The use of controlled-release glass for the controlled delivery of bioactive materials

CRG can provide a useful supplement to other methods of controlled delivery. Some advantages of this approach are: The constituents of the CRG can be limited to biologically safe ionic species such as Na+, Ca2+ and PO4(3-). The release system is completely soluble in water and no residue remains. There is no evidence of any mechanism for biodegradation of the CRG and so one possible cause of premature or accelerated release is eliminated. The absolute release rate can be selected anywhere in a spectrum covering several orders of magnitude and the rate-controlling process has zero-order kinetics. The release rate can be selected to be pH-sensitive or pH-independent. Complex temporal release-rate patterns can be obtained readily by the choice of geometrical shape or composition profile of the device. The controlled release of organics or other heat-sensitive materials which cannot be incorporated in the glass can be realized by the use of composite structures in which the CRG is the rate-controlling constituent. A number of different functions can be performed by a single CRG-based device. For example, CRG can be used as a biomedical resorbable material in surgery and the CRG structural component can release an AM as it dissolves. Similarly the CRG of the sinter-composite used for organic AM release can itself release any selected inorganic adjuvant. CRG boluses containing either copper or cobalt and weighing approx. either 70 g or 15 g, have been administered to both cattle and sheep. More than 90% of the boluses remained either in the reticulum of trace element remained after dosing.(ABSTRACT TRUNCATED AT 250 WORDS)