Cell-induced biodegradation of poly(L-lactic acid) fiber-reinforced poly(e-caprolactone) scaffolds for bone regeneration.

Polymer blending can be used in alternative to copolymerisation for tailoring the biodegradation rate of aliphatic polyesters. To evaluate in vitro degradation mechanism and kinetics, poly(-caprolactone)-poly(L-lactic acid) (PCL-PLLA) scaffolds were immersed in different aqueous media and characterized at different degradation times by vibrational spectroscopy and thermal analysis. To evaluate the role of cells in degradation, the same techniques were used to comparatively characterize the scaffolds incubated with both stromal cells from bone marrow (MSC) and osteoblasts (HOB) from orthopaedic patients. The PCL-PLLA composites were hollow cylindrical samples consisting of PLLA fibers embedded in a PCL matrix. PLLA fibers (75dtex) impregnated in the PCL (65000Da)/DMAc (Dimethylacetamide)/NaCl system were wound with an angle of 45° on Teflon coated steel mandrel by a winding machine (mod. AS LAB 101). DMAc was then removed by ethanol, and NaCl crystals by water. The in vitro biodegradation was investigated under sterile conditions at 37°C in different media: saline phosphate buffer at pH 7.4 (SPB), esterase in SPB, 0.01 M NaOH solution and simulated body fluid at pH 7.4 (SBF). The samples were analyzed before and after biodegradation for 4 weeks by polarized micro-Raman spectroscopy, thermogravimetry (TG) and differential scanning calorimetry (DSC). MSC and HOB were isolated from marrow/bone fragments obtained during surgery for total hip replacement and cultivated in -MEM with 10% FBS on the PCL-PLLA samples for 4 weeks. Among the in vitro degradation media, the NaOH solution induced the highest weight loss in the PCL-PLLA scaffolds, confirming the catalytic effect of the OH- ion on degradation. Accordingly, the samples degraded in NaOH solution showed the most pronounced composition and morphology changes: thermal analysis showed an enrichment in the PCL component, suggesting a preferential involvement of the more hydrophilic PLLA component in degradation. At the same time, the crystallinity of both polymeric components increased. The Raman results confirmed these findings. In particular, as regards the PLLA component, the observed spectral changes were explained in terms of structural rearrangements and decrease of the polymeric chain length. The I875/I923 and I1050/I1103 intensity ratios were identified as marker of the degradation extent. The NaOH solution was found to induce the highest degradation rate. Raman analysis showed that also the PLLA fibres in the samples incubated with HOB and MSC underwent significant structural rearrangements, although to a lower extent than in NaOH solution; MSC were more aggressive than HOB.