Development of a biodegradable biopolymer from renewable natural resources suitable for additive manufacturing and bone tissue engineering

Abstract

Bone tissue engineering scaffolds fabricated by additive manufacturing can offer an alternative treatment option to currently used bone graft methodologies. Chitosan, a biocompatible and biodegradable naturally derived polymer, offers great promise as a biomaterial for tissue engineering applications. Chitosan scaffolds have previously been fabricated using additive manufacturing techniques, however, the use of crosslinkers, weak mechanical stability and structural resolution of fabricated scaffolds remain problematic. Therefore, in this study the researchers aimed to develop a biopolymer blend that can be used to fabricate scaffolds using a thermal printing technique that is suitable for bone tissue engineering applications. Additionally, the potential of this biopolymer blend as an antibacterial coating for titanium implants was investigated. In the present study chitosan was prepared using ascorbic acid blended with poly(vinyl acetate), a biocompatible synthetic polymer, to aid the printing process. Formulation optimisation was performed to establish optimal component (chitosan, poly(vinyl acetate) and ascorbic acid) ratios. Based on stability, chitosan with concentrations of 2%, 3% and 4%, prepared using 1% ascorbic acid and 1% poly(vinyl acetate) was selected (PVAc composite 2% CS, PVAc composite 3% CS and PVAc composite 4% CS). Surface morphology showed that PVAc composite 2% CS was non-porous, while the 3% and 4% chitosan counterparts were porous. All three PVAc composite films were biodegradable and showed sufficient swelling properties. Biocompatibility was evaluated by means of an indirect cytocompatibility assay, using two different cell lines: human gingival fibroblast and human foetal osteoblast cells. Cell viability for all PVAc composite films exceeded 90%, surpassing the ISO 10993 standard of 70% cell viability for a biomedical device to be considered safe. The biocompatibility of PVAc composite films was also confirmed through cell morphology and cell attachment studies. AM simulation demonstrated the printability of PVAc composite 3% CS and PVAc composite 4% CS hydrogels. These hydrogels were directly printed using a moderate temperature (± 95°C), well below the decomposition temperature of chitosan. Layered scaffolds were fabricated, and ultrastructural surface morphology showed porous scaffolds. PVAc composite hydrogels showed antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis, the two bacterial strains most commonly associated with implant-related infections, as wells as gram-negative Escherichia coli. These antibacterial properties present in the hydrogels may prove to be beneficial when used as a coating agent for titanium implants or as a scaffold to prevent bacterial growth. As a proof of concept, PVAc composite hydrogels were used to coat porous titanium discs using dip-coating method. Results indicated that the hydrogels successfully coated the titanium discs with varying surface coverage and thickness. Although coating was not optimal for these titanium discs, the obtained results showed the potential of these hydrogels as antibacterial coatings for medical implants. The present study set the foundation for future work in developing a patient-specific scaffold that can be used as a biomedical implant to overcome the limitations and disadvantages accompanying bone grafting treatments.