Polymer and Glass-Ceramics Composite Scaffolds for Bone Tissue Engineering

Abstract

The use of conventional bone repair techniques involving bone grafts has limited potential because of the likelihood of disease transmission and because of their limited supply. Bone tissue engineering is a potential alternative to overcome these limitations, which enables implant scaffolds to stimulate tissue formation directly in-vivo. It is a technique aimed at induced bone regeneration by combining different biomaterials and other functional materials. Arrays of biomaterials have been used in bone tissue engineering due to their attractive properties, such as osteo-conductivity and biocompatibility. The widely used materials include biodegradable polymers and ceramics such as hydroxyapatite, bioactive glasses and glass ceramics.

Natural polymers like alginate, gelatin and chitosan are attractive biomaterials because of their close resemblance with extra-cellular matrix components, thus making them highly biocompatible. However, these polymers suffer from poor bioactivity and low strength. Making a composite scaffold using the bioactive glass-ceramics and polymer can improve the toughness and mechanical stability of the scaffold while maintaining good bioactivity and biocompatibility.

The glass-ceramics (GC) in the system P2O5-Na2O-CaO-SiO2 was synthesized using sol gel technique. The GC showed to contain combeite crystalline phase which is important for bioactivity and bio-dissolution of the GC. The GC showed good bioactivity and biocompatibility. The GC powder was used in the fabrication of composite scaffold. Two types of scaffolds were fabricated where GC was used; (a) as filler in a polymer (chitosan, alginate and gelatin) matrix scaffolds prepared by freeze drying method, and (b) as a ceramic skeleton in the sponge replicated GC scaffolds those coated with three different polymers.

The composite scaffolds prepared by freeze drying showed highly macroporous (~80%) structures with good pore connectivity which is ideal for bone tissue engineering application. In general, composite scaffolds showed the improvement of different properties such as mechanical strength, bioactivity, cell adhesion, alkaline phosphatase activity and osteogenicity with increase in GC powder loading in polymer matrix of the scaffold. Among all, gelatin based scaffolds showed highest compressive strength exhibiting 5.8 MPa in the scaffold containing 5 wt% GC. Gelatin based scaffolds also showed excellent cell adhesion and proliferation compared to the other. Alginate-chitosan-GC based scaffolds showed improved strength compared to chitosan-GC based scaffolds and better cell proliferation compared to alginate-GC scaffolds.

Sponge replication was used to prepare GC scaffolds doped with 6 wt% titania through sintering of GC. The strength of the porous GC scaffold was improved by doping with titania which acts as a sintering additive. The strength of the scaffolds was further improved by coating with alginate, gelatin and chitosan. Among all, gelatin coated GC scaffolds showed highest compressive strength and relatively better cell adhesion properties. Microtomography was used for in-detail examination of pore characteristics in scaffolds. The scaffolds exhibited highly porous architecture with open pores. A clear understanding of pore size distribution was obtained. The scaffolds showed macoporous structure ideal for bone tissue engineering. The pore sphericity, orientation and interconnectivity were analyzed in details. The results demonstrated that the composite scaffolds are potential candidates for bone tissue engineering.