Hendrikus H.M. Rolevink

Preparation of asymmetric gas separation membranes with high selectivity by a dual-bath coagulation method

A new method for the preparation of gas separation membranes in a one-step procedure is presented, where common, non-volatile solvents can be used in the polymer solution. It concerns contacting of a polymer solution with two successive nonsolvent baths, whereby the first bath initiates the formation of a dense top layer and the second bath gives the actual polymer precipitation. Membranes made by this method will have high gas selectivity and do not need any additional coating. The new technique was used to make polyethersulfone (PES) hollow fibres from solutions consisting of 35% (w/w) polymer and 10% glycerol in N-methylpyrrolidone (NMP). High selectivities were obtained when using glycerol or 1-pentanol as the first nonsolvent and water as the second one. For a feed gas of 25 vol.% of CO2 in methane the intrinsic selectivity of PES [alpha (CO2/CH4) = 50] was easily obtained, without the necessity of an additinal coating step. By a step-wise, liquid exchange removal of residual fluids in the fibres, an improvement in flux could be obtained. This was accompanied by a somewhat lower selectivity compared to that of directly air-dried fibres.

Stabilization of supported liquid membranes by interfacial polymerization top layers

In this paper, a new method of stabilizing supported liquid membranes is presented. The stabilization is based on the application of polymeric top layers to the surface of microfiltration membranes, preventing loss of the liquid membrane phase out of the support pores. The modified microfiltration membranes were used as supports for supported liquid membranes and tested on selective nitrate transport and stability. Screening experiments revealed that most applied top layers did not hinder the transport of nitrate ions. However, a few were able to improve the stability of the liquid membranes. Best results were obtained when piperazine (PIPA) and trimesoyl chloride (TMCl) were used as monomers. For Accurel polypropylene supports with PIPA/TMCl top layer, nitrate flux was constant at the initial 18 × 10−10 mol cm−2 s−1 for 350 h of simulated operation. For uncoated supported liquid membranes (SLMs), the flux decreased within one day from 18 × 10−10 to almost 0 mol cm−2 s−1. Scanning electron microscopy investigations revealed a particular, rippled surface texture of layers prepared with these monomers.

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 degrees C was low (0.02-0.33 mg/cm(2)) 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 x 10(-6) cm/s), has very low electrical resistance (0.9-1.5 komega cm(2)) and the TM adsorption to it is low (0.15 mg/cm(2)). The therapeutic plasma TM concentration is achievable by application of this membrane in realistic sizes (5-64 cm(2)) and by application of current densities between 0.13 and 0.5 mA/cm(2).

Hollow-fiber-supported liquid membranes with improved stability for nitrate removal

This paper describes the development of a hollow-fiber-supported liquid membrane (HFSLM) for the removal of nitrate ions from water. Two different membrane modules were designed which differed in length of the fibers. In order to test the HFSLMs on nitrate flux and stability, two set-ups were used: one in which feed and strip were recirculated, and one for the continuous removal of nitrate. Furthermore, part of the experiments were carried out using fibers with a toplayer of piperazine and trimesoyl chloride at the lumen side to increase the stability of the HFSLM. Nitrate fluxes of the HFSLMs were only slightly lower than those of flat-sheet SLMS despite the much larger thickness of the fiber wall. In both set-ups, the nitrate flux decreased in time. By applying a toplayer on the lumen side of the fibers, the lifetime of the liquid membrane was raised. SEM observations showed the toplayer, although defect-free, to be nonuniform in morphology, which resulted in difficulties in the reproducibility of the results.

Passive and Iontophoretic Controlled Delivery of Salmon Calcitonin Through Artificial Membranes

The development of a transdermal delivery system for drug molecules of high molecular weight (peptides or proteins) is nowadays a great scientific and commercial challenge. For these molecules, the passive transport through the skin is generally very low and should be enhanced by the application of the electrical current (a method called iontophoresis). A very important component of a transdermal iontophoretic system is the artificial membrane, which acts as the interface between the drug reservoir and the skin. The optimum membrane should (i) provide an effective drug delivery; (ii) have low electrical resistance and (ii) have low drug adsorption. In this work, the selection of membrane(s) for a transdermal iontophoretic salmon calcitonin (sCT, MW approximately 3500) system is performed. The passive and iontophoretic transport of sCT through porous artificial membranes, the sCT adsorption to them and the electrical resistance of all porous membranes in iontophoretic experiments is studied. The sCT transport through the membranes is compared with that through human skin, and based on the above three criteria the optimum membranes are selected for the sCT transdermal system.

In Vitro Evaluation of a Hydroxypropyl Cellulose Gel System for Transdermal Delivery of Timolol

In this work, the development of a gel reservoir for a timolol (TM) transdermal iontophoretic delivery system is investigated. TM gel is prepared using hydroxypropyl cellulose (HPC) and the permeability of TM from the gel through an artificial membrane (Polyflux) and pig stratum corneum (SC) is studied. For a constant TM donor concentration, the TM transport across the Polyflux membrane alone decreases when the concentration of the gel increases due to increase of the gel viscosity. For constant gel concentration, however, the TM permeation across the membrane increases when the TM donor concentration increases. In addition, no effect of the electrical current (iontophoresis, current density 0.5 mA cm-2) on the TM permeation is found. For the combination of the Polyflux membrane with pig SC, the TM transport is much lower than for the membrane alone and the SC fully controls the TM delivery. In this case, the application of electrical current enhances the TM delivery 13-15 times in comparison to passive (no current) transport. According to our estimation, the daily TM dose (10-60 mg) can be delivered by an iontophoretic patch with Polyflux membrane area of 6-36 cm2 containing 20% (w/w) HPC gel and 15 mg cm-3 of TM.