Abstract
Development of a tissue engineered bone graft requires efficient bioactivity screening of biomaterials in clinically relevant three-dimensional systems. The authors analyzed the relative osteogenic potential of two three-dimensional biomaterials--type I collagen and poly(L-lactide-co-glycolide) (PLGA)--to support in vitro mineralization of human mesenchymal stem cells. Human mesenchymal stem cells were seeded onto three-dimensional PLGA or type I collagen scaffolds; incubated in osteogenic media; and harvested at 1, 4, and 7 days. Messenger RNA expression was analyzed using quantitative real-time reverse-transcriptase polymerase chain reaction for osteogenic (i.e., alkaline phosphatase, osteocalcin, bone sialoprotein, Runx2/core binding factor α-1) and angiogenic (i.e., vascular endothelial growth factor and interleukin-8) markers. Alkaline phosphatase enzyme activity was measured at 4 and 7 days. Mineralization was detected by alizarin red staining and micro-computed tomographic imaging at 8 and 12 weeks. Mineral composition was analyzed by solid-phase nuclear magnetic resonance spectroscopy. Early osteogenic and angiogenic markers, and alkaline phosphatase enzyme activity, were up-regulated on PLGA versus collagen scaffolds. However, long-term mineralization endpoints favored type I collagen. By 8 weeks, human mesenchymal stem cells on collagen exhibited significantly higher mineral density by micro-computed tomographic and alizarin red staining than PLGA scaffolds. Both biomaterials deposited calcium hydroxyapatite as determined by nuclear magnetic resonance spectroscopy. The authors' findings suggest that despite early PLGA induction of osteogenic gene expression, long-term mineralization occurs earlier and to a greater extent on type I collagen, highlighting collagen as a potential bone tissue engineering scaffold in the human mesenchymal stem cell niche. When screening the relative osteoinductive profiles of three-dimensional bone tissue engineering scaffolds in vitro, the authors recommend including long-term endpoints of osteogenesis.
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