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)