Robocast Zn- and Co-doped bioactive glass/tricalcium phosphate scaffolds for bone regeneration

Bone tissue engineering requires scaffolds that synergize mechanical strength with bioactivity. This study aimed to develop and characterize 3D-printed zinc (Zn)- and cobalt (Co)-doped 45S5 bioactive glass (BG)/β-tricalcium phosphate (TCP) composite scaffolds for enhanced bone regeneration. Sol-gel-synthesized BG powders, doped with 3–15% Zn or 1–5% Co, were combined with TCP (50:50 ratio) to fabricate porous scaffolds via robocasting. Scaffolds were screened for cytocompatibility (MTT assay) and ion release (ICP-OES). The optimal compositions (3% Zn and 1% Co) were characterized for mechanical strength, in vitro bioactivity in SBF, and osteogenic potential using hADMSCs through qPCR, ALP activity, immunocytochemistry, and Alizarin Red staining. The 3% Zn- and 1% Co-doped scaffolds demonstrated excellent cytocompatibility (≥ 90% hADMSC viability) with controlled ion release. They exhibited compressive strengths of 15.67–20.24 MPa, matching cancellous bone, and significantly accelerated hydroxyapatite formation in SBF. Biologically, the scaffolds induced distinct, stage-specific osteogenic responses. Zn-doping preferentially enhanced early osteogenesis, marked by significantly higher collagen type I (COL-1) expression at day 21 and the highest ALP activity at day 14. In contrast, Co-doping specifically promoted late-stage maturation, resulting in superior osteocalcin (OCN) expression and a 2.5-fold increase in calcium mineralization compared to undoped controls, as quantified by Alizarin Red staining. Immunocytochemistry confirmed this trend, with robust expression of both COL-1 and osteopontin in the doped groups. The results demonstrate that Zn²⁺ and Co²⁺ ions confer complementary biological functions within BG/TCP scaffolds, effectively promoting sequential stages of osteogenesis. The robocast scaffolds successfully combine mechanical competence with enhanced osteoinductivity, presenting a highly promising platform for the repair of load-bearing bone defects.