Research On Phosphorylated Chitosan Composites For Bone Tissue Engineering

It is hard for single material to satisfy the demands of bone tissue engineeringfor scaffolds. Therefore, hybrid scaffold with novel properties has been a focus ofbiomaterial research, which combined with different materials together.Hydroxyapatite (HA) has similar chemical composition to inorganic mineral ofnatural bone, with high mechanical strength and bioactivity. However, thebrittleness and hard-degradation limit its use in the field of bone tissueengineering. Chitosan (CS) is a important cationic natural polymer material. Ithas a wide application prospect in bio-medical field due to its specific propertiessuch as biodegradability, regrowth, nontoxic, biocompatibility and bio-function.However, lack of bioactivity and low mechanical strength make it difficult to usein reconstruction of complicated site. It could overcome their shortcomings bycombining with the CS and HA. Although there was much progress in research ofCS/HA composites, up to now, few of the achievements could accord withclinical use due to many reasons such as the lack of interfacial bonding betweenorganic and inorganic phase.In order to obtain better performance, many researchers have added anotherpolymer material as a reinforcing phase, for example, phosphorylated chitosan(PCS). Chemical modification of materials is one of the prime methods togenerate new functions. The existence of amine groups and hydroxyl groups inchitosan is highly advantageous for conducting modification reactions. Recently,several chemical methods have been employed for the preparation ofphosphorylated derivatives of chitosan. PCS could possess metal chelating andbiocompatible properties. So, if combining the PCS, CS and HA together to takeadvantage of their beneficial properties and get rid of their shortcomings, it willbe hopeful to obtain a good bone substitute material.In this paper, PCS powder was prepared by the reaction of chitosan andorthophosphoric acid. PCS/CS/HA composites with different weight ratios wereprepared through the coprecipitation method. The composites were formed intorods for compressive strength test. The analysis results illustrated that the PCS had been successfully synthesized by introducing some phosphate groups into theCS in this study. In addition, the effect of aging on properties of HA wasinvestigated. The results showed that the aging could improve stability of crystalsand obtain precipitation with complete crystal. The compressive strength of thecomposite rod was measured. The maximum value of compressive strength wasmeasured about 70.25 MPa corresponding to the PCS/CS/HA composite rod witha weight ratio of 30/30/40, which has an enormous potential in bone tissueengineering area.The bioactivity of composite sheet with a weight ratio of 30/30/40 soaking inSBF was studied. The results indicated that there was promotion of microporousstructure of sheet surface to adhesion and proliferation of osteocytes. Thecomposites formed with citric acid possess better bioactivity due to containingcitrate. The composite rod still maintain 64% of original compressive strengthafter soaking in SBF for 20 days. Meanwhile, mechanisms of biomineralizationand biodegradation were discussed. Furthermore, scaffold with essentialcompressive strength which accords with the requirement of bone tissueengineering was prepared.