Semipermeable polymeric coatings

Most of the oral sustained-release products are diffusional layer tablets coated with an insoluble polymer, such as a tablet with a biodegradable matrix or an osmotic controlled tablet. The mechanism involves the drug dissolved within the semipermeable polymeric coating. After water absorption, the tablet matrix generates an osmotic pressure, which drives the drug solution out through a tiny hole in the coated tablet. 

Semipermeable polymeric coatings have been used in the textile industry for making breathable clothing. In the wound-management industry, semipermeable films are also... 

Langmuir-Blodgett films may have value in many applied areas of traditional interest to the industrial chemist, such as adhesion, encapsulation, and catalysis. The permeability characteristics of monolayer assemblies may also find application as synthetic membranes for ultrafine filtration, gas separation, and reverse osmosis. For example, Albrecht et al. (44) proved the eflSciency of polymeric diacetylene monolayers on semipermeable supports in reducing the flow of CH4. One interesting possibility lies in using LB monolayers as lubricants in magnetic tape technology. Unpublished reports have indicated that frictional coeflScients can be reduced markedly when the tape is coated with a few monolayers. In applications such as those listed previously, difiSculties may well be encountered with the mechanical stability of the films. To date, relatively little research has been carried out in this area. 

Polymeric or proteinaceous microspheres are used to introduce drugs to specific locations in the body. The coating material acts as a semipermeable membrane, permitting slow release and high concentration of a drug at the desired site. Enzymes, hormones, and other biochemical substances can be temporarily immobilized by this technique. 

---