Recent developments in MISI Introduction

Minimally invasive surgery (MIS) is becoming more and

more common in hospitals. These procedures are performed

through tiny incisions instead of one large opening. Because

the incisions are small, patients tend to have quicker recovery

time and less discomfort than with conventional surgery — all

with the same benefits.

However, with this method, a surgical operation is

performed by the help of: a small endoscopic camera; several

long, thin, rigid instruments.

II Bionic Design of Microjoint for Minimally Invasive

Surgical Instrument

A microjoint for minimally invasive surgery based on bionic

design like an insect leg has been developed. This microjoint is

comprised of two materials which have different stiffness

characteristics. First of all, the microjoint was designed based

on analythical approach and determined the using of SU-8 and

PDMS as materials of designed joint. The advantages of

proposed microjoint are as follows: (1) Small (less than 2 mm),

(2) Flexibility, (3) High I/O ratio, and (4) Biocompatibility.

Through the basic experiment, it has been confirmed that the

developed joint has a potential for application of endoscopic

surgery such as Endoscopic Sub-mucosal Dissection (ESD).

Proposed joint is small (2 mm), and it can insert to the

channel of oral endoscope to assist of the surgical procedure, as

shown in Fig.1 followed.

Fig.1 Concept of bionic design and application to the

medical device

Fig.2 below shows the fabrication process flow, SU-8 and

PDMS for proposed joint. This exoskeletal structure of

microjoint is fabricated by stacking the several layers, which

are made by photolithography. The fabrication process is after

the design of the dimensions and the simulation or calculation

for enough bend and stiffness.

Fig.2 Process flow of the joint

III A Piezoresistive Based Tactile Sensor

A novel tactile sensor is proposed for use in minimally

invasive surgery to provide surgeons with tactile information.

The sensing element of the sensor relies on a piezoresistive

material. The proposed sensor measures contact force as well as

the relative hardness of soft contact objects. Experimental test

results confirm the ability of the sensor to distinguish between

two different elastomeric materials. Such materials resemble

two different biological tissues.

Fig.3 Sensor Design

As illustrated in Fig.3, the proposed sensor consists of an

elastic beam laid on two supports located on both right and left

sides of the sensor.

In fact, piezoresistive films are selected as the sensing

elements of the sensor because of: (1) their fast response to

static and dynamic loads, (2) their ability to be micro–

fabricated, and (3) their low sensitivity to external noise.

The three piezoresistive films that are placed in the bottom of

the sensor structure measure the total contact force applied to

the top of the sensor. At the same time, the fourth film, which is

placed between the sensor beam and the filler material,

measures the deflection of the beam, caused by contacting a soft

object. The more the deformation of the contact object, the more

the deflection of the beam and the more the output of the middle

top piezoresistive film.

The range and the resolution of the sensor can be fine-tuned

by changing the design parameters of the sensor.

As a result, the sensor would be miniaturized enough for

integration into the small space available at the tips of MIS

graspers.

IV A PZT Bimorph Actuator

By optimizing the thickness of the piezoceramic layers, and

by allowing the voltage applied to each segment to vary,

dramatic improvements in deflection and force are obtained

when compared to a standard straight bimorph actuator. The

motivation for this design is the need in the field of minimally

invasive surgery for improved grasping tools, where a pair of

optimized bimorph actuators can be used as a simple grasping

device.

Fig.4 PZT Bimorph.

A piezoelectric bimorph actuator is created by laminating

layers of piezoelectric ceramic material (PZT) onto a thin

sandwich beam or plate. When opposing voltages are applied to

the two ceramic layers, a bending moment is induced in the

beam Fig.4. A pair of cantilevered piezoelectric bimorph

actuators can be used as a simple grasping device, where the

bimorph actuators are used as active “fingers” as shown in

Fig.5.

Fig.5 Bimorph Grasper

V Conclusions

This report has showed several state-of-the-art researches in

MIS (Minimally Invasive Surgery) related about bio-micro-

machine. From microjoint, piezoresistive tactile sensor to PZT

bimorph, it implies that MEMS technology could be highly

applied at any aspects in any fields relevant to bio-micro-

machine.

VI References

[1] Hirofumi O., Tomohiro K., and Fumihito A., “Bionic Design

of Microjoint for Minimally Invasive Surgical Instrument”

IEEE Biomechnics., pp. 297–299, 2011.

[2] Atieh A. et al., “A Piezoresistive Based Tactile Sensor for

Use in Minimally Invasive Surgery” IEEE Bioengineering

Conference, pp. 1–2, 2011.

[3] David J. et al., “Optimal Design of a PZT Bimorph Actuator

for Minimally Invasive surgery” SPIE Smart Structures and

Materials, pp. 321-335, 2000.