Research On Osteogenic And Antibacterial Properties Of 3D Printed Poly (L-lactic Acid) Composite Bone Implants

Poly-L-lactic acid（PLLA）possesses good biocompatibility,degradability and mechanical properties,is widely used in many tissue regeneration fields,including bone tissue repair.However,PLLA does not possess osteogenic activity,which greatly limits its effect on bone repair.Meanwhile,the bone implantation process is usually accompanied by bacterial infection,which may even lead to graft failure in severe cases,threatening the life and health of patients.Therefore,in this paper,we propose to prepare zinc（Zn）and silver（Ag）doped silica-based mesoporous nanoparticles and introduce them into PLLA scaffolds to construct 3D printed PLLA composite bone scaffolds,which can confer osteogenic and antibacterial functions to the bone scaffolds through the slow release of functional Zn and Ag ions from silica-based mesoporous nanoparticles,respectively;preparing near-infrared light responsive Zn S-Ti₃C₂ bio-heterojunction using in situ growth technology,compounded with PLLA and fabricated into composite bone scaffold by 3D printing technology,realized the osteogenic and antibacterial dual function design of bone scaffold through photothermal/hydrogen sulfide（H₂S）gas synergistic antibacteria and Zn ion enabling bone regeneration.The main research contents and the innovation points of this paper are as follows.1.For the lack of osteogenic activity of PLLA bone scaffolds,Zn-MS was proposed to be introduced into PLLA scaffolds.MS can act as a good carrier to prevent the burst release of Zn ions at the initial stage and provide a safe ion release system for bone scaffolds.The ion release experiments showed that composite bone scaffolds can release Zn ions continuously for up to 14days.Cellular experiments showed that the composite scaffold could promote cell adhesion and upregulate the expression of osteogenic-related genes RUNX2 and COL-I.2.To address the problem that bacterial infection at the initial stage of bone scaffold implantation.We proposed to add Ag-MBG nanoparticles to PLLA scaffold,and the mesoporous structure of MBG can well retard the release of Ag ions and avoid the cytotoxicity.The ion release experiments showed that the composite bone scaffold can continuously release Ag ions for up to 28days.The released Ag ions can disrupt the bacterial membrane and induce the production of oxidative stress inside the bacteria,thus killing them efficiently.Antibacterial experiments showed that the bacterial inhibition rate of the scaffold was 81%when the incorporation ratio of Ag-MBG was 4%.3.Given the key role of good osteogenic activity and antibacterial properties in the bone regeneration and repair process.The innovative hydrothermal method was used to grow Zn S nanoparticles in situ on the surface of Ti₃C₂,and the composite material was introduced into the PLLA scaffold using 3D printing technology to realize the dual functional integration design of osteogenic and antibacterial bone scaffolds.p H-responsive degradation of Zn S can release H₂S gas in the acidic microenvironment of bacteria and destroy the dense biofilm of bacteria.Meanwhile,Ti₃C₂,as a photothermal material,can produce local thermal effect under the excitation of near-infrared light to further kill the bacteria after biofilm disruption.The results of photothermal experiments showed that the temperature of the scaffold could be increased from 27.5°C to 51°C under the irradiation of NIR light.The antibacterial experiments showed that the inhibition rates of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli were 84.7%and 90.3%,respectively,under the irradiation of NIR light.In addition,cellular experiments showed that the sustained release of Zn ions from the scaffold could promote the proliferation and differentiation of mouse bone marrow mesenchymal stem cells（m BMSCs）cells.