Delivery system, implantable

TOF-SIMS has important potentials in many areas of life science, in fundamental and applied research as well as in product development and control. This holds for the characterization of biological cells and tissues, of sensor and microplate arrays, of drug delivery systems, of implants, etc. In all these areas, relevant surfaces feature a very complex composition and structure, requiring the parallel detect ion of many different molecular species as well as metal and other elements, with high sensitivity and spatial resolution requirements, which are exactly met by TOF-SIMS. 

A., and Hower, J. F., Sustained delivery of narcotic antagonists from lactic.glycolic acid copolymer implants, in Polymeric Delivery Systems (R. J. Kostelnik, ed.), Gordon and Breach, New York, 1978, Chap. 4. 

These results open the exciting possibility of using degradable, tyrosine-derived polymers as "custom-designed" antigen delivery devices. On the other hand, our results indicate that the immunological properties of tyrosine-derived polymers will have to be carefully evaluated before such polymers can be considered for use as drug delivery systems or medical implants. 

Recently, water-soluble protein fractions, isolated from extracts of bone matrix, were incorporated into a collagen matrix and shown to induce bone (67,68) and cartilage formation both in vitro and in vivo (69,70). In the latter studies, in the absence of the collajgen delivery system, the proteins were incapable of inducing cartilage formation in vivo when implanted intramuscularly into mice. The success of this approach appears to depend on delivering the active agents at an effective dose over an extended time period. 

Controlled and sustained drug delivery has recently begun to make an impression in the area of treatment of dental diseases. Many researchers have demonstrated that controlled delivery of antimicrobial agents, such as chlorhexidine [128-130], ofloxacin [131-133], and metronidazole [134], can effectively treat and prevent periodontitis. The incidence of dental caries and formation of plaque can also be reduced by controlled delivery of fluoride [135,136]. Delivery systems used are film-forming solutions [129,130], polymeric inserts [132], implants, and patches. Since dental disease is usually chronic, sustained release of therapeutic agents in the oral cavity would obviously be desirable. 

One of the most obvious ways to provide sustained-release medication is to place the drug in a delivery system and inject or implant the system into the body... 

P. J. Blackshear, Implantable pumps for insulin delivery Current clinical status, in Drug Delivery Systems, Fundamentals and Techniques (P. Johnson and J. G. Lloyd-Jones, eds.), Ellis Horwood, Chichester, 1987, p. 139. 

F Lescure, D Bichon, JM Anderson, E Doelker, ML Pelaprat, RJ Gurny. Acute histopathological response to a new biodegradable polypeptidic polymer for implantable drug delivery system. Biomed Mater Res 23 1299-1313, 1989. 

Despite the evidence for the cytotoxicity of CNTs, there are an increasing number of published studies that support the potential development of CNT-based biomaterials for tissue regeneration (e.g., neuronal substrates [143] and orthopedic materials [154—156]), cancer treatment [157], and drug/vaccine delivery systems [158, 159]. Most of these applications will involve the implantation and/or administration of such materials into patients as for any therapeutic or diagnostic agent used, the toxic potential of the CNTs must be evaluated in relation to their potential benefits [160]. For this reason, detailed investigations of the interactions between CNTs/CNT-based implants and various cell types have been carried out [154, 155, 161]. A comprehensive description of such results, however, is beyond the scope of this chapter. Extensive reviews on the biocompatibility of implantable CNT composite materials [21, 143, 162] and of CNT drug-delivery systems [162] are available. 

A pharmacotectonics concept was illustrated by researchers, in which drug-delivery systems were arranged spatially in tissues to shape concentration fields for potent agents. NGF-releasing implants placed within 1-2 mm of the treatment site enhanced the biological function of cellular targets, whereas identical implants placed mm from the target site of treatment produced no beneficial effect (Mahoney and Saltzman, 1999). Because of some limitations with controlled delivery systems, alternatives such as encapsulation of cells that secrete these factors are discussed in the next section. 

Erdmann et al. (2000) report the fabrication of devices for the localized delivery of salicylic acid from the poly(anhydride-co-ester)s mentioned in Section II.C. A unique feature of this drug delivery system is that the drug compound is part of the polymer backbone. Devices were implanted intraorally and histopathology was reported (Erdmann et al., 2000). Chasin et al. (1990) review fabrication and testing of implantable formulations for other drugs including angiogenesis inhibitors for treatment of carcinomas and bethanechol for the treatment of Alzheimer s disease. 

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