3 research outputs found
Oxygen-Purged Microfluidic Device to Enhance Cell Viability in Photopolymerized PEG Hydrogel Microparticles
Encapsulating
cells within biocompatible materials is a widely
used strategy for cell delivery and tissue engineering. While cells
are commonly suspended within bulk hydrogel-forming solutions during
gelation, substantial interest in the microfluidic fabrication of
miniaturized cell encapsulation vehicles has more recently emerged.
Here, we utilize multiphase microfluidics to encapsulate cells within
photopolymerized picoliter-volume water-in-oil droplets at high production
rates. The photoinitiated polymerization of polyethylene glycol diacrylate
(PEGDA) is used to continuously produce solid particles from aqueous
liquid drops containing cells and hydrogel forming solution. It is
well understood that this photoinitiated addition reaction is inhibited
by oxygen. In contrast to bulk polymerization in which ambient oxygen
is rapidly and harmlessly consumed, allowing the polymerization reaction
to proceed, photopolymerization within air permeable polydimethylsiloxane
(PDMS) microfluidic devices allows oxygen to be replenished by diffusion
as it is depleted. This sustained presence of oxygen and the consequential
accumulation of peroxy radicals produce a dramatic effect upon both
droplet polymerization and post-encapsulation cell viability. In this
work we employ a nitrogen microjacketed microfluidic device to purge
oxygen from flowing fluids during photopolymerization. By increasing
the purging nitrogen pressure, oxygen concentration was attenuated,
and increased post-encapsulation cell viability was achieved. A reaction-diffusion
model was used to predict the cumulative intradroplet concentration
of peroxy radicals, which corresponded directly to post-encapsulation
cell viability. The nitrogen-jacketed microfluidic device presented
here allows the droplet oxygen concentration to be finely tuned during
cell encapsulation, leading to high post-encapsulation cell viability
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