Preparation, Structure Optimization And Properties Of Porous Hydroxyapatite Microspheres

Porous microcarrier has a wide range of research and potential in tissue engineering fielddue to its relatively low density, high specific strength, high specific surface area, light weightand other advantages. However, the complex preparation process and higher demands oftechnical conditions limit its production and application. Hydroxyapatite, the main inorganiccomponent of human skeleton and tooth, has good biocompatibility, biological activity and boneconductibility, which is an ideal material for bone tissue repair. However, there are still a lot ofproblems about the structure of porous hydroxyapatite microcarrier, such as low porosity, poorpore connectivity and uncontrollable diameters of pores and so on, which thus restrict itsapplication in bone tissue engineering. Therefore, the preparation of hydroxyapatite porousmicrocarrier with controllable pore shape/diameter and high pore connectivity is a researchhotspot in the field.In this paper, resorcinol-formaldehyde resin microspheres are prepared firstly by the sol-gelmethod and micro-emulsion method, the effects of sodium carbonate catalyst, prepolymerizationtemperature, concentration of the surfactants and stirring speed on the size and morphology ofthe prepared resorcinol-formaldehyde resin microsphere are investigated; secondly,hydroxyapatite microspheres are prepared using the obtained resorcinol-formaldehyde resinmicrosphere and/or camphene as the porogens and gelatin as the adhesive by the water-in-oilmicroemulsion system similarly. Porous hydroxyapatite microspheres are obtained after theporogens are removed through sintering heat treatment. The effects of porogen types,ingredients and the sintering parameters on the pore structure and compressive strength ofobtained microspheres are discussed. The results and conclusions are as follows:1. The reaction condition has little effect on the sphericity of resorcinol-formaldehyde resinmicrospheres. Microspheres with better spherical shape can always be prepared with thismethod. However, the reaction conditions, including sodium carbonate catalyst,prepolymerization temperature, concentration of the surfactants and stirring speed, can all affectthe size of the prepared resin microspheres strongly. The size of the prepared resin microspherescan be increased with the addition of sodium carbonate catalyst, the increase of the prepolymerization temperature, reduction of the surfactants concentration and the stirring speedin the reaction system. The resorcinol-formaldehyde resin microspheres with a size range of3-126μm can be prepared through the adjustment of reaction parameters.2. Using the prepared resorcinol-formaldehyde resin microsphere and camphene asporogens and gelatin as the adhesive, hydroxyapatite microspheres are prepared through thewater-in-oil microemulsion method. After removing the porogen of this microsphere throughsintering heat treatment, porous hydroxyapatite (HA) microspheres with high pore connectivitycan be obtained. Macropores in hydroxyapatite microspheres can be prepared afterresorcinol-formaldehyde resin microspheres were removed from hydroxyapatite matrix, the poresize can be determined by the size of the used resin microspheres. The interconnected pores canbe obtained via the sublimation of camphene and the diameter of the pores are less than10μmwithin hydroxyapatite microspheres. By taking the camphene and resin microspheres assynergetic porogen, porous hydroxyapatite microspheres with macropores and porous structuresof connectivity are prepared.3. The prepared resorcinol-formaldehyde resin microsphere and camphene are used assynergetic porogen to fabricate porous hydroxyapatite microspheres. As camphenes increase, themicropores on the surface of and inside the hydroxyapatite microspheres increase, meanwhile,the size of macroporous increases; with the increase of the amount of resorcinol-formaldehyderesin microspheres, the number of macropores inside the hydroxyapatite microspheres increaseand it is easy to form holes of larger size because of the clustering of resorcinol-formaldehyderesin microspheres; in the same quality of resorcinol-formaldehyde resin microspheres, the sizeof macroporous inside hydroxyapatite microspheres increases, while the number of macroporousdecreases along with the increase of the size of resin microspheres; The open-pore size on thesurface of microspheres would decrease with the rising temperature of heat treatment from800to1200℃and the change is more obvious at1200℃, but the size dose not change with theelongation of dwell time at1200℃, which imply the influence of dwell time on it is relativelyweak.4. The compressive strength of the prepared hydroxyapatite microspheres would decreasealong with the increase of additive amount of resorcinol-formaldehyde resin microspheres or camphene, while the size of resorcinol-formaldehyde resin microspheres has little impact on thecompressive strength of hydroxyapatite microspheres. The heat treatment with a highertemperature for hydroxyapatite microspheres helps to increase the compressive strength ofhydroxyapatite microspheres, however, the holding time has little effect on the compressivestrength.