Browsing by Author "Balakrishnan, B"

Now showing 1 - 7 of 7
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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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    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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    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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    Self-cross-linking biopolymers as injectable in situ forming biodegradable scaffolds
    (BIOMATERIALS, 2005)
    The injectable polymer scaffolds which are biocompatible and biodegradable are important biomaterials for tissue engineering and drug delivery. Hydrogels derived from natural proteins and polysaccharides are ideal scaffolds for tissue engineering since they resemble the extracellular matrices of the tissue comprised of various amino acids and sugar-based macromolecules. Here, we report a new class of hydrogels derived from oxidized alginate and gelatin. We show that periodate-oxidized sodium alginate having appropriate molecular weight and degree of oxidation rapidly cross-links proteins such as gelatin in the presence of small concentrations of sodium tetraborate (borax) to give injectable systems for tissue engineering, drug delivery and other medical applications. The rapid gelation in the presence of borax is attributed to the slightly alkaline pH of the medium as well as the ability of borax to complex with hydroxyl groups of polysaccharides. The effect of degree of oxidation and concentration of alginate dialdehyde, gelatin and borax on the speed of gelation was examined. As a general rule, the gelling time decreased with increase in concentration of oxidized alginate, gelatin and borax and increase in the degree of oxidation of alginate. Cross-linking parameters of the gel matrix were studied by swelling measurements and trinitrobenzene sulphonic acid (TNBS) assay. In general, the degree of cross-linking was found to increase with increase in the degree of oxidation of alginate, whereas the swelling ratio and the degree of swelling decreased. The gel was found to be biocompatible and biodegradable. The potential of the system as an injectable drug delivery vehicle and as a tissue-engineering scaffold is demonstrated by using primaquine as a model drug and by encapsulation of hepatocytes inside the gel matrix, respectively. (C) 2004 Elsevier Ltd. All rights reserved.
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    Tween 20-modified poly(vinyl chloride) exhibits enhanced blood-compatibility
    (POLYMER INTERNATIONAL, 2005) Balakrishnan, B; James, NR; Jayakrishnan, A
    Poly(vinyl chloride) (PVC) resin was modified by grafting the non-ionic surfactant poly(oxyethylene 20 sorbitan) monolaurate (Tween (R) 20) using isocyanate chemistry. PVC was aminated using ethylenediamine and coupled with hexamethylene diisocyanate. Tween 20 was then reacted with the polymer, resulting in the grafting of the surfactant. The polymer modification was confirmed using infrared and X-ray photo-electron spectroscopy. Films of modified polymer were cast from a solution of tetrahydrofuran. The surface of films prepared from the modified polymer showed increased hydrophilicity as evidenced by contact-angle measurements. The solid/water free energy of the modified polymer surface was nearly a quarter of the energy of the bare PVC surface. Static platelet adhesion studies using platelet-rich plasma demonstrated significantly reduced adhesion onto a modified PVC surface compared with unmodified PVC. Data obtained demonstrate that modification of polymers with Tween 20 may be an interesting way of imparting protein- and cell-repelling characteristics to them, thereby improving their blood-compatibility. (c) 2005 Society of Chemical Industry.