High-strength 3d Printed Three-periodic Minimal Surfaces Hydroxyapatite Scaffold For Bone Repair

The mechanical compatibility of repair materials to the human body is an important criterion in the process of bone repair,especially in the repair of large segmental bone defects.The construction of porous structural repair scaffolds with good mechanical properties and pro osteogenic properties can promote the smooth progress of the bone repair process.Bioactive ceramics,similar in composition to the inorganic components of natural bone tissue,are an excellent material for bone repair.However,current scaffolds for bone repair prepared based on bioceramic materials mostly suffer from insufficient mechanical properties,and current solutions,such as regulating composition or surface modification,are able to play a very limited role.Therefore,starting from the structural design of scaffolds,it is clinically important to achieve reinforcement through structural mechanical means as one of the best strategies to effectively solve such problems.The three-period minimal surfaces are surfaces that are periodically repeated in three dimensional directions in space with a mean curvature of zero,and this type of structure is ideal for the structural design of scaffolds for bone repair.In this research,we intend to obtain the structure parameters and to control the structure by studying the implicit equations and parameters of the three-period minimal surface structure,explore the design scheme of its application to bone repair scaffolds,design and prepare three-period minimal surface bone repair scaffolds with different structures by 3D printing via hydroxyapatite stereolithography,and evaluate their connectivity,surface regularity and cellular osteogenesis performance,and briefly discuss the differences in cellular osteogenesis performance.The results show that the prepared three-period minimal surface structure scaffold has good connectivity,no cytotoxicity,and is more conducive to cell adhesion,proliferation and osteogenic differentiation.The compressive properties of the three-period minimal surface structures were analyzed and predicted from the stress concentration perspective by finite element analysis to simulate the stress distribution and strain level of different structures in the compressive stress.Compressive strength the 3D printed hydroxyapatite scaffolds with different structures were tested again by mechanical compression experiments to obtain the actual compressive strength of the different structures,which was verified with the finite element analysis results.Finite element analysis results showed that the three-period minimal surface structures resulted in significantly less stress concentration than the cross-hatch structures when subjected to compressive stress,and the compressive test results also indicated that the compressive strength of the three-period minimal surface structures was significantly higher than that of the cross-hatch intersection,in which the maximum compressive strength of the SplitP scaffolds could reach 150 MPa,which met the human cortical bone strength demand.Secondly,SplitP structure and cross-hatch structure scaffolds were selected to be implanted into the bone marrow cavity of the femurs of New Zealand white rabbits,and the scaffolds were harvested for Micro-CT scanning and three-dimensional reconstruction at different times after implantation,while the femoral samples containing scaffolds were compression tested to evaluate their in vivo biomechanical performance,and histological sections were stained and analyzed.Micro-CT and histological section results showed that the SplitP scaffolds had a significantly higher level of newly formed bone at the pre implantation stage in vivo than the scaffolds with cross-hatch,however,the difference in the total amount of new bone between the two structures in the later stage is not significant.The mechanical test results also showed that the level of new bone in the 4th to the 8th week.At week 12,the compressive load of the femur sample implanted with the SplitP structure scaffold was significantly higher than that of the cross-hatch structure scaffold,and reached the maximum value of 1965.690 N at the 12 th week.In conclusion,this study focuses on solving the problems such as biomechanical discomfort of bioceramic materials in precision regenerative repair of bone,and designs 3D printed hydroxyapatite scaffolds with tunable compressive strength based on three-period minimal surface structures that can meet the demands of bone defect regenerative at different sites.This kind of mechanical reinforcement scheme by structure design is expected to provide a new solution for the design of scaffolds for bone repair,which is of great research significance and clinical value.