In Vitro Mechanical Property Evaluation of Chitosan-Based Hydrogels Intended for Vascular Graft Development.

Vascular grafts made of synthetic polymers perform poorly in cardiac and peripheral bypass applications. In these applications, chitosan-based materials can be produced and shaped to provide a novel scaffold for vascular tissue engineering. The goal of this study was to evaluate in vitro the mechanical properties of a novel chitosan formulation to assess its potential for this scaffold. Two chitosan-based hydrogel tubes were produced by modulating chitosan concentration. Based on the standard ISO 7198:1998, the hydrogel tubes were characterized in vitro in terms of suture retention strength, tensile strength, compliance, and burst pressure. By increasing chitosan concentration, suture retention value increased to reach 1.1 N; average burst strength and elastic moduli also increased significantly. The compliance seemed to exhibit a low value for chitosan tubes of high concentration. By modulating chitosan concentration, we produced scaffolds with suitable mechanical properties to be implanted in vivo and withstand physiological blood pressures.

A nano-hydroxyapatite--pullulan/dextran polysaccharide composite macroporous material for bone tissue engineering.

Research in bone tissue engineering is focused on the development of alternatives to allogenic and autologous bone grafts that can stimulate bone healing. Here, we present scaffolds composed of the natural hydrophilic polysaccharides pullulan and dextran, supplemented or not with nanocrystalline hydroxyapatite particles (nHA). In vitro studies revealed that these matrices induced the formation of multicellular aggregates and expression of early and late bone specific markers with human bone marrow stromal cells in medium deprived of osteoinductive factors. In absence of any seeded cells, heterotopic implantation in mice and goat, revealed that only the composite macroporous scaffold (Matrix + nHA) (i) retained subcutaneously local growth factors, including Bone Morphogenetic Protein 2 (BMP2) and VEGF165, (ii) induced the deposition of a biological apatite layer, (iii) favored the formation of a dense mineralized tissue subcutaneously in mice, as well osteoid tissue after intramuscular implantation in goat. The composite scaffold was thereafter implanted in orthotopic preclinical models of critical size defects, in small and large animals, in three different bony sites, i.e. the femoral condyle of rat, a transversal mandibular defect and a tibial osteotomy in goat. The Matrix + nHA induced a highly mineralized tissue in the three models whatever the site of implantation, as well as osteoid tissue and bone tissue regeneration in direct contact to the matrix. We therefore propose this composite matrix as a material for stimulating bone cell differentiation of host mesenchymal stem cells and bone formation for orthopedic and maxillofacial surgical applications.