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      Preparation, Characterization and Activity of a Peptide-Cellulosic Aerogel Protease Sensor from Cotton

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          Abstract

          Nanocellulosic aerogels (NA) provide a lightweight biocompatible material with structural properties, like interconnected high porosity and specific surface area, suitable for biosensor design. We report here the preparation, characterization and activity of peptide-nanocellulose aerogels (PepNA) made from unprocessed cotton and designed with protease detection activity. Low-density cellulosic aerogels were prepared from greige cotton by employing calcium thiocyanate octahydrate/lithium chloride as a direct cellulose dissolving medium. Subsequent casting, coagulation, solvent exchange and supercritical carbon dioxide drying afforded homogeneous cellulose II aerogels of fibrous morphology. The cotton-based aerogel had a porosity of 99% largely dominated by mesopores (2–50 nm) and an internal surface of 163 m 2·g −1. A fluorescent tripeptide-substrate (succinyl-alanine-proline-alanine-4-amino-7-methyl-coumarin) was tethered to NA by (1) esterification of cellulose C6 surface hydroxyl groups with glycidyl-fluorenylmethyloxycarbonyl (FMOC), (2) deprotection and (3) coupling of the immobilized glycine with the tripeptide. Characterization of the NA and PepNA included techniques, such as elemental analysis, mass spectral analysis, attenuated total reflectance infrared imaging, nitrogen adsorption, scanning electron microscopy and bioactivity studies. The degree of substitution of the peptide analog attached to the anhydroglucose units of PepNA was 0.015. The findings from mass spectral analysis and attenuated total reflectance infrared imaging indicated that the peptide substrate was immobilized on to the surface of the NA. Nitrogen adsorption revealed a high specific surface area and a highly porous system, which supports the open porous structure observed from scanning electron microscopy images. Bioactivity studies of PepNA revealed a detection sensitivity of 0.13 units/milliliter for human neutrophil elastase, a diagnostic biomarker for inflammatory diseases. The physical properties of the aerogel are suitable for interfacing with an intelligent protease sequestrant wound dressing.

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          Is there new hope for therapeutic matrix metalloproteinase inhibition?

          Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that form a family of 24 members in mammals. Evidence of the pathological roles of MMPs in various diseases, combined with their druggability, has made them attractive therapeutic targets. Initial drug discovery efforts focused on the roles of MMPs in cancer progression, and more than 50 MMP inhibitors have been investigated in clinical trials in various cancers. However, all of these trials failed. Reasons for failure include the lack of inhibitor specificity and insufficient knowledge about the complexity of the disease biology. MMPs are also known to be involved in several inflammatory processes, and there are new therapeutic opportunities for MMP inhibitors to treat such diseases. In this Review, we discuss the recent advances made in understanding the role of MMPs in inflammatory diseases and the therapeutic potential of MMP inhibition in those conditions.
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            Converting nitrogen into protein--beyond 6.25 and Jones' factors.

            The protein content in foodstuffs is estimated by multiplying the determined nitrogen content by a nitrogen-to-protein conversion factor. Jones' factors for a series of foodstuffs, including 6.25 as the standard, default conversion factor, have now been used for 75 years. This review provides a brief history of these factors and their underlying paradigm, with an insight into what is meant by "protein." We also review other compelling data on specific conversion factors which may have been overlooked. On the one hand, when 6.25 is used irrespective of the foodstuff, "protein" is simply nitrogen expressed using a different unit and says little about protein (s.s.). On the other hand, conversion factors specific to foodstuffs, such as those provided by Jones, are scientifically flawed. However, the nitrogen:protein ratio does vary according to the foodstuff considered. Therefore, from a scientific point of view, it would be reasonable not to apply current specific factors any longer, but they have continued to be used because scientists fear opening the Pandora's box. But because conversion factors are critical to enabling the simple conversion of determined nitrogen values into protein values and thus accurately evaluating the quantity and the quality of protein in foodstuffs, we propose a set of specific conversion factors for different foodstuffs, together with a default conversion factor (5.6). This would be far more accurate and scientifically sound, and preferable when specifically expressing nitrogen as protein. These factors are of particular importance when "protein" basically means "amino acids," this being the principal nutritional viewpoint.
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              Lightweight, Superelastic, and Mechanically Flexible Graphene/Polyimide Nanocomposite Foam for Strain Sensor Application.

              The creation of superelastic, flexible three-dimensional (3D) graphene-based architectures is still a great challenge due to structure collapse or significant plastic deformation. Herein, we report a facile approach of transforming the mechanically fragile reduced graphene oxide (rGO) aerogel into superflexible 3D architectures by introducing water-soluble polyimide (PI). The rGO/PI nanocomposites are fabricated using strategies of freeze casting and thermal annealing. The resulting monoliths exhibit low density, excellent flexibility, superelasticity with high recovery rate, and extraordinary reversible compressibility. The synergistic effect between rGO and PI endows the elastomer with desirable electrical conductivity, remarkable compression sensitivity, and excellent durable stability. The rGO/PI nanocomposites show potential applications in multifunctional strain sensors under the deformations of compression, bending, stretching, and torsion.
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                Author and article information

                Contributors
                Role: Academic Editor
                Role: Academic Editor
                Role: Academic Editor
                Role: Academic Editor
                Journal
                Sensors (Basel)
                Sensors (Basel)
                sensors
                Sensors (Basel, Switzerland)
                MDPI
                1424-8220
                26 October 2016
                November 2016
                : 16
                : 11
                : 1789
                Affiliations
                [1 ]Southern Regional Research Center, USDA, New Orleans, LA 70124, USA; krystal.fontenot@ 123456ars.usda.gov (K.R.F.); nicolette.prevost@ 123456ars.usda.gov (N.T.P.); brian.condon@ 123456ars.usda.gov (B.D.C.)
                [2 ]Division of Chemistry of Renewable Resources, University of Natural Resources and Life Sciences Vienna, Konrad-Lorenz-Straße 24, Tulln an der Donau A-3430, Austria; nicole.gk.pircher@ 123456gmail.com (N.P.); falk.liebner@ 123456boku.ac.at (F.L.)
                Author notes
                [* ]Correspondence: vince.edwards@ 123456ars.usda.gov ; Tel.: +1-504-286-4360
                Article
                sensors-16-01789
                10.3390/s16111789
                5134448
                27792201
                1042827c-8b71-4574-b7c5-5a82df51850a
                © 2016 by the authors; licensee MDPI, Basel, Switzerland.

                This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 15 July 2016
                : 12 October 2016
                Categories
                Article

                Biomedical engineering
                elastase peptide,cellulosic aerogels,human neutrophil elastase,biosensor,chronic wounds

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