In vitro biodegradation and osteoconductivity of poly(epsilon-caprolactone)/poly(L-lactic acid) composites for bone tissue engineering.

none8Poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) have attracted considerable attention in several biomedical applications because of their biodegradability. Polymer blending can be used in alternative to copolymerisation for tailoring the biodegradation rate. This study was aimed at evaluating the in vitro biodegradation of PCL/PLLA composites as well as their osteoconductive ability, which was tested using both stromal cells (MSC) and osteoblasts (HOB) from orthopaedic patients. The PCL/PLLA composites were hollow cylindrical samples consisting of PLLA fibres embedded in a PCL matrix. PLLA fibres (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), 0.01 M NaOH solution and simulated body fluid at pH 7.4 (SBF). The samples were analysed before and after biodegradation for 14 days by 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 5 weeks. TG analysis allowed to determine the composition of the PCL/PLLA composite: it was constituted by 85% of PCL and 15% of PLLA. The former and the latter were found to have 69% and 63% of crystallinity, respectively (DSC measurements). After 14 days of degradation, the samples degraded in NaOH solution were characterised by higher weight losses (about 5%) than those degraded in SPB and SBF, demonstrating the catalytic effect of the OH- ion on degradation. The TG analysis of a sample degraded in NaOH solution showed that it was constituted by 88% of PCL. This result demonstrates that degradation preferentially involved the most hydrophilic PLLA units, which leave the composite with a consequent enrichment in the PCL component. However, also the PCL component was affected by degradation; in fact, DSC analysis showed that both PCL and PLLA components became slightly more crystalline. The changes observed in the micro-Raman spectra are consistent with conformational rearrangements in the PLLA fibre. The observed increase in crystallinity is not surprising: actually, in semi-crystalline polymers degradation starts in the amorphous part; if this part leaves the polymer, the crystallinity degree increases. MSC and HOB were shown to adhere and grow onto the composite with a slightly different rate; at 5 weeks the number of bone-forming cells was quite the same. Using SEM HOB were seen to spread along the PLLA fibres. Conclusions: Both PCL and PLLA components were found to be involved in degradation. A long-term study of biodegradation is needed for evaluating the biodegradation behaviour of PCL/PLLA composites. In fact, knowledge of the rate and mechanism is a key factor for designing high-performing PCL/PLLA biomedical devices. The composite proved a suitable scaffold for both MSC and HOB up to 5 weeks.noneM. Di Foggia; S. Pagani; G. Ciapetti; D. Martini; F. Causa; V. Guarino; P. Taddei; C. FagnanoM. Di Foggia; S. Pagani; G. Ciapetti; D. Martini; F. Causa; V. Guarino; P. Taddei; C. Fagnan