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Séminaire de Anette Larsson

Mass transport through microstructured mixed ethylcellulose and hydroxypropylcellulose films – a project within SuMo BIOMATERIALS


Mass transport through microstructured mixed ethylcellulose and hydroxypropylcellulose films – a project within SuMo BIOMATERIALS

Anette Larsson

Chalmers University of Technology, Gothenburg, Sweden

SuMo BIOMATERIALS is a competence center focusing on mass transport in porous biomaterials. Mass transport is a key factor behind many applications like swelling of hydrogels, drug release, drying of paint films, etc. Within the center new methods to measure mass transport and methods to predict structures and mass transport rates are developed. The combination of mass transport measurements and predictions opens for design of new materials with tuned mass transport properties.
The way of working within SuMo will be exemplified by the release of metoprolol succinate from film coated pellets, a process which involves several interesting mass transport phenomena. For example, during the coating step the solvent (ethanol) is transported to the surface of the wet coating and evaporates. This leads to a gradual increase in the concentration of the remaining components, ethylcellulose (EC) and hydroxypropylcellulose (HPC). At a certain concentration the polymers start to phase separate, following the spinodal decomposition mechanism, into domains rich in EC or HPC. At higher polymer concentrations the viscosity increases, which leads to a decrease in the transport rate of the polymers. The final microstructure in the dry film depends on the mass transport processes taking place during the coating step, where both the mass transport rate of the solvent and the transport of the polymers during the coating step are essential.
After immersion of the EC/HPC film into an aqueous medium water will be transported into the film and the HPC phases will swell, dissolve and leach out. This transport causes formation of pores and these pores will determine the drug release rate. Therefore, since the phase separation is depending on the molecular weight of the polymers, the drug release can be controlled by the choice of the polymers.
A method to predict the mass transport through the porous film was also developed and can be used for further fine tuning of the drug release rate.