3D-Printed Functionally Graded PCL-HA Scaffolds with Multi-Scale Porosity

Functionally graded scaffolds (FGSs) designed for bone tissue regeneration exhibit three-dimensional (3D) constructs with spatially varying pores, mirroring the natural bone structure, aiming to offer temporary support and a conducive environment for cells during tissue regeneration in defect sites. While existing research on FGSs has primarily focused on altering pore architecture and tuning biomechanical properties for improved tissue regeneration, limited exploration exists on 3D spatially varying FGSs with multiscale porosity to closely mimic natural bone. In this study, we fabricated and investigated FGSs with macropores varying radially and longitudinally, along with micropores within the struts. Utilizing nonsolvent-induced phase separation integrated with 3D printing, we printed poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) composite scaffolds with both uniform and FG geometries. Two HA content variations (10 and 20 wt %) were employed to assess their impact on scaffold properties. Rheological analysis of polymer suspensions gauged the viscosity and shear stress. Thermogravimetric analysis (thermal gravimetric analysis) determined PCL decomposition and the final HA content in the scaffold. Morphological properties, including porosity, pore size, and pore distribution, were evaluated using microcomputed tomography (micro-CT), while field-emission scanning electron microscopy imaged scaffold surface and cross-sectional morphology. Mechanical tests (compression and tension) assessed the scaffold strength. In vitro assays with MC3T3-E1 preosteoblast cells measured cell viability and alkaline phosphatase enzyme activity in uniform and FGSs with 10% and 20% HA content. Results confirmed that the achieved porosity levels provided sufficient strength and supported effective cell proliferation. Cell culture results demonstrated that uniform scaffolds with 10% HA promoted osteogenesis with slow cell proliferation, whereas FGSs with 20% HA promoted both proliferation and osteogenesis of preosteoblast cells. Overall, the structural, compositional, and biological characterization indicated that both uniform and FGSs provide suitable environments for bone tissue regeneration, with functionally graded scaffold morphology potentially offering a favorable environment for cell response.