Kinetic modelling as a tool for the design of a vascular bioartificial pancreas: feedback between modelling and...

A bioartificial pancreas is a system which contains isolated islets of Langerhans protected against immune rejection by an artificial membrane, permeable to glucose and insulin, but not to lymphocytes and immunoglobulins. However, it is necessary to design a device which performs as a closed-loop insulin delivery system, more specifically which rapidly responds to a change in the recipient's blood glucose concentration by an appropriate change in insulin release. We have designed a system intended to be connected as an arteriovenous shunt of the recipient; islets are placed between two flat ultrafiltration membranes, and blood circulates successively above the upper, and below the lower, membrane, in reverse direction. A complete kinetic model of glucose transfer from blood to the islet compartment, of insulin generation by the islets displaying a biphasic insulin pattern, and of insulin transfer into the bloodstream was described, and parameters were calculated on the basis of experimental data obtained when islets of Langerhans were perfused in vitro with a synthetic buffer. The resulting calculations indicated that both diffusional and convective transfers were involved in glucose and insulin mass transfer across the membrane, the contribution of diffusion being the most important. The geometry of the system was therefore modified in order to decrease the resistance to flow inside the blood channel. This should increase, at a given hydrostatic pressure, the blood flow rate, and thereby improve the diffusional transfer of insulin. This should also decrease the thrombogenicity of the device.(ABSTRACT TRUNCATED AT 250 WORDS)