The emergence of a pandemic affecting the respiratory system can result in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19. However, there is limited knowledge available on the performance of various commonly available fabrics used in cloth masks. Importantly, there is a need to evaluate filtration efficiencies as a function of aerosol particulate sizes in the 10 nm to 10 μm range, which is particularly relevant for respiratory virus transmission. We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations. Although the filtration efficiencies for various fabrics when a single layer was used ranged from 5 to 80% and 5 to 95% for particle sizes of <300 nm and >300 nm, respectively, the efficiencies improved when multiple layers were used and when using a specific combination of different fabrics. Filtration efficiencies of the hybrids (such as cotton−silk, cotton−chiffon, cotton−flannel) was >80% (for particles <300 nm) and >90% (for particles >300 nm). We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration. Cotton, the most widely used material for cloth masks performs better at higher weave densities (i.e., thread count) and can make a significant difference in filtration efficiencies. Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60% decrease in the filtration efficiency, implying the need for future cloth mask design studies to take into account issues of "fit" and leakage, while allowing the exhaled air to vent efficiently. Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.

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This work describes the fabrication of numerous hydrogel microstructures (μ-gels) via a process called "surface molding." Chemically patterned elastomeric-assembly substrates were used to organize and manipulate the geometry of liquid prepolymer microdroplets, which, following photo-initiated crosslinking, maintained the desired morphology. By adjusting the state of strain during the crosslinking process, a continua of structures could be created using one pattern. These arrays of μ-gels have stimuli-responsive properties that are directly applicable to actuation where the basis shape and array geometry of the μ-gels can be used to rationally generate microactuators with programmed motions. As a method, "surface molding," represents a powerful addition to the soft-lithographic toolset that can be readily applied to the simultaneous synthesis of large numbers of geometrically and functionally distinct polymeric microstructures.

Advanced manufacturing strategies have enabled large-scale, economical, and efficient production of electronic components that are an integral part of various consumer products ranging from simple toys to intricate computing systems; however, the circuitry for these components is (by and large) produced via top-down lithography and is thus limited to planar surfaces. The present work demonstrates the use of reconfigurable soft microreactors for the patterned deposition of conductive copper traces on flat and embossed two-dimensional (2D) substrates as well as nonplanar substrates made from different commodity plastics. Using localized, flow-assisted, low-temperature, electroless copper deposition, conductive metallic traces are fabricated, which, when combined with various off-the-shelf electronic components, enabled the production of simple circuits and antennas with unique form factors. This solution-phase approach to the patterned deposition of functional inorganic materials selectively on different polymeric components will provide relatively simple, inexpensive processing opportunities for the fabrication of 2D/nonplanar devices when compared to complicated manufacturing methods such as laser-directed structuring. Further, this approach to the patterned metallization of different commodity plastics offers unique design opportunities applicable to the fabrication of planar and nonplanar electronic and interconnect devices, and other free-form electronics with less structural "bloat" and weight (by directly coating support elements with circuitry).