Artificial pancreas using living beta cells:. effects on glucose homeostasis in diabetic rats.

An artificial pancreas consisting of beta cells cultured on synthetic semipermeable hollow fibers was tested in rats with alloxan-induced diabetes. When implanted ex vivo as arteriovenous shunts in the circulatory system these devices lowered concentrations of plasma glucose from 533 to between 110 and 130 milligrams per 100 milliliters, increased concentrations of plasma insulin, and restored intravenous glucose tolerance tests essentially to normal.

Transport characterization of membranes for immunoisolation.

This study relates to the diffusive transport characterization of hollow fibre membranes used in implantable bio-hybrid organs and other immunoisolatory devices. Techniques were developed to accurately determine the mass transfer coefficients for diffusing species in the 10(2)-10(5) MW range, validated and then used to study one membrane type known to effectively immunoisolate both allografts and xenografts in vivo. Low-molecular-weight diffusing markers included glucose, vitamin B12 and cytochrome C; higher-molecular-weight molecules were bovine serum albumin, immunoglobulin G, apoferritin and a range of fluorescein-tagged dextrans. Overall and fractional mass transfer coefficients through the hollow fibres were determined using a resistance-in-series model for transport. A flowing dialysis-type apparatus was used for the small-molecular-weight diffusants, whereas a static diffusion chamber was used for large-molecular-weight markers. For diffusion measurements of small-molecular-weight solutes, convective artefacts were minimized and the effect of boundary layers on both sides of the membrane were accounted for in the model. In measuring diffusion coefficients of large-molecular-weight species, boundary layer effects were shown to be negligible. Results showed that for small-molecular-weight species (< 13,000 MW) the diffusion coefficient in the membrane was reduced relative to diffusion in water by two to four times. The diffusion rate of large-molecular-weight species was hindered by several thousand-fold over their rate of diffusion in water.

Effect of membrane composition and structure on solute removal and biocompatibility in hemodialysis.

Effect of membrane composition and structure on solute removal and biocompatibility in hemodialysis. Significant changes in extracorporeal membranes have occurred over the past five decades in which hemodialysis (HD) has been available as a therapy for both acute renal failure (ARF) and end-stage renal disease (ESRD). For cellulosic membranes, these changes have included a reduction in thickness, hydroxyl group substitution, and an increase in pore size. These modifications have resulted in enhanced efficiency of small solute removal, a broader spectrum of overall solute removal, and an attenuation of complement activation in comparison to the thick, unsubstituted cellulosic membranes of low permeability used in the early days of HD therapy. Synthetic membranes, originally developed specifically for use in high-flux HD and hemofiltration, have also evolved during this same time period. In fact, the initially clear distinction between low-flux regenerated cellulosic and high-flux synthetic membranes has become blurred, as membrane formulators have developed products designed to appeal to enthusiasts for both membrane formats. The purpose of this review is to characterize both the solute removal and biocompatibility characteristics of dialysis membranes according to their composition (that is, polymeric makeup) and structure. In this regard, the manner in which membrane biocompatibility interacts with flux is highlighted.

Plasma therapy at Klinikum Grosshadern: a 15-year retrospective.

Immediately after the availability of highly permeable membranes in 1979, membrane plasma separation was introduced as a mode of extracorporeal blood purification by the nephrology group at Klinikum Grosshadern of the Ludwig Maximilians University of Munich (F.R.G.). The new therapy was applied primarily in the management of immunologically mediated renal and extrarenal disorders as well as in paraproteinemias. We also have witnessed a widespread application of this extracorporeal treatment as a last resort in otherwise refractory clinical conditions. Over the years, the group at Grosshadern has contributed to the development, as well as to the laboratory and clinical testing, of new plasma separation membranes, simplified plasmapheresis formats (e.g., spontaneous membrane plasma separation), and several plasma fractionation procedures (e.g., cascade filtration, adsorption). Whenever indicated and possible, plasma fractionation procedures, rather than unselective plasma exchange, are performed in an appropriate clinical situation.

Kinetics of hemodiafiltration. I. In vitro transport characteristics of a hollow-fiber blood ultrafilter.

The transport characteristics of a hollow-fiber blood ultrafilter were studied in vitro to provide an understanding of the factors which control solute removal rate and to permit design of a full-scale clinical device. The dependence of ultrafiltrate flux on transmembrane pressure difference, protein concentration, flow rate, and fiber geometry was correlated in terms of available theoretical analyses. Solute rejection was 1.0 for albumin and decreased to nearly zero for solutes of several thousand molecular weight. An analysis of overall hemodiafilter behavior showed that blood and ultrafiltrate flow rates of 200 ml. per minute can be attained with a device of reasonable size which would provide an inulin whole blood clearance of about 100 ml. per minute.