Preparation And Properties Of Injectable Low Exothermic Drug-loaded Magnesium Phosphate-based Composite Bone Cement

Magnesium and phosphorus are important constituents of human bones and play an important role in bone metabolism,reconstruction and regeneration;therefore,various magnesium phosphate biomaterials have been developed.Magnesium phosphate cement(MPC)is receiving more and more attention among various’ magnesium phosphate biomaterials,It has been widely studied as a bone repair material due to its self-curing properties,adhesion,high strength in early curing,biodegradability and good biocompatibility.However,the rapid hydration reaction of MPC leads to poor handling performance and high exothermic temperature during the hydration reaction,limiting the further application of MPC in clinical practice.In this thesis,MPC was modified with Poly(y-glutamic acid)(y-PGA),Calcium sulfate hemihydrate(CSH)and drug-loaded wheat gluten microspheres(Wheat gluten,WG)to meet the clinical requirements for MPC performance.The effects of y-PGA,CSH and drug-loaded WG microspheres on the handling performance,hydration products,exothermic hydration temperature,mechanical strength,in vitro bioactivity,in vitro degradation and in vitro cytocompatibility of MPC were systematically investigated.The results showed that the MPC modified by γ-PGA,CSH and drug-loaded WG microspheres had good handling performance,low exothermic hydration temperature,good mechanical properties and in vitro biocompatibility,and the ability of sustained drug release and the porous structure formed during degradation were important for promoting bone regeneration and repair.Combined with the above research objectives and significance,the research in this paper focuses on the following three aspects:(1)Preparation and performance study of y-PGA-modified magnesium phosphate bone cement:In this part,we first successfully prepared tri-magnesium phosphate(TMP),trimagnesium phosphate pentahydrate(TMPP),magnesium hydrogen phosphate trihydrate(MHP),and amorphous magnesium phosphate(AMP)by precipitation method,alkaline magnesium carbonate template method and microwave-assisted method.By selecting the above-prepared powder as the solid phase component of MPC and diammonium hydrogen phosphate(DAHP)as the liquid phase to prepare MPC,the results showed that the MPC prepared by TMP showed better self-curing properties and early mechanical strength.Therefore,TMP powder prepared by the chemical precipitation method was selected as the main solid phase component of MPC in this thesis.Due to the defects of MPC prepared by TMP,such as poor handling performance,the high exothermic temperature of hydration,rapid hydration reaction and insufficient mechanical strength of MPC prepared by TMP.In order to overcome these defects and obtain MPC with good overall performance,this chapter introduces a peptide γ-PGA with a large number of free carboxyl groups in the side chains into the solid phase powder,which is intended to slow down the hydration reaction rate of MPC and prolong the setting time,and to improve the mechanical strength of the bone cement by chelating the carboxyl groups contained in y-PGA with the Mg2+released during the hydration reaction of MPC.The effects of different contents of γ-PGA on MPC handling performance,hydration products,hydration exothermic temperature,mechanical properties,in vitro bioactivity,in vitro degradation properties and in vitro cytocompatibility were systematically investigated.The results showed that the final setting time of MPC was prolonged from 3.7±0.6 min to 5.5±0.7 min at γ-PGA content of 10%.The injectability rate was increased from 52.4±3.0%to 89.2±0.8%,and the compressive strength after three days of curing was increased from 29.5 ± 5.4 MPa to 57.22±9.4 MPa.In vitro cell culture experiments showed that the 10%γ-PGA modified MPC samples had good cell adhesion properties and biocompatibility.(2)Preparation and characterization of CSH synergistic γ-PGA-modified magnesium phosphate-based composite bone cement:According to the results of the last part,to further improve the deficiencies of MPC with too fast solidification and too high exothermic hydration temperature,this part introduced CSH with good biocompatibility and biodegradability to retard its hydration reaction based on the above MPC composite system.The effects of different levels of CSH in concert with 10%γPGA on the handling performance,hydration products,exothermic hydration temperature,in vitro degradation rate,in vitro bioactivity and in vitro cytocompatibility of magnesium phosphate-based composite bone cement were systematically investigated.The results showed that when the CSH content was in the range of 10%-30%,increased CSH content gradually prolonged the setting time,and the exothermic hydration temperature was steadily reduced.When the CSH content was 30%,the final setting time was prolonged from 5.5±0.7 min to 11.2±1.3 min,and the maximum hydration exothermic temperature was reduced from 39.3±1.0℃ to 23.0±1.4℃,which avoided the possible damage to human tissues due to high exothermic temperature of hydration in clinical use.In addition,CSH could regulate the in vitro degradation performance of MPC,and the degradation rate of composite bone cement with 30%CSH increased from 12.1±0.3%to 21.7±0.4%at day 21.In vitro cell culture experiments showed that the prepared magnesium phosphate-based composite bone cement had good biocompatibility and cell adhesion properties.(3)Preparation and performance study of wheat gluten microspheres compounded with CSH/y-PGA modified magnesium phosphate-based composite bone cementTo expand the application of MPC,the need for drug therapy during bone repair and the need for pores to provide space for bone tissue and blood vessel growth was addressed.In this chapter,porous WG microspheres were first prepared,and Doxorubicin(Dox)was used as a drug model loaded into porous WG microspheres to study the drug loading and drug release ability of the microspheres.Based on the above composite magnesium phosphate cement(CMPC),drug-loaded WG microspheres were introduced into CMPC to systematically study the handling performance,mechanical properties,hydration products,exothermic temperature of hydration,in vitro bioactivity and in vitro cytocompatibility of WG microspheres compounded with CMPC.Its ability of sustained drug release and the porous structure formed during degradation was further investigated.The results indicated that the encapsulation rate of drug-loaded WG microspheres was 81.5%,39.6±34.6%of the drug was released at 72 h.The CMPC compounded with WG microspheres maintained good handling performance and early strength,and compressive strength increased from 21.6±1.0 MPa to 29.2±2.1 MPa after three days of hydration,and the maximum exothermic temperature decreased from 23.0±1.4℃ to 21.3±0.7 ℃.The results of in vitro cell experiments showed that WG microspheres compounded with CMPC had cell adhesion properties and cytocompatibility.In addition,through drug release and degradation of the microspheres,the bone cement had the ability to continuously release drugs to treat bone defect sites and porous structures that provide space for tissue and vascular growth.Finally,when comparing the binding force of the prepared drug-loaded WG microspheres composite CMPC and TCP bone cement with that of the bone defect model(556.1 N ± 62.4 N),the drug-loaded WG microspheres composite CMPC showed good osseointegration properties with a binding force of 991.5 N ± 252.3 N in the defective sheep vertebrae.