Transdermal timolol delivery from a Pluronic gel

In this work, the transdermal timolol (TM) delivery from a Pluronic F127 (PL) gel reservoir was investigated. Both gel concentration and the artificial membrane are used to regulate the TM delivery through pig stratum corneum (SC). At low PL concentrations and for high pore size membranes, the SC mainly controls the TM delivery. At high PL concentrations and for low pore size membranes, the contribution of the system (gel + artificial membrane) to the TM delivery becomes significant

Insight into the transport of hexane-solute systems through tailor-made composite membranes

This work presents composite membranes comprising poly(acrylonitrile) (PAN) as the support and polydimethylsiloxane (PDMS) as the selective top layer. For sunflower oil/hexane and polyisobutylene (PIB)/hexane, the permeation characteristics of these membranes for various feed concentrations and pressures are studied. For each system, the effect of transmembrane pressure upon the flux and retention of the PAN/PDMS composite membrane is investigated. Osmotic phenomena similar to those of aqueous systems are observed and interpreted using the van¿t Hoff equation. The hexane flux increases linearly with the applied pressure and the solution-diffusion model seems to describe satisfactory the aspects of its transport to these systems. The hexane permeability decreases with the increase of the feed concentration. Its normalization by the viscosity inside the swollen membrane (according to the Stokes¿Einstein diffusion phenomenon) and the swelling degree of the membrane results in a constant value quantifying the hexane transport independent of the solute present in the feed mixture. The flux of the solute (oil or PIB) increases linearly with the applied pressure as well, especially at low feed concentrations when the membrane swelling is higher, indicating coupling of solute transport to solvent flux. For the same feed solution concentration, the effect of flux coupling (solvent-induced solute dragging) decreases with the molecular weight of the solute. Ultimately, when the applied pressure increases; the increase of hexane flux is much higher than the corresponding solute (oil or PIB) flux resulting to an increase of the membrane retention

Effect of PDMS cross-linking degree on the permeation performance of PAN/PDMS composite nanofiltration membranes

This work focuses on the effect of poly(dimethyl siloxane) (PDMS) cross-linking on the permeation performance of the poly(acrylonitrile) (PAN)/PDMS nanofiltration (NF) composite membrane. PDMS membrane of various cross-linking degrees could be obtained by changing the ratio of a vinyl-terminated pre-polymer over a hydride cross-linker, 10/0.7, 10/1 and 10/2.\ud \ud The hexane permeability (Phexane) through the PAN/PDMS composite membrane prepared at pre-polymer/cross-linker ratio of 10/0.7 is higher than at ratio of 10/1 (4.5 and 3.1 lm¿2 h¿1 bar¿1, respectively), due to the higher membrane swelling. The Phexane through the PAN/PDMS prepared at pre-polymer/cross-linker ratio of 10/2 is however higher than through the composite membrane prepared at 10/1 ratio (4.1 and 3.1 lm¿2 h¿1 bar¿1). This result is not consistent with the swelling findings of the dense, free-standing PDMS membranes and might be due to the lower pore intrusion of the composite membrane prepared at ratios of 10/2 compared to 10/1 and/or due to the heterogeneous quality of the silicone network. The ¿apparent¿ viscosity inside the membrane and the membrane swelling are the most critical factors affecting the hexane permeability through all composites. Nevertheless, the composite membranes prepared at various pre-polymer/cross-linker ratios have similar oil and/or PIB retention probably due to the high swelling of the silicone network

Delivery of timolol through artificial membranes and pig stratum corneum

The in vitro passive and iontophoretic (applied current density: 0.5 mA/cm2) timolol (TM) permeability from a liquid solution through pig stratum corneum (SC) is found to be 0.9 ± 0.5 × 10-6 and 3.9 ± 0.9 × 10-6 cm/s, respectively. The in vitro iontophoretic TM delivery through the combination of artificial porous membranes with pig SC is investigated as well. When the meso-porous PES-30 membrane is applied, the SC mainly controls the TM delivery. When the microporous NF-PES-10 membrane is applied, both the membrane and the SC contribute to controlling the delivery of TM. When the microporous LFC 1 membrane is applied, the TM delivery is membrane controlled. In all cases, however, the efficiency of the TM delivery is low and would need to be improved for the development of a commercially viable product

Controlled transport of timolol maleate through artificial membranes under passive and iontophoretic conditions

The passive and iontophoretic permeability of timolol maleate (TM) through porous and dense artificial membranes was investigated in order to select the most optimal membrane for a transdermal drug delivery system. For the meso-porous membranes (pore diameter 2–50 nm), the TM permeability for passive diffusion and iontophoresis was practically the same. For the micro-porous membranes (pore diameter<2 nm), a significant transport contribution of iontophoresis was observed, which was more pronounced when higher current densities were applied. The electrical resistance of all the porous membranes was lower than the electrical resistance of human skin. For dense membranes, passive and iontophoretic TM permeability was significantly lower than for porous membranes and in most cases their electrical resistance was comparable or even higher than the resistance of human skin. For most of the membranes studied the average adsorption of TM at 37 °C was low (0.02–0.33 mg/cm2) and independent of the TM concentration. For the meso-porous mixed cellulose acetate–cellulose nitrate membrane the TM adsorption was significantly higher and increased with the TM concentration. Based on our results, the optimum membrane for an iontophoretic transdermal TM delivery system is the LFC 1 micro-porous membrane because it mainly controls the TM delivery (TM iontophoretic permeability: 0.86×10−6 cm/s), has very low electrical resistance (0.9–1.5 kΩ cm2) and the TM adsorption to it is low (0.15 mg/cm2). The therapeutic plasma TM concentration is achievable by application of this membrane in realistic sizes (5–64 cm2) and by application of current densities between 0.13 and 0.5 mA/cm2

Role of membrane surface in concentration polarization at cation exchange membranes

Cation exchange membranes made of blends of sulphonated polyetherether ketone (S-PEEK) and poly(ether sulphone) (PES) were thoroughly characterized with respect to their concentration polarization properties. Current¿voltage curves and chronopotentiometry reveal some extent of membrane heterogeneity. Membranes cast on a glass plate and dried in air are characterized and the current¿voltage curves are determined for each of the two membrane sides (glass side contact and air side contact). Detailed analysis of the plateau length at the limiting current density reveals differences as the orientation of the membrane towards the feed is changed. The plateau length of the air side of the membrane always shows larger values compared to the glass side. Moreover, we discovered that the plateau length of the glass side remains constant whereas the air side value increases over a period more than 500 h approaching a quasi-equilibrium value, asymptotically. These data are the first ones suggesting an influence of orientation on the concentration polarization behavior as well as relaxation phenomena occurring in cation exchange membranes. The paper discusses strategies to gain new fundamental insight in the relationship between membrane morphology and transport properties by for instance microstructuring the surface