Drug-release materials

These biopolymers can be used for the immobilization of metal ions not only with the final objective of metal recovery (and subsequent valorization by desorption or chemical/thermal destmction of the polymer matrix) but also for elaborating new materials or designing new applications. Depending on the metal immobilized on the biopolymer, it is possible to design new sorbents (immobilization of iron on alginate [119], of molybdate on chitosan [59], for As(V) removal, of silver on chitosan for pesticide removal [120]), supports for affinity chromatography [121], antimicrobial material [122], drug release material [123], neutron capture therapy [124], and photoluminescent materials [125]. These are only a few... 

PHB films in the rat for several months [188]. No inflammatory activity was detected. The authors claimed that the final degradation product might be D(-)-3-hydroxybutyrate, a physiological compound always present in the human body as an energy source and that PHB might be used as a slow drug-releasing material buried inside the body [188]. 

Rate of hydration of the polymeric materials has been shown to be an important consideration in regard to drug release. Gilding and Reed (24) demonstrated that water uptake increases as the glycolide ratio in the copolymer increases. The extent of block or random structure in the copolymer can also affect the rate of hydration and the rate of degradation (25). Careful control of the polymerization conditions is required in order to afford reproducible drug release behavior in a finished product. Kissel (26) showed drastic differences in water uptake between various homopolymers and copolymers of caprolactone, lactide, and glycolide. 

Hendren, R. W., Reel, J. R., and Pitt, G. C., Measurement of drug release rates from sustained delivery devices in vivo. Fort Lauderdale, Florida, Controlled Release Society, Proc. 11th Int. Symp. Control. Rel. Bioact. Materials. 110-111, 1984. 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

In order to produce an adequate tablet formulation, certain requirements, such as sufficient mechanical strength and desired drug release profile, must be met. At times this may be a difficult task for the formulator to achieve, due to poor flow and compactibility characteristics of the powdered drug. This is of particular importance when one only has a small amount of active material to work with and cannot afford to make use of trial-and-error methods. The study of the physics of tablet compaction through the use of instrumented tableting machines (ITMs) enables the formulator to systematically evaluate his formula and make any necessary changes. 

A challenge in designing liposome systems is the assessment of drug release from such systems in vitro. Use of agarose gel matrices has been reported as one approach to evaluate the release kinetics of liposome-encapsulated materials in the presence of biological components [68],... 

M Westerberg, C Nystrom. Physicochemical aspects of drug release. XVII. The effect of drug surface area coverage to carrier materials on drug dissolution from ordered mixtures. Int J Pharm 90 1-17, 1993. 

The past two decades have produced a revival of interest in the synthesis of polyanhydrides for biomedical applications. These materials offer a unique combination of properties that includes hydrolytically labile backbone, hydrophobic bulk, and very flexible chemistry that can be combined with other functional groups to develop polymers with novel physical and chemical properties. This combination of properties leads to erosion kinetics that is primarily surface eroding and offers the potential to stabilize macromolecular drugs and extend release profiles from days to years. The microstructural characteristics and inhomogeneities of multi-component systems offer an additional dimension of drug release kinetics that can be exploited to tailor drug release profiles. 

The development of new polyanhydrides has sparked researchers to developed new device fabrication and characterization techniques, instrumentation, and experimental and mathematical models that can be extended to the study of other systems. The growing interest in developing new chemistries and drug release systems based on polyanhydrides promises a rich harvest of new applications and drug release technologies, as well as new characterization techniques that can be extended to other materials. Future endeavors will likely focus on multicomponent polyanhydride systems, combining new chemical functionalities to tailor polyanhydrides for specific applications. 

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