ZIF-8 functionalized PCL/BG composite scaffolds with improved bioactivity and osteogenic differentiation

Bone tissue engineering requires scaffolds with balanced mechanical strength, bioactivity, and biological performance. In this study, three-dimensional (3D) printed polycaprolactone (PCL) scaffolds incorporating 40, 45, and 50 wt% sol–gel-derived 58 S bioactive glass (BG) nanoparticles were fabricated, followed by surface functionalization with a ZIF-8 metal–organic framework to develop a dual bulk–surface modified system. Among the investigated compositions, the scaffold containing 45 wt% BG exhibited the highest compressive strength (~ 35 MPa) and was selected as the optimized formulation for subsequent biological evaluation. Cross-sectional SEM and EDS analyses confirmed the homogeneous dispersion of Ca, Si, and P elements throughout the polymer matrix. The optimized scaffold demonstrated controlled degradation behavior and pronounced apatite-forming ability in simulated body fluid. Quantitative Zn²⁺ ion release analysis over 28 days revealed a sustained and controlled release profile (0.05–0.69 ppm) without burst release, indicating the structural stability of the ZIF-8 coating and maintaining ion concentrations within a non-toxic range. In vitro studies using MG-63 osteoblast-like cells showed significantly enhanced cell viability, adhesion, and proliferation in the ZIF-8-modified scaffold compared to the uncoated group (p < 0.05). Furthermore, gene expression analysis demonstrated significant upregulation of osteogenic markers (ALP, Col1A1, Runx2, and OCN) in the surface-functionalized scaffold, confirming its osteoinductive potential. Overall, the combined high BG loading and ZIF-8 surface modification strategy resulted in a mechanically competent, bioactive, and biologically enhanced scaffold, highlighting its promise as a multifunctional platform for bone tissue engineering applications.