| Current research in the area of skeletal reconstruction includes the engineering of biological tissues to repair bone defects, as well as the development of bioactive implant coatings that stimulate new bone synthesis. Tissue engineering utilizes biologically-modified biomaterials to better mimic the in vivo environment, and thus, stimulate tissue regeneration more readily. This approach often includes the functionalization of surfaces with protein signaling domains, such as the cell attachment peptide, RGD.; Calcium phosphates, in particular hydroxyapatite (HA), are highly osteoconductive biomaterials that mimic the natural constituent of bone, and are widely used for orthopedic and dental applications. Their unique ability to adsorb proadhesive proteins from blood, which create a matrix for bone cell activities, directly contributes to their osseointegration. Given that HA is highly adsorptive, we questioned whether modifying the surface of HA with proadhesive peptides would stimulate mesenchymal stem cell (MSC) adhesion processes beyond that which adsorbed serum proteins already facilitate, and consequently, whether this modification would provide a biological benefit.; Collectively, this dissertation provides a foundation for understanding the mechanisms that regulate MSC adhesion processes to biomimetically-functionalized HA surfaces. We demonstrated that RGD sequences and adsorbed serum proteins cooperatively regulate MSC attachment and spreading on RGD-functionalized HA. Furthermore, we elucidated an effective means to ionically tether peptides to the surface of HA via a glutamate domain. We observed that RGD, alone, is not sufficient to promote a favorable morphology for osteoblastic differentiation, and we were unable to completely rescue this effect with proteoglyan-binding peptides (FHRRIKA or KRSR), known contributors to cell spreading and stress fiber formation. In this study, adsorbed serum proteins provide a preferable substrate for maximal cell adhesion and spreading on HA compared to the selected biomimetic-modifications. As noted, it is thought that the favorable bioactivity of HA results from its capacity to adsorb proteins from body fluids; thus, any biomimetic modification of HA should be measured against the beneficial effects of adsorbed serum/blood proteins. Collectively, these findings underscore the importance of considering the biomaterial's interaction with endogenous processes, such as protein adsorption, in light of any biomimetic modifications made to the biomaterial. |
