3D printed PCL-nHAp composite implants for the treatment of segmental bone defects: in vivo application in a rabbit model

The management and treatment of long bone defects are challenging clinical problems. In this study, in order to address the need for load bearing implants for segmental defects, 3D printed cylindrical implants of poly(caprolactone) (PCL) and nanohydroxyapatite (nHAp) composites were prepared and applied as lateral segments to the femurs of New Zealand white rabbits. The results of PCL-nHAp implant group obtained 6 weeks after the procedure were compared with those of the autografts. There was no significant difference between the yield and ultimate loads of autograft group and the implant group. Histological studies demonstrated similar new bone formation in both groups. Also, a sizeable callus formation around the autografts and bone ingrowth to the 3D printed implants were observed, and x-ray studies confirmed the formation of the callus. An increase was detected in the bone density around the defect site for both test groups. SEM revealed close interaction between the newly formed bone tissue and the struts of the 3D printed implant. mRUST values, which is an indicator of tissue healing, increased continuously during 6 weeks. In conclusion, 3D printed, 1.5 cm long cylindrical nHAp-PCL implants exhibited excellent bone healing and biomechanical stability in the large lateral segmental bone defects of the rabbits even in a relatively short implantation time as 6 weeks. We believe that these implants could serve as an alternative to autografts in the treatment of long bone defects.