Browsing by Author "Jayakrishnan, A."

Now showing 1 - 4 of 4
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    On imparting radiopacity to a poly(urethane urea)
    (BIOMATERIALS, 2007)
    A poly(urethane urea) (PUU) synthesized from 2,4-toluene diisocyanate (TDI) and polyethylene glycol (PEG) with ethylenediamine (ED) as the chain extender was rendered radiopaclue by attaching 3,4,5-triiodobenzoic acid (T1B) onto the polymer backbone. The radiopaque polyurethane obtained was characterized by infra red (IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-radiography. By optimizing the reaction conditions, it was possible to carry out the modification without adversely affecting the properties of the starting polymer significantly. IR spectral evidence suggested that the hydrogen bonded structure of PUU remained undisrupted even after modification. However, the product exhibited altered thermal characteristics when compared to the parent polymer. Degradation characteristics as observed from the TGA remained unchanged, while one of the glass transitions got shifted to a lower temperature. The observed changes in thermal characteristics were explained on the basis of possible inter-phase mixing and the changes in the close packing of the polymer chains by the introduction of bulky iodine atoms. (C) 2007 Published by Elsevier Ltd.
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    Self-gelling primaquine-gum arabic conjugate: An injectable controlled delivery system for primaquine
    (BIOMACROMOLECULES, 2007)
    Primaquine, an 8-aminoquinoline, forms a cross-linked gel with periodate-oxidized gum arabic rapidly by simply mixing the drug with the oxidized polysaccharide due to Schiff's base formation between the two amino groups of primaquine and the aldehyde groups in the oxidized polysaccharide. The speed of gelation is determined by the degree of oxidation of polysaccharide, its quantity, and the drug payload. Estimation of the cross-linking density of the gels showed that the higher is the degree of oxidation of gum arabic, the higher is the cross-linking density. In vitro release of primaquine into phosphate buffered saline (PBS) at 37 degrees C demonstrated that the extent of release depended on the cross-linking density and drug payload. Repeated extraction using PBS soon after gel formation showed that not all of the primaquine was conjugated to the polysaccharide and the release seen in vitro was mostly from the unconjugated drug especially from matrices with higher cross-linking density. The gels were found to degrade in PBS, the kinetics of degradation being dependent on the cross-linking density. Cytotoxicity evaluation using MTT assay against L-929 mouse fibroblasts showed that oxidized gum arabic having a degree of oxidation of 50% was only very mildly cytotoxic at a concentration of 0.025 g/mL. An injectable, biodegradable drug depot with controlled release of primaquine over several days or weeks would be advantageous for long-term delivery of this drug against malaria or leishmaniasis, and the present study shows that a primaquine-polymer conjugate that can be formed in situ could be an interesting possibility.
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    Synthesis and characterization of iodinated polyurethane with inherent radiopacity
    (BIOMATERIALS, 2009)
    The synthesis and characterization of polyurethane (PU) with excellent radiopacity for medical and allied applications are reported. Bisphenol-A (BPA) was iodinated to obtain 4,4'-isopropylidinedi-(2,6-diiodo-phenol) (IBPA) which was used as a chain extender for the preparation of a radiopaque PU. The PU was prepared by reacting 4,4'-methylenebis(phenyl isocyanate) (MIDI), poly(tetramethylene glycol) (PTMG) and IBPA in 2.2:1.2:1 molecular ratio and is characterized by infrared spectroscopy (IR), thermogravimetry (TGA), dynamic mechanical analysis (DMA), energy dispersive X-ray analysis (EDX), gel permeation chromatography (GPC) and X-radiography. X-ray images showed that the PU prepared using IBPA as the chain extender is highly radiopaque. An in vitro cytotoxicity test using L929 mouse fibroblast cells shows that the PU is non-cytotoxic. The outlined synthesis of a PU with radiocontrast properties opens up the possibility of synthesizing many different kinds of radiopaque PUs with desirable range of physical properties exploiting the versatility in their chemical synthesis. (C) 2009 Elsevier Ltd. All rights reserved.
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    Synthesis and evaluation of ampicillin-conjugated gum arabic microspheres for sustained release
    (JOURNAL OF PHARMACY AND PHARMACOLOGY, 2007)
    Ampicillin was conjugated to periodate-oxidized gum arabic (GA), a branched polysaccharide, to form the imino conjugate of the drug and the polysaccharide. The water-soluble conjugate was dispersed by sonication in a mixture of toluene and liquid paraffin in the presence of a non-ionic surfactant as droplet stabilizer and fabricated into microspheres by heat denaturation at 80 degrees C to obtain spheres less than 2 mu m in diameter. These microspheres did not undergo dissolution in water on prolonged incubation. in-vitro release of ampicillin into phosphate buffer from the microspheres was slow and sustained with a cumulative release between 10 and 25% of the drug content in 10 days depending on the degree of oxidation of GA and the drug payload. Release into simulated gastric fluid was faster due to faster hydrolysis of the drug-GA bond in the acid medium, but when the medium was changed to intestinal fluid, the release was slowed down. Ampicillin released was functionally active and inhibited the growth of S. aureus and E. coli in cultures, although not as actively as free ampicillin. The microspheres underwent slow biodegradation on prolonged incubation in aqueous media. These studies show that ampicillin conjugated with oxidized GA and fabricated into microspheres possesses sustained-release characteristics for prolonged periods.