Implantable reservoir for supplemental insulin delivery on demand by external compression

Previously, a small implant of compressed insulin in palmitic acid provided a basal dose to reduce hyperglycaemia for 42 +/- 12 d in rats with induced diabetes. This study describes a silicone implant that can be used for preprandial dose supplements. The device consists of two compartments assembled by attaching a 9 mm diameter foam ring to a 6 mm diameter ring of the same material. The assembly is then enclosed between two membranes, and an annular external wall. Before sealing, a 6 mg piece of compressed insulin (Zn) is inserted into the smaller ring with 2 mg tetracycline to hinder microbial growth. The top membrane is pierced once with an 18 gauge needle, and the device is tested by implanting under the abdominal skin of diabetic rats. Serous fluid soon enters to fill the 141 microliter internal volume through the orifice and dissolves some of the insulin which does not leak out. Sidewise compression weekly over the skin fold of the unanesthetized animal shows that the insulin remained potent until used up after 154 d. When compressed daily, the insulin supply lasted for 24 +/- 4 d and maintained the blood glucose consistently at 3.4 +/- 1.1 mM/l for 6-8 h each day. The dependable device is refillable percutaneously by injection of an insulin suspension.