Synthesis of an injectable biodegradable biomimetic macroporous hydrogel scaffold for bone tissue engineering
Mikos, Antonios G.
Doctor of Philosophy
The objective of this work was to direct cell-biomaterial interaction by utilizing materials that reduce non-specific cell adhesion and covalently modify them with a cell adhesive peptide sequence to promote cell adhesion by a specific receptor-ligand interaction. The potential of poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) based hydrogels as biomimetic materials for controlling osteoblastic cell interaction and modulating cell response was examined. First, the block copolymer P(PF-co-EG) was synthesized by transesterification of the homopolymers poly(propylene fumarate) and methoxy poly(ethylene glycol) to result in a block copolymer with terminal poly(ethylene glycol) (PEG) blocks. The effect of the PEG block length on the thermoreversible properties of the copolymer in water was examined. Next, P(PF-co-EG)-based hydrogels were crosslinked to thin films. Increasing the PEG block length of P(PF-co-EG) reduced marrow stromal osteoblast adhesion. Hydrogels were bulk-modified with an RGDS ligand attached to the backbone of the hydrogel with a PEG spacer arm. Marrow stromal osteoblast adhesion and migration was found to be dependent on the bulk concentration of RGDS peptide. In addition, the availability of the RGDS peptide at the surface of the bulk-modified hydrogels was dependent on the ratio of the PEG block length of P(PF-co-EG) and the PEG spacer arm linking the peptide to the hydrogel. A model biotin ligand was utilized to quantify the surface concentration of biotin bulk-modified hydrogels using an enzyme linked immunosorbent assay. Macroporous hydrogels based on P(PF-co-EG) were synthesized by the same free-radical crosslinking approach as the thin film with potential for in situ formation. The effects of the free-radical initiation system and the carbon dioxide porogen precursor on the extent of crosslinking and morphology of the resulting macroporous hydrogel were examined. Moreover, these macroporous hydrogels were found to degrade hydrolytically in a bulk fashion with a decrease in material properties and dry weight, and no significant difference in porosity of the hydrogels. Degradation was dependent on the crosslinking density of the hydrogel. Finally, marrow stromal cells showed markers typical of differentiation to the osteoblastic phenotype when cultured for 28 days under conditions to promote their osteoblastic phenotype on RGDS-modified biomimetic macroporous hydrogels.
Cell biology; Polymer chemistry; Biomedical engineering