Enzyme-activated drug delivery systems

Some active materials are carriers for drugs (drug delivery systems), some have immobilized peptides to enable cell adhesion or migration, some are degradable by hydrolysis or by specific enzyme action. Some contain bioactive agents (e.g., heparin, thrombomodulin) to prevent coagulation or platelet activation while others incorporate bioactive groups to enhance osteo-conduction. Many include polyethylene oxide to retard protein adsorption and this is perhaps the closest we have come to a kind of inertness. 

Other drug-delivery systems may include double emulsions, usually W/O/W, for transporting hydrophilic dmgs such as vaccines, vitamins, enzymes, hormones [441], The multiple emulsion also allows for slow release of the delivered drug and the time-release mechanism can be varied by adjusting the emulsion stability. Conversely, in detoxification (overdose) treatments, the active substance migrates from the outside to the inner phase. 

Liposomes have been used for years as components of drug delivery systems, and as transdermal carriers of active ingredients in the cosmetic industry (307, 308). More recently, liposomes have found use in the food and nutritional supplement industries. Keller (308) lists more than a dozen nutritional products on the market that have been formulated with novel liposome-based delivery systems. In the food area, hposomes have been studied for their ability to encapsulate and provide controlled release of enzymes (309, 310), and liposome-encapsulated enzymes have been used to accelerate the ripening of cheese (311). 

But the different degradation processes, PHB catalyzed by enzymes and acid-base catalyst and PLA just by acid-base catalyst, determine to a considerable extent the degradation and/or resorption times of both materials and therefore the areas for human and veterinary medical use. These materials are used in human or veterinary medicine, or they are presently being tested in the in vitro phase, for example, as resorbable sutures, for blood vessel repair, drug-delivery systems, bandages, scaffolds for producing retard materials for coupling active substances, cells and... 

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