EXPERIMENT 1 – 1.2mm PROTRUSION

y = 36.341x - 0.0002

-0.001

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0 0.00005 0.0001 0.00015 0.0002 0.00025

Time /s

Dis

pla

cem

ent

/m


In Figure 8, due to the unclear images from t=0.00004s to t=0.00006s, no points were plotted there. The velocity of the jet was calculated to be 36.3 ms-1.

Figure 7: Jet image at end of observation


Jet tip

1.95mm


Jet tip

1.95mm

Jet tip

1.95mm



Jet tip

Jet tip

Figure 12: Creation of water jet (0.8mm bubble protrusion, frame 12 - 17, 0 – 0.00005s after start)

Water jet created from bubble apex

Figure 13: Bubble split (0.8mm bubble protrusion, frame 18 - 32, 0.00006 – 0.0002s after start)

Right half Left

Figure 14: Bubble reformation and elongation (0.8mm protrusion, frames 32 - 204, 0.0002 – 0.00204s after start)

Original protrusion level

Figure 15: Eventual stabilising of 1.2mm protrusion bubble (500 frames, 0.005s onwards)

II EXPERIMENT 2

Shown below are images of 2 selected jet tips.

III EXPERIMENT 3

There are three broad stages in which the bubble reacts to the change in pressure which brings about the water jet.

Stage 1 is the collapse of the part where the bubble is hit. The apex of the bubble collapses towards the capillary tube and the water jet is created here. This is shown in Figure 12.

After that, the bubble divides into two connected halves as shown in Figure 13.

Stage 2 would involve the reformation of the bubble and an elongation of the bubble as shown in Figure 14. Repeated tries have shown that the bubble attempts to split at this stage. However, the splitting arising from instability is much less obvious. Elongation has also sometimes resulted in the pinching off of bubbles.

Stage 3 will be the continual collapsing and elongation of the bubble with splitting. However, it becomes less obvious such that the bubble is seen to be only expanding and contracting while it stabilizes. The end-result is somewhat similar to the initial bubble. This is shown in Figure 15.

Figure 11: Destabilised jet tip 0.8mm protrusion Exposure time: 1/119 000 sec

Figure 10: Well-defined jet tip 1.2mm protrusion Exposure time: 1/119 000 sec



4 DISCUSSION

Through Experiment 1, the velocity of the jet at 5kV setting was found out to be 36.341 ms-1 or 130.83kmh-1. Although this falls short of the expected 300 kmh-1, it shows that cavitation activities at the surface of a curved meniscus do have the potential to reach extremely high velocities. The short time it takes for the jet and bubble to complete the major movements (0.008~0.010s) is proves again the jet’s fast motion. For the duration of the observation, the jet velocity was fairly constant allowing for a high accuracy in the determination of the jet velocity hence increasing the reliability of the data. It is also established that increasing the extent of protrusion of the bubble will increase the corresponding velocity of the jet (Figure 16) and this can have major implications.

0

5

10

15

20

25

30

35

40

0 0.0005 0.001 0.0015

Protrusion height of bubble /m

Jet

velo

city

/m

Figure 16: Jet velocity against protrusion height of the bubble

The shape of the tip of the jet as determined from Experiment 2 is also very sharp (<0.05mm is diameter) and considering the high velocity of the jet, the jet is fully capable of penetrating hard objects. The diameter of the jet cannot be determined accurately due to limitations of the camera settings. Comparing both jets at 1.2 and 0.8mm protrusion, the jet produced by the bubble at 0.8mm protrusion appears to destabilize as it reaches greater heights. In Experiment 3, it is confirmed that the extent of protrusion of the bubble provides an indication of how stable a jet will be. At larger protrusions, it is observed that the motion of the bubble seems less drastic and less obvious implying a more stable movement of the bubble and the jet. From the three experiments, there are a few conclusions made:

1) The jets move at a velocity of about 40ms-1 and increasing the extent of

bubble protrusion increases the jet velocity.

2) Jets normally have well-defined sharp tips

3) The larger is the extent of protrusion of the bubble, the more stable the resultant jet is.

There are many applications of these fluid jets. Firstly, since increasing the bubble protrusion increases the velocity of the jet, bubbles with larger protrusions up to a certain limit can be used to produce water jets at higher velocities. Since the kinetic energy of the jet varies with the square of its velocity [8], increasing the bubble radius can actually lead to high energy bursts of jets. Combining this with the sharp tip of the jet, these high energy jets are fully capable of exerting a large pressure3 on any surface. However, more research needs to be done on the limit of the bubble extension before the jet velocity ceases to increase. Other factors such as applied voltage can also be varied and the resulting jet velocity can be investigated to see if jet velocity increases or not. One of its uses would be the ability of these fluid needles4 to deliver medicines or vaccines to cells without breaking the cell surface membrane. This can be achieved by replacing the water in the container with the desired medicine/vaccine/solution. With better resolution of the camera, the jet tip can be calculated to smaller values of few micrometers. This would allow for easy penetration of the jet carrying medicine into the cell membrane. Due to the high speed of the jet, the cell membrane would reform from the fast disturbance quickly [10] and hence, no damage is done as shown by the reforming of the bubble after the water jet has passed through in Experiment 3. Furthermore, due to the small surface area targeted, fluid jets can perform drug delivery to very specific cells for example in the case of delivering drugs to cancerous cells to kill them while maintaining healthy cells. Large molecules that are unable to enter a cell can also be transferred in this manner. By increasing the bubble protrusion on which the cavitation activity occurs, the stability of the bubble can be increased allowing for more accurate applications of the fluid needles.

3 Pressure exerted by an object on the surface is inversely related to its surface area of contact [9]. 4 Fluid needles refer to the water jets that are shaped like needles and fluid in nature



Using fluids in breaking kidney stones has some advantages. For example, drugs that hasten the healing of the kidney can be transported into the kidney while shattering the kidney stones. Other practical uses of the fluid needles can include construction works where large forces are needed sometimes to drill or dig holes. These fluid needles can be used on a large scale for such purposes.

5 CONCLUSION

Through this project, the velocities of fluid needles have been investigated together with the shape of the jet under different degrees of protrusions of the concave liquid meniscus. Conclusions have also been made about these results obtained after various tries.

Other areas of research include how the skin can be penetrated by fluid without causing damage to deliver drugs externally. Also, since using fluids to destroy kidney stones may result in fluid retention in the kidney which may be detrimental for the patient, the right amount of fluid needed can be further researched upon.

With the vast possibilities that fluid dynamics offers, more research should be done in this field in order to unravel such possibilities and hopefully, new doors can be opened to this dynamic field of fluid physics.

ACKNOWLEDGEMENTS

This project would not have been possible without the help of the following people:

1) My Assistant Professor Claus-Dieter Ohl for his careful guidance and patience with me throughout the course of the project

2) Dr Silvestre Roberto Gonzalez Avila for his unyielding support, help and most importantly, encouragement throughout the course of the project

3) Nanyang Technological University School of Physical and Mathematical Sciences Physics class of 2009 John for his great help during the designing

of the experimental set-up in the Design Phase of the project

4) Exel Mitsui Precision Tools for fabricating the experimental set-up nicely

5) Tandiono for his help in the lab

6) Mdm Low Hwee Miang, Miss Fong Wai Yee and Mr Wong Wee Meng from Anglo-Chinese Junior College for their support and reminders of the different stages of the project

7) Nanyang Technological University for providing me with the opportunity to embark on this research project

And all others who have helped me in one way or another.

REFERENCE

[1] Borkent, Bram M, Manish Arora, and Claus-Dieter Ohl. "Reproducible cavitation activity in water-particle suspensions." (2007): 1406-1412. Web. 28 Dec 2009. <http://www1.spms.ntu.edu.sg/~cdohl/publication/JASAb_07.pdf>

[2] “Shots without needles - A safer, cheaper way to get vaccines where they are needed most." Path: Jet injector. 2009. PATH: a catalyst for global health, Web. 28 Dec 2009. http://www.path.org/projects/jet_injector.php

[3] “Stones - Surgical Treatment." Urology Channel. 23 Jul 2008. Health Communities, Web. 28 Dec 2009. http://www.urologychannel.com/kidneystones/treatment-surg.shtml

[4] “Master's Thesis Report." Micro scale jetting by shock wave interaction. 7500 AE Enschede, The Netherlands: Physics of Fluids Group, Faculty of Science and Technology, University of Twente, 2006. Print

[5] “Design of piezoelectric transducer” Dreyerl,, Thomas, Werner Krauss, Edgar Bauer, and Rainer E. Riedlinger. "Investigations of Compact Self Focusing Transducers using Stacked Piezoelectric



Elements for Strong Sound Pulses in Therapy." 2000 IEEE Ultrasonics Symposium. (2000): 1-2. Print

[6] JUNGE, M. ARORA, L., and Claus-Dieter Ohl. "Cavitation Cluster Dynamics in Shock-Wave Lithotripsy." World Federation for Ultrasound in Medicine & Biology. (2005): 2-3. Print

[7] “Gravitational destabilizing” RADWAN, AHMED E. "Magnetogravitodynamic Instability of a Cylindrical Fluid Jet acting upon a general varying magnetic field A." Department of Mathematics, Faculty of Science, Ain-Shams University, Abbassia, Cairo, Egypt Kluwer Academic Publishers 182 (1991): 85-96. Web. 28 Dec 2009. <http://www.springerlink.com/content/k773768231589470/fulltext.pdf?page=1>

[8] “Relationship between kinetic energy and velocity” "Kinetic energy." Wikipedia. 27 Dec 2009. Wikimedia Foundation, Inc, Web. 28 Dec 2009. <http://en.wikipedia.org/wiki/Kinetic_energy>

[9] “Relationship between pressure and surface area of contact” “Pressure." Wikipedia. 29 Dec 2009. Wikimedia Foundation, Inc, Web. 28 Dec 2009. http://en.wikipedia.org/wiki/Pressure#Formula

[10] “Reforming of bubble after penetration” Ohl, Claus-Dieter, and R. Ikink. "Shock-wave-induced jetting of micron-size bubbles." Physical review letters. 90.21 (2003): 1. Print



APPENDIX



Top box smaller

Side

Base

Side Larger

Top Top box larger

Parts of the experimental set-up

APPENDIX A

Simple sketch of experimental set-up and picture of experimental set-up

APPENDIX B Design sketches of the experimental set-up

106mm

70mm

Lithotripter

Transparent acrylic boards

Sketch of experimental set-up (Point A corresponds to Point A in Figure 1)

A

Picture of experimental set-up



APPENDIX C Full experimental set-up

Full experimental set-up

Pulse/Delay generator

Mercury lamp

Photron camera

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