Control of the pilocarpine release rate through hydrogels by plasma treatment

The rate of release of an aqueous solution of pilocarpine hydrochloride sequestered in hydrogel-type materials can be reduced by plasma treatment of the polymer surface. Two plasma techniques were used. The first involves exposure of the hydrogel to the effects of a glow discharge sustained in argon, a process known as CASING. (Crosslinking by Active Species of Inert Gases). The second technique involves the deposition of a thin film by plasma polymerization of organic gases. The gases used in this study were ethane, ethylene and tetrafluoroethylene. Hydrogels were prepared by photopolymerization of 2-hydroxymethyl methacrylate (HEMA), and copolymerization of HEMA with methyl acrylate. The CASING treatment was found to be least effective. The most successful method was the plasma polymerization of tetrafluoroethylene, which yielded an order of magnitude reduction in the flux rate of pilocarpine with a film thickness of 0.25micronm. Polymerization conditions bringing about a crack-resistant film were critical in obtaining the best results.

Reduction of progesterone release rate through silicone membranes by plasma polymerization

An investigation was performed to determine the effectiveness of thin plasma-polymerized films and CASING for controlling the flux of progesterone through poly-(dimethyl siloxane) membranes. It was concluded that up to 40-fold reductions in flux could be achieved with plasma-polymerized films. The principal factors affecting the extent of flux reduction were the nature of the monomer used (ethylene, ethane and tetrafluoroethylene), the film thickness, and the deposition conditions. CASING (Crosslinking by Activated Species of Inert Gases) of the poly-(dimethyl siloxane) membrane surface also proved effective in reducing the flux of progesterone through it.

Recent Advances in Glass Transitions in Polymers

Since the publication of our review “Glass Transition in Polymers” in 1966, a number of interesting advances have been made in this field. The present article is intended to be an addendum to this review, reporting the progress that has been made by various workers during the past three years. In addition, a number of topics were not covered in the previous article due to the relatively incomplete understanding at that time. These will now be discussed. This is not because these topics are at present fully understood. Rather, we hope it will serve as a progress report to stimulate further interest in areas where further work is needed. The numbering systems and notations in this paper will follow those in the previous article for the sake of continuity.