Fibrous PCL/PLLA Scaffolds Obtained by Rotary Jet Spinning and Electrospinning

Rotary jet spinning (RJS) and electrospinning are techniques to obtain fibrous scaffolds. RJS is a simple method, which fabricates three-dimensional fibers by exploiting a high-speed rotating nozzle, creating a polymer jet which stretches until solidification, and does not require high voltage. In opposite, electrospinning technique needs the presence of an external electric field to create fiber from the polymeric jet solution. This article investigates both processes using two different biocompatible polymers: Poly(L-lactic acid) (PLLA) and Poly(e-caprolactone) (PCL). Samples were characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimeter, and Fourier-transform infrared spectroscopy. Morphological observations showed the efficiency of both techniques in obtaining nanofibers. Thermal analyses of data indicate immiscible property of different blends and the total solvent evaporation. In vitro cytocompatibility test showed that RJS and electrospinning samples exhibited good cytocompatibility. Based on these results, it may be concluded that the fibers obtained with both technologies are non-cytotoxicity and with good biocompatibility, and might be suitable for applications as scaffold for cell growth.CAPESFAPESPBiofabris-INCTBiomaterials Laboratory PUC/SP SorocabaUniv Estadual Campinas, Fac Engn Mecan, Campinas, SP, BrazilPontificia Univ Catolica, Sao Paulo, SP, BrazilUniv Fed ABC, Ctr Ciencias Nat & Humanas, Santo Andre, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, SP, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, SP, BrazilFAPESP: 2013/19372-0Web of Scienc

Fibrous PCL/PLLA Scaffolds Obtained by Rotary Jet Spinning and Electrospinning

<div><p>Rotary jet spinning (RJS) and electrospinning are techniques to obtain fibrous scaffolds. RJS is a simple method, which fabricates three-dimensional fibers by exploiting a high-speed rotating nozzle, creating a polymer jet which stretches until solidification, and does not require high voltage. In opposite, electrospinning technique needs the presence of an external electric field to create fiber from the polymeric jet solution. This article investigates both processes using two different biocompatible polymers: Poly(L-lactic acid) (PLLA) and Poly(ε-caprolactone) (PCL). Samples were characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimeter, and Fourier-transform infrared spectroscopy. Morphological observations showed the efficiency of both techniques in obtaining nanofibers. Thermal analyses of data indicate immiscible property of different blends and the total solvent evaporation. In vitro cytocompatibility test showed that RJS and electrospinning samples exhibited good cytocompatibility. Based on these results, it may be concluded that the fibers obtained with both technologies are non-cytotoxicity and with good biocompatibility, and might be suitable for applications as scaffold for cell growth.</p></div

Fibrous PCL/PLLA Scaffolds Obtained by Rotary Jet Spinning and Electrospinning

<div><p>Rotary jet spinning (RJS) and electrospinning are techniques to obtain fibrous scaffolds. RJS is a simple method, which fabricates three-dimensional fibers by exploiting a high-speed rotating nozzle, creating a polymer jet which stretches until solidification, and does not require high voltage. In opposite, electrospinning technique needs the presence of an external electric field to create fiber from the polymeric jet solution. This article investigates both processes using two different biocompatible polymers: Poly(L-lactic acid) (PLLA) and Poly(ε-caprolactone) (PCL). Samples were characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimeter, and Fourier-transform infrared spectroscopy. Morphological observations showed the efficiency of both techniques in obtaining nanofibers. Thermal analyses of data indicate immiscible property of different blends and the total solvent evaporation. In vitro cytocompatibility test showed that RJS and electrospinning samples exhibited good cytocompatibility. Based on these results, it may be concluded that the fibers obtained with both technologies are non-cytotoxicity and with good biocompatibility, and might be suitable for applications as scaffold for cell growth.</p></div

Influence on microstructure and hardness resulting from the addition of 4% ag in the alloy al-4% cu solidified unidirectionally

Diversas aplicações industriais, tais como nos setores automotivo e aeronáutico, que necessitam de resistência e tenacidade, utilizam ligas do sistema Al-Cu. As ligas do sistema ternário Al-Cu-Ag são empregadas como modelo para o estudo de ligas eutéticas ternárias, além do uso em certo número de aplicações técnicas. Estudos relacionados aos efeitos da adição de Ag em ligas do sistema Al-Cu solidificadas em regime transitório, sob aspectos microestruturais e de microdureza, não são encontrados na literatura. Nesse sentido, o objetivo principal deste trabalho consiste na investigação dos efeitos da adição de 4%Ag na liga Al-4%Cu solidificada unidirecionalmente no sentido vertical ascendente em regime transitório, abordando análises de microestrutura, microdureza e parâmetros de solidificação dados pela velocidade de crescimento (VL) e pela taxa de resfriamento (Ṫ). São apresentadas leis experimentais para as ligas Al-4%Cu e Al-4%Cu-4%Ag que correlacionam os espaçamentos dendríticos primário (λ1) e secundário (λ2) com VL e Ṫ. Foram realizadas análises de Difração de Raios-X (DRX) para a caraterização das fases cristalinas dos compostos presentes na microestrutura das ligas. O difratograma da liga binária mostrou a presença dos intermetálicos θ-Al2Cu, Al-Cu, Al4Cu9 e Al6Fe e, para o caso da liga ternária, adicionalmente foi detectado o intermetálico µ-Ag3Al. Composições químicas de regiões do contorno da dendrita, assim como de seu interior, foram obtidas com o auxílio de um microscópio eletrônico de varredura (MEV) acoplado a um sistema de análise por energia dispersiva (EDS). Diversas posições ao longo do lingote foram analisadas através da técnica de Fluorescência de Raios-X (FRX) com objetivo de se detectar a existência de macrossegregação. Constatou-se que a microdureza não é influenciada pelas duas formas de espaçamentos da matriz rica em Al. Os intermetálicos ρ-Ag2Al e µ-Ag3Al são responsáveis pelo aumento de dureza devido a sua interação com o espaçamento dendrítico terciário e outros intermetálicos204CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2012/08494-0; 2013/09267-0; 2013/23396-7Al-Cu alloys are used in several industrial applications, such as automotive and aerospace manufacturing, which demand mechanical strength and toughness performances. The Al-Cu-Ag ternary alloy system has been investigated to obtain a better understanding on ternary eutectic alloys besides its inherent applications. However, studies concerning the effects on microstructure and hardness due to Ag addition on Al-Cu alloys solidified under transient conditions, are not found in literature. In this sense, the main objective of this work consists in investigating the solidification parameters such as growth (VL) and cooling (Ṫ) rate, microstructure and microhardness regarding the effects of adding 4wt% Ag on a Al-4wt%Cu alloy unidirectionally solidified vertically upwards under unsteady-state solidification conditions. Experimental growth laws correlating the primary (λ1) and secondary (λ2) dendritic spacings with growth and cooling rate are proposed for Al-4wt%Cu and Al-4wt%Cu-4wt%Ag alloys. X-Ray Diffraction (XRD) analyses were performed in order to determine the crystalline phases of the compounds present in the alloys microstructure. The diffractogram of the binary alloy showed the presence of θ-Al2Cu, Al-Cu, Al4Cu9 and Al6Fe intermetallics and, for the case of the ternary alloy, the µ-Ag3Al intermetallic was detected. Chemical compositions at the boundary regions of the dendrite as also inside the dendrite were obtained using scanning electron microscope (SEM) connected to an Energy-Dispersive Spectrometer (EDS) system. Several positions along the ingot were analyzed through the X-Ray Fluorescence (XRF) technique permitting the detection of macrosegregation occurrence. It is shown that the microhardness is not influenced by both spacing patterns of the Al-rich matrix. The ρ-Ag2Al and µ-Ag3Al intermetallics are responsible for the increase in hardness due to the interaction with ternary dendrite arm spacing and other intermetallicsOs autores agradecem ao IFSP, CNPq e à FAPESP (processos 2012/08494-0, 2013/09267-0, 2013/23396-7) pelo apoio dado a este trabalh

Experimental investigation on microstructure and mechanical properties of direct squeeze cast Al–13%Si alloy

Для литья под давлением характерно приложение давления к заготовке при ее затвердевании, вследствие чего активизируются различные физические процессы, которые влияютна металлургические свойства литых сплавов. Выполненное экспериментальное исследование свидетельствует о влиянии уровня давления на микроструктуру и механические характеристики сплава Al–13%Si. Показано, что давление при литье в интервале 0,1...100 МПа приводит к уменьшению зерен, улучшению прочностных свойств и повышению твердости по Виккерсу в центральной части образцов. При давлении 100...150 МПа наблюдаются высокие предварительные деформации при высокой температуре литья и укрупнение зерен, в результате чего ухудшаются прочностные свойства и уменьшается твердость. Анализ микрофотографий на электронном микроскопе показывает, что при давлении до 100 МПа механизм разрушения является более вязким, чем при повышенном давлении. Это позволяет оптимизировать уровень давления с целью предотвращения ухудшения свойств и ликвации материала в процессе литья под давлением.Для лиття під тиском характерно прикладення тиску до заготовки при її твердінні, в результаті чого активізуються різні физичні процеси, що впливають на металургійні властивості литих сплавів. Експериментальне дослідження свідчить про вплив рівня тиску намікроструктуру і механічні характеристики сплаву Al–13%Si. Показано, що тиск при литті в інтервалі 0,1...100 МПа призводить до зменшення зерен, покращанню міцнісних властивостей і підвищенню твердості по Віккерсу в центральній частині зразка. При дії тиску 100...150 МПа мають місце високі попередні деформації за високої температури лиття і збільшення зерен. У результаті цього погіршуються міцнісні властивості і зменшується твердість. Аналіз мікрофотографій на електронному мікроскопі показує, що при дії тиску до 100 МПа механізм руйнування є більш в’язким, ніж при підвищеному тиску. Це дозволяє оптимізувати рівень тиску з метою запобігання погіршення властивостей і ліквації матеріалу в процесі лиття під тиском