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

Unidirectional solidification of Zn-Mg alloys : microstructural evolution, mechanical properties and corrosion resistance

Orientador: Amauri GarciaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: A adição de Mg para melhorar a estabilidade à corrosão de recobrimentos de Zn, é uma prática comum na produção de componentes de uso na construção civil e na indústria automotiva. O Zn é um metal biocompatível, biodegradável e bioabsorvível e essencial na nutrição humana. Apresenta ainda baixo ponto de fusão (420°C), boa resistência à corrosão e baixa reatividade no estado líquido. O Mg é um metal atóxico, biodegradável e biocompatível, no entanto, suas ligas apresentam elevada taxa de corrosão em meios fisiológicos. Sabe-se que o Zn é mais nobre que o Mg, e que a adição de Mg em ligas de Zn pode afetar positivamente tanto o comportamento mecânico quanto a resistência à corrosão. Em geral os comportamentos mecânico e eletroquímico das ligas Zn-Mg são influenciados diretamente por características microestruturais. Estudos experimentais enfatizando fatores relacionados à parâmetros da microestrutura, bem como sua correlação com propriedades mecânicas e químicas são escassos na literatura. No presente trabalho, foram realizados experimentos de solidificação unidirecional com ligas hipoeutéticas e hipereutéticas Zn-Mg ao longo de uma extensa faixa de taxas de resfriamento para a análise da evolução da microestrutura. Ligas Zn-Mg hipoeutéticas diluídas (0,3 e 0,5%Mg) apresentaram uma zona colunar curta seguida de zona equiaxial até o topo dos lingotes, enquanto as demais ligas examinadas apresentaram macroestrutura equiaxial ao longo de todo o comprimento dos lingotes. Mostra-se que a microestrutura é formada por uma matriz rica em Zn de diferentes morfologias e por misturas eutéticas competitivas (Zn-Zn11Mg2 e Zn-Zn2Mg). Para as ligas com 0,3 e 0,5%Mg, a matriz rica em Zn é caracterizada por células tipo placa de altas taxas de resfriamento (>9.5ºC/s e 24ºC/s, respectivamente), seguida de uma transição morfológica granular/dendrítica para taxas de resfriamento mais baixas. Em contrapartida, os lingotes das ligas hipoeutéticas (1,2 e 2,2%Mg) apresentaram uma matriz rica em Zn formada somente por grãos dendríticos equiaxiais, enquanto as ligas hipereutéticas (3,15 e 5,15%Mg), por grãos eutéticos equiaxiais de micromorfologia lamelar. Resultados de fluorescência de raios X mostraram a ocorrência de macrossegregação de Mg ao longo do comprimento de todos os lingotes unidirecionais, induzida por diferenças de densidade. São propostas leis experimentais de crescimento relacionando os espaçamentos entre células tipo placa, dendrítico primário e secundário e eutético com parâmetros térmicos de solidificação, ou seja, taxa de resfriamento e velocidade de solidificação. A combinação de macrossegregação de Mg e a evolução das escalas microestruturais em todos os lingotes unidirecionais das ligas Zn-Mg analisadas, conduziu a microdurezas Vickers essencialmente constantes ao longo dos comprimentos dos lingotes, entretanto, com o aumento no teor de Mg de 0,3 a 5,15 % a microdureza aumentou de 58 HV0,5 a 130 HV0,5. Ensaios de tração foram realizados apenas para as ligas Zn-0,3%, 1,2% e 3,15%Mg, sendo que a liga Zn-3,15%Mg, com morfologia microestrutural eutética, apresentou maiores valores de alongamento específico, limite de escoamento e limite de resistência à tração. A fim de se obter uma comparação direta com as propriedades mecânicas de tração, os ensaios de corrosão também foram realizados nas ligas Zn-Mg de mesmas composições, em uma solução de 0,06M de NaCl. Para a liga Zn-0,3%Mg, a amostra de micromorfologia celular tipo placa, da zona colunar, apresentou maior resistência à corrosão. As ligas Zn-1,2%Mg e Zn-3,15%Mg, de morfologia totalmente equiaxial, mostraram melhores resistências à corrosão associadas a amostras mais afastadas da base refrigerada, ou seja, de microestruturas mais grosseiras. Palavras-chave: Ligas Zn-Mg; Solidificação Transitória; Microestrutura; Propriedades Mecânicas; Resistência à CorrosãoAbstract: The addition of Mg to improve corrosion stability of Zn coatings is a technologically common practice for corrosion protection of products of use in the civil and automotive industries. These alloys show also potential application in biomedical implants. Zn is a biocompatible, biodegradable and bioabsorbable metal essential in human nutrition. It also has a low melting point (420 °C), good corrosion resistance and low reactivity in the liquid state. Mg is a non-toxic, biodegradable and biocompatible metal; however, its alloys have a high corrosion rate in physiological media. It is known that Zn is nobler than Mg, and that the addition of Mg to Zn alloys can positively affect both mechanical behavior and corrosion resistance. In general the mechanical and electrochemical behavior of Zn-Mg alloys is directly influenced by microstructural characteristics. Experimental studies emphasizing factors related to microstructure parameters as well as their correlation with mechanical and chemical properties are scarce in the literature. In the present work, transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic and hypereutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. Dilute hypoeutectic alloys Zn-Mg (0.3 and 0.5wt%Mg) alloys are shown to have a short columnar zone followed by an equiaxed zone up the top of the castings, while the other alloys examined are characterized by equiaxed macrostructures along the entire length of the castings. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-Zn11Mg2 and Zn-Zn2Mg). For 0.3 and 0.5wt%Mg alloys, the Zn-rich matrix is shown to be characterized by high cooling rates plate-like cells (cooling rates > 9.5ºC/s and 24ºC/s, respectively), followed by a granular-dendritic morphological transition for lower cooling rates. In contrast, the hypoeutectic alloys castings (1.2 and 2.2wt%Mg) are shown to have the Zn-rich matrix formed only by dendritic equiaxed grains, while the hypereutectic alloys (3.15 and 5.15wt%Mg), by equiaxed eutectic grains of lamellar micromorphology. Results from X-ray fluorescence showed the occurrence of Mg macrosegregation along the length of all directionally solidified castings, induced by differences in density. Experimental growth laws are proposed relating the plate-like cellular interphase, the primary and secondary dendritic arm and the eutectic interphase spacings to solidification thermal parameters, i.e. cooling rate, and growth rate. The combination of Mg macrosegregation and the evolution of microstructural length scales in all the Zn-Mg alloys castings examined, has led to essentially constant Vickers microhardness along the length of the castings, however, with the increase in the alloys Mg content from 0.3 to 5.15wt%, the microhardness increased from 58 HV0.5 to 130 HV0.5. Tensile tests were carried for Zn-0.3, 1.2 and 3.15wt%Mg alloys and the Zn-3.15wt%Mg alloy, with eutectic microstructure, is shown to have higher elongation, yield strength and ultimate tensile strength. In order to obtain a direct comparison with tensile test results, the corrosion tests were also carried out in alloys of same compositions in a 0.06M NaCl solution. The Zn-0.3wt%Mg alloy showed better corrosion behavior associated with the sample of cellular plate-like micromorphology from the columnar region. The Zn-1.2 and 3.15 wt% Mg alloys, having equiaxed morphology, were shown to have better corrosion resistances associated with samples of coarser microstructures. Keywords: Zn-Mg alloys; Transient Solidification; Microstructure; Mechanical Properties; Corrosion ResistanceDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânica155863/2013-4CNP

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