PubMed · 8134833
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1994-03-25. Materials science.. https://pubmed.ncbi.nlm.nih.gov/8134833/
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The author approaches ethical questions raised by use of methadone in opiates addiction: reduction of drug phenomenon to a strict medical problem, illusion of technical mastery, responsibility of pharmaceutical engineering, medicine under repressive constraint, reduction of damages linked to prohibition. The communication ends on a question about management of drug problems which today encourages a healthy vision of consumption behaviour rather than a "good way of use".
The performance of membrane filters is limited by concentration polarisation and membrane fouling. High shear rates reduce these effects but can damage delicate cells and proteins in biological fluids. Secondary flows to promote fluid mixing, and hence enhance filtration, can be highly effective, but usually carry the penalty of complexity. Oscillatory flow over furrowed or dimpled membrane surfaces (vortex mixing) has been shown to be very efficient in the microfiltration and oxygenation of blood, but carries the added complexity of oscillatory flow and the need to thermoform the membranes. To allow the use of asymmetric or rigid membranes, a new form of vortex mixing has been studied, in which the membranes are flat and form parallel channels. Feed flow is oscillatory and passes back-and-forth across ladder-like flow deflectors to generate standing vortex waves. Flow visualisation studies and numerical calculations of standing vortex waves (SVW) were undertaken to help optimise flow parameters and flow deflector geometry. Flat plate membrane ultrafilters were built and evaluated for different geometries of flow deflector, using solutions of bovine serum albumin (BSA) as the test fluid. Very high filtration rates were measured with BSA concentrations ranging from 1 to 24%. A SVW ultrafilter was compared with a Millipore Pellicon ultrafilter using BSA as the test fluid. Filtration flux was similar at low concentrations of BSA, but was greater by a factor of 4.5 in the SVW device at high concentrations of BSA.
The oxygen permeability passing through the gauze layer and the actual and apparent volumetric oxygen transfer rate, KLa and (KLa)app, respectively, were determined in specially designed Erlenmeyer flasks, which have an oxygen electrode inserted in the middle part of flasks. The oxygen transfer rate was determined by sulfite oxidation. As a result, the oxygen permeability passing through 8 layers of gauze at 37 degrees C, 220 rpm, with 50 ml sulfite solution in a 500-ml flask was 43.7 mol/m.h atm; as the oxygen partial pressure decreased by 6.1%, the value of KLa increased by 100%; the relationship between rotational speed of shaker, n(rpm); volume of flask, V(ml); liquid content in flask, VL(ml); temperature of shaker, t(degrees C) and KLa, as well as (KLa)app (1/h) were: [formula: see text]