The hydroxyapatite modified 3D printed poly L-lactic acid porous screw in reconstruction of anterior cruciate ligament of rabbit knee joint: a histological and biomechanical study

Abstract

Background To observe the changes of bone mass in bone tunnel and the healing of tendon-bone interface after reconstruction of anterior cruciate ligament with hydroxyapatite (HA) modified 3D-printed PLLA porous screw and autogenous tendon graft in rabbits. Methods The PLLA porous screws which meet the requirements of the experiment are prepared by 3D printing technology. The PLLA porous screws were prepared by surface modification of PLLA-HA porous screws by electrostatic layer by layer self-assembly (ELSA) technology. Scanning electron microscope (SEM) was used to observe the surface morphology of scaffolds before and after modification. Determination of porosity of Screw support by liquid replacement method. Forty male New Zealand white rabbits were randomly divided into two groups. The right ACL was reconstructed with autologous tendons and the tendons were fixed with porous screws in the lateral femoral tunnel: PLLA group was fixed with PLLA screw bracket, and PLLA-HA group was fixed with PLLA-HA porous screw. Micro-CT scans were performed at 12 weeks after operation to measure the osteogenesis of the femoral tunnel in each group. Histological examination was performed to observe the tendon bone healing in the femoral tunnel. Biomechanical experiments were carried out to observe and compare the failure load and stiffness after transplantation. Result The preparation of PLLA porous screws by 3D printer meets the design requirements, and the voids in the stents are uniformly distributed and interconnected. After surface modification, HA is uniformly distributed in PLLA screw stents. At 12 weeks after operation, the bone formation indexes (BV/TV, Tb.N,Tb.Th) in PLLA-HA group were higher than those in PLLA group, while Tb.Sp was lower than that in PLLA group. The new bone is uniformly distributed in the bone tunnel along the screw channel. Histology showed that there was more type I collagen bone in PLLA-HA group than in PLLA group. Biomechanical experiments showed that the failure load and stiffness of PLLA-HA group were significantly higher than those of PLLA group (P < 0.05). Conclusion HA modified 3D printed bioabsorbable screws can promote tendon healing in bone tunnel by increasing bone growth.