Acellular Bone Colonization and Aggregate Culture Conditions Diversely Influence Murine Periosteum Mesenchymal Stem Cell Differentiation Potential in Long-TermIn VitroOsteoinductive Conditions

Periosteum contains mesenchymal stem cells (Pe-MSCs) that contribute to normal bone growth, healing, and turnover; understanding Pe-MSC capabilities may shed light over the treatment of bone defects using tissue engineering. Bone tissue regeneration needs in vitro bone precursors or stem cell coculture onto specific scaffolds but, despite extensive research in the field, very little is known about the matrix structure of the tissue-engineered tissues and the scaffold's effects on cell differentiation. To this purpose we have selected a clonal population (murine Pe-MSCs) that was seeded and differentiated onto an acellular bone scaffold. Cell differentiation was assessed after 3 months and 1 year by molecular, histological, biochemical, and biophysical analyses and results were compared with the same osteoinduced clonal cells cultured as cellular aggregates. Our data show that Pe-MSCs cultured onto acellular bone scaffold develop a complex three-dimensional matrix and an osteoblastic phenotype but do not produce hydroxyapatite (HA); moreover, they seem able to reabsorb the colonized bone scaffold. On the contrary, cells cultured as three-dimensional aggregates differentiate and produce osteoblastic markers and HA nanocrystals.