Augmented Repair and Regeneration of Critical Size Rabbit Calvaria Defects with 3D Printed Silk Fibroin Microfibers Reinforced PCL Composite Scaffolds

Treatment of critical size defects is quite challenging, often requiring autologous bone grafts for bone regeneration. A massive volume of autologous bone is essential during this process to fill the defect leading to donor site morbidity. Although 3D printed PCL scaffolds are frequently utilised for bone correction procedures, there have been reports of delayed PCL biodegradation and inadequate bone tissue formation. To enhance the regenerative potential, in this study, silk in the form of silk fibroin microfibers are reinforced into the PCL matrix to form the composite. Two silk variations were used: Antheraea mylitta and Bombyx mori, and has been proven to promote cell proliferation, adhesion, and osteogenic potential. This work creates 8 mm critical size defects in a rabbit calvaria model to test for the first time ever the ability of 3D printed PCL-silk scaffolds to regenerate bone tissue. Micro-CT imaging and histological examination performed 6 and 12 weeks after implantation revealed that the PCL-silk scaffold-augmented defects considerably outgrew their PCL-scaffold-only counterparts and the control group in terms of neo-bone formation. By 6 weeks, PCL-silk scaffolds had 47.4–50.3% of bone growth that was twice as high as PCL scaffolds alone (16.7–19.9%). Similarly, by 12 weeks, the PCL-silk group had four times more (80–87.3%) new bone tissue production than the PCL group (18.6–22.4%). The promise of silk fibroin-reinforced PCL biomaterial for pre-clinical and clinical studies for craniofacial reconstructive applications is thus supported by these results.