Development of a vibration driven endoscopic deviceL. Gerovasi, B. Picasso

Department of Mechanical Engineering, University of Cagliari,Piazza D’Armi, 09123 Cagliari, Italy - E-mail: picasso@unica.it

This paper presents the main aspects of a research work aimed at developing an autonomous endoscopic device, capable of exploring the entire gastrointestinal tract. Some of the ideas concerning the locomotion system of this innovative endoscope were inspired by biological structures such as those found in insects and intestinal parasites. Initially a thorough bibliographic study has been carried out, involving the frontiers of medicine, biology and engineering. The following aspects have been studied in detail: anatomy and physiology of digestive tract, the chemical physical and morphological aspects of the intestinal surface, traditional and innovative endoscopic techniques, invertebrate locomotion mechanics, biology inspired adhesion mechanisms and locomotion produced by harmonic force excitation.

The efficiency of traditional endoscopy is limited by the following problems: only a limited portion of the gastrointestinal tract can be explored, the procedure is traumatic for the patient and difficulties arise when attempting to pass bends or stenoses. Two main aspects were focused in our study, namely adhesion and advancement. A propulsion device acted by a miniature vibrator was developed and tested. Locomotion is produced by a particular contact surface which produces asymmetrical friction forces. A mathematical model of the propulsion mechanics has also been developed. An equipment to measure friction coefficients on biological tissues is now under development.

TOTAL LENGTH (contracted) = 85 mm

TOTAL LENGTH (elongated) = 145 mm

TOTAL MASS = 30 grams

Clampingactuators

Bellowactuators

Clampingactuators

Bellowactuators

CCDcamera

Optic fibrebundles

SurgicaltoolchannelAir/water

channel

CCDcamera

Optic fibrebundles

SurgicaltoolchannelAir/water

channel

Prototype colonoscopewith CCD Storzcamera (1998)

The test bench to measure friction parameters

Endoscopy means direct visual examination of any part of the interior of the body through an optical viewing instrument. Modern endoscopes are narrow, steerable, flexible, cylindrical instruments. They usually contain several channels and are equipped with fibre optics for illumination and viewing. Other channels allow: washing of the area under view, suction, inflation with harmless gas to make viewing easier, the use of snares, cauteries, forceps and other small operating instruments, the use of lasers, and the devices for taking biopsy specimens.

Given Imaging Ldt. • M2A

M2A, capsule endoscopy, is a non-invasive diagnostic device for use in the gastrointestinal tract. Natural peristalsis moves the capsule smoothly and painlessly throughout the gastrointestinal tract, transmitting color video images as it passes. This information is then transmitted via an array of sensors secured to the abdomen, to a datarecorder affixed to a belt worn around the patient's waist. The examination can be conducted while the patient continues normal daily activities.In detail: 1 optical dome, 2 focus lens, 3 ultra white leds, 4 CMOS 90.000 pixel, 5 batteries, 6 data elaboration unit, 7 antenna.Operating time: 6-8 hours

Characteristics of the section:

• length (medium in vivo) 1200 mm• external diameter 30-35 mm• thickness 3-5 mm

The section appears macroscopically circular, with frequent mucosal folds, that are risen cross-sectionally to the axis of the digestive tract for a part of the section and very rarely for the entire area of passage. Moreover the entire internal surface is covered by the intestinal villi that are small shelves that are risen perpendicular to the mucosa.

Small intestine, Jejunum

Characteristics of the section:

• length (medium in vivo) 1600 mm• external diameter 20-25 mm• thickness 3-4 mm

The section appears macroscopically circular, with rare mucosal folds, that are risen cross-sectionally to the axis of the digestive tract for a part of the section. The entire internal surface is covered of the intestinal villi, but in less dense way regarding the jejunum.

Small intestine, Ileus

Characteristics of the section:

• length (medium in vivo) 1420 mm• external diameter (start) 65-70 mm• external diameter (end) 25-30 mm• thickness 6-7 mm

The large intestine extends from the ileocecal junction to the anus. On the surface, you can identify bands of longitudinal muscle fibres called taeniae coli, each about 5mm wide. There are three bands and they start at the base of the appendix and extend from the cecum to the rectum. The sacculations, called haustra, are characteristic features of the large intestine, and distinguish it from the rest of the intestinal tract.

Large intestine, Colon

Today it is very diffused electronic videoendoscopy that couples the traditional instruments to the possibilities offered by the computer.

Advantages

• Optimum image quality• Enormous number of tools• Taking biopsy specimens• Stability of position

Drawbacks

• Small intestine is unreachable• Traumatic for the patient• Difficulty in passing stenosis• Perforation of digestive tract (rare)

RF System Lab. • NORIKA

Norika, capsule endoscopy, is also non invasive diagnostic device. But power supply is obtained by induction through patient worn vest. So the capsule is completely battery free.The capsule is capable of a controlled rotation around its longitudinal axis, to improve the capability of viewing all interesting areas.To allow for future developments, approximately 40% of the internal space is unoccupied. A potential usage is to store surgical knives and scissors to get tissue samples. But the implementation is not ready yet.The quality of image (400.000 pixel) is good, and the focus adjustment function is implemented.

Yesterday Today Tomorrow

Conclusions

The development of advanced endoscopic devices aimed at trespassing traditional limits and drawbacks of conventional endoscopy.The feasibility of a self propelling endoscopic unit was demonstrated. A few vibration driven devices based on unsymmetrical friction were analysed and tested. A mathematical model of propulsion was also developed.The need for an accurate measurement of the friction coefficients on biological tissues led to the design and construction of a dedicated equipment.The previous results are the background to develop a new advanced endoscopic device to be used in clinical experiments.

Gross weight: 70g

Length:70mm

Motors EccentricMasses

Batteries

Unsymmetriccontact surface

First Prototype

Second Prototype: Cross-section

Second Prototype: details of motors

2 nd Prototype: dimensions φ 31 x 61 mm

3 rd Prototype: Cross-section φ 25 x 50 mm

Third Prototype: details of motors

Eccentricmasses

Motion's equation with asymmetrical friction

• Sinusoidal excitation

• Asymmetrical friction

•F,a,b: constants

Time

Dis

pla

cem

ent

⋅−=⋅−⋅⋅=

)tanh()()()cos(

xbaxmgxtFxm

µµω

Hydrodynamic model:motion's equation

Dis

pla

cem

ent

Time

CCD andlight area Motors Batteries

Batteries

Batteries

• Controlled Speed Motor• load cell

• wires

The tissue is kept constantly moist with physiological solution. The moving surface is pushed against the tissue by a known weight. Speed, weight and surface can be changed.

==

⋅⋅=⋅⋅

⋅⋅⋅⋅−⋅

0)0(0)0(

)cos(2

2

xx

tFxhmclb

xm f

ωµ