Browsing by Author "Jayakrishnan, A"

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    A floating-type oral dosage form for piroxicam based on hollow polycarbonate microspheres: In vitro and in vivo evaluation in rabbits
    (JOURNAL OF CONTROLLED RELEASE, 2002)
    A floating type dosage form (FDF) of piroxicam in hollow polycarbonate (PC) microspheres capable of floating on simulated gastric and intestinal fluids was prepared by a solvent evaporation technique. Incorporation efficiencies of over 95% were achieved for the encapsulation. In vitro release of piroxicam from PC microspheres into simulated gastric fluid at 37 C showed no significant burst effect. The amount released increased with time for about 8 h after which very little was found to be released up to 24 h. In intestinal fluid, the release was faster and continuous and at high drug payloads, the cumulative release reached above 90% in about 8 h. In vivo evaluation of different dosage forms of piroxicam such as free drug, drug-encapsulated microspheres and microspheres along with a loading dose of free drug in rabbits showed multiple peaking in the plasma concentration-time curve suggesting enterohepatic recirculation of the drug. Pharmacokinetic analysis showed that the bioavailability from PC microspheres alone was about 1.4 times that of the free drug and it was about 4.8 times for the dosage form consisting of the microspheres plus the loading dose. The elimination half life was increased by about three times for the microsphere preparation alone and nearly about six times for the dosage form comprising of microspheres and a loading dose in comparison to the free drug. Data obtained in this study demonstrated that FDF of piroxicam in PC microspheres was capable of sustained delivery of the drug for longer periods with increased bioavailability. (C) 2002 Elsevier Science B.V. All rights reserved.
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    A photochemical method for immobilization of azidated dextran onto aminated poly(ethylene terephthalate) surfaces
    (POLYMER INTERNATIONAL, 2008) Bhat, VT; James, NR; Jayakrishnan, A
    BACKGROUND: Dextran, a bacterial polysaccharide, has been reported to be as good as poly(ethylene glycol) in its protein-rejecting and cell-repelling abilities. In addition, the multivalent nature of dextran is advantageous for surface grafting of biologically active molecules. We report here a method to photochemically bind dextran hydrogel films to aminated poly(ethylene terephthalate) (PET) surfaces in aqueous media using a heterobifunctional crosslinker, 4-azidobenzoic acid. In order to achieve this, dextran was first functionalized with the crosslinker using carbodiimide chemistry followed by photo-crosslinking and immobilization onto the nucleophile-rich aminated PET surfaces. RESULTS: The presence of the immobilized dextran on PET was verified by attenuated total-reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and contact angle measurements. The grafted surface was highly hydrophilic due to the heavily hydrated polysaccharide network on the surface as demonstrated by the near zero water contact angle. CONCLUSION: A photochemical method for surface immobilization of dextran onto aminated PET using aryl azide chemistry is a facile technique to generate highly hydrophilic and more hemocompatible surfaces. The aryl nitrenes generated by photolysis produce a metastable, electron-deficient intermediate, azacycloheptatetraene, which is believed to be responsible for the simultaneous crosslinking of dextran and its immobilization onto the aminated PET surface. The aryl azide chemistry reported here for dextran could be useful as a versatile technique for surface modification of other nucleophile-rich polymers to create dextran- or similar polysaccharide-immobilized surfaces. (c) 2007 Society of Chemical Industry.
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    Amphotericin B-gum arabic conjugates: Synthesis, toxicity, bioavailability, and activities against Leishmania and fungi
    (PHARMACEUTICAL RESEARCH, 2007)
    Purpose. Gum arabic, a branched polysaccharide consisting of more than 90% arabinogalactan having a molecular weight around 250,000 Da is the oldest and best known of all natural gums. The objective of the present investigation was to examine whether amphotericin B (AmB), the polyene antibiotic when conjugated to periodate oxidized gum arabic still retained its anti-fungal and anti-leishmanial activity and to evaluate its toxicity and bioavailability.Methods. AmB conjugated to the oxidized polysaccharide through Schiff's linkages in the unreduced (imine) and reduced (amine) forms were characterized for the drug content, hemolytic potential, molecular mass, in vitro release and were examined for anti-fungal activity against Candida albicans and Cryptococcus neoformans and for anti-leishmanial activity against promastigotes of Leishmania donovani in culture. Toxicity and bioavailability were evaluated by intravenous (i.v) injections of the conjugates in mice and rabbits respectively.Results. The conjugates were found to be non-hemolytic and mice withstood a dosage of 20 mg (AmB)/kg body weight of both conjugates. Histological examination of the internal organs of mice showed no lesions in kidney, brain, heart or liver. Estimation of the residual drug in the internal organs 7 days post injection showed that the spleen still retained 8.4 +/- 0.53 mu g/g of tissue. AmB was found to be released from both conjugates in vitro although the release from the imine conjugate was much faster than from the amine conjugate. The concentrations inhibiting parasite growth by 50% (IC50) values for the imine conjugate against promastigotes of L. donovani LV9 and DD8 strains were 0.37 +/- 0.04 and 1.44 +/- 0.18 mu M respectively. The IC50 values for the amine conjugates were much higher. The minimum inhibitory concentration (MIC) against C. albicans and C. neoformans was in the range of 0.5-0.9 mu g/mL for both imino and amino conjugates. The bioavailability of the conjugate in rabbits showed that the imine conjugate maintained a plasma concentration in the range of 20 to 5 mu g/mL while for the amine conjugate it was in the range of 17 to 3 mu g/mL over 24 h.Conclusions. The drug conjugates were stable, non-hemolytic and non-toxic to the internal organs of the animal and showed good anti-fungal and anti-leishmanial activity in vitro. In spite of the large molecular weight of the polysaccharide, AmB from the conjugates showed bioavailability after i.v injection. Since the highest concentration of AmB was found in the spleen after a single injection, these conjugates may have potential in anti-leishmanial therapy.
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    Antitumour activity of mitoxantrone-loaded chitosan microspheres against Ehrlich ascites carcinoma
    (JOURNAL OF PHARMACY AND PHARMACOLOGY, 1996) Jameela, SR; Latha, PG; Subramoniam, A; Jayakrishnan, A
    Glutaraldehyde cross-linked chitosan microspheres containing the antineoplastic agent mitoxantrone were prepared and the antitumour activity was evaluated against Ehrlich ascites carcinoma in mice by intraperitoneal injections. The tumour inhibitory effect was followed by monitoring animal survival time and change in body weight for a period of 60 days. While the mean survival time of animals which received 2 mg and 1 mg of free mitoxantrone intraperitoneally was 2.1 and 4.6 days, respectively, animals which received 2 mg mitoxantrone via microspheres showed a mean survival time of 50 days. Five out of 8 animals treated using microspheres lived beyond 60 days. The percentage ratio mean survival time of the treated group divided by the mean survival time of the untreated group for animals treated using mitoxantrone-loaded chitosan microspheres containing 2 mg of the drug was 290 compared with 12.2 for those which received 2 mg of the free drug. The antitumour effect of mitoxantrone-loaded microspheres against Ehrlich ascites carcinoma was much higher than that of doxorubicin-loaded microspheres reported by previous workers. Our data demonstrate the potential of mitoxantrone-loaded chitosan microspheres for sustained drug delivery to minimize drug toxicity and maximize therapeutic efficacy.
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    Bacterial adhesion onto azidated poly(vinyl chloride) surfaces
    (JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, 2002)
    A plasticized poly(vinyl chloride) surface was modified by azidation using sodium azide in the presence of a phase transfer catalyst in aqueous media. Subsequent to azidation, the surface was crosslinked using ultraviolet radiation. Contact angle measurements showed that the surface became hydrophilic on azidation whereas photoirradiation did not have any further effect on the hydrophilicity of the azidated surface. Control, azidated, and photo-crosslinked surfaces were exposed to two strains of bacteria commonly implicated in device infection such as Staphylococcus aureus and Escherichia coli. Whereas the control and photocrosslinked surfaces showed no significant difference in bacterial adhesion, the azidated surface showed significantly reduced adhesion to both strains. Data obtained indicate that the presence of an intact azide function on the polymer Surface is responsible for the reduced bacterial adherence and the surface hydrophobicity/hydrophilicity did not exert any effect in the present case. Although azides are known to be effective only against Gram-negative species, surprising was the observation that the azidated polymer surface was equally effective against a Gram-positive species such as S. aureus. Because sodium azide is routinely used as a preservative to prevent bacterial and fungal growth in many microbiology reagents and diagnostic kits, covalent binding of the azide onto a polymer surface or synthesizing azide containing polymers may be an interesting method to investigate in tackling the problem of bacterial adhesion and colonization of medical devices. (C) 2002 Wiley Periodicals, Inc.
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    Chemical modification of poly(vinyl chloride) resin using poly(ethylene glycol) to improve blood compatibility
    (BIOMATERIALS, 2005)
    Poly(vinyl chloride) (PVC) was aminated by treating the resin with a concentrated aqueous solution of ethylenediamine. The aminated PVC was then reacted with hexamethylene diisocyanate to incorporate the isocyanate group onto the polymer backbone. The isocyanated PVC was further reacted with poly(ethylene glycol) (PEG) of molecular weight 600 Da. The modified polymer was characterized using infrared and X-ray photoelectron spectroscopy (XPS) and thermal analysis. Infrared and XPS spectra showed the incorporation of PEG onto PVC. The thermal stability of the modified polymer was found to be lowered by the incorporation of PEG. Contact angle measurements on the surface of polymer films cast from a tetrahydrofuran solution of the polymer demonstrated that the modified polymer gave rise to a significantly hydrophilic surface compared to unmodified PVC. The solid/water interfacial free energy of the modified surface was 3.9 ergs/cm(2) as opposed to 18.4ergs/cm(2) for bare PVC surface. Static platelet adhesion studies using platelet-rich plasma showed significantly reduced platelet adhesion on the surface of the modified polymer compared to control PVC. The surface hydrophilicity of the films was remarkably retained even in the presence of up to 30 wt % concentration of the plasticizer di-(2-ethylhexyl phthalate). The study showed that bulk modification of PVC with PEG using appropriate chemistry can give rise to a polymer that possesses the anti-fouling property of PEG and such bulk modifications are less cumbersome compared to surface modifications on the finished product to impart anti-fouling properties to the PVC surface. (C) 2004 Elsevier Ltd. All rights reserved.
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    Doxorubicin-Polysorbate 80 conjugates: targeting effective and sustained delivery to the brain
    (RSC pharmaceutics, 2024-05) Ram Prasad, S; Leena, SS; Deepthi, A; Resmi, AN; Jayasree, RS; Sandhya, KS; Jayakrishnan, A
    Targeting therapeutic agents to the brain to treat the central nervous system (CNS) diseases is a major challenge due to the blood-brain-barrier (BBB). In this study, an attempt was made to deliver a model drug such as doxorubicin (DOX) to the brain in a mice model through DOX-Polysorbate 80 (DOX-PS80) conjugates. DOX was successfully conjugated with the non-ionic surfactant Polysorbate 80 (PS80) by carbamate linkage and the conjugate was characterized by different spectroscopic techniques such as FTIR, UV-Visible and NMR. The DOX conjugation efficacy was found to be 43.69 ± 4.72 %. The in vitro cumulative release of DOX from the conjugates was found to be 4.9 ± 0.8 % in PBS of pH 7.3 and 3.9 ± 0.6 % in simulated cerebrospinal fluid (CSF) of pH 7.3 at the end of 10 days. In vitro BBB permeability assay was carried out using bEnd.3 cells and DOX-PS80 conjugate showed a 3-fold increase in BBB permeability compared to controls. In vitro cytotoxicity assay using U251 human glioblastoma cells showed an IC50 value of 38.10 µg/mL for DOX-PS80. Cell uptake studies revealed that DOX-PS80 was effectively taken up (90%) by the bEnd.3 and U251 cells and localized in cytoplasm at the end of 24 h. Tumor spheroid assay and in vivo experiments in Swiss albino mice demonstrated the possibility of DOX-PS80 conjugate crossing the BBB and delivering the drug molecules to the target site for treating CNS disorders.
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    Evaluation of an in situ forming hydrogel wound dressing based on oxidized alginate and gelatin
    (BIOMATERIALS, 2005)
    Wound dressings that can be formed in situ offer several advantages over the use of preformed dressings such as conformability without wrinkling or fluting in the wound bed, ease of application and improved patient compliance and comfort. Here we describe such an in situ forming hydrogel wound dressing from gelatin, oxidized alginate and borax. Periodate oxidized alginate rapidly cross-links proteins such as gelatin in the presence of borax to give in situ forming hydrogels that are both non-toxic and biodegradable. The composite matrix has the haemostatic effect of gelatin, the wound healing-promoting feature of alginate and the antiseptic property of borax to make it a potential wound dressing material. The hydrogel was found to have a fluid uptake of 90% of its weight which would prevent the wound bed from accumulation of exudates. The water vapour transmission rate (WVTR) of the hydrogel was found to be 2686 + 124 g/m(2)/day indicating that the hydrogel can maintain a moist environment over wound bed in moderate to heavily exuding wound which would enhance epithelial cell migration during the healing process. The wound healing efficacy of hydrogel was evaluated in experimental full thickness wounds using a rat model which demonstrated that within 2 weeks, the wound covered with gel was completely filled with new epithelium without any significant adverse reactions. These in situ forming hydrogels fulfil many critical elements desirable in a wound dressing material. (c) 2005 Elsevier Ltd. All rights reserved.
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    Evaluation of the effect of incorporation of dibutyryl cyclic adenosine monophosphate in an in situ-forming hydrogel wound dressing based on oxidized alginate and gelatin
    (BIOMATERIALS, 2006)
    Cyclic adenosine monophosphate (cAMP) has long been regarded as a second messenger and a regulator of human keratinocyte proliferation. To explore more effective wound management, dibutyryl cyclic adenosine monophosphate (DBcAMP), a lipophilic analog of cAMP was incorporated into an in situ-forming hydrogel wound dressing based on periodate-oxidized alginate and gelatin. In vitro release of DBcAMP from the matrix into phosphate buffered saline was slow and increased with time. Only 50-60% of the compound was released into the medium over a period of 2 days suggestive of a sustained release into the wound bed over a period of few days. The wound-healing efficacy of the DBcAMP-incorporated dressing was evaluated on experimental full-thickness wounds in a rat model. It was found that dressing promoted wound healing leading to complete re-epithelialization of wounds within 10 days, whereas control wounds took 15 days for complete re-epithelialization. Data obtained in this Study showed that the presence of DBcAMP accelerated healing and re-epithelialization of full-thickness wounds. (c) 2005 Elsevier Ltd. All rights reserved.
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    Glutaraldehyde as a fixative in bioprostheses and drug delivery matrices
    (BIOMATERIALS, 1996)
    The use of glutaraldehyde as a fixative in bioprostheses and drug delivery matrices is reviewed. The chemistry of glutaraldehyde cross-linking and its effect on the biological performance of a number of bioprostheses such as tissue heart valves, vascular grafts, pericardial patches, tendon grafts and drug delivery matrices are examined.
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    Iodination of plasticized poly(vinyl chloride) in aqueous media via phase transfer catalysis
    (JOURNAL OF APPLIED POLYMER SCIENCE, 2002) Lakshmi, S; Jayakrishnan, A
    Nucleophilic substitution of chlorine on plasticized poly(vinyl chloride) (PVC) was carried out using potassium iodide (KI) in the presence of a phase transfer catalyst (PTC) in aqueous media. Iodination was confirmed using energy dispersive X-ray analysis (EDAX). The extent of iodination was studied with respect to time, temperature, concentration of the reactants, as well as different PTCs. Among the different PTCs examined, tetrabutylammonium bromide (TBAB) and tetrabutylammonium hydrogen sulfate (TBAH) were found to be highly efficient for the reaction. About 25% increase in weight was observed for PVC sheets iodinated under optimal reaction conditions. The thermal stability of the modified PVC was found to be impaired upon iodination. The iodinated PVC released iodide ions when kept in distilled water, as evidenced by UV spectroscopy. Sustained release of iodide ion in distilled water was followed up for about 30 days. (C) 2002 John Wiley Sons, Inc.
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    Migration resistant, blood-compatible plasticized polyvinyl chloride for medical and related applications
    (ARTIFICIAL ORGANS, 1998)
    Plasticized polyvinyl chloride (PVC), although not a blood-compatible polymer, is the material of choice for the manufacture of blood bags and hemodialysis tubing throughout the world. PVC is usually plasticized with di-(2-ethylhexyl phthalate) (DEHP) to impart flexibility and low temperature properties to the final product. DEHP belongs to a class of agents called hypolipidemic hepatocarcinogens, and it migrates in small quantities into the storage medium such as blood, plasma, or serum, resulting in a number of toxic effects. It has been shown that the migration resistance and blood compatibility of flexible PVC could be significantly improved by grafting polyethylene glycol (PEG), the most blood-compatible polymer known today, onto the surface of flexible PVC by the classical Williamson ether synthesis reaction. The technique is simple and versatile enough to produce blood-compatible, migration resistant PVC surfaces for many medical applications. The method may also find use for preventing plasticizer migration from PVC cling films and polyvinylidene chloride films used extensively in food packaging.
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    Modified gum arabic cross-linked gelatin scaffold for biomedical applications
    (MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 2014) Sarika, PR; Cinthya, K; Jayakrishnan, A; Anilkumar, PR; James, NR
    The present work deals with development of modified gum arabic cross-linked gelatin scaffold for cell culture. A new biocompatible scaffold was developed by cross-linking gelatin (Gel) with gum arabic, a polysaccharide. Gum arabic was subjected to periodate oxidation to obtain gum arabic aldehyde (GAA). GAA was reacted with gelatin under appropriate pH to prepare the cross-linked hydrogel. Cross-linking occurred due to Schiff's base reaction between aldehyde groups of oxidized gum arabic and amino groups of gelatin. The scaffold prepared from the hydrogel was characterized by swelling properties, degree of cross-linking, in vitro degradation and scanning electron microscopy (SEM). Cytocompatibility evaluation using L-929 and HepG2 cells confirmed non-cytotoxic and non-adherent nature of the scaffold. These properties are essential for generating multicellular spheroids and hence the scaffold is proposed to be a suitable candidate for spheroid cell culture. (C) 2014 Elsevier B.V. All rights reserved.
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    Oxidized chondroitin sulfate-cross-linked gelatin matrixes: A new class of hydrogels
    (BIOMACROMOLECULES, 2005)
    A naturally occurring glycosaminoglycan such as chondroitin-6-sulfate was first converted in to its aldehyde derivative by periodate oxidation and used as a cross-linking agent for gelatin giving rise to a new class of hydrogels. Cross-linking was predominantly due to Schiff's base formation between the c-amino groups of lysine or hydroxylysine side groups of gelatin and the aldehyde groups in oxidized chondroitin sulfate. The hydrogels were prepared from chondroitin sulfate with different degrees of oxidation and gelatin. They were characterized for degree of cross-linking, cross-linking density, equilibrium swelling, water vapor transmission rate, internal structure, and blood-compatibility. Degree of cross-linking of the gels determined by trinitrobenzene sulfonic acid assay showed that, the higher the degree of oxidation of the polysaccharide, the higher the degree of cross-linking. Examination of the internal structure by scanning electron microscopy showed that the hydrogels were highly porous in nature with interconnecting pores ranging from 50 to 200 mu m. Equilibrium swelling showed that the gels retained about 90% water and did not undergo dehydration rapidly. The hydrogels were nontoxic and blood-compatible. Since an important phase of early wound healing has been shown to involve secretion of glycosaminoglycans such as chondroitin sulfate by fibroblasts which form a hydrophilic matrix suitable for remodeling during healing, this new class of hydrogels prepared from chondroitin sulfate and gelatin without employing any extraneous cross-linking agents are expected to have potential as wound dressing materials.
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    Periodate oxidation of sodium alginate in water and in ethanol-water mixture: a comparative study
    (CARBOHYDRATE RESEARCH, 2005)
    Periodate oxidation of sodium alginate in aqueous solution as well as a dispersion in 1: 1 ethanol-water was examined. The oxidation proceeded smoothly in both media, and the kinetics of oxidation was Surprisingly similar. Polymer cleavage was observed in both media. but it was extensive in ethanol-water. The weight-average molar mass (M-w) of the oxidized product obtained from aqueous solution showed a gradual decrease with increase in the periodate concentration, whereas, except for very high periodate equivalent, the change in M-w was not reflected with increase in concentration of periodate in ethanol-water. The oxidized alginate obtained from the ethanol-water mixture was found to be more efficient in crosslinking proteins such as gelatin, leading to hydrogels. Oxidation of a dispersion has the advantage of generating large quantities of the oxidized alginate in higher yield with one reaction using less solvent. (c) 2005 Elsevier Ltd. All rights reserved.
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    Phase transfer catalysed surface modification of plasticized poly(vinyl chloride) in aqueous media to retard plasticizer migration
    (POLYMER, 1996) Jayakrishnan, A; Sunny, MC
    Plasticized poly(vinyl chloride) (PVC) sheets were surface modified by nucleophilic substitution of chlorine by azide in aqueous media under phase transfer conditions. PVC was reacted with a 40% solution of sodium azide in water using tetrabutyl ammonium bromide as the phase transfer catalyst. The reaction was conducted at temperatures ranging from 50 to 80 degrees C for various periods of time (1-4 h). The azidated PVC surface was then irradiated using u.v. light with a 125W lamp for various time periods to crosslink the surface. Migration of the plasticizer di-(2-ethylhexyl phthalate) from surface modified and unmodified PVC was examined in a potential organic extractant such as hexane. It was found that considerable reduction in the migration of the plasticizer could be achieved by this technique depending on the extent of azidation of the PVC surface and the irradiation dose. Determination of the stress/strain properties of PVC sheets before and after modification showed that there was around 30% reduction in these properties after surface modification. However, the values were still much above the minimum prescribed for vinyl chloride polymers used in biomedical applications. Copyright (C) 1996 Elsevier Science Ltd.
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    Photocross-linking of dithiocarbamate-substituted PVC reduces plasticizer migration
    (POLYMER, 1998) Lakshmi, S; Jayakrishnan, A
    Medical grade poly(vinyl chloride) (PVC) sheets and tubes were surface modified by nucleophilic substitution of chlorine atoms of PVC by photoactive N,N-diethyl dithiocarbamate (DTC) in aqueous media in the presence of a suitable phase transfer catalyst (PTC) at 55 degrees C. The modified surface was cross-linked by irradiation with u.v. light in an attempt to create a barrier for the diffusion of the plasticizer di-(2-ethylhexyl phthalate) (DEHP). Of the various PTCs examined for the reaction, tetrabutyl ammonium salts were found to be very effective, whereas crown ethers such as 18-crown-6 was least effective. The effect of concentration of PTC and DTC, time of reaction and irradiation dose on the extent of plasticizer migration was examined in petroleum ether for various periods of time at 30 degrees C. The migration of DEHP from PVC modified under optimum conditions was less than 5% in 120 h, whereas the unmodified PVC lost virtually all its plasticizer (> 30%) during the same period. Determination of the stress-strain properties of modified PVC sheets showed a reduction of approximately 30%. However, the values were still within the range prescribed for vinyl chloride plastics used for medical applications. (C) 1997 Elsevier Science Ltd.
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    Polyurethane thermoplastic elastomers with inherent radiopacity for biomedical applications
    (JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 2012) Kiran, S; James, NR; Jayakrishnan, A; Joseph, R
    Synthesis and characterization of three different radiopaque thermoplastic polyurethane elastomers are reported. Radiopacity was introduced to the polyurethanes by incorporating an iodinated chain extender, namely, 4,4'-isopropylidinedi-(2,6-diiodophenol) (IBPA), into the polymer chain during polyurethane synthesis. Radiopaque polyurethanes (RPUs) were synthesized by reacting 4,4'-methylenebis(phenyl isocyanate) (MDI), IBPA, and three different diols. The polyols used for the synthesis were polypropylene glycol, polycaprolactone diol, and poly(hexamethylene carbonate) diol. RPUs were characterized by infrared spectroscopy, contact angle measurements, thermogravimetry, dynamic mechanical analysis, energy dispersive X-ray analysis, gel permeation chromatography, X-ray fluorescence spectroscopy, and X-radiography. X-ray images showed that all RPUs prepared using IBPA as the chain extender are highly radiopaque compared with an Aluminum wedge of equivalent thickness. Elemental analysis revealed that the polyurethanes contained 1819% iodine in the polymer matrix. The RPUs developed have radiopacity equivalent to that of a polymer filled with 20 wt % barium sulfate. Results revealed that RPUs of wide range of properties may be produced by incorporating different diols as the soft chain segment. Cell culture cytotoxicity studies conducted using L929 cells by direct contact test and MTT assay proved that these RPUs are noncytotoxic in nature. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2012.
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    Polyurethanes with radiopaque properties
    (BIOMATERIALS, 2006)
    An aliphatic, commercially available, medical grade polyurethane, Tecoflex 80 A was made radiopaque by coupling a 5-iodine-containing molecule, N-(2,6- diiodocarboxyphenyl)-3,4,5-triiodo benzamide (DCPTB) onto the polymer backbone. DCPTB was synthesized by coupling 4-ainino-3,5-diiodobenzoic acid and 3,4,5-triiodobenzoic acid using dicyclohexyl carbodiimide. Radiopaque polyurethane thus obtained was characterized by IR, TGA, DSC and X-radiography. By optimizing the reaction conditions, it was possible to incorporate about 8% iodine in the polymer (wt/wt) to achieve radiopacity almost equivalent to that of a 2mm thick aluminium wedge. However, the products differed from the starting polymer in thermal characteristics. The starting polymer showed two endothermic transitions, the first one due to glass transition of the soft segment and the second one due to disruption of the hard segments. After modification, the second transition shifted to a lower temperature, while the first transition remained unaltered. Also, the modified polymers showed reduced thermal stability compared to the starting polymer. These observations could be explained on the basis of the reduced extent of intermolecular hydrogen bonding among the hard segments of the end product. Radiopaque polyurethanes are expected to have significant advantage over their non-radiopaque counterparts in many medical and related applications. (c) 2005 Elsevier Ltd. All rights reserved.
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    Preparation and evaluation of photocrosslinkable chitosan as a drug delivery matrix
    (JOURNAL OF APPLIED POLYMER SCIENCE, 2002) Jameela, SR; Lakshmi, S; James, NR; Jayakrishnan, A
    Epichlorohydrin (1-chloro-2,3-epoxypropane) was reacted with sodium azide in the presence of a phase transfer catalyst to obtain 1-cliloro-2-hydroxy-3-azidopropane, which was further coupled onto chitosan to prepare. a photocrosslinkable derivative of the biopolymer. Elemental analysis and infrared (IR) spectroscopy confirmed the incorporation of azide groups onto chitosan. Films were cast from an aqueous acetic acid solution of azidated chitosan containing a model drug, such as theophylline. Irradiation of the film with ultraviolet (UV) light led to crosslinking of the drug incorporated film. IR spectra indicated complete surface crosslinking within 2 h of irradiation. Release of theophylline from uncrosslinked and crosslinked films was examined in simulated gastric and intestinal fluids without enzymes at 37 degreesC. The release of the drug from the crosslinked films was slower than the release from uncrosslinked films. Although the system is far from being optimized to obtain sustained release of a pharmacologically active agent for long periods, the data obtained indicate the possibility of developing photocrosslinkable matrices of biopolymers, such as chitosan, for sustained drug delivery with many advantages over chemical crosslinking. (C) 2002 Wiley Periodicals, Inc.