Advanced Materials Forum III

Volumes 514-516

doi: 10.4028/

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Authors: Mani Prabaharan, João P. Borges, M.H. Godinho, João F. Mano
Abstract: The objective of this work was to prepare polysaccharide-based gels exhibiting liquid crystalline properties. Such systems may be used in some optical or in biomedical applications, where biodegradability is required. Chitosan is a derivative of chitin, widely used in a series of medical applications. Due to its rigid structure, chitosan or its derivatives may show lyotropic mesophases in certain conditions. In this work, chitosan solutions were prepared by mixing completely the polysaccharide with different concentration of formic, acetic and monochloroacetic acids at room temperature. X-ray diffraction patterns of the gels did not show the existence of a crystalline structure. Finger-prints texture observed by polarised optical microscopy was attributed to a cholesteric liquid crystalline phase that usually develops in concentrated solutions. Values of the nematic chiral pitch (P) were determined in function of acid solution concentration. The critical concentrations (C*) to form a lyotropic liquid crystalline phase in formic, acetic and monochloroacetic acids were determined, and the obtained values were confronted with the expected critical concentration based on the Flory formalism. The critical concentration values were found to be dependent upon the acid used.
Authors: Rangasamy Jayakumar, Rui L. Reis, João F. Mano
Abstract: N-Carboxymethyl chitosan (NCMC) is a water soluble derivative of chitosan. The NCMC beads were prepared by using ionotropic gelation process with the counter polyanion tripolyphoshate at pH 4.0 and characterized by scanning electron microscopy. The swelling behavior of the beads at different time intervals was monitored at different pH conditions. The in vitro drug release behavior in various pH solutions was studied using indomethacin as a model drug with two different concentrations (0.3 and 0.6% w/w). The release percent of indomethacin from NCMC beads was found to increase with increasing of pH in phosphate buffer solution medium due to the ionization of carboxymethyl group and high solubility of indomethacin in alkaline medium. These results indicated that the NCMC beads are useful for controlled drug delivery systems through oral administration by avoiding the drug release in the highly acidic gastric fluid region of the stomach.
Authors: António J. Salgado, Ya Ming Wang, João F. Mano, Rui L. Reis
Abstract: The molecular weight and crystallinity of systems based on poly(L-lactic acid) PLLA is an important issue as it can influence, besides the general physical properties of the polymer, the patterns of cell adhesion, proliferation and cell morphology. The objective of the present study was to evaluate how crystallinity and molecular weight of PLLA influence the referred parameters. Four conditions were tested: low molecular weight amorphous and semi-crystalline PLLA disks, and high molecular weight amorphous and semi-crystalline PLLA disks, obtained from hot press. The thermal properties of the studied materials were accessed by differential scanning calorimetry. For the cell culture studies a human osteosarcoma cell line (SaOS-2) was chosen. Disks were immersed in a cell suspension containing 5x104 cells/ml and kept in culture for periods up to two weeks. Cell viability and proliferation of SaOS-2 cells was assessed by MTS test and a total protein assay, respectively. The adhesion and morphology of SaOS-2 cells on PLLA disks was assessed by scanning electronic microscopy. Results showed that cell viability was not affected by the different tested conditions. However, cell proliferation was increased in the high molecular weight amorphous samples and cells seemed to have higher adhesion patterns on semi-crystalline samples. This is probably happening due to different rates of integrin interaction with the substrate leading to different patterns of focal adhesion points formation.
Authors: Cláudia M.S. Ranito, Carlos A. Nogueira, Joaquim Domingues, Fátima Pedrosa, Fernando A. Costa Oliveira, João P. Borges
Abstract: A conventional method of chemical precipitation was used to produce hydroxyapatite (HAp) powders, with a molar ratio of Ca/P=1.67, for biomedical applications. The aim of this work was to study the effect of four control factors, namely pH, reaction temperature, reagent concentration and flow rate addition, at three levels, on the Ca/P ratio of the synthesized powders, using the Taguchi design of experiments method. Nine powders were synthesized using Ca(NO3)2ּ4H2O and (NH4)2HPO4 as starting reagents. The Ca/P molar ratio of each powder was determined by ICP-AES. Data obtained were used in the Taguchi’s design of experiments to optimize the Ca/P molar ratio. Results showed that the pH of the reaction is the main control parameter (74% contribution) affecting the Ca/P molar ratio of the powders. Therefore, attention should be paid to the control of the pH during the synthesis, in order to obtain HAp powders in a reproducible fashion. High pH values (9.5) and reaction temperature at 70 °C favoured the synthesis of HAp powders with a Ca/P ratio close to the target value of 1.67.
Authors: Eugenio Luís Solla, Jacinto P. Borrajo, Pio González, Julia Serra, Stefano Chiussi, Betty León, Mariano Pérez Amor
Abstract: The bioactive properties of hydroxyapatite (HA) are well known in the implant industry and coatings of HA have been used to enhance the adhesion of living tissue to metal prostheses. Pulsed laser deposition (PLD) in a water vapour atmosphere is an appropriate method for the production of crystalline HA coatings. In this work the effect of RF plasma on thin films of HA grown by PLD at different substrate temperatures has been studied. The physicochemical properties of the films were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), showing that the incorporation of RF discharge in the deposition chamber can lead to changes in the crystallinity and deposition rate of the films but substrate temperature still plays the most important role.
Authors: Luís M. Ferreira, António N. Falcão, M. Helena Gil
Abstract: Graft copolymerization induced by gamma radiation has being used as a tool to modify the surface properties of a range of polymeric substrates. This work describes the use of this technique for the grafting of 2-hydroxyethyl methacrylate (HEMA) branches onto low-density polyethylene (LDPE) surface, in order to improve its hydrophilic properties. Sample preparation protocols were selected from previous work in order to obtain films with high grafting yields. The obtained PE-g-HEMA films were characterized by thermal analysis techniques (DSC and TGA), and by Fourier transform infrared spectroscopy (FTIR). The results obtained show that, upon irradiation, there is some loss of cristalinity of the copolymer backbone, but also that the samples keep a good thermal stability. The water uptake of the samples was evaluated. Hydration levels up to near 95 % with a ydration/dehydration average ratio of 1:5 were obtained.
Authors: Nuno A.F. Almeida, Maria Helena F.V. Fernandes
Abstract: In silicate glasses the kinetics of apatite layer formation is usually rapid but the adhesion to the base glass is poor. Glass ceramics promote a stronger bonding between layer and substrate but decrease the rate of the apatite layer formation. In this work a glass of composition (wt%) 54,89%C3P-24,81%SiO2-20,30%MgO has been studied. This glass was heat treated at four temperatures (840 °C, 870 °C, 890 °C and 910 °C) to obtain glass ceramics with different contents of the same crystalline phase. A calcium magnesium phosphate phase was formed in all glass ceramics in a volume percent increasing with temperature. The apatite layer precipitated after immersion in simulated body fluid (SBF) formed faster on the glass than on the glass ceramics and a decrease in the amount of apatite formed was observed with the increase in crystallinity. It was generally concluded that heat treatment can turn a reactive glass into glass ceramics of different surface behaviors, from bioactive to quasi bio inert materials.
Authors: S. Eugénio, M. Sivakumar, Rui Vilar
Abstract: In the present work, dentin samples extracted from human molar teeth were treated with 248 nm wavelength pulsed laser radiation at fluences between 0.5 and 20 J/cm2. The surfaces were characterised by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and x-photoelectron spectroscopy (XPS). Two distinct behaviours were observed in what concerns the evolution of surface morphology with fluence and number of pulses. In some samples the surface remained flat, independently of the fluence and covered by a layer of resolidified material and redeposited ablation particles, which often occluded the dentinal structure. In other samples the surface topography depended on radiation fluence. For fluences below 1 J/cm2, intertubular dentin was preferentially removed, originating a columnar structure where columns were centred on the dentinal tubules and constituted by peritubular dentin. The height of the columns increased with the number of laser pulses. When fluence exceeded 1 J/cm2 the processed surface remained flat, covered with a fine resolidified layer. These distinct behaviours of dentin can be explained by differences in the constitution of this composite biological material. Despite the topographic changes observed, the mineral phase of dentin (apatite) remained unaltered and collagen was removed only from the outermost superficial layers of the processed material. This fact is explained by the constitution and structure of dentin and by the physical properties and electronic structure of its main constituents. Taking into consideration the results obtained and the bond type and properties of the constituents of dentin, it is suggested that the ablation of collagen occurs by a photochemical mechanism while the ablation of apatite is photothermal.
Authors: Sandra C.P. Cachinho, Paula A.A.P. Marques, Rui N. Correia
Abstract: A study is reported on the influence of surface morphology, chemistry and albumin adsorption on the in vitro mineralization of titanium. Albumin is the most abundant protein in plasma and was chosen as a pre-incubation medium for titanium substrates previously conditioned by mechanical, thermal and chemical treatment. Subsequent mineralization studies were performed in carbonated simulated inorganic plasma (CSIP) physiologically buffered with CO2/HCO3 -. The results indicate that surface morphology and albumin adsorption contribute to the development of a B-carbonated apatite deposit and, furthermore, that the buffer system may alter the role of albumin in mineralization.
Authors: Tânia Costa, Ana Paula Serro, Eduardo Pires, Rogerio Colaço
Abstract: The influence of sterilization with γ-irradiation in the properties of plasma sprayed hydroxyapatite (HAp) coatings used for medical implants is investigated in this work. HAp coatings were applied on titanium alloy substrates by plasma spraying and then submitted to 1 and 10 cycles of sterilization with γ-irradiation. As-applied HAp coatings were used as control samples. Afterwards, the modifications on the samples, induced by the irradiation process, were evaluated by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Water contact angle measurements as well as adhesion tests were also carried out in order to evaluate the influence of the irradiation process on the wettability and mechanical behaviour of the HAp coatings. No microstructural modifications were detected by X-ray diffraction after sterilization. However, the results show that sterilization with γ-irradiation originates modifications of the surface of HAp, as detected by a change of color of the coatings and by the XPS analysis. Nevertheless, these modifications do not result in significant changes in the wettability and mechanical behaviour of the HAp coatings.

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