Laser Additive Manufacturing And Cell Response Study Of Self-generating Functional Bone Scaffold

The number of patients with bone defects due to an aging population,traffic accidents,bone tumors and osteoarthritis is increasing every year,and how to repair bone defects has become an urgent problem.Electrical stimulation has great potential in regulating bone cell growth and accelerating bone tissue regeneration,but the need for external power supply and wires limits its further application.Therefore,the article proposes the use of selective laser sintering（SLS）to prepare bio-piezoelectric or photoelectric materials into bone scaffolds with self-powered functions.On the one hand,the piezoelectric or optoelectronic materials can be converted into electrical signals in response to external stress or light,which can directly stimulate cell or tissue growth without external power supply and wires;on the other hand,SLS has unique discrete-stacking characteristics that allow it to create a shape that matches the patient’s defective area,meeting the patient’s individual needs for a bone scaffold.The specific work in this paper is as follows:1.It was proposed to use the interface polarization locking technology to realize the efficient generation of piezoelectric active phase during laser forming,and construct a self-generating bone scaffold with good piezoelectric activity.Specifically,polyaniline（PANI）was prepared by in situ oxidative polymerization on molybdenum disulfide（Mo S₂）nanosheets to form PANI-Mo S₂,and then PANI-Mo S₂was added to the piezoelectric polyvinylidene fluoride（PVDF）bone scaffold prepared by SLS.The Mo-S dipole in Mo S₂and theπelectron cloud on N atom in PANI lock the-CH₂dipole in PVDF through electrostatic and hydrogen bonding,respectively,forcing-CH₂to be arranged vertically on the base surface of Mo S₂and biased to one side of the PVDF main chain,and the evenly distributed PANI-Mo S₂can be used as a platform to realize interfacial polarization locking,thus forming a fully reverse plane sawtooth configuration of electroactiveβ-PVDF and showing polarization characteristics.Compared with the PVDF group,the open-circuit voltage and short-circuit current of the 1.0PANI-Mo S₂/PVDF bone scaffold group increased by 277.8%and 323.3%,respectively,due to the increase of the electroactiveβ-PVDF content of the former.In vitro cell results showed that the bone scaffolds of each group had good biocompatibility,and enhanced electrical stimulation effectively promoted the growth of stem cells and improved the biological activity of alkaline phosphatase.2.An oxygen vacancy repair technique was proposed to repair oxygen vacancy defects on piezoelectric materials to achieve improved electrical properties of piezoelectric bone scaffolds.Specifically,barium titanate（BaTiO₃）was synthesized in situ on graphene oxide（GO）nanosheets using a hydrothermal reaction,and then BaTiO₃-GO was added to levopolylactic acid（PLLA）and prepared into a bone scaffold by SLS technology.On the one hand,the presence of numerous oxygen-containing functional group edge sites on GO nanosheets could be used as nucleation sites for the synthesis of BaTiO₃,which inhibited the generation of oxygen vacancy defects in BaTiO₃;on the other hand,the partial reduction of GO could be used as the conductive phase of the bone scaffold due to the permeation theory,which made the internal resistance of the conductive path of PLLA/BaTiO₃-GO bone scaffold smaller,and the addition to the bone scaffold could improve the polarization charge.The addition of the PLLA/BaTiO₃-GO bone scaffold could improve the mobility of the polarized charge,which resulted in less loss of current during charging and discharging,and thus improved the output electrical performance.Piezoelectric tests showed that the open-circuit voltage and short-circuit current of PLLA/BaTiO₃-GO bone scaffold were 10.6 V and 147.3n A,respectively.Furthermore,cells on the PLLA/BaTiO₃-GO bone scaffold showed the larger spreading area and the better proliferation and differentiation.3.A bone scaffold with dual photoelectric-piezoelectric self-stimulation was proposed using a photoelectric-piezoelectric synergistic technique.Specifically,bismuth sulfide（Bi₂S₃）was grown in situ in the piezoelectric material BaTiO₃and then introduced into the PLLA bone scaffold to prepare a dual electrostimulated bone scaffold with photoelectric-piezoelectricity.On the one hand,the intimate interfacial contact between BaTiO₃and Bi₂S₃with unique Bi-O covalent bond is very favorable for charge separation and transfer in Bi₂S₃-BaTiO₃;on the other hand,due to the piezoelectric effect of BaTiO₃,the acoustic pressure generated by ultrasonic vibrations will induce the generation of a spatial electric field on the surface of Bi₂S₃-BaTiO₃.Meanwhile,the electrons and holes generated by Bi₂S₃under light illumination will move toward the positive potential surface and negative potential surface of Bi₂S₃-BaTiO₃,respectively,driven by Coulomb forces,thus preventing the rapid compounding of electron-hole pairs.The results show that the Bi₂S₃-BaTiO₃composite exhibits lower photoluminescence intensity and higher transient photocurrent density.In vitro cellular experiments showed that PLLA/Bi₂S₃-BaTiO₃bone scaffolds could promote the adhesion and growth of stem cells and enhance the bioactivity of alkaline phosphatase and alizarin red,promote the inward flow of cellular calcium ions,and thus have great potential for pro-osteoclast regeneration.