3D Printing And Evaluation Of Manganese Incorporated Scaffolds For Bone Regeneration

With the rapid development of society and aging of population,the number of patients with bone injury is increasing rapidly.Repair and reconstruction of challenging bone defects that cannot heal naturally is always a major challenge in clinical orthopedics.Traditional materials for bone repair cannot fully meet clinical needs.Therefore,new materials with multiple functions need to be developed.After bone injury,vascular dysfunction and insufficient osteoblasts may hinder bone healing.The conventional treatment of bone defects in the clinic is fixation and regeneration of bone with bone grafts collected from patients or compatible donors.These techniques have potential disadvantages,such as size mismatch,inconvenient imaging,inflammation,short of mechanical strength and biological activity.In order to solve the above problems,this study developed a dual-function scaffold that could assist imaging and promote osteogenesis.This study utilized the functions of manganese dioxide(MnO₂)nanoparticles,such as imaging,promoting bone regeneration and regulating the microenvironment of the injured site.These biodegradable scaffolds were prepared with polylactic acid(PLLA)and manganese dioxide(MnO₂).The addition of MnO₂ nanoparticles was designed to generate Mn²⁺and oxygen during the degradation process,improve the activity of osteoblasts and regulate the microenvironment in bone repair.Firstly,PLLA/MnO₂ composite scaffolds with pore size of 0.4 mm and good pore connectivity were prepared by low-temperature deposition 3D printing technology.The surface of composite scaffolds was hydrophilic and their mechanical properties met the requirements of bone repair.Degradation tests showed that PLLA/MnO₂ composite scaffolds could maintain long-term structural stability in the degradation medium and the release of manganese ions was small and controllable.The degradation of composite scaffolds did not have a great impact on the surrounding environment,which met the requirements of long-term implantation.Secondly,the performance of PLLA/MnO₂ composite scaffolds in imaging was evaluated.It was verified that composite scaffolds containing manganese could be imaged under CT/MRI dual-mode and the imaging effect under MRI had p H responsiveness and hydrogen peroxide responsiveness.This imaging property could be used to achieve noninvasive,quantitative assessment of the microenvironment and to monitor bone defect area after surgery.Thirdly,the feasibility of PLLA/MnO₂ composite scaffolds for bone repair was evaluated.Composite scaffolds showed good biocompatibility and promoted the adhesion and proliferation of osteoblasts on scaffolds.Scratch experiment and Transwell experiment showed that low concentration(2?M)of Mn ion promoted cell migration and diffusion.Osteoblasts exhibited excellent migration ability on these composite scaffolds.Cells could grow into the holes of porous scaffolds and presented a three-dimensional growth.Finally,therapeutic effects of PLLA/MnO₂ composite scaffolds in bone repair was evaluated from the perspectives of angiogenic activity,microenvironment regulation and osteogenic activity.Angiogenesis experiments showed that low concentration of manganese ions can promote the expression of VEGF protein in cells,thus promoted the formation of vascular network.The results showed that the composite scaffolds could remove the excess ROS in the microenvironment and protect cells from ROS induced apoptosis.The results of the osteogenic induction of mesenchymal stem cells by manganese ions showed that manganese ions had osteogenic activity in the early and late stages of osteogenic differentiation and could induce the formation of mineralized nodules.Therefore,composite scaffolds have certain functions in bone repair and bone induction.In conclusion,the PLLA/MnO₂ composite scaffolds prepared in this study have great potential in the field of bone defect treatment and is expected to realize dual functions of both assisted imaging and osteogenesis promotion.