M.Sc Thesis

M.Sc StudentSchmidt Orit
SubjectHydrogel Scaffolds and Mechanical Stimulation for Cartilage
Tissue Engineering
DepartmentDepartment of Biomedical Engineering
Supervisors ASSOCIATE PROF. Dror Seliktar


Cyclic strain deformation of isolated chondrocytes seeded in encapsulating hydrogels represents an elegant system for investigation the effects of dynamic mechanical stimulation on chondrocyte metabolism. Other studies have shown that chondrocyte mechanotransduction is associated with both cell compression as well as perturbations of focal adhesion complexes involving cell surface integrin activity. The present study aims to examine the effect of dynamic stimulation on chondrocyte metabolism and explore the role of cell-scaffold interactions and whole cell compression in chondrocyte mechanotransduction using encapsulating poly(ethylene glycol) (PEG) hydrogel scaffolds and primary bovine chondrocytes. A novel compression perfusion bioreactor was developed to apply cyclic compressive strain to cell-seeded constructs with uniform loading environment. Scaffolds made from poly(ethylene glycol) diacrylate (PEGDA) hydrogels with or without fibrinogen molecules as instructive elements were seeded with chondrocytes and immediately confined to growth chambers and subjected to 15% dynamic compressive strain and 1Hz frequency. Perfusion of culture medium was facilitated by an external peristaltic-pump driven flow loop that re-circulates medium directly to each construct chamber at a rate of 2 ml/min. All cell experiments were carried out for two weeks in dynamic and free swelling control culture. At the end of each experiment, the cell-seeded constructs were removed and tested in order to characterize the effects of mechanical stimulation and the instructive element on the cellular metabolism. Dynamic strain stimulation resulted in a 37% and 38% increase in the levels of sulfated glycosaminoglycan (sGAG) in the PEG and PEG-fibrinogen constructs, respectively, after 2 weeks of stimulation, when compared to free swelling controls. There was no significant difference in morphology, viability, type II collagen expression, or DNA content of strain-stimulated and free swelling constructs after 2 weeks. Comparing results of the PEG-fibrinogen scaffold with PEG scaffold did not show significant differences between the two, even following 2 weeks of dynamic mechanical stimulation.  Accordingly, these findings indicate that while cell deformations cause metabolic changes in chondrocytes seeded in PEG hydrogels, it is difficult to discover the role of instructive elements in enhancing chondrocyte mechanotransduction in encapsulating scaffolds subjected to physical deformations.  It is suggested that cell deformations in this system cause cytoskeleton reorganizations which dominate the mechanotrandsuction pathways and eclipse the response to cell-scaffold mechanotransduction. This work emphasizes the importance of mechanical and biochemical coupling as it pertains to cartilage tissue engineering