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At least 163 records · Page 9Linked to original sources
PubMed2005

Aging and microwave effects on alginate/chitosan matrices.

The influence of microwave irradiation on the drug release properties of freshly prepared and aged alginate, alginate-chitosan and chitosan beads was investigated. The beads were prepared by extrusion method with sulphathiazole as a model drug. The dried beads were subjected to microwave irradiation at 80 W for 10 min, 20 min or three consecutive cycles of 10 and 20 min, respectively. The profiles of drug dissolution, drug content, drug stability, drug polymorphism, drug-polymer interaction, polymer crosslinkage and complexation were determined by dissolution testing, drug content assay, differential scanning calorimetry and Fourier transform infra-red spectroscopy. The chemical stability of drug embedded in beads was unaffected by microwave conditions and length of storage time. The release property of drug was mainly governed by the extent of polymer interaction in beads. The aged alginate beads required intermittent cycles of microwave irradiation to induce drug release retarding effect in contrast to their freshly prepared samples. Unlike the alginate beads, the level of polymer interaction was higher in aged alginate-chitosan beads than the corresponding fresh beads. The drug release retarding property of aged alginate-chitosan beads could be significantly enhanced through subjecting the beads to microwave irradiation for 10 min. No further change in drug release from these beads was observed beyond 30 min of microwave irradiation. Unlike beads containing alginate, the rate and extent of drug released from the aged chitosan beads were higher upon treatment by microwave in spite of the higher degree of polymer interaction shown by the latter on prolonged storage. The observation suggested that the response of polymer matrix to microwave irradiation in induction of drug release retarding property was largely affected by the molecular arrangement of the polymer chains.

Alginates↗
PubMed2002

Design of controlled-release solid dosage forms of alginate and chitosan using microwave.

The influence of microwave irradiation on the drug release properties of alginate, alginate-chitosan and chitosan beads was investigated. The beads were prepared with the highest possible concentration of polymer by an extrusion method. Sulphathiazole was selected as a model drug. The beads were subjected to microwave irradiation at various combinations of irradiation power and time. The profiles of drug dissolution, drug content, drug stability, drug polymorphism, drug-polymer interaction, polymer crosslinkage and complexation were determined by dissolution testing, drug content assay, differential scanning calorimetry (DSC) and fourier transform infra-red spectroscopy (FTIR). The chemical stability of the drug entrapped in the beads was unaffected by the microwave irradiation. However, the drug in the chitosan beads underwent polymorphic changes. Polymorphic changes were prevented by means of drug-alginate interaction in alginate and alginate-chitosan beads. Changes in the polymorphic state of drug were found to have insignificant effect on the drug release profiles of chitosan beads. The release-retarding property of alginate and alginate-chitosan beads was significantly enhanced by subjecting the beads to microwave irradiation. Positively charged calcium ions and chitosan are known to interact with negatively charged alginate. DSC and FTIR analyses indicated that the reduction in rate and extent of drug released from the treated beads was primarily due to additional formation of non-ionic bonds, involving alginate crosslinkage and alginate-chitosan complexation. The results showed that microwave technology can be employed in the design of solid dosage forms for controlled-release application without the use of noxious chemical agents.

Alginates↗
PubMed1996

Non-invasive in vivo characterization of release processes in biodegradable polymers by low-frequency electron paramagnetic resonance spectroscopy.

Using stable free radicals (nitroxides) whose spectra reflect microviscosity and pH, low-frequency electron paramagnetic resonance (EPR) spectroscopy was used to characterize the release pattern of subcutaneous implants of poly(D,L-lactide-co-glycolide) (PLGA) continuously and non-invasively in living mice. No significant changes occurred during the first days after implantation. After about 1 week, the recorded EPR spectra gave direct evidence for the formation of compartments with high mobility and increasing acidity in the delivery system. The contribution of the mobile part of the spectrum increased with time, but no remarkable decay of the overall signal intensity was observed during the second week. The EPR signals decayed rapidly after 3 weeks. The experimental data are consistent with bulk hydrolysis as the dominating mechanism of release and are not consistent with a surface-controlled pattern of degradation. The formation of acidic compartments in the delivery system may have significant effects on drug stability, drug solubility, bioavailability, pharmacokinetics, and ultimately on therapeutic efficiency. In particular, the finding of areas of low pH within the polymer raise the possibility that hydrolysable drugs may undergo degradation in the implant prior to their release. Our results demonstrate that EPR is a valuable tool for characterizing such drug delivery systems in vivo.

Animals↗