Chitosan based polymer/bioglass composites for tissue engineering applications

Composite scaffolds formed from polymers and bioglasses have been widely explored for applications in regenerative medicine as they have suitable organic/inorganic structures and properties similar to human hard tissue. Yet, these materials have only been used for non-load-bearing or low load-bearing purposes as they have limited mechanical strength while research is focused on improving their properties. One method of improving mechanical strength is by covalently bonding the organic and inorganic phases. This has been successfully achieved in Class ll hybrids which have covalent bonding between polymers and bioglasses. As well as improving mechanical strength, the chemical connection of the two phases results in simultaneous degradation. The currently available composite scaffolds use collagen for the polymer phase which can cause allergic reactions and transmit pathogens. An alternative natural polymer is chitosan which has been used to create scaffolds with bioglass avoiding the issues arising from collagen. Additionally, using cross-linking agents has been shown to strengthen chitosan hydrogels improving their mechanical properties. A promising natural cross-linker is genipin which has lower toxicity than other cross-linking agents while producing hydrogels with improved mechanical properties compared to pure chitosan. In this paper we offer an overview of requirements, structures and currently available composite scaffolds for tissue engineering applications. We discuss the limitations of the currently available materials and consider the potential of covalently bonded hybrids particularly in relation to chitosan-based materials and the added benefits of genipin cross-linking.