Microporous Foam Research Articles

Multiple unit gastroretentive drug delivery systems: A new preparation method for low density microparticles

The aim of this study was to develop a new preparation method for low density foam-based, floating microparticles and to demonstrate the systems' performance in vitro. Major advantages of the novel preparation technique include: (i) short processing times, (ii) no exposure of the ingredients to high temperatures, (iii) the possibility to avoid toxic organic solvents, and (iv) high encapsulation efficiencies close to 100%. Floating microparticles consisting of polypropylene foam powder, model drug [chlorpheniramine maleate (CPM), diltiazem HCl, theophylline or verapamil HCl] and polymer [Eudragit RS or polymethyl methacrylate (PMMA)] were prepared by soaking the microporous foam carrier with an organic solution of drug and polymer and subsequent drying. The effects of various formulation and processing parameters on the resulting in vitro floating behaviour, internal and external particle morphology, drug loading, in vitro drug release and physical state of the incorporated drug were studied. Good in vitro floating behaviour was observed in most cases and a broad variety of drug release patterns could be achieved by varying the drug loading and type of polymer. Interestingly, PMMA-based microparticles showed incomplete drug release with verapamil HCl. This restriction could be overcome by forming the free base of the drug prior to microparticle preparation. In contrast to the salt, the free base acted as a plasticizer for PMMA, resulting in sufficiently high diffusion coefficients and, consequently, complete drug release. The low density microparticles were compressed into rapidly disintegrating tablets in order to provide an administrable oral dosage form.

Multiple unit gastroretentive drug delivery systems: a new preparation method for low density microparticles.

The aim of this study was to develop a new preparation method for low density foam-based, floating microparticles and to demonstrate the systems' performance in vitro. Major advantages of the novel preparation technique include: (i) short processing times, (ii) no exposure of the ingredients to high temperatures, (iii) the possibility to avoid toxic organic solvents, and (iv) high encapsulation efficiencies close to 100%. Floating microparticles consisting of polypropylene foam powder, model drug [chlorpheniramine maleate (CPM), diltiazem HCl, theophylline or verapamil HCl] and polymer [Eudragit RS or polymethyl methacrylate (PMMA)] were prepared by soaking the microporous foam carrier with an organic solution of drug and polymer and subsequent drying. The effects of various formulation and processing parameters on the resulting in vitro floating behaviour, internal and external particle morphology, drug loading, in vitro drug release and physical state of the incorporated drug were studied. Good in vitro floating behaviour was observed in most cases and a broad variety of drug release patterns could be achieved by varying the drug loading and type of polymer. Interestingly, PMMA-based microparticles showed incomplete drug release with verapamil HCl. This restriction could be overcome by forming the free base of the drug prior to microparticle preparation. In contrast to the salt, the free base acted as a plasticizer for PMMA, resulting in sufficiently high diffusion coefficients and, consequently, complete drug release. The low density microparticles were compressed into rapidly disintegrating tablets in order to provide an administrable oral dosage form.

Clariant Masterbatches expands foaming agent family

Soft rubber foams like poly(ethylene-co-vinyl acetate) (EVA) are industrially applied in a broad range of products, including sports gear, insulation materials and drug delivery systems. In contrast to glassy polymers, few studies in literature concern the foaming of soft rubbers using supercritical carbon dioxide. In this study, open microporous matrices of EVA have been formed with CO2. Prior to the foam expansion, sorption and swelling isotherms of CO2 in EVA have been measured and the obtained isotherms have been correlated using the Sanchez–Lacombe equation of state. Additionally, a pressure-independent diffusion coefficient of CO2 in EVA has been obtained from these experiments. The microporous foams have been formed by a pressure quench of the CO2-swollen polymer matrix. Sorption pressure as well as temperature and decompression times appear to determine the pore size and bulk density of the foam. These parameters allow for a control of the foam structure of EVA rubbers.

Transfer Reaction to Solvents in Free-Radical Polymerisation of Some Acrylate Monomers and Its Effect on Foam Density

One method of production of low-density polymeric foams is to dissolve a monomer and a photo-initiator in a solvent and to polymerise by means of free radical polymerisation. The gel produced is precipitated in a non-solvent and subsequent super critical drying produces a low-density micro-porous foam. In some cases, the observed densities of the foam were significantly higher than expected. There is evidence to believe that this could be due to a chain transfer reaction to the solvent used in polymerisation.

Preparation of A Low Density Polymer Foam with Dopants

Low density microcellular foams containing dispersed high atomic number material have been produced. The work done by R. Simandl et al., using phase inversion of a binary solvent system and poly (4-methyl 1-pentene) to produce microporous polymer foams was successfully duplicated. 1 To enhance the diagnostic properties of the material, molybdenum, a high Z material, was dispersed throughout the foam. We have been able to incorporate the molybdenum into the foam structure while maintaining a relatively low bulk density. Foam samples with initial molybdenum concentrations up to 25 wt % and with bulk densities as low as 15 mg/cc have been produced. The uniformity of the molybdenum dispersion has not yet been quantitatively characterized but does vary from sample to sample.

Low surface energy polymers and surface-active block polymers: II. Rigid microporous foams by emulsion polymerization

Block polymerization of different weight ratios of 2-( p-t-butylphenyl)-2-oxazoline (B) and 2-ethyl-2-oxazoline (E) with methyl p-nitrobenzenesulfonate as the initiator gave diblock co-oligomers with narrow molecular weight distributions in 100% yields. Co-oligomers with 40–50 wt% of B were excellent inverse emulsifiers for styrene/water ( St W ) polymerization: water-in-oil solid emulsions with internal phase ratios as high as 90% have been obtained using small amounts of the oligomers (⩾1 wt% of the total system). The total surface area of the water droplets is approximately proportional to the number of surfactant molecules, and thus the average pore diameter is proportional to the water volume divided by the surfactant concentration. For any given St W volume ratio, there is a maximum amount of emulsifier which can produce stable solid foams; higher amounts cause the emulsions to break.