The ion seeps tonight: Assessing ionic transport in multilayered nanocomposites

Figure 6 – Schematic of cation (M+) transport through an organized multilayered composite. Controlling ion transport across membranes and interfaces is one of the central themes challenging technological pursuits ranging from corrosion to energy storage and chemical separations. Here, we present several examples in which we have studied the application of multilayer nanocomposites to regulate ion transport. These composites comprise organized layers of functional or structural elements, integrated within composites such that the specific nanostructure and composition of the materials play important roles in defining ionic interactions and mobility. In cases such as corrosion inhibition, thin film composite coatings are intended to block ionic transport, retarding deleterious corrosion reactions. We show that by manipulating the materials chemistry of highly organized polymer clay nanocomposite thin film barriers, it is possible to significantly increase corrosion resistance of steel samples in a simulated sea water environment. In contrast, for energy storage applications such as batteries, composite separators capable of rapid ionic diffusion are desired for high current performance. We explore how layered composite structures may provide effective ion diffusion planes, leading to promising ionic conductivity in new solid state separators. Finally, in chemical separations, the selective transport of ions becomes important. We examine how manipulating the chemical and electrostatic composition of layered polyelectrolyte materials leads to preferential cation transport through these composite structures, a key property for an effective separations membrane. These different technologies exemplify how the principles governing ion transport through multilayered materials can be adapted for widely varied applications, and they illustrate the potential for this materials development strategy to enable new classes of functional composite materials. Please click Additional Files below to see the full abstract

Systematic Screening of Drosophila Deficiency Mutations for Embryonic Phenotypes and Orphan Receptor Ligands

This paper defines a collection of Drosophila deletion mutations (deficiencies) that can be systematically screened for embryonic phenotypes, orphan receptor ligands, and genes affecting protein localization. It reports the results of deficiency screens we have conducted that have revealed new axon guidance phenotypes in the central nervous system and neuromuscular system and permitted a quantitative assessment of the number of potential genes involved in regulating guidance of specific motor axon branches. Deficiency “kits” that cover the genome with a minimum number of lines have been established to facilitate gene mapping. These kits cannot be systematically analyzed for phenotypes, however, since embryos homozygous for many deficiencies in these kits fail to develop due to the loss of key gene products encoded within the deficiency. To create new kits that can be screened for phenotype, we have examined the development of the nervous system in embryos homozygous for more than 700 distinct deficiency mutations. A kit of ∼400 deficiency lines for which homozygotes have a recognizable nervous system and intact body walls encompasses >80% of the genome. Here we show examples of screens of this kit for orphan receptor ligands and neuronal antigen expression. It can also be used to find genes involved in expression, patterning, and subcellular localization of any protein that can be visualized by antibody staining. A subset kit of 233 deficiency lines, for which homozygotes develop relatively normally to late stage 16, covers ∼50% of the genome. We have screened it for axon guidance phenotypes, and we present examples of new phenotypes we have identified. The subset kit can be used to screen for phenotypes affecting all embryonic organs. In the future, these deficiency kits will allow Drosophila researchers to rapidly and efficiently execute genome-wide anatomical screens that require examination of individual embryos at high magnification

Genomic structure and alternative splicing of murine R2B receptor protein tyrosine phosphatases (PTPκ, μ, ρ and PCP-2)

BACKGROUND: Four genes designated as PTPRK (PTPκ), PTPRL/U (PCP-2), PTPRM (PTPμ) and PTPRT (PTPρ) code for a subfamily (type R2B) of receptor protein tyrosine phosphatases (RPTPs) uniquely characterized by the presence of an N-terminal MAM domain. These transmembrane molecules have been implicated in homophilic cell adhesion. In the human, the PTPRK gene is located on chromosome 6, PTPRL/U on 1, PTPRM on 18 and PTPRT on 20. In the mouse, the four genes ptprk, ptprl, ptprm and ptprt are located in syntenic regions of chromosomes 10, 4, 17 and 2, respectively. RESULTS: The genomic organization of murine R2B RPTP genes is described. The four genes varied greatly in size ranging from ~64 kb to ~1 Mb, primarily due to proportional differences in intron lengths. Although there were also minor variations in exon length, the number of exons and the phases of exon/intron junctions were highly conserved. In situ hybridization with digoxigenin-labeled cRNA probes was used to localize each of the four R2B transcripts to specific cell types within the murine central nervous system. Phylogenetic analysis of complete sequences indicated that PTPρ and PTPμ were most closely related, followed by PTPκ. The most distant family member was PCP-2. Alignment of RPTP polypeptide sequences predicted putative alternatively spliced exons. PCR experiments revealed that five of these exons were alternatively spliced, and that each of the four phosphatases incorporated them differently. The greatest variability in genomic organization and the majority of alternatively spliced exons were observed in the juxtamembrane domain, a region critical for the regulation of signal transduction. CONCLUSIONS: Comparison of the four R2B RPTP genes revealed virtually identical principles of genomic organization, despite great disparities in gene size due to variations in intron length. Although subtle differences in exon length were also observed, it is likely that functional differences among these genes arise from the specific combinations of exons generated by alternative splicing

Hygiene considerations during the collection, storage and processing of source-separated urine into a marketable fertilizer

Laboratory and field studies along with inactivation data from the literature are used to model bacteria inactivation during urine storage and struvite production. The model is used to evaluate urine storage and struvite drying under the fluctuating temperature and relative humidity. Recommendations are made to enhance microbial inactivation during urine storage and struvite production in low-resource field settings and to promote the safety of using urine-derived fertilizers

Towards sustainable sanitation: Identifying and mitigating microbial health risks in the production of urine-derived fertilizers

Sanitation systems that systematically recover and reuse waste can promote social enterprise, reduce discharge of harmful nutrients, pathogens and other contaminants to the environment, replace synthetic fertilizer sources, and increase access to sanitation for improved human health. However, one significant obstacle towards successfully modernizing sanitation practices is the need to assure human health safety in the production and application of waste-derived products. This is especially important in resource-poor settings, where an added challenge to safe waste reuse is limited financial capacity for technology implementation. This project seeks to identify and reduce human and environmental health risks in the collection of urine and its processing into a fertilizer (struvite) in a large decentralized sanitation system in Durban, South Africa, where a network of over 80,000 urine-diverting dry toilets (UDDTs) is in place. A screening of fecal pathogens in source-separated urine was conducted to assess microbial health hazards. Rotavirus, Adenovirus and Shigella spp. were identified as the most frequently occurring pathogens. Occupational exposure to Rotavirus in urine via surface-to-hand followed by hand-to-mouth transfer was then evaluated to quantify the relative microbial health risks associated with urine collection and fertilizer production. The microlevel activity time series (MLATS) method was selected for the exposure assessment. First person videography of urine collection and processing was coded into high-resolution data yielding the frequency, duration, and chronology of contacts between each study participant hand and each surface. Additionally, a tracer exposure study was conducted to measure the volume of urine contacted by study participants. A model was constructed using this data to simulate the concentrations expected of pathogens on worker hands and potential dose of pathogens ingested from intermittent hand-to-mouth contacts. Study participants contacted visibly wet, presumably urine-contaminated surfaces more frequently during the production of struvite than during the collection of urine (e.g., 10 vs. 3 wet-surface contacts/hr). The tracer study revealed that during the production of struvite, study participant gloves contacted 0.04 – 50 ml urine per batch of struvite produced. Nevertheless, the probability of Rotavirus infection associated with single dose events from presumed hand-to-mouth contacts was somewhat low during struvite production (e.g., median P(response) [ 95% CI] = 1.5×10-4 [1.4×10-5 , 5.4×10-4] per dose for 10K simulations). This exposure may be unacceptable if urine collection and fertilizer production system is conducted at scale or if multiple hand-to-mouth contacts occur during urine handling. In the context of resource reuse, source-separated urine is often falsely considered “sterile” or nearly so. Urine treatment via storage can reduce pathogen concentrations in struvite reactor influent to reduce exposure. Fertilizer production techniques that reduce human contact with urine during processing such as automated reactors should be favored. This study is unique in its approach to accurately model the time-dependent concentration of pathogens on hands due to urine contamination and to quantify the consequent exposure potential using videography, fecal contamination analysis in urine and on surfaces and a tracer study. Quantitatively identifying risks in this way is an important strategy for identifying and overcoming barriers to safe and sustainable sanitation

Towards sustainable sanitation: Mitigating microbial health risks in the production of urine-derived fertilizers

To identify and address health and safety challenges, first, I conducted a screening of fecal pathogens in source-separated urine. The pathogen inactivation performance of two innovative fertilizer production technologies was then evaluated in laboratory and field conditions. An in-depth assessment of the main mechanisms leading to pathogen inactivation during fertilizer production suggested nuanced adjustments in the treatment to yield more hygienic outcomes. Finally, occupational exposure and risks of infection during fertilizer production were evaluated using innovative exposure analysis techniques and modeling. Quantitatively identifying risks in this way will allow development of strategies to promote innovation and overcome barriers to safe and sustainable sanitation