Optimizing a scaffoldless approach for cartilage tissue engineering
Elder, Benjamin Daniel
Athanasiou, Kyriacos A.
Doctor of Philosophy
Articular cartilage has a poor intrinsic healing response, so tissue engineering provides a promising approach for cartilage regeneration. The major objective of this proposal was to enhance the self-assembling process, used in articular cartilage tissue engineering, by investigating the effects of construct confinement, hydrostatic pressure application, and growth factor addition. First, the effects of construct confinement in different directions and at different times were investigated. It was demonstrated that construct confinement resulted in enhanced biomechanical properties in the direction orthogonal to the confinement surface, either by enhancing collagen organization or by increasing collagen production. Next, the effects of hydrostatic pressure at different timepoints, magnitudes, and frequencies on the biomechanical and biochemical properties of self-assembled constructs were determined. It was demonstrated that the application of static hydrostatic pressure, at 10 MPa, for 1 h/day, from days 10-14 days led to significant increases in compressive and tensile properties, accompanied by significant increases in GAG and collagen content, respectively. To our knowledge, this was the first study to demonstrate increases in the biomechanical properties of tissue from pure HP application. Furthermore, the effects of exogenous application of growth factors, at varying concentrations, dosages, and combinations, with and without hydrostatic pressure, were assessed on the biochemical and biomechanical properties of engineered constructs. A systematic approach was used to determine the effects of BMP-2, IGF-I, and TGF-beta1, alone and in combination, on the functional properties of engineered constructs. This was the first study to demonstrate significant increases in both compressive and tensile biomechanical properties as a result of growth factor treatment. Also, for the first time, synergistic and additive effects on construct biomechanical and biochemical properties were found when combining growth factor treatment with hydrostatic pressure application. Finally, the effects of various decellularization treatments were examined, and it was determined that it was possible to remove cells while maintaining construct functional properties. The results presented in this thesis are exciting, as they have allowed for a better understanding of the self-assembling process, and have allowed the self-assembled constructs to mature into functional articular cartilage, as evidenced by biomechanical and biochemical properties spanning native tissue values.