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Fiber-based materials provide critical capabilities for biomedical applications. Microfluidic fiber fabrication has recently emerged as a very promising route to the synthesis of polymeric fibers at the micro and nanoscale, providing fine control over fiber shape, size, chemical anisotropy, and biological activity. This Progress Report summarizes advanced microfluidic methods for the fabrication of both microscale and nanoscale fibers and illustrates how different methods are enabling new biomedical applications. Microfluidic fabrication methods and resultant materials are explained from the perspective of their microfluidic device principles, including co-flow, cross-flow, and flow-shaping designs. It is then detailed how the microchannel design and flow parameters influence the variety of synthesis chemistries that can be utilized. Finally, the integration of biomaterials and microfluidic strategies is discussed to manufacture unique fiber-based systems, including cell scaffolds, cell encapsulation, and woven tissue matrices.

All bacteria shed outer membrane vesicles (OMVs) loaded with a diverse array of small molecules, proteins, and genetic cargo. In this study we sought to hijack the bacterial cell export pathway to simultaneously produce, package, and release an active enzyme, phosphotriesterase (PTE). To accomplish this goal the SpyCatcher/SpyTag (SC/ST) bioconjugation system was utilized to produce a PTE-SpyCatcher (PTE-SC) fusion protein and a SpyTagged transmembrane porin protein (OmpA-ST), known to be abundant in OMVs. Under a range of physiological conditions the SpyTag and SpyCatcher domains interact with one another and form a covalent isopeptide bond driving packaging of PTE into forming OMVs. The PTE-SC loaded OMVs are characterized for size distribution, number of vesicles produced, cell viability, packaged PTE enzyme kinetics, OMV loading efficiency, and enzyme stability following iterative cycles of freezing and thawing. The PTE-loaded OMVs exhibit native-like enzyme kinetics when assayed with paraoxon as a substrate. PTE is often toxic to expression cultures and has a tendency to lose activity with improper handling. The coexpression of OmpA-ST with PTE-SC, however, greatly improved the overall PTE production levels by mitigating toxicity through exporting of the PTE-SC and greatly enhanced packaged enzyme stability against iterative cycles of freezing and thawing.

Solid state gas sensors are a core enabling technology to a range of measurement applications including industrial, safety, and environmental monitoring. The technology associated with solid-state gas sensors has evolved in recent years with advances in materials, and improvements in processing and miniaturization. In this review, we examine the state-of-the-art of solid state gas sensors with the goal of understanding the core technology and approaches, various sensor design methods to provide targeted functionality, and future prospects in the field. The structure, detection mechanism, and sensing properties of several types of solid state gas sensors will be discussed. In particular, electrochemical cells (solid and liquid), impedance/resistance based sensors (metal oxide, polymer, and carbon based structures), and mechanical sensing structures (resonators, cantilevers, and acoustic wave devices) as well as sensor arrays and supporting technologies, are described. Development areas for this field includes increased control of material properties for improved sensor response and durability, increased integration and miniaturization, and new material systems, including nano-materials and nano-structures, to address shortcomings of existing solid state gas sensors.

Platinum nanourchins supported on microfibrilated cellulose films (MFC) were fabricated and evaluated as hydrogen peroxide catalysts for small-scale, autonomous underwater vehicle (AUV) propulsion systems. The catalytic substrate was synthesized through the reduction of chloroplatinic acid to create a thick film of Pt coral-like microstructures coated with Pt urchin-like nanowires that are arrayed in three dimensions on a twodimensional MFC film. This organic/inorganic nanohybrid displays high catalytic ability (reduced activation energy of 50-63% over conventional materials and 13-19% for similar Pt nanoparticle-based structures) during hydrogen peroxide (H2O2) decomposition as well as sufficient propulsive thrust (>0.5 N) from reagent grade H2O2 (30% w/w) fuel within a small underwater reaction vessel. The results demonstrate that these layered nanohybrid sheets are robust and catalytically effective for green, H2O2-based micro-AUV propulsion where the storage and handling of highly explosive, toxic fuels are prohibitive due to sizerequirements, cost limitations, and close person-to-machine contact. ABSTRACT: Platinum nanourchins supported on microfibrilated cellulose films (MFC) were fabricated and evaluated as hydrogen peroxide catalysts for small-scale, autonomous underwater vehicle (AUV) propulsion systems. The catalytic substrate was synthesized through the reduction of chloroplatinic acid to create a thick film of Pt coral-like microstructures coated with Pt urchin-like nanowires that are arrayed in three dimensions on a two-dimensional MFC film. This organic/inorganic nanohybrid displays high catalytic ability (reduced activation energy of 50−63% over conventional materials and 13−19% for similar Pt nanoparticle-based structures) during hydrogen peroxide (H 2 O 2 ) decomposition as well as sufficient propulsive thrust (>0.5 N) from reagent grade H 2 O 2 (30% w/w) fuel within a small underwater reaction vessel. The results demonstrate that these layered nanohybrid sheets are robust and catalytically effective for green, H 2 O 2 -based micro-AUV propulsion where the storage and handling of highly explosive, toxic fuels are prohibitive due to size-requirements, cost limitations, and close person-to-machine contact.

Background & AimsCrohn’s disease is an inflammatory bowel disease that affects the ileum and is associated with increased cytokines. Although interleukin (IL)6, IL17, IL21, and IL22 are increased in Crohn’s disease and are associated with disrupted epithelial regeneration, little is known about their effects on the intestinal stem cells (ISCs) that mediate tissue repair. We hypothesized that ILs may target ISCs and reduce ISC-driven epithelial renewal.MethodsA screen of IL6, IL17, IL21, or IL22 was performed on ileal mouse organoids. Computational modeling was used to predict microenvironment cytokine concentrations. Organoid size, survival, proliferation, and differentiation were characterized by morphometrics, quantitative reverse-transcription polymerase chain reaction, and immunostaining on whole organoids or isolated ISCs. ISC function was assayed using serial passaging to single cells followed by organoid quantification. Single-cell RNA sequencing was used to assess Il22ra1 expression patterns in ISCs and transit-amplifying (TA) progenitors. An IL22-transgenic mouse was used to confirm the impact of increased IL22 on proliferative cells in vivo.ResultsHigh IL22 levels caused decreased ileal organoid survival, however, resistant organoids grew larger and showed increased proliferation over controls. Il22ra1 was expressed on only a subset of ISCs and TA progenitors. IL22-treated ISCs did not show appreciable differentiation defects, but ISC biomarker expression and self-renewal–associated pathway activity was reduced and accompanied by an inhibition of ISC expansion. In vivo, chronically increased IL22 levels, similar to predicted microenvironment levels, showed increases in proliferative cells in the TA zone with no increase in ISCs.ConclusionsIncreased IL22 limits ISC expansion in favor of increased TA progenitor cell expansion.

Synthetically modified proteins, such as gelatin methacryloyl (GelMA), are growing in popularity for bioprinting and biofabrication. GelMA is a photocurable macromer that can rapidly form hydrogels, while also presenting bioactive peptide sequences for cellular adhesion and proliferation. The mechanical properties of GelMA are highly tunable by modifying the degree of substitution via synthesis conditions, though the effects of source material and thermal gelation have not been comprehensively characterized for lower concentration gels. Herein, the effects of animal source and processing sequence are investigated on scaffold mechanical properties. Hydrogels of 4–6 wt% are characterized. Depending on the temperature at crosslinking, the storage moduli for GelMA derived from pigs, cows, and cold‐water fish range from 723 to 7340 Pa, 516 to 3484 Pa, and 294 to 464 Pa, respectively. The maximum storage moduli are achieved only by coordinated physical gelation and chemical crosslinking. In this method, the classic thermo‐reversible gelation of gelatin occurs when GelMA is cooled below a thermal transition temperature, which is subsequently “locked in” by chemical crosslinking via photocuring. The effects of coordinated physical gelation and chemical crosslinking are demonstrated by precise photopatterning of cell‐laden microstructures, inducing different cellular behavior depending on the selected mechanical properties of GelMA.

Cell encapsulation is critical for many biotechnology applications including environmental remediation, bioreactors, and regenerative medicine. Here, the development of biohybrid microfibers comprised of encapsulated bacteria in hydrogel matrices produced on‐chip using microfluidics is reported. The fiber production process utilizes hydrodynamic shaping of a cell‐laden core fluid by a miscible sheath fluid. Production of the fibers containing viable bacteria was continuous in contrast to the more typical methods in which cells infiltrated or were attached to prepared fibers. The biohybrid fibers were composed of poly (ethylene glycol dimethacrylate) matrices and individually both E. coli and B. cereus were explored as model cellular payloads. Post processing growth curves (24 h) of bacteria within fibers were in excellent agreement with that of controls suggesting minimal impact. Finally, the biohybrid fibers showed even distribution of encapsulated cells and >90% cell viability.