Study On Extraction Process Of Hydroxyapatite Of Pig Bones In Ionic Liquids

Hydroxyapatite (HAP) is the main inorganic component of natural bone tissue. It is regarded as bone repair replacement material with the high performance because of possessing biocompatibility and bone conduction effect. The major products are made by artificial synthesis. There are some differences with human hydroxyapatite on the structure performance. The products from natural pig bones are more close to human body. Ionic liquids have good solubility, non-toxic harmless and environment protecting. Hydroxyapatite was extracted from pig bones which were dissolved directly by the ionic liquids. It embodies the effective utilization of renewable resources.Hydroxyapatite was synthesized by chemical precipitation method, using Ca(NO3)2·4H2O and (NH4)2HPO4 as raw materials. The yield of hydroxyapatite was used as the experiment target. The better result was showed by orthogonal experiments: n(Ca)/n(P)=1.67, reaction temperature 40℃, (NH4)2HPO4 dropping speed 1.0 mL/min, pH 9～10, concentration of Ca(NO3)2·4H2O and (NH4)2HPO4 0.15 mol/L, assembly time 24 h. The yield of hydroxyapatite was around 84.6% under the better condition. Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied for the analysis of the product.The bromo-l-ethyl-3-methyl-imidazolium ionic liquids ([EMIM]Br) dissolved the pig bones. Dissolution temperature, mass ratio of pig bones and [EMIM]Br and dissolution time were investigated. Exploring by single factor experiments range of process parameters, the main parameters were used for the orthogonal experiments. The better process conditions were dissolution temperature 220℃,mass ratio of pig bones and [EMIM]Br 1:30, and dissolution time 50 min. The ration of dissolved pig pones was around 68% under the better condition.Hot stage polarized optical microscopy (POM) was used to observe the dissolution process of pig bones in [EMIM]Br.Pig bones were regenerated with water as precipitant, oil phase as dispersion medium, and adding dispersant. Process parameter scopes were groped through single factor experiments. The primary parameters were selected to do orthogonal tests. The better process conditions were obtained. Hydroxyapatite was extracted by changing the post-processing method. The extraction process conditions were mass ratio of paraffin and dissolved pig bones 48:0.13, dispersion temperature 95℃, mass ratio of dispersant K12 and dissolved pig bones 1.2:13, dispersion time 40 min, stewing time 24 h. The mass ratio of extraction hydroxyapatite and dissolved pig bones was 1.9:13. FIIR, XRD and SEM were applied for the analysis of extraction product. The results showed that hydroxyapatite which is similar to human bone was extracted from pig bones.According to special structure and properties of the pig bones and [EMIM]Br, the dissolution process of pig bones in [EMIM]Br was put forward. Bone collagen was dissolved by [EMIM]Br and hydroxyapatite was released because of the small particles, scattering in the [EMIM]Br ionic liquids. And the mechanism of bone collagen dissolving in [EMIM]Br was verified.The research has the characteristics:simple preparation conditions, small negative effects on the environment, short time, and matching with human bone structure. This technology can provide a new approach for further development of human hard tissue replacement materials and theoretical support for the process control of dissolving biomass in ionic liquids.