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Biomedical subjects

M Sivakumar

Publications and source records attributed to M Sivakumar.

At least 19 recordsLinked to original sources
PubMed2006

Influence of tubule orientation on cone-shaped texture development in laser-ablated dentin.

In the present paper, the influence of tubule orientation on surface texture development was studied. Specimens of dentin with a wide range of tubule orientations were extracted from caries-free human teeth, processed using KrF laser radiation, and analyzed by scanning electron microscopy. When a transverse cross section of dentin cut perpendicularly to the tooth axis is processed with KrF laser radiation, a cone-like topography develops in the inner dentin where tubules are parallel to the laser beam. When laser processing is carried out in the outer dentin, because tubules are significantly tilted with respect to the laser beam, flat surfaces are achieved. The surface texture after laser processing depends effectively on the angle between the tubules and the laser beam. The dependency of cone growth on tubule orientation was confirmed using a simple differential ablation model.

Collagen↗
PubMed2006

Niacin affects cell adhesion molecules and plasminogen activator inhibitor-1 in HepG2 cells.

BACKGROUND: Beyond lipid-modifying actions, niacin lowers the risk of atherothrombotic events by lowering prothrombotic factors like fibrinogen. Plasminogen activator inhibitor type 1 (PAI-1) is a potential factor for atherogenesis and thrombosis, increased in acute myocardial infarctions and restenosis after angioplasty. Cell adhesion molecules (CAM) mediate adhesion, recruitment and migration of white blood cells through vascular surfaces, an essential process in atherogenesis. ICAM-1 is a significant predictor of future coronary events. Whether niacin affects ICAM-1 expression is unknown. We studied the effects of niacin on PAI-1 and CAM using HepG2 cells. METHODS: HepG2 cells were cultured in DMEM until 90% confluent. After serum starvation, cells were exposed to DME/F12 containing niacin. Transforming growth factor-beta (TGF-beta) was added directly to cell media. Cell lysate and conditioned media were collected for measurement of PAI-1 by ELISA. For measurement of ICAM, cells were treated with tumor necrosis factor-alpha (TNF-alpha) instead. The effect of niacin on mRNA expression of ICAM-1 was studied using RT-PCR. RESULTS: Niacin reduced the TGF-beta-induced rise by 30% to 55% (p=0.002). The differences in degree of PAI-1 reduction, between different niacin concentrations, were not statistically significant. Niacin reduced TNF-alpha-induced rise in ICAM-1 levels by 66% to 89% (p<0.0001), but did not significantly affect TNF-alpha-induced rise in PECAM-1. Semiquantitative RT-PCR analysis showed that reduced TNF-alpha-induced rise in ICAM-1 mRNA expression significantly by 17% (p=0.001). CONCLUSIONS: Treatment with niacin suppressed PAI-1 and ICAM-1 levels in HepG2 cells. Further studies to understand the mechanistic pathways of this suppression, could further explain benefits of niacin in prevention of atherosclerotic disease, and offer therapeutic avenues against the rising burden of atherothrombotic disease.

Cell Adhesion Molecules↗
PubMed2005

Transdermal drug delivery using ultrasound-theory, understanding and critical analysis.

This review focuses on a unique transdermal drug delivery enhanced by the action of ultrasound, referred as sonophoresis. Sonophoresis is an active form of transdermal delivery which enhances the transport of permeants, such as drugs through cell membranes as a result of ultrasonic energy. Ultrasonic sound waves cause acoustic cavitation, the resultant effects of which microscopically disrupt the lipid bilayers of the stratum corneum and thereby influencing the influx of permeants. Sonophoresis increases the penetration of various low molecular weight drugs as well as high molecular weight proteins. The objective of this review is to account the role of ultrasound parameters and the associated cavitational effects, gained through a number of investigations, in order to facilitate the understanding of this method.

Administration, Cutaneous↗
PubMed2005

Small threat and contraband detection with TNA-based systems.

The detection of small threats, such as explosives, drugs, and chemical weapons, concealed or encased in surrounding material, is a major concern in areas from security checkpoints to UneXploded Ordnance (UXO) clearance. Techniques such as X-ray and trace detection are often ineffectual in these applications. Thermal neutron analysis (TNA) provides an effective method for detecting concealed threats. This paper shows the effectiveness of Ancore's SPEDS, based on TNA, in detecting concealed liquid threats and differentiating live from inert mortar shells.

Chemical Warfare↗
PubMed2003

Preparation, characterization, and in vitro release of gentamicin from coralline hydroxyapatite-alginate composite microspheres.

In this work, composite microspheres were prepared from bioactive ceramics such as coralline hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2)] granules, a biodegradable polymer, sodium alginate, and an antibiotic, gentamicin. Previously, we have shown a gentamicin release from coralline hydroxyapatite granules-chitosan composite microspheres. In the present investigation, we attempted to prepare composite microspheres containing coralline hydroxyapatite granules and sodium alginate by the dispersion polymerization technique with gentamicin incorporated by absorption method. The crystal structure of the composite microspheres was analyzed using X-ray powder diffractometer. Fourier transform infrared spectra clearly indicated the presence of per-acid of sodium alginate, phosphate, and hydroxyl groups in the composite microspheres. Scanning electron micrographs and optical micrographs showed that the composite microspheres were spherical in shape and porous in nature. The particle size of composite microspheres was analyzed, and the average size was found to be 15 microns. The thermal behavior of composite microspheres was studied using thermogravimetric analysis and differential scanning calorimetric analysis. The cumulative in vitro release profile of gentamicin from composite microspheres showed near zero order patterns.

Alginates↗
PubMed2002

Bioactivity and osseointegration study of calcium phosphate ceramic of different chemical composition.

Synthetic hydroxyapatite (HA) and tricalcium phosphate (TCP) are promising bone-substitute materials in the orthopaedic and dental fields, as their chemical composition is similar to that of bone. This study investigated the osseointegration performance of carbonated biphasic calcium phosphate (CBCP) ceramics containing carbonated hydroxyapatite and tricalcium phosphate prepared by microwave irradiation, in femoral defects of dogs. The defects were created as 3-mm holes on the lateral aspect of femur and filled with the implant material. The serum was collected postoperatively and biochemical assays for alkaline phosphatase activity levels were carried out. The animals' defective sites were radiographed at 4, 8, and 12 weeks. The radiographic results showed that the process of ossification started after 4 weeks and the defect was completely filled with new bone after 8 weeks. Histological examination of the tissue showed the osteoblastic activity inducing the osteogenesis in the defect. The complete haversian system with osteoblastic and osteoclastic activity and bone remodelling process were observed after 12 weeks. The alkaline phosphatase activity levels also correlated with the formation of osteoblast cells. This calcium phosphate ceramic has proved to work well as a biocompatible implant and as an osteoconductive and osteoinductive material for the filling of bone defects.

Animals↗
PubMed2002

Preparation, characterization and in vitro release of gentamicin from coralline hydroxyapatite-gelatin composite microspheres.

Composite microspheres have been prepared from bioactive ceramics such as coralline hydroxyapatite [CHA, Ca10(PO4)6(OH)2] granules, a biodegradable polymer, gelatin and an antibiotic, gentamicin. In our earlier work, we have shown a gentamicin release from CHA granules--chitosan composite microspheres. In the present investigation, an attempt was made to prepare the composite microspheres containing coralline hydroxyapatite and gelatin (CHA-G), which were prepared by the dispersion polymerization technique and the gentamicin was incorporated by the absorption method. The crystal structure of the composite microspheres was analyzed using X-ray powder diffractometer. The Fourier transformed infrared spectrum clearly indicated the presence of amide and hydroxyl groups in the composite microspheres. Scanning electron micrographs and optical micrographs show that the composite microspheres are spherical in shape and porous in nature. The particle size of composite microspheres was analyzed and the average size was found to be 16 microm. The thermal behavior of composite microspheres was studied using thermogravimetric analysis and differential scanning calorimetric analysis. The cumulative in vitro release profile of gentamicin from composite microspheres showed near zero order patterns.

Biocompatible Materials↗
PubMed2002

Ultrasound mediated alkaline hydrolysis of methyl benzoate--reinvestigation with crucial parameters.

In the present work hydrolysis of methyl benzoate was carried out using aqueous sodium hydroxide solution at room temperature in the presence of ultrasound since otherwise the same reaction takes place at relatively high temperature. Also, the above hydrolysis reaction was investigated at a relatively larger scale with the variation in parameters influencing the emulsification process and hence the reaction rates. It has been observed that the position of ultrasound source on the liquid-liquid interface is a crucial parameter affecting the two-phase emulsification rates. The poor bulk mixing occurring in the presence of ultrasound alone with an increase in the volume of the reaction mixture and its consequent effect on the reaction kinetics has been conclusively established. These studies have shown that the use of ultrasound with mechanical stirring can result in substantial reduction in the overall power consumption, especially for reaction systems like hydrolysis that do not require very high temperatures and pressures generated by cavitation.

Journal Article↗
PubMed2001

Regiochemical control in intramolecular cyclization of methylene-interrupted epoxydiols.

[reaction: see text] Methylene-interrupted epoxydiols have multiple regiochemical routes for cyclization. The 5-exo process is the most prevalent under acidic conditions. However, the regioselectivity can be controlled by the appropriate choice of acid promoter and pendant groups adjacent to the epoxide. The 5-exo product is obtained exclusively without the presence of a carbocation-stabilizing pendant group. Alkenyl and thiophenyl groups adjacent to the epoxide alter the regioselectivity and enable access to the 5-endo tetrahydrofuran and 6-endo tetrahydropyran products.

Journal Article↗
PubMed2001

Is Posner Schlossman syndrome benign?

PURPOSE: To determine the clinical course of patients with Posner Schlossman syndrome (PSS). DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Fifty-three eyes of 50 patients. METHODS: The case notes of all patients with PSS seen at the Uveitis Clinic of Singapore National Eye Centre were reviewed for evidence of glaucoma damage and risk factors. MAIN OUTCOME MEASURES: Visual field and optic disc changes consistent with glaucoma. RESULTS: There were 28 men and 22 women, and their mean age at onset was 35 years. Fourteen eyes (26.4%) were diagnosed to have developed glaucoma as a result of repeated attacks of PSS. Patients with 10 years or more of PSS have a 2.8 times higher risk (95% confidence interval 1.19-6.52) of developing glaucoma compared with patients with less than 10 years duration of the disease. Nine eyes (17%) underwent glaucoma filtering surgery with antimetabolites. Their postoperative follow-up ranged from 15 to 50 months (mean, 37 months). Four eyes continued to have episodes of iritis after surgery, and one of these eyes had elevated intraocular pressure during the event. CONCLUSIONS: A significant number of patients with PSS have glaucoma develop over time, and they need to have their optic disc appearance and visual fields carefully monitored.

Adolescent↗
PubMed2001

Ultrasound enhanced degradation of Rhodamine B: optimization with power density.

Degradation of Rhodamine B, a waste water dye effluent was studied under the influence of ultrasound. In the present study, optimization of this degradation was carried out with power parameters, namely, power density (W/ml) and power intensity (W/cm2) using different ultrasonic equipments. From the studies, it has been observed that the degradation does not increase indefinitely with an increase in the power parameters, but instead, it reaches an optimum value and then decreases with a further increase in the power parameters. Also, these optima were not the same in all the ultrasonic equipments in which these studies were carried out. Difference in the type of acoustic field generated may be responsible for the different power optima observed with different ultrasonic equipments. The comparative study of the degradation of Rhodamine B using various ultrasonic equipments establishes a relationship between the area-specific parameter (intensity) and the volume-specific parameter (density) of reactivity.

Journal Article↗
PubMed2000

Malignancy in HIV/AIDs: a single hospital experience.

BACKGROUND AND OBJECTIVES: Our hospital serves an area with a significant number of patients seropositive for the human immunodeficiency virus (HIV). Intravenous drug abuse and heterosexual exposure are by far the predominant risk factors for HIV and acquired immunodeficiency syndrome (AIDS). Seven percent of these patients develop malignancies. Our aim was to study the types of tumor, their distribution, and to evaluate the patients' outcome. METHODS: Of 3,578 patients with HIV infection or AIDS treated between 1993 and 1998, 245 had 1 or more malignancies. Information was collected on age, sex, race, predisposing risk factors for AIDS, malignancies, symptoms at presentation, the time of the onset of AIDS, CD4 cell counts, pathology findings, and mortality. RESULTS: Although aspects of our patients resembled those of previously studied groups of patients with AIDS, there also were ways in which our patients differed from those other groups. Of our patients, 21. 6% had non-AIDS-defining (NAD) invasive malignancies. This was considerably higher than the rate in most studies. Twenty-seven patients with such malignancies died during the study. Forty-two other patients had pre-invasive cancers. Among patients having AIDS-defining (AD) malignancies, 55.9% died, a fact that was related to patients' low CD4 cell counts and late presentation. Our 97 patients with Kaposi sarcoma included 22 women, a relatively high number that may be related to the fact that most of our patients were intravenous drug abusers or had become infected by heterosexual transmission of HIV. CONCLUSIONS: AIDS is associated with a high risk of malignancy and an unusual spectrum of tumors. Patients with invasive tumors have advanced disease at the time of initial presentation. Those with AD tumors have a worse prognosis than patients with NAD tumors. The impact of highly active antiretroviral therapy on both AD and NAD tumors needs to be further evaluated.

AIDS-Related Complex↗
PubMed2000

Synthesis and characterization of functional gradient materials using Indian corals.

The partial conversion of coralline hydroxyapatite (HA) into tricalcium phosphate (TCP) catalyzed by the thermal decomposition of silver oxide was investigated. The thermal analysis of HA powder mixed with 5 mol % Ag2O indicated the decomposition of silver oxide to be around 550 degrees C in the presence of HA. Subsequently a functional gradient structure was formed by spreading silver oxide on one surface of the HA compact of diameter 10 mm and then firing at 700 degrees C in air. The X-ray powder diffraction analysis confirmed the formation of alpha-TCP induced by the Ag2O decomposition. The content of alpha-TCP of the sintered pellet was found to decrease with the increasing depth from the surface of the pellet. In vitro solubility study in phosphate buffer of pH 7.2 showed the stability of the biphasic material as in between HA and TCP.

Journal Article↗
PubMed1999

Postoperative inflammation: extracapsular cataract extraction versus phacoemulsification.

PURPOSE: To quantitatively compare postoperative inflammation after extracapsular cataract extraction (ECCE) with that after phacoemulsification in an Asian population. SETTING: Singapore National Eye Center, Singapore. METHODS: In this prospective, randomized, double-masked clinical trial, patients having cataract surgery were randomized to receive ECCE (n = 16) or phacoemulsification (n = 18). Diabetics were excluded. Two surgeons performed both types of surgery and implanted a 6.0 mm optic intraocular lens. Inflammation was assessed qualitatively by slitlamp grading of cells and flare and quantitatively using the Kowa flare meter. One independent postoperative investigator performed the slitlamp examination and laser flare meter readings. RESULTS: The ECCE and phacoemulsification groups were comparable (P > .05) in age, sex, ethnicity, and preoperative flare levels. The combined slitlamp inflammatory scores (anterior chamber cells and flare) and mean laser flare meter readings showed the ECCE group had significantly higher mean flare measurements than the phacoemulsification group at days 4 (P = .0012), 8 (P = .0013), 15 (P = .0013), 30 (P = .0004), and 60 (P = .0164). Flare levels in the ECCE group returned to preoperative values by the second month; the phacoemulsification group achieved preoperative levels by 1 month. The clinical inflammatory assessment score correlated closely to the flare level readings. CONCLUSION: Phacoemulsification induced less inflammation than ECCE, with the difference most marked in the first month after surgery.

Aged↗
PubMed1999

Pseudo-aneurysm of the carotid bifurcation secondary to radiation.

Pseudoaneurysms of the extracranial carotid vessels have a varied etiopathogenesis. Cases have been attributed to spontaneous rupture, following tonsillectomy or peritonsillar abscesses, trauma, postanastamotic and, rarely, postirradiation, and ECMO. The authors present a case of a pseudoaneurysm involving the carotid artery bifurcation following radiation therapy. A saphenous vein graft was used to establish continuity between the common and the internal carotid arteries. A vascular shunt was used to maintain cerebral perfusion during surgery. This case highlights the technical difficulties encountered in correcting this condition. This case exemplifies the technical difficulties that are encountered in a complicated case such as this. Numerous previous operations and radiotherapy compounded the hazards of the surgical procedure. Although technically challenging, every attempt must be made to resect pseudoaneurysms caused by radiation induced vascular damage.

Aneurysm, False↗
PubMed1998

The distribution and transmission of Actinobacillus actinomycetemcomitans in families with localized juvenile periodontitis.

The prevalence and distribution of A. actinomycetemcomitans in families where at least one family member (proband) suffered from localized juvenile periodontitis was investigated. 25 probands with localized juvenile periodontitis (LJP) and their 78 close family members were screened for the presence of A. actinomycetemcomitans. Among these 25 families, 10 contained at least one additional family member colonized with oral A. actinomycetemcomitans. Genomic DNA from subgingival A. actinomycetemcomitans strains from each of the probands and their family members were amplified and characterized by the polymerase chain reaction (PCR) using a single primer known to distinguish A. actinomycetemcomitans strains. The PCR products from each strain were separated by electrophoresis on a 1% submarine agarose gel containing ethidium bromide and visualized by UV light transillumination. The studies showed that 41.2% of the parents and 58% of the siblings in this LJP-based population harbored the bacterium. Comparison of the PCR generated amplitypes showed that there was a wide distribution of amplitypes among the probands and immediate relatives. No clear transmission paths were observed in this specific population.

Adolescent↗
PubMed1998

A case series of ocular disease as the primary manifestation in sarcoidosis.

Sarcoidosis is an idiopathic, systemic, non-caseating, granulomatous disease with protean clinical manifestations. This disease is highly prevalent in the southern states of United States of America, especially among African-Americans, but uncommon among Asians. Though sarcoidosis concerns physicians of virtually all specialties, it is particularly important to ophthalmologists since a significant number of patients will seek initial medical examination because of ocular disease. Out of the 262 cases of uveitis examined at the Singapore National Eye Centre over a period of two years, 9 cases were diagnosed as sarcoidosis. We report here 4 patients with active sarcoidosis who presented to us with ocular symptoms as the first and primary manifestation of the disease. All 4 patients developed symptoms and signs of systemic sarcoidosis at a later date. The ocular manifestations included simultaneous bilateral chronic granulomatous iridocyclitis, intermediate uveitis, posterior uveitis characterised by vasculitis with candle wax drippings, and optic nerve head granuloma.

Adult↗