Slow-release devices

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). 

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. 

The aim of this study was to investigate the design possibilities and fluoride release rates for a novel biodegradable slow-release device for the prevention of paediatric dental caries. The design possibilities include colour, shape, size and placement within the buccal cavity. The release rate of fluoride was analysed on a weekly basis to examine the potential as a slow-release device, which would allow a constant level of fluoride to be present in the mouth over a period of weeks or months depending on the patient s circumstances. 

Aaltonen AS et al (2000) Efficacy of a slow release device containing fluoride, xylitol and sorbitol in preventing infant caries. Acta Odontol Scand 58(6) 285-292 Batchelor L, Loni A, Canham LT, Hasan M, Coffer J (2012) Manufacture of mesoporous silicon from living plants and agricultural waste an environmentally fiiendly and scalable process. 

In the Netherlands, Rodenburg built up a plant for the transformation of potato wastes generated by the fried potatoes industry. The waste is fermented and the resulting granulate is used for the injection moulding of slow release devices. The claimed capacity is of 40000 tons/year. Rodenburg material is sold under the Solanyl trademark. 

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. 

Dosages and routes of administration Morphine is available in different salt forms but the hydrochloride and sulfate (Vermeire and Remon, 1999) are used preferentially. The compound can be administered by the oral, parenteral or intraspinal route. Oral application is preferred for chronic pain treatment and various slow release forms have been developed to reduce the administration frequency to 2-3 times per day (Bourke et al., 2000). Parenteral morphine is used in intravenous or intramuscular doses of 10 mg, mostly for postoperative pain and self-administration devices are available for patient-controlled analgesia (PCA). Morphine is additionally used for intraspinal (epidural or intrathecal) administration. Morphine is absorbed reasonably well in the lower gastrointestinal tract and can be given as suppositories. 

As reported in Table 1, from G. Oberdoster and coauthors,1 NPs may be distinguished as natural and anthropogenic, the latter being divided into Unintentional or Intentional. Although their toxicity is still under debate, many intentionally prepared NPs are used in medical devices, such as for the slow release of drugs or anticancer agents. 

Sustained release intravitreal dexamethasone implants have a potential use in reducing ocular inflammation and treating PVR. The device consists of a 5 mg pellet of dexamethasone coated with 10% PVA and EVA giving a mean release rate of 1.2 0.1 pg/hr over a period of 5 months. A slow release daunomycin implant was fabricated by loading the polysulfone capillary fibre with 1% w/w of daunomycin in tristearin. The controlled release is attributed to the diffusion-retardant properties of the fat. An experimental evaluation of the kinetics and efficacy of this device in a rabbit model at 15 fig and 30 fig/ device resulted in a therapeutically sustained level of daunomycin for up to 21 days after device implantation. Exhausted devices have to be removed surgically, which is an important limitation. 

In practice, two other disadvantages have also been observed. For very slow releasing components it has been found that the decrease in weight over a reasonable time period can be too small to detect on the balance required to accommodate the weight of the release device itself. Secondly, adsorption or absorption of materials from the atmosphere by the release device itself can sometimes actually result in a weight gain with time. 

Poly(e-caprolactone) (PCL) is a biodegradable, non-toxic polymer of the polyester family suitable for implantable or injectable delivery devices (7). The degradation of PCL occurs at a very slow rate via the hydrolyzation of ester bonds, making it ideal for long term delivery systems (7). Previous studies (8-13) find that 35-55% of the initial hydrophilic drug load was released rapidly from PCL nano and micro particles, within a few hours. This burst was followed by slow release over timescales of weeks to months 8-13). 

Major polymer applications hot-melt coatings, hot-melt adhesives, wall covering adhesives, paints, tubing, sporting goods, footwear, baby products, controlled release devices, wire and cable (semiconductor shields, automotive wire, automotive ignition, low-smoke cable), asphalt modification, slow burning candles, cap liners... 

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