Surface modification of polysulfone based hemodialysis membranes with layer by layer self assembly of polyethyleneimine/alginate-heparin: A simple polyelectrolyte blend approach for heparin immobilization

This study intends to improve blood compatibility of polysulfone (PSF) membranes by generating a nonthrombogenic surface through heparin immobilization. To achieve this task, the support membrane prepared from a blend of PSF and sulfonated polysulfone (SPSF) was modified with layer by layer (LBL) deposition of polyethyleneimine (PEI) and alginate (ALG) and heparin blended with ALG was immobilized only on the outermost surface of the LBL assembly. The results have shown that the adsorption of human plasma proteins and platelet activation on the LBL modified membranes decreased significantly compared with the unmodified PSF and PSF-SPSF blend membranes. Furthermore, blending ALG with a small amount of heparin remarkably prolonged the APTT values of heparin free PEI/ALG coated membranes. It is envisaged that the use of a blend of HEP and ALG only in the terminating layer of the LBL assembly can be an economical and alternative modification technique to create nonthrombogenic surfaces

The effects of urease immobilization on the transport characteristics and protein adsorption capacity of cellulose acetate based hemodialysis membranes

In this study, cellulose acetate (CA) based hemodialysis membranes were prepared by a dry phase inversion method and the influences of urease immobilization on the clearing performance and protein adsorption capacity of the membranes were investigated. Permeation experiments have shown that modification of CA membranes with urease immobilization not only enhanced the transport rate of urea but also increased the permeation coefficients of uric acid and creatinine by changing the structure of the membrane. Furthermore, the protein adsorption capacity of the CA membranes decreased. On the other hand, the mechanical strength of the modified CA membrane did not change significantly compared with that of the unmodified one. A mathematical model was derived to determine the rate of mass transfer of urea through modified CA membranes. Model predictions along with the experimental data suggest that urease immobilization can be used as an alternative method in preparing CA based hemodialysis membranes with improved transport characteristics and biocompatibility through reduced protein adsorption capacities.İzmir Institute of Technology Grant 2005 İYTE 3

Development of antioxidant food packaging materials with controlled release properties

In this study, cellulose acetate (CA) films with different morphological features were prepared in order to control the release rates of low molecular weight natural antioxidants, L-ascorbic acid and L-tyrosine. Increasing CA content in the casting solution decreased the average pore size and porosity of the films, thus, reduced the diffusion rates of both antioxidants through the films. Although both antioxidants have similar molecular weights, L-tyrosine released into water much more slowly than L-ascorbic acid. The highest antioxidant activity in release test solutions was observed with highly porous L-tyrosine containing films. However, when the porosity of the films reduced, the antioxidant activity of L-ascorbic acid released into solution was found to be higher due to trapping of significant amount of L-tyrosine in dense films. The use of different antioxidants caused different changes in morphological and mechanical properties of the CA films. Varying the structural features of the films with the preparation conditions or using different surfaces of the films allowed the controlled release of each antioxidant. © 2009 Elsevier Ltd. All rights reserved

Preparation and characterization of polyacrylonitrile membranes modified with polyelectrolyte deposition for separating similar sized proteins

One of the challenges faced by ultrafiltration membranes is to separate proteins with a small difference in their molecular weights. Recently, some researchers tried to overcome this problem by using charged membranes. This study examined the use of layer by layer deposition of polyelectrolytes on the chemically-modified polyacyronitrile membrane to increase the selectivity of the ultrafiltration. The membranes were prepared by wet-phase inversion technique and polyethylenimine (PEI) and alginate (ALG) were chosen as cationic and anionic polyelectrolytes for the modification of the surfaces. Sieving coefficient data were obtained with myoglobin and lysozyme as model proteins. The influences of solution pH, ionic strengths of the protein and polyelectrolyte solution and the number of polyelectrolyte bilayers on both selectivity and throughput were investigated. The highest selectivity and throughput were achieved with the 1-bilayer PEI-ALG coated polyacrylonitrile (PAN) membrane. Increasing the number of coating bilayers or the ionic strength of the protein solution or adding salt into the polyelectrolyte coating solution decreased both the maximum selectivity and throughput of the modified membranes.Izmir Institute of Technology; 2009IYTE0

Novel low-fouling membrane bioreactor (MBR) for industrial wastewater treatment

A novel antifouling coating of ultrafiltration (UF) commercial membranes, based on a polymerisable bicontinuous microemulsion (PBM) technique, was developed and tested for the first time in a membrane bioreactor (MBR) using an artificial model textile dye wastewater and compared with a commercial uncoated UF membrane. The results showed that the commercial MBR module faced severe fouling problems whereas the novel coated PBM MBR module reduced the fouling significantly. The analysis of fouling rate using a resistance model confirms that PBM coated membrane has a higher antifouling effect. The antimicrobial properties of the PBM membrane contributed by polymerisable cationic surfactant acryloyloxyundecyltriethylammonium bromide (AUTEAB) guaranteed an anti-biofouling effect preventing the growth of microorganisms on the membrane surface. In addition, the PBM MBR module showed 10±1% higher blue dye removal efficiency and a similar rate of COD removal efficiency of about 95±1% compared to commercial module. However, water permeability was slightly lower due to extra resistance of the PBM coating. Root mean squared (RMS) roughness measurement and analysis of AFM images confirmed that the stable novel membrane coating still existed and showed antimicrobial effect even after 105 days of operation. The results obtained demonstrated the potential of the low fouling PBM membrane.European Union within BioNexGen project (CP-FP-246039-2 EU-FP7

Gelatin-based 3D conduits for transdifferentiation of mesenchymal stem cells into Schwann cell-like phenotypes

In this study, gelatin-based 3D conduits with three different microstructures (nanofibrous, macroporous and ladder-like) were fabricated for the first time via combined molding and thermally induced phase separation (TIPS) technique for peripheral nerve regeneration. The effects of conduit microstructure and mechanical properties on the transdifferentiation of bone marrow-derived mesenchymal stem cells (MSCs) into Schwann cell (SC) like phenotypes were examined to help facilitate neuroregeneration and understand material-cell interfaces. Results indicated that 3D macroporous and ladder-like structures enhanced MSC attachment, proliferation and spreading, creating interconnected cellular networks with large numbers of viable cells compared to nanofibrous and 2D-tissue culture plate counterparts. 3D-ladder-like conduit structure with complex modulus of ∼0.4 × 106 Pa and pore size of ∼150 μm provided the most favorable microenvironment for MSC transdifferentiation leading to ∼85% immunolabeling of all SC markers. On the other hand, the macroporous conduits with complex modulus of ∼4 × 106 Pa and pore size of ∼100 μm showed slightly lower (∼65% for p75, ∼75% for S100 and ∼85% for S100β markers) immunolabeling. Transdifferentiated MSCs within 3D-ladder-like conduits secreted significant amounts (∼2.5 pg/mL NGF and ∼0.7 pg/mL GDNF per cell) of neurotrophic factors, while MSCs in macroporous conduits released slightly lower (∼1.5 pg/mL NGF and 0.7 pg/mL GDNF per cell) levels. PC12 cells displayed enhanced neurite outgrowth in media conditioned by conduits with transdifferentiated MSCs. Overall, conduits with macroporous and ladder-like 3D structures are promising platforms in transdifferentiation of MSCs for neuroregeneration and should be further tested in vivo. Statement of Significance This manuscript focuses on the effect of microstructure and mechanical properties of gelatin-based 3D conduits on the transdifferentiation of mesenchymal stem cells to Schwann cell-like phenotypes. This work builds on our recently accepted manuscript in Acta Biomaterialia focused on multifunctional 2D films, and focuses on 3D microstructured conduits designed to overcome limitations of current strategies to facilitate peripheral nerve regeneration. The comparison between conduits fabricated with nanofibrous, macroporous and ladder-like microstructures showed that the ladder-like conduits showed the most favorable environment for MSC transdifferentiation to Schwann-cell like phenotypes, as seen by both immunolabeling as well as secretion of neurotrophic factors. This work demonstrates the importance of controlling the 3D microstructure to facilitate tissue engineering strategies involving stem cells that can serve as promising approaches for peripheral nerve regeneration.US Army Medical Research and Materiel Command (W81XWH-11-1-0700); Stem Cell Biology Fund; Stanley Endowed Chai

Layer-by-layer surface modification of poly(ether sulfone) membranes using polyelectrolytes and AgCl/TiO2 xerogels

In this study, the layer-by-layer (LbL) assembly method was employed to modify a commercial polyethersulfone (PES) membrane by successive adsorption of chitosan and alginate as cationic and anionic polyelectrolytes. To enhance anti-biofouling property, pure, PEG mixed and PEGylated AgCl/TiO2 xerogels were incorporated solely in the top layer of the LbL-modified membranes. Organic and biological foulings were addressed separately using alginate and Escherichia coli bacteria suspensions as the organic and biological model foulants, respectively. LbL-modifying the commercial PES membrane successively with chitosan and alginate polyelectrolyte multilayers prevented organic fouling extensively. In addition, we found that AgCl/TiO2-incorporated membranes show higher water permeability and improved resistance to biological fouling as compared to the PES membrane. Silver amounts in consecutively collected permeate samples were quantified by ICP-MS analysis to assess the stability of AgCl/TiO2-incorporated layers. Silver loss per filtration cycle followed an increasing trend initially, up to a filtration volume totaling 3000L/m2, leading to 4.2% reduction in the immobilized silver amount. After that, silver loss per filtration cycle stabilized at ~7.44μg/L, which extrapolates to ~265 days time-span for the remaining silver to be released at a filtration rate of ~1000L/m2 h. Antibacterial activity tests showed that AgCl/TiO2-incorporated layers do not permit bacterial growth on the membrane surface.European Union (246039

Modeling the drug release from hydrogel-based matrices

In this work the behavior of hydrogel-based matrices, the most widespread systems for oral controlled release of pharmaceuticals, has been mathematically described. In addition, the calculations of the model have been validated against a rich set of experimental data obtained working with tablets made of hydroxypropyl methylcellulose (a hydrogel) and theophylline (a model drug). The model takes into account water uptake, hydrogel swelling, drug release, and polymer erosion. The model was obtained as an improvement of a previous code, describing the diffusion in concentrated systems, and obtaining the erosion front (which is a moving boundary) from the polymer mass balance (in this way, the number of fitting parameters was also reduced by one). The proposed model was found able to describe all the observed phenomena, and then it can be considered a tool with predictive capabilities, useful in design and testing of new dosage systems based on hydrogels