Cell-Laden Particulate-Composite Hydrogels with Tunable Mechanical Properties Constructed with Gradient-Interface Hydrogel Particles

Hydrogels have long been studied as cell encapsulants for engineered tissue, yet diffusive limitations, suboptimal mechanical properties, and poor cell distribution limit the use of single-phase hydrogels for complex tissues scaffolds. Here, a composite hydrogel structure is presented to overcome these limitations. It is shown that oxygen inhibition during chain-growth photopolymerization of microgel particles can be used to directly manipulate the interfacial bond strength between two hydrogel interfaces in the particulate-composite hydrogels. Using this principle, a cell-laden particulate-composite hydrogel is fabricated that overcomes the low cell viability of a single-phase hydrogel, while allowing the stiffness to be arbitrarily tuned

One Step Encapsulation of Mesenchymal Stromal Cells in PEG Norbornene Microgels for Therapeutic Actions

Cell therapies require control over the cellular response under standardized conditions to ensure continuous delivery of therapeutic agents. Cell encapsulation in biomaterials can be particularly effective at providing cells with a uniformly supportive and permissive cell microenvironment. In this study, two microfluidic droplet device designs were used to successfully encapsulate equine mesenchymal stromal cells (MSCs) into photopolymerized polyethylene glycol norbornene (PEGNB) microscale (∼100–200 μm) hydrogel particles (microgels) in a single on-chip step. To overcome the slow cross-linking kinetics of thiol–ene reactions, long dithiol linkers were used in combination with a polymerization chamber customized to achieve precise retention time for microgels while maintaining cytocompatibility. Thus, homogeneous cell-laden microgels could be continuously fabricated in a high-throughput fashion. Varying linker length mediated both the gel formation rate and material physical properties (stiffness, mass transport, and mesh size) of fabricated microgels. Postencapsulation cell viability and therapeutic indicators of MSCs were evaluated over 14 days, during which the viability remained at least 90%. Gene expression of selected cytokines was not adversely affected by microencapsulation compared to monolayer MSCs. Notably, PEGNB-3.5k microgels rendered significant elevation in FGF-2 and TGF-β on the transcription level, and conditioned media collected from these cultures showed robust promotion in the migration and proliferation of fibroblasts. Collectively, standardized MSC on-chip encapsulation will lead to informed and precise translation to clinical studies, ultimately advancing a variety of tissue engineering and regenerative medicine practices

One Step Encapsulation of Mesenchymal Stromal Cells in PEG Norbornene Microgels for Therapeutic Actions

Cell therapies require control over the cellular response under standardized conditions to ensure continuous delivery of therapeutic agents. Cell encapsulation in biomaterials can be particularly effective at providing cells with a uniformly supportive and permissive cell microenvironment. In this study, two microfluidic droplet device designs were used to successfully encapsulate equine mesenchymal stromal cells (MSCs) into photopolymerized polyethylene glycol norbornene (PEGNB) microscale (∼100–200 μm) hydrogel particles (microgels) in a single on-chip step. To overcome the slow cross-linking kinetics of thiol–ene reactions, long dithiol linkers were used in combination with a polymerization chamber customized to achieve precise retention time for microgels while maintaining cytocompatibility. Thus, homogeneous cell-laden microgels could be continuously fabricated in a high-throughput fashion. Varying linker length mediated both the gel formation rate and material physical properties (stiffness, mass transport, and mesh size) of fabricated microgels. Postencapsulation cell viability and therapeutic indicators of MSCs were evaluated over 14 days, during which the viability remained at least 90%. Gene expression of selected cytokines was not adversely affected by microencapsulation compared to monolayer MSCs. Notably, PEGNB-3.5k microgels rendered significant elevation in FGF-2 and TGF-β on the transcription level, and conditioned media collected from these cultures showed robust promotion in the migration and proliferation of fibroblasts. Collectively, standardized MSC on-chip encapsulation will lead to informed and precise translation to clinical studies, ultimately advancing a variety of tissue engineering and regenerative medicine practices