A stiff bioink for hybrid bioprinting of vascularized bone tissue with enhanced mechanical properties.

3D bioprinting is an emerging technique in tissue engineering that is advantageous for fabricating intricate tissues. However, challenges arise in bioprinting functional, implantable tissues. Commonly utilized hydrogel bioinks, while offering desirable printability and a cell-friendly environment, often lack the mechanical robustness necessary for post-printing maturation, handling, and implantation. These limitations are particularly relevant for bone tissue. Treatment of bone loss resulting from trauma or infection poses a significant clinical challenge. While surgical interventions exist, they frequently lead to complications and limited outcomes. Thus, a strategy to enhance the mechanical integrity of bioprinted constructs compatible with cells is needed. This study presents a novel hybrid bioprinting approach to create mechanically robust, vascularized bone tissue. A reinforcing bioink composed of a poly(lactic-co-glycolic) acid (PLGA), hydroxyapatite (HA), and polyethylene-glycol microparticles blend, which is thermosensitive due to a reduced glass transition temperature (∼36 °C), enabling sintering at physiological conditions is co-printed with a cell-laden, ECM-based hydrogel. The microparticles sinter at 37 °C, forming a porous, stiff scaffold. The hybrid bioprinted constructs demonstrate high cell viability, vascular network formation, and osteogenic differentiation. In vivo implantation in a rat femoral defect reveals superior bone regeneration compared to acellular controls. This study highlights the potential of hybrid bioprinting for creating tissues exhibiting high cell viability and enhanced mechanical properties, allowing for their handling and implantation.