The use of poly(l-lactide) and RGD modified microspheres as cell carriers in a flow intermittency bioreactor for tissue engineering cartilage

The use of biodegradable microcarriers as initial supports for tissue engineering has been demonstrated to be advantageous for maintaining a differentiated cell phenotype; the high surface area also allows rapid cell expansion. Poly l-lactide (PLLA) is a significant member of a group of polymers regarded as bioresorbable and has been widely used for manufacturing 3D scaffolds for tissue engineering. In this study, the hypothesis that PLLA microspheres could be surface modified using RGD peptide sequences to improve the cell adhesion and function of those cells in contact with PLLA was tested. Using this type of approach it may be possible to generate larger structures that contain a high cell number relative to the amount of polymer, whilst remaining free from mass transport limitations. PLLA microspheres were prepared using an oil-in-water solvent-evaporation technique and then an RGD-motif was incorporated onto the microspheres surface by conjugation to improve cell attachment and function. Both PLLA and GRGDSPK modified PLLA microspheres were used as cell microcarriers for chondrocytes cultured in a flow intermittency bioreactor. At the same time, the degradation of the microspheres has been studied after 7, 14, 21, 28, 35, 49 and 56 days. The molecular weight of the PLLA microspheres was determined by Gel Permeation Chromatography. The morphology was assessed by scanning electron microscopy, and the thermal properties determined by Differential Scanning Calorimetry. It was demonstrated that the RGD modified and pure PLLA microspheres degraded gradually at a steady rate over the experimental period, which would provide a controlled degradation profile, both could serve as cell microcarriers because of their thermal and mechanical stabilities. The microspheres with RGD surface modification enhanced cell adhesion and increased the cell numbers in the microspheres aggregates.