ABSTRACT:To control the release of insulin in response to the concentration of glucose, a glucose-responsive polymer membrane was designed by combining a glucose oxidase (GOD) immobilized membrane, a sensor for glucose, with a poly(amine) membrane which regulates the permeation rate of insulin. The permeability of insulin was increased by the addition of glucose. Gluconic acid produced by an enzymatic reaction between GOD and glucose induced a decrease in the pH value of the medium. This caused the protonation of tertiary amino groups in the membrane resulting in an increase in the water content of the poly( amine) membrane. The permeability of insulin through a complex membrane thus increases with glucose concentration.KEY WORDS Glucose I Insulin I Glucose Oxidase I Poly(amine) I Membrane I Permeation I Swelling I Recently, many investigations have been carried out on the controlled release systems of drugs utilizing polymeric materials and maintaining the concentration of drugs in plasma within a therapeutic range for extended periods of time. 1 Langer et al. demonstrated that ethylene-vinyl acetate copolymers impregnated with insulin maintained diabetic blood glucose levels near normal levels for one month. 2 In comparison with insulin infusion pumps, the advantage of these implantable polymer pellets is that large amounts of insulin can be concentrated in a small volume as opposed to a mechanized pumping which must be refilled daily. 3 However, the insulin release rate from these pellets dose not depend on variation in blood glucose levels and minor surgery is required for their implant and retrieval.For an ideal insulin delivery system, insulin release should be controlled directly by the amount of blood glucose present at any particular time. This requires a continual feedback between the blood glucose level and insulin release rate. Brownlee et al. proposed a self regulating insulin delivery system based on a combination of biological modulations and controlled release. 4 The design of this delivery system utilizes the concept of competitive and complementary binding behavior of concanavalin A with glucose and glycosilated insulin.We reported in a previous paper that the permeation rate of insulin through an amphiphilic polymer membrane can be controlled by the water fraction of the membrane. 5 We also reported a preparation method for a polymer membrane capable of regulating the permeation of insulin in response to change in the concentration of glucose. 6 The membrane

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Hydrogen in Metals J Pd -Cu Binary and Pd -Cu-Au Ternary Solid Solution Alloys p-c Isotherms J ThermodynamicsThermodynamic quantities for absorption of hydrogen by Pd-Cu alloys with up to atom fraction of Xc, = 0.2, and by Pd -Cu-Au ternary alloys with up to (Xc, + XAu) = 0.2, where X,, = XAu, have been determined at temperatures between 273 K and 423 K and hydrogen pressures up to 1000 Torr by measurements of the pressure-composition isotherms. The hydrogen absorption characteristics of these alloys have been compared with that of the previously reported Pd -Au binary alloys. The room temperature lattice parameters of hydrogen-free Pd -Cu -Au alloys increases with the solute content, albeit by a small amount. The relative partial molar enthalpy, AH!, at infinite dilution in Pd-Cu-Au alloys increases in exothermicity with increasing (Cu + Au) content, and the alloy composition dependence of the AH! value falls near the mid-points between those of each Pd-Cu and Pd-Au binary alloy. The relative partial molar entropy, Ash, at infinite dilution in Pd -Cu -Au alloys decreases with the solute content, and the AS! values at the same alloying content are larger than that of Pd-Au alloys, but are smaller than that of Pd -Cu alloys. The [H -Cu + H -Au] pair interaction energies between the dissolved hydrogen and the substitutional solute atoms in the ternary alloys have been evaluated according to a quasi-chemical model with zeroth order approximation by taking into account the "constant pressure" to "constant volume" correction. The hydrogen solubility behaviour at low hydrogen concentration in Pd-Cu-Au ternary alloys can be described as due to the counteraction of the repulsive H-Cu pair interaction and the attractive H -Au pair one in the Pd host lattice. The stability of the P-phase hydride at a given temperature in Pd-Cu-Au alloys decreases with the solute content, and the alloy composition dependence of the stability is also placed near the mid-points between those for each Pd-Cu and Pd-Au binary alloy.

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Thermodynamic quantities for absorption of hydrogen by Pd95–xYxAg5 solid solution alloys with up to x = 6.3 at.% Y have been determined from measurements of pressure‐composition isotherms at temperatures between 273 K and 473 K and hydrogen pressures up to 1000 Torr. The hydrogen absorption characteristics have been compared with those of the previously reported Pd–Ag and Pd–Y binary alloys. The relative partial molar enthalpy, ΔHH0, at infinite dilution of hydrogen in Pd95–xYxAg5 alloys increases in exothermicity with increasing Y content from that of Pd–5.0 at.% Ag, almost parallel to that in Pd–Y binary alloys. The relative partial molar entropy, ΔSH0, at infinite dilution in the ternary alloys decreases with Y content from that of Pd–5.0 at.% Ag alloy. The hydrogen solubility behavior at low hydrogen concentration in the Pd–Y–Ag alloys under a “constant volume” condition can be described as due to mainly the strong H–Y attractive pair interaction in the Pd host lattice. The stability of β‐hydride and hydrogen concentration at αmax phase boundary increase following alloying with Y from that of Pd–5.0 at.% Ag alloy, respectively, and the changes in the properties with Y content are similar to that in Pd–Y binary alloys.