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1.
Lupus Sci Med ; 10(2)2023 11 24.
Artigo em Inglês | MEDLINE | ID: mdl-38007228

RESUMO

OBJECTIVE: To examine the efficacy and safety of telitacicept in the treatment of patients with SLE in everyday clinical practice. METHODS: Seventy-two patients with active SLE who received telitacicept for more than 24 weeks at multiple centres in China between 2019 and 2022 were retrospectively identified. Twenty-one of these patients received 52 continuous weeks of treatment with telitacicept. Treatment outcomes were analysed separately according to whether patients had renal or haematological abnormalities. Trajectory analysis was performed to identify patients with a limited response. Factors contributing to a limited response were explored by multivariable logistic regression analysis. RESULTS: After treatment with telitacicept for 4, 12, 24 and 52 weeks, 22.22%, 54.17%, 72.22% and 80.95% of patients, respectively, achieved an SLE Responder Index 4; 8.33%, 26.39%, 34.72% and 47.62% achieved a Lupus Low Disease Activity State; and 0%, 4.17%, 8.33% and 23.81% achieved remission. Significant decreases in serum IgA, IgG and IgM levels were observed at 4 weeks and showed a downward trend at 12, 24 and 52 weeks. The median 24-hour urinary protein declined from 1323.5 mg to 224.0 mg in patients with lupus nephritis after treatment with telitacicept for 52 weeks. Furthermore, a large proportion of patients (10 of 13) with haematological abnormalities recovered after 52 weeks of treatment with telitacicept. No severe adverse events were reported during the observation period. Age appeared to have a negative impact on treatment efficacy. CONCLUSIONS: Telitacicept demonstrated favourable efficacy and safety in patients with active SLE and improved the renal and haematological manifestations of the disease.


Assuntos
Lúpus Eritematoso Sistêmico , Nefrite Lúpica , Humanos , Lúpus Eritematoso Sistêmico/complicações , Lúpus Eritematoso Sistêmico/tratamento farmacológico , Estudos Retrospectivos , Nefrite Lúpica/tratamento farmacológico , Resultado do Tratamento
2.
Molecules ; 26(2)2021 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-33467083

RESUMO

Chitosan is the only cationic polysaccharide found in nature. It has broad application prospects in biomaterials, but its application is limited due to its poor solubility in water. A novel chitosan derivative was synthesized by amidation of chitosan with 18ß-glycyrrhetinic acid and sialic acid. The chitosan derivatives were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and measurement of the zeta potential. We also investigated the solubility, cytotoxicity, and blood compatibility of chitosan derivatives. 18ß-glycyrrhetinic acid and sialic acid could be grafted onto chitosan molecular chains. The thermal stability of the synthesized chitosan derivatives was decreased and the surface was positively charged in water and phosphate-buffered saline. After chitosan had been modified by 18 ß-glycyrrhetinic acid and sialic acid, the solubility of chitosan was improved greatly in water and phosphate-buffered saline, and percent hemolysis was <5%. Novel amphiphilic chitosan derivatives could be suitable polymers for biomedical purposes.


Assuntos
Quitosana , Ácido Glicirretínico/análogos & derivados , Teste de Materiais , Ácido N-Acetilneuramínico , Linhagem Celular , Quitosana/análogos & derivados , Quitosana/síntese química , Quitosana/química , Quitosana/farmacologia , Ácido Glicirretínico/química , Ácido Glicirretínico/farmacologia , Humanos , Ácido N-Acetilneuramínico/química , Ácido N-Acetilneuramínico/farmacologia , Solubilidade
3.
Biomed Pharmacother ; 117: 109204, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31387177

RESUMO

We wished to investigate the role of a tilapia skin collagen polypeptide (TSCP; molecular weight <3 kDa) in alleviating liver and kidney injuries in aging mice induced by d-galactose (d-gal) and its underlying mechanism of action. First, we characterized TSCP. TSCP was passed through a 3-kDa ultrafiltration membrane, desalted in water by a solid-phase extraction column, purified further by reverse phase-high performance liquid chromatography, and analyzed by electrospray ionization mass spectrometry and tandem mass spectrometry. TSCP contained 17 types of amino acids (AAs) and 41 peptide chains of length 7 AAs to 22 AAs. The content of free AAs and total AAs of TSCP was 13.5% and 93.79%, respectively. Next, we undertook animal experiments. Mice were injected once-daily with D-gal (300 mg/kg body weight, s.c.) for 8 weeks, and TSCP was administered simultaneously once-daily by intragastric gavage. TSCP could visibly improve the decreased body weight, depressed appetite, and mental deterioration of mice triggered by d-gal. TSCP could also alleviate d-gal-induced damage to the liver and kidneys according to histopathology (especially high-dose TSCP). Consistent with these macroscopic and pathologic changes, TSCP could also prevent d-gal-induced increases in serum levels of alanine aminotransferase, aspartate transaminase, alkaline phosphatase, lipid peroxidation, creatinine and uric acid, as well as decreases in serum levels of immunoglobulin (Ig)G and IgM. Moreover, TSCP improved the activities of superoxide dismutase, catalase, and glutathione peroxidase, but also inhibited the increases in the levels of malondialdehyde and inducible nitric oxide synthase expression in the liver and kidneys of d-gal-treated mice. These results suggest that TSCP can alleviate the injuries to the liver and kidneys in aging mice induced by d-gal, and that its mechanism of action might be, at least partially, associated with attenuation of oxidative stress and enhancement of immune function.


Assuntos
Colágeno/farmacologia , Galactose/efeitos adversos , Rim/efeitos dos fármacos , Fígado/efeitos dos fármacos , Peptídeos/farmacologia , Substâncias Protetoras/farmacologia , Tilápia/metabolismo , Alanina Transaminase/metabolismo , Animais , Antioxidantes/metabolismo , Aspartato Aminotransferases/metabolismo , Catalase/metabolismo , Glutationa Peroxidase/metabolismo , Rim/metabolismo , Peroxidação de Lipídeos/efeitos dos fármacos , Fígado/metabolismo , Masculino , Malondialdeído/metabolismo , Camundongos , Estresse Oxidativo/efeitos dos fármacos , Superóxido Dismutase/metabolismo
4.
Molecules ; 24(14)2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31315269

RESUMO

Mussel adhesive proteins (MAPs) have a unique ability to firmly adhere to different surfaces in aqueous environments via the special amino acid, 3,4-dihydroxyphenylalanine (DOPA). The catechol groups in DOPA are a key group for adhesive proteins, which is highly informative for the biomedical domain. By simulating MAPs, medical products can be developed for tissue adhesion, drug delivery, and wound healing. Hydrogel is a common formulation that is highly adaptable to numerous medical applications. Based on a discussion of the adhesion mechanism of MAPs, this paper reviews the formation and adhesion mechanism of catechol-functionalized hydrogels, types of hydrogels and main factors affecting adhesion, and medical applications of hydrogels, and future the development of catechol-functionalized hydrogels.


Assuntos
Bivalves/química , Catecóis/química , Animais , Bivalves/metabolismo , Di-Hidroxifenilalanina/química , Sistemas de Liberação de Medicamentos , Hidrogéis , Proteínas/metabolismo , Aderências Teciduais , Cicatrização
5.
J Geriatr Cardiol ; 16(5): 395-400, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31217792

RESUMO

BACKGROUND: Diabetes is frequently associated with poor prognosis among acute myocardial infarction (AMI) patients. Patients with these comorbidities often have atypical symptoms and subsequent delay in treatment. Few studies have reported detailed AMI symptoms in patients with diabetes. This study compared AMI symptoms and presentation characteristics between diabetics and non-diabetics. METHODS: We included patients from the China AMI registry diagnosed with AMI between January 2013 and September 2014. Baseline characteristics, symptomology, and delay in treatment were compared between diabetics and non-diabetics. Multivariable logistic regression analysis was used to explore independent predictors of atypical symptoms. RESULTS: A total of 4450 (20.2%) patients had diabetes. They were older, more often women, higher in body mass index, and more likely to have non-ST segment elevation myocardial infarction. Fewer diabetic patients presented with persistent precordial chest pain (63.1% vs. 68%, P < 0.0001), diaphoresis (60.1% vs. 65.6%, P < 0.0001), fatigue (16.7% vs. 18.3%, P = 0.0123), and incontinence (0.4% vs. 0.7%, P = 0.0093). Time to hospital presentation was longer among patients with diabetes than those without. In multivariable analysis, diabetes was identified as an independent predictor of atypical symptoms (OR: 1.112, 95% CI: 1.034-1.196). CONCLUSIONS: Our study is the first large-scale study providing evidence that diabetics are less likely to present with typical chest pain and more likely to experience treatment delay when suffering from an AMI. Our results may increase clinician awareness of recognizing AMI patients rapidly to reduce diagnosis and treatment delay, particularly in the context of diabetes.

6.
Membranes (Basel) ; 9(1)2019 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-30626053

RESUMO

In this study, the porous composite films of carboxymethyl chitosan/alginate/tranexamic acid were fabricated, with calcium chloride as the crosslinking agent and glycerin as a plasticizer. The composite films were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The properties of the composite films, including water absorption, air permeability, and cumulative release rate, were tested. In addition, their hemostatic performance was evaluated. The results showed that the appearance of the films with good adhesion was smooth and porous. FTIR showed that chemical crosslinking between carboxymethyl chitosan and sodium alginate was successful. The excellent cumulative release of tranexamic acid in the composite films (60⁻80%) gives the films a significant procoagulant effect. This has good prospects for the development of medical hemostasis materials.

7.
Mar Drugs ; 16(8)2018 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-30081571

RESUMO

Effective hemostasis is vital to reduce the pain and mortality of patients, and the research and development of hemostatic materials are prerequisite for effective hemostasis. Chitosan (CS), with good biodegradability, biocompatibility and non-toxicity, has been widely applied in bio-medicine, the chemical industry, the food industry and cosmetics. The excellent hemostatic properties of CS have been extensively studied. As a result, chitosan-based composite hemostatic materials have been emerging. In this review, the hemostatic mechanism of chitosan is briefly discussed, and then the progress of research on chitosan-based composite hemostatic materials with multiple forms such as films, sponges, hydrogels, particles and fibers are introduced. Finally, future perspectives of chitosan-based composite hemostatic materials are given. The objective of this review is to provide a reference for further research and development of effective hemostatic materials.


Assuntos
Materiais Biocompatíveis/farmacologia , Coagulação Sanguínea/efeitos dos fármacos , Quitosana/farmacologia , Hemorragia/terapia , Hemostáticos/farmacologia , Animais , Organismos Aquáticos/química , Materiais Biocompatíveis/química , Materiais Biocompatíveis/uso terapêutico , Células Sanguíneas/efeitos dos fármacos , Quitosana/química , Quitosana/uso terapêutico , Técnicas Hemostáticas , Hemostáticos/química , Hemostáticos/uso terapêutico , Humanos
8.
Food Chem ; 264: 277-283, 2018 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-29853377

RESUMO

The mechanism of the thermal degradation and the toxicity of the thermal degradation products of agar were studied using TG/DTA, Fourier-transform infrared spectroscopy and pyrolysis gas chromatography/mass spectrometry. It was found that the thermal degradation of agar is a single-step reaction, the thermal degradation temperature (T0, Tp, Tf) increases with increasing gel strength (P) and the influence of P on the thermal degradation rate is modest. The thermal degradation of agar is an exothermic reaction, and the activation energy of the reaction increases with increasing P. In the thermal degradation, agar is first decomposed into 3,6-anhydropyran galactopyranose and galactopyranose, then 3,6-anhydropyran galactopyranose, and finally furyl hydroxymethyl ketone, through loop opening, dehydration and hydrogen transfer. Galactopyranose follows three degradation pathways, and its final degradation products are 3,4-atrosan, d-allose, furfural and 5-(hydroxymethyl)-2-furancarboxaldehyde. Of the degradation products, furyl hydroxymethyl ketone, furfural, and 5-(hydroxymethyl)-2-furancarboxaldehyde show some toxicity to humans.


Assuntos
Ágar/química , Ágar/toxicidade , Furaldeído/química , Galactose/química , Cromatografia Gasosa-Espectrometria de Massas , Glucose/química , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura , Termogravimetria
9.
Mar Drugs ; 16(6)2018 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-29794973

RESUMO

Chitosan oligosaccharide (COS), a natural polysaccharide with good antioxidant and anti-inflammatory properties, is the depolymerized product of chitosan possessing various biological activities. The present study was designed to investigate the possible anti-aging effect of COS on the aging model mouse induced by d-galactose (d-gal) and explore the underlying mechanism. In the experiment, 48 male Kunming mice (KM mice) were randomly divided into the normal group, model group, positive group, and low-medium-high dose polysaccharide groups (300, 600, 1200 mg/kg/day). The results showed that COS, by intragastric gavage after subcutaneous injection of d-gal (250 mg/kg/day) into the neck of mice consecutively for eight weeks, gradually recovered the body weight, the activity of daily living, and organ indices of mice, as well as effectively ameliorated the histological deterioration of the liver and kidney in mice triggered by d-gal. To be specific, COS obviously improved the activities of antioxidant enzymes in liver and kidney of KM mice, including catalase (CAT), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD), as well as decreased malondialdehyde (MDA) levels when compared with those in model group mice. Furthermore, COS not only elevated the diminished levels of serum immunoglobulin G (IgG) and IgM induced by d-gal, but also significantly inhibited the d-gal-caused upregulation of serum alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), uric acid (UA) and creatinine (CREA) levels as compared with those of mice in the model group. These results demonstrate that COS has an obvious anti-aging activity in d-gal-induced subacute aging mice, the mechanism of which, to some extent, is associated with enhancing the antioxidant defenses, reducing oxidative stress, and improving the immune function of aging model mice.


Assuntos
Envelhecimento/efeitos dos fármacos , Antioxidantes/farmacologia , Quitosana/farmacologia , Oligossacarídeos/farmacologia , Estresse Oxidativo/efeitos dos fármacos , Envelhecimento/imunologia , Alanina Transaminase/sangue , Animais , Aspartato Aminotransferases/sangue , Peso Corporal/efeitos dos fármacos , Catalase/metabolismo , Galactose/imunologia , Glutationa Peroxidase/metabolismo , Sistema Imunitário/efeitos dos fármacos , Imunoglobulina G/sangue , Imunoglobulina M/sangue , Rim/efeitos dos fármacos , Rim/patologia , Fígado/efeitos dos fármacos , Fígado/enzimologia , Fígado/patologia , Masculino , Malondialdeído/sangue , Camundongos , Modelos Animais , Superóxido Dismutase/metabolismo
10.
Int J Biol Macromol ; 112: 1191-1198, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29408210

RESUMO

The purpose of this study was to develop a promising burns dressing. Chiosan (CS) has been widely used as biomaterials, in combination with marine peptides (MPs) extracted from seawater cultured Tilapia, the newly developed material Chitosan-Marine Peptides hydrogels (CSMP) in this study showed antibacterial activity, pro-cell proliferation and migration, well burning healing. Pathological examinations by HE staining demonstrated that CSMP had pronounced wound healing efficiencies. In burn wounds treated with CSMP, reepithelialization and collagen fiber deposition were observed on day 7, the epithelium was completely regenerated by day 14, and the wounds were completely healed by day 21. Furthermore, CSMP can up-regulate the expression of FGF2 and VEGF. Collectively, these results suggest that CSMP may enhance cell migration and promote the skin regeneration, which demonstrates the potential application of CSMP in burning healing.


Assuntos
Queimaduras/tratamento farmacológico , Queimaduras/patologia , Quitosana/uso terapêutico , Hidrogéis/uso terapêutico , Peptídeos/uso terapêutico , Tilápia/metabolismo , Cicatrização/efeitos dos fármacos , Animais , Antibacterianos/farmacologia , Morte Celular/efeitos dos fármacos , Linhagem Celular , Movimento Celular/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , Quitosana/farmacologia , Feminino , Fator 2 de Crescimento de Fibroblastos/metabolismo , Hidrogéis/farmacologia , Masculino , Camundongos , Testes de Sensibilidade Microbiana , Peptídeos/farmacologia , Coelhos , Pele/patologia , Espectroscopia de Infravermelho com Transformada de Fourier , Fator A de Crescimento do Endotélio Vascular/metabolismo
11.
Exp Gerontol ; 103: 27-34, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29275159

RESUMO

Skin photoaging (SP) is a premature skin-aging damage after repeated exposure to ultraviolet (UV) radiation, mainly characterized by oxidative stress and inflammatory disequilibrium, which makes skin show the typical symptoms of photoaging such as coarse wrinkling, dryness, irregular pigmentation and laxity. Chitosan oligosaccharide (COS), a natural polysaccharide with good humectant property, is the depolymerized product of chitosan with various biological activities, among which the antioxidant and anti-inflammatory effects have been frequently reported in recent years. However, no existing invivo study indicates whether COS has direct protective effect on UV-induced SP. In the current research, we investigated the potential preventive effect of COS against UV-caused damage in hairless mouse dorsal skin. The data showed that COS, by topical application after each UV-radiation for 10weeks, effectively inhibited the undesirable changes on the skin induced by UV. To be specific, COS obviously alleviated the macroscopic and histopathological damages of mice skin, via mitigating the disrupted collagenous fibers, as well as improving the relative content of type I collagen and the amount of total collagen. Furthermore, COS effectively inhibited the levels of pro-inflammatory cytokines such as TNF-α, IL-1ß and IL-6, and markedly improved the activities of antioxidant enzymes (SOD, GSH-Px, CAT), as well as the content of skin hydroxyproline and moisture. These findings demonstrated that this natural polysaccharide attenuated UV-induced SP, at least in part, by virtue of favorable regulation of antioxidant and anti-inflammatory status, which presumably worked in concert to maintain the morphology and level of dermal collagen.


Assuntos
Antioxidantes/farmacologia , Quitosana/farmacologia , Colágeno Tipo I/metabolismo , Oligossacarídeos/farmacologia , Envelhecimento da Pele/efeitos dos fármacos , Animais , Colágeno/metabolismo , Feminino , Malondialdeído/metabolismo , Camundongos , Camundongos Pelados , Camundongos Endogâmicos BALB C , Estresse Oxidativo/efeitos dos fármacos , Pele/patologia , Pele/efeitos da radiação , Superóxido Dismutase/metabolismo , Raios Ultravioleta/efeitos adversos
12.
Mar Drugs ; 15(11)2017 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-29112116

RESUMO

Classic hypotheses of Alzheimer's disease (AD) include cholinergic neuron death, acetylcholine (ACh) deficiency, metal ion dynamic equilibrium disorder, and deposition of amyloid and tau. Increased evidence suggests neuroinflammation and oxidative stress may cause AD. However, none of these factors induces AD independently, but they are all associated with the formation of Aß and tau proteins. Current clinical treatments based on ACh deficiency can only temporarily relieve symptoms, accompanied with many side-effects. Hence, searching for natural neuroprotective agents, which can significantly improve the major symptoms and reverse disease progress, have received great attention. Currently, several bioactive marine products have shown neuroprotective activities, immunomodulatory and anti-inflammatory effects with low toxicity and mild side effects in laboratory studies. Recently, chitosan (CTS), chitooligosaccharide (COS) and their derivatives from exoskeletons of crustaceans and cell walls of fungi have shown neuroprotective and antioxidative effects, matrix metalloproteinase inhibition, anti-HIV and anti-inflammatory properties. With regards to the hypotheses of AD, the neuroprotective effect of CTS, COS, and their derivatives on AD-like changes in several models have been reported. CTS and COS exert beneficial effects on cognitive impairments via inhibiting oxidative stress and neuroinflammation. They are also a new type of non-toxic ß-secretase and AChE inhibitor. As neuroprotective agents, they could reduce the cell membrane damage caused by copper ions and decrease the content of reactive oxygen species. This review will focus on their anti-neuroinflammation, antioxidants and their inhibition of ß-amyloid, acetylcholinesterase and copper ions adsorption. Finally, the limitations and future work will be discussed.


Assuntos
Doença de Alzheimer/tratamento farmacológico , Quitina/análogos & derivados , Quitosana/análogos & derivados , Quitosana/uso terapêutico , Quitina/química , Quitina/uso terapêutico , Inibidores da Colinesterase/química , Inibidores da Colinesterase/uso terapêutico , Cobre , Humanos , Oligossacarídeos
13.
Drug Deliv ; 21(7): 548-52, 2014 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-24215307

RESUMO

N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) is hydro-soluble chitosan (CS) derivative, which can be obtained by the reaction between epoxypropyl trimethyl ammonium chloride (ETA) and CS. The preparation parameters for the synthesis of HTCC were optimized by orthogonal experimental design. ETA was successfully grafted into the free amino group of CS. Grafting of ETA with CS had great effect on the crystal structure of HTCC, which was confirmed by the XRD results. HTCC displayed higher capability to form nanoparticles by crosslinking with negatively charged sodium tripolyphosphate (TPP). Ribavrin- (RIV-) loaded HTCC nanoparticles were positively charged and were spherical in shape with average particle size of 200 nm. More efficient drug encapsulation efficiency and loading capacity were obtained for HTCC in comparison with CS, however, HTCC nanoparticles displayed faster release rate due to its hydro-soluble properties. The results suggest that HTCC is a promising CS derivative for the encapsulation of hydrophilic drugs in obtaining sustained release of drugs.


Assuntos
Química Farmacêutica/métodos , Quitosana/síntese química , Portadores de Fármacos/síntese química , Nanopartículas/química , Ribavirina/síntese química , Antivirais/administração & dosagem , Antivirais/síntese química , Quitosana/administração & dosagem , Portadores de Fármacos/administração & dosagem , Nanopartículas/administração & dosagem , Ribavirina/administração & dosagem , Difração de Raios X
14.
Compos Sci Technol ; 67(15): 3130-3139, 2007 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32287828

RESUMO

A novel natural rubber/silica (NR/SiO2) nanocomposite is developed by combining self-assembly and latex-compounding techniques. The results show that the SiO2 nanoparticles are homogenously distributed throughout NR matrix as nano-clusters with an average size ranged from 60 to 150 nm when the SiO2 loading is less than 6.5 wt%. At low SiO2 contents (⩽4.0 wt%), the NR latex (NRL) and SiO2 particles are assembled as a core-shell structure by employing poly (diallyldimethylammonium chloride) (PDDA) as an inter-medium, and only primary aggregations of SiO2 are observed. When more SiO2 is loaded, secondary aggregations of SiO2 nanoparticles are gradually generated, and the size of SiO2 cluster dramatically increases. The thermal/thermooxidative resistance and mechanical properties of NR/SiO2 nanocomposites are compared to the NR host. The nanocomposites, particularly when the SiO2 nanoparticles are uniformly dispersed, possess significantly enhanced thermal resistance and mechanical properties, which are strongly depended on the morphology of nanocomposites. The NR/SiO2 has great potential to manufacture medical protective products with high performances.

15.
J Nanosci Nanotechnol ; 6(2): 541-6, 2006 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-16573058

RESUMO

A novel natural rubber/silica (NR/SiO2) nanocomposite with a SiO2 loading of 4 wt% is developed by incorporating latex compounding with self-assembly techniques. The SiO2 nanoparticles are homogenously distributed throughout the NR matrix as spherical nano-clusters with an average size of 75 nm. In comparison with the host NR, the thermal resistance of the nanocomposite is significantly improved. The degradation temperatures (T), reaction activation energy (E), and reaction order (n) of the nanocomposite are markedly higher than those of the pure NR, due to significant retardant effect of the SiO2 nanoparticles.


Assuntos
Borracha/química , Dióxido de Silício/química , Temperatura Alta , Cinética , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão
17.
J Nanosci Nanotechnol ; 6(12): 3934-8, 2006 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-17256356

RESUMO

The morphology of self-assembled poly(vinyl alcohol)/silica (PVA/SiO2) nanocomposites is investigated with atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that the SiO2 nanoparticles are homogenously distributed throughout the PVA matrix in a form of spherical nano-cluster. The average size of the SiO2 clusters is below 50 nm at the low contents (SiO2 < or =5 5 wt%), while particle aggregations are clearly observed and their average size markedly increases to 110 nm when 10 wt% SiO2 is loaded. The thermogravimetric analysis (TGA) shows that the nanocomposite significantly outperforms the pure PVA in the thermal resistance. By using a multi-heating-rate method, the thermal degradation kinetics of the nanocomposite with a SiO2 content of 5 wt% is compared to the PVA host. The reaction activation energy (E) of the nanocomposite, similar to the pure PVA, is divided into two main stages corresponding to two degradation steps. However, at a given degradation temperature, the nanocomposite presents much lower reaction velocity constants (k), while its E is 20 kJ/mol higher than that of the PVA host.


Assuntos
Cristalização/métodos , Modelos Químicos , Modelos Moleculares , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Álcool de Polivinil/química , Dióxido de Silício/química , Simulação por Computador , Cinética , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Nanotecnologia/métodos , Tamanho da Partícula , Transição de Fase , Propriedades de Superfície , Temperatura de Transição
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