Browsing by Author "Sivakumar, R"

Now showing 1 - 17 of 17
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    Biochemical lesions of platelets stored as concentrates in PVC bags
    (INDIAN JOURNAL OF MEDICAL RESEARCH, 1997)
    Acid-base status of platelet suspension during storage is a measure of the gas permeability of the bag material. To assess the efficacy of the bags available in our market to store platelets, we compared biochemical lesions of platelets stored in an Indian polyvinyl chloride (PVC) triple bag against a Japanese PVC bag standardized for 5 days platelet storage. Platelet concentrates prepared in both control and test PVC bags were stored for 72 h. Two ml samples were drawn 1 h after preparation, and then at 24 h intervals, for analysis. Our data show that the mean pH value in the test bags was maintained above 6.5. However, the CO2 tension was high and O-2 tension was low. We also analyzed malondialdehyde (MDA) formation which is a measure of arachidonic acid metabolism, and seemed to be unaffected in stored platelets. Lactate dehydrogenase (LDH) was not released into the plasma excessively anti hence significant platelet lysis was absent during storage. Hypotonic shock response (HSR) of platelets stored in both test and control bags was comparable, indicating the possibility of satisfactory post-transfusion recovery.
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    Dense hydroxy apatite ceramics through gel casting technique
    (MATERIALS LETTERS, 1996) Varma, HK; Sivakumar, R
    A simple gel casting process is described for the preparation of uniform green HAP (hydroxy apatite) ceramic bodies. Such green compacts were observed to sinter more uniformly compared to the compacts derived by the dry pressing technique. The samples were sintered at temperatures ranging between 1100 and 1250 degrees C for 2 h. The sintering characteristics of the compacts were assessed by density measurements, microhardness variations and scanning electron microscopy. The highest density was obtained for gel cast samples, i.e. > 99%, when they, were sintered at 1200 degrees C for 2 h. The microstructure of the above sample was highly uniform. The improved uniformity in structure and properties of the sintered gel cast samples would make them suitable for better dental and orthopaedic implants.
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    Evaluation of the sharpness of concentric needle electrodes by a penetration test.
    (Frontiers of medical and biological engineering : the international journal of the Japan Society of Medical Electronics and Biological Engineering, 2001)
    This paper deals with a method to evaluate the sharpness of the concentric needle electrode (CNE) and the consistency of sharpness on repeated penetration. An aluminum foil of standard thickness and properties was used as the penetration medium. A load profile was obtained as a function of time, and has been correlated with the shape and quality of grinding of the tip of the CNE. This load profile can be used as a quality evaluation method. This method is utilized for the assessment of the impairment of the needle tip on repeated penetration and hence for comparison of different needle electrode models.
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    Ferric iron-containing molecularly imprinted polymer as an adsorbent for cholesterol
    (ADSORPTION SCIENCE & TECHNOLOGY, 2003) Sreenivasan, K; Sivakumar, R
    Molecular imprinting is an elegant approach to the synthesis of polymers with predetermined recognition properties, the technique of molecular imprinting involving arranging the functional monomers around the print molecules prior to polymerisation. Molecularly imprinted polymers (MlPs) show a remarkable ability to bind print molecule from a mixture of entities which are close in structure. One of the serious drawbacks of MlPs is their low adsorption capacity and one approach to improving this relies on the use of chemically modified monomers in the synthesis of the MlPs. This report discusses the synthesis and evaluation of an MIP based on ferric acrylate as an adsorbent for cholesterol.
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    Haemolytic potential of hydroxyapatite and beta-tricalcium phosphate bioceramic powders
    (PROCEEDING OF THE FIRST REGIONAL CONFERENCE - IEEE ENGINEERING IN MEDICINE & BIOLOGY SOCIETY AND 14TH CONFERENCE OF THE BIOMEDICAL ENGINEERING SOCIETY OF INDIA, 1995) Varma, HK; Mohanan, PV; Rathinam, K; Sivakumar, R
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    Imparting recognition sites in poly(HEMA) for two compounds through molecular imprinting
    (JOURNAL OF APPLIED POLYMER SCIENCE, 1999) Sreenivasan, K; Sivakumar, R
    So far, molecularly imprinted polymers (MIPs) have been synthesized and evaluated as selective matrices for single components. It may be possible to impart multiple recognition sites in MIPs, which could be used as elements capable of binding more than one component. Such systems could advantageously be used in the design of sensors having the ability to sense more than one compound at a time. This communication discusses such a possibility by imprinting sites for two model compounds, namely, salicylic acid and hydrocortisone in poly(2-hydroxy ethyl methacrylate). (C) 1999 John Wiley & Sons, Inc.
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    Impedance measurement system for concentric needle electrodes
    (PROCEEDING OF THE FIRST REGIONAL CONFERENCE - IEEE ENGINEERING IN MEDICINE & BIOLOGY SOCIETY AND 14TH CONFERENCE OF THE BIOMEDICAL ENGINEERING SOCIETY OF INDIA, 1995) Khambete, ND; Shashidhara, J; Bhuvaneshwar, GS; Sivakumar, R
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    Interaction of molecularly imprinted polymers with creatinine
    (JOURNAL OF APPLIED POLYMER SCIENCE, 1997) Sreenivasan, K; Sivakumar, R
    Memory sites toward clinically relevant creatinine have been imparted in polymers based on methacrylic acid, AT-vinyl pyrrolidine, and 2-hydroxy ethyl methacrylate by the technique of molecular imprinting. The polymers are subjected to interaction with creatinine and creatine, a molecule of close resemblance with creatinine. The results show that selectivity is largely governed by the nature of the monomer. The reusability of the polymer is also demonstrated. (C) 1997 John Wiley & Sons, Inc.
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    Morphological & ultrastructural changes of platelet concentrates stored in PVC bags
    (INDIAN JOURNAL OF MEDICAL RESEARCH, 1997)
    To assess the effect of storage bags on platelets, we studied the morphological and ultrastructural changes of samples drawn from platelet concentrates (PC) prepared and stored in triple, poly vinyl chloride (PVC) bags, manufactured in India. Using the scanning electron microscopy, we demonstrate formation of long pseudopods, and interaction through these to form aggregates. When platelets were stored at 23+/-2 degrees C, morphological changes were severe compared to the deleterious effects when kept at 22+/-0.5 degrees C. Ultrastructural analysis also showed that maintenance of discoid shape and prevention of granule secretion could be improved by storing the platelets at 22+/-0.5 degrees C. Significant degree of platelet fragmentation took place when the storage temperature was high. The morphology score done for platelets stored st both 22+/-0.5 degrees C and 23+/-2 degrees C showed that preservation of discoid shape was better with the former.
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    On the development of an apatitic calcium phosphate bone cement
    (BULLETIN OF MATERIALS SCIENCE, 2000) Komath, M; Varma, HK; Sivakumar, R
    Development of an apatitic calcium phosphate bone cement is reported. 100 mu Particles of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) were mixed in equimolar ratio to form the cement powder. The wetting medium used was distilled water with Na2HPO4 as accelerator to manipulate the setting time. The cement powder, on wetting with the medium, formed a workable putty. The setting times of the putty were measured using a Vicat type apparatus and the compressive strength was determined with a Universal Testing Machine. The nature of the precipitated cement was analyzed through X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and energy dispersive electron microprobe (EDAX). The results shelved the phase to be apatitic with a calcium-to-phosphorous ratio close to that of hydroxyapatite. The microstructure analysis using scanning electron microscopy (SEM) showed hydroxyapatite nanocrystallite growth over particulate matrix surface. The structure has an apparent porosity of similar to 52%. There were no appreciable dimensional or thermal changes during setting. The cement passed the in vitro toxicological screening (cytotoxicity and haemolysis) tests. Optimization of the cement was done by manipulating the accelerator concentration so that the setting time, hardening time and the compressive strength had clinically relevant values.
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    On the relevance and requirements of biomaterials
    (BULLETIN OF MATERIALS SCIENCE, 1999) Sivakumar, R
    The technological orientation of current medical practice is reflected in the effective utilization of a number of diagnostic and therapeutic devices. Synthetic and natural biomaterials alone or in combination form the basis for development of such devices that are in contact with different tissues. The effect of materials on tissues and vice versa needs to be understood to ensure safety and effectiveness of the devices. This calls for biological evaluation of materials and devices, in addition to a spectrum of recommended toxicological testing of materials depending upon the duration and the type of tissue in contact with. Besides being non-toxic, the material is required to meet the functional requirements with the appropriate host response which is termed as biocompatibility. This paper reviews the evolution and the requirements of biomaterials. The in vitro and in vivo evolution methodologies are highlighted based on our experience in developing blood bag, dental composite, hydroxyapatite and fibrin glue. The requirements of biomaterials in the current context of advances in the fields of tissue engineering and biomimetics is outlined.
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    Polymeric precursor route for the preparation of calcium phosphate compounds
    (CERAMICS INTERNATIONAL, 1998) Varma, HK; Kalkura, SN; Sivakumar, R
    A polymeric combustion synthesis is described for the preparation of calcium phosphate compounds. The polymeric gel containing calcium and phosphate ions were synthesised by concentrating a solution of calcium nitrate and ethyl phosphate. When the above gel was introduced to a furnace kept at 500 degrees C, a self combustion reaction was observed, leaving behind a calcium phosphate precursor powder. The above powder on heat treatment at 1000 degrees C resulted in beta-TCP, HAP or a mixture of the two phases depending on the Ca/P ratio in the gel. Dependence of Ca/P ratio on the composition of the calcium phosphate phase was studied by XRD. The morphological features of the precursor as well as the heat treated compounds were studied by SEM. The method offers an easy route for the preparation of beta-TCP or HAP in the powder or in the porous form. (C) 1998 Elsevier Science Limited and Techna S.r.l. All rights reserved.
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    Short term tissue response to carbon fibre: A preliminary in vitro and in vivo study
    (BULLETIN OF MATERIALS SCIENCE, 1998) Mohanty, M; Kumary, TV; Lal, AV; Sivakumar, R
    Carbon in the form of pyrolytic carbon coating is used in a number of implantable medical devices. Carbon-reinforced carbon composite and other forms of diamond-like carbon coatings are being evaluated for their many potential biomedical applications. There is also a possibility of using carbon in fibre form. Though the possibility of using the fibre form of carbon in skeletal and dental implants has been recognized, a detailed study of tissue reaction to carbon fibre has not been reported so far. In this paper, we describe in vitro and irt vivo evaluation of carbon fibre in bone and muscle. Good cell and tissue biocompatibility of the material was observed in bone and muscle. New bone was present in contact with the fibres. Results of this study indicate that carbon fibre has potential in non-load bearing applications, such as skeletal repair and as ligament prosthesis.
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    Structural studies on bovine bioprosthetic tissues and their in vivo calcification: Prevention via drug delivery
    (BIOMATERIALS, 1996)
    Cardiovascular calcification, the formation of calcium phosphate deposits in cardiovascular tissue, is a common end-stage phenomenon affecting a wide variety of bioprostheses. To study the process of calcification in tissue prosthetics, glutaraldehyde-treated bovine pericardium, dura mater and fascialata were implanted subcutaneously in rats and retrieved 21 days later and thereby morphological findings were correlated with biochemically determined levels of calcium. Transmission electron microscopy showed that calcification primarily involved the surface of collagen fibrils and the interfibrillar spaces. The deposition of calcium was higher with dura and fascia prostheses compared to pericardium. However, the release of Fe3+ ions from chitosan matrix had substantially inhibited the deposits of calcium in all implanted tissues. It seems that the structural and anatomical features of the tissue is one of the important factors for tissue-associated calcification. It is also confirmed that glutaraldehyde-preserved pericardium is the most suitable material for the development of cardiac prosthesis, with an appropriate drug combination therapy for prevention of pathological calcification.
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    Tensile set behavior of Foley catheter balloons
    (JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, 1999)
    The removal of indwelling urinary balloon catheters from patients is usually associated with many problems. The problems such as balloon deflation failure; encrustations on balloons, eyes, and lumen; and catheter associated infections are widely discussed in the literature. The tensile set exhibited by the catheter balloon material could also play a role and further complicate the removal process. This article addresses this issue by comparing the tensile set behavior of the balloon material from three commercially available Foley catheters, The balloon materials were subjected to aging in synthetic urine at 37 degrees C for 28 days to simulate clinical conditions. The deflation time of catheter balloons aged in similar conditions were also measured. It was found that different brands of catheters exhibited statistically significant differences in their properties. The tensile set data of the aged samples could be correlated with the deflation time of the balloons. The clinical significance of the tensile set is also highlighted. (C) 1999 John Wiley & Sons; Inc.
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    The mechanism of material removal in laser fusion cutting
    (LASERS IN ENGINEERING, 1996) Bharti, A; Sivakumar, R
    Laser cutting is rapidly emerging as a cost effective alternative to the conventional cutting specially, in sheet metal cutting. Its application have grown much faster than its basic understanding. The present study has been performed to develop a comprehensive understanding of the laser fusion cutting (FC). Mechanisms those are operative during the laser FC have been identified using the cutting data from the extensive parametric study of laser cutting of 304 stainless steel. They have been identified as splashing of molten substrate, vaporisation and fracture in the semisolid state. They predominently operate during successive stages of FC as the cut progress through cross section. As a result of which three distinct zones are generally formed on the cut surface. Schemes for characterization of laser cut surface and evaluation of cutting performance have also been proposed. Effect of various process variables on cutting performance have been discussed in detail. Based on proposed mechanisms an approach to obtain a quality cut with minimum specific energy and material loss has been outlined.
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    Water vaporization from heated tissue: An in vitro study by differential scanning calorimetry
    (LASERS IN SURGERY AND MEDICINE, 1996)
    Background and Objective: The heat balance equation is central to modeling laser vaporization of tissue. Because about 70% of tissue is water, energy loss due to water vaporization becomes an important consideration in modeling. In this study, the rate and pattern of water vaporization from various animal tissues studied by differential scanning calorimetry (DSC) are reported. StudyDesign/Materials and Methods: DSC thermograms of fresh muscle, liver, and kidney tissues were made at heating rates of 2 degrees C/min, 5 degrees C/min, and 10 degrees C/min in the temperature range of 30-150 degrees C. Thermograms of vacuum-dried muscle sample were also made to establish that the endotherms obtained were essentially due to the water in the tissue.Results and Conclusion: Two broad peaks-one below and the other above 100 degrees C-are seen in all the endotherms. The peaks are attributed to the structural and compositional features of tissue and tissue water. The two-stage vaporization pattern has importance in modeling tissue heating by a continuous-wave Nd:YAG laser. (C) 1996 Wiley-Liss, Inc.