Silicone microparticles for drug delivery applications

Drug delivery systems aim to provide safe and efficient delivery of drugs. One category of drug delivery systems is microparticles which have versatile properties. Large surface to volume ratio enhances solubility of loaded drug. Due to small size, microparticles can be administered locally. In addition, microparticles keep loaded drug safe from degradation until the drug is released to the surrounding tissue. Properties of microparticles can be greatly modified by altering their composition material, morphology and size. Due to these properties, microparticles may improve bioavailability of poorly soluble drugs, enable administration of easily degraded drugs, reduce dosing frequency and increase patient compliance. This research focuses on production of porous and non-porous polydimethylsiloxane (PDMS) microparticles via single and double emulsions which are made by stirring. PDMS was chosen as a composition material for the microparticles due to its biocompatibility, biostability and ability to control permeability of the drug through its polymer network. The results of the study show that the size of emulsion droplets can be decreased by increasing the stirring speed and the size distribution of droplets can be narrowed by increasing the stirring time. Aqueous solutions of surfactants and glycerol were tested as continuous phases to stabilise emulsion droplets showing that glycerol stabilises droplets more effectively. Thermal and UV-light crosslinkable PDMSs were tested. UV-light induced crosslinking is shown to be more suitable in the emulsion methods due to rapid crosslinking at lower temperatures. Produced microparticle batches via the single emulsion method had the mean size of 7.4 – 4.6 µm and coefficient of variance of 43 % at the lowest case. In double emulsion method, methylene blue as a model compound is entrapped into PDMS microparticles. To enable release of larger drug molecules e.g., peptides or proteins polyethylene glycol 300 (PEG 300) was used as porogen in preparation of PDMS microparticles. Formation of pores was confirmed by scanning electron microscopy (SEM).