Biological Reinforced Concrete for Cartilage Repair With 3D Printing.

The development of biomimetic cartilage constructs (BCCs) with natural extracellular matrix (ECM) microenvironments and topological cues to accelerate the reconstruction of natural articular cartilage (NAC) after injury is challenging due to its complex structure, low cellular content, and less vascularity. Inspired by concrete rebar structure, a biomimetic cartilage named "biological reinforced concrete" is fabricated, with collagen fiber orientation transitioning from parallel to perpendicular, replicating the ECM microenvironments and complex construct of NAC. 3D-printed ultrafine fiber networks (UFNs) served as a degradable "biorebars", while a hybrid biohydrogel acted as "biocement". The stem cells are utilized as "bioactive aggregates". The biocement is developed by combining and screening various biohydrogels to mimic an ECM microenvironment conducive to the formation of NAC. By adjusting the fiber scale and spacing of the UFNs, the mechanical properties of the biomimetic cartilages are controlled to resemble those of NAC. Additionally, the UFNs guided the directed growth of cells and the orderly secretion of ECM. Subsequently, the developed BCCs are implanted into an osteochondral defect, and after 4 months, they successfully reconstructed the complex structure of cartilage with mechanical properties closely resembling those of NAC. The biological reinforced concrete offers a customizable and universal strategy for tissue regeneration.