Cells communicate with each other through secreting and releasing proteins and vesicles. Many cells can migrate. In this study, we report the discovery of migracytosis, a cell migration-dependent mechanism for releasing cellular contents, and migrasomes, the vesicular structures that mediate migracytosis. As migrating cells move, they leave long tubular strands, called retraction fibers, behind them. Large vesicles, which contain numerous smaller vesicles, grow on the tips and intersections of retraction fibers. These fibers, which connect the vesicles with the main cell body, eventually break, and the vesicles are released into the extracellular space or directly taken up by surrounding cells. Since the formation of these vesicles is migration-dependent, we named them “migrasomes”. We also found that cytosolic contents can be transported into migrasomes and released from the cell through migrasomes. We named this migration-dependent release mechanism “migracytosis”.

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Using DNA as programmable, sequence specific ‘glues’, shape-controlled hydrogel units are self-assembled into prescribed structures. Here we report that aggregates are produced using hydrogel cubes with edge length ranging from 30 micrometers to 1 millimeter, demonstrating assembly across scales. In a simple one-pot agitation reaction, 25 dimers are constructed in parallel from 50 distinct hydrogel cube species, demonstrating highly multiplexed assembly. Using hydrogel cuboids displaying face-specific DNA glues, diverse structures are achieved in aqueous and in interfacial agitation systems. These include dimers, extended chains, and open network structures in an aqueous system; and dimers, chains of fixed length, T-junctions, and square shapes in the interfacial system, demonstrating the versatility of the assembly system.

Microscale technologies, such as microfluidic systems, provide powerful tools for building biomimetic vascular-like structures for tissue engineering or in vitro tissue models. Recently, modular approaches have emerged as attractive approaches in tissue engineering to achieve precisely controlled architectures by using microengineered components. Here, we sequentially assembled microengineered hydrogels (microgels) into hydrogel constructs with an embedded network of microchannels. Arrays of microgels with predefined internal microchannels were fabricated by photolithography and assembled into 3D tubular construct with multi-level interconnected lumens. In the current setting, the sequential assembly of microgels occurred in a biphasic reactor and was initiated by swiping a needle to generate physical forces and fluidic shear. We optimized the conditions for assembly and successfully perfused fluids through the interconnected constructs. The sequential assembly process does not significantly influence cell viability within the microgels indicating its promise as a biofabrication method. Finally, in an attempt to build a biomimetic 3D vasculature, we incorporated endothelial cells and smooth muscle cells into an assembled construct with a concentric microgel design. The sequential assembly is simple, rapid, cost-effective and could be used for fabricating tissue constructs with biomimetic vasculature and other complex architectures.

The promise of cell therapy for repair and restoration of damaged tissues or organs relies on administration of large dose of cells whose healing benefits are still limited and sometimes irreproducible due to uncontrollable cell loss and death at lesion sites. Using a large amount of therapeutic cells increases the costs for cell processing and the risks of side effects. Optimal cell delivery strategies are therefore in urgent need to enhance the specificity, efficacy, and reproducibility of cell therapy leading to minimized cell dosage and side effects. Here, we addressed this unmet need by developing injectable 3D microscale cellular niches (microniches) based on biodegradable gelatin microcryogels (GMs). The microniches are constituted by in vitro priming human adipose-derived mesenchymal stem cells (hMSCs) seeded within GMs resulting in tissue-like ensembles with enriched extracellular matrices and enhanced cell-cell interactions. The primed 3D microniches facilitated cell protection from mechanical insults during injection and in vivo cell retention, survival, and ultimate therapeutic functions in treatment of critical limb ischemia (CLI) in mouse models compared with free cell-based therapy. In particular, 3D microniche-based therapy with 10 5 hMSCs realized better ischemic limb salvage than treatment with 10 6 freeinjected hMSCs, the minimum dosage with therapeutic effects for treating CLI in literature. To the best of our knowledge, this is the first convincing demonstration of injectable and primed cell delivery strategy realizing superior therapeutic efficacy for treating CLI with the lowest cell dosage in mouse models. This study offers a widely applicable cell delivery platform technology to boost the healing power of cell regenerative therapy.C ell-based regenerative therapy holds great promise for repair and restoration of damaged tissues or organs with numerous clinical trials and preclinical animal testing reported for treating complex diseases (1). Common route of cell administration for clinical cell therapy is based on either systematic administration (e.g., i.v. infusion), relying on cells homing to the lesion sites (2), or direct injection of cells into the damaged tissues (3). However, therapeutic benefits of the administered cells are still limited and sometimes irreproducible due to cell loss and cell death (4). Taking cell therapy for ischemic heart diseases as an example, only ∼5% of mesenchymal stem cells (MSCs) survived after being transplanted into an infarcted porcine heart (5). Mechanical damage during injection, high rate of cell loss and leakage to surrounding tissues, cell death due to lack of appropriate cell-cell and cell-matrix interactions in the ischemic and inflammatory lesion tissues could all contribute to poor cell retention, survival, functionality, and reproducibility of the treatment (6, 7).A rational solution to enhance the therapeutic efficacy and reproducibility of cell therapy is to administer a large dose of cells to ensure sufficient number of functional cells ...

The role of pathological angiogenesis on liver fibrogenesis is still unknown. Here, we developed fibrotic microniches (FμNs) that recapitulate the interaction of liver sinusoid endothelial cells (LSECs) and hepatic stellate cells (HSCs). We investigated how the mechanical properties of their substrates affect the formation of capillary-like structures and how they relate to the progression of angiogenesis during liver fibrosis. Differences in cell response in the FμNs were synonymous of the early and late stages of liver fibrosis. The stiffness of the early-stage FμNs was significantly elevated due to condensation of collagen fibrils induced by angiogenesis, and led to activation of HSCs by LSECs. We utilized these FμNs to understand the response to anti-angiogenic drugs, and it was evident that these drugs were effective only for early-stage liver fibrosis in vitro and in an in vivo mouse model of liver fibrosis. Late-stage liver fibrosis was not reversed following treatment with anti-angiogenic drugs but rather with inhibitors of collagen condensation. Our work reveals stage-specific angiogenesis-induced liver fibrogenesis via a previously unrevealed mechanotransduction mechanism which may offer precise intervention strategies targeting stage-specific disease progression.

Despite the wide applications, systematic mechanobiological investigation of 3D porous scaffolds has yet to be performed due to the lack of methodologies for decoupling the complex interplay between structural and mechanical properties. Here, we discover the regulatory effect of cryoprotectants on ice crystal growth and use this property to realize separate control of the scaffold pore size and stiffness. Fibroblasts and macrophages are sensitive to both structural and mechanical properties of the gelatin scaffolds, particularly to pore sizes. Interestingly, macrophages within smaller and softer pores exhibit pro-inflammatory phenotype, whereas anti-inflammatory phenotype is induced by larger and stiffer pores. The structure-regulated cellular mechano-responsiveness is attributed to the physical confinement caused by pores or osmotic pressure. Finally, in vivo stimulation of endogenous fibroblasts and macrophages by implanted scaffolds produce mechano-responses similar to the corresponding cells in vitro, indicating that the physical properties of scaffolds can be leveraged to modulate tissue regeneration.

Tissue engineered conduits have great promise for bridging peripheral nerve defects by providing physical guiding and biological cues. A flexible method for integrating support cells into a conduit with desired architectures is wanted. Here, a 3D-printing technology is adopted to prepare a bio-conduit with designer structures for peripheral nerve regeneration. This bio-conduit is consisted of a cryopolymerized gelatin methacryloyl (cryoGelMA) gel cellularized with adipose-derived stem cells (ASCs). By modeling using 3D-printed “lock and key” moulds, the cryoGelMA gel is structured into conduits with different geometries, such as the designed multichannel or bifurcating and the personalized structures. The cryoGelMA conduit is degradable and could be completely degraded in 2-4 months in vivo. The cryoGelMA scaffold supports the attachment, proliferation and survival of the seeded ASCs, and up-regulates the expression of their neurotrophic factors mRNA in vitro. After implanted in a rat model, the bio-conduit is capable of supporting the re-innervation across a 10 mm sciatic nerve gap, with results close to that of the autografts in terms of functional and histological assessments. The study describes an indirect 3D-printing technology for fabricating cellularized designer conduits for peripheral nerve regeneration, and could lead to the development of future nerve bio-conduits for clinical use.