Browsing by Author "Thomas, V"

Now showing 1 - 12 of 12
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    Diethylene glycol acrylate-n-vinyl pyrrolidone copolymer resins for bone cement applications
    (INDIAN JOURNAL OF ENGINEERING AND MATERIALS SCIENCES, 2000) Celin, D; Thomas, V; Jayabalan, M
    Biodegradable and injectable monomer diethylene glycol acrylate (DGA) and diethylene glycol acrylate-n-vinyl pyrrolidone (DGA-VP) blends have been prepared and evaluated their suitability for bone cement applications. Studies on the setting of the monomer DGA and the blend DGA-VP have been carried out using a free radical initiator. Lower setting time is observed with the monomer in comparison with that of the blend. The degradation of cured PDGA and P(DGA-VP) polymeric materials has been evaluated in simulated physiological fluids. Studies on degradation in hydrolytic and oxidative media reveal faster degradation during initial period of aging followed by slower and steady state degradation. br vitro degradation studies show more hydrolytic degradation in PDGA while both hydrolytic and oxidative degradation in P(DGA-VP) in comparison to that of PDGA. Also, the biocompatible comonomer (VP) enhances biodegradation of aliphatic polyester PDGA.
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    In vitro studies on the effect of physical cross-linking on the biological performance of aliphatic poly(urethane urea) for blood contact applications
    (BIOMACROMOLECULES, 2001)
    The effect of physical cross-Linking in candidate cycloaliphatic and hydrophobic poly(urethane urea) (4,4'-methylenebis(cyclohexylisocyanate), H12MDI/hydroxy-terminated polybutadiene, HTPBD/hexamethylene-diamine, HDA) and poly(ether urethane urea)s (H12MDI/HTPBD-PTMG/HDA) on the in vitro calcification and blood-material interaction was studied. All the candidate poly(urethane urea)s and poly(ether urethane urea)s elicit acceptable hemolytic activity, cytocompatibility, calcification, and blood compatibility in vitro. The studies on blood-material interaction reveal that the present poly(urethane urea)s are superior to polystyrene microtiter plates which were used for the studies on blood-material interaction. The present investigation reveals the influence of physical cross-link density on biological interaction differently with poly(urethane urea) and poly(ether urethane urea)s. The higher the physical cross-link density in the poly(urethane urea)s, the higher the calcification and consumption of WBC in whole blood. On the other hand, the higher the physical cross-link density in the poly(ether urethane urea)s, the lesser the calcification and consumption of WBC in whole blood. However a reverse of the above trend has been observed with the platelet consumption in the poly(urethane urea)s and poly(ether urethane urea)s.
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    Polypropylene fumarate/phloroglucinol triglycidyl methacrylate blend for use as partially biodegradable orthopaedic cement
    (BIOMATERIALS, 2001)
    Polypropylene fumarate/phloroglucinol triglycidyl methacrylate oligomeric blend-based bone cement was studied. Higher the percentage of phloroglucinol triglycidyl methacrylate, lesser the setting time. An optimum setting time could be arrived with 50: 50 blend composition of the two oligomers. Composite cement of 50:50 blend prepared with hydroxyapatite granules of particle size 125 mum binds bovine rib bones. The tensile strength of this adhesive bond was found to be 1.11 kPa. The thermal studies suggest the onset of cross-linking reaction in the cured blend if the blend is heated. The absence of softening endotherm in the cured blend shows the thermosetting-like amorphous nature of blend system, which may restrict the changes in creep properties. The in vitro biodegradation studies reveal possible association of calcium ions with negatively charged units of degrading polymer chain resulting in slow down of degradation. Relatively slow degradation was observed in Ringer's solution. The study reveals the potential use of polypropylene fumarate/phloroglucinol triglycidyl methacrylate as partially degradable polymeric cement for orthopaedic applications. (C) 2001 Elsevier Science Ltd. All rights reserved.
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    Porphyrin and doxorubicin mediated nanoarchitectonics of copper clusters: a bimodal theranostics for cancer diagnosis and treatment in vitro
    (J Mater Chem B., 2024-01) Joseph, M; Rahman Pathiripparambath, MS; Thomas, V; Tharayil, H; Jayasree, RS; Nair, LV
    Nanoarchitectonics, an emerging strategy, presents a promising alternative for developing highly efficient next-generation functional materials. Multifunctional materials developed using nanoarchitectonics help to mimic biological molecules. Porphyrin-based molecules can be effectively utilized to design such assemblies. Metal nanocluster is one of the functional materials that can shed more insight into developing nanoarchitectonic materials. Herein, an inherently near-infrared (NIR) fluorescing copper nanocluster (CuC)-mediated structural assembly via protoporphyrin IX (PPIX) and doxorubicin (Dox) is demonstrated as the functional material. Dox-loaded porphyrin-mediated CuC assembly shows singlet oxygen generation and 66% drug release at 15 min. Furthermore, the efficacy of this material is tested for cancer diagnosis and bimodal therapeutic strategy due to the fluorescing ability of the cluster and loading of PPIX as well as the drug, respectively. The nanoarchitecture exhibits targeted imaging and 83% cell death in HeLa cells upon laser irradiation with 10 nmoles and 20 nmoles of PPIX and Dox, respectively.
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    Role of left atrial compliance in determination of left atrial pressures in pure mitral stenosis and the effect of age on it - A hemodynamic study in patients undergoing balloon mitral valvotomy
    (AMERICAN JOURNAL OF CARDIOLOGY, 2006) Namboodiri, NKK; Thomas, V; Tharakan, JA; Krishnamoorthy, KM; AjithKumar, VK; Harikrishnan, S; Dora, KSK; Nair, K; Sivasankaran, S; Titus, T
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    Studies on poly(propylene fumarate-co-ethylene glycol) based bone cement
    (BIO-MEDICAL MATERIALS AND ENGINEERING, 2000)
    Poly( propylene fumarate-co-ethylene glycol) random (PPF-1) and block (PPF-2) copolymer oligomers were prepared. Comparing the setting characteristics of PPF-1 and PPF-2 with comonomer n-vinyl pyrrolidone (n-VP) and swelling characteristics of cured PPF-1 and PPF-2, lower setting temperature and setting time was observed with the former leading to higher swelling coefficient and lower cross link density in the cured PPF-1. Due to the high swelling coefficient and low setting exothermic temperature associated with PPF-1, the bone cement was prepared from PPF-1, n-VP and hydroxyapatite (HAP).The in vitro degradation studies reveal lesser weight loss and deformation of PPF-1/n-VP/HAP based cured resin in Ringer's solution and phosphate buffered saline in comparison with that of PPF-1/n-VP cured resin. Though the bone cement composite has adequate mechanical properties with HAP, the compressive strength and modulus of the composite aged in Ringer's solution and PBS reduced appreciably which is due to extensive hydration and plasticization by the PEG unit. However, the bone-binding and bond strength of the bone cement determined as the load for separation of bones was found to be similar to that of fast setting calcium phosphate - atelocollagen (5%) bone cement. The bone cement PPF-1/n-VP/HAP could be used as scaffold for correcting the bone defects.
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    Studies on polyurethane potting compound based on HDI-TMP adduct for fabrication of haemodialyzer
    (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 2001)
    Polyurethane potting compounds based on hexamethylene diisocyanate-trimethylol propane (HDI-TMP) adduct (Component "A") and polypropylene glycol, polyethylene glycol and castor oil (Component "B") were prepared as potential compounds for the fabrication of haemodialyzer. The setting characteristics of the potting compounds having isocyanate index 2.0 are better than those compounds having 1.35. The aging stability of PEG and PPG based potting compounds are poorer than those of castor oil based potting compounds. Appreciable hydrolytic, oxidative and chemical stability could be observed with castor oil based potting compounds of HDI-TMP adduct. (C) 2001 Kluwer Academic Publishers.
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    Studies on polyurethane potting compound based on isocyanurate of aliphatic diisocyanate for fabrication of a haemodialyser
    (JOURNAL OF BIOMATERIALS APPLICATIONS, 2000)
    Polyurethane potting compounds based on multifunctional isocyanurate of aliphatic diisocyanate, hexamethylene diisocyanate (HDI-IC) as Component A and polypropylene glycol, polyethylene glycol and castor oil (Component B) were prepared as potential potting compounds for the fabrication of a haemodialyser. The setting characteristics of the potting compounds having isocyanate index 2.54 are better than those of the compounds having 1.77. The ageing stability of castor oil and PPG-based potting compounds having isocyanate index 2.54 is better than that of PEG oil-based potting compounds. Appreciable hydrolytic, oxidative and chemical stability could be observed with HDI-IC/PPG/2.54 potting compounds for development of haemodialyser, oxygenator, etc.
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    Studies on the effect of virtual crosslinking on the hydrolytic stability of novel aliphatic polyurethane ureas for blood contact applications
    (JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, 2001)
    The effect of virtual crosslinking on the hydrolytic stability of completely aliphatic novel poly(urethane ureas), HFL9-PU1 (hard-segment content 57.5%) and HFL13-PU2 (hard-segment content 67.9%) based on 4,4'-methylene bis(cyclohexyl isocyanate) (H12MDI)-hydroxyterminated polybutadiene-1,6-hexamethylene diamine, was studied. Fourier transform infrared-attenuated total refectance and wide-angle X-ray diffraction studies revealed hydrogen-bonding interaction and microphase separation and formation of crystallites by short- and long-range ordering in hard-segment domains. Three-dimensional net-works from hydrogen bonding in the present polymers lead to virtually crosslinking and insolubility. These polymers were noncytotoxic to L929 fibroblast cells. The hemolytic potential is below the accepted limit. The studies on in vitro biostability in Ringer's solution, phosphate buffered saline, and papain enzyme revealed no weight loss. The infrared spectral studies revealed changes in the surface, especially on HFL9-PU1 aged in Ringer's solution and phosphate buffered saline, and no changes when aged in papain. The marginal changes noticed in tensile properties were attributed to the changes in degree of hydrogen bonding and associated rearrangement of molec;lar structure in the bulk. The results revealed that the lesser the crosslinking in virgin polymer, the higher the crosslinking in aged polymer and vice verse. Increased crosslinking during aging provided increased tensile properties in the aged polymer over the virgin polymer and vice versa. For comparison, an aliphatic polyetherurethane urea (HFL16-PU3) was also synthesized using poly(oxy tetra methylene glycol) in addition to the above reactants. Though both HFL9-PU1 and HFL16-PU3 contained the same hard-segment content, the aged sample of the latter showed decreased tensile properties with increased crosslinking during aging in contrast to the former. This was attributed to less microphase separation in the virgin HFL16-PU3 polymer. (C) 2001 John Wiley & Sons, Inc.
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    Synthesis and Evaluation of Carboxy-Terminated Poly(trimethylene propane trifumarate)-Poly(ethylene glycol) as a Biodegradable Mucoadhesive Resin
    (ADVANCES IN POLYMER TECHNOLOGY, 2013) Jency, PJ; Thomas, V; Jayabalan, M
    Carboxy-terminated poly(trimethylene propane trifumarate) (CT-TPF) oligomers were prepared as a mucoadhesive resin using different process variables. The process variables influence the condensation and molecular size and reactivity of the resin leading to different resins with variation in reactivity and molecular size. Four oligomers were prepared by refluxing at different temperatures, TPF1 (refluxing at 70-80 degrees C for 15 min), TPF2 (refluxing at 80-100 degrees C for 60 min), TPF3 (refluxing at 120-140 degrees C for 15 min), and TPF4 (refluxing at 120-140 degrees C for 30 min). A process parameter with refluxing at 120-140 degrees C for 30 min resulted in a higher molecular weight fast setting resin, TPF4 (M-n 2700, M-w 2920 and polydispersity 1.08). Hydrogel adhesives were prepared using TPF4 resin, poly(ethylene glycol) dimethacrylate (PEGDMA, M-n 750), and n-vinyl pyrrolidone. TPF4 undergoes setting with setting time 8 +/- 0.55 min with PEGDMA and n-vinyl pyrrolidone. The present hydrogel adhesive has higher shear holding time, 105 +/- 3 s and peel strength 13 +/- 0.002 kg/m at the speed of 0.022 m/s. The aging of the cured adhesive in the simulated biological fluids reveals gradual degradation due to the cross-linked nature of the cured adhesive. The cured hydrogel adhesive is cytocompatible with L929 fibroblast cells. (C) 2013 Wiley Periodicals, Inc.
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    Synthesis of hydrolytically stable low elastic modulus polyurethane-urea for biomedical applications
    (POLYMER INTERNATIONAL, 2000) Jayabalan, M; Lizymol, PP; Thomas, V
    Polyurethane-urea without ether linkages was synthesised using dicyclohexyl-methane diisocyanate (SMDI), hydroxy-terminated polybutadiene (HTPBD) and m-phenylenediamine (PDA). The hydrolytic stability of this polymer was investigated under in vitro conditions using Ringer's solution and phosphate-buffered saline, and the stability of candidate polyurethane-urea polymers was compared with that of polyurethane prepared with SMDI, HTPBD and I,4-butanediol [BD]. The change of tensile properties, hardness and surface properties in the aged polymer is significant for polyurethane when compared with those of polyurethane-urea polymer. The in vitro study revealed possible applications of polyurethane-urea for long-term biomedical applications. (C) 2000 Society of Chemical Industry.
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    The effect of virtual cross linking on the oxidative stability and lipid uptake of aliphatic poly(urethane urea)
    (BIOMATERIALS, 2002)
    In vitro oxidative degradation and lipid sorption of aliphatic, low elastic modulus and virtually cross-linked poly(urethane urea)s based on 4,4' methylene bis(cyclohexyl isocyanate), hydroxy terminated poly butadiene and hexamethylene diamine were evaluated. The aged samples revealed no weight loss in the oxidation medium. The IR spectral analyses revealed the stability of unsaturated double bonds at 964 cm(-1) (characteristic for polybutadiene soft segment) with no change in peak intensity. The poly(tetramethylene glycol) (PTMG)-added poly(ether urethane urea) polymer also revealed no disappearance of IR peaks for ether and unsaturated double bonds in samples aged in vitro oxidation medium. All the polymers have shown increase in weight due to lipid up take in lipid-rich medium (palm oil) but it was rather low in Dulbecco's modified eagle medium (DMEM) cholesterol. The slight change in mechanical properties of the present polymers in oxidation and DMEM is due to the rearrangement of molecular structure with virtual cross links of hydrogen bonding (physical cross linking) without degradation and plasticization effect of lipid. The influence of these media on the rearrangement of virtual cross links has been observed. Higher the virtual cross-link density, lesser is the loss of tensile properties of poly(urethane urea)s in the oxidation medium and vice versa. On the other hand, higher the virtual cross-link density of poly(urethane urea), higher is the loss of ultimate tensile strength and stress at 100% strain and vice versa in DMEM medium. (C) 2001 Elsevier Science Ltd. All rights reserved.