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Biomedical subjects

S T Lee

Publications and source records attributed to S T Lee.

At least 37 records · Page 2Linked to original sources
PubMed2003

FTIR spectroscopic studies of the stabilities and reactivities of hydrogen-terminated surfaces of silicon nanowires.

Attenuated total reflection Fourier transform infrared (FTIR) spectroscopy was used to characterize the surface species on oxide-free silicon nanowires (SiNWs) after etching with aqueous HF solution. The HF-etched SiNW surfaces were found to be hydrogen-terminated; in particular, three types of silicon hydride species, the monohydride (SiH), the dihydride (SiH(2)), and the trihydride (SiH(3)), had been observed. The thermal stability of the hydrogen-passivated surfaces of SiNWs was investigated by measuring the FTIR spectra after annealing at different elevated temperatures. It was found that hydrogen desorption of the trihydrides occurred at approximately 550 K, and that of the dihydrides occurred at approximately 650 K. At or above 750 K, all silicon hydride species began to desorb from the surfaces of the SiNWs. At around 850 K, the SiNW surfaces were free of silicon hydride species. The stabilities and reactivities of HF-etched SiNWs in air and water were also studied. The hydrogen-passivated surfaces of SiNWs showed good stability in air (under ambient conditions) but relatively poor stability in water. The stabilities and reactivities of the SiNWs are also compared with those of silicon wafers.

Journal Article↗
PubMed2003

Small-diameter silicon nanowire surfaces.

Small-diameter (1 to 7 nanometers) silicon nanowires (SiNWs) were prepared, and their surfaces were removed of oxide and terminated with hydrogen by a hydrofluoric acid dip. Scanning tunneling microscopy (STM) of these SiNWs, performed both in air and in ultrahigh vacuum, revealed atomically resolved images that can be interpreted as hydrogen-terminated Si (111)-(1 x 1) and Si (001)-(1 x 1) surfaces corresponding to SiH3 on Si (111) and SiH2 on Si (001), respectively. These hydrogen-terminated SiNW surfaces seem to be more oxidation-resistant than regular silicon wafer surfaces, because atomically resolved STM images of SiNWs were obtained in air after several days' exposure to the ambient environment. Scanning tunneling spectroscopy measurements were performed on the oxide-removed SiNWs and were used to evaluate the electronic energy gaps. The energy gaps were found to increase with decreasing SiNW diameter from 1.1 electron volts for 7 nanometers to 3.5 electron volts for 1.3 nanometers, in agreement with previous theoretical predictions.

Journal Article↗
PubMed2003

Suppression of insulin-like growth factor signalling pathway and collagen expression in keloid-derived fibroblasts by quercetin: its therapeutic potential use in the treatment and/or prevention of keloids.

BACKGROUND: Keloids are characterized by abnormal proliferation of fibroblasts and overproduction of collagen. Insulin-like growth factor (IGF)-I is mitogenic for fibroblasts and a stimulatory factor for collagen synthesis. OBJECTIVES: We have assessed the in vitro effects of quercetin on proliferation, collagen synthesis and the expression of the IGF system in keloid-derived fibroblasts. METHODS: Fibroblasts were isolated from earlobe keloids and exposed to quercetin at different concentrations. The inhibitory effects of quercetin on fibroblast proliferation were assayed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, Western and Northern blot analyses. RESULTS: Quercetin inhibited keloid fibroblast (KF) proliferation in a dose-dependent manner. Significant growth inhibition was observed on day 2 of culture. The dose required for 50% growth inhibition was approximately 25 microg mL-1. Collagen 1 expression was significantly decreased while collagen 3 was almost undetectable following quercetin treatment. Basal levels of IGF-I receptor (IGF-IR) beta subunits, p85 subunit of phosphatidylinositol 3-kinase, c-Raf, phospho-Raf-1, phospho-MEK 1/2, phospho-mitogen-activated protein kinase, phospho-Elk-1 and phospho-Akt-1 were significantly reduced when KF cells were exposed to quercetin for 24 h. Blocking IGF-IR activity with IGF-IR antibody or neutralizing endogenous IGF-I activity with IGF-I antibody led to significant growth inhibition suggesting the role of IGF-I in regulation of KF proliferation. CONCLUSIONS: Because the IGF system plays an important part in fibroblast cell proliferation and collagen production, the described activities of quercetin on the IGF system and collagen expression may provide a novel approach for the use of quercetin in treatment and/or prevention of hypertrophic scar and keloid.

Blotting, Northern↗
PubMed2003

Treatment of metal-contaminated water and vertical distribution of metal precipitates in an upflow anaerobic bioreactor.

A lab-scale upflow anaerobic bioreactor filled with granular sludge and cow manure was operated for 140 days to determine the mechanism of metal removal and the vertical distribution of metal precipitates. Heavy metal ions were removed in the order of Cu2+, Cd2+, Zn2+, Fe2+ and Mn2+ with respect to the height in the reactor. The solid phase analysis showed that the heavy metals were mostly precipitated in the form of metal sulfides by sulfate reduction The contents of metal precipitates in the reactor were as follows: (i) Cd and Zn were highest in the bottom, (ii) Fe was highest at the low-middle layer, and (iii) Mn was increased with the height in the reactor. The vertical distribution of metal sulfides in the reactor was directly related to the solubility product (Ksp). Results obtained in this study suggest a feasibility of the application to separate precipitation metal-containing wastewater.

Bacteria, Anaerobic↗
PubMed2003

Evaluation of vaccination against methyllycaconitine toxicity in mice.

The purpose of this study was to determine whether larkspur toxins conjugated to protein carriers would promote active immunity in mice. Mice were injected with several larkspur toxin-protein conjugates or adjuvant alone to determine whether the resulting immunological response altered animal susceptibility to methyllycaconitine, the major toxic larkspur alkaloid. Although vaccinations increased the calculated lethal dose 50% (LD50) for intravenous methyllycaconitine toxicity, overlapping confidence intervals did not provide evidence of differences between the vaccinated and control groups. In the lycoctonine conjugate (LYC)-vaccinated group, mouse survival was related (P = 0.001) to serum titers for methyllycaconitine doses up to 4.5 mg/kg of body weight. When mice withlow antibody titers were removed from the vaccinated groups in which titer was related to survival, the recalculated LD50 estimates were 20% greater than the LD50 of the control group. However, the 95% confidence intervals of the recalculated LD50 groups overlapped with the control groups. Overall, these results suggest that vaccination altered methyllycaconitine toxicity in mice and that vaccination may be useful in decreasing the effects of larkspur toxins in animals. Additional studies are warranted to continue development of potential larkspur vaccines for livestock.

Aconitine↗
PubMed2002

The mechanism of diamond nucleation from energetic species.

A model for diamond nucleation by energetic species (for example, bias-enhanced nucleation) is proposed. It involves spontaneous bulk nucleation of a diamond embryo cluster in a dense, amorphous carbon hydrogenated matrix; stabilization of the cluster by favorable boundary conditions of nucleation sites and hydrogen termination; and ion bombardment-induced growth through a preferential displacement mechanism. The model is substantiated by density functional tight-binding molecular dynamics simulations and an experimental study of the structure of bias-enhanced and ion beam-nucleated films. The model is also applicable to the nucleation of other materials by energetic species, such as cubic boron nitride.

Journal Article↗
PubMed2002

Reductive growth of nanosized ligated metal clusters on silicon nanowires.

The reductive growth of metal clusters on silicon nanowires (SiNWs) is reported. The HF-etched SiNWs were found to reduce ligated Au-Ag clusters of single size, shape, composition, and structure. In the process, the surfaces of the SiNWs were reoxidized. The reductive cluster growth on the SiNW surface was followed by high-resolution transmission electron microscopy (HRTEM). The reduced metal clusters grew to different sizes in the nanometer regime (1-7 nm in diameter) on the SiNW surfaces. At sizes greater than approximately 7 nm, they tend to separate from the SiNW surfaces. Further growth and/or agglomeration of these colloidal particles to sizes greater than roughly 25 nm in diameter eventually causes the particles to precipitate from solution. Two interesting phenomena, the "sinking cluster" and the "cluster fusion" processes, were observed under TEM.

Journal Article↗
PubMed2002

Primary antiphospholipid syndrome presenting with abdominal angina and splenic infarction.

The antiphospholipid syndrome is an autoimmune hypercoagulability syndrome in which a wide variety of thromboembolic diseases may occur. Gastrointestinal manifestations associated with vascular occlusion include Budd-Chiari syndrome, hepatic and splenic infarction, pancreatitis, omental and intestinal infarction, and esophageal variceal bleeding due to portal vein thrombosis, but chronic mesenteric ischemia associated with mesenteric arterial thrombosis is very rare in this syndrome. We experienced a female patient with primary antiphospholipid syndrome with abdominal angina and splenic infarction associated with celiac trunk and mesenteric arterial thromboses. This is the first report describing chronic mesenteric ischemia and splenic infarction in a patient with primary antiphospholipid syndrome.

Abdominal Pain↗
PubMed2002

Monitoring the denitrification of wastewater containing high concentrations of nitrate with methanol in a sulfur-packed reactor.

Biological denitrification of high nitrate-containing wastewater was examined in a sulfur-packed column using a smaller amount of methanol than required stoichiometrically for heterotrophic denitrification. In the absence of methanol, the observed nitrate removal efficiency was only about 40%, and remained at 400 mg NO(3)(-)-N/l, which was due to an alkalinity deficiency of the pH buffer and of CO(2) as a carbon source. Complete denitrification was achieved by adding approximately 1.4 g methanol/g nitrate-nitrogen (NO(3)(-)-N) to a sulfur-packed reactor. As the methanol concentration increased, the overall nitrate removal efficiency increased. As influent methanol concentrations increased from 285 to 570, 855, and 1,140 mg/l, the value of Delta mg alkalinity as CaCO(3) consumed/Delta mg NO(3)(-)-N removed increased from -1.94 to -0.84, 0.24, and 0.96, and Delta mg SO(4)(2-) produced/Delta mg NO(3)(-)-N removed decreased from 4.42 to 3.57, 2.58, and 1.26, respectively. These results imply the co-occurrence of simultaneous autotrophic and heterotrophic denitrification. Sulfur-utilizing autotrophic denitrification in the presence of a small amount of methanol is very effective at decreasing both sulfate production and alkalinity consumption. Most of methanol added was removed completely in the effluent. A small amount of nitrite accumulated in the mixotrophic column, which was less than 20 mg NO(2)(-) -N/l, while under heterotrophic denitrification conditions, nitrite accumulated steadily and increased to 60 mg NO(2)(-) -N/l with increasing column height.

Bioreactors↗
PubMed2002

[Individually CAD-CAM technique designed, bioresorbable 3-dimensional polycaprolactone framework for experimental reconstruction of craniofacial defects in the pig].

METHODS: Twenty orbital defects (2 x 2 cm) were created in ten adult Yorkshire pigs. Two software products (Velocity and Mimix) were evaluated with regard to image processing, three-dimensional reconstruction, and fabrication of individually shaped polycaprolactone (PCL) scaffolds to reconstruct these defects. Four different techniques were tested for the reconstruction: group 1 = no reconstruction, group 2 = polylactide sheet, group 3 = PCL scaffold, group 4 = bone marrow-coated PCL scaffold. The pigs were sacrificed at 3 months. RESULTS: In group 1 soft tissue scar formation could be found, but without any new bone. Group 2 showed a thick fibrous capsule around the PLLA sheet, whereas at the border zone of the defect signs of new bone formation could be detected. In group 3 the PCL scaffolds were filled with fibrous tissue and some areas that showed new bone formation (6.4% of the area of the defect). In group 4 the new bone formation (17.8% of the area of the defect) was significantly higher in quantity than in group 3. CONCLUSION: The PCL scaffold coated with bone marrow seems to be a material that effectively provides osteoinduction with formation of new bone. Long-term results at 12 months are still pending.

Absorbable Implants↗
PubMed2002

Increased 21-hydroxylase and shutdown of C(17,20) lyase activities in testicular tissues of the grouper (Epinephelus coioides) during 17alpha-methyltestosterone-induced sex inversion.

The metabolism in vitro of [(3)H]17-hydroxyprogesterone by gonadal tissues of the grouper (Epinephelus coioides) during 17alpha-methyltestosterone (MT)-induced female-to-male sex inversion was examined. In the female phase, C(17,20) lyase, 5beta-reductase, 3alpha/beta-HSD, 20beta-HSD, and 17beta-HSD activities resulted in the biosynthesis of 5beta-pregnans and 5beta-androstanes (including 5beta-androstane-3alpha/beta, 17beta-diol, 3alpha/beta, 17alpha-dihydroxy-5beta-pregnen-20-one, and 5beta-androstane-3,17-dione). In the MT-induced male phase, however, the abrogation of C(17,20) lyase activity and the concomitant activation of 21alpha-hydroxylase/11beta-hydroxylase resulted in the preferential synthesis of polar 21alpha-hydroxlyated 5beta-pregnans (5beta-pregnan-3beta,17alpha,20beta,21alpha-tetrol and 3beta,20beta,21alpha-trihydroxy-5beta-pregnan-3-one) and corticosteroids (11-deoxycortisol and cortisol). Interestingly, synthesis of these 21alpha-hydroxylated 5beta-pregnans and corticosteroids was uniquely compartmentalized in only testicular tissues of the MT-induced males. This study shows that there is selective activation of specific steroidogenic enzymes in the different sexual phases leading to the synthesis of metabolites that may be involved in regulating sex inversion of the grouper.

17-alpha-Hydroxyprogesterone↗
PubMed2002

Atlantoaxial rotatory subluxation in skeletally immature patients.

Treatments of atlanto-axial rotatory subluxation in children are generally conservative. Previous reports have proposed that surgical treatment be reserved for fixed rotatory subluxation of more than 3 months duration, irreducible deformity or cases of recurrence. Six skeletally immature patients with Fielding type III atlanto-axial rotatory subluxation were treated conservatively with or without subsequent atlanto-axial arthrodesis. The follow-up period for all the cases exceeded 18 months. Results and outcomes were analysed with an emphasis on the delay until diagnosis, causes of delays in diagnosis and factors influencing the necessity of surgical intervention. Neither mortality nor major morbidity was noted in any cases in this study. In our experience, type III fixed rotatory subluxation of 6 weeks duration will potentially recur. We recommend early surgery for type III fixed rotatory subluxation of more than than 3 months' duration, with atlanto-axial arthrodesis being a safe and effective procedure in children.

Atlanto-Axial Joint↗
PubMed2002

An anthropometric analysis of indices of severity in the unilateral cleft lip.

The aim of this study was to analyze the relationships among three key anthropometric parameters in the unilateral cleft lip to determine the correlations, if any, among these indices of severity. Using a standardized anthropometric documentation protocol, preoperative measurements of 125 unilateral cleft lips (103 complete and 22 incomplete) were performed under general anesthesia by a single surgeon at the time of primary lip repair at the age of 3 months. The following key measurements were analyzed statistically: (1) the philtral height difference (PHD) between the cleft and noncleft sides, (2) the nasal floor width difference (NFWD) between the cleft and noncleft sides, and (3) the cleft width (CW). The mean values of all three indices were greater in the complete group versus the incomplete group. These differences were statistically significant. Linear relationships were obtained between NFWD and GAP, between PHD and GAP, and between PHD and NFWD in the complete group. In contrast, the relationships between PHD and GAP, and between PHD and NFWD were nonlinear in the incomplete group. These findings suggest that there was a strong correlation between the transverse and vertical tissue deficiencies in the complete cleft lip. In incomplete clefts, however, this correlation did not exist. In other words, the incomplete cleft lip can be associated with a severely short philtrum even in the presence of a relatively mild transverse tissue deficit. Therefore, it is not necessarily easier to repair an incomplete cleft lip in terms of the correction of the vertical tissue deficiency.

Cephalometry↗
PubMed2002

Nocardia pseudovaccinii sp. nov.

Comparative 16S rDNA studies of Nocardia type and reference strains revealed that strain DSM 43406T, identified as Nocardia vaccinii, was wrongly classified. The strain was aerobic, gram-positive and produced scarce, white, branched aerial mycelium and a beige-red substrate mycelium. The reverse side of the colonies was yellow-orange. It showed chemotaxonomic markers that were consistent with its classification in the genus Nocardia. The mycolic acids had chain lengths from 50 to 58 carbon atoms. The 16S rDNA sequence showed the highest similarity to Nocardia nova (97.7%) and N. vaccinii (97.6%), but the strain could be clearly separated from these species and other members of the N. vaccinii cluster by significant differences in biochemical test results and unique fatty acid and mycolic acid patterns. These data led to the conclusion that the isolate represents a novel species within the genus Nocardia, for which the name Nocardia pseudovaccinii sp. nov. is proposed. The type strain is strain AR 368,38366-20T (= DSM 43406T = NRRL B-24154T).

DNA, Bacterial↗
PubMed2002

Birth prevalence of Down syndrome in Singapore from 1993 to 1998.

OBJECTIVE: To examine the livebirth prevalence rate of Down Syndrome in Singapore from 1993 to 1998. DESIGN: Index cases for the National Birth Defects Register were obtained from all neonatal nurseries in Singapore, all hospital discharge summaries, cytogenetic and pathology reports from all pathology laboratories in Singapore and from the compulsory reporting of all termination of pregnancy cases and stillbirths delivered. SETTING: Information for the Register was obtained from case notes retrieved from the medical record offices, antenatal clinics, cytogenetic laboratories, pathology departments and the Registry of Births and Deaths. SUBJECTS: All foetuses with Trisomy 21 diagnosed prenatally together with livebirths and stillbirths with Down Syndrome diagnosed at or after birth were identified from the Registry database. MAIN OUTCOME MEASURES: Prevalence of Down Syndrome RESULTS: From 1993 to 1998, there were 295 Down Syndrome livebirths, four stillbirths and 197 Down Syndrome foetuses aborted. There has been an increasing number of Down Syndrome foetuses diagnosed antenatally ending in termination and this is accompanied by a falling trend in the Down Syndrome livebirth rate in the same years from 1.17 to 0.89 per 1000 total live births. This is despite an expected increase in Down Syndrome livebirth rate obtained by modelling maternal Down Syndrome age-related risks on the maternal age distribution over the years. CONCLUSIONS: The livebirth prevalence of Down Syndrome in Singapore has fallen over the years from 1.17/1000 livebirths in 1993 to 0.89/1000 livebirths in 1998 due to antenatal diagnosis and selective termination.

Abortion, Induced↗