Ultra low density and highly crosslinked biocompatible shape memory polyurethane foams

We report the development of highly chemically crosslinked, ultra low density (～0.015 g/cc) polyurethane shape memory foams synthesized from symmetrical, low molecular weight, and branched hydroxyl monomers. Sharp single glass transitions (T_g) customizable in the functional range of 45–70 °C were achieved. Thermomechanical testing confirmed shape memory behavior with 97–98% shape recovery over repeated cycles, a glassy storage modulus of 200–300 kPa, and recovery stresses of 5–15 kPa. Shape holding tests under constrained storage above the T_g showed stable shape memory. A high volume expansion of up to 70 times was seen on actuation of these foams from a fully compressed state. Low in vitro cell activation induced by the foam compared with controls demonstrates low acute bio‐reactivity. We believe these porous polymeric scaffolds constitute an important class of novel smart biomaterials with multiple potential applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

On a linearization technique for solving the quadratic set covering problem and variations

In this paper we identify various inaccuracies in the paper by Saxena and Arora (Optimization 39:33–42, 1997). In particular, we observe that their algorithm does not guarantee optimality, contrary to what is claimed. Experimental analysis has been carried out to assess the value of this algorithm as a heuristic. The results disclose that for some classes of problems the Saxena–Arora algorithm is effective in achieving good quality solutions while for some other classes of problems, its performance is poor. We also discuss similar inaccuracies in another related paper.     

Integrated microfluidic platform for rapid antimicrobial susceptibility testing and bacterial growth analysis using bead-based biosensor via fluorescence imaging

The paper describes a droplet-based microfluidic method for phenotypic-based antimicrobial susceptibility testing (AST). In particular, this micro-droplet-based phenotypic assay evaluates susceptibility of different bacterial strains towards antibiotics by tracking effects on individual bacterial cells, including changes in bacterial cell number and morphology. The platform was validated by applying the method to test the responses of E. coli ATCC 25922 and 6937 (a clinical isolate), in spiked urine samples at a concentration of 5 × 10⁴ cfu mL^?1, to the antibiotics ceftazidime and levofloxacin. Both E. coli strains showed dose-dependent inhibition of bacterial replication and morphological alteration. These correlated well with minimal inhibitory concentrations determined by the reference broth microdilution method. Discrete bacterial divisions and morphological changes were observed within 20 min of on-chip incubation, demonstrating performance of rapid AST directly on urine samples. As proof-of-concept, specific bead-based biosensors were tested for capture and detection of E. coli for on-bead proliferation. The method has the attractive feature of allowing the detection of at least one bacterium per bead in less than 30 min. It can potentially be used to isolate a specific bacterial strain directly from patient urine samples for AST monitoring.

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Graphical Abstract (A) Schematic of the droplet microfluidic chip for bacterial detection and Antibiotic Susceptibility Testing (AST); (B) Time lapse proliferation images of green fluorescent protein expressing E. coli in droplets. (C) Bacterial proliferation on the bead-based sensor.

     

Synthesis of new heterocycles through the reaction of β-lapachone with 1,2-diamines using Triton X-100 surfactant as catalyst in aqueous medium

An efficient and an environmentally benign protocol has been developed for the synthesis of new naphtha-azaquinoxaline and naphtha-benzoquinoxaline derivatives from the reaction of β-lapachone, a naturally occurring 1,2-naphthoquinone with various 1,2-diamines using surfactant as catalyst in aqueous medium. This method has advantage of easy handling and good yield of products in shorter time. The structures were assigned with the help of analytical and ¹H, ¹³C NMR, IR, and mass spectral studies.     

Isolation and Functional Characterization of a Novel Seed-Specific Promoter Region from Peanut

The importance of using tissue-specific promoters in the genetic transformation of plants has been emphasized increasingly. Here, we report the isolation of a novel seed-specific promoter region from peanut and its validation in Arabidopsis and tobacco seeds. The reported promoter region referred to as groundnut seed promoter (GSP) confers seed-specific expression in heterologous systems, which include putative promoter regions of the peanut (Arachis hypogaea L.) gene 8A4R19G1. This region was isolated, sequenced, and characterized using gel shift assays. Tobacco transgenics obtained using binary vectors carrying uidA reporter gene driven by GSP and/or cauliflower mosaic virus 35S promoters were confirmed through polymerase chain reaction (PCR), RT-PCR, and computational analysis of motifs which revealed the presence of TATA, CAAT boxes, and ATG signals. This seed-specific promoter region successfully targeted the reporter uidA gene to seed tissues in both Arabidopsis and tobacco model systems, where its expression was confirmed by histochemical analysis of the transgenic seeds. This promoter region is routinely being used in the genetic engineering studies in legumes aimed at targeting novel transgenes to the seeds, especially those involved in micronutrient enhancement, fungal resistance, and molecular pharming.     

Application of Fragment‐Based Screening to the Design of Inhibitors of Escherichia coli DsbA

The thiol‐disulfide oxidoreductase enzyme DsbA catalyzes the formation of disulfide bonds in the periplasm of Gram‐negative bacteria. DsbA substrates include proteins involved in bacterial virulence. In the absence of DsbA, many of these proteins do not fold correctly, which renders the bacteria avirulent. Thus DsbA is a critical mediator of virulence and inhibitors may act as antivirulence agents. Biophysical screening has been employed to identify fragments that bind to DsbA from Escherichia coli. Elaboration of one of these fragments produced compounds that inhibit DsbA activity in vitro. In cell‐based assays, the compounds inhibit bacterial motility, but have no effect on growth in liquid culture, which is consistent with selective inhibition of DsbA. Crystal structures of inhibitors bound to DsbA indicate that they bind adjacent to the active site. Together, the data suggest that DsbA may be amenable to the development of novel antibacterial compounds that act by inhibiting bacterial virulence.     

Lie Regular Generators of General Linear Groups

In this article, we introduce the idea of Lie regular elements and study 2 × 2 Lie regular matrices. It is shown that the linear groups GL(2, ?_{2 ⁿ} ), GL(2, ? _{p ⁿ} ), and GL(2, ?_2p ) (where p is an odd prime) can be genrated by Lie regular matrices. Presentations of linear groups GL(2, ?₄), GL(2, ?₆), GL(2, ?₈), and GL(2, ?₁₀) are also given.     

On Representations of Classical Groups Over Principal Ideal Local Rings of Length Two

We study the complex irreducible representations of special linear, symplectic, orthogonal, and unitary groups over principal ideal local rings of length two. We construct a canonical correspondence between the irreducible representations of all such groups that preserves dimensions. The case for general linear groups has already been proved by the author.