of disposable diagnostic test kits. Polystyrene, nylon acrylamide, dextrans, and agarose have all been used for attachment of antibodies and antigens. In all of these uses, nonspecific binding has to be minimized because it limits sensitivity and makes interpretation of test results very difficult. Therefore, the need to understand interfacial biointeractions will continue to be paramount.

New materials, such as block copolymers containing polypeptides and segmented poly(ether urethanes), have been shown to have specific affinity for proteins. These hybrid materials may prove to be one of the best ways to incorporate both function and structure into the same molecule. For example, it may be possible to incorporate a specific cell-binding segment of a protein into a synthetic polymer, with the latter providing the scaffold and processing capability. Thus, one can tailor polymers to specific biomolecular and diagnostic functions.

Controlled Drug Release

Interest in drug delivery research is increasing for a number of reasons: the need for systems to deliver novel, genetically engineered pharmaceuticals, the need to target delivery of anticancer drugs to specific tumors, the need to develop patentable sustained delivery systems, and the need to increase patient compliance. Polymers are essential for all the new delivery systems, including transdermal patches, microspheres, pumps, aerosols, ocular implants, and contraceptive implants. The major disease areas that are expected to benefit from development of new delivery systems include chronic degenerative diseases, such as central nervous system disorders associated with aging, cancer, cardiovascular and respiratory diseases, chemical imbalances, and cellular dysfunction. Delivery to difficult-to-reach areas such as the brain is desirable, and progress is being made in the area through the use of polyanhydrides, as is discussed in the vignette "Implanted Polymers for Drug Delivery." Success in this area will be rewarded with improved quality of life and longevity.

Several drug release technologies have become clinically and commercially important. They can be classified into various categories by their mechanism of release: (1) diffusion-controlled systems, where the drug is released by solution-diffusion through a polymeric membrane or embedded into a polymeric matrix where the matrix controls the rate of delivery from the system; (2) erosion-controlled systems, where the drug release is activated by dissolution of the polymer, disintegration of the polymer, or chemical/biodegradation; or (3) osmotically controlled systems, where the contents are released by the rate of osmotic absorption of water from the environment, thereby displacing the drug from the reservoir. Any of these mechanisms can be employed to develop controlled-release delivery systems for oral, transdermal, implant insert, or intravenous administration, although some mechanisms are superior to others for certain



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