Prospective on the use of bacterial cellulose as an antimicrobial edible film

Food and beverage packaging has been the target of an intensive conceptual revolution in the past twenty years, moving further away from the mere passive barriers highly dependent on petrochemical-based raw materials. The recent trends of the state of the art food packages consist of smart packages that are preferentially green manufactured due to environmental concerns, and edible, making it more practical to consume and simultaneously minimizing the resultant waste. Some of these smart packages are able to diagnose and inform “in real-time” the consumer/retailer of the encased food’s quality (intelligent packaging). Other packages are responsible for an active interaction with the food or food’s atmosphere increasing the products shelf life, improving its organoleptic and/or health properties (active packaging). The food and beverage packaging market is estimated to represent 1 trillion dollars by 2015 in the United States alone, making this field of research an interesting area to explore.The main goal of this work is to produce a novel edible packaging film with antimicrobial properties. The purpose of including a food grade antimicrobial compound is to delay the growth of microbial flora and thus increasing the food’s safety and delaying its spoilage. For the packaging main raw material we have chosen the bacterial cellulose, which may represent an interesting alternative to the classic plastic casings, since this natural biopolymer possess a high toughness (Young’s modulus of approx. 15 - 35 GPa), a low density (1.25 g cm-3), a high crystallinity (95%), it is biocompatible, is highly pure (total absence of hemicelluloses and pectin’s), provides a high surface area for modification (37 m2g-1), and finally, its low cost. As food-grade antimicrobial compound we selected the lactoferrin, a bilobar iron binding glycoprotein with a widely reported bactericidal effect. Different approaches are being used to covalently bind the protein onto bacterial cellulose. The preliminary antimicrobial effectiveness of the modified bacterial cellulose films is assessed by inhibition halo tests

Professor Pimenta Claro (1957-2018): Pioneer in dynamics of mechanical systems at the University of Minho

This work highlights the importance of Professor Pimenta Claro in the genesis and development of a new scientific area at the Department of Mechanical Engineering of the University of Minho, namely Dynamics of Mechanical Systems. Professor Pimenta Claro initiated his academic career in October 1980, coming from industry, where he was a well-recognized engineer in the field of mechanical design. Professor Pimenta Claro concluded his Pedagogical Aptitude and Scientific Capacity Tests (PAPCC) – MSc equivalent – in 1987, with dissertation title “Estudo Comparativo das Previsões Teóricas do Desempenho de Chumaceiras Radiais Hidrodinâmicas com Resultados Experimentais”. Professor Pimenta Claro received his doctorate degree in 1994 with thesis “Reformulação de Método de Cálculo de Chumaceiras Radiais Hidrodinâmicas – Análise do Desempenho Considerando Condições de Alimentação” under the mentorship of Professor Sousa Miranda, which was in fact the first PhD in Mechanical Engineering defended at the University of Minho. In 1997, Professor Pimenta Claro broken with his past background – classical tribology – to open a new research domain – Dynamics of Mechanical Systems. Since then, Professor Pimenta Claro has coordinated and participated in several scientific projects both with national and international partners, as well as projects with industrial partners. Professor Pimenta Claro was author of numerous publications, including scientific papers, books, conference papers, etc., and supervised PhD and MSc students. From 2007 to 2013 he coordinated the research group called Dynamics of Mechanical Systems. Professor Pimenta Claro was also pioneer and responsible for the creation of new courses on dynamics of mechanical systems offered in different degrees at the School of Engineering of the University of Minho. Thus, the main purpose of this work is to highlight Pimenta Claro’s contributions to the vast scientific area of Dynamics of Mechanical Systems at the Department of Mechanical Engineering of the University of Minho

Surface-ATRP of PEGMA onto polydimethyl siloxane for biomedical applications

Silicone rubber (poly(dimethyl siloxane; PDMS)), is extensively used for biomedical implants due to its low toxicity, flexible processing techniques, long-term endurance and good blood compatibility. However, the presence of low molecular weight organic molecules and catalyst residues that cause host systemic inflammatory reactions. The hydrophobic nature of PDMS also allows microbial adhesion followed by infection. Hydrophilic PDMS surfaces would be of great value in inhibiting biofilm formation thus prolonging the lifetime of the implants. This could be obtained by surface-initiated atom transfer radical polymerization (ATRP). The robustness and versatility of ATRP allow the preparation of functional bioactive surfaces, including antifouling, antibacterial, stimuliresponsive, biomolecule-coupled and micropatterned surfaces.[1-3] We aim at establishing the experimental conditions allowing the surface-grafting of polyethylene glycol methacrylate (PEGMA) by surface attaching an initiator (1- trichlorosilyl-2-(chloromethylphenyl)ethane) onto PDMS (Sylgard ® 184). Here, cooper is being used as a metal catalyst and 2,2'-Bipyridine as a ligant. Polymerizations are being assayed in aqueous media. The native smooth and transparent surface of the PDMS could be preserved following polymerization (as confirmed by SEM). FTIR-ATR also showed the presence of PEGMA polymer chains. By contact angle measurement, a change in the surface hydrophobicity was observed, the values changing from 114º to 60º, following 30h polymerization. Work is in progress to optimize the modification of PDMS by PEGMA surface-ATRP. This implies following up the polymer chain growth kinetics, surface characterization by XPS, FTIR-ATR, SEM and contact angle measurements. Static and dynamic microbial adhesion, as well as biocompatibility studies are also envisaged

Bacterial cellulose as a feasible cell carrier for Retinal Pigment Epithelium cell transplantation

Retinal Pigment Epithelium (RPE) cell transplantation is a potential therapy for retinal degenerative diseases that affect millions of people worldwide. However, for its use in cell therapy, RPE cells need to be transplanted as a functional cell monolayer, thus requiring a carrier substrate. An ideal substrate for this application should support acquisition and/or maintain the RPE phenotype; allow fluid transport and metabolites exchange; enable easy surgical manipulation; be well tolerated in the subretinal space; and biodegrade or integrate over time. Several biomaterials have been studied for this application, such as collagen, poly-L-lactic acid, gelatin, fibrinogen, deepithelialized amniotic membrane, among others. Although growth of healthy RPE has been achieved on both biodegradable and non biodegradable, synthetic and biologic substrates, only an exceptionally low number of these substrates show acceptable tissue response. Growth of RPE cell monolayers on bacterial cellulose (BC) surfaces presents itself as an interesting alternative for the replacement of both the RPE in degeneration and the compromised Bruch’s membrane (BM) in retinal degenerative diseases. BC, produced by Gluconacetobacter xylinum, is a safe, non-degradable biomaterial and can be obtained with a thickness similar to BM, while maintaining its stability. The implantable substrate’s functionality and durability depend on the bulk properties of the material and BC presents the ideal bulk properties for this application. In this regard, diffusion studies showed that BC presents the porosity and diffusion properties required for the transport of nutrients across the substrate (up to 300kDa diffusion). Additionally, biological response is governed by several surface properties: chemistry, topography, roughness, charge, energy and wettability. Although the wettability of unprocessed BC is not ideal, we have improved it through acetylation and coating of its surface with extracellular matrix (ECM, extracted from porcine urinary bladders). Indeed, the extent of surface wettability modification after BC surface acetylation was evaluated by water contact angle measurements, showing an increase from 20° to 75°, approximately. Moreover, we also demonstrated, by trypan blue dye exclusion and MTS assays, that RPE cell monolayers are viable and able to proliferate in BC substrates with ECM. These results were also confirmed by scanning electron microscopy, which showed that cells retained their normal morphology. Overall, results obtained so far demonstrated that both BC coating with ECM and BC acetylation improved the substrate performance, envisaging its potential application as a feasible RPE cell carrier.FEB

A STEADY PSEUDO-COMPRESSIBILITY APPROACH BASED ON UNSTRUCTURED HYBRID FINITE VOLUME TECHNIQUES APPLIED TO TURBULENT PREMIXED FLAME PROPAGATION

A pseudo-compressibility method for zero Mach number turbulent reactive flows with heat release is combined with an unstructured finite volume hybrid grid scheme. The spatial discretization is based on an overlapped cell vertex approach. An infinite freely planar flame propagating into a turbulent medium of premixed reactants is considered as a test case. The recourse to a flamelet combustion modeling for which the reaction rate is quenched in a continuous way ensures the uniqueness of the turbulent flame propagation velocity. To integrate the final form of discretized governing equations, a three-stage hybrid time-stepping scheme is used and artificial dissipation terms are added to stabilize the convergence path towards the final steady solution. The results obtained with such a numerical procedure prove to be in good agreement with those reported in the literature on the very same flow geometry. Indeed, the flame structure as well as its propagation velocity are accurately predicted thus confirming the validity of the approach followed and demonstrating that such a numerical procedure will be a valuable tool to deal with complex reactive flow geometries

Die Optimierung von Poly(Dimethylsiloxan) für biomedizinische Anwendungen durch oberflächeninitiierte Atom-Transferradikal-Polymerisation

Project BIOSURFA ref. PTDC/SAU-BEB/73498/200

CD26/DPPIV and response to hepatitis B vaccination

The prevention of hepatitis B is important, since it is responsible for significant morbidity and mortality around the world. Unfortunately, hepatitis B vaccine does not always induce protective immunity. The lack of immune response to vaccine (non-responders) can depend on individual characteristics. The objective of this study was to correlate the CD26/DPPIV cellular expression and DPPIV serum activity with HBV vaccine response and its possible role as an indicator of immune competence acquisition. We also determined the cellular expression of CD3, CD19, CD56 and CD25 in peripheral blood T lymphocytes. Blood samples were obtained from 28 healthy human volunteers who were enrolled with a vaccination program. There were "responders" (RM = 13) and "non-responders" (NRM = 15), after vaccination. The lymphocyte populations were identified by flow cytometry. DPPIV serum activity was measured fluorimetrically. CD26 expression in responders (55.9 +/- 7.7%) versus in non-responders (51.9 +/- 7.0%) did not show a significant difference. The DPPIV serum activity in responders compared to in non-responder subgroup (59.9 +/- 8.4/50.3 +/- 10.6U/L) showed, however, a significant difference (P < 0.05). The expression of CD3, CD19 and CD56 on peripheral lymphocytes was similar between responders and non-responders. The expression of CD3CD26 (52.2 +/- 8.6%) and CD3CD25 (10.9 +/- 3.8%) in responders versus the expression of CD3CD26 (48.0 +/- 5.7%) and CD3CD25 (8 +/- 4.6%) in non-responders did not show statistically significant difference. CD25 referred as a marker of T lymphocyte activation was increased in responders (15.8 +/- 4.5%) versus in non-responders (10.1 +/- 4.8%), showing a significant difference (P = 0.003). It was, however, impossible to demonstrate an increase in CD3CD25 and CD3CD26 in the responder subgroup. This suggests that different lymphocyte subsets other than T cells are implicated in the response to hepatitis B vaccination

Forbidden subgraphs and the König-Egerváry property

The matching number of a graph is the maximum size of a set of vertex-disjoint edges. The transversal number is the minimum number of vertices needed to meet every edge. A graph has the König-Egerváry property if its matching number equals its transversal number. Lovász proved a characterization of graphs having the König-Egerváry property by means of forbidden subgraphs within graphs with a perfect matching. Korach, Nguyen, and Peis proposed an extension of Lovász's result to a characterization of all graphs having the König-Egerváry property in terms of forbidden configurations (which are certain arrangements of a subgraph and a maximum matching). In this work, we prove a characterization of graphs having the König-Egerváry property by means of forbidden subgraphs which is a strengthened version of the characterization by Korach et al. Using our characterization of graphs with the König-Egerváry property, we also prove a forbidden subgraph characterization for the class of edge-perfect graphs. © 2013 Elsevier B.V. All rights reserved.Fil:Bonomo, F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Durán, G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Grippo, L.N. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Safe, M.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The colorful Helly theorem and general hypergraphs

AbstractThe definition of the Helly property for hypergraphs was motivated by the Helly theorem for convex sets. Similarly, we define the colorful Helly property for a family of hypergraphs, motivated by the colorful Helly theorem for collections of convex sets, by Lovász. We describe some general facts about the colorful Helly property and prove complexity results. In particular, we show that it is Co-NP-complete to decide if a family of p hypergraphs is colorful Helly, even if p=2. However, for any fixed p, we describe a polynomial time algorithm to decide if such family is colorful Helly, provided at least p−1 of the hypergraphs are p-Helly