A multi-scale theoretical paradigm to model the complex interactions between macromolecules and polymeric membranes membranes

Abstract

The overall aim of the work was to provide a complete Multiscale Model of macromolecules interactions to simulate different processes and bioprocesses where such interactions, among different macromolecules and between macromolecules and polymeric surface, strongly determine the system behaviour. The adsorption of proteins on material surfaces is an essential biological phenomenon in nature, which shows a wide application prospect in many fields, such as membrane based processes, biosensors, biofuel cells, biocatalysis, biomaterials, and protein chromatography. Therefore, it is of great theoretical and practical significance to study the interfacial adsorption behaviour of proteins and their structuration and aggregation in order to describe concentration polarization phenomena in separation processes. It is worthwhile remarking that ab-initio simulations allow the estimation of parameters without exploiting any empirical or experimental methodology. In the present work, an improved multiscale model aimed at describing membrane fouling in the UltraFiltration (UF) process was proposed. The proteins-surface interactions were accurately computed by first-principle-based calculations. Both the effective surface of polysulfone (PSU) and the first layer of proteins adsorbed on the membrane surface were accurately modelled. At macroscopic scale, an unsteady-state mass transfer model was formulated to describe the behaviour of a typical dead-end UF process. The adsorption of an enzyme, i.e. the phosphotriesterase (PTE), on polysulfone (PSU) membrane surface was investigated as well through a double-scale computational approach. The results of such a formulated model were useful to obtain a detailed knowledge about enzyme adhesion and to give precise indications about the orientations of its binding site. One of the most important challenges is to use the stochastic approach adding an improved nano- and micro-scale step to the well-established multiscale procedure. The implementation of a Monte Carlo algorithm was performed with the aim of investigating the fouling structure during membrane operation like different micro-equilibrium states. The final aim of the work was to carry out the calculation of both Osmotic Pressure and Diffusion Coefficient in the fouling cake by the already-performed Monte Carlo simulations. Furthermore, the so-obtained parameters were exploited in macroscopic CFD simulations so as to calculate the overall resistance of the deposit accumulated on membrane surface during filtration.