Designing appropriate biomaterials to control osteoprogenitor differentiation and function is paramount for regenerative medicine applications. Here, we utilized a photopolymerizable, synthetic poly(ethylene glycol) (PEG) platform that provides a highly regulated microenvironment due to its resistance to protein adsorption. This hydrogel material was systematically altered with various chemical functionalities to affect signaling pathways, influence osteogenesis, maintain phenotype, and promote extracellular matrix (ECM) production and mineralization. Several biologically-inspired molecules were examined for the control of osteoprogenitor cell function. The adhesive, fibronectin-derived moiety, RGDG₁₃PHSRN improved osteoblast adhesion and reduced ECM production. Heparin-functionalized gels supported both human mesenchymal stem cell (hMSC) survival and osteogenic differentiation. hMSC integrin linked kinase production was found to support cell survival in the absence of matrix interactions, and this approach should enable fundamental studies of three-dimensional cell functions in response to extrinsic signals.

To better understand and exploit the complexities of extracellular signals on cell functions for biomaterials design, two high-throughput screening techniques were developed. First, a spotting technique, useful for studying discrete concentrations of material modifications, was utilized to study osteoblast adhesion and function in response to the order and spacing of the peptide epitopes RGD and PHSRN. This technique was utilized to study hMSC proliferation and differentiation as a function of gel chemical functionality and it was found that adipogenic, chondrogenic, and osteogenic differentiation could be initiated by altering chemical functionality alone. A gradient methodology was also developed and used to study the relationship between adhesive ligand concentration and cell attachment and migration.

Exploiting knowledge gained in the previous studies, more sophisticated biomaterial microenvironments were used to present multiple signals to hMSCs. Intracellular signaling pathways of hMSCs were manipulated by delivering fluvastatin to gel-encapsulated hMSCs. Fluvastatin increased hMSC bone morphogenetic protein 2 (BMP2) production and induced osteogenesis. When combined with BMP2-sequestering, heparin-functionalized hydrogels, fluvastatin increased osteogenesis over fluvastatin delivery alone outlining how bidirectional signaling can enhance hMSC function. These studies outline strategies to systematically develop biomaterial niches for three-dimensional cell culture and demonstrate how material chemistry can be used to manipulate cell functions. This knowledge enables fundamental and applied research towards the rational design of materials for hMSC encapsulation and delivery for bone regeneration applications.