Development of a microgripper for a collagen fibril tension test

Abstract

Fibrillar collagens are the most abundant structural proteins in humans. They are major constituents in connective tissues like tendon, skin, bone, and the vasculature, where they largely determine the mechanical behaviour. Deterioration of collagen is linked to several widespread diseases like arteriosclerosis or tendinopathy, which result in impaired tissue mechanics. In this context, the macromechanics of collagenous tissues are reasonably well understood, but many aspects of the unique mechanical properties of collagen fibrils, which represent the smallest microscopical structural unit, remain unknown. To obtain a better understanding of collagen fibril mechanics, get insights into the microscopic principles that govern the strength of connective tissues, as well as understanding the importance of collagen cross-linking, tensile tests are conducted on collagen fibrils. However, so far no standardized test procedure has been established. No experiments with high statistical relevance have been conducted, due to shortcomings in current testing methods, which result in very laborious and costly experiments. As part of a project with the overall goal to significantly reduce the cycle time for collagen fibril tension tests compared to current methods, a micro gripper for collagen fibrils has been developed in this diploma thesis. The fabrication of the gripper designs was carried out by means of two-photon polymerization (2PP). Various designs were fabricated, examined for geometric and structural integrity and checked for capability through qualitative tensile tests of collagen fibrils. The project also included the generation of a finite element model for validation of the gripper design with respect to structural integrity under load. A series of parameters were established to assess the capability of the micro gripper in silico and give insights into the expected magnitudes of errors compared to the current methods. It was found that the utilization of a micro gripper for collagen fibril tension tests does not significantly falsify the measurements and can therefore be used for future experiments.