Human adipose-derived stem cells (hASCs) : a useful tool to screen biomaterials for bone Regeneration

Mesenchymal stem cells have already been successfully used in association with specific scaffolds to repair tissue damages; in particular, human adipose-derived stem cells posses several features, such as their great multi-differentiative potential and their reduced immunogenicity, that make them suitable candidates for many tissue engineering applications. We used hASCs to screen several biomaterials which can be used for bone regeneration as titanium (TIT) and two different types of chemically-modified titanium (TAA and TAAK) disks, polyurethane sponges (PU) and silicon carbide-plasma enhanced chemical vapor deposition (SiC-PECVD) to evaluate their influence on growth and osteogenic differentiation of these cells. In order to set the best experimental conditions to use hASCs in future orthopaedic clinical applications, we compared the osteogenic potential of hASCs pre-differentiated for 14 days or directly differentiated on scaffolds. Both undifferentiated and differentiated hASCs adhere to the tested biomaterials and colonize them without any evidence of cytotoxicity; to evaluate the osteogenic differentiation of hASCs cultured both on plastic and on scaffolds for 14 and 21 days we quantified the Alkaline Phosphatase activity (ALP) and the calcified extracellular matrix deposition, respectively early and late differentiation markers. TIT and TAA disks possess good osteoinductive properties: indeed undifferentiated hASCs show an ALP activity increased of 32.4% and 68.1% and an extracellular calcium deposition of 54.3% and 82.3% when cultured on TIT and TAA respectively, in comparison to cells maintained for 14 days on monolayer. In contrast, TAAK is not able to promote hASCs osteogenic differentiation. We also observed an osteo-inductive effect by PU sponges, indeed their presence for 14 and 21 days with undifferentiated hASCs produces an increase in ALP activity of 692.2% and 250.5%, respectively. As expected, TIT, TAA and PU sponges show their osteo-inductive properties also on osteogenic-differentiated hASCs. SiC-PECVD, a novel and promising biocompatible material, shows an osteo-inductive effect on undifferentiated hASCs: ALP levels and calcium deposition are increased of 72.3% and 24.5%, respectively, in comparison to undifferentiated cells on monolayer; however the presence of SiC-PECVD does not affect differentiated hASCs. Furthermore, we observed that hASCs, either pre-differentiated and directly differentiated on all the tested scaffolds, do not behave differently suggesting that a pre-differentiation step is not required for future clinical applications, reducing the ex vivo cellular manipulation process. This study demonstrates that the cytotoxicity and the osteo-inductive properties of several biomaterials can be easily evaluated using hASCs; these cells, with their ability to grow and differentiate towards different cellular lineages such as osteogenic, chondrogenic, myogenic and endothelial, even in the presence of scaffolds, are good candidates for many regenerative medicine applications. Moreover the high availability and the ease of culture of hASCs make them suitable to test drugs and to study their mechanism of action.