A Mussel-inspired Persistent Ros-scavenging,electroactive,and Osteoinductive Scaffold Based On Electrochemical-driven In Situ Nanoassembly

Conductive polymers are promising materials for bone regeneration because they can regulate cell behavior through electrical stimulation.In addition,conductive polymers are anti-oxidative agents,and can be used to protect cells and tissues from excessive reactive oxygen species?ROS?damage.However,conductive polymers lack affinity to cells and osteoinductivity,which has limited their applications in tissue engineering.Therefore,it is necessary to develop an electroactive composite material with good cell affinity,bone induction and long-term antioxidant activity.Herein we present an electroactive,cell affinitive,persistent ROS-scavenging and osteoinductive porous Ti scaffold by on-surface in situ assembly of polypyrrole-polydopamine-hydroxyapatite?PPy-PDA-HA?film through a layer-by-layer pulse electrodeposition?LBL-PED?method.The mechanism of in situ synthesis of PPy-PDA NPs and HA NPs in LBL-PED process was studied.The mechanism of repeatable and efficient ROS scavenging over a long period of time was investigated.It was proved that HA and electrical stimulation?ES?synergistically promote osteogenic cell differentiation on PPy-PDA-HA films.The porous titanium scaffold has been successfully applied to the repair and regeneration of bone tissue.The main contents are divided into three parts:1.A method for in-situ polymerization of polypyrrole-polydopamine nanoparticles?PPy-PDA NPs?and hydroxyapatite nanoparticles?HA NPs?on two-dimensional titanium mesh surface by LBL-PED was developed.During the electrodeposition process,catechol groups of PDA and PO₄^3-doped in PPy can provide binding sites for Ca²⁺adsorption to synthesize HA NPs in situ.Similarly,in the HA layer assembled by HA NPs,Ca²⁺and PO₄^3-of HA can provide sites for the polymerization of PPy and PDA to form PPy-PDA NPs in situ.The SEM and EDS indicated that the PPy-PDA NPs and HA NPs were uniformly distributed in the coating,thus enhancing the stability of the coating.2.PPy-PDA NPs with high efficiency,long-term and recoverable antioxidative ability were obtained by co-deposition of DA and Py,and further aseemble to form PPy-PDA-HA coating.PPy-PDA-HA coating has a large number of catechol groups which can participate in redox reaction.And the ability of PDA to dope into PPy chain makes PPy easier to be oxidized and lose electrons to scavenge free radicals.The 1-diphenyl-2-picrylhydrazyl?DPPH?free radical scavenging experiment proved that PPy-PDA-HA coating had long-term effective and recoverable free radical scavenging ability.The in vitro ROS scavenging experiment showed that PPy-PDA-HA coating could protect cells from excessive ROS invasion.3.Due to the uniform distribution of PPy-PDA NPs and HA NPs in the coating,the PPy-PDA-HA coating can promote the bone regeneration.PDA could endow PPy with good cell affinity,thus enhancing cell adhesion and proliferation under electrical stimulation?ES?,which was proved by morphology and MTT test.HA and ES could synergistically up-regulate the expression of osteogenesis-related genes,which was indicated by result of osteogenic differentiation and gene expression.In vivo experiments show that the PPy-PDA-HA coating can induce new bone to grow into the scaffold,effectively reduced the area of bone defect and achieved good effect of bone repair.Ultimately,the PPy-PDA-HA porous scaffold exhibited excellent bone regeneration ability by utilizing the synergistic effects of electroactivity,cell affinity,and anti-oxidative activity of the PPy-PDA NPs and the osteoinductivity of HA NPs.This study provides a new strategy for functionalizing porous scaffolds that shows great promise as an implant for tissue regeneration.