(182ae) Combining Phosphorylated Chitosan-Xanthan Complexes and PCL to Obtain Bilayered Periosteum-like Scaffolds for Bone Regeneration

Many diseases may affect the bone tissue, resulting in structural defects and leading to impairment of its functions. The worldwide incidence of bone fractures and the expenses for their treatment are very high. Conventional treatments are inefficient in the case of large defects and more specialized treatment modalities are required to enhance tissue repair. Tissue engineered scaffolds able to mimic the periosteum, a vascularized bilayer membrane present in bone tissue, may improve bone regeneration in severe lesions, since it can provide essential biological cues for the healing process. In this work, a bilayered engineered periosteum was developed by combining natural and synthetic polymers. A chemical modification was performed in chitosan (Ch), a biodegradable and biocompatible polysaccharide, by introducing phosphate groups to its structure. Phosphate groups bind calcium ions and may induce the formation of a calcium phosphate layer that promotes the osteoconduction of polymeric implants. Moreover, surface binding of signaling molecules such as growth factors can stimulate the osteoinductivity of the material. The phosphorylated polymer (Chp) was used to produce chitosan-xanthan complexes (Chp-X), which were combined with a polycaprolactone (PCL) membrane produced by solvent casting/particulate leaching. This combination originates a porous Ch-X layer matrix designed to be in direct contact with the bone and capable of recruiting growth factors and inducing differentiation of host stem cells into bone cells, and a porous PCL outer layer that acts as long-term support for cell growth with slower biodegradation rate. Three different scaffold formulations were compared: Chp-X/PCL, and Ch-X/PCL and single-layer-PCL (as controls). The scaffolds were characterized regarding visual and morphological aspects (thickness, surface roughness, pore size), as well as physicochemical properties (uptake capacity and mass loss in aqueous media) and mechanical behavior (tensile strength and elongation at break). Adhesion between different layers was observed for both Chp-X/PCL and Ch-X/PCL membranes. Dual-layered devices present thickness of about 4.5 mm when hydrated. Despite periosteum thickness is lower (maximum of 1.8 mm), the thickness of the studied devices reduces as consequence of normal tissue compression once they are implanted in the body and also due to degradation in vivo. Surface microroughness was observed, which is known to enhance the stimulatory effects of bone morphogenetic proteins on bone mineralization. Average pore size of up to 900 µm was observed for polysaccharide layers and much smaller pores for PCL layer. Contrary to single-layer-PCL membranes, bilayered scaffolds show high uptake of aqueous media, which facilitates the transport of nutrients and metabolites within the matrices. The mass loss of these scaffolds reaches up to 11% after 7 days in water, while single-layer-PCL matrix do not degrade during the same time. Mechanical testing of hydrated scaffold samples showed that the major contribution to the resistance of dual-layered devices comes from PCL layer. Considering the intended application as periosteum substitutes, the scaffolds herein studied show attractive physical, physicochemical and mechanical properties for the intended purpose.

Acknowledgements: The authors acknowledge the support from CAPES-Brazil and CNPq-Brazil.