Osteogenic differentiation of adipose tissue-derived mesenchymal stem cells cultured on a scaffold made of silk fibroin and cord blood platelet gel

Biomaterials used in scaffold fabrication may be made of ceramics, biodegradable metals, synthetic and natural polymers. They generally promote cell attachment and proliferation and are biodegradable, usually generating non-toxic degradation products1. Silk fibroin (SF), one of the main proteins of silk worm Bombyx mori filaments, is a natural material that has been extensively investigated for its potential in textile, biomedical, photonic and electronic applications2. Moreover, SF is a biocompatible and biodegradable protein material that has been widely used as surgical suture for centuries. In recent years, new biomedical applications have been envisaged given the environmental stability, remarkable mechanical properties, controlled proteolytic biodegradability and morphological flexibility of this material thanks to the possibility of controlling its molecular structure and morphology through material processing and chemical modification3. As a naturally derived biomaterial, SF possesses outstanding mechanical properties, such as flexibility and tensile strength, and has demonstrated good biocompatibility both in vitro and in vivo4,5. SF is considered to be a useful material that facilitates collagen synthesis and re-epithelialisation in the treatment of skin injuries5,6. Platelet gel is a blood component obtained through a process of gelification of a fresh or frozen/thawed platelet concentrate, which has been traditionally prepared from platelet-rich plasma derived from peripheral blood7. More recently, a procedure to obtain platelet gel from human umbilical cord blood has been developed and patented (US patent 8,501,170). Platelet gel has been found to be an interesting and useful product, rich in growth factors, able to support tissue regeneration in dentistry, oral-maxillofacial and bone surgery, wound healing and soft tissue injuries5,8,9. The therapeutic effects of platelet gel are attributed primarily to the release of growth factors (such as platelet derived growth factor-BB, transforming growth factor-beta1, fibroblast growth factor-basic), which exhibit chemotactic and mitogenic properties. However, other authors hypothesise that the fibronectin content that comes with the platelet gel preparation may exert an extra bioactive effect on the cells and tissues, such as matrix metalloproteinase activation10,11. Human mesenchymal stem cells derived from adipose tissue (ADMSC) are an attractive source of cell therapy for the regeneration of damaged tissues, because of these cells’ capacity for self-renewal and differentiation into various cell lineages12. The relatively easy protocols for ADMSC isolation and expansion in culture, and the fact that these cells seem to be immunologically well tolerated, make them an attractive candidate for new studies in translational clinical research13. Accordingly, ADMSC have already been clinically tested for the reconstruction of bone defects with promising results14. Hence, bone tissue engineering approaches should focus on the stimulation and optimisation of the osteogenic differentiation process. This study was aimed at testing the hypothesis that a SF scaffold associated with human cord blood platelet gel (CBPG) may represent an innovative treatment to improve bone regeneration. Although the advantages of using platelet gel from adult blood15 and a SF scaffold in bone regeneration have been independently reported, for the first time this study investigated the effects of’ combined use of CBPG and SF on osteogenic differentiation of ADMSC16.