Preparation And Representation Of Calcium Polyphosphate/Silicon Nitride Composite Biomimetic Bone Scaffold

With the progress of science and technology,people’s living standards are constantly improving.The human life is lengthening,and the aging of the population is aggravating.Osteoporosis and the injury of bone tissue caused by disease and trauma have attracted by people’s attention,and need to be solved urgently by academic and medical circles.Calcium Polyphosphate,CPP,is a kind of calcium phosphate ceramic material,which has been paid more and more attention because of good biocompatibility,bone conduction,biodegradability and mechanical strength.However,in the process of making CPP by sintering,the properties of CPP are different due to the change of crystalline form,and the degree of polymerization also affects the properties.At the same time,silicon nitride bioceramic material has a brighter application prospect in medical implants.And it has good mechanical properties,osteoconductivity and biocompatibility.Therefore,in this paper,by changing the sintering temperature and holding time,CPP powders with different polymerization degrees and different crystal forms were designed and prepared.CPP ceramics and Si3N4/CPP composite ceramics were prepared through molding and sintering process.Furthermore,porous and gradient porous ceramic samples were prepared by controlling the content of porogen,and the phase composition and properties were explored.CPP powders with different crystal types and different degrees of polymerization were obtained by changing the sintering temperature and holding time.And CPP ceramic samples were prepared through compression molding and sintering.The properties of the materials were analyzed.The results show that the crystal form obtained by holding at 500℃ for different time is distinction.Among them,theγ-type CPP was obtained by holding for 1 h and 5 h,and the γ-type and β-type coexistence were obtained after holding for 10 h and 15 h,indicating that 500℃ was within the crystal form transition temperature range,and the holding time increased,and the degree of crystal form transition increased.When the temperature is holding for 10 h,the crystalline form of CPP is γ-type and β-type coexist at 500-600℃ and all β-type CPP at 650-950℃.CPP ceramic materials with different polymerization degrees are obtained by different holding time.The degree of polymerization varies with insulation as time increases,the corresponding compressive strength increases at first and then decreases.The sample with the highest strength corresponds to a holding time of 10 h,and the strength reaches 18.45 MPa;when the holding time continues to increase to 15 h,while the degree of polymerization increases,the compressive strength of the material decreases,and the microscopic morphology shows that the particles are relatively large.That may cause some particles to increase and agglomerate due to long holding time,which affects the bonding performance.The porosity of porous CPP ceramic materials increases with the increase of porogen content,and the compressive strength decreases correspondingly.When the volume ratio of the porogen is 30%,the porosity is close to 60%and the compressive strength is 4.96 MPa.The microscopic morphology of the gradient porous CPP material can clearly show the three-layer structure,and the bonding between the layers is good.Compared’with the CPP of.the single uniform pore agent layer,the gradient porous CPP ceramic structure has higher mechanical strength,and the porosity is still higher and better overall performance,which is beneficial to its application as a bone replacement implant.The results of CPP ceramic materials immersed in Tris solution and SBF solution in vitro show that the greater the degree of polymerization,the slower the degradation rate.But the degradation in SBF solution is faster than Tris solution.After 28 days of degradation,corrosion pores and cracks were formed on the surface of the sample,and fine granular apatite containing carbonate groups was deposited on the surface.After being degraded in the SBF solution,the compressive strength of the material was reduced to about 1/2 of its original value.Among them,the CPP ceramic specimens kept for 10 hours had the highest strength,which was 9.65 MPa.Based on the performance research of CPP ceramic materials,different ratios of Si3N4/CPP composite ceramic samples and porous composite ceramic samples were prepared from the dispersion and sintering system of the mixed powder,and the phase,microstructure and strength were observed to compare the materials after adding Si3N4 performance.Then research the change of the material in the in vitro immersion process.The results show that the compressive strength of Si3N4/CPP composite ceramic materials with different proportions increases with the increase of Si3N4 content.When the composite ratio is 40:60,the compressive strength reaches 24.88 MPa,which is about 35%higher than that of pure CPP ceramic.Porous Si3N4/CPP composite ceramic materials have different mechanical properties base on the content and particle size of the porogen.When the particle size of the porogen is 80-120 mesh,the maximum compressive strength can reach 9.57 MPa.When the particle size is 50-80 mesh,the highest compressive strength is 8.76 MPa.With the increase of the porogen content,the microscopic appearance of the composite ceramic shows an increase in the pore size of the surface,and the large pores contain smaller pores,which is conducive to the adhesion of bone cells around the implant and the growth of bone tissue and blood vessels.The degradation rate of composite ceramics increases with the increase of Si3N4 content when Si3/CPP composite ceramic materials with different-ratios are immersed in Tris solution and SBF solution in vitro.It is indicating that Si3N4 can improve the degradation performance of composite materials.After the material is soaked,bone-like hydroxyapatite is produced on the surface.When Si3N4 accounts for 40%,the distribution of the deposits is wider,the size is more uniform,and the shape is spherical particles.After the composite ceramic is immersed in the SBF solution,the compressive strength decreases,and the greater the Si3N4 content,the more the strength decreases.Because the Si3N4 in the material is eroded by the SBF solution,a gap is formed at the junction of the two substances in the composite material,the binding force is reduced,and the strength decreases,and this phenomenon will increase with the increase of the Si3N4 content.