Laser Additive Fabrication And Properties Of Polymer/Montmorillonite Composite Bone Scaffold

Large segmental bone defects caused by traffic accidents,sports injuries,bone tumors,osteomyelitis and other diseases seriously threaten the health of patients.It is of great significance to realize the repair and regeneration of damaged bone tissue.Biocompatible polymers such as polycaprolactone（PCL）and polyglycolic acid（PGA）have been approved by the US Food and Drug Administration for clinical use.Large segmental bone defects caused by traffic accidents,sports injuries,bone tumors,osteomyelitis and other diseases seriously threaten the health of patients.It is of great significance to realize the repair and regeneration of damaged bone tissue.Biocompatible polymers such as polycaprolactone（PCL）and polyglycolic acid（PGA）have been approved by the US Food and Drug Administration for clinical use.Montmorillonite（MMT）meets the requirements of advanced basic materials proposed by Made in China2025.It has unique interlayer structure,high surface activity and strong cation exchange ability.The mechanical properties of the composite materials can be improved obviously by inserting monomer or polymer chain into the MMT lamellae and forming intercalated composite structures.In addition,as the carrier of antibacterial drugs,MMT can insert metal cations,organic cations or photosensitizers with antibacterial effects into the interlayer of MMT to play a slow-release role,so as to prepare stable and long-lasting antibacterial agents.Polymer bone scaffolds usually have advantages of good biocompatibility and degradability,but there are many common problems such as difficult preparation of porous structures,insufficient mechanical properties,and bacterial infection associated with bone implantation.Therefore,based on the structural and physical and chemical characteristics of MMT,the intercalated polymer/montmorillonite composite functional material is constructed,which is expected to prepare the composite bone scaffold with excellent performance to repair the defect tissue.The main research contents of this thesis are as follows:1.Aiming at the difficulty in preparing the porous structure of bone scaffolds,polymer/montmorillonite composite bone scaffolds were prepared by selective laser sintering technology.The mechanism of heat transfer and powder binding in laser sintering process was analyzed,the influence mechanism of different process parameters on the sintering properties of the scaffold was studied,the influence of MMT content on the mechanical and biological properties of PCL/MMT composite bone scaffold was evaluated,and the preparation process of polymer/montmorillonite composite bone scaffold was optimized.2.In view of the deterioration of mechanical properties of inorganic MMT and organic polymer due to poor interface bonding,the intercalation composite method was proposed by using silane coupling agent to organically modify MMT and inserting PCL molecular chain to achieve intercalation,so as to improve the interface compatibility between MMT and polymer,thus enhancing the mechanical properties of polymer/montmorillonite composite bone scaffold.The effect of improving interfacial bonding on mechanical properties of composite bone scaffolds and the mechanism of promoting dispersion and interfacial stress transfer were evaluated.It was revealed that the silane coupling agent,as an interfacial coupling bridge,formed a bond between MMT and PCL,and interlaminar composite structures produced interlayer locking effect.The tensile strength and modulus of PCL/10%modified MMT composite bone scaffold with 10 wt%modified MMT increased by1.83 and 5.25 times,and the compressive strength and modulus increased by 1.08 and 3.78 times,respectively,compared with PCL/10%modified MMT composite bone scaffold with the same amount of MMT.3.Considering that bacterial infection is likely to occur after bone scaffold transplantation,the introduction of antibacterial cations in the interlayer of MMT through Cu²⁺ion exchange reaction gives the polymer/montmorillonite composite bone scaffold lasting antibacterial activity.The antibacterial properties（such as turbidity,bacteriostatic rate and bacteriostatic zone）of PGA/Cu-MMT composite bone scaffolds with different contents of Cu²⁺intercalated MMT（Cu-MMT）in PGA matrix were evaluated,and the Cu²⁺release behavior of scaffolds after immersion in PBS solution was studied.It was revealed that the MMT layer has a blocking effect,which can delay the ionic diffusion and the erosion of aqueous solution,so that Cu²⁺had a fast release period of about 3 days and a slow release period of 28 days.After soaking 28 days,the release amount of Cu²⁺was 73.0 mg/L,which could realize the slow controlled release of Cu²⁺between layers and play a long-term antibacterial function.4.In view of the limitation of antibacterial performance of Cu²⁺as a single antibacterial agent,based on the improvement of interface compatibility by organic modification,organic/inorganic composite antibacterial agent was introduced into MMT layers by Cu²⁺intercalation and quaternary ammonium salt modification,and the polymer/montmorillonite composite bone scaffold with antibacterial activity and mechanical strengthening was prepared.The effect of Cu²⁺intercalation and quaternary ammonium salt modification on the antibacterial properties of composite bone scaffold was studied.It was revealed that more quaternary ammonium salt was inserted into the MMT after increasing the spacing of MMT layers by Cu²⁺.The quaternary ammonium salt made the MMT surface positively charged and thus absorbed negatively charged bacteria through electrostatic adsorption.The synergistic mechanism of reactive oxygen species produced by organic/inorganic antibacterial agents was achieved,and the antibacterial rate of PGA/Cu-CMMT composite scaffold against Escherichia coli reached 98.1%.In addition,the compression strength and modulus of PGA/Cu-CMMT composite scaffold were increased by 23.9%and 22.1%as compared with PGA/MMT composite scaffold by using quaternary ammonium salt as the coupling bridge to improve interface bonding.Pictures:70,Tables:10,References:156...