Engineering 3D functional tissue constructs using self-assembling cell-laden microniches.

Tissue engineering using traditional size fixed scaffolds and injectable biomaterials are faced with many limitations due to the difficulties of producing macroscopic functional tissues. In this study, 3D functional tissue constructs were developed by inducing self-assembly of microniches, which were cell-laden gelatin microcryogels. During self-assembly, the accumulation of extracellular matrix (ECM) components was found to strengthen cell-cell and cell-ECM interactions, leading to the construction of a 'native' microenvironment that better preserved cell viability and functions. MSCs grown in self-assembled constructs showed increased maintenance of stemness, reduced senescence and improved paracrine activity compared with cells grown in individual microniches without self-assembly. As an example of applying the self-assembled constructs in tissue regeneration, the constructs were used to induce in vivo articular cartilage repair and successfully regenerated hyaline-like cartilage tissue in the absence of other extrinsic factors. This unique approach of developing self-assembled 3D functional constructs holds great promise for the generation of tissue engineered organoids and repair of challenging tissue defects. STATEMENT OF SIGNIFICANCE: We developed 3D functional tissue constructs using a unique gelatin-based microscopic hydrogel (microcryogels). Mesenchymal stem cells (MSCs) were loaded into gelatin microcryogels to form microscopic cell-laden units (microniches), which were induced to undergo self-assembly using a specially designed 3D printed frame. Extracellular matrix accumulation among the microniches resulted in self-assembled macroscopic constructs with superior ability to maintain the phenotypic characteristics and stemness of MSCs, together with the suppression of senescence and enhanced paracrine function. As an example of application in tissue regeneration, the self-assembled constructs were shown to successfully repair articular cartilage defects without any other supplements. This unique strategy for developing 3D functional tissue constructs allows the optimisation of stem cell functions and construction of biomimetic tissue organoids.