Interface-engineered 3D-printed PCEC/collagen composite scaffold for large bone defect repair under static and mechanical stimulation

The repair of large traumatic bone defects remains a huge challenge in orthopedic clinics due to the complicated environment of bone healing involving bone regeneration and vascularization in the defect region. This is even more pronounced with an aging population worldwide. To address this, a novel interface-engineered scaffold was developed by integrating a bone-mimetic collagen type I/nano-hydroxyapatite (CI-nHA) matrix with a 3D- printed poly(ε-caprolactone)-polyethylene glycol 20k-poly(ε-caprolactone) (PCL-PEG20k-PCL, PCE20kC) triblock copolymer framework. The scaffold formed biofunctional interfaces with both enhanced mechanical support and promoted cell-material interaction. It exhibited interconnected multi-scale pores and a compressive modulus of ~37 MPa, comparable to cancellous bone. After culturing with preosteoblasts (MC3T3) under osteogenic conditions for 4 weeks, it showed promoted osteoblast proliferation, differentiation and matrix mineralization. The reinforced architecture further upregulated osteogenic transcription factors of RUNX2 and BMP-2. Moreover, when cultured with endothelial cells, it promoted early angiogenic activity within 5 days, indicating interface- mediated vascularization. Furthermore, when subjected to mechanical stimulation in a bioreactor with simulated physiological mechanical condition, the reinforced scaffold supported osteoblast viability and enhanced early mineralization evidenced by increasing gene expression of ALP and OCN after 1 week of intermittent mechanical stimulation. Overall, this interface-engineered scaffold integrates precise 3D architecture with collagen- functionalized surfaces to effectively support bone regeneration under both static and mechanical conditions, highlighting its translational potential for large bone defect repair.