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 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 obtained after 6 weeks of implantation were compared with the autografts. Although the maximum load determined in the 3-point bending tests for the autografts (93±56 N) was higher than the composite implants (57±5 N), histological studies demonstrated similar new bone formation in both test 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 in the bone density around the defect site was detected 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.