Release device

Initially, the ability to incorporate biomolecules during the growth of conducting polymers and to expel these molecules by electrical stimulation was seen as a means to develop novel controlled-release systems79-80 for active ingredients such as anticancer drugs (flouracil)81 or anti-inflammatories (dexamethasone).82 

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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. 

Choi, N. S., and Heller, J., Erodible agent releasing device comprising poly(ortho esters) and poly(ortho carbonates), U.S. Patent 4,138,344, February 6, 1979. 

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

Here we might note that cobalt(II) hydroxide, but not the oxide, also forms cements (Allen et al., 1984 Mansion Gleed, 1985 Prosser et al., 1986). It also is used in controlled-release devices for supplying trace elements to cattle and sheep. Nothing is known of its structure. 

This chapter is devoted to a miscellaneous group of aqueous acid-base cements that do not fit into other categories. There are numerous cements in this group. Although many are of little practical interest, some are of theoretical interest, while others have considerable potential as sustained-release devices and biomedical materials. Deserving of special mention as biomedical materials of the future are the recently invented polyelectrolyte cements based on poly(vinylphosphonic adds), which are related both to the orthophosphoric acid and poly(alkenoic add) cements. 

Initial tests in the rat revealed a high degree of tissue compatibility of Dat-Tyr-Hex derived polymers. More detailed tests are now in progress. In addition, tyrosine derived polymers are currently being evaluated in the formulation of an intracranial controlled release device for the release of dopamine, in the design of an intraarterial stent (to prevent the restenosis of coronary arteries after balloon angioplasty), and in the development of orthopedic implants. The use of tyrosine derived polymers in these applications will provide additional data on the biocompatibility of these polymers. 

Fig. 15 Drawing showing the optimum placement of an intravitreal sustained-release device in the eye. (From Ref. 224.)...

Sustained- and controlled-release devices for drug delivery in the vaginal and uterine areas are most often for the delivery of contraceptive steroid hormones. The advantages in administration by this route—prolonged release, minimal systemic side effects, and an increase in bioavailability—allow for less total drug than with an oral dose. First-pass metabolism that inactivates many steroid hormones can be avoided [183,184],... 

The hormone-releasing devices have a closer resemblance to standard methods of sustained release because they involve the release of a steroid compound by diffusion [198,199]. The Progestasert, a reservoir system, is shown in Fig. 16. Progesterone, the active ingredient, is dispersed in the inner reservoir, surrounded by an ethylene/vinyl acetate copolymer membrane. The release of progesterone from this system is maintained almost constant for 1 year. The effects of release are local, with none of the systematic side effects observed with orally administered contraceptives [200-207]. 

The lack of simple and reliable application systems is a major problem to be solved before the introduction of this biocontrol agent into practical control strategies. Mixing fungal chlamydospores into a feed supplement was used in most plot and field studies as an application system (Larsen, 2000). Incorporation into various types of feed blocks or mineral licks, as well as slow-release devices, may also become feasible (Thamsborg et al., 1999 Chandrawathani et al., 2003). 

Reithmeier, H., Herrmann, J., and Gopferich, A., Lipid microparticles as a parenteral controlled release device for peptides, Journal of Controlled Release, 2001, 73, 339-350. 

Initial and boundary conditions, which are necessary for solving Eq. (15) and (16), allow for the appropriate description of the experimental conditions imposed upon the drug release device. The solutions of Eqs. (15) and (16) subject to a number of boundary conditions that can be applied to various in vitro and ex vivo experiments have been obtained (Crank and Park, 1968). 

The encapsulation and release of l,3-bis(2-chloroethyl)nitrosourea (BCNU) in P(CPP-SA) 20 80 wafers was the first implantable controlled release device based on polyanhydrides that was FDA-approved and marketed (Gliadel ) (Chasin et al., 1988). BCNU was encapsulated by two techniques, trituration and co-dissolution, resulting in different release profiles (Chasin et al., 1990, 1991). The triturated samples released faster than those prepared by co-dissolution, presumably due to more homogeneous loading in the samples prepared by co-dissolution. 

Minabe M, Suzuki F, Umemoto T Intra-pocket antibiotic therapy using resorbable and non-resorbable slow-release devices containing tetracycline. Periodontal Clin Investig 2000 22 14-21. 

Should not be fastened with locks other than antipanic catches or other quick releasing devices. 

Fusible Link - A release device activated by the heat effects of a fire. It usually consists of two pieces of metal joined by a low melting point solder. Fusible links are manufactured at various temperature ratings and are subject to varying normal maximum tension. When installed and the fixed temperature is reached, the solder melts and the two metal parts separate, initiating desired actions. 

An examination of all detectors, expellant gas container(s), releasing devices, piping, hose assemblies, nozzles, signals, and all auxiliary equipment. 

All dry chemical systems should be tested, which should include the operation of the detection system, signals and releasing devices, including manual stations and other associated equipment. A discharge of the dry chemical normally is not part of this test. 

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