Effect of hydroxyapatite particles on stem cell response in nanofiber scaffolds

Rotator cuff tears are among the most common shoulder injuries that require surgery. High failure rates of biological graft-based repairs underscore the need for functional alternatives. Specifically, functional grafts must incorporate the gradient of mineralization from tendon to bone in order to be biomimetic. In this study, effects of varying concentrations of mineral content in aligned nanofiber scaffolds on human mesenchymal stem cells (hMSC) are evaluated. It is hypothesized that mineral content will regulate cell response, matrix deposition, and integrin gene expression. hMSC were seeded on aligned nanofiber scaffolds of polylactide-co-glycolide with 0%, 10%, and 15% hydroxyapatite content, and were maintained in chondrogenic medium. Cell proliferation (n=5), collagen deposition (n=5), and gene expression (n=5) for Collagen X, Sox9, osteopontin, osteonectin, and osteocalcin were determined over 42 days. Cell number was found to differ between the non-mineralized and mineralized groups. Significant increase in collagen deposition over time was observed in mineralized scaffold groups, and the 15% group showing significantly higher deposition than the 0% group by day 42. Lower expressions of chondrocyte hyperotrophy marker Collagen X and chondrogenic marker Sox9 and maintained high expressions of osteogenic markers osteopontin, osteonectin, and osteocalcin suggest an osteogenic lineage for the stem cells. In conclusion, addition of HA particles influenced hMSC proliferation, matrix deposition, and may induce an osteogenic differentiation response from the stem cells.