Monolith devices

RAC publications include data summaries for specific component types, such as hybrid microcircuits, small, medium and large-scale integration digital devices, linear and interface devices, digital monolithic devices, and discrete semiconductors. In addition, there are reliability and equipment maintenance data books that provide the failure and repair time data on military electronic equipment by application such as subsystem. 

Strobel et al. (101) reported a unique approach to delivery of anticancer agents from lactide/glycolide polymers. The concept is based on the combination of misonidazole or adriamycin-releasing devices with radiation therapy or hyperthermia. Prototype devices consisted of orthodontic wire or sutures dip-coated with drug and polymeric excipient. The device was designed to be inserted through a catheter directly into a brain tumor. In vitro release studies showed the expected first-order release kinetics on the monolithic devices. 

Figure 15 Mechanisms of drug release from thermosensitive monolithic devices.

The positive effect of convection of the substrate solution on mass transfer can be observed even better with macromolecular substrates that undergo processes such as protein digestion. For example, Fig. 9 compares reversed-phase chromatograms of cytochrome c digests obtained by cleavage with trypsin immobilized in both packed and molded column reactors, and clearly demonstrates the much higher activity of the monolithic device under otherwise similar circumstances [90]. 

The first monolithic devices have been presented at the same time by a group at NIST and a group at the Physical Electronics Laboratory (PEL) of ETH Zurich [77-81]. The NIST chip hosts an array of microhotplates integrated with transistor switches and a readout amplifier for the sensitive layer. The device presented by PEL includes an analog temperature controller and a logarithmic converter for reading out the sensor values. This was the first monolithic realization of an embedded system architecture with integrated microhotplate. 

There are two principal types of monolithic device. If the active agent is dissolved in the polymer medium, the device is called a monolithic solution. Examples of this type of device are pesticide-containing cat and dog collars to control ticks and fleas. Such devices are often used when the active agent is a liquid some polymers [for example, poly(vinyl chloride)] can easily sorb up to 20 % or more of these liquids. However, if the solubility of the active agent in the... 

Figure 8. Calculated amount absorbed from monolithic devices versus experimentally determined values.

Controlled release formulations are a recent innovation in which the pesticide is incorporated into a carrier, generally a polymeric material (Scher, 1999). The rate of release of the pesticide is determined by the properties of the polymer itself as well as environmental factors. There are mainly two types of CR formulations reservoir devices and monolithic devices. As shown in Figure 2.1, in the reservoir device, the toxicant is enclosed in capsules of thin polymeric material to become microcapsules (1-100 pm in diameter), e.g., Penncap-M microcapsules (methyl parathion). In the monolithic device, the toxicant is uniformly... 

Epitaxy—The growth of crystalline layers of semiconducting materials in a layered structure. Integrated circuits—Complex electronic circuits fabricated using multiple growth and lithography/ pattern transfer stages to produce many miniature electronic elements on a monolithic device. 

Microfabrication technology used to manufacture microreactors also introduces many advantages, most notably the ability to rapidly and cheaply mass-produce devices. The low cost of microfabricated devices makes it possible for these devices to be disposable, a characteristic desirable for many medical applications. Rapid scale-up of production by operating many microreactors in parallel can also be accomplished. Microfabrication also presents the opportunity for complete systems in a single monolithic device or systems on a chip as microreactors are incorporated with chemical sensors and analysis devices, microseparation systems, microfluidic components, and/or microelectronics. 

Monolithic Devices—In these systems the drug is homogeneously dispersed within a bioerodible polymer matrix, and release of the drug can be controlled either by diffusion or by polymer erosion. If erosion of the matrix is very much slower than drug diffusion, then release kinetics follow the Higuchi model (37) and drug release rate decreases exponentially with time, following t dependence over a major portion of the release rate. 

One approach to surface erodibility is to prepare a polymer that contains linkages that are stable in base but are very labile in acid. Because one such linkage is an ortho ester, poly(ortho esters) are currently under intensive development as monolithic devices for zero order drug release 1). 

Liu, Y., C.B. Rauch, R.L. Stevens, R Lenigk, J. Yang, D.B. Rhine, and P. Grodzinski. DNA amplification and hybridization assays in integrated plastic monolithic devices. Anal Chem. 2002, 74(13), 3063-3070... 

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