Long-Term Insect Repellent Electrospun Microfibers from Recycled Poly(ethylene terephthalate).

In recent years, there has been an increase in the incidence of insect-borne diseases. Topically applied insect repellents are used to prevent these infectious diseases, but concerns of skin permeability and rapid evaporation rates have made way for alternative preventative methods. Encapsulation of insect repellents in polymeric materials allows for nonskin contact methods of repellent delivery with extended-release profiles without the need for reapplication. Poly(ethylene terephthalate) (PET) is widely used in textiles as well as food packaging and other single-use applications. This short product lifespan makes PET a major environmental pollutant; thus, recycling of PET is of great interest and utility. We report on the fabrication and evaluation of recycled PET microfibers containing N,N-diethyl-meta-toluamide (DEET) and picaridin and the first evaluation of dual repellent loading (DEET/picaridin) via electrospinning. The electrospun microfibers displayed a repellent retention up to 97% within the polymer network upon processing. Release profiles were characterized by isothermal thermogravimetric analysis (TGA). Hansen solubility parameters correlated release profiles with the chemical affinity between PET and the repellent substrate. Insect repellency was assessed against live mosquitoes using a novel bioassay method. Repellency was observed to be as high as 100% for over 1 week and 80% for over 3 weeks. Our method allows for long-lasting repellency with the potential for large-scale textile manufacturing.

Extremophilic behavior of catalytic amyloids sustained by backbone structuring.

Enzyme function relies on the placement of chemistry defined by solvent and self-associative hydrogen bonding displayed by the protein backbone. Amyloids, long-range multi-peptide and -protein materials, can mimic enzyme functions while having a high proportion of stable self-associative backbone hydrogen bonds. Though catalytic amyloid structures have exhibited a degree of temperature and solvent stability, defining their full extremophilic properties and the molecular basis for such extreme activity has yet to be realized. Here we demonstrate that, like thermophilic enzymes, catalytic amyloid activity persists across high temperatures with an optimum activity at 81 °C where they are 30-fold more active than at room temperature. Unlike thermophilic enzymes, catalytic amyloids retain both activity and structure well above 100 °C as well as in the presence of co-solvents. Changes in backbone vibrational states are resolved in situ using non-linear 2D infrared spectroscopy (2DIR) to reveal that activity is sustained by reorganized backbone hydrogen bonds in extreme environments, evidenced by an emergent vibrational mode centered at 1612 cm-1. Restructuring also occurs in organic solvents, and facilitates complete retention of hydrolysis activity in co-solvents of lesser polarity. We support these findings with molecular modeling, where the displacement of water by co-solvents leads to shorter, less competitive, bonding lifetimes that further stabilize self-associative backbone interactions. Our work defines amyloid properties that counter classical proteins, where extreme environments induce mechanisms of restructuring to support enzyme-like functions necessary for synthetic applications.

Predicting bilgewater emulsion stability by oil separation using image processing and machine learning.

Bilgewater is a shipboard multi-component oily wastewater, combining numerous wastewater sources. A better understanding of bilgewater emulsions is required for proper wastewater management to meet discharge regulations. In this study, we developed 360 emulsion samples based on commonly used Navy cleaner data and previous bilgewater composition studies. Oil value (OV) was obtained from image analysis of oil/creaming layer and validated by oil separation (OS) which was experimentally determined using a gravimetric method. OV (%) showed good agreement with OS (%), indicating that a simple image-based parameter can be used for emulsion stability prediction model development. An ANOVA analysis was conducted of the five variables (Cleaner, Salinity, Suspended Solids [SS], pH, and Temperature) that significantly impacted estimates of OV, finding that the Cleaner, Salinity, and SS variables were statistically significant (p < 0.05), while pH and Temperature were not. In general, most cleaners showed improved oil separation with salt additions. Novel machine learning (ML)-based predictive models of both classification and regression for bilgewater emulsion stability were then developed using OV. For classification, the random forest (RF) classifiers achieved the most accurate prediction with F1-score of 0.8224, while in regression-based models the decision tree (DT) regressor showed the highest prediction of emulsion stability with the average mean absolute error (MAE) of 0.1611. Turbidity also showed a good emulsion prediction with RF regressor (MAE of 0.0559) and RF classifier (F1-score of 0.9338). One predictor variable removal test showed that Salinity, SS, and Temperature are the most impactful variables in the developed models. This is the first study to use image processing and machine learning for the prediction of oil separation for the application of bilgewater assessment within the marine sector.

Surfactant Modulated Phase Transitions of Liquid Crystals Confined in Electrospun Coaxial Fibers.

Confinement of liquid crystals (LCs) in polymeric fibers offers a promising strategy to control liquid crystal response to external stimuli. Here, the confinement of 4-cyano-4'-pentylbiphenyl (5CB), a nematic liquid crystal, within the core of coaxially electrospun fibers composed of poly(vinylpyrrolidone) (PVP) containing different surfactants is discussed. The effects of surfactant type, surfactant concentration, and core flow rate (confinement) on the LC behavior were demonstrated using polarized optical microscopy, scanning electron microscopy, differential scanning calorimetry, Raman, and dielectric spectroscopy. Introduction of surfactant dopants of varying hydrophilic and hydrophobic components into the sheath altered the interfacial interaction between the PVP sheath and the 5CB core of the fibers. Significant effects on the LC nematic to isotropic phase transition were attributed to changes in surface anchoring between the sheath and core. Confinement of nematic LCs in surfactant doped polymeric fibers demonstrates a facile method for tuning LC phase behavior.

Identification and characterization of bilgewater emulsions.

Literature on bilgewater focuses on empirically determined treatment methods and lacks specific information on emulsion characteristics. Therefore, this review discusses potential emulsion stabilization mechanisms that occur in bilgewater and evaluates common approaches to study their behavior. Current knowledge on emulsion formation, stabilization, and destabilization is outlined to provide researchers and bilgewater treatment operators with the knowledge needed to determine emulsion prevention and treatment strategies. Furthermore, a broad assessment of bilgewater emulsion characterization techniques, from general water quality analysis to advanced droplet stability characterization methods are discussed in detail. Lastly, a survey of typical bilgewater characteristics and information on standard synthetic bilgewater mixtures used in the testing of oil pollution abatement equipment are presented. Overall, the goal of this article is to provide a better understanding of physical and thermodynamic properties of emulsions to help improve bilgewater treatment and management.

Air Activated Self-Decontaminating Polydicyclopentadiene PolyHIPE Foams for Rapid Decontamination of Chemical Warfare Agents.

The threat of chemical warfare agents (CWA) compels research into novel self-decontaminating materials (SDM) for the continued safety of first-responders, civilians, and active service personnel. The capacity to actively detoxify, as opposed to merely sequester, offending agents under typical environmental conditions defines the added value of SDMs in comparison to traditional adsorptive materials. Porous polymers, synthesized via the high internal phase emulsion (HIPE) templating, provide a facile fabrication method for materials with permeable open cellular structures that may serve in air filtration applications. PolyHIPEs comprising polydicyclopentadiene (polyDCPD) networks form stable hydroperoxide species following activation in air under ambient conditions. The hydroperoxide-containing polyDCPD materials react quickly with CWA simulants, Demeton-S and 2-chloroethyl ethyl sulfide, forming oxidation products as confirmed via gas chromatography mass spectrometry. The simplicity of the detoxification chemistry paired with the porous foam form factor presents an exciting opportunity for the development of self-decontaminating filter media.

Hemostatic and Absorbent PolyHIPE-Kaolin Composites for 3D Printable Wound Dressing Materials.

A novel hemostatic and absorbent wound dressing material compatible with 3D printing is developed to address deficiencies in current wound dressing protocol. The design involves an open celled, microporous hydrogel foam via a high internal phase emulsion (HIPE) template with biocompatible components and tunable hemostatic character by kaolin loading, the viscosity and cure kinetics of which are tailored for 3D printing applications. The use of nontoxic mineral oil organic phase results in cytocompatability with human dermal fibroblasts. Kaolin distribution is shown by X-ray diffraction and elemental dispersive spectroscopy to be exfoliated and dispersed in the hydrogel dressing. In addition to demonstrating high fluid absorption and noncytotoxicity of relevant cell lines, the high internal phase emulsion polymers (polyHIPEs) also match the hemostatic performance of commercial wound dressing materials. Furthermore, the polyHIPEs display the requisite rheological properties for 3D printing that result in the fabrication of a prototype dressing with hierarchical porosity and a large number of controllable form factors.

Environmental Effects on Zirconium Hydroxide Nanoparticles and Chemical Warfare Agent Decomposition: Implications of Atmospheric Water and Carbon Dioxide.

Zirconium hydroxide (Zr(OH)4) has excellent sorption properties and wide-ranging reactivity toward numerous types of chemical warfare agents (CWAs) and toxic industrial chemicals. Under pristine laboratory conditions, the effectiveness of Zr(OH)4 has been attributed to a combination of diverse surface hydroxyl species and defects; however, atmospheric components (e.g., CO2, H2O, etc.) and trace contaminants can form adsorbates with potentially detrimental impact to the chemical reactivity of Zr(OH)4. Here, we report the hydrolysis of a CWA simulant, dimethyl methylphosphonate (DMMP) on Zr(OH)4 determined by gas chromatography-mass spectrometry and in situ attenuated total reflectance Fourier transform infrared spectroscopy under ambient conditions. DMMP dosing on Zr(OH)4 formed methyl methylphosphonate and methoxy degradation products on free bridging and terminal hydroxyl sites of Zr(OH)4 under all evaluated environmental conditions. CO2 dosing on Zr(OH)4 formed adsorbed (bi)carbonates and interfacial carbonate complexes with relative stability dependent on CO2 and H2O partial pressures. High concentrations of CO2 reduced DMMP decomposition kinetics by occupying Zr(OH)4 active sites with carbonaceous adsorbates. Elevated humidity promoted hydrolysis of adsorbed DMMP on Zr(OH)4 to produce methanol and regenerated free hydroxyl species. Hydrolysis of DMMP by Zr(OH)4 occurred under all conditions evaluated, demonstrating promise for chemical decontamination under diverse, real-world conditions.

Hemostatic kaolin-polyurethane foam composites for multifunctional wound dressing applications.

There are numerous challenges associated with the acute care of traumatic limb injuries in forward military settings. A lack of immediate medical facilities necessitates that the wound dressing perform multiple tasks including exudate control, infection prevention, and physical protection of the wound for extended periods of time. Here, kaolin was incorporated into recently developed robust polyurethane (PU) hydrogel foams at 1-10wt% in an effort to impart hemostatic character. ATR-IR and gel fraction analysis demonstrated that the facile, one-pot synthesis of the PU hydrogel was unaffected by kaolin loading, as well as the use of a non-toxic catalyst, which significantly improved cytocompatibility of the materials. Kaolin was generally well dispersed throughout the PU matrix, though higher loadings exhibited minor evidence of aggregation. Kaolin-PU composites exhibited burst release of ciprofloxacin over 2h, the initial release rates of which increased with kaolin loading. Kaolin loading imparted excellent hemostatic character to the PU foams at relatively low loading levels (5wt%). This work demonstrates the simple and inexpensive synthesis of robust, hemostatic, and absorptive kaolin-PU foams that have promising potential as multifunctional wound dressing materials.

Electrospun gelatin biopapers as substrate for in vitro bilayer models of blood-brain barrier tissue.

Gaining a greater understanding of the blood-brain barrier (BBB) is critical for improvement in drug delivery, understanding pathologies that compromise the BBB, and developing therapies to protect the BBB. In vitro human tissue models are valuable tools for studying these issues. The standard in vitro BBB models use commercially available cell culture inserts to generate bilayer co-cultures of astrocytes and endothelial cells (EC). Electrospinning can be used to produce customized cell culture substrates with optimized material composition and mechanical properties with advantages over off-the-shelf materials. Electrospun gelatin is an ideal cell culture substrate because it is a natural polymer that can aid cell attachment and be modified and degraded by cells. Here, we have developed a method to produce cell culture inserts with electrospun gelatin "biopaper" membranes. The electrospun fiber diameter and cross-linking method were optimized for the growth of primary human endothelial cell and primary human astrocyte bilayer co-cultures to model human BBB tissue. BBB co-cultures on biopaper were characterized via cell morphology, trans-endothelial electrical resistance (TEER), and permeability to FITC-labeled dextran and compared to BBB co-cultures on standard cell culture inserts. Over longer culture periods (up to 21 days), cultures on the optimized electrospun gelatin biopapers were found to have improved TEER, decreased permeability, and permitted a smaller separation between co-cultured cells when compared to standard PET inserts.

Development of antimicrobial peptides (AMPs) for use in self-decontaminating coatings.

Antimicrobial peptides (AMPs) are a class of short polypeptides usually associated with the host organism's innate immune system. AMPs have been identified in a wide range of host organisms, including plants, amphibians, fish, and humans. These peptides usually consist of 30-100 amino acids and are most often cationic. In addition to a net positive charge, AMPs often are amphipathic, containing both hydrophobic and hydrophilic domains. This property allows for increased interaction with and insertion into negatively charged cell walls and membranes of microbes. Because of the prevalence of antibiotic resistance among common human pathogens, recent research into AMPs has revolved around the attempt to increase the availability of drugs to which microbes are susceptible. Because the mechanism of kill for AMPs is different from that of most conventional antibiotics, which tend to be very specific in their targets, AMPs are thought to be a very attractive future substitute for traditional antibiotics. The development of novel self-decontaminating surfaces containing two AMPs previously isolated from Chrysophrys major is reported. These AMPs, Chrysophsin-1 and -3, demonstrated 1-4 logs kill of both Gram-positive and Gram-negative bacteria when incorporated into control acrylic coating systems.