M Alberta Araújo

Publications (3)11.41 Total impact

• Source

  Available from: Eugénio C. Ferreira

  Article: Determination of diffusion coefficients of glycerol and glucose from starch based thermoplastic compounds on simulated physiological solution.

  M Alberta Araújo, Eugénio C Ferreira, António M Cunha, Manuel Mota
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  ABSTRACT: Blends of corn starch with poly(ethylene-vinylalcohol) copolymer (SEVA-C) have been studied and reported as biodegradable. These materials are known to be sensitive to enzymatic action, evidencing a degradation of the starch phase in alpha-amylase assays. However, from the physical-chemical point of view the degradation of the blend is mainly associated with the leaching of glycerol, since other compounds are not released and no carbohydrates were found in the degradation solution. Based on these results, the present work attempts to determinate the respective diffusion coefficients. Four different experiments were performed, using samples with different thicknesses that were immersed in a simulated physiological solution. High performance liquid chromatography (HPLC) was used to separate the sugar derivatives and glycerol from the degradation solutions. The obtained data were fitted to an empirical model to allow the estimation of the diffusion coefficient for glycerol and glucose, based on the analytical solution for Fick's law of diffusion, and a good agreement was found (R(2) equals approximately 1). The glycerol leaches quickly out during the first few days of immersion, stabilizing thereafter, presenting greater diffusion coefficients for thicker samples. As the quantity of saccharides in the solution remains almost invariable along the experiments, this work also confirms that the degradation process is difficult without the action of enzymes.
  Journal of Materials Science Materials in Medicine 04/2005; 16(3):239-46. · 2.32 Impact Factor
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  Available from: uminho.pt

  Article: Enzymatic degradation of starch-based thermoplastic compounds used in protheses: identification of the degradation products in solution.

  M Alberta Araújo, António M Cunha, Manuel Mota
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  ABSTRACT: Apart from favourable physico-chemical and mechanical properties, the most important requirement for a biodegradable polymer to be used in medical applications is its biocompatibility and the non-cytotoxicity of its degradation products. Their combined effect should assure the safe material degradation under controlled kinetics. The present work analyses the degradation behaviour of blends of corn starch with poly(ethylene-vinyl alcohol) copolymer (SEVA-C). The characterization included long-term degradation trials on simulated physiological solution with alpha-amylase up to 200 days. The degradation solutions were analysed by several techniques. High-performance liquid chromatography (HPLC) and colorimetric methods were used to monitor the liberation of carbohydrate as a consequence of starch hydrolysis by alpha-amylase. The hydration degree was followed by thermogravimetric analysis (TGA). Several degradation products such as carbohydrates ranging from C6 to C18 were identified. After alpha-amylase action, biodegradation was more pronounced in the first 100 days, after which the biodegradation rate decreased probably due to the structure and porosity of the material. The action of alpha-amylase solely led to the starch degradation, in contrast with other assays without enzymes where no carbohydrates were found in the degradation solutions.
  Biomaterials 07/2004; 25(13):2687-93. · 7.40 Impact Factor
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  Available from: uminho.pt

  Article: Changes in morphology of starch-based prothestic thermoplastic material during enzymatic degradation.

  M Alberta Araújo, António M Cunha, Manuel Mota
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  ABSTRACT: This work evaluates the structural changes of an interpenetrated starch thermoplastic blend withstanding different enzymatic alpha-amylase degradation periods (up to 200 days), and establishes the relationships between the kinetics degradation rate and the structure of the material. It characterises the different stages of the enzymatic degradation process on starch/ethylenevinyl-alcohol blends, based on the attack of the connected starch domains that can be accessed by the enzymatic solution. The completely encapsulated starch particles remain practically unchanged. Furthermore, it was also found that the enzymatic degradation process was limited after 100 days of immersion. In order to understand such phenomenon several techniques were used, namely differential scanning calorimetry, contact-angle measurements, high-performance liquid chromatography, Fourier transform infrared spectrometry, scanning electron microscopy and atomic force microscopy. The materials were evaluated with respect to the enzymatic degradation rate, surface morphology and degradation behaviour. The results show that the ethylene-vinylalcohol phase wraps the starch domains, preventing the respective degradation. Consequently, the degraded material in the solution comes only from the starch particles that could be reached by the enzyme.
  Journal of Biomaterials Science Polymer Edition 02/2004; 15(10):1263-80. · 1.69 Impact Factor