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The diffusion of peritoneal dialysis (PD) at home is somewhat restricted by the difficulty of transport and storage of a large amount of dialytic solutions. This problem is exacerbated in the case of hemodialysis. With the aim of producing pure water to be used in preparing the solution for peritoneal dialysis, or for hemodialysis in general, as one example, we purified the spent dialysate solution from PD. Experiments were carried out with 24 dialysate solutions taken from 8 patients. Pure water was obtained by means of a thermodialysis process in a hollow fiber reactor operating under nonisothermal conditions. Results show that the yield of the nonisothermal process is dependent on the temperature difference applied across the hydrophobic membranes. The production of pure water per square meter of membrane and per hour was equal to 0.55 or 1.2 or 2.0 liters, with a temperature difference of 11 degrees C or 21 degrees C or 28 degrees C, respectively. These results encourage the use of the thermodialysis process in the production of pure water for clinical uses.

A hollow-fiber enzyme reactor, operating under isothermal and nonisothermal conditions, was built employing a polypropylene hollow fiber onto which beta-galactosidase was immobilized. Hexamethylenediamine and glutaraldehyde were used as spacer and coupling agent, respectively. Glucose production was studied as a function of temperature, substrate concentration, and size of the transmembrane temperature gradient. The actual average temperature differences across the polypropylene fiber, to which reference was done to evaluate the effect of the nonisothermal conditions, were calculated by means of a mathematical approach, which made it possible to know, using computer simulation, the radial and axial temperature profiles inside the bioreactor and across the membrane. Percent activity increases, proportional to the size of the temperature gradients, were found when the enzyme activities under nonisothermal conditions were compared to those measured under comparable isothermal conditions. Percent reductions of the production times, proportional to the applied temperature gradients, were also calculated. The advantage of employing nonisothermal bioreactors in biotechnological industrial process was discussed.

The behaviour of five different hydrophobic beta-galactosidase derivatives, obtained by grafting different amount of butylmethacrylate (BMA) on planar nylon membranes, has been studied under isothermal and non-isothermal conditions.Under isothermal conditions the effect of the grafting percentage on the enzyme activity has been studied as a function of pH, temperature and substrate concentration. Independently from the parameters under observation, the yield of the catalytic process reaches the maximum value at a grafting percentage value equal to 21%. The apparent K(m) values result linearly increasing with the increase of the grafting percentage, while the apparent V(max) exhibits a maximum value.Under non-isothermal conditions, a decrease of the apparent K(m) values and increase of the apparent V(max) has been found in respect to the same values obtained under isothermal conditions.The percentage activity increases induced by the presence of a temperature gradient have been found to decrease with the increase of the percentage of graft BMA.A parameter correlating the percentage increase of enzyme activity under non-isothermal conditions with the hydrophobicity of the catalytic membrane has also been identified. This parameter is the ratio between thermoosmotic and hydraulic permeability.Results have been discussed in terms of reduction of diffusion limitations for substrate and products movement towards or away from the catalytic site by the process of thermodialysis.The usefulness of using non-isothermal bioreactors in industrial biotechnological processes has been confirmed.

The dynamic and steady-state responses as well as the response times of a glucose biosensor have been studied under isothermal and non-isothermal conditions as a function of analyte concentration. The presence of a temperature gradient across the catalytic membrane system improved the biosensor characteristics, because the dynamic and steady-state responses increased and the response times decreased under non-isothermal conditions. For example, a macroscopic temperature difference of 20 degrees C applied across the catalytic membrane system increases the biosensor sensitivity of 70% and reduces of 50% its response time. The dependence of the observed effects on the magnitude of the temperature difference applied has been correlated with the substrate (and products) transport across the catalytic membrane system due to the process of thermodialysis.

The results obtained with a glucose biosensor operating under non-isothermal conditions are presented and discussed. Glucose oxidase, immobilized onto Nylon membranes, was used as biological element. An amperometric two electrodes system was employed to measure the anodic current produced by oxidation of hydrogen peroxide. Non-isothermal conditions were characterised in terms of the temperature difference, delta T = Tw - Tc, and of the average temperature of the system, Tav = (Tw + Tc)/2, Tw and Tc being the temperature in the warm and cold half-cells constituting the biosensor. Comparison between the functioning of the biosensor under isothermal and non-isothermal conditions was performed. It was found that, under non-isothermal conditions, the dynamic response and sensitivity increased, while the response times and the detection limit decreased, if comparison was done with the same parameters measured under isothermal conditions. The increase of the dynamic response was found to be proportional to the applied temperature gradient.

Catalytic membranes, obtained by immobilizing thermophilic beta-glycosidase onto nylon supports, were used in a nonisothermal bioreactor to study the effect of temperature gradients on the rate of enzyme reaction. Two experimental approaches were carried out to explain the molecular mechanisms by which the temperature gradients affect enzyme activity. The results showed that the thermophilic enzyme behaved as the mesophilic beta-galactosidase, exhibiting an activity increase which was linearly proportional to the transmembrane temperature difference. The efficiency of the system proposed was determined by calculating two constants, alpha and beta, which represent respectively the percentage increase of enzyme activity when a temperature difference of 1 degrees C or a temperature gradient of 1 degrees C cm-1 were applied across the catalytic membrane. The increase of enzyme activity in nonisothermal bioreactors entailed a proportional reduction of production times. The advantages in using thermophilic enzymes immobilized in nonisothermal bioreactors are also discussed., (Copyright 1998 John Wiley & Sons, Inc.)

The beta-galactosidase activity of Kluyveromyces fragilis cells immobilized in a kappa carrageenan gel was studied in a bioreactor functioning under isothermal and non-isothermal conditions. We observed an increase in enzyme activity which was found to be proportional to the intensity of the temperature gradient applied across the biocatalytic membrane, as well as to the average temperature of the bioreactor. The efficiency of such a non-isothermal bioreactor was calculated with respect to the yield of a bioreactor working under comparable isothermal conditions and was evaluated in terms of reduction of processing times in industrial applications. The possibility that enzyme activity in living cells is affected by non-isothermal conditions naturally existing owing to metabolic heat production is also discussed.

The behaviour of the enzyme invertase, located on the cell wall of baker's-yeast cells and entrapped in a gelatin membrane, was studied under isothermal and non-isothermal conditions. The reaction rate linearly increased with the applied transmembrane temperature gradient, with reference either to the average temperature or to the temperature on the warm side of the catalytic membrane. These results were obtained both when the bioreactor was operated under conditions of closed volumes and when the substrate-containing solutions are recirculated. The mathematical relationships have been elaborated between the temperatures read in the working solutions and those on the two faces of the catalytic membrane. Since the temperature difference across the membrane is smaller than that indicated by the thermocouples, the observed effects are greater than expected. The potential advantages of the use of a non-isothermal bioreactor in processes of industrial interest are discussed.

The aim of the present study is to ascertain whether transmembrane temperature gradients couple with transport of electric charge in living cells of Valonia utricularis and eventually measure the thermodynamic coupling coefficient (s). Simple experimental procedures are described that allow generation of temperature gradients of predetermined sense and intensity across the cell membrane. Simultaneous measurement of the potential difference is ensured by standard electrophysiological methods. The mathematical expressions that allow quantitative treatment of experimental results are indicated in the article and are based on standard nonequilibrium thermodynamic and electrophysiological formalism. The value of the coupling coefficient between temperature gradient and flow of electric charge is indicated and concisely discussed in terms of possible mechanisms of ionic membrane transport.

Thermodiffusive transport of trace elements that play important roles in living organisms, such as molybdenum, nickel, copper, and vanadium, was studied in a nonisothermal biphasic system comprised of a liquid solution and jelly layers. Our intent was to mimic the effects of temperature gradients on prebiological evolution. Conditions were found, similar to those probably existing during development of early eobionts, under which all the elements tested were concentrated within the heated jelly. Nonisothermal matter transport through grossly porous artificial membranes--the process of thermodialysis--was next investigated to assess the behavior of compartmentalized, i.e., membrane bound, eobionts. Particular interest was dedicated to the continuity of nonisothermal transport phenomena in the homogeneous and heterogeneous (membrane) systems and to the ability of compartmentalized eobionts to withstand osmotic swelling by means of thermoosmotic transport. Interestingly enough, under the experimental conditions adopted, sodium/potassium countertransport is also found, suggesting a very early physicochemical origin of the sodium-potassium pump. Surprisingly enough, evidence of teleonomic behavior appears in those very simple analogs of prebiological systems.

Temperature-sensitive mutants of phage alpha were subjected to short pulses of permissive temperature at various times during the lytic cycle. All the mutants showed an optimal response to the permissive pulse at a specific time after infection. The optimal responses of the mutants belonging to the same complementation group fell close together in the same time interval; the optimal responses of mutants contained in 20 different complementation groups were more or less uniformly scattered throughout the lytic cycle. Temperature sensitivity, therefore, seems to afford, at least in the case of phage alpha, an independent way of grouping the genes in an ordered sequence with respect to the steps they control.