Controlled-release substrate

Desirable fixative properties superior to PVP homopolymer can be specified by judicious selection of the amount of vinyl acetate. Hair sprays are limited in the molecular weight of the resin because if they are too hLgh the resulting viscosity of the formulation will result in a poor (coarse) spray pattern. Increasing the VP/VA ratio causes properties to increase in the direction shown by the arrows. Other applications for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives, pharmaceutical tablet coatings, binders, and controlled-release substrates. 

Other applications for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives (140), pharmaceutical tablet coatings, binders, and controlled-release substrates. 

The requirements for a good controlled release substrate are demanding. Evaporation rates change with chemical structure, dose, time, temperature, and air speed, and one needs to be able to predict or control rates as these variables change. Also, sex pheromones generally consist of mixtures and often the components have different volatilities. Thus, one also needs to be able to predict or control component ratios in the vapor. These are affected by ratios in the substrate, time, and temperature. 

This report focuses on natural rubber as the controlled release substrate, and in the physical form of the commercially available sleeve stopper containing a septum and usually referred to as a rubber septum. Interest in this material developed because the rubber septum releases pheromone by only one mechanism (3), and therefore is amenable to systematic study. Also, in many empirical studies the rubber septum had proven to be efficacious for use in traps monitoring insect flight activity, and knowledge of its release characteristics would improve its usefulness. Research that contributes to an understanding of the factors controlling evaporation rates of insect pheromones from natural rubber septa is critically summarized here. 

Coated fertilizers achieve controlled release by coating a soluble fertilizer core (substrate) with a water-insoluble barrier which limits the access of water to the fertilizer and thus limits its dissolution rate. 

Allcock HR, Shawn R, and Scopelianos AG. Poly [(amino acid ester) phosphazenes] as substrates for the controlled release of small molecules. Biomaterials, 1994, 1, 5563-5569. 

Kohler, A., Cascio, P., Leggett, D. S., Woo, K. M., Goldberg, A. L., and Finley, D. The axial channel of the proteasome core particle is gated by the Rpt2 ATPase and controls both substrate entry and product release. Molecular Cell 2001, 7, 1143-1152. 

The sample preparation vacuum line (often called spray-on line ) should allow for (a) controlled mixing of the host gas with the substrate (or with other components that are added to the matrix) by manometric techniques and (b) the controlled release of the gas (mixture) toward the inlet system of the cryostat. These conditions are met by a vacuum line that incoporates a storage bulb for the gas (mixture), inlets for attachment of evacuable containers that allow degassing of the substrate prior to its mixing with the host gas, pressirre gauges that cover suitable ranges, a needle valve that allows the controlled release of the gas, possibly via a flowmeter, and interfaces to the bottles that contain the host gas(es), and to the inlet system that is attached to the vacuum shroud of the cryostat. 

Electrostatic coating has been developed recently to allow for the deposition of thin polymeric films without the need for any solvent. Films are formed when a charged particle is attracted to a substrate of opposite charge.41 An example is the Accudep controlled release system.42... 

Since cellulose and cellulose derivatives have found wide acceptance in the cosmetic, pharmaceutical and medical industries, much work is currently focusing on highly selective modification of cellulose ethers (as well as cellulose esters) for highly targeted controlled release characteristics. Interaction with water, and interaction with a variety of co-substrates under conditions varying in temperature, ionic strength, pH, etc., has opened avenues for the use of cellulose ethers in drug delivery. This field has recently been reviewed [78,79]. 

Stancell et. al. ( 0) reported the possible use of ultrathin films deposited onto relatively permeable substrates as permselective membranes. Ultrathin and highly crosslinked coatings effectively distinguish between molecules of different sizes and increase the permselectivity of the substrate film. Chang et. al. ( ) demonstrated that the permeability coefficient of silicone rubber to oxygen decreased noticeably after depositing a plasma-polymerized ethylene film on the surface. Colter, et. al. (92.93) found similar effects of plasma polymerized films as diffusion barriers in controlled-released drug delivery systems. 

As for other supercritical processes, it is possible to micronize one substrate or more—for instance, to encapsulate an active substance in a biocompatible polymer. In such a case, the purpose is to obtain a controlled-release system of the active substance, and both materials (the active ingredient and the polymer) must be dissolved in the CO2 mixture. Depending on the relative solubility of the two materials in the supercritical medium, one can obtain an encapsulated product or a composite matrix of the two products (26-28). 

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