Biodegradable hollow microfibres for tissue engineering and drug delivery applications

Tissue engineering represents one of the most important areas of application of polymeric biomaterials. Synthetic and biological polymers are employed to produce tissue–engineering scaffolds. Several techniques are currently used to construct highly porous three–dimensional scaffolds able to aid cell organisation and to guide tissue regeneration. Among these techniques, fibre bonding was used in this study to produce non–woven meshes based on polymer hollow microfibres. The development of hollow fibres allows for creating bioactive scaffolds whereby biological components such as growth factors and particle systems loaded with specific drugs can be introduced into the cavity of the fibres. In order to create scaffolds for human tissue replacement, polycaprolactone (PCL) fibres, poly(L–lactic acid) (PLLA) fibres and bioartificial fibres based on PLLA and polysaccharides were developed. An apparatus able to produce this kind of fibres was designed and created in collaboration with GIMAC (Castronno, Italy). Preliminary in vitro experiments were performed by using ovine fibroblasts and human osteosarcoma cells. SEM (Scanning Electron Microscopy) images obtained after 8 and 6 weeks culture, respectively, showed a very large number of cells well adherent and spread onto the fibre surface. These results were also confirmed by staining with haematoxylin and also by Alamar Blue, MTT and Neutral red tests. During the last year the project focused on the replacement of human cartilage in vitro. The idea was to use hollow microfibres based on PLLA and dextran or chitosan in order to create a favourable substrate for chondrocytes. Porous fibres were created to enhance nutrients (polysaccharides) to the chondrocytes and also for the delivery of incorporated factors. Bovine chondrocytes, isolated from articular knee cartilage were seeded on PCL and PDM1 (PLLA–dextran with low wall–porosity) meshes and cultured for two–weeks. Histological analysis confirmed the presence of chondrocytes inside the scaffolds. Studies were performed in order to test the potential of the investigated materials for chondrogenic differentiation of human bone marrow stem cell (HBMSC) by recombinant human transforming growth factor–B1 (TGF–B1). This work involved investigation of cell activity and viability (Alamar Blue™, Live–Dead Stain), cell morphology studies by SEM, and glycosaminoglycan (GAG) analysis. These in vitro tests were carried out for 28 days, the Alamar Blue test and Live–Dead stain showed adequate stem cell adhesion and proliferation, but GAG analysis resulted not enough sensible. Degradation studies of these scaffolds were performed at 37°C in simulated body fluid (SBF). The results collected by gravimetric analysis, pH measurements and FTIR spectroscopy showed that PLLA–based scaffolds are completely degraded after five–months whereas PCL–based supports just started the process.