Preparation And Properties Of HAP/CS Injectable Hydrogels

The aim of this study was to explore the hydroxyapatite(HAP)/Chitosan(CS) hydrogels preparation, and study their performance. These hydrogels can be applied to the areas of the injectable bone repair to overcome the shortcomings of hydroxyapatite which is not injectable, and also endow the hydrogels with osteoconductivity.Hydroxyapatite particles were prepared by a W/O/W Multiple Emulsion Method, the inner aqueous phase was dipotassium hydrogen phosphate solution, cyclohexane was in the middle as oil phase, the outer aqueous phase was calcium nitrate solution. The composition of the products were analyzed by XRD,FT-IR. Mass-transfer mechanism was analyzed, Ca2+ diffused into the inner aqueous phase and reacted under alkaline condition with HPO42- there to produce hydroxyapatite. The effects of temperature, reaction time and pH value on the products composition and morphology was discussed. When the reaction was carried out at 10℃, hollow spheres with diameter of approximately 300nm were obtained. Stuffed particles with the same diameter were obtained at 50℃.The following reasons interpret this phenomenon:When the temperature is low Ca2+ diffuses more slowly, so the consumption mass of Ca2+ in the inner aqueous phase is greater than the diffusion capacity, the reaction only took place between the interface of inner aqueous phase and oil phase, so be hollow spheres was obtained. When the reaction time is 24h, only a few spheres formed, most of the products were fragments; when the reaction time extended to 60h, almost all of the products were spheres. When the pH value was 8, the main composition was monetite; when the pH was 10 or 12, the main composition was hydroxyapatite. As the pH value increased, hydroxyapatite content increased. When the pH value was 8, the products were fragment, when the pH is greater than 10, hollow spheres formed.The sodium alginate and dipotassium hydrogen phosphate dissolved in the water phase together, the oil phase and outer aqueous phase were the same as above, Hydroxyapatite/alginate composite materials were prepared by a W/O/W Multiple Emulsion Method, composition of composite materials were hydroxyapatite and alginate which was characterized by XRD and FT-IR, the morphology of the products were spheres with diameters of 0.2～1μm analyzed by SEM; and TEM showed the spheres were stuffed. The reaction process was as follows:when Ca2+ in the outer aqueous phase diffused into the inner aqueous phase, two reactions occurred at the same time, reacted under alkaline condition with HPO42- there to produce hydroxyapatite, and formed calcium alginate hydrogels in the way of ionic crosslinking of sodium alginate. The composite materials were formed by coprecipitation of hydroxyapatite and calcium alginate. Organic compounds were removed at high temperature, and hydroxyapatite was obtained. SEM,TEM showed the products were hollow spheres.CS, HAP/CS, and HAP/alginate/CS hydrogels were prepared by CS/GP system, marked as Gel,Gel2 andGel3, Xerogel were obtained by freeze-drying. Gel formation time was measured by container upside-down method, Gel formation time of Gell, Gel2, and Gel3 were 31min,29min,7min.The Gel3 sol system contained sodium alginate which was anionic polymer and had a strong ionic interaction between chitosan, a cationic polymer. The pH values of each system were measured, Gell, Gel2, and Gel3 sol system can be stable in the neutral condition. Swelling behavior were tested, Gel2,and Gel3 had greater equilibrium swelling ratio than gel1 because of larger network contraction of Gel1; and water absorption rate Gel2 and Gel3 were faster than Gel1. The internal structure of these hydrogels were observed by SEM, three-dimensional pore structure can be observed in Gell,Gel2,and Gel3.The diameter of large hole in Gel2 was approximately 100μm, the diameter of hole in Gell was less than 50μm, the diameter of hole in Gel3 was in between. Compressive strength test showed Gel2 and Gel3 had better compression performance than Gel1.