Biomimetic Preparation And Performance Of PVDF Based Piezoelectric Bone Scaffolds

The repair of bone tissue defects has always been a major clinical challenge in orthopedics.Artificial bone has become a research hotspot in the field of bone tissue repair due to its wide source,no risk of disease transmission,shape structure,chemical composition and other advantages.With the development of material science and additive manufacturing technology,artificial bone has been able to achieve bionic bone tissue structure,but there is still the problem of weak ability to induce cell proliferation and differentiation.To solve the above problem,the microenvironment of bone cell and tissue growth is constructed through biomimetic strategies,which is of great significance for improving the osteogenesis activity of artificial bone and accelerating bone repair.In addition,physical stimulation（electrical stimulation,magnetic stimulation,etc.）plays an important regulatory role in the adhesion,proliferation and differentiation of osteoblasts.In this paper,we aim to use the characteristics of selective laser sintering technology to prepare porous artificial bone scaffolds layer by layer and free molding,to achieve precise regulation and personalized customization of the porous structure of artificial bone scaffolds,and to use the inherent piezoelectric properties of piezoelectric materials to complete the biomimetic of bone electro-microenvironment,thereby promoting the repair and regeneration of bone tissue.The specific research work of the thesis is as follows:1.PVDF-based piezoelectric composite scaffolds were prepared by selective laser sintering technology,and the piezoelectricity of PVDF was used to achieve biomimicry of the bone electric microenvironment,and the piezoelectric performance of PVDF was improved by the introduction of graphene oxide（GO）.The results show that the oxygen-containing functional group of GO can form a strong hydrogen bond with the fluorine group of PVDF,which will induce the transformation of theαphase in PVDF to theβphase,thereby improving the piezoelectric performance of the scaffold.With the introduction of GO,the hydrophilicity of stents has been significantly improved.In vitro cell culture experiments have shown that due to the improvement of piezoelectricity,PVDF/0.3GO composite scaffolds can promote cell proliferation and differentiation.In addition,under the nano-enhanced action of GO,the compressive strength and tensile strength of PVDF/0.3GO composite scaffolds increased by97.9%and 24.5%,respectively.2.In view of the low piezoelectric constant of PVDF,it is difficult for a single carbon material to improve the piezoelectric constant of the stent.It is proposed to introduce barium titanate with high electrical constant into PVDF matrix,and use carbon layer and barium titanate to construct a core-shell structure to obtain a high-performance piezoelectric artificial bone scaffold.The results show that the core-shell structure can well solve the problem that piezoelectric ceramics are difficult to fully polarize due to the difference in dielectric constant between ceramics and polymers.Under the action of mechanical pressure of 0.5 MPa,BT@C-1/PVDF obtained the highest open-circuit voltage of 5.7 V and the highest short-circuit current of 79.8 n A.The cell experiment results showed that the BT@C-1/PVDF scaffold could release electrical stimulation to promote cell proliferation and differentiation under the action of ultrasonic stimulation.Furthermore,due to the strengthening effect of rigid particles,the tensile and compressive strengths of the BT@C-1/PVDF scaffolds were increased by 22.6%and71.4%,respectively.3.Ferric oxide（Fe₃O₄）nanoparticles are ideal micro-magnetic sources,which can provide the function of magnetic stimulation for artificial bone scaffolds,and combined with PVDF can realize artificial bone scaffolds with electromagnetic dual stimulation.However,Fe₃O₄nanoparticles are prone to agglomeration.It is proposed to support Fe₃O₄ nanoparticles on the surface of graphene oxide（GO）by in situ growth technology to construct a nanosystem to solve the problems of agglomeration and weak interfacial bonding of Fe₃O₄ nanoparticles.On one hand,Fe₃O₄ nanoparticles grown on GO can achieve good dispersion.On the other hand,the formation of strong hydrogen interactions between the oxygen-containing groups on the GO surface and the fluorine groups of PVDF can improve the poor interfacial bonding between Fe₃O₄nanoparticles and the PVDF matrix.The results show that the Fe₃O₄magnetic nanoparticles provide the composite scaffold with a magnetic field around it.The saturation magnetization of the PVDF/GO@Fe₃O₄ composite scaffold was 2.0 emu/g,and at the same time,the PVDF/GO@Fe₃O₄ composite scaffold exhibited the highest piezoelectric output due to the phase transition of PVDF induced by GO.The cell experiment results showed that the cells exhibited the largest spreading area and the best proliferation and differentiation on the PVDF/GO@Fe₃O₄ composite scaffold.