Biomechanical study of human tissues/organs for the sake of MIS (Minimal Invasive Surgery) Essay

The following article deals with the Biomechanical study of human tissues/organs for the sake of MIS (Minimal Invasive Surgery). For this purpose experiment is performed on different parts (mucosa-submucosa, serosa-muscle and intact layer) of stomach (Gastric Wall) to evaluate the mechanical characteristics of each part. So that it could be treated accordingly.
For the experiment pig stomachs were used under suitable conditions so as to make sure of the integrity of necessary properties of the parts. Pigs were of 140 pounds there age was of 18-20 weeks. Pig stomachs are used as they are similar to the human ones.
The samples were divided in two groups, one for greater curvater and one for smaller. Both groups had three samples, and each sample was about 120 mm long and 10 mm wide. All samples were prepared and tested at a room temperature of 20+-3C and relative humidity of 60+-5%. During the tests, the stomach samples were sprayed with physiological saline to keep the parts hydrated.
For carrying out the experiment Universal Testing Machine (HY0580-Made in Shanghai China) was used for applying common operations such as tensile, compression, relaxing, creep etc. on different samples (Longitudinal, Circumferential) of stomach.
This model could be used to apply a load of 1mN to 100N. Also it could stretch the material up to 800mm.
The sample is gripped on the machine using special medical grips to ensure that no tissue damage is done to the sample. The initial length of sample was 100mm.
Several tests were performed on the various samples. First loading-unloading test was performed in which the sample was stretched at a rate of 1 mm/sec also it was stretched to a length of 12mm. The loading and unloading stresses in first two cycles were not same due to strain softening while for the third cycle they coincide with each other. This process in a way behaved as a pre-process step.
The curves clearly show that required tensile is greater for mucosa-submucosa layer while least for serosa-muscle layer. Correspondingly, the force for longitudinal direction is greater than circumferential and likewise stress required for greater curvature is larger than for small curvature.
Then Relaxation and Creep tests were performed in which sample was stretched at a rate of 6 mm/sec to achieve an elongation of 12mm. Then the sample was held at this elongation for 300 seconds.
In relaxation test the stretch ratio was kept to be a constant and the graphs show that maximum stress relaxation was achieved in circumferential direction and also in mucosa-submucosa layer. While least was obtained in longitudinal direction and also in serosa-muscle layer. So the layer which can undergo maximum deformation is mucosa-submucosa layer and in circumferential direction.
In creep test the stress was kept at a constant. The graphs show that for initial 100 seconds the stretch ratio varies drastically while it progressively slows down. Maximum variation was achieved in circumferential direction and also in mucosa-submucosa layer. While least was obtained in longitudinal direction and also in serosa-muscle