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The Effect of the Mixtures of Photoinitiators in Polymerization Efficiencies

NEUMANN, Miguel G.; SCHMITT, Carla C.; HORN JR., Marco A.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
ENG
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The photoinitiated polymerization of methyl methacrylate using the mixtures of camphorquinone (CQ) and acylphosphine oxides (monoacylphosphine oxide, MAPO or bisacylphosphine oxide,BAPO) was studied to determine the possible synergistic effects. The addition of the acylphosphines to CQ resulted in an increase of the polymerization rate compared with CQ alone. On the other hand, a significant decrease of the polymerization quantum yield is observed for the mixtures compared with the pure acylphosphines. Therefore, the increase in the polymerization efficiency of the two rnixtures studied, MAPO/CQ and BAPO/CQ (compared with CQ) can be traced to the larger light absorption range, rather than to the onset of new mechanisms. The presence of the coinitiator ethyl 4-dimethylaminobenzoate, EDB, always present in CQ formulations, has no effect at all on the rates of polymerization photoinitiated by the acylphosphine oxides. From the point of view of photopolymerization quantum yields, an antagonistic effect is observed because Of the energy transfer of the M more efficient initiator (MAPO or BAPO) to the less efficient one (CQ). (C) 2008 Wiley Periodicals, Inc. j Appl Polym Sci 112: 129-134, 2009; FAPESP, Brazil[03/07770-4]; CNPq[471310/2006-9]

Evaluation of the light polymerization efficiency of copolymers used in dental formulations by differential scanning calorimetry

RIGOLI, Isabel C.; RIGA, Alan T.; CAVALHEIRO, Carla C. S.; NEUMANN, Miguel G.; CAVALHEIRO, Eder T. G.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
ENG
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Different compositions of visible-light-curable triethylene glycol dimethacrylate/bisglycidyl methacrylate copolymers used in dental resin formulations were prepared through copolymerization photoinitiated by a camphorquinone/ethyl 4-dimethylaminobenzoate system irradiated with an Ultrablue IS light-emitting diode. The obtained copolymers were evaluated with differential scanning calorimetry. From the data for the heat of polymerization, before and after light exposure, obtained from exothermic differential scanning calorimetry curves, the light polymerization efficiency or degree of conversion of double bonds was calculated. The glass-transition temperature also was determined before and after photopolymerization. After the photopolymerization, the glass-transi-tion temperature was not well defined because of the breadth of the transition region associated with the properties of the photocured dimethacrylate. The glass-transition temperature after photopolymerization was determined experimentally and compared with the values determined with the Fox equation. In all mixtures, the experimental value was lower than the calculated value. Scanning electron microscopy was used to analyze the morphological differences in the prepared copolymer structures. (C) 2007 Wiley Periodicals...

Evaluation of Postpolymerization as a Function of the Storage Time of Triethylene Glycol Dimethacrylate/2,2-Bis[4-(2-Hydroxy-3-Methacryloxy-Prop-1-Oxy)-Phenyl]-propane Bisphenyl-alpha-Glycidyl Ether Dimethacrylate Copolymers Used in Dental Resins by Differential Scanning Calorimetry and Dynamic Mechanical Analysis

RIGOLI, Isabel C.; CAVALHEIRO, Carla C. S.; NEUMANN, Miguel G.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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The aim of this work was to evaluate the effect of the storage time on the thermal properties of triethylene glycol dimethacrylate/2,2-bis[4-(2-hydroxy-3-methacryloxy-prop-1-oxy)-phenyl]propane bisphenyl-alpha-glycidyl ether dimethacrylate (TB) copolymers used in formulations of dental resins after photopolymerization. The TB copolymers were prepared by photopolymerization with an Ultrablue IS light-emitting diode, stored in the dark for 160 days at 37 degrees C, and characterized with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy with attenuated total reflection. DSC curves indicated the presence of an exothermic peak, confirming that the reaction was not completed during the photopolymerization process. This exothermic peak became smaller as a function of the storage time and was shifted at higher temperatures. In DMA studies, a plot of the loss tangent versus the temperature initially showed the presence of two well-defined peaks. The presence of both peaks confirmed the presence of residual monomers that were not converted during the photopolymerization process. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 679-684, 2009; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP Fundacao de Amparo a Pesquisa do Estado de Sao Paulo[05/01618-1]; FAPESP Fundacao de Amparo a Pesquisa do Estado de Sao Paulo[02/03448-8]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

"Fotopolimerização iniciada por tioxantona e outros indicadores - Estudos fundamentais e aplicações"; "Photopolymerization initiated by thioxanthone and other initiators - Fundamental studies and applications"

Ferreira, Giovana Chimello
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/03/2006 PT
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A cinética de fotopolimerização do monômero metacrilato de metila (MMA) foi investigada usando o fotoiniciador tioxantona (TX) e o co-iniciador trietilamina (TEA), a fim de elucidar o mecanismo de fotopolimerização. A dilatometria foi usada como técnica para a determinação das cinéticas de polimerização. Determinaram-se os rendimentos quânticos de polimerização. Os estados excitados foram estudados por fluorescência estática para determinar as constantes de supressão de fluorescência pela amina e pelo monômero. Medidas de fotólise por pulso de laser permitiram obter o espectro de absorção triplete-triplete da tioxantona, bem como a constante de supressão do estado triplete. Os resultados mostraram que a supressão ocorre por um processo colisional no estado singlete e que os radicais eficientes na fotoiniciação são originados da amina TEA. A massa molecular média dos polímeros obtidos foi determinada por medidas de cromatografia de permeação em gel (GPC). Em uma segunda etapa, foi investigada a polimerização fotoiniciada por fotoiniciadores usados em resinas dentárias, canforquinona (CQ), 1,2-fenilpropanodiona (PPD), Lucirin e Irgacure. A velocidade de polimerização foi acompanhada por dilatometria usando excitação acima de 348 nm. Obteve-se os rendimentos quânticos de polimerização e os polímeros foram caracterizados por GPC. A maior constante de velocidade de polimerização obtida foi para o Irgacure e o maior rendimento quântico de polimerização obtido foi para o Lucirin. As diferenças na eficiência da polimerização são atribuídas à formação de radicais e à capacidade de gerar radicais a partir da absorção da luz incidente. Por fim...

Efeito da mistura de fotoiniciadores acilfosfínicos e canforquinona na eficiência da polimerização; Effect of mixed acylphosphines and camphorquinone photoinitiators in polymerization efficiencies

Horn Júnior, Marco Antonio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/01/2008 PT
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Foi estudado o processo de fotopolimerização iniciado através de misturas dos fotoiniciadores, acilfosfínicos (MAPO e BAPO), com canforquinona (CQ). Também foi investigada a existência de um possível efeito sinérgico durante a fotoiniciação. A eficiência de polimerização das duas misturas, MAPO/CQ e BAPO/CQ, foi determinada por actinometria. A fotodilatometria foi a técnica utilizada para o acompanhamento das cinéticas de polimerização. A adição do co-iniciador EDB não apresentou efeito nas velocidades de polimerização iniciadas pelos fotoiniciadores acilfosfínicos. Do ponto de vista do rendimento quântico de polimerização, um efeito antagonístico foi observado devido a transferência de energia a partir dos fotoiniciadores mais eficientes (MAPO ou BAPO) para o menos eficiente, canforquinona (CQ).; The photopolymerization processes involving two different photoinitiators: acylphosphine oxides (MAPO and BAPO) and camphorquinone (CQ) were studied in order to determine possible synergistic effects. The polymerization efficiency of the two mixtures, MAPO/CQ and BAPO/CQ, was studied using actinometry. The polymerization kinetics was followed by photodilatometry. The presence of the coinitiator EDB had no effect in the polymerization rate initiated by the acylphosphine oxides. From the point of view of photopolymerization quantum yields...

Alteração de temperatura na dentina durante o procedimento restaurador com resina composta variando as fontes fotopolimerizadoras; Temperature alteration in dentin according to the photopolymerization source during composite-resin restorations

Savaris, Cristiane
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/01/2009 PT
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O objetivo deste estudo foi avaliar a influência do tipo de fonte luminosa e da espessura do remanescente dental no aumento de temperatura na câmara pulpar durante a fotopolimerização de uma resina composta. Métodos: Utilizaram-se 96 fragmentos (6x7 mm) obtidos a partir das superfícies vestibulares de incisivos bovinos que foram divididos em 2 grupos e 4 subgrupos (n=12), de acordo com a fonte de luz (LED e luz halógena) e da espessura de remanescente dental (3,5 mm; 3,0 mm; 2,0 mm e 1,0 mm). Foram preparadas cavidades de classe I (3x2 mm), deixando a espessura dos respectivos remanescentes dentais, e restauradas com uma resina composta. A variação de temperatura foi captada por termopares posicionados na dentina do teto da câmara pulpar durante a fotopolimerização (20s) do agente adesivo e de cada incremento de resina composta. Foi considerado o maior valor de temperatura registrado durante todo o procedimento restaurador e também durante a fotopolimerização de cada incremento de resina composta. Os dados foram analisados usando ANOVA e Teste de Fisher (α=5%). Resultados: O LED promoveu maiores (p<0,05) valores de temperatura do que a luz halógena; os valores mais baixos de temperatura foram (p<0,05) para 3,5 mm de espessura e os maiores para os remanescentes de 1 mm de espessura de remanescente dental; não houve diferença significativa (p>0...

Microfabricação por fotopolimerização via absorção de dois fótons; Two-photon absorption photopolymerization microfabrication

Gomes, Vinicius Tribuzi Rodrigues Pinheiro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 10/02/2009 PT
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Neste trabalho usamos pulsos de femtossegundos na fabricação de estruturas poliméricas em escala microscópica, através da técnica de fotopolimerização via absorção de dois fótons. Graças ao confinamento espacial da polimerização, resultante do processo de absorção de dois fótons, este método permite a fabricação de microestruturas tridimensionais complexas, com alta resolução, visando diversas aplicações tecnológicas, de fotônica até biologia. Inicialmente, desenvolvemos a técnica de fotopolimerização via absorção de dois fótons, desde a implantação da montagem óptica até a confecção dos sistemas de movimentação e controle do posicionamento do feixe laser. Através da fabricação e caracterização de microestruturas, produzidas em resinas acrílicas, o sistema foi aperfeiçoado permitindo a produção de microestruturas da pordem de 30um com razoável resolução espacial. Uma vez que a maior parte as microestruturas reportadas na literatura são elementos passivos, ou seja, suas propriedades ópticas não podem ser controladas por meios externos, numa segunda etapa deste projeto produzimos microestruturas opticamente ativas. Neste caso, a microfabricação foi feita em resinas acrílicas dopadas Rodamina B...

Síntese e caracterização de nanopartículas núcleo-casca de poliestireno e polimetacrilato de metila obtidas por polimerização em emulsão sem emulsificante e fotoiniciada.; Synthesis and characterization of core-shell nanoparticles of polystyrene and poly(methyl metacrylate) obtained by emulsifier-free emulsion polymerization and photopolymerization.

Carranza Oropeza, María Verónica
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/09/2011 PT
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O objetivo do trabalho foi sintetizar e caracterizar nanopartículas de poliestireno e polimetacrilato de metila com morfologia núcleo-casca obtidas através da polimerização em emulsão sem emulsificante em dois estágios e através da fotopolimerização. Nos experimentos avaliou-se a influência de diferentes condições operacionais baseadas em fatores cinéticos sobre os dois estágios da polimerização. As condições avaliadas para o primeiro estágio de preparação de núcleos foram: a temperatura do processo, a concentração de iniciador e de monômero, e o efeito de agentes modificadores de superfície (sal, co-monômero e reticulante). Para o segundo estágio de formação da casca as condições avaliadas foram: a concentração e o regime de alimentação de monômero. Os resultados experimentais mostraram que uma relação de co-monômero e reticulante é a melhor alternativa para preparar núcleos estáveis e de diâmetros pequenos. Assim, o revestimento uniforme dos núcleos é obtido no segundo estágio e com isso a morfologia núcleo-casca em equilíbrio é alcançada. Dois sistemas experimentais (reator convencional e reator fotoquímico) foram propostos e avaliados na sua eficiência para obter partículas com este tipo de morfologia no segundo estágio (formação do revestimento). As diversas técnicas de caracterização indicaram a formação de morfologia núcleo-casca na maioria dos casos estudados para os dois sistemas propostos. Por sua vez...

Estudo da fotopolimerização de monomeros monofuncionais e multifuncionais para produção e recobrimento de lentes oftalmicas; Study of photopolymerization of monofunctional and multifunctional monomers for production and coating of ophthalmic lenses

Patricia Bogalhos Lucente Fregolente
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 14/03/2006 PT
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Atualmente, o mercado procura materiais com qualidades ópticas que satisfaçam as exigências dos usuários e que possuam facilidades de processamento. De forma geral, para um polímero apresentar boas propriedades ópticas, este necessita ter boas características como alto índice de refração, alta transmitância da luz, baixo peso específico, resistência ao impacto, estabilidade dimensional pós cura e estabilidade por exposição à luz e ao calor. Industrialmente, utiliza-se para a fabricação de lentes oftálmicas, a técnica de polimerização térmica, ou cura térmica. Dessa maneira, necessita-se de um tempo de cura muito longo (cerca de 20 horas) para evitar defeitos nas lentes. Entretanto, a cura através de irradiação de luz ultra-violeta (UV) permite obter os mesmos tipos de materiais e com características semelhantes com um tempo de processo reduzido em até poucos minutos. No presente trabalho, para confecção das lentes foram estudados os seguintes monômeros e oligômeros: metacrilato de metila (MAM), 1,6-Hexanediol diacrilato (HDODA), diacrilato uretano alifático tetrafuncional (Ebecryl 284) e diacrilato epóxi bisfenol-A (Ebecryl 3700) e para cada formulação o fotoiniciador 2- hidroxi-2-metil-1-fenilpropanona (Darocure 1173). O tempo de fotocura da mistura dura entre 4 a 7 minutos...

Influence of photopolymerization light source on enamel shear bond strength after bleaching

Loretto,Sandro Cordeiro; Braz,Rodivan; Lyra,Arine Maria Víveros de Castro; Lopes,Luís Mário
Fonte: Fundação Odontológica de Ribeirão Preto Publicador: Fundação Odontológica de Ribeirão Preto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2004 EN
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This study evaluated the influence of 3 different photopolymerization sources on enamel shear bond strength after bleaching with 10% carbamide peroxide. Seventy-two incisive bovine teeth were randomly divided into 6 groups (n=12) according to bleaching treatment and photopolymerization source used: G1 - Bleached / Halogen lamp; G2 - Not bleached / Halogen lamp (control); G3 - Bleached / Light-emitting diodes (LED); G4 - Not bleached / Light-emitting diodes (LED) (control); G5 - Bleached / Xenon plasma arc; G6 - Not bleached / Xenon plasma arc (control). Experimental groups were exposed to bleaching agent for a period of 14 days, with a daily contact of 4 h and then stored in artificial saliva at 37ºC. Control groups were stored in artificial saliva at 37ºC for same period of bleaching treatment. Procedures for bonding composite resin to enamel were carried out according to manufacturer instructions. After storage in distilled water at 37ºC for 24 hours, all samples were submitted to shear bond strength test. G2 had the highest mean value (14.86 MPa) while G5 had the lowest (12.32 MPa). The comparison of groups by 2-way ANOVA showed that there were no significant differences for either of the factors considered in this study (bleaching and photopolymerization source)...

The effect of insertion and photopolymerization techniques on microleakage of Class V cavities: a quantitative evaluation

França,Fabiana Mantovani Gomes; Hori,Frederico Seidi; Santos,Alex José Souza dos; Lovadino,José Roberto
Fonte: Sociedade Brasileira de Pesquisa Odontológica - SBPqO Publicador: Sociedade Brasileira de Pesquisa Odontológica - SBPqO
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2005 EN
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The aim of this in vitro study was to evaluate by spectrophotometry the influence of the incremental technique and progressive light curing in the microleakage of Class V cavities. Forty samples were prepared with class V cylindrical cavities on the buccal root surface of bovine incisive teeth and filled with composite resin (Z250). The samples were divided into four groups: I: cavity was bulk filled and the composite was light cured for 40 seconds; Group II: cavity was bulk filled and a "soft-start" polymerization was used; Group III: cavity was filled with the incremental technique in two coats and light cured for 40 seconds; Group IV: cavity was filled with the incremental technique in two coats and light cured with "soft-start" polymerization. After the restoration, the specimens were thermally stressed for 3,000 cycles in bath at 5 ± 2°C and 55 ± 2°C, protected with nail enamel, colored with 2% methylene blue and cut into sections. These sections were triturated and the dye was recovered with PA ethanol and the supernatant was evaluated. The data were submitted to ANOVA and the results showed the following averages: bulk filled and conventional photopolymerization (I) 0.06075 µg/ml; bulk filled and progressive photopolymerization (II) 0.04030 µg/ml; incremental insertion and conventional photopolymerization (III) 0.04648 µg/ml; incremental insertion and progressive photopolymerization (IV) 0.04339 µg/ml. No significant statistic differences were observed among the mean values. The Degulux "soft-start" equipment probably emits too high initial light intensity to promote progressive photopolymerization.

Transdermal photopolymerization for minimally invasive implantation

Elisseeff, J.; Anseth, K.; Sims, D.; McIntosh, W.; Randolph, M.; Langer, R.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 16/03/1999 EN
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Photopolymerizations are widely used in medicine to create polymer networks for use in applications such as bone restorations and coatings for artificial implants. These photopolymerizations occur by directly exposing materials to light in “open” environments such as the oral cavity or during invasive procedures such as surgery. We hypothesized that light, which penetrates tissue including skin, could cause a photopolymerization indirectly. Liquid materials then could be injected s.c. and solidified by exposing the exterior surface of the skin to light. To test this hypothesis, the penetration of UVA and visible light through skin was studied. Modeling predicted the feasibility of transdermal polymerization with only 2 min of light exposure required to photopolymerize an implant underneath human skin. To establish the validity of these modeling studies, transdermal photopolymerization first was applied to tissue engineering by using “injectable” cartilage as a model system. Polymer/chondrocyte constructs were injected s.c. and transdermally photopolymerized. Implants harvested at 2, 4, and 7 weeks demonstrated collagen and proteoglycan production and histology with tissue structure comparable to native neocartilage. To further examine this phenomenon and test the applicability of transdermal photopolymerization for drug release devices...

Characterization of Photopolymerization of Dentin Adhesives as a Function of Light Source and Irradiance

Ye, Qiang; Wang, Yong; Williams, Karen; Spencer, Paulette
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/2007 EN
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Manufacturers have attempted to address the limitations associated with dentin bonding by eliminating as many steps as possible in the bonding protocol. Theoretically, this approach increases the efficiency of the procedure and reduces technique sensitivity. These trends are reflected in the introduction of all-in one, single-step adhesive systems; the increased concentration of acidic resin monomers in these systems allows for simultaneous etching and priming of the prepared dentin surface. Ideally, the degree of monomer conversion would be high enough that the acidic reaction would be self-limiting. The purpose of this study was to investigate the effect of light irradiance and source on the photopolymerization of three commercial dental adhesives by monitoring the double bond conversion as a function of time during and after irradiation. The photopolymerization curing efficiency of the commercial adhesives investigated in this study varied as a function of light source and distance. The use of LED performed better than the halogen light in terms of polymerization rate and degree of conversion for the commercial single-step, sixth generation adhesive, Adper Prompt. In contrast, polymerization of commercial single-bottle, fifth generation adhesive...

Poly(ethylene glycol) Hydrogels formed by Thiol-Ene Photopolymerization for Enzyme-Responsive Protein Delivery

Aimetti, Alex A.; Machen, Alexandra J.; Anseth, Kristi S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Degradable hydrogels have been extensively used in biomedical applications such as drug delivery, and recent interest has grown in hydrogels that degrade in recognition of a cellular response. This contribution describes a poly(ethylene glycol) (PEG) hydrogel platform with human neutrophil elastase (HNE) sensitive peptide cross-links formed using thiol-ene photopolymerization rendering the gel degradable at sites of inflammation. Further, protein therapeutics can be physically entrapped within the network and selectively released upon exposure to HNE. HNE responsive hydrogels exhibited surface erosion where the degradation kinetics was influenced by changes in peptide kcat, concentration of HNE, and concentration of peptide within the gel. Using this platform, we were able to achieve controlled, zero-order release of bovine serum albumin (BSA) in the presence of HNE, and release was arrested in the absence of HNE. To further exploit the advantages of surface eroding delivery systems, a smaller protein (carbonic anhydrase) was delivered at the same rate as BSA and only dependent on gel formulation and environmental conditions. Also, protein release was predicted from a 3-layered hydrogel device using mass loss data. Lastly, the bioactivity of lysozyme was maintained above 90% following the exposure to thiol-ene photopolymerization conditions.

Distinct Photopolymerization Efficacy on Dentin of Self-etch Adhesives

Zhang, Y.; Wang, Y.
Fonte: SAGE Publications Publicador: SAGE Publications
Tipo: Artigo de Revista Científica
Publicado em /08/2012 EN
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The effect of application mode on polymerization effectiveness of self-etch adhesives with different pHs has rarely been studied. We applied 2 self-etch adhesives—Adper Prompt L-Pop (APLP, pH ~ 0.8) and Adper Easy-Bond (AEB, pH ~ 2.5)—to dentin with or without agitation (dynamic or static application), to investigate photopolymerization efficacy on dentin, and to understand the role of chemical interaction/reaction between adhesives and dentin. Micro-Raman spectra and imaging were acquired across the dentin/adhesive (D/A) interface. The degree of conversion (DC) of each adhesive as a function of position was calculated. SEM-EDS was used to obtain the elemental distribution along the interface. Photopolymerization efficacies of the two self-etch adhesives on dentin were apparently different. APLP exhibited decreasing DCs as the distance from the D/A interface became greater for both application modes, while the DCs for the dynamic mode were much higher than those for the static mode. As for AEB, the DCs remained almost constant across the adhesive layer and showed no significant difference between two modes. Raman spectral analysis disclosed that the chemical interaction between dentin and adhesives was responsible for the observations. We also verified this by tracking the distribution of the elements Ca and P in the adhesive layers.

Facile preparation of photodegradable hydrogels by photopolymerization

Ki, Chang Seok; Shih, Han; Lin, Chien-Chi
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Photodegradable hydrogels have emerged as a powerful material platform for studying and directing cell behaviors, as well as for delivering drugs. The premise of this technique is to use a cytocompatible light source to cleave linkers within a hydrogel, thus causing reduction of matrix stiffness or liberation of matrix-tethered biomolecules in a spatial-temporally controlled manner. The most commonly used photodegradable units are molecules containing nitrobenzyl moieties that absorb light in the ultraviolet (UV) to lower visible wavelengths (~280 to 450 nm). Because photodegradable linkers and hydrogels reported in the literature thus far are all sensitive to UV light, highly efficient UV-mediated photopolymerizations are less likely to be used as the method to prepare these hydrogels. As a result, currently available photodegradable hydrogels are formed by redox-mediated radical polymerizations, emulsion polymerizations, Michael-type addition reactions, or orthogonal click chemistries. Here, we report the first photodegradable poly(ethylene glycol)-based hydrogel system prepared by step-growth photopolymerization. The model photolabile peptide cross-linkers, synthesized by conventional solid phase peptide synthesis, contained terminal cysteines for step-growth thiol-ene photo-click reactions and a UV-sensitive 2-nitrophenylalanine residue in the peptide backbone for photo-cleavage. Photolysis of this peptide was achieved through adjusting UV light exposure time and intensity. Photopolymerization of photodegradable hydrogels containing photolabile peptide cross-linkers was made possible via a highly efficient visible light-mediated thiol-ene photo-click reaction using a non-cleavage type photoinitiator eosin-Y. Rapid gelation was confirmed by in situ photo-rheometry. Flood UV irradiation at controlled wavelength and intensity was used to demonstrate the photodegradability of these photopolymerized hydrogels.

Photopolymerization of phosphoric acid ester-based self-etch dental adhesives

ZHANG, Ying; WANG, Yong
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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The objective of the study was to gain more understanding on the photopolymerization mechanism and the role of individual monomers in the polymerization behavior of a PAE-based self-etch adhesive system with the presence of HAp and water. The photo-polymerization process of the model adhesive system (2MP / HEMA) was monitored by using real-time attenuated total reflectance Fourier transform infrared (ATR/FT-IR) technique. The effect of monomer ratio, HAp incorporation, and water content were investigated. The degree of conversion (DC) and the polymerization rate (PR) of the adhesives were determined to evaluate the polymerization efficacy. The results showed that the DC and PR increased consistently as the 2MP content increased from 30% to 70%, while they declined drastically as the 2MP content was further elevated to 100%. The incorporation of HAp considerably increased the DC and PR; however, the increase in water content was found to have negative influence on the photopolymerization.

A Versatile Synthetic Extracellular Matrix Mimic via Thiol-Norbornene Photopolymerization

Fairbanks, Benjamin D.; Schwartz, Michael P.; Halevi, Alexandra E.; Nuttelman, Charles R.; Bowman, Christopher N.; Anseth, Kristi S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Synthetic hydrogels with engineered, cell-mediated degradation sites are an important category of biomimetic materials. Here, hydrogels are synthesized by a step-growth reaction mechanism via a radically mediated thiol-norbornene (thiol-ene) photopolymerization. This reaction combines the advantages of ideal, homogeneous polymer network formation, facile incorporation of peptides without post-synthetic modification, and spatial and temporal control over the network evolution into a single system to produce proteolytically degradable poly(ethylene glycol) (PEG) peptide hydrogels. Using a thiol-ene photopolymerization, rapid gelation times are achieved, while maintaining high cell viability for cell encapsulation. The enzyme- and cellresponsive characteristics are demonstrated by tailoring the rate of spreading of human mesenchymal stem cells (hMSCs) through both the selection of proteolytically degradable crosslinkers and the density of the adhesion peptide RGDS. Furthermore, cellular function is manipulated spatially within the thiol-ene hydrogels through biochemical photopatterning. The high degree of spatial and temporal control over gelation, combined with robust material properties, makes thiol-ene hydrogels an excellent tool for a variety of medical and biological applications.

Monitoring of visible light photopolymerization of an epoxy/dimethacrylate hybrid system by Raman and near-infrared spectroscopies

Asmussen, Silvana Valeria; Schroeder, Walter Fabian; Dell'erba, Ignacio Esteban; Vallo, Claudia Ines
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
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Hybrid systems formulated with epoxy and methacrylate monomers at mass fraction either 50:50 or 75:25 were studied. The individual monomer conversions during photopolymerization with visible light were monitored by Raman and near-infrared spectroscopies. The rate of polymerization and final degree of conversion of the methacrylate groups were raised when the epoxy monomer was present. This is attributed to enhancement of the mobility of the reactive species caused by the presence of the epoxy monomer. Conversely, the earlier vitrification of the system due to the faster polymerizing methacrylate network resulted in reduced conversion of epoxy rings.; Fil: Asmussen, Silvana Valeria. Universidad Nacional de Mar del Plata; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina;; Fil: Schroeder, Walter Fabian. Universidad Nacional de Mar del Plata; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina;; Fil: Dell'erba, Ignacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina;; Fil: Vallo...

High-Performance Photoinitiating Systems for Free Radical Photopolymerization. Application to Holographic Recording

Ibrahim, Ahmad; Di Stefano, Luciano; Tarzi, Olga Inés; Tar, Haja; Ley, Christian; Allonas, Xavier
Fonte: Wiley Publicador: Wiley
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
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The photoinitiating systems (PIS) usable in free radical photopolymerization are briefly reviewed. Apart conventional Type I and Type II photoinitiators, three-component photoinitiating system exhibiting a photocyclic behaviour are discussed. The mechanism of photoreaction are presented, highlighting the role of a redox additive which react with the photoinitiator photoproduct. Recent applications in holography recording are described showing that the selection of a PIS plays a crucial role in this application.; Fil: Ibrahim, Ahmad. University of Haute Alsace. Laboratory of Macromolecular Photochemistry and Engineering; Francia;; Fil: Di Stefano, Luciano. University of Haute Alsace. Laboratory of Macromolecular Photochemistry and Engineering; Francia;; Fil: Tarzi, Olga Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono; Argentina;; Fil: Tar, Haja. University of Haute Alsace. Laboratory of Macromolecular Photochemistry and Engineering; Francia;; Fil: Ley, Christian. University of Haute Alsace. Laboratory of Macromolecular Photochemistry and Engineering; Francia;; Fil: Allonas, Xavier. University of Haute Alsace. Laboratory of Macromolecular Photochemistry and Engineering; Francia;