Chitosan-Bioglass and chitosan-apatite-wollastonite composites for bone tissue engineering

Abstract

Synthetic inorganic-organic composites are of interest for bone tissue engineering as an alternative to natural grafts since they resemble the structure of the natural bone and degrade over time, enabling the new bone to grow. In this study, two types of composite materials- chitosan hydrogels with Bioglass 45S5 (BG) particles, and BG and apatite-wollastonite (AW) scaffolds coated with the chitosan hydrogel- have been investigated. Ceramics have been used for high mechanical strength, while chitosan was added to increase flexibility of the composites. Genipin was used as a low toxicity cross-linker, in order to improve stability of the chitosan hydrogels. The aim of this PhD research was to assess the properties of the chitosan- BG and AW composites and aid their advancement to in vitro and in vivo studies. The composites were analysed using scanning electron microscopy (SEM), FTIR spectroscopy, fluorescence intensity (FI) measurement and compression test. The BG-hydrogels and the hydrogel coated BG and AW scaffolds were immersed in the simulated body fluid (SBF) for up to 2 weeks and their structure and mechanical properties were examined. Results showed that BG addition to the chitosan hydrogels improved the mechanical properties both before and after immersion in SBF, but affected the FI measurement. Before coating both BG and AW scaffolds had a porous structure (pores 100-300 μm), while the treatment before SEM imaging affected the porosity of the coated scaffolds. Some apatite deposition was observed on the uncoated BG scaffolds after immersion in SBF for 2 weeks. AW scaffolds were mechanically stronger than BG scaffolds, independent of the coating or testing conditions (before or after SBF), with compressive stress up to 5.68 MPa for AW scaffolds compared to 1.20 MPa for BG scaffolds, reaching the lower limit of the cancellous bone. However, the coating did not improve the mechanical properties of the scaffolds. Nevertheless, after immersion in SBF (for up to 2 weeks), hydrogel coated BG scaffolds had higher compressive stress (~ 0.95 MPa) than uncoated BG scaffolds (~ 0.65 MPa).