Preparation Of Macro/nano Structure Hydroxyapatite And Its Application

The macro/nano structure of hydroxyapatite on the surface could produce different physical,chemical and biological effects,suggesting its potential biomedical and environmental applications.However,it is still a big challenge to reconstruct the multilevel hierarchical structure of natural hydroxyapatite.So,attempt to delicate tailor the macro/nano structure of hydroxyapatite is of significance in many fields.Based on the theory of biomineralization,we explored the regulation and structure control of hydroxyapatite crystals and synthesized the controllable macro/nano structure by the combination of hard and soft templates to mimick the bimineralization.The process includes the use of different hard templates such as artificially synthesized tricalcium phosphate ceramics,calcium silicate ceramics and hydroxyapatite ceramics as well as natural enamel,bone and clam,the use of acidic molecules as the soft template,and then the add of the interaction between amorphous calcium phosphate?ACP?and acidic molecules on the hard template surface.Furthermore,we explored the potential application of the macro/nano structure of hydroxyapatite in the field of bio-hard tissue repair or replacement and heavy metal adsorption.The main research contents and results are described as follows:1.In the regulation of soft and hard templates,the rod-like structures from nanometer,submicron to micron,nanosheets,rod-sheet composite structure and oriented nanorods have been fabricated and mineralized on the tricalcium phosphate,calcium silicate and hydroxyapatite ceramics surface.The effects of amino acid species,reaction solutions and different hard templates were studied to explore the mechanism of hydroxyapatite crystals formation.The results show that glutamate could affect the p H of the solution,change the saturation on the solid-liquid interface by complexing with Ca²⁺ ion,and its own as a soft template to regulate the crystal growth.Besides,it was found that tricalcium phosphate and calcium silicate could provide a source of calcium by self-dissolution to affect the the growth of mineralized crystals as the hard temple.Hydroxyapatite ceramic as a hard template could regulate the oriented growth of mineralized hydroxyapatite by reducing the interface energy of crystal nucleation.The obtained different structures of mineralized hydroxyapatite provide a wide selection for the study of the macro/nano structures and its biological effects,and also provide reference for the selection and design of bone repair materials.2.Since the glutamate and the hard temple could affect the regrowth of mineralized hydroxyapatite in the above experimental system,we proposed a novel way to chemically regenerate the enamel structure by mimicking the interaction of amorphous calcium phosphate and acidic proteins during the natural enamel formation.The elastinlike polypeptide?ELP?or glutamate could assist the process for in situ regeneration of the dental enamel in oral similar environment.A series of characteristics were conducted to explore the orientation mechanism in the morphology,composition,ion concentration and surface charge during the process.The results showed that the formation of the calcium-rich ELP-ACP complex on the surface of enamel crystals was the key step,where the ELP could adsorb and stabilize on the ACP with the binding of carboxyl groups with Ca²⁺ ions,meanwhile,the free carboxyl groups of ELP chelated with the Ca²⁺ ions from the solution.The locally formed calcium-rich ELP-ACP complexes act as seed crystallites in situ and direct the nucleation and orientation.Then,the regenerated enamel apatite structure was infiltrated with dental resin.The remineralized enamel revealed not only excellent mechanical property,which was highly close to that of the original enamel,but also revealed high chemical stability against acid erosion.This biomimetic method could achieve the structure and function repair of damaged enamel.3.Based on the relationship between structures and its performance of hydroxyapatite,we developed natural bone and clam shells as raw materials to prepare differnt nano-structured hydroxyapatite and explored their performance of Pb2+ ions adsorption.The effect of time,initial concentrations and p H values were explored on the adsorption of Pb2+ ions.The formed nano-structured hydroxyapatite crystals on the natural materials could significantly improve the adsorption capacity of Pb2+ ions,and their adsorption processes could be described by the pseudo-second order kinetic model and Langmuir isotherm model.The results showed that the maximum adsorption capacities of nano-structured bone is about 3 time of the bone without nanostructure.The nano-rod and nano-sheet of hydroxyapatite were obtained with different phosphorus sources using clam shell as raw materials,through the direct hydrothermal solid-phase conversion method.The maximum adsorption capacity of nano-rod hydroxyapatite is 1666.7 mg?g-1,which is much higher than that of the hydroxyapatite materials converted from calcium carbonate by other methods.Moreover,the adsorption performance of nano-rod hydroxyapatite is much better than that of nanosheet crystals,which confirmed that the specific surface area and crystal crystallinity have an effect on Pb2+ ions adsorption effect.In summary,with the regulation of acidic functional groups and different hard temples,we prepaired a variety of hydroxyapatite with controllable morphologies,which provided the possibility to find suitable bone repair materials.After that,we regenerated the enamel structure in situ by biomimetic mineralization under mild conditions.The re-mineralized enamel infiltrated with dental resin revealed excellent mechanical property and high chemical stability against acid erosion.The prepared nano-structured hydroxyapatite from the natural bone and clam shells by mineralization could significantly improve the adsorption of Pb2+ ions.Our results further contribute to understand macro/nano structure control of mineralized hydroxyapatite and develop its application in tissue repair and environmental management.