Controlled drug release by the pore structure in polydimethylsiloxane transdermal patches

The use of polydimethylsiloxanes (PDMS) as a drug carrier in transdermal adhesive patches is limited and there is insufficient data on the polymer structure and diffusivity, especially when additives modify the matrix. PDMS films with liquid additives (10% w/w): silicone oil (SO), polyoxyethylene glycol (PEG) or propylene glycol (PG) were prepared and indomethacin (IND; 5% w/w) was incorporated as a model active substance. The microstructure of the PDMS matrix and its permeability to water was investigated and correlated to the kinetics of the in-vitro IND release from the film. Three microscopic techniques were used to characterize in detail the microstructure of PDMS films: scanning electron microscopy, fluorescent microscopy and atomic force microscopy. PDMS films with hydrophilic PEG or PG showed different two-phase structures. A two-fold increase in steady-state flux of IND and increased water transport in the presence of PEG was attributed to the pore-like channels created by this polar solvent in the PDMS matrix. This effect was not observed in the films with PG, where only discontinuous droplet-like structures were visible. All additives significantly changed the tensile parameters of the films but the effects were not very pronounced

The importance of the molecular weight of ethyl cellulose on the properties of aqueous-based controlled release coatings

Previous investigations of aqueous based ethyl cellulose (EC) latex dispersions have mainly focused on the commercially available viscosity grade 20\ua0cps. In this study, dispersions of EC with varying viscosity grades (which correspond to molecular weights), ranging from 4 to 100 cps, were produced and characterised. The dispersions showed particle sizes around 200\ua0nm and highly negative ?-potentials (approx. ?100\ua0mV), which indicated stable dispersions as confirmed by sedimentation studies. The different latexes were used to produce free-standing film coatings. We hypothesised that the different viscosity grades of EC would result in different properties of the films. We found that an increase in viscosity grade (and higher molecular weight) resulted in lower coalescence between the particles during film formation and thus to higher water permeability than in film coatings of lower molecular weight. After exposure to water the EC 4\ua0cps and 20\ua0cps film coatings had a more porous structure in the side facing the air during production and drying after immersion in water. Molecular weight is therefore a factor that should be considered when producing pharmaceutical coatings for controlled release

Preparation of cellulose-based sponges for wound dressing and healing

For healing of chronic or burn wounds, polymeric sponges have been recently applied. Due to a high absorption capacity, noncitotoxicity and good swelling capabilities, for their production natural polymers are often used. In this study, macroporous regenerated cellulose was evaluated as a matrix for wound dressing materials. Active compounds, such as antibiotic neomycin and phenolic compound quercetin were immobilized in the cellulosic matrix aimed to promote wound healing process. Active compounds in the sponges were immobilized alone or with water-soluble hydroxyethylcellulose or carboxymethylcellulose. It was found that the way of preparation of sponges can affect their porosity, moisture absorption and drying rate. The best sponges for wound dressing materials were formed from freeze-dried macroporous regenerated cellulose in which was later immobilised hydroxyethylcellulose or carboxymethylcellulos with active compounds

Mathematical modelling of the drug release from an ensemble of coated pellets

Background and Purpose: Coated pellets are widely used as oral drug delivery systems, being highly accepted by patients and with several advantages compared to single unit devices. However, their behaviour needs to be elucidated so as to improve the effectiveness of the formulations and reduce production costs. In spite of this important issue, few mathematical modelling studies have been attempted, mostly due to the complexities arising from the system's polydispersity (non-homogeneous multiple-unit particulate systems), which has been scarcely investigated using mechanistic models. Experimental approach: A mechanistic mathematical model was developed that was able to describe the single pellet behaviour in terms of hydration, drug dissolution, diffusion and release and particle size. This model was then extended to describe and predict the behaviour of mono- and polydispersed ensembles of pellets. Key Results: The polydispersity arising from the size and distribution of the inert core was shown to have a minimal effect on the drug release profile, whereas the thickness and distribution of the polymeric film was found to be the key parameter determining the drug release. Conclusions and Implications: The mechanistic model developed, which is capable of determining the polydispersity of the drug delivery system, was able to predict the release kinetics from ensembles of pellets and to highlight the key parameters that need to be controlled in the production of pellet-based drug delivery systems, demonstrating its use as a powerful predictive tool

Characterization of cellulose based sponges for wound dressings

Cellulose based sponges were developed by freeze-drying of regenerated cellulose gels and characterizedas a potential wound dressing. Morphological characteristics were analyzed by means of micro-computedtomography. The results showed that the porosity of the sponges reached 75%, the pores were inter-connected and their size ranged from 10 to 1200 m with a mean pore diameter of 750 m. Due tohydrophilicity of cellulose and high specific surface area (14.5 mm2/mm3) the sponges possess highsorption of simulated wound fluids (approx. 210%) and high water vapour transmission ability. Dif-ferent active compounds, such as polyphenols from Calendula officinalis or Chamomilla recutita extracts(1 day diffusion experiment), silver nanoparticles (1, 2 and 4 days diffusion experiments) were immo-bilized into the sponges in order to improve wound dressing performance. Release kinetics of silvernanoparticles and polyphenols from the sponges were investigated. The sponges incorporated with sil-ver, showed antibacterial activity against Staphylococcus epidermidis. Thus, these cellulose based spongesare promising wound dressing materials for fester and infected wounds

Determination of the release mechanism of Theophylline from pellets coated with Surelease®—A water dispersion of ethyl cellulose

The aim of this study was to investigate the water transport over free standing films based on the aqueous ethyl cellulose (EC) coating Surelease®and the drug (Theophylline) release mechanism from coated pellets. It was found that the main drug release rate from pellets was controlled by a diffusion mechanism. However, the drug release rate was altered by addition of sodium chloride to the external release medium. A decrease in the drug release rate when sodium chloride is added to the release medium has traditionally been used to indicate an osmotic drug release mechanism. However, our findings that the release rate decreased by sodium chloride addition could be explained by sodium chloride diffusing through the coating layer into the inner parts of the pellets, decreasing the solubility of Theophylline. This gave a reduced drug concentration gradient over the coating layer and thus a slower release rate. Furthermore, this study shows, as expected, that the transport of water through Surelease®films into the pellets was faster than the transport out of Theophylline (approx. seven times), which was the reason why the pellets were swelling during the release. It was also shown that the drug release rate, determined for both whole dose release and for single pellets, decreased with increasing thickness (from 16 to 51 μm) of the coating layer controlling the drug release rate