Advanced Drug Delivery Reviews 55 (2003): 315328.)
Drug release from IDD devices is not constant, and "burst" effects are still observed. In addition, drug release cannot be controlled after implantation of IDD devices. Biochips have been developed to precisely control the amount of drug released. Biochips are usually fabricated using silicon and contain a number of mini-wells with precisely controlled sizes, each capable of holding a few hundred nanoliters. These mini-wells are loaded with drugs and are covered with caps of thin metal foils (usually gold) that are connected to the wires on the face of the chips (Figure 16-6).-10! When electrical signal is applied, the current dissolves the metal covers and releases the drug. Biochips can be implanted beneath the skin or into more specific areas such as the spinal cord or brain. The electronics package outside the chips receives a radiofrequency instruction through a built-in antenna to order a microprocessor to control the melting of metal foils. MicroCHIPS, Inc., is one of the key companies developing this technology. Preclinical studies in animals using biochips developed by MicroCHIPS, Inc., have shown good biocompatibility without significant side effects. Once successfully developed, the biochip-based drug-delivery technology will allow for precisely controlled drug administration to patients.
Figure 16-6. A biochip for controlled release developed by Robert Langer and coworkers. (a) Schematic drawing of biochip; (b) a single reservoir. (Reprinted with permission from J. T. Santini, M. J. Cima, and R. Langer, "A controlled-release microchip," Nature 397, no. 6717 (Jan. 28, 1999):
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