Microparticles for oral delivery and cell encapsulation using membrane emulsification
thesisposted on 17.11.2017 by Serena Morelli
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
Microparticles have been extensively investigated for pharmaceutical applications, more specifically they have been widely applied as carrier of drug molecules, proteins, enzymes, DNA and cells. In this work, the Membrane Emulsification (ME) technique was employed for the manufacturing of uniform sized emulsions with predictable drop size. The liquid drops produced were, in a second step, converted to microparticles. ME is a process which consists in pressing the dispersed phase through the micropores of a membrane into the emulsion continuous phase. The investigation of the best operating conditions of emulsion production, the emulsion composition and the optimization of the formulations for the production of microparticles using the technique of ME were the aim of this thesis work. For the preliminary tests the Dispersion Cell system (lab-scale device) was used with nickel or stainless steel microengineered disk membranes with cylindrical pores. W/O emulsions were mainly produced. During the process of emulsion production the main parameters studied were the shear stress applied, the dispersed phase flux, the membrane type and the emulsifier type. The use of a simplified model based on a force balance was used for the drop size prediction. The maximum shear stress reached is used for the calculations. It was shown that the model gave a more accurate drop diameter prediction when the flux of the dispersed phase is low. For the solidification of the polymeric drops a reaction of (chemical or ionic) crosslinking or a physical method (thermal gelation) was employed. Influence of the solidification process was evaluated on the final product. The most important factors affecting the process of particles formation studied were the type of crosslinker used together with its concentration and the reaction time. It was shown that the crosslinking reaction is directly affecting the properties of the final product: the capability of the particles to swell in an aqueous media, the pH sensitivity of the material, the release rate of an encapsulated model compound. The microparticles produced were loaded with copper, sodium salicylate and Blue Dextran as model molecules and yeast as probiotic cells. The release was assayed with time and, accordingly with the application, in acidic (pH= 1.2- 3), neutral (pH= 7- 7.3) or basic (pH= 8) environment. Formulations were optimized to achieve a sustained release (using Poly (Vinyl) alcohol (PVA) as polymeric material), a release into the stomach acidic environment (using PVA blended with chitosan (CS)), a release (of probiotics) in the intestine- colon area having III a neutral- basic environment (using gelatine coated microparticles) or for cells immobilization (using alginate as polymeric matrix). The technique of ME was evaluated as a novel method for cell encapsulation, the use of membranes with the appropriate pore size led to the generation of drops containing cells and possible occurrence of cell filtration by the membrane was prevented. In order to demonstrate the cell survival to the encapsulation process, tests of the released yeast capability to metabolize glucose with time and cells dyeing with fluorescent probes were performed. For an industrial application of the process of microparticles production using ME, the Dispersion Cell was substituted by the Pulsed (Oscillatory) Flow system. The use of this device presents some advantages for the process scale up as the manufacturing of emulsions with a high dispersed phase concentration (emulsions concentrated up to 30% were successfully produced) with a single pass through the membrane module and possibility to solidify the drops right after their production. The operating parameters of the process were investigated for the production of W/O emulsions using this system, furthermore the possible application of a differently coated (FAS coated) membrane (instead of the classical PTFE coated) was evaluated for multiple uses.
- Aeronautical, Automotive, Chemical and Materials Engineering
- Chemical Engineering