Research On The Calcium Phosphate Biomaterial For Bone Morphogenetic Protein-2(BMP-2)Adsorption Performance

Calcium phosphates biomaterials(CaP)are similar to the inorganic components of the human bone hard tissue,which has good biological compatibility,biological activity and bone incuction have been widely used as bone repaired or substitution materials in clinic,and their excellent biological properties have also arouse wide concern in biomedical.When the implant materials contact with the organism,protein will be spontaneously adsorption to surface,and the amount of adsorption protein is affected by various factors,mainly including the roughness and topology of the material’surface,protein composition,conformation and distribution.Therefore,it is very important in studying the CaP ceramic surface’ protein adsorption behavior,especially the bone related protein specific adsorption onto the CaP ceramics biological activity.Based on the above analysis,in this work,this paper carried out the nano calcium phosphate based materials to improve the biological activity,with bone morphogenetic protein 2(BMP-2)was selected as a model protein,through the improvement of the phase structure and surface topological morphology,systematically study the intrinsic link between CaP biomaterials surface structure and protein specific adsorption,at the same time,study on the mechanism of CaP ceramics protein adsorption.In addition,the morphology,structures and properties of the obtained CaP materials have been investigated by scanning electron microscopy(SEM),the specific surface area of the tester(BET),X-ray diffractiometer(XRD),Fourier transform infrared spectrometer(FTIR)and circular dichroism(CD)techniques.The effect of the materials’surface topography and phase composition on protein adsorption process is of great significance for designing CaP ceramic material surfaces.The main contents in this work are listed in the following:1.Hydroxyapatite(HA)and Biphasic calcium phosphate(BCP)were obtained by chemical precipitation method.The as-obtained materials was characterized by scanning electron microscopy(SEM),the specific surface area of the tester(BET),X-ray diffractiometer(XRD)and Fourier transform infrared spectrometer(FTIR).The effect of phase compositions of calcium phosphate(CaP)ceramics on their bone morphogenetic protein-2(BMP-2)adsorption behaviors in phosphate saline buffer(PBS).Langmuir,Frundlich and Temkin isotherm models were used to describe the adsorption of BMP-2 onto CaP ceramics.The Langmuir isotherm model fit the equilibrium data better than the Frundlich and Temkin isotherm models.The pseudo-second-order kinetic model is suitable for the description of the adsorption kinetics,and 240 minutes is thought to be the optimal adsorption time.Polyacrylamide gel electrophoresis(SDS-PAGE)results showed that the BCP material has stronger adsorption capacity with BMP-2 than HA material.The difference adsorption of HA and BCP is the surface hydrophobicaity snd electrostatic interaction.BCP strong surface hydrophobicity and large surface area effect the BMP-2 adsorption.A possible adsorption mechanism has been proposed.The electrostatic interaction plays an important role in the adsorption processes.2.Three different topographies of hydroxyapatite(HA)materials sheet-HA,rod-HA,and whisker-HA were synthesized using chemical precipitation method and hydrothermal method.The as-obtained materials were testified by X-ray diffraction(XRD),Fourier transform infrared(FT-IR),Brunauer-Emmett-Teller(BET),Field emission scanning electron microscopy(FE-SEM)and circular dichroism(CD).We have systematically investigated the adsorption kinetics and thermodynamics of Bone morphogenetic proteins(BMP-2)on the three different topography surfaces of HA,respectively.The results showed that the maximum adsorption capacities of HA-sheet,HA-rod and HA-whisker were(219.96± 10.18),(247.13±12.35),and(354.67±17.73)μg/g,respectively.Kinetic parameters,rate constants,equilibrium adsorption capacities and related correlation coefficients,for each kinetic model were calculated as well as discussed.It demonstrated that the adsorption of BMP-2 onto HA could be described by the pseudo second-order equation.Adsorption of BMP-2 onto HA followed the Langmuir isotherm.It confirmed that compared with other samples HA-whisker had more adsorption sites for its high specific surface area which could provide more opportunities for protein molecules.The adsorption processes were endothermic(△H>0),spontaneous(△G<0)and entropy increasing(△S>0).A possible adsorption mechanism is physisorption inculding the electrostatic attraction and the hydrogen bond,which is the major process of adsorption.In addition,the BMP-2 could be adsorbed to the surface which existed slight conformational changes by FT-IR and CD.