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Generating 3D bone cell networks in vitro that mimic the dynamic process during early bone formation remains challenging. Here, we report a synthetic biodegradable microporous hydrogel for efficient formation of 3D networks from human primary cells, analysis of cell-secreted extracellular matrix (ECM) and microfluidic integration. Using polymerization-induced phase separation, we demonstrate dynamic in situ formation of microporosity (5–20 µm) within matrix metalloproteinase-degradable polyethylene glycol hydrogels in the presence of living cells. Pore formation is triggered by thiol-Michael-addition crosslinking of a viscous precursor solution supplemented with hyaluronic acid and dextran. The resulting microporous architecture can be fine-tuned by adjusting the concentration and molecular weight of dextran. After encapsulation in microporous hydrogels, human mesenchymal stromal cells and osteoblasts spread rapidly and form 3D networks within 24 hours. We demonstrate that matrix degradability controls cell-matrix remodeling, osteogenic differentiation, and deposition of ECM proteins such as collagen. Finally, we report microfluidic integration and proof-of-concept osteogenic differentiation of 3D cell networks under perfusion on chip. Altogether, this work introduces a synthetic microporous hydrogel to efficiently differentiate 3D human bone cell networks, facilitating future in vitro studies on early bone development. Generating 3D bone cell networks in vitro that mimic the dynamic process during early bone formation is vital for creating in vitro models of bone development for disease modeling and drug testing, but remains challenging. Herein, the authors report a synthetic biodegradable microporous hydrogel for in vitro generation of functional human bone cell networks in 3D and microfluidic integration. [ABSTRACT FROM AUTHOR]

The creation of multi‐tissue auricular transplants for the treatment of microtia is a challenge due to the complex and layered structure of this anatomical tissue. A novel casting technique for the 3D biofabrication of heterogeneous, multi‐layered, and human‐scale tissue transplants using eluting agarose molds is presented. The molds are generated by casting agarose into custom 3D‐printed containers, termed metamolds, optimized to facilitate the hydrogel casting process based on geometric and topological constraints. Casting yields high resolution (50 µm) and allows for subsequent casting of further hydrogel layers on the transplant. Multi‐layered auricular constructs are fabricated on a cartilage core consisting of a hyaluronic acid‐alginate double network and an adjacent gelatin‐based dermal layer. Bonding between adjacent layers is achieved by orthogonal physical and enzymatic crosslinking of residual functional groups between each layer. Material composition and culture duration are optimized for each layer allowing for maturation into cartilaginous and pre‐vascularized dermal tissues. To demonstrate the scalability of this technique for the biofabrication of human‐sized transplants, bi‐layered human‐sized ears are cast. Overall, this novel casting technique offers a promising approach for the fabrication of complex tissue grafts, overcoming the limitations of other traditional biofabrication methods. [ABSTRACT FROM AUTHOR]

Achieving regeneration of articular cartilage is challenging due to the low healing capacity of the tissue. Appropriate selection of cell source, hydrogel, and scaffold materials are critical to obtain good integration and long-term stability of implants in native tissues. Specifically, biomechanical stability and in vivo integration can be improved if the rate of degradation of the scaffold material matches the stiffening of the sample by extracellular matrix secretion of the encapsulated cells. To this end, a novel 3D-printed lactide copolymer is presented as a reinforcement scaffold for an enzymatically crosslinked hyaluronic acid hydrogel. In this system, the biodegradable properties of the reinforced scaffold are matched to the matrix deposition of articular chondrocytes embedded in the hydrogel. The lactide reinforcement provides stability to the soft hydrogel in the early stages, allowing the composite to be directly implanted in vivo with no need for a preculture period. Compared to pure cellular hydrogels, maturation and matrix secretion remain unaffected by the reinforced scaffold. Furthermore, excellent biocompatibility and production of glycosaminoglycans and collagens are observed at all timepoints. Finally, in vivo subcutaneous implantation in nude mice shows cartilage-like tissue maturation, indicating the possibility for the use of these composite materials in one-step surgical procedures., (© 2021 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)