University of Akron

About: University of Akron is a education organization based out in Akron, Ohio, United States. It is known for research contribution in the topics: Polymer & Polymerization. The organization has 17401 authors who have published 29127 publications receiving 702386 citations. The organization is also known as: The University of Akron.

Mimicking biological stress–strain behaviour with synthetic elastomers

Abstract: A polymer code based on a triplet of parameters—network strand length, side-chain length and grafting density—enables materials to be designed with specific combinations of mechanical properties to mimic biological materials. Controlling mechanical properties, such as stress–strain behaviour, in synthetic polymers often involves screening many samples with different molecular weights, compositions and architectures, and iterating towards the desired properties. However, it is difficult to predict what molecular make-up will yield the desired stress–strain curve, particularly in the case of strain-hardening materials that mimic the mechanical properties of biological tissues such as cartilage, muscle and lungs. Here, Sergei Sheiko and colleagues develop a method to derive grafting density, side-chain length and network strand length for brush- and comb-like polymer networks. This triplet of parameters can be calculated directly from a given stress–strain curve, enabling researchers to predict and synthesize a specific composition and architecture to get the desired mechanical properties, rather than relying on trial-and-error, synthesis-heavy approaches. Despite the versatility of synthetic chemistry, certain combinations of mechanical softness, strength, and toughness can be difficult to achieve in a single material. These combinations are, however, commonplace in biological tissues, and are therefore needed for applications such as medical implants, tissue engineering, soft robotics, and wearable electronics1,2,3,4,5,6,7,8,9. Present materials synthesis strategies are predominantly Edisonian, involving the empirical mixing of assorted monomers, crosslinking schemes, and occluded swelling agents, but this approach yields limited property control2,10,11,12,13,14,15,16. Here we present a general strategy for mimicking the mechanical behaviour of biological materials by precisely encoding their stress–strain curves in solvent-free brush- and comb-like polymer networks (elastomers). The code consists of three independent architectural parameters—network strand length, side-chain length and grafting density. Using prototypical poly(dimethylsiloxane) elastomers, we illustrate how this parametric triplet enables the replication of the strain-stiffening characteristics of jellyfish, lung, and arterial tissues.

Biosensors Based on Aligned Carbon Nanotubes Coated with Inherently Conducting Polymers

Abstract: The use of multiwalled aligned carbon nanotubes provides a novel electrode platform for inherently conducting polymer based biosensors. The example used here to highlight the usefulness of such a platform is the polypyrrole based glucose oxidase system for detection of glucose. The use of these three dimensional electrodes offers advantages in that large accessible enzyme loadings can be obtained within an ultrathin layer. It has also been found that the detection of H2O2 at these new electrode structures containing iron loaded nanotube tips can be achieved at low anodic potentials. The result is a sensitive and selective glucose sensor.

Polyimide Aerogels Cross-Linked through Amine Functionalized Polyoligomeric Silsesquioxane

Abstract: We report the first synthesis of polyimide aerogels cross-linked through a polyhedral oligomeric silsesquioxane, octa(aminophenyl)silsesquioxane (OAPS). Gels formed from polyamic acid solutions of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), bisaniline-p-xylidene (BAX) and OAPS were chemically imidized and dried using supercritical CO2 extraction to give aerogels having density around 0.1 g/cm3. The aerogels are greater than 90 % porous, have high surface areas (230 to 280 m2/g) and low thermal conductivity (14 mW/m-K at room temperature). Notably, the polyimide aerogels cross-linked with OAPS have higher modulus than polymer reinforced silica aerogels of similar density and can be fabricated as both monoliths and thin films. Thin films of the aerogel are flexible and foldable making them an ideal insulation for space suits, and inflatable structures for habitats or decelerators for planetary re-entry, as well as more down to earth applications.

An Efficient Algorithm for Multi-Item Scheduling

Abstract: A number of resource-allocation problems, including that of multi-item scheduling, may be solved approximately as large linear programs, as in Manne [Management Sci. 4, 115-135 1958]. Dzielinski and Gomory [Management Sci. 11, 874-890 1965] applied the Dantzig-Wolfe decomposition principle to this problem. Here, the problem is attacked directly, using a column generation technique and Dantzig and Van Slyke's generalized upper-bounding method [J. Comp. and Syst. Sci. 1, 213-226 1967]. For problems involving I items and T time periods, one need deal with a basis matrix of dimension only T by T. A lower bound on the optimal cost may be developed, and intermediate solutions all have Manne's integer property loc. cit.. Computational experiments, including an option for pricing out subproblem solutions until none is useful, show a number of iterations to optimality of from one-half to one-ninth the number required by the decomposition principle with work per iteration remaining approximately the same. Extensions of the basic model are also described. These form the core of an automated production-scheduling and inventory-control system, currently being used by a major U. S. manufacturer. Computational experience with this extended model is presented.