Resumen de Development and characterization of bioartificial polysulfone membranes for proton transport applications
Proton-exchange membrane fuel cells (PEMFCs) are promising technology as clean and efficient power source in the twenty-first century. Essential characteristics of those materials are high ion conductivity and selectivity, very good chemical and thermal stability, good mechanical properties and low production cost. One of the strategies for development of such membranes is design of bioinspired materials. Those materials are composed of biological and non-biological component, what connects the advantages of artificial polymeric films with biofunctionality of proteins. Nevertheless biomolecule immobilization is a challenging task, due to incompatibilities with polymer or lose of protein’s biological activity.
The aim of this work was to develop a material combining robustness of polymer and bioactivity of protein. Polysulfone is known from its outstanding chemical, thermal and mechanical stability, and moreover, it was proved to be compatible with many biological components. Those characteristics, together with possibility of functionalization and facility in films preparation, make it to be a good base material for creation of bioartificial membrane. Gramicidin is a biological membrane ion channel, known from fast and selective transport of monopositively charged ions. Its transport properties studied also at elevated temperatures suggests its applicability in fuel cells applications.
Two different strategies for protein attachment: physical and chemical immobilization. Physical immobilization is considered to be a good strategy of protein immobilization, without affecting of their biofunctionality. Nevertheless, chemical attachment is stronger and prevent protein detachment. In this dissertation, two physical immobilization methods and one chemical immobilization method were evaluated. First, physical method was immobilization via entrapment, which consist of direct protein insertion into the polymeric matrix. The second method, was physical immobilization with use of magnetite nanoparticles, which consist of Surfactant/Gramicidin micelles formation and their immobilization on nanoparticles immersed in a membrane film. The chemical immobilization method was performed via glutaraldehyde coupling, which is known as a good method for covalent attachment of biomolecules to the artificial materials.
Accurate characterization of membrane is important to describe and understand occurring transport phenomena and is essential for further process optimization and material improvement. In this thesis, obtained membranes were characterized in terms of morphology, interaction with water and transport properties. Moreover, Surfactant/Gramicidin micelles were examined in terms of their biological activity and thermophysical properties. Experimental results were analysed by means of statistical analysis. Additionally, ion permeability results were evaluated in terms of agreement with the Nernst-Einstein model.
The membrane system proposed herein have a potential to be used as ion exchange membranes, because its design combines the good mechanical properties of polysulfone and the selective ionic transport properties of Gramicidin. Moreover, the presented method intend to deliver a quick and easy way of membranes production, possibly easy to scale up. In this dissertation we present design and characterization of polysulfone membrane containing Gramicidin, immobilized via three strategies: two physical and one chemical method. Results show that influence of protein immobilization on membrane morphology was minimized. Immobilized protein changes hydrophobic and water swelling properties of the membrane (decrease of CA up to 25.2º and increase of water uptake up to 1.28 mg of water per mg of membrane). Physical protein immobilization by entrapment method does not improve membrane transport properties. Physical immobilization with use of magnetite nanoparticles and chemical immobilization via glutaraldehyde coupling improves ion transport properties (decrease of Ohmic resistance from 1366 Ω•cm2 to 373 after physical immobilization, and to 455 Ω•cm2 after chemical immobilization in the case of H+ transport, and increase of H+ diffusion rate from 7.02E-04 to 7.89E-03 cm2s-1 in the case of physical immobilization and from 2.23E-03 to 7.53E-03 cm2s-1 in the case of chemical immobilization). The use of magnetite nanoparticles in the membrane resulted in remarkable proton conductivity, in the range of 10-2 to 10-3 S/cm. Also, the influence of preparation solution was evaluated. For membranes containing –OH and–NH2 functionalized nanoparticles protein immobilization performed is more effective when performed in water and PBS respectively. Chemical immobilization is more effective when prepared in PBS buffer solution. The best performance in terms of ion transport selectivity was presented by the MNP-OH membranes with Gramicidin immobilized physically, which exhibit also the highest conductivity (0.71 S/cm for H+). The highest diffusion permeability values was obtained for the membrane with chemically immobilized Gramicidin, prepared in PBS buffer solution (0.009 cm2/s for Na+) which has also relatively high conductivity (0.45 S/m for H+) and good selectivity values. Biological activity trial shows that Gramicidin maintains its antibacterial properties when the methanol is present in preparation solution. Micelles composed of surfactant Triton X100 and Gramicidin are biologically active in both, solution and immobilized on a membrane surface. Membranes with immobilized micelles have higher resistance to bacteria growth.
