Study On Preparation And Properties Of Osteoinductive And Injectable Calcium Phosphate-Based Bone Repair Materials

Nowadays, with the developing of material science, medical science and biology, there has been a huge reformation happened to orthopaedics: the bone defects repair material developed from the bioinert material into bioactive implantation, and the technique of orthopaedic surgery developed from large wound into minimal invasive technology, whose purpose was relieving the pain of patients and reducing the syndromes. As a result, seeking for a more ideal material which owns the properties of injectability and self-setting became the key point. So the aim of present study is to develop a novel bone repair material which could inject from a syringe and get a porous structure after seting, as well as had osteoinductivity.This study was based on the in situ setting properties of CPC, which properties were improved. The solid phase included two systems:β-TCP system and TTCP+DCPA system. The liquid phase was the weak acidic solution of chitosan. Chitosan has favorable biocompatibility, which has high viscosity in solution. The incorporation of chitosan could improve the handling properties of CPC. The liquid phase contained citric acid could strongly improve the hydration rate of CPC, which shortened the setting time and increased the compressive strength of CPC. In addition, the weak acidic environment around the biomaterials could accelerate the degradation of calcium phosphate cement, which was important to bone tissue engineering scaffold.The advantages ofβ-TCP system CPC consisted in simple technique and easy available raw materials. The optimal constitution of the cement was established according to setting time and compressive strength. When the liquid phase contained 2%CS, 20%CA and 5%glucose (wt%), and P/L=0.6g/mL, the setting time of cement was 7.20±0.50min and the compressive strentgth was 21.40±0.83MPa. The cement liquid, powder to liquid ratio, particle size and HA seed could influence the setting time and compressive strength of the cement. The hydration production was HA (77.2%, wt%) and DCPD (22.8%, wt%) by XRD analysis. When mixed the liquid phase and solid phase, one side,β-TCP was changed to CDHA, then HA; on the other side,β-TCP was changed toβ-Ca₂P₂O₇ andγ-Ca₂P₂O₇, then DCPD.In the TTCP+DCPA system, all the by-production disappeared by neutralization reaction, with keeping the pH value of system unchanged. The hydration production was HA. The chemical process of CPC hydration was studied. These processes were controlled by dissolution and precipitation chemical reaction. The relative stabilities of the various calcium phosphate salts are the major driving forces for the hydration reaction of CPC slurry at the different pH value. HA is the least soluble phase at pH＞4.2, other calcium phosphate salts present in an aqueous solution in this pH range will tend to dissolve and reprecipitate as HA. The kinetic model of hydration reaction was established. In the initial 2h, hydration reaction rate was controlled by the dissolution of CPC powder. After 2h, hydration reaction rate was controlled by diffusion of solution in the HA production.The effects of preparing conditions, such as powder to liquid ratio and particle size, on setting time , compressive strength and pH value of calcium phosphate cement, which was composed of TTCP and DCPA, were investigated systematically. With the increase of powder to liquid ratio and decrease particle sizes, the setting time became short and the compressive strength increased. The optimal condition was that the liquid phase contained 3%CS, 5%CA and 15%glucose, P/L=0.8g/mL, and powders were ball milling for 40 hours. The setting time of the cement was 7.20±0.39min, and the compressive strength was 30.2±0.8MPa. The hydration and setting process were affected significantly by particle size of the starting reactants. The smaller TTCP particle in the CPC can shorten the setting time. The smaller DCPA particle can increase the compressive strength of the cement. The different matches of the starting particle sizes could adjust the variation of pH values in the slurry. The balanceable pH value of the cement was 7.30～9.50.The preparation and properties of porous CPC scaffold were studied in this paper. The porous CPC scaffold was based on the TTCP+DCPA system. The pore-forming agent was water-soluble mannitol. The mannitol crystals would quickly dissolve upon contact with the physiological liquid in vivo to create macropores for bone ingrowth. The macroporous CPC was a kind of injectable scaffold. Pore sizes of the scaffold were 100～300μm. The total porosity of the scaffold was 75.1±1.2% when 70% mannitol was contained in the solid phase.Biocompatibility and biological safety of two systems CPC were evaluated by a series of in vitro and in vivo studies including simulated body fluid (SBF) test, cell culture and animal experiments. Through the SBF test, we observed that the CPC ofβ-TCP system could induce Ca and P ions to deposit the surface quickly. The cell cultivation test showed that the cytocompatibility of the material was good. The animal experiments showed that the material was nontoxic and osteoconductive. The porous CPC scaffold of TTCP+ DCPA system had ectopic osteogenesis when the scaffold was implanted into the muscle pouches in the thigh of rabbits. The porous CPC scaffold had osteoinductivity.