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1.
Int J Mol Sci ; 24(6)2023 Mar 21.
Artículo en Inglés | MEDLINE | ID: mdl-36982979

RESUMEN

Gut microbes are closely associated with disease onset and improvement. However, the effects of gut microbes on the occurrence, prevention, and treatment of benign prostatic hyperplasia (BPH) are still unclear. We investigated the alteration of gut microbiota with implications for the diagnosis, prevention, and treatment of BPH and identified correlations among various indicators, including hormone indicators, apoptosis markers in BPH, and finasteride treatment models. BPH induction altered the abundance of Lactobacillus, Flavonifractor, Acetatifactor, Oscillibacter, Pseudoflavonifractor, Intestinimonas, and Butyricimonas genera, which are related to BPH indicators. Among these, the altered abundance of Lactobacillus and Acetatifactor was associated with the promotion and inhibition of prostate apoptosis, respectively. Finasteride treatment altered the abundance of Barnesiella, Acetatifactor, Butyricimonas, Desulfovibrio, Anaerobacterium, and Robinsoniella genera, which are related to BPH indicators. Among these, altered abundances of Desulfovibrio and Acetatifactor were associated with the promotion and inhibition of prostate apoptosis, respectively. In addition, the abundances of Lactobacillus and Acetatifactor were normalized after finasteride treatment. In conclusion, the association between apoptosis and altered abundances of Lactobacillus and Acetatifactor, among other gut microbes, suggests their potential utility in the diagnosis, prevention, and treatment of BPH.


Asunto(s)
Microbioma Gastrointestinal , Hiperplasia Prostática , Masculino , Humanos , Finasterida/farmacología , Finasterida/uso terapéutico , Hiperplasia Prostática/tratamiento farmacológico , Próstata , Apoptosis
2.
Front Microbiol ; 13: 858192, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35655996

RESUMEN

Knowledge of the impact of the gut microbiota on human health has increased, and modulation of the bacterial community is now considered a therapeutic target for various diseases. Certain novel bacterial species have probiotic properties associated with improvement in obesity and related metabolic disorders. The relative abundance of Butyricimonas spp. is correlated with metabolic parameters; however, the physiological role of Butyricimonas in metabolic improvement is unclear. In this study, live and heat-killed Butyricimonas virosa were administered to mice with high-fat diet (HFD)-induced obesity. Both live and heat-killed B. virosa ameliorated HFD-impaired body weight, serum glucose level, insulin resistance, and liver steatosis. Moreover, activation of the glucagon-like peptide-1 receptor (GLP-1R) and peroxisome proliferator-activated receptor α (PPARα) was observed in the liver, and the expression levels of insulin receptor substrate (IRS)-1, IRS-2, Toll-like receptor 5 (TLR5), and zonula occludens-1 (ZO-1) were upregulated in the ileum. Finally, we demonstrated that the effect of B. virosa treatment on glucose regulation may be linked to the upregulation of GLP-1R in the liver and is not a result of colonization of the gut by B. virosa or B. virosa-produced butyrate. Our results provide a rationale for the development of Butyricimonas spp.-based therapeutics and prophylactics for hyperglycemia.

3.
PLoS One ; 17(5): e0268695, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35584179

RESUMEN

Testosterone undecanoate is a hormone agent with long-acting potential and is used for testosterone replacement therapy for hypogonadism. This study was designed to investigate application of testosterone undecanoate in maintaining high androgen levels for inducing benign prostatic hyperplasia more conveniently than that for testosterone propionate. We conducted two-part studies to determine the optimal dosage and dosing cycle for efficient and stable induction of benign prostatic hyperplasia using testosterone undecanoate. In the injection dosage substudy, single testosterone undecanoate dose (125, 250, 500, 750, or 1000 mg/kg body weight) was administered, and the optimal concentration was determined for 8weeks by measuring changes in testosterone, dihydrotestosterone, and 5-alpha reductase levels. And then, testosterone undecanoate was administered at the optimal dose at intervals of 1, 2, 3, or 4 weeks for 12weeks to induce benign prostatic hyperplasia. The injection dosage substudy showed dose-dependently higher and more stable levels of testosterone in groups administrated testosterone undecanoate than in groups administered testosterone propionate. In the injection cycle substudy, testosterone undecanoate-administered group stably maintained high levels of testosterone, dihydrotestosterone, and 5-alpha reductase compared with testosterone propionate-administered group for the same injection cycle; moreover, the prostate measurements, an important sign of benign prostatic hyperplasia, were significantly increased. Based on these two substudies, we determined the optimal conditions for inducing benign prostatic hyperplasia stably and more conveniently than that for testosterone propionate. This study suggests an extended application of testosterone undecanoate for inducing benign prostatic hyperplasia that can improve research reliability considering the half-life of testosterone as well as injection dosage and concentration.


Asunto(s)
Hiperplasia Prostática , Propionato de Testosterona , Animales , Colestenona 5 alfa-Reductasa , Dihidrotestosterona , Humanos , Masculino , Hiperplasia Prostática/tratamiento farmacológico , Ratas , Ratas Wistar , Reproducibilidad de los Resultados , Testosterona/análogos & derivados , Testosterona/uso terapéutico
4.
J Ethnopharmacol ; 279: 114349, 2021 Oct 28.
Artículo en Inglés | MEDLINE | ID: mdl-34171398

RESUMEN

ETHNOPHARMACOLOGICAL RELEVANCE: Saussurea costus (synonym: Aucklandia lappa Decne) is a medicinal plant distributed in Yunnan, Guangxi, and Sichuan in China. In traditional Korean medicine, the plant parts (especially the root-"radix aucklandiae") is widely used to treat vomiting, diarrhea, and inflammation. However, little has been reported on its effect on benign prostatic hyperplasia (BPH), which is common in middle-aged men. AIM OF THE STUDY: BPH is caused by apoptosis imbalance and inflammation due to aging of the prostate. Therefore, the aim of this was to prove the efficacy of S. costus by analyzing its effect on the biological mechanisms leading to BPH progression. MATERIALS AND METHODS: Wistar rats were injected subcutaneously with a single dose of testosterone (125 mg/kg) to induce BPH, and were later administered with S. costus (20, 40 mg/kg). After 12 weeks, histological changes in the prostate and hormone regulation factors were assessed in all animals. Furthermore, apoptotic protein and apoptotic body values were analyzed to confirm the improvement of apoptosis imbalance, and inflammatory cytokines were analyzed to confirm the anti-inflammatory efficacy of S. costus. RESULTS: In the serum and tissue of S. costus-treated BPH rats, a significant reduction in prostate weight, prostate index, and hormone regulation factors was observed. S. costus also increased the levels of apoptosis marker proteins and reduced the levels of inflammatory cytokines. It also decreased the expression of B-cell lymphoma 2 (BCL-2) and increased the expression of BCL-2 associated X protein (BAX) in the prostate. Histological changes such as epithelial thickness significantly increased in BPH induced group but significantly decreased in the S. costus-treated groups (p < 0.001). CONCLUSIONS: S. costus may prevent and treat BPH occurrence by modulating inflammation and apoptosis imbalance.


Asunto(s)
Apoptosis/efectos de los fármacos , Extractos Vegetales/farmacología , Hiperplasia Prostática/tratamiento farmacológico , Saussurea/química , Animales , Antiinflamatorios/administración & dosificación , Antiinflamatorios/aislamiento & purificación , Antiinflamatorios/farmacología , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Relación Dosis-Respuesta a Droga , Inflamación/tratamiento farmacológico , Inflamación/patología , Masculino , Extractos Vegetales/administración & dosificación , Hiperplasia Prostática/patología , Ratas , Ratas Wistar
5.
Immune Netw ; 21(2): e15, 2021 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-33996171

RESUMEN

Abnormal inflammatory responses are closely associated with intestinal microbial dysbiosis. Oral administration of Qmatrix-diabetes-mellitus complex (QDMC), an Aloe gel-based formula, has been reported to improve inflammation in type 2 diabetic mice; however, the role of the gut microbiota in ameliorating efficacy of QDMC remains unclear. We investigated the effect of QDMC on the gut microbiota in a type 2 diabetic aged mouse model that was administered a high-fat diet. Proinflammatory (TNF-α and IL-6) and anti-inflammatory (IL-4 and IL-10) cytokine levels in the fat were normalized via oral administration of QDMC, and relative abundances of Bacteroides, Butyricimonas, Ruminococcus, and Mucispirillum were simultaneously significantly increased. The abundance of these bacteria was correlated to the expression levels of cytokines. Our findings suggest that the immunomodulatory activity of QDMC is partly mediated by the altered gut microbiota composition.

6.
World J Mens Health ; 39(2): 315-323, 2021 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-31749336

RESUMEN

PURPOSE: Sesquiterpene lactones, which are found in plants of the Asteraceae family, contain costunolide (CO) and dehydrocostus lactone (DCL) as indicator material. CO, in particular, has been reported to possess varied pharmacological activity, including anti-inflammatory, antibacterial, and antioxidant effects. This study was designed to characterize the effects of CO and DCL on benign prostate hyperplasia (BPH). MATERIALS AND METHODS: Rats were injected subcutaneously daily for 8 weeks with 5 mg/kg testosterone to induce prostatic hyperplasia. Wistar rats were randomly divided into 5 groups of 10 animals each and received the following treatment: I. Normal control group; II. BPH-induced group; III. CO group (0.075 mg/kg); IV. DCL group (0.075 mg/kg); and V. Finasteride group (0.8 mg/kg). After treatment, changes in prostate weight and serum biochemical indices, serum dihydrotestosterone level, and mRNA levels of BCL2 were measured and histological examinations performed. RESULTS: Absolute and relative prostate weight in the indicator material treated groups, as well as prostate volume, decreased compared to those in the disease-induced group. Epithelial cell thickness increased significantly in the disease-induced group, with a significant decrease being observed in the CO group. The level of the anti-apoptotic protein BCL2 (B-cell lymphoma 2) tended to decrease to a greater extent in the DCL group than in the disease-induced group. CONCLUSIONS: In this study, we confirmed that the indicator materials (CO and DCL) can help suppress the development of BPH.

7.
Front Microbiol ; 10: 1947, 2019.
Artículo en Inglés | MEDLINE | ID: mdl-31551944

RESUMEN

Dysbiosis of the gut microbiota is a contributing factor for obesity-related metabolic diseases such as hyperglycemia and hyperlipidemia. Pharmacotherapy for metabolic diseases involves the modulation of gut microbiota, which is suggested to be a potential therapeutic target. In this study, the modulation of gut microbiota by statins (cholesterol-lowering drugs: atorvastatin and rosuvastatin) was investigated in an aged mouse model of high-fat diet-induced obesity, and the association between gut microbiota and immune responses was described. Atorvastatin and rosuvastatin significantly increased the abundance of the genera Bacteroides, Butyricimonas, and Mucispirillum. Moreover, the abundance of these genera was correlated with the inflammatory response, including levels of IL-1ß and TGFß1 in the ileum. In addition, oral fecal microbiota transplantation with fecal material collected from rosuvastatin-treated mouse groups improved hyperglycemia. From these results, the effect of statins on metabolic improvements could be explained by altered gut microbiota. Our findings suggest that the modulation of gut microbiota by statins has an important role in the therapeutic actions of these drugs.

8.
Immune Netw ; 19(4): e28, 2019 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-31501716

RESUMEN

IL-18 is a crucial pro-inflammatory cytokine that mediates chronic intestinal inflammation. Metformin, an anti-diabetic drug, was reported to have ameliorative effects on inflammatory bowel disease. Recently, the mechanism of action of metformin was explained as a modulation of gut microbiota. In this study, fecal microbiota transplantation (FMT) using fecal material from metformin-treated mice was found to upregulate the expression of GLP-1 and pattern-recognition receptors TLR1 and TLR4 for the improvement in hyperglycemia caused by a high-fat diet. Further, FMT downregulated the expression of the inflammatory cytokine IL-18. Within the genera Akkermansia, Bacteroides, and Butyricimonas, which were promoted by metformin therapy, Butyricimonas was found to be consistently abundant following FMT. Our findings suggest that modulation of gut microbiota is a key factor for the anti-inflammatory effects of metformin which is used for the treatment of hyperglycemia.

9.
Nutrients ; 10(12)2018 Dec 01.
Artículo en Inglés | MEDLINE | ID: mdl-30513715

RESUMEN

Metabolic syndrome is characterized by a combination of several metabolic disorders, including obesity, hyperglycemia, and hyperlipidemia. A simultaneous occurrence is one of the most crucial features of metabolic syndrome; therefore, we selected an animal model in which this would be reflected. We fed C57BL/6N mice a high-fat diet for 23 weeks to develop metabolic syndrome and examined the efficacy of Rubus occidentalis (RO) for hyperglycemia and hypercholesterolemia. Oral administration of RO for 16 weeks improved hyperglycemia as indicated by significantly decreased fasting glucose levels and a glucose tolerance test. Improvements were also observed in hypercholesterolemia, in which significant decreases in serum total cholesterol, non-high-density lipoprotein (non-HDL) cholesterol, apolipoprotein A-1, and apolipoprotein B levels were observed. The time comparison of major biomarkers, observed at the initiation and termination of the experimental period, consistently supported the beneficial effects of RO on each metabolic phenotype. In addition, RO treatment attenuated the excessive fat accumulation in hepatic and adipose tissue by decreasing the size and number of lipid droplets. These results suggested that RO simultaneously exerted antihyperglycemic and antihyperlipidemic effects in mice with diet-induced metabolic syndrome.


Asunto(s)
Glucemia/metabolismo , Dieta Alta en Grasa , Metabolismo de los Lípidos/efectos de los fármacos , Síndrome Metabólico/tratamiento farmacológico , Fitoterapia , Extractos Vegetales/uso terapéutico , Rubus , Tejido Adiposo/efectos de los fármacos , Tejido Adiposo/metabolismo , Animales , Colesterol/sangre , Prueba de Tolerancia a la Glucosa , Hipercolesterolemia/tratamiento farmacológico , Hipercolesterolemia/metabolismo , Hiperglucemia/tratamiento farmacológico , Hiperglucemia/metabolismo , Hipoglucemiantes/farmacología , Hipoglucemiantes/uso terapéutico , Hipolipemiantes/farmacología , Hipolipemiantes/uso terapéutico , Lipoproteínas/sangre , Hígado/efectos de los fármacos , Hígado/metabolismo , Masculino , Síndrome Metabólico/metabolismo , Síndrome Metabólico/patología , Ratones Endogámicos C57BL , Extractos Vegetales/farmacología
10.
Gut Microbes ; 9(2): 155-165, 2018 03 04.
Artículo en Inglés | MEDLINE | ID: mdl-29157127

RESUMEN

The gut microbiota is a contributing factor in obesity-related metabolic disorders. The effect of metformin on the gut microbiota has been reported; however, the relationship between the gut microbiota and the mechanism of action of metformin in elderly individuals is unclear. In this study, the effect of metformin on the gut microbiota was investigated in aged obese mice. The abundance of the genera Akkermansia, Bacteroides, Butyricimonas, and Parabacteroides was significantly increased by metformin in mice fed a high-fat diet. Metformin treatment decreased the expression of IL-1ß and IL-6 in epididymal fat, which was correlated with the abundance of various bacterial genera. In addition, both fecal microbiota transplantation from metformin-treated mice and extracellular vesicles of Akkermansia muciniphila improved the body weight and lipid profiles of the mice. Our findings suggest that modulation of the gut microbiota by metformin results in metabolic improvements in aged mice, and that these effects are associated with inflammatory immune responses.


Asunto(s)
Dieta Alta en Grasa/efectos adversos , Epidídimo/inmunología , Microbioma Gastrointestinal/efectos de los fármacos , Metformina/farmacología , Obesidad/metabolismo , Obesidad/microbiología , Factores de Edad , Animales , Bacterias/clasificación , Bacterias/efectos de los fármacos , Glucemia/efectos de los fármacos , Peso Corporal/efectos de los fármacos , Modelos Animales de Enfermedad , Epidídimo/efectos de los fármacos , Heces/microbiología , Microbioma Gastrointestinal/fisiología , Regulación de la Expresión Génica/inmunología , Interleucina-1beta/genética , Interleucina-6/genética , Metabolismo de los Lípidos/efectos de los fármacos , Masculino , Metformina/uso terapéutico , Ratones , Ratones Endogámicos C57BL , Obesidad/tratamiento farmacológico , Obesidad/inmunología
11.
Biosci Biotechnol Biochem ; 81(3): 595-603, 2017 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-27884090

RESUMEN

We developed spontaneous diet-induced metabolic disease in mice by feeding them a high-fat diet for 23 weeks and administered Aloe QDM complex for 16 weeks to examine its restorative effect on immune disorders and metabolic syndrome. A series of immune functional assays indicated Aloe QDM complex enhanced lymphocyte proliferation and antigen-specific immunity as determined by the restored functions of cytotoxic T lymphocytes (CTL) and IgG production. The elevated serum TNF-α level was also regulated by Aloe QDM complex treatment, which suggested its complex therapeutic potential. As for metabolic phenotypes, oral administration of Aloe QDM complex significantly improved diabetic symptoms, including high fasting glucose levels and glucose tolerance, and distinctly alleviated lipid accumulation in adipose and hepatic tissue. The simultaneous restoration of Aloe QDM complex on metabolic syndrome and host immune dysfunction, especially on the specific CTL killing was first elucidated in our study.


Asunto(s)
Aloe/química , Síndrome Metabólico/tratamiento farmacológico , Extractos Vegetales/farmacología , Linfocitos T Citotóxicos/efectos de los fármacos , Tejido Adiposo/efectos de los fármacos , Tejido Adiposo/patología , Administración Oral , Animales , Glucemia/metabolismo , Dieta Alta en Grasa/efectos adversos , Modelos Animales de Enfermedad , Hiperglucemia/tratamiento farmacológico , Hiperglucemia/etiología , Hiperlipidemias/tratamiento farmacológico , Hiperlipidemias/etiología , Inmunoglobulina G/sangre , Metabolismo de los Lípidos/efectos de los fármacos , Masculino , Síndrome Metabólico/etiología , Ratones Endogámicos C57BL , Extractos Vegetales/química , Plantas Medicinales/química , Linfocitos T Citotóxicos/inmunología , Factor de Necrosis Tumoral alfa/sangre
12.
Biomol Ther (Seoul) ; 25(2): 140-148, 2017 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-27737523

RESUMEN

Hyperlipidemia, which is closely associated with a fatty diet and aging, is commonly observed in the western and aged society. Therefore, a novel therapeutic approach for this disease is critical, and an immunological view has been suggested as a novel strategy, because hyperlipidemia is closely associated with inflammation and immune dysfunction. In this study, the effects of an aqueous extract of Rubus occidentalis (RO) in obese mice were investigated using immunological indexes. The mice were fed a high-fat diet (HFD) to induce hyperlipidemia, which was confirmed by biochemical analysis and examination of the mouse physiology. Two different doses of RO and rosuvastatin, a cholesterol synthesis inhibitor used as a control, were orally administered. Disturbances in immune cellularity as well as lymphocyte proliferation and cytokine production were significantly normalized by oral administration of RO, which also decreased the elevated serum tumor necrosis factor (TNF)-α level and total cholesterol. The specific immune-related actions of RO comprised considerable improvement in cytotoxic T cell killing functions and regulation of antibody production to within the normal range. The immunological evidence confirms the significant cholesterol-lowering effect of RO, suggesting its potential as a novel therapeutic agent for hyperlipidemia and associated immune decline.

13.
Biochem Biophys Res Commun ; 478(3): 1242-7, 2016 09 23.
Artículo en Inglés | MEDLINE | ID: mdl-27565724

RESUMEN

This study was designed to characterize the potential therapeutic effects of two statin drugs commonly used to treat dyslipidemia in inflammation-linked metabolic disorders related to type 2 diabetes. Atorvastatin (10 mg/kg/day) and rosuvastatin (3 mg/kg/day) were administered to mice with diet-induced obesity (DIO). The statins lowered serum total and LDL cholesterol levels, and improved the atherogenic index and cardiac risk index. Furthermore, the drugs decreased fasting glucose levels, improved glucose tolerance, and decreased fat tissue weight and adipocyte size; this was accompanied by an overall body weight loss tendency. The statins also improved antigen-specific immunity. The killing activity of cytotoxic T cells and exacerbation of IgG secretion levels were considerably normalized. Most importantly, serum tumor necrosis factor-α and interleukin 6 levels decreased, while their RNA expression levels in fat tissue were regulated by the statins as well. This study is the first to indicate that low doses of atorvastatin and rosuvastatin, the dosing regimen for which has been controversial, could significantly improve diabetes-related metabolic disorders, and could modulate pro-inflammatory cytokines, alleviating inflammation and simultaneously restoring overall humoral and cell-mediated immunity.


Asunto(s)
Atorvastatina/uso terapéutico , Enfermedades Metabólicas/tratamiento farmacológico , Enfermedades Metabólicas/inmunología , Rosuvastatina Cálcica/uso terapéutico , Tejido Adiposo/metabolismo , Tejido Adiposo/patología , Animales , Atorvastatina/farmacología , Citocinas/sangre , Dieta Alta en Grasa , Epítopos , Glucosa/metabolismo , Homeostasis , Inmunidad , Mediadores de Inflamación/metabolismo , Metabolismo de los Lípidos , Masculino , Enfermedades Metabólicas/sangre , Enfermedades Metabólicas/fisiopatología , Ratones Endogámicos C57BL , Tamaño de los Órganos , ARN Mensajero/genética , ARN Mensajero/metabolismo , Rosuvastatina Cálcica/farmacología
14.
ACS Nano ; 5(9): 6916-24, 2011 Sep 27.
Artículo en Inglés | MEDLINE | ID: mdl-21894965

RESUMEN

Reproducible dry and wet transfer techniques were developed to improve the transfer of large-area monolayer graphene grown on copper foils by chemical vapor deposition (CVD). The techniques reported here allow transfer onto three different classes of substrates: substrates covered with shallow depressions, perforated substrates, and flat substrates. A novel dry transfer technique was used to make graphene-sealed microchambers without trapping liquid inside. The dry transfer technique utilizes a polydimethylsiloxane frame that attaches to the poly(methyl methacrylate) spun over the graphene film, and the monolayer graphene was transferred onto shallow depressions with 300 nm depth. The improved wet transfer onto perforated substrates with 2.7 µm diameter holes yields 98% coverage of holes covered with continuous films, allowing the ready use of Raman spectroscopy and transmission electron microscopy to study the intrinsic properties of CVD-grown monolayer graphene. Additionally, monolayer graphene transferred onto flat substrates has fewer cracks and tears, as well as lower sheet resistance than previous transfer techniques. Monolayer graphene films transferred onto glass had a sheet resistance of ∼980 Ω/sq and a transmittance of 97.6%. These transfer techniques open up possibilities for the fabrication of various graphene devices with unique configurations and enhanced performance.

15.
ACS Nano ; 5(4): 2433-9, 2011 Apr 26.
Artículo en Inglés | MEDLINE | ID: mdl-21361332

RESUMEN

Understanding and engineering the domain boundaries in chemically vapor deposited monolayer graphene will be critical for improving its properties. In this study, a combination of transmission electron microscopy (TEM) techniques including selected area electron diffraction, high resolution transmission electron microscopy (HR-TEM), and dark field (DF) TEM was used to study the boundary orientation angle distribution and the nature of the carbon bonds at the domain boundaries. This report provides an important first step toward a fundamental understanding of these domain boundaries. The results show that, for the graphene grown in this study, the 46 measured misorientation angles are all between 11° and 30° (with the exception of one at 7°). HR-TEM images show the presence of adsorbates in almost all of the boundary areas. When a boundary was imaged, defects were seen (dangling bonds) at the boundaries that likely contribute to adsorbates binding at these boundaries. DF-TEM images also showed the presence of a "twinlike" boundary.

16.
ACS Nano ; 5(1): 321-8, 2011 Jan 25.
Artículo en Inglés | MEDLINE | ID: mdl-21162551

RESUMEN

Using micro-Raman spectroscopy, the thermal conductivity of a graphene monolayer grown by chemical vapor deposition and suspended over holes with different diameters ranging from 2.9 to 9.7 µm was measured in vacuum, thereby eliminating errors caused by heat loss to the surrounding gas. The obtained thermal conductivity values of the suspended graphene range from (2.6 ± 0.9) to (3.1 ± 1.0) × 10(3) Wm(-1)K(-1) near 350 K without showing the sample size dependence predicted for suspended, clean, and flat graphene crystal. The lack of sample size dependence is attributed to the relatively large measurement uncertainty as well as grain boundaries, wrinkles, defects, or polymeric residue that are possibly present in the measured samples. Moreover, from Raman measurements performed in air and CO(2) gas environments near atmospheric pressure, the heat transfer coefficient for air and CO(2) was determined and found to be (2.9 +5.1/-2.9) and (1.5 +4.2/-1.5) × 10(4) Wm(-2)K(-1), respectively, when the graphene temperature was heated by the Raman laser to about 510 K.

17.
ACS Nano ; 4(11): 6557-64, 2010 Nov 23.
Artículo en Inglés | MEDLINE | ID: mdl-20942443

RESUMEN

Mechanical properties of ultrathin membranes consisting of one layer, two overlapped layers, and three overlapped layers of graphene oxide platelets were investigated by atomic force microscopy (AFM) imaging in contact mode. In order to evaluate both the elastic modulus and prestress of thin membranes, the AFM measurement was combined with the finite element method (FEM) in a new approach for evaluating the mechanics of ultrathin membranes. Monolayer graphene oxide was found to have a lower effective Young's modulus (207.6 ± 23.4 GPa when a thickness of 0.7 nm is used) as compared to the value reported for "pristine" graphene. The prestress (39.7-76.8 MPa) of the graphene oxide membranes obtained by solution-based deposition was found to be 1 order of magnitude lower than that obtained by others for mechanically cleaved graphene. The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.


Asunto(s)
Grafito/química , Fenómenos Mecánicos , Óxidos/química , Módulo de Elasticidad , Análisis de Elementos Finitos , Membranas Artificiales , Microscopía de Fuerza Atómica , Nanoestructuras/química , Estrés Mecánico
18.
Nano Lett ; 10(11): 4328-34, 2010 Nov 10.
Artículo en Inglés | MEDLINE | ID: mdl-20957985

RESUMEN

The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 to nearly 30°. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility up to about 16,000 cm(2) V(-1) s(-1) at room temperature.


Asunto(s)
Cristalización/métodos , Gases/química , Grafito/química , Membranas Artificiales , Nanoestructuras/química , Nanoestructuras/ultraestructura , Sustancias Macromoleculares/química , Ensayo de Materiales , Conformación Molecular , Nanotecnología/métodos , Tamaño de la Partícula , Propiedades de Superficie
20.
ACS Nano ; 4(1): 540-6, 2010 Jan 26.
Artículo en Inglés | MEDLINE | ID: mdl-20055476

RESUMEN

There has been no attempt to date to specifically modify the nodes in carbon nanotube (CNT) networks. If the nodes can be modified in favorable ways, the electrical and/or thermal and/or mechanical properties of the CNT networks could be improved. In an attempt to influence the performance as a transparent conductive film, gold nanoparticles capped with the amino acid cysteine (Au-CysNP) have been selectively attached at the nodes of multiwalled carbon nanotubes (MWCNTs) networks. These nanoparticles have an average diameter of 5 nm as observed by TEM. FTIR and XPS were used to characterize each step of the MWCNT chemical functionalization process. The chemical process was designed to favor selective attachment at the nodes and not the segments in the CNT networks. The chemical processing was designed to direct formation of nodes where the gold nanoparticles are. The nanoparticles which were loosely held in the CNT network could be easily washed away by solvents, while those bound chemically remained. TEM results show that the Cys-AuNPs are preferentially located at the nodes of the CNT networks when compared to the segments. These nanoparticles at the nodes were also characterized by a novel technique called diffraction scanning transmission electron microscopy (D-STEM) confirming their identity. Four-probe measurements found that the sheet resistance of the modified CNT networks was half that of similarly transparent pristine multiwalled CNT networks.

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