Development of an Active Catheter Mechanism using IPMC for in vivo Inspection

JoMA (2014) 1-10 © STM Journals 2014. All Rights Reserved

Journal of Mechatronics and Automation

www.stmjournals.com

Development of an Active Catheter Mechanism using

IPMC for in vivo Inspection

Dillip Kumar Biswal, Dibakar Bandopadhya*, Santosha Kumar Dwivedy Department of Mechanical Engineering, Indian Institute of Technology Guwahati,

Guwahati, Assam, India

Abstract An active catheter mechanism designed and developed for body parts (interiors, oral)

inspection using active polymeric actuator i.e. ionic polymer metal composite (IPMC).

The first step is achieved by fabricating the low cost silver (Ag) electrode IPMC following the chemical decomposition method. When a voltage is applied, the catheter

yields a transverse movement; at the same time can exhibit forward and backward motion enables it to inspect wide range of area. Low driving voltage (maximum 1.2V)

ensures safety in clinical application inside the body parts. An experimental setup of the

mechanism has been developed using optical fiber for inspection purpose. A generalized mathematical model of the mechanism has been derived for fluid medium actuation and

is tested both in air and water to determine the effect of interactive forces during

operation and the results are discussed.

Keywords: Active catheter, IPMC, in-vivo, optical fiber, heaviside function

*Author for Correspondence E-mail: [email protected]

INTRODUCTION Active materials are nowadays utilized

successfully for interventional diagnosis and

therapy for their biocompatibility and

suitability for smooth and safe operation.

Active catheter is one such mechanism where

active materials such as shape memory alloys

(SMA), electro-active polymers (EAPs) and

piezoelectric materials (PZT) are successfully

used over the few years. Recently, there has

been tremendous progress and demand for

minimally invasive surgical (MIS) tools

essential for medical diagnostics and

treatment. Such tools sometimes use active

catheter system that operates by giving a force

input and rely on the intrinsic mechanical

property of long flexible catheter to transmit

the motion to the distal tip. Drawbacks like

hysteresis and recoiling results in poor

controllability of these systems. Hence, there

is deficiency in getting the desired accuracy

and repeatability for desired position. Shape

memory alloy (SMA) actuators have been

used in the past for active catheter by utilizing

their shape recovery effect with a heating

above phase transformation temperature [1–6].

Literatures showed that to fabricating multi-

dimensional bending mechanism for active

catheter, complex assembly processes, such as

accurate alignment and gluing of multiple

SMA actuators on a cylindrical surface of the

catheter were necessary [1,2,4]. Even though,

catheters made up of SMA are able to provide

a large bending, their slow response and high

operating temperature limits their applications.

Some of the advanced catheter designs with

active tip movement and controllable functions

have been proposed and developed.

Conducting polymers (CP) are also among the

leading design active materials for their

attractive features like large strain, low

operating voltage and suitability for

miniaturization [7–10]. In contrast to the shape

memory alloys, conducting polymers do not

require high operating current [11,12] making

them particularly suitable for in-vivo

biomedical applications. Electro-active

polymers (EAPs) exhibit properties most

closely matching those of natural muscles like

low density, short response time, resilience

and large actuation strains. Among various

Active Catheter Mechanism for In vivo Inspection Biswal et al.

__________________________________________________________________________________

JoMA(2014) 1-10 © STM Journals 2014. All Rights Reserved

types of EAPs, ionic polymer metal

composites (IPMCs) are especially prominent

material to be used in the active catheter

system due to their large bending actuation

with very low input voltage (1–2V).

Furthermore, few conductive polymers offer

higher stiffness than IPMCs, an important

attribute make it suitable often in catheter

design [13]. IPMC actuators have also been

suggested to be used in active catheter

application as well [14].

Operator’s skill is crucial to insert and guiding

the conventional catheter into a narrow and

complex fluid conduit or into the mouth for

imaging and inspection; because the catheter

and the guide wire do not possess the active

actuation capability. However, for advanced

navigation, active self actuation is needed for

the catheter or the guide wire to move in the

desired direction [15,16]. Further, redundancy

may be achieved by adding bending motion to

the guide wire also. Thus, active guide wire

system with self bending motion can navigate

the conventional non-active catheters into a

narrow and complex conduit such as blood

vessel. Further, engaging a twisting control

mode outside of the body, the guide wire can

move in multiple-directions even if it exhibits

one-directional bending function. Current

active catheter designs lack effective two

dimensional control of motion. Such motions

are important in procedures such as

angiography, stent deployment, and

aneurysms. Optical coherence tomography

(OCT) imaging technique nowadays is utilized

successfully for cross sectional imaging of

highly scattered medium such as biological

tissue [17]. OCT technique has also been used

over the past few years for imaging of

sectarian structures such as skin, retina, blood

vessels, oral cavities, gastrointestinal tracts

etc. This technique employs linear scanning

procedure by an optical beam actuated across a

target to create a 2D image. In the past, several

actuation mechanisms were developed for

actuation of optical fiber such as piezoelectric

material in cantilever configuration [18, 3].

Thermoelectric actuator and electrostatic

actuator were also used to swing a micro-

electromechanical mirror and the rotation of

electromagnetic devices (e.g., a galvanometer

shaft) by [19] and a micro-electromechanical

motor by Tran et al. [20]. Even though, these

actuation mechanisms have met the linear

scanning requirement however, they typically

require a relatively high driving voltage

[1,3,4,18] or a complicated instrumental

structure.

In the present study, Ag-IPMC actuator has

been chosen for their attractive features such

as low cost, low actuation voltage, small size,

high strain, compliance, biocompatibility, and

ease of fabrication make it suitable for active

catheter application. Past literatures showed

that limited work has been carried out using

active materials such as IPMC for design and

development of active catheter system. This

motivates to develop a low cost active catheter

system using smart material such as IPMC

suitable for in-vivo medical application. The

main objectives of the present work is to

design and develop a novel optical catheter

probe mechanism using ionic polymer metal

composite (IPMC) for medical applications

i.e., suitable for oral or inside the body

inspection. The main feature of the mechanism

is that it yields a controlled transverse

movement; at the same time can produce

forward-backward movement with low driving

voltage (maximum 1.2 V). This transverse

movement along with the to-and-from linear

motion of the catheter enables it to inspect

wide range of working area. Especially, low

driving voltage ensures safety for clinical

application inside of the body parts. Details of

the design and development of the catheter

mechanism are outlined. A generalized

theoretical model of the mechanism is derived

for fluid medium actuation taking into account

of the interactive forces of the catheter with

the medium. An experimental setup of the

catheter mechanism has been developed and is

tested both in air and water and the results are

discussed. Linear motion of the catheter

improves the flexibility i.e., enable it to take

images covering additional area maintaining

the same input voltage. The low cost Ag-

IPMC catheter mechanism has the potential

for applications in endoscope as well.

DESIGN AND DEVELOPMENT The first step of this work is to fabricate the

Ag-IPMC actuator. Nafion-117 membrane of

thickness 0.183 mm with an equivalent weight

(EW) of 1100 g/mol (purchased from Ion

Power Inc., New Castle DE, 19720 USA) is

used as the base polymer. The multi-steps

fabrication process comprises pretreatment of

Journal of Mechatronics and Automation Volume 1, Issue 1

__________________________________________________________________________________________


Nafion membrane, adsorption, and reduction

and developing. In various steps, silver nitrates

GR (AgNO3), ammonia solution (NH3),

sodium hydroxide (NaOH), dextrose

anhydrous GR (C6H12O6) chemicals are used

for fabrication. At the primary stage, the pre-

treated Nafion membrane is immersed in

NaOH, 0.5 mol/L solution followed by

Diamminesilver (I) hydroxide [Ag(NH3)2OH],

0.15 mol/L solution, subsequently Na+ and Ag

(NH3)2+ diffuse into the membrane via ion-

exchange process. C6H12O6 (0.088 mol/L)

acts as the reducing agent and initiates

deposition of silver particles over the Nafion

membrane surface. Finally, all sides of the

coated membrane are trimmed to avoid any

shorting between the surfaces and the final

IPMC is obtained. The details of the

fabrication process can be found in the

literature [21].

Active Catheter System

Active catheter system in medical application

demand characteristics such as the actuator

should be simple in structure, biocompatible,

non-acidic, rugged in handling, and suitable to

work well within interior of body parts. In this

work, optical fiber is chosen (attached from

the base to the end-tip) with the IPMC actuator

for imaging of targeted area. Optical fiber, a

very fine cylindrical glass fiber allows light

signals to travel from one end to the other. The

characteristics of optical fiber i.e., very light in

weight and flexible (easily twistable) makes it

suitable in the medical field where bright

lights need to be focused on a target well

within the body without a clear line-of-sight

path. Under electric potential, the actuator

bends in either direction and at the same time

controlled in-and-out motion perform

inspection of the affected area through optical

beam. Further, the light intensity of the

catheter can be controlled by adjusting the

active length of the catheter make it suitable

for getting improved vision of the uneven

interior. The schematic diagram of the

catheter with active and inactive portions is

shown in Figure 1. The length of the catheter

inside of the tube is assumed to be the inactive

and remains passive during inspection process.

Figure 1 shows the working mechanism of the

catheter with its active and passive length and

its variation for an input voltage V. Figure 2

shows the photograph of the developed active

catheter mechanism with optical fiber.

Fig. 1: Schematics of Preliminary Designs of a Forward Moving Active Catheter with an Optical Fiber.

Fig. 2: Photograph of the Developed Active Catheter Mechanism.


__________________________________________________________________________________


An IPMC actuator of size 45 x 2 x 0.2 mm is

fabricated and equipped with a

polytetrafluoroehhylene (PTFE) hollow tube

of small diameter (1 mm) along the length of

the IPMC strip through the surface by glue.

The setup i.e., IPMC with optical fiber is then

connected with the power source. The whole

arrangement of actuator probe is then inserted

into a catheter tube. When a voltage is applied,

the optical fiber along with IPMC follows a

bending path and in a process the directed

light inspects the affected area. Further, the to-

and-from motion mechanism enhances the

flexibility and enables it to inspect additional

area with same input voltage. Further, the

proposed catheter can be designed suitably for

examining the interior of a bodily organ in

fluid medium.

Fig. 3: Schematic Diagram of the Working Mechanism of the Active Catheter.

GENERALIZED MATHEMATICAL

MODEL OF ACTUATION A schematic diagram of the catheter

mechanism with axis of motion is shown in

Figure 3. The IPMC actuator has a uniform

rectangular cross section and is fixed at one

end. Other than actuation in air, such as

viscous fluid medium, the bending model of

the catheter needs to explicitly take into

account the interaction forces between the

actuator and fluid medium. Thus, in this work

a mathematical model has been derived

incorporating fluid interaction forces

necessary for controlling the tip position with

input voltage. Inside the fluid medium, the

actuator experiences counter actuation forces

owing to the viscosity and its oscillation. The

effect of viscous/drag force is often neglected

in air, but becomes significant when the

actuator operates in a denser medium such as

water/serum. As the actuator moves through

the fluid medium, a bouncy force also acts to

resist the motion. Thus both the forces i.e.,

drag and bouncy forces are taken into

consideration while formulating the expression

for bending moment. Euler-Bernoulli beam

theory is followed for modeling the end-tip

deflection of the actuator. The model has been

tested in water and compared with the results

obtained in air.

The drag force ( dgF ) experienced by the

actuator can be expressed as:

where, f is the mass density of the fluid, is

the velocity of the object relative to fluid, A is

the acting area, and DC is the drag coefficient.

The bouncy force ( bF ) developed can be

expressed as:

where, disV is the volume of the displaced fluid

and can be expressed as: ,

where, is the active length, dw and h are the

width and thickness of the IPMC. Hence, the

expression for effective bending moment

developed in a fluid medium can be expressed

as:

[ ] {

} [ ]


__________________________________________________________________________________________


where, 0M is the bending moment produced in

air and is obtained as

, X and

ix

denote the length of the actuator along the

axis. 1,2,3.......i n denotes number of

increments. The Heaviside function is defined

as:

[ ] [ ]

Subsequently, tip position ( ) of the

actuator is obtained as shown in the Figure 4.

where, is the flexural rigidity and is the

tip angle of IPMC actuator.

Calculation of Path Length

Under input potential, the end-tip of the

catheter with optical probe moves on a path

that directly measures the workspace. Further,

with change in active length, the bending path

and hence the measured workspace of affected

region changes for each input voltage. This

further can be adjusted by changing the length

of the actuator and controlling the input

voltage.

Initial position

Final position

Distance traveled

Fig. 4: Underwater Actuation of the Ag-IPMC Actuator for an Input of 1 V DC.

Figure 5 shows the geometrical configuration

of the bending path followed by the catheter.

OA is the initial length of the actuator before

activation. and are the tip positions

( ,x yp p ) while in motion and is the

effective length for an input voltage V.

1 2and are the angles between the initial

and final position after voltage V is applied. l

is the length and S is the path travelled by the

tip of the catheter. The effective length ( can be obtained as:

√

The angle ( ) between the initial position and

measured position (after input voltage) can be

obtained as:

(

)


__________________________________________________________________________________


Fig. 5: Schematic Diagram for Obtaing the Total Path Traveled by the Catheter Tip.

RESULTS AND DISCUSSION Simulation results are shown for a catheter

with an IPMC actuator of cross section

taking into account of the data

as given in the Tables 1 and 2. The initial

active length of the actuator is taken 20 mm

and then increased by 5 mm at each

subsequent step.The modulus of elasticity is

taken 82 MPa (obtained experimentally).

Table 1: Positions Obtained for Various Input Voltages in Air for Different Length of IPMC.

Environment Input potential

Air 0.2V 0.4V 0.6V 0.8V 1.0V

Active length Positions (rad)

Length=20 mm

Length=25 mm

Length=30 mm

0.2433

0.3407

0.4634

0.4866

0.6814

0.9268

0.7299

1.0221

1.3902

0.9732

1.3628

1.8536

1.2165

1.7035

2.3170

Table 2: Positions Obtained for Various Input Voltages in Water for Different Length of IPMC.

Environment Input potential

Water 0.2V 0.4V 0.6V 0.8V 1.0V

Active length Positions (rad)

Length=20 mm

Length=25 mm

Length=30 mm

0.2338

0.3257

0.4428

0.4675

0.6515

0.8856

0.7013

0.9772

1.3284

0.9351

1.3029

1.7712

1.1688

1.6287

2.2140

Constant curvature bending of IPMC strip is

assumed and a relationship between voltage

and tip angle is established using linear curve

fitting approximation technique with a quality

factor (R2) 0.9729 and is given in Eq. (8).

Figures 6 and 7 show the path of the catheter

in air and underwater for various input

voltage. Figure 6 shows the path for an input

of 0.6 V (both positive and negative) while

Figure 7 shows the results for an input of 1V.

Three times active length of the catheter is

changed i.e., 20, 25 and then 30 mm

maintaining the same input voltage. It is

clearly observed that with increase in active

length, working path span increases results in

enhancement of ability of the mechanism to

inspect additional working area.


__________________________________________________________________________________________


Fig. 6: Path Followed by the Catheter Probe for an Input Of 0.6 V (A) Open Environment (Air)

(B) Underwater.

Fig. 7: Total Path Travelled by the Tip of the Catheter for an Input of 1.0 V (A) Open Environment (air)

(B) Underwater.

EXPERIMENTS The functioning of the catheter mechanism has

been studied by conducting experiment both in

air and fluid medium i.e. underwater. A

fabricated IPMC sample of size 4

is prepared for the experimentation.

An optical fiber is attached over the surface of

the IPMC and connects with the power source.

Before the experiment, the IMPC actuator is

tested in water alone to figure out the

interactive forces during operation. Figure 4

shows the underwater actuation of the IPMC

for an input of 1 V separately. It is observed

that the actuator experiences significant

counteract forces during motion in denser fluid

medium such as water compared to air. Figure

8 shows the initial and bending configuration

(after the voltage is applied) of the catheter

for an input of 1 V. The voltage is applied at

the fixed passive end through a copper strip; as

a result free end of catheter illuminate the

affected area. The initial active length of the

actuator is chosen 20 mm and the results are

shown in the Figures 9 and 10 and discussed.


__________________________________________________________________________________


Fig. 8: Photograph of the Active Catheter System

in Water for an Input 1 V.

Figure 9 shows that imaging path of the

catheter enhances with increase in active

length of the actuator. For assessment, with an

input , the catheter tip moves 28.5 and

27.464 mm path in air and underwater,

respectively. However, as the active length

changes to 25 mm, the working path amplifies

to 48.8 mm in air and 46.9 mm underwater

maintaining the same input voltage. Figure 10

shows the comparative results on total

working path of the catheter for an input 1.2 V

for three consecutive active length of the

IPMC. It is observed that due to counteract

forces in denser fluid medium i.e., water in

this case, the catheter undergoes losses results

in drop of the working area. These results also

validate that the catheter mechanism is

suitable for spawning multiple image taking

path for in-vivo inspection of affected zone.

4.5

4.75

5

5.25

5.5

5.75

6

6.25

6.5

6.75

7In air

Under water

Sca

nn

ing

pa

th (

mm

)

2.05

2.1

2.15

2.2

2.25

2.3

2.35

2.4

2.45 In air

Under water

3.3

3.4

3.5

3.6

3.7

3.8

3.9

4

4.1

4.2

4.3 In air

Under water

Sca

nn

ing

pa

th (

mm

)

Sca

nn

ing

pa

th (

mm

)

(c) Active length = 30 mm

S1

S6

S5

S4

S2 S

3

S6

S5

S4

S3

S2

S1

S6

S5

S4

S3

S2

S1

(b) Active length = 25 mm(a) Active length = 20 mm

0.2:0.2:1.2 V 0.2:0.2:1.2 V

0.2:0.2:1.2 V

Fig. 9: Path Followed by the Catheter Tip for Various Input Voltage (Both Air and Water).


__________________________________________________________________________________________


0

10

20

30

40

50

60

70

80In air

Under water

Tota

l sc

an

nin

g p

ath

(m

m)

Active length (mm)

20 mm 25 mm 30 mm

Fig. 10: Comparative Study on Path of Actuation (Both in Air and Water) Travelled by the Catheter

for an Input 1.2 V.

Table 3: Incremental Imaging Path Obtained for Various Input Voltages in Open Environment (Air).

Voltage

()

Change in path length

active length

(20 mm)

active length

(25 mm)

active length

(30 mm)

0.2V

0.4V

0.6V

0.8V

1.0V

1.2V

0

0

0

0

0

0

3.64

7.26

10.8

14.19

17.38

20.34

8.41

17.95

26.54

34.59

41.9

48.33

Table 3 enlists increase in path length for

various input voltage separately. It is clearly

shown that path of the catheter probe

significantly increases whilst maintaining the

same input voltage.

CONCLUSION An active catheter mechanism of IPMC

actuator has been designed and developed. A

generalized mathematical model has been

derived for fluid medium actuation taking into

account of the fluid interaction forces.

Experiments are conducted both in air and

water to determine the resistance encountered

during actuation and the results are verified

with the simulation results. The novelty of the

catheter mechanism is that the length of the

IPMC actuator varies with input voltage

results in multiple image-taking paths and thus

can cover wide range of working area with

same input voltage. The to-and-from motion

mechanism enhances the focusing area and

also suitable for adjusting the light intensity.

Apart from oral and dental cavity inspection,

the low cost Ag-IPMC mechanism has the

potential to be used in endoscope.

ACKNOWLEDGMENT The ‘corresponding author’ thankful for the

partial financial support from Department of

Science and Technology (DST), Government

of India under SERC FAST Track Scheme

(SR/FTP/ETA - 076/2009).

REFERENCES 1. Lim A., Lee S., Thin Tube-Type Bending

Actuator Using Planar S-Shaped Shape

Memory Alloy Spring, Technical Digest of

the 10th International Conference on

Solid-State Sensors and Actuators

(Transducers 99), Sendai, 1999; 2: 1894–

1895p.


__________________________________________________________________________________


2. Park K-T., Esashi M., A Multilink Active

Catheter with Polyimide-Based Integrated

CMOS Interface Circuits, J.

Microelectromech. S. 1999; 8: 349–357p.

3. Haga Y., Maeda S., Esashi M., Bending,

Torsional and Extending Active Catheter

Assembled using Electroplating,

Proceeding of the IEEE International

Micro Electro Mechanical Systems

Conference, (MEMS 2000) Miyazaki,

2000; 181–186p.

4. Mineta T., Mitsui T., Watanabe Y., et al.

Batch Fabricated Flat Meandering Shape

Memory Alloy Actuator for Active

Catheter, Sensor Actuator A: Physical,

2001; 88: 112–120p.

5. Tung A.T., Park B-H., Niemeyer G., et al.

Laser-Machined Shape Memory Alloy

Actuators for Active Catheters,

IEEE/ASME Trans. Mechatronics, 2007;

12: 439–446p.

6. Mineta T., Deguchi T., Makino E., et al.

Fabrication of Cylindrical Micro Actuator

by Etching of TiNiCu Shape Memory

Alloy Tube, Sensor Actuator A: Physical,

2011; 165: 392–398p.

7. Wang X-L., Oh II-K., Lu Jun., et al.

Biomimetic Electro-Active Polymer Based

on Sulfonated Poly (styrene-b-ethylene-

co-butylene-b-styrene), Mater. Lett. 2007;

61: 5117–5120p.

8. Fang B.K., Ju M-S., Lin C-C. A New

Approach to Develop Ionic Polymer-Metal

Composites (IPMC) Actuator: Fabrication

and Control for Active Catheter Systems,

Sensor Actuator A: Physical, 2007; 137:

321–329p.

9. Lee K.K.C., Munce N.R., Shoa T., et al.

Fabrication and Characterization of Laser-

Micro Machined Polypyrrole-Based

Artificial Muscle Actuated Catheter,

Sensor Actuators A, 2009; 153: 230–236p.

10. John S.W., Alici G., Cook C.D. Inversion-

Based Feed Forward Control of

Polypyrrole Trilayer Bender Actuators,

IEEE/ASME Trans. Mechatronics, 2010;

15: 149–156p.

11. Haga Y., Tanshashi Y., Esashi M. Small

Diameter Active Catheter Using Shape

Memory Alloy, Proceeding of IEEE

MEMS, Heidelberg, Germany 1998; 419–

424p.

12. Madden J., Vandesteeg N., Anquetil P., et

al. Artificial Muscle Technology: Physical

and Naval Prospects, IEEE J. Oceanic

Eng. 2004; 29: 706–728p.

13. Carry J., Fahim A., Munro M., Design of

Braided Composite Cardiovascular

Catheter based on Required Axial,

Flexural, and Torsional Rigidities, J.

Biomed. Mater. Res. - Part B Appl.

Biomater. 2004; 70: 73–81p.

14. Wang Y., Bachmam M., Li G-P., et al.

Low-Voltage Polymer-Based Scanning

Cantilever for in vivo Optical Coherence

Tomography, Opt. Lett. 2005; 30: 53–55p.

15. Boppart S.A., Bouma B.E., Pitris C., et al.

Forward-Imaging Instrumented for Optical

Coherence Tomography, Opt. Lett. 1997;

22: 1618–1620p.

16. Pan Y., Xie H., Fedder G.K. Endoscopic

Optical Coherence Tomography based on

a Microelectromechanical Mirror, Opt.

Lett.. 2001; 26: 1966–1968p.

17. Huang D., Swanson E.A., Lin C.P., et al.

Optical Coherence Tomography, Science,

1991; 254: 1178–1181p.

18. Kaneko S., Aramaki S., Arai K., et al.

Multi-Freedom Tube Type Manipulator

with SMA Plate, Proceeding of the

International Symposium on

Microsystems, Intelligent Materials and

Robots, Sendai, Japan, 1995; 87–90p.

19. Bouma B.E., Tearney G.J., Power-

Efficient Nonreciprocal Interferometer and

Linear-Scanning Fiber-Optic Catheter for

Optical Coherence Tomography, Opt. Lett.

1999; 24: 531–533p.

20. Tran P.H., Mukai D.S., Brenner M., et al.

In vivo Endoscopic Optical Coherence

Tomography by Use of a Rotational

Micro-Electromechanical System Probe,

Opt. Lett. 2004; 29: 1236–1238p.

21. Dillip Kumar Biswal, Dibakar

Bandopadhya, Santosha Kumar Dwivedy,

Preparation and experimental investigation

of thermo-electro-mechanical behavior of

Ag-IPMC, Actuator 2004; 13 (5): 777–

82p.

Development of an Active Catheter Mechanism using IPMC for in vivo Inspection

Documents

Transcript of Development of an Active Catheter Mechanism using IPMC for in vivo Inspection