Biomolecule immobilization has attracted the attention of various fields such as fine chemistry and biomedicine for their use in several applications such as wastewater, immunosensors, biofuels, et cetera. The performance of immobilized biomolecules depends on the substrate and the immobilization method utilized. Electrospun nanofibers act as an excellent substrate for immobilization due to their large surface area to volume ratio and interconnectivity. While biomolecules can be immobilized using adsorption and encapsulation, covalent immobilization offers a way to permanently fix the material to the fiber surface resulting in high efficiency, good specificity, and excellent stability. This review aims to highlight the various covalent immobilization techniques being utilized and their benefits and drawbacks. These methods typically fall into two categories: (1) direct immobilization and (2) use of crosslinkers. Direct immobilization techniques are usually simple and utilize the strong electrophilic functional groups on the nanofiber. While crosslinkers are used as an intermediary between the nanofiber substrate and the biomolecule, with some crosslinkers being present in the final product and others simply facilitating the reactions. We aim to provide an explanation of each immobilization technique, biomolecules commonly paired with said technique and the benefit of immobilization over the free biomolecule.

As potential high surface area for selective capture in diagnostic or filtration devices, biotin-cellulose nanofiber membranes were fabricated to demonstrate the potential for specific and bio-orthogonal attachment of biomolecules onto nanofiber surfaces. Cellulose acetate was electrospun and substituted with alkyne groups in either a one- or two-step process. The alkyne reaction, confirmed by FTIR and Raman spectroscopy, was dependent on solvent ratio, time, and temperature. The two-step process maximized alkyne substitution in 10/90 volume per volume ratio (v/v) water to isopropanol at 50 °C after 6 h compared to the one-step process in 80/20 (v/v) at 50 °C after 48 h. Azide-biotin conjugate “clicked” with the alkyne-cellulose via copper-catalyzed alkyne-azide cycloaddition (CuAAC). The biotin-cellulose membranes, characterized by FTIR, SEM, Energy Dispersive X-ray spectroscopy (EDX), and XPS, were used in proof-of-concept assays (HABA (4′-hydroxyazobenzene-2-carboxylic acid) colorimetric assay and fluorescently tagged streptavidin assay) where streptavidin selectively bound to the pendant biotin. The click reaction was specific to alkyne-azide coupling and dependent on pH, ratio of ascorbic acid to copper sulfate, and time. Copper (II) reduction to copper (I) was successful without ascorbic acid, increasing the viability of the click conjugation with biomolecules. The surface-available biotin was dependent on storage medium and time: Decreasing with immersion in water and increasing with storage in air.

Commercially available children’s cloth masks range widely in material type and fabric structures, methods of construction, layering, and shape, and there is a lack of sizing systems, anthropometric data or guidelines specifically targeting the fit assessment and design of cloth face masks for children 4-6 years old. To better identify and understand the cloth face mask fit and functional needs of children ages 4-6 years old, the researchers embarked on interdisciplinary in-depth study to investigate commercial market offerings of children’s face masks, identify consumer perspectives, and explore mask design improvements through design research. By triangulating results from survey feedback, commercial market content analysis, and wear trial observations, the researchers were able to identify important design criteria that can be used in the improvement of children’s cloth face mask design: size, comfort, dexterity, movement, and thermal comfort. These criteria were used to iteratively develop new mask prototypes involving a 3D printed head form, traditional sewing and hand patternmaking skills, and the creation of multiple mask versions to explore the design criteria listed above. The designs were interpreted through Bye’s (2010) Problem-Based Design Research (PBDR) framework, which identifies common design research practices in the field on a spectrum and situates PBDR as a process centered on a problem as impetus for design through which artifacts are developed.

Various textiles have previously been evaluated for use in cloth face masks as a reusable option to help control the spread of respiratory viruses, but only their initial performance was tested. In this study, a broad range of fabrics (3 knit, 7 woven, and 3 nonwoven) were characterized for filtration efficiency (FE) and air permeability (AP) before and after 40 decontamination cycles by home laundry, microwave-generated steam, or dishwasher sterilization. AP was quantified following ASTM D737, and FE was assessed using NaCl aerosol in a simulated breathing system. While most fabrics maintained or improved their FE after 40 decontamination cycles, the AP of many fabrics decreased due to detergent buildup, fiber breakage, and fabric shrinkage. Tightly woven cotton fabrics had unacceptably low AP and FE performance. Knit and nonwoven structures had the best balance of properties, and although they are not recommended for use in single-layer masks, they have potential use in multilayer masks.

The second component of this three-paper series studying cloth face masks for children ages 4 to 6 years old concentrates on optimizing aerosol capture and air permeability through fabric selection. Material choices were evaluated in two modes: Flat Filter (FF) and Head Form (HF). FF isolates material factors while HF simulates the performance of the constructed masks on a 3D printed child head form. In FF mode, higher filtration efficiency correlated to lower air permeability in both reusable commercial and experimental face masks regardless of fiber contents, fabric structures, and number of layers. Our prototype face mask developed in design exploration successfully captured 37 ± 12% of 0.3 μm, 87 ± 3% of 0.5 μm, and 87 ± 2% of 1.0 μm particles while maintaining good air permeability, moisture capture, and aerosolized salt capture in HF mode. Sealing masks to minimize outward leakage reduced particle capture up to 64%. Particle leakage data captured at the eye level of the head form illuminated the synergy between mask design, material choice, and fit.

IRB exemption approval. Of the three participants, the 6-year-old boy Size 7 and a head form in size 8R (based on ASTM D6458-12) 3D printed from the scan of a sixyear-old boy from Size North America dataset were included in the fit analysis. The selection of the scan was based on 3D-printability of the ears in consideration of all the head anthropometry data in a normative band. The two heads were scanned with a Structure sensor, capturing their faces with and without wearing the eight purchased commercial face masks. Visual fit analyses then conducted by two researcher expert-judges evaluated set and ease using a 5-point Likerttype rating scale (1=too tight, 3=good fit, 5=too loose). Face masks patterns were traced and imported to Adobe Illustrator and ImageJ to illustrate the nested patterns and obtain their surface area. Chi-square non-parametric test were used for statistical analysis with JMP Pro 15.0.0 software. Fabric performance for breathability and FE was evaluated on deconstructed mask samples. Multilayer samples were assembled in the sequence of the original mask. Air permeability was measured following ASTM D737-18. A simulated breathing apparatus consisting of a large animal respirator, aerosol generator, filter holder, and multi-channel particle counter was employed to assess the exhaled aerosol capture of 0.3 μm, 0.5 μm, and 1.0 μm sized particles by the various flat fabric samples. Samples were weighed by their individual layers before testing, directly after testing (wet), and 24 hours after testing (dry). Wet Pickup was calculated as a ratio of the difference between the wet and dry weights and the initial weight. Results, Discussion, and ConclusionResults of this study indicate issues with the fit, filtration, size, wear, and comfort of masks for children ages 4-6 including poor overall fit leading to slippage from proper positioning and fogging of glasses, thermal and ear discomfort, and difficulty with donning/doffing. From the market research and Qualtrics survey, the most common mask attributes were a shaped style, stretch ear loops, two layers of woven cotton, and an all-over surface print. Masks with a fitted shape around the nose, mouth and under chin coverage were most preferred, and those with highest coverage area were found to provide better fit based on results from the structured set and ease analysis of scanned heads. Evaluation of FE and air permeability showed a weak correlation between aerosol capture and breathability. No significant difference in wet pickup was measured between masks made of hydrophobic materials and masks made of hydrophilic materials, except for the 3-layered tightly woven cotton poplin mask. A balance between breathability and FE is impacted by the types of mask materials and number of layers, including moisture retention against the wearer's face, overall thermal comfort, and protection. Concerns of poor fit, comfort, and breathability among commercially available children's face masks are consistently indicated by these collective results. For the fit a...

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