Development of Injectable, Dual Thermally and Chemically Gelling Hydrogels for Craniofacial Bone Tissue Engineering
Vo, Tiffany N
Mikos, Antonios G
Doctor of Philosophy
The objective of this work was to design a novel injectable hydrogel system capable of delivering osteoprogenitor cell populations for the minimally invasive regeneration of craniofacial bone. To this end, injectable and biodegradable hydrogels comprising thermogelling macromers and diamine-functionalized crosslinkers were developed that undergo dual thermogelation at physiological temperature and concomitant chemical crosslinking. The thermogelling macromers and crosslinker were each successfully synthesized and their physicochemical properties such as swelling behavior, mechanical properties, and degradation as a function of polymer content, crosslinking density, crosslinker length, and degree of hydrogel hydrophilicity were established. Each of these factors was found to have no significant effects on hydrogel cytocompatibility when tested with cells in vitro, except in the highest concentrations in a solution osmolality-dependent manner. Biocompatibility of the acellular hydrogels was established in a critical size rat cranial defect through analysis of the tissue response and fibrous capsule. The hydrogels also demonstrated an ability to undergo a hydrophobicity-dependent mineralization and partial bony bridging in vivo despite the absence of cells, bioactive factors, or initial mineral content. To evaluate the hydrogel system as a cell delivery vehicle, hydrogel composites were created through incorporation of gelatin microparticles and rat mesenchymal stem cells were encapsulated for a period of 28 days. Cell viability and mineralization were enhanced, whereas markers of osteogenic differentiation were modulated with gelatin microparticle loading. Altering the cell encapsulation density and osteogenic predifferentiation resulted in only in short-term effects on in vitro osteogenesis, suggesting optimization of cells is required. Investigation of the stem cell-laden composite hydrogels in vivo demonstrated significant mineralization, bony bridging, and most promising, direct bone-implant contact and tissue infiltration that are not commonly observed with hydrogels in this orthotopic model. The results suggest that these injectable, dual-gelling hydrogels show great potential for stem cell delivery in craniofacial bone tissue engineering applications.
mesenchymal stem cells; mineralization; rat cranial defect