Spatially Controlled Organic/Inorganic Hybrids Designed to Enhance Cellular Response.

Abstract

Bone is a complex organ that serves many functions. However, in cases of trauma, congenital malformations, and skeletal disorders, impaired healing occurs. Bone tissue engineering is an alternative to conventional therapies such as bone grafting. The work presented in this dissertation involves the development of a bone engineering approach whereby coprecipitation, a biomimetic strategy to precipitate bone-like apatite onto a biomaterial, is used to incorporate biomolecules in a spatially-controlled manner. The global hypothesis was that the coprecipitation of biomolecules with apatite can enhance cell response compared to adsorption, specifically: 1) enhancing transfection efficiency by coprecipitating DNA-lipoplexes with apatite and 2) enhancing osteogenic differentiation by coprecipitating multiple growth factors in a spatially controlled manner within apatite. Coprecipitation spatially localized protein within apatite and allowed for higher protein retention compared to adsorption. Applying these advantages towards gene delivery, the coprecipitation of DNA-Lipoplexes transfected cells with a higher efficiency compared to adsorption and polymer incorporation methods. To provide the design criteria for a multiple growth factor delivery system to better mimic in vivo conditions, BMP-2 and FGF-2 were chosen due to their roles in osteogenesis. The concentrations and sequence of BMP-2 and FGF-2 had significant effects on osteogenic differentiation of BMSCs cultured on TCPS, with low concentrations of FGF-2 enhancing DNA content, and high concentrations of BMP-2 enhancing osteogenesis. Delivery of FGF-2 followed by BMP-2 or delivery of BMP-2 followed by BMP-2 and FGF-2 enhanced osteogenic differentiation compared to simultaneous delivery. For the hybrid delivery system, the individual release profiles of BMP-2 and FGF-2 were significantly affected by the concentration used during coprecipitation. Utilizing coprecipitation to control BMP-2 and FGF-2 localization within apatite to mimic the sequential exposure required by BMSCs, minimal effects on DNA and osteogenic differentiation were demonstrated. The presence of mineral may have delayed or inhibited osteogenic response with a possible compensation upon sequential delivery. These organic/inorganic delivery systems have the potential of delivering multiple biomolecules to better mimic spatiotemporal gradients in the in vivo environment. Utilizing this novel approach to better simulate the cellular environment by manipulating interfaces can facilitate the development of multiple tissue systems.