Poly(ε-Caprolactone)/Sodium Bicarbonate/β-Tricalcium Phosphate Composites: Surface Characterization and Early Biological Response

Bone graft substitutes combining the mechanical features of poly-epsilon-caprolactone (PCL) and the bioactivity of beta-tricalcium phosphate (beta-TCP) have been widely reported in the literature. Surprisingly, however, very little is known about the incorporation of carbonate at a biomimicking level. The authors studied beta-TCP/PCL composites at 20 wt.% and 40 wt.%, either enriched or not with sodium bicarbonate (at 2 wt.% and 4 wt.%), through SEM and EDX analyses; surface free energy estimation; pH measurement after 1, 2, and 3 days of incubation in cell media; nanoindentation; and a protein adsorption test with bovine serum albumin. The early biological response was assessed using adipose mesenchymal stem cells, as an established in vitro model, via cellular adhesion (20 min), spreading (24 h), and viability assays (1, 3, 7 days). By increasing the beta-TCP content, the composites' hardnesses and Young's moduli (EiT) were improved, as well as their protein adsorption compared to neat PCL. Sodium bicarbonate increased the polar component of the surface energy, alkalinized the composite with a higher beta-TCP content, and attenuated its early negative cell response. Further investigation is needed to deepen the knowledge of the mechanisms underpinning the mechanical features and long-term biological behavior.