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Endogenous Growth Factor Gene Expression Profile of Bone Marrow Stromal Cells on 3D Porous Poly(Propylene Fumarate)/Hydroxyapatite Nanocomposites

Kyobum Kim, Department of Chemical and Biomolecular Engineeringt, University of Maryland, 2113 Chemical and Nuclear Eng Bldg, College Park, MD 20742, Minal Patel, Fishcell Department of Bioengineering, University of Maryland, 3740 Jeong.H.Kim Engineering Bldg, College Park, MD 20742, David Dean, Department of Neurological Surgery, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, Antonios Mikos, Department of Bioengineering, Rice University, 6100 Main Street, MS-142, Houston, TX 77005, and John P. Fisher, Fischell Department of Bioengineering, University of Maryland, 3238 Jeong H. Kim Building, College Park, MD 20742-2111.

Hydroxyapatite (HA) nanoparticles have been investigated for improving the surface properties of tissue engineered scaffolds due to their structural similarity to organic substances and inorganic minerals in bone. Photocrosslinked poly(propylene fumarate) (PPF) is a promising bone-tissue engineering scaffold due to its biodegradability and mechanical strength. Incorporation of HA with PPF would be a promising strategy to create an osteoconductive nanocomposite material and to enhance cellular responses, including endogenous osteogenic signal expression. We hypothesize that the intracellular signaling mechanisms among a transplanted cell population are largely influenced by the surrounding environment. To examine this relationship, we have investigated the effect of HA nanoparticle concentration in PPF on the osteogenic signal expression among rat bone marrow stromal cells (BMSCs) cultured on a 3D porous PPF/HA scaffold. Our specific hypothesis is that an increase in HA nanoparticle concentration would promote osteogenic signaling by augmenting the surface roughness and hydrophilicity, and therefore enhancing BMSC attachment and function. BMSCs were isolated from rats then cultured for 2 wks on PPF/HA scaffold (0, 10, 20, and 30 wt% HA in PPF, 6 mm in diameter and 1.5 mm in thickness). Cell attachment on the scaffold surfaces was demonstrated by scanning electron microscopy. Osteodifferentiation was tracked by alkaline phosphates and osteocalcin mRNA expression by quantitative reverse transcriptase - polymerase chain reaction (qRT-PCR). Endogenous osteogenic signals of interest include bone morphogenetic protein-2, transforming growth factor-β1, platelet-derived growth factor-A, and fibroblast growth factor-2. This work demonstrates a relationship between tissue engineered construct properties with HA nanoparticles and osteogenic signal expression as well as the possibility of regulating the signal expression level by biomaterial modulation.