Preparation And Properties Of Calcium Polyphosphate/Silica Composite Porous Scaffolds

With the continuous improvement of the world’s scientific and technological level,people’s pursuit of living standards is also constantly improving.The serious aging of the population and the bone tissue defects caused by diseases have received more and more attention.The research and development of implantable materials for bone tissue repair has become a hot spot in the field of bone tissue engineering research.Calcium polyphosphate(CPP)is an inorganic polymer with both the structure of polymer materials and the physical and chemical properties of inorganic materials.The inorganic composition and chemical structure similar to natural bone has become a bioimplantable material with broad application prospects,which has attracted the attention of more and more researchers of bone tissue engineering materials.However,CPP still has shortcomings such as high brittleness and mismatch between the degradation rate and the original osteogenesis rate,which limit the further clinical application of CPP materials in bone tissue repair.In this paper,CPP bioceramic materials with different properties and structures were prepared by high temperature sintering method,and the effects of sintering system and porogen on the porous structure and properties of CPP were studied.The Si element with good bioactivity and osteoinductivity was introduced into the CPP material,and the CPP/SiO2 composite ceramic material was designed and prepared.Through the analysis of its microstructure and properties,the effect of the addition of SiO2 on the performance of CPP ceramics were explored.In this paper,calcium dihydrogen phosphate(Ca(H2PO4)2)is used as raw material to prepare CPP precursor by pre-sintering.After pressing and molding,CPP bioceramics are prepared by high-temperature sintering method.CPP precursor powders with different degrees of polymerization and different crystal types can be obtained by changing the pre-sintering temperature and holding time.After sintering at 400℃ and holding for 10 h,the CPP precursor powder mainly exists in the y-CPP crystal form;in the range of 550℃ to 950℃,γ-CPP and β-CPP coexist;in the range of 550℃ to 950℃,the β-CPP crystal form exists.There are also differences in the crystal form at different times at 500℃.When the temperature is kept at 500℃ for 1 h and 5 h,CPP exists in the γ-CPP crystal form.When the holding time is increased to 10 h and 15 h,β-CPP crystal appears in CPP.It exists in two crystal forms,γ-CPP and β-CPP.Different pre-sintering holding time will also affect the mechanical properties and degradation properties of CPP ceramic materials.With the increase of pre-sintering holding time,the compressive strength of CPP ceramic materials first increases and then decreases.29.92MPa.When the pre-sintering holding time continued to increase to 15 h,the compressive strength of the CPP ceramic material decreased to 26.73 MPa.Combined with the micro-morphological analysis,it was concluded that when the pre-sintering holding time was too long,the particle size and distribution of CPP were not uniform,which affected the structural integrity of CPP.With the increase of holding time,the degradation rate of CPP ceramic material in Tris buffer and SBF simulated body fluid decreased,that is,the degradation rate was faster when the holding time was 1 h.Different CPP ceramic materials were prepared by holding at 500℃ for 10 h as the pre-sintering,followed by final sintering at 850℃ for different times(5 min,1.5 h,3 h,4.5 h).The compressive strength of the CPP ceramic material first increased and then decreased,and the law was the same as that of the pre-sintering experiment.When the final sintering holding time is 1.5 h,the compressive strength of CPP ceramics is the highest.The shorter the holding time,the faster the degradation rate of the CPP ceramic material.Using stearic acid as a pore-forming agent,porous CPP ceramic materials were prepared by sintering pore-forming method.With the increase of stearic acid addition,the porosity of CPP ceramic materials increased,and the compressive strength decreased.When it is 10%,the porosity is 45.5%,and the compressive strength is 19.73 MPa;when the addition amount increases to 50%,the porosity is 69.2%,and the compressive strength is 2.45 MPa.In order to simulate the gradient structure design of human cartilage tissue,a gradient porous CPP ceramic material was prepared according to the volume ratio of dense layer/transition layer/macroporous layer of 1:2:7.Compared with the porosity structure,the gradient porous structure improves the compressive strength of the ceramic material and improves the buffer load effect of the sample while ensuring the porosity.In view of Si,it is mostly introduced into various biomaterials in the form of bioglass and porous silica,and it shows good osseointegration ability,osteoinductive and osteoconductive ability.In this paper,SiO2 was selected to be introduced into CPP to prepare CPP/SiO2 composite bioceramic materials.Through relevant characterization and analysis,the influence of SiO2 addition on the microscopic morphology and performance of CPP was explored.With the increase of SiO2 addition,the mechanical properties of CPP/SiO2 gradient porous composite ceramics increased first and then decreased.When the SiO2 addition was 3%,it reached the highest,reaching 8.53 MPa,which was 30%higher than that of pure CPP ceramics.When the addition of SiO2 exceeds 10%,the compressive strength of CPP/SiO2 composite ceramics is lower than that of pure CPP ceramics.Compared with the particle shape and size of CPP ceramics,the surface particle uniformity of CPP/SiO2 composite ceramics is improved.When the addition of SiO2 is 1%and 3%,the particle size uniformity of the composite ceramics is better,the particle size is small,and the bonding between particles is better;when the addition of SiO2 is 5%,the particle size of the ceramic surface continues to decrease,but The distribution is partially uneven,resulting in local performance degradation.In the process of Tris immersion,with the increase of SiO2 addition,the degradation rate of CPP/SiO2 composite ceramics increased first and then decreased.When the SiO2 addition was 5%,the degradation rate was the fastest,and the weight loss rate reached 1.93%after 28 days of immersion,which is 5 times that of pure CPP ceramic material.In the SBF soaking process,the influence law is similar to that of the Tris soaking experiment.When the addition amount of SiO2 is 5%,the degradation rate is the fastest.down to 50%of the pre-soak level.After soaking,microspherical calcium and phosphorus compounds appeared on the surface of CPP,which was larger than that of pure CPP ceramics,indicating that the addition of SiO2 could promote the degradation of CPP ceramic materials.