Now showing 1 - 10 of 12
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    Facile, shear-induced, rapid formation of stable gels of chitosan through in situ generation of colloidal metal salts
    (01-01-2018)
    Ravishankar, Kartik
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    Kanniyappan, Hemalatha
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    Shelly, K. M.
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    A novel method of preparing chitosan gels using in situ generated negatively-charged colloidal salts of a variety of metal ions is described. Their potential as scaffolds for tissue-engineering and as recoverable catalysts in aza-Michael addition is demonstrated here. Given their wide range of properties, they have broad scope for applications.
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    Valorization of agro-wastes for the biosynthesis and characterization of polyhydroxybutyrate by Bacillus sp. isolated from rice bran dumping yard
    (01-04-2021)
    Krishnan, Sivakumar
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    Chinnadurai, Gandhi Shree
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    Ravishankar, Kartik
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    Perumal, Palani
    Investigations have been made to determine the usage of inexpensive agro-waste products as an alternative carbon source for the production of degradable bacterial polyester. Among 33 bacterial isolates, a gram-positive bacterium PPECLRB-16 isolated from rice bran dumping yard was found to accumulate a relatively higher quantity of PHB and identified as Bacillus sp. through 16S rRNA gene sequence analysis. The higher PHB producing bacterial isolate was grown with different inexpensive agro-wastes to determine the suitable carbon source for its growth and PHB production. The one-factor-at-a-time approach comparatively enhanced PHB yield (5.64 g/L) when grown for 48 h with 1.5% (w/v) of defatted oil cake at a pH of 7.0. The bacterially accumulated PHB was isolated from the cells, purified, and characterized using solid-state 13C NMR, FT-IR, Powder XRD, TGA, GPC, Tensile and HR-SEM analyses. The hydrophobicity and printing accessibility of recovered PHB were demonstrated using contact angle measurement by coating on different surfaces. The results obtained in the present investigation have thrown light on the potential usage of agro-waste by-products, mainly oil cake, as an appropriate carbon source for the commercial production of PHB by Bacillus sp. in a cost-effective way.
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    Publication
    Biocompatible Porous Scaffolds of Chitosan/Poly(EG- ran-PG) Blends with Tailored Pore Size and Nontoxic to Mesenchymal Stem Cells: Preparation by Controlled Evaporation from Aqueous Acetic Acid Solution
    (31-08-2018)
    Sadhasivam, Balaji
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    Ravishankar, Kartik
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    Desingh, Rajpreeth
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    Subramaniyam, Rajalakshmi
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    The preparation of porous films (average size variation from 1 to 32 μm) of a 1:1 blend of chitosan with poly(EG-ran-PG) by the controlled evaporation of water from a 2 wt % aqueous acetic acid solution is reported. Interestingly, the blend exhibited porosity that could be tailored from 1 to 32 μm with the temperature of preparation of the blend film. The powder X-ray diffraction, Fourier transform infrared, and differential scanning calorimetry analyses of the films suggested the formation of partially miscible blends. Temperature-induced phase separation of the blend appears to be the mechanism of pore formation. The tensile strength, cytotoxicity, and biocompatibility of the blend films for the growth of mesenchymal stem cells were assessed vis-a-vis chitosan. The 1:1 blend film was observed to lack cytotoxicity and was also viable for the growth of mesenchymal stem cells. The tensile properties of the 1:1 blend were superior to those of the chitosan film. The simple preparation of porous, nontoxic, and biocompatible films could find use as a scaffold in the growth of tissue, and especially bone tissue, in wound dressing, and in filtration if a better control over pore size is achieved.
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    Rapid, solvent-free synthesis of amorphous, photoluminescent, carbon nanodots from imidazole and maleic anhydride solids
    (05-08-2019)
    Ravishankar, Kartik
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    Shelly, K. M.
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    Narayanan, Abathodharanan
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    A facile, rapid, and sustainable synthesis of amorphous, photoluminescent, carbon nanodots in high yields (∼51%), by cogrinding of maleic anhydride and imidazole, is reported for the first time. The heat liberated during the exothermic oligomerization of maleic anhydride, initiated by imidazole in the solid state, was identified to be the cause of carbonization of the reaction mixture. These carbon nanodots showed very low cytotoxicity toward mesenchymal stem cells, even at very high concentrations (1 mg/mL). Having the highest adsorption capacity for ammonia among unmodified carbons reported to date (∼19.3 mg/g), these carbon nanodots could be used for the removal of ammonia from the gas phase. In addition, these carbon nanodots could be used as an ionotropic cross-linker for chitosan, to prepare stable gels, suitable for a wide variety of applications. In contrast to the present solid-state methodologies which involve the use of hazardous chemicals or high temperatures, this solvent-free method of preparing carbon nanodots is sustainable, facile, safe, and inexpensive.
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    Facile chemical modification of poly(vinyl alcohol) to an organosoluble, flame-retardant copolymer using dichloroacetic acid
    (05-10-2023)
    Km, Shelly
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    Ravishankar, Kartik
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    Applications of poly(vinyl alcohol) (PVOH) are largely limited due to its poor flame resistance. In this work, organosolubility, and flame resistance are imparted to PVOH through green chemical transformation using dichloroacetic acid (DCAA). Unlike the conventional solvent-based strategies, PVOH was modified by simply mixing it with DCAA and heating the mixture without employing any additional reagents/catalysts/solvents. This resulted in the formation of a random copolymer, poly(vinyl alcohol-co-vinyl dichloroacetate), which was not soluble in water but was soluble in organic solvents such as acetone, methanol, and dimethylsulfoxide. Furthermore, the copolymer was inherently self-extinguishing, and did not melt drip or show glowing combustion. Additionally, dummy currency notes coated with this copolymer displayed exceptional self-extinguishing and non-glowing properties when removed from the flame, proving the copolymer's suitability for flame-retardant sizing/coating applications.
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    Green, Solid-State Synthesis of Maleated Chitosan and Ionotropic Gelation with Chitosan
    (05-11-2018)
    Ravishankar, Kartik
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    Shelly, K. M.
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    Desingh, Raj Preeth
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    Subramaniyam, Rajalakshmi
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    Narayanan, Abathodharanan
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    We, for the first time, report a green, solid-state method for synthesizing maleated chitosan, wherein maleation is brought about by stirring chitosan flakes in molten maleic anhydride. In a similar manner, other derivatives like succinated chitosan could also be prepared. Maleated chitosan, given its polyanionic nature in solution form, could be further used to cross-link chitosan polycation through electrostatic complexation. The resulting "all-chitosan" gel, having very low cytotoxicity and a conducive surface for cell attachment, could be used as scaffolds for tissue engineering. In this context it is to be noted that presently, maleation of chitosan has been invariably carried out in solution phase, using harsh, environmentally aggressive solvents such as DMSO, DMF, acetamide and the like.
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    Statistical augmentation of polyhydroxybutyrate production by Isoptericola variabilis: Characterization, moulding, in vitro cytocompatibility and biodegradability evaluation
    (01-01-2021)
    Krishnan, Sivakumar
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    Chinnadurai, Gandhi Shree
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    Ravishankar, Kartik
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    Perumal, Palani
    This study aimed to explore the production of polyhydroxybutyrate (PHB), a polyhydroxyalkanoate (PHA), which has been widely considered as a potential substitute for the synthetic polymers. Among 53 actinomycete isolates, 11 of them were found to be PHB positive and the quantity of PHB from the positive isolates varied from 10.5 to 29.82 wt% on a dry cell weight basis. A strain designated as PPLAT 012, accumulated relatively higher PHB and has been identified as Isoptericola variabilis by 16S rRNA gene sequence analysis. An effort has also been made to optimize the PHB production by the hyper-producing strain using the conventional, one-factor-at-a-time, and statistical response surface methodologies and the maximum PHB production (46.18%) in DSMZ medium, amended with 12% glucose and 9% potassium nitrate with a pH of 7.0. Further, the characteristic properties such as processability, cytocompatibility and biodegradability of the extracted PHB was also demonstrated. The physical properties of the recovered PHB was further improved by blending with PLA and the resultant blends were characterized. The present investigation has demonstrated that the isolate, Isoptericola variabilis, could be utilized as a potential source for the production of PHB with desirable characteristics, suitable for biomedical applications.
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    Wear-induced mechanical degradation of plastics by low-energy wet-grinding
    (01-12-2018)
    Ravishankar, Kartik
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    Ramesh, Praneeth Srivanth
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    Sadhasivam, Balaji
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    Mechanical degradation of polymers reported so far, utilize cutting, impact or attrition for size reduction, which is very different from the low-magnitude forces experienced by the polymers during their service life. In this work, we have studied the effect of such low-magnitude forces, on the polymeric materials, using a low-energy rolling compression-type wet-grinder. The rolling compression action produces shear and compression on the polymer, leading to abrasion and resulting in the formation of crazes, micro-cracks and chip-offs, akin to the wearing. Measurements using Raman spectroscopy showed that the shear forces, generated upon grinding, produced strains on the polymer backbone, which upon sufficient build-up, results in chain scission at the points of physical entanglement. These homolytic chain scissions produced “mechano”radicals, which were confirmed by radical-scavenging using DPPH. The ensuing reduction in the molecular weight was further analyzed using GPC, light scattering and viscometry. Surprisingly, XRD measurements showed strain-induced crystallization as well. In order to theoretically validate the studies, a probabilistic model, explaining the “complex” response of the molecular weight distribution and the PDI upon mechanical degradation, has also been presented. Crosslink density function was incorporated to explain the preferential chain scission of the high molecular weight species, leading to a gradual reduction in the average molar mass.
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    Facile preparation of biocompatible macroporous chitosan hydrogel by hydrothermal reaction of a mixture of chitosan-succinic acid-urea
    (01-11-2019)
    Govindaraj, Prabha
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    Abathodharanan, Narayanan
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    Ravishankar, Kartik
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    The facile preparation of macroporous, super water absorbing, biocompatible hydrogels of chitosan involving the hydrothermal reaction of a mixture of chitosan (CH), succinic acid (SA) and urea (UR), all of which are sustainable materials, is reported. The structure of the dry CHSAUR was ascertained by CP MAS-SS NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, powder x-ray diffraction analysis (PXRD), and thermogravimetric analysis (TGA). The principle role of UR in the synthesis was identified as the source of ammonia, which increased the pH of the acidic chitosan solution with reaction time, leading to the formation of the insoluble hydrogel of chitosan accompanied by the formation of pores of different sizes and volumes. In addition, a small fraction of urea participated in chemical reaction with the primary hydroxyl groups in the sixth position of the glucosamine repeat units of chitosan resulting in carbamate linkages. The as-prepared hydrogel, following workup and methanol extraction, was found to be chitosan crosslinked with succinic acid through electrostatic interaction. It was macroporous with percentage porosity varying between 49.4% to 64.2%. It also exhibited different extents of water uptake with the maximum of 760 ± 20 g/g being for the one prepared with the weight ratio of 1: 4: 4 of chitosan: succinic acid: urea. The absorption of water is found to arise out of the porosity as well as presence of water attracting chitosan ammonium cation-succinate electrovalent bonds that are formed by the reaction between SA and ammonium cation of the chitosan backbone. The absorption of saline water was relatively poor suggesting that the saline water absorption might be arising largely due to the presence of micropores and specific interaction. The hydrogels exhibited Herschel-Bulkley rheological behavior. The extraction of CHSAUR with 0.1 N NaOH in methanol resulted in the removal of the physical crosslinks, consisting of succinate anions; the presence of chitosan with porous morphology was confirmed additionally by copper (+2) adsorption. In contrast to the widely reported method of preparing microporous chitosan scaffold of cylindrical shape that takes several days to a week, the present method offers a simple means of preparing macroporous chitosan of any shape and size in very large scale with soft foam-like morphology. With its biocompatibility towards mouse fibroblast cells it could find applications in drug delivery, biodegradable super water absorbency and haemostatic applications.
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    Solvent-less carboxymethylation-induced electrostatic crosslinking of chitosan
    (31-12-2023)
    Km, Shelly
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    Ravishankar, Kartik
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    Lobo, Nitin Prakash
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    Baskar, Ramaganthan
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    The successful N-carboxymethylation and concomitant crosslinking of solid chitosan upon heating its mixture with solid monochloroacetic acid, without the use of solvents or catalysts, is reported. The N-carboxymethylation was confirmed through the analysis of the partially depolymerized product using NMR spectroscopy, as well as a control reaction with lysine. This transformation was facilitated by the nucleophilic nature of the free amine group in the repeating unit of chitosan, which possesses lone pair of electrons capable of attacking the carbon center bearing the leaving group and displacing the leaving group in a concerted manner. The crosslinking, on the other hand, was established by the observed insolubility in aqueous acidic solutions, even when subjected to prolonged heating at 60 °C. This crosslinking occurs due to the electrostatic interactions between the carboxylate groups and the adjacent ammonium groups, as supported by evidence from FTIR spectroscopy and a control reaction involving ethyl chloroacetate. The resulting crosslinked carboxymethyl chitosan demonstrated its usefulness in the adsorption of methyl orange and fluorescein, as well as functioning as an organic catalyst for aza-Michael addition, Hantzsch reaction, and substituted perimidine synthesis.