Hydrogels of enzymatically modified dextrin

Dextrin is a glucose-containing saccharide polymer linked by α-(1→4) D-glucose units and is produced by partial hydrolysis of starch. Hydrolysis can be accomplished by the use of acid, enzymes, or by a combination of both. In this work, the Bacillus subtilis protease Proleather FG-F catalyzed the transesterification of the soluble polysaccharide with vinyl acrylate (VA), using anhydrous dimethylsulfoxide (DMSO) as reaction medium. Different degrees of substitution (DS, defined as the amount of acrylate groups per 100 glucopyranose residues) ranging from 11 to 19 % were achieved by controlling the molar ratio of VA to dextrin. Dextrin derivatized with VA (dextrin-VA) was characterized by gel permeation chromatography. Gels were obtained by free radical polymerization of aqueous solutions of dextrin-VA with different degrees of substitution and monomer concentration. Swelling experiments have been performed in order to determine the gel pore sizes. Specific physical properties, as degradation behaviour were also evaluated. These hydrogels are being developed as scaffold materials for bioactive molecule and cell delivery, tissue engineering and a variety of other biomedical applications

The effect of an RGD-Human Chitin-Binding Domain fusion protein on the adhesion of fibroblasts to reacetylated chitosan films

Biomaterials used for tissue engineering applications must provide a structural support for the tissue development and also actively interact with cells, promoting adhesion, proliferation and differentiation. To achieve this goal, adhesion molecules may be used, such as the tripeptide Arg-Gly-Asp (RGD). RGD was found to be the major functional amino acid sequence responsible for cellular adhesion. This sequence can be used to elicit specific cellular responses and it has been extensively demonstrated that RGD sequence improves cell adhesion, spreading and proliferation in different materials. Chitosan and chitin represent a family of biopolymers, made up of b(14)-linked N-acetyl-Dglucosamine and D-glucosamine subunits. Due to their biodegradability and biocompatibility, chitin and chitosan, are widely studied for biomedical applications. A method based on the use of a human Carbohydrate-Binding Module, with affinity for chitin, was tested as an alternative approach to the chemical grafting of bioactive peptides. This approach would simultaneously allow the production of recombinant peptides (alternatively to peptide synthesis) and provide a simple way for the specific and strong adsorption of the peptides to the biomaterial. A fusion recombinant protein, containing the RGD sequence fused to a human chitin-binding module (ChBM), was expressed in E. coli. The adhesion of fibroblasts to reacetylated chitosan (RC) films was the model system selected to analyse the properties of the obtained proteins. Thus, the evaluation of cell attachment and proliferation on polystyrene surfaces and reacetylated chitosan films, coated with the recombinant proteins, was performed using mouse embryo fibroblasts 3T3. The results show that the recombinant proteins affect negatively fibroblasts anchorage to the materials surface, inhibiting its adhesion and proliferation. We also conclude that this negative effect is fundamentally due to the human chitinbinding domain

A Model to Improve the Accuracy of WSN Simulations

Simulation studies have been extensively adopted in the networking research community. Nevertheless, the performance of the software components running within the network devices is often not modeled by generic network simulators. This aspect is particularly important in wireless sensor networks (WSN). As motes present very limited computing resources, the overhead of the software components cannot be ignored. Consequently, WSN simulation results may diverge significantly from the reality. After showing experimentally the validity of this assumption, the paper proposes a set of generic equations to model the performance of WSN software components. Validation tests using contention and multiplexing-based MAC protocols show that the inclusion of the proposed model in a WSN simulator improves the confidence degree in the simulation results significantly

Modelling the impact of software components on wireless sensor network performance

Network Simulators are often used to study multiple aspects of data communications in distinct scenarios, including wireless sensor networks (WSN). However, the performance of the software components running in the network nodes is normally neglected by the simulators. This aspect is particularly important in WSNs, as nodes have very limited computing resources. In order to study the impact of software components on WSN performance, a simulated WSN and a physical WSN were setup in the IEEE 802.15.4 domain. Tests revealed that the simulator must take into account the software components of the WSN to produce realistic results. To achieve this, new parameters are proposed to model the impact of the software components on a physical WSN. Tests measuring the packet round-trip delay, delivery error ratio, and duplicated packet ratio showed that the inclusion of this model in a simulator improves significantly the accuracy of the results when compared with those obtained in a physical WSN

A time-slot scheduling algorithm for e-health wireless sensor networks

http://www.ieee-healthcom.org/2010/about.htmlFor e-health wireless sensor networks presenting significant traffic loads, MAC protocols based on deterministic scheduling algorithms are consensually considered more adequate than protocols based on random access algorithms. Indeed, TDMA-based MAC protocols are able to control the delay bound and save power by eliminating collisions. However, these protocols always require some expedite scheme to assign the superframe time-slots to the network devices that need to transmit data. Knowing that patients of an e-health wireless network are normally monitored by the same number and types of motes, originating a regular traffic pattern, a simple collaborative time-slot allocation algorithm can be achieved, as introduced in this paper. In the proposed algorithm, the announcement of time-slot allocation by the network coordinator is avoided, which helps to improve the packet delivery ratio and reduce the energy consumption in the e–health wireless network.(undefined

New dextrin-vinylacrylate hydrogel : studies on protein diffusion and release

New dextrin hydrogels with degrees of substitution (DS) from ca. 10% (DS 10) to 70% (DS 70) were prepared by radical polymerization of aqueous solutions of vinylacrylate (VA)-derivatized dextrin. A preliminary analysis on the potential of these hydrogels for the controlled release of bioactive molecules was carried out. The protein (bovine serum albumin) diffusion coefficients on the hydrogels were calculated using the lag-time analysis. Values in range 10−7 cm2/s were obtained for DS 20 and DS 40 and a smaller value of 10−8 cm2/s arised upon DS increasing to 70%, revealing the dependence of the diffusivity on the crosslinking density. The release of BSA from dextrin-VA hydrogels, in the presence of amyloglucosidase was shown to be mainly dependent on the diffusion and, to a smaller extent, on the degradation kinetics. The protein release can be tailored from days to months by varying the DS.This research was supported by Fundacao para a Ciencia e a Tecnologia under Grant SFRH/BD/17482/2004 and FUNCARB POC-TI/BIO/45356/2002

New hydrogel obtained by chitosan and dextrin-VA co-polymerization

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Comparative study of cellulose fragmentation by enzymes and ultrasound

The stability in aqueous suspensions of two particulate celluloses, Sigmacell type 100 and Avicel PH101, was analyzed. The effect of the presence of a cellulase from Trichodenna reesei, ionic strength, and ultrasonic agitation on the fragmentation/aggregation phenomena was studied. Particle size distributions of the powders were obtained with three different particle sizers: the Galai CIS 100, the Coulter Multisizer II, and the Malvem 2600c. The differences in the obtained absolute values are discussed according to the measuring principles of each technique; however, the overall conclusions are independent of the particle sizer used. The enzyme breaks up the Avicel aggregates more effectively than ultrasound while the Sigmacell particles are stable under the present experimental conditions. The stabilizing effect of cellulases was tentatively explained using the DLVO (Derjaguin, Landau, Verweye, and Overbeek) theory. The adsorbed enzyme did not change significantly the zeta potential of the fibers; hence, the stabilizing effect was attributed to a reduction in the attractive van der Waals forces and hydration effects

Production and characterization of a new dextrin based hydrogel

Dextrin is a polymer composed of α-(1→4) D-glucose units produced by partial hydrolysis of starch. In this work, the transesterification of the soluble polysaccharide with vinyl acrylate (VA) was carried out in anhydrous dimethylsulfoxide (DMSO). The effect of the water activity and of the enzyme Proleather, on the reaction rates, was analysed. Different degrees of substitution (DS) ranging from ca. 10% to 70% were obtained by controlling the molar ratio of VA to dextrin. Gels were obtained by free radical polymerization of dextrin-VA, with different degrees of substitution and monomer concentration, in water. A comprehensive solid state-NMR analysis of the hydrogels was performed. These hydrogels are being developed as scaffold materials for bioactive molecule and cell delivery, tissue engineering and a variety of other biomedical applications

Development of a hybrid dextrin hydrogel encapsulating dextrin nanogel as protein delivery system

Dextrin, a glucose polymer with low molecular weight, was used to develop a fully resorbable hydrogel, without using chemical initiators. Dextrin was first oxidized (oDex) with sodium periodate and then cross-linked with adipic acid dihidrazide, a nontoxic cross-linking molecule. Furthermore, a new bidimensional composite hydrogel, made of oxidized dextrin incorporating dextrin nanogels (oDex-nanogel), was also developed. The oDex hydrogels showed good mechanical properties and biocompatibility, allowing the proliferation of mouse embryo fibroblasts 3T3 cultured on top of the gel. The gelation time may be controlled selecting the concentrations of the polymer and reticulating agent. Both the oDex and oDex-nanogel hydrogels are biodegradable and present a 3-D network with a continuous porous structure. The obtained hybrid hydrogel enables the release of the dextrin nanogel over an extended period of time, paralleling the mass loss curve due to the degradation of the material. The dextrin nanogel allowed the efficient incorporation of interleukin-10 and insulin in the oDex hydrogel, providing a sophisticated system of controlled release. The new hydrogels present promising properties as an injectable carrier of bioactive molecules. Both proteins and poorly water-soluble low-molecular-weight drugs are efficiently encapsulated in the nanogel, which performs as a controlled release system entrapped in the hydrogel matrix.V.C. and D.S. were supported by the grants SFRH/BD/27359/2006 and SFRH/BD/64571/2009, respectively, from Fundacao para a Ciencia e Tecnologia (FCT), Portugal. We thank FCT funding through PTDC and COMPETE