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Biomedical subjects

Rui L Reis

Publications and source records attributed to Rui L Reis.

32 records · Page 2Linked to original sources
PubMed2004

Electrochemical behavior of different preparations of plasma-sprayed hydroxyapatite coatings on Ti6Al4V substrate.

The corrosion behavior of four different preparations of plasma-sprayed hydroxyapatite (HA) coatings on Ti6Al4V substrates in static Hank's balanced salt solution was investigated using dc potentiodynamic and ac impedance techniques. Two different nominal thicknesses, 50 microm and 200 microm, and two different spraying conditions, were considered. The electrochemical impedance experiments proved this technique to be very suitable for the investigation of the electrochemical behavior of surgical implant alloys when they are coated with HA, which is characterized by the dissolution and passivation characteristics of the underlying metal substrate. Because the coatings are porous, ionic paths between the electrolytic medium and the base material can eventually be produced, resulting in the corrosion of the coated metal. Differences in the corrosion resistance of the coated materials were detected, and a relevant model for the description of the coating degradation in the biosimulating solution was proposed. The model consisted of the description of the coated system in terms of a two-layer model of the surface film. Significant differences in electrochemical behavior for similar nominal thicknesses of HA coatings obtained under different spraying conditions were found.

Alloys↗
PubMed2004

Optimization of the formulation and mechanical properties of starch based partially degradable bone cements.

Previous studies have shown the possibility of developing in-situ polymerizable hydrogels that disclose a range of properties that might allow for their use as bone cements. Their main advantage is to be partially degradable, which is important to allow bone ingrowth (better fixation). In addition, their uptake of water makes them less agressive for the tissues, disclosing better fatigue properties and ideal for release of drugs when in service. This work reports a statistical study of the formulation of partially degradable acrylic bone cements that include on their composition corn starch/cellulose acetate blends (SCA). The aim was to optimize a set of properties (mechanical, swelling/degradation and curing) by changing the values of some parameters such as SCA amount and particle size and molar ratio of the acrylic monomers. Statistical tests demonstrated that the most important parameter was the molar ratio of monomers, with the SCA percentage also playing a role. It was possible to develop formulations with mechanical properties in the range of ASTM specifications and with polymerization temperatures lower than those of commercial acrylic cements. Some formulations were subsequently selected for tensile and dynamic mechanical thermal analysis (DMA) tests, under dry and wet conditions.

Biodegradation, Environmental↗
PubMed2004

Hydrophilic matrices to be used as bioactive and degradable bone cements.

Two different hydrophilic systems were investigated regarding their suitability to be used as enzymatically degradable and highly bioactive bone cements. They contained either acrylic acid (AA) or 2-hydroxyethyl methacrylate (HEMA) as the hydrophilic monomer. Swelling, degradation, mechanical and bioactivity tests were employed to characterise their behaviour. Although both of the systems were very hydrophilic, only the one containing HEMA was able to form an apatite-like layer on its surface. Moreover, this system could be degraded by amylolytic enzymes at a rate easily controlled by the incorporation of different amounts of enzyme to the formulation, as shown by the evolution of the mechanical properties, weight loss and glucose concentration in the solution. These results show these novel systems have a great potential to induce bone ingrowth inside the pores created during the degradation of the material, therefore establishing a strong interface with the tissue.

Absorbable Implants↗
PubMed2003

Effect of flow perfusion on the osteogenic differentiation of bone marrow stromal cells cultured on starch-based three-dimensional scaffolds.

This study aims to investigate the effect of culturing conditions (static and flow perfusion) on the proliferation and osteogenic differentiation of rat bone marrow stromal cells seeded on two novel scaffolds exhibiting distinct porous structures. Specifically, scaffolds based on SEVA-C (a blend of starch with ethylene vinyl alcohol) and SPCL (a blend of starch with polycaprolactone) were examined in static and flow perfusion culture. SEVA-C scaffolds were formed using an extrusion process, whereas SPCL scaffolds were obtained by a fiber bonding process. For this purpose, these scaffolds were seeded with marrow stromal cells harvested from femoras and tibias of Wistar rats and cultured in a flow perfusion bioreactor and in 6-well plates for 3, 7, and 15 days. The proliferation and alkaline phosphatase activity patterns were similar for both types of scaffolds and for both culture conditions. However, calcium content analysis revealed a significant enhancement of calcium deposition on both scaffold types cultured under flow perfusion. This observation was confirmed by Von Kossa-stained sections and tetracycline fluorescence. Histological analysis and confocal images of the cultured scaffolds showed a much better distribution of cells within the SPCL scaffolds than the SEVA-C scaffolds, which had limited pore interconnectivity, under flow perfusion conditions. In the scaffolds cultured under static conditions, only a surface layer of cells was observed. These results suggest that flow perfusion culture enhances the osteogenic differentiation of marrow stromal cells and improves their distribution in three-dimensional, starch-based scaffolds. They also indicate that scaffold architecture and especially pore interconnectivity affect the homogeneity of the formed tissue.

Animals↗
PubMed2003

Degradation characteristics of hydroxyapatite coatings on orthopaedic TiAlV in simulated physiological media investigated by electrochemical impedance spectroscopy.

This paper concentrates on the degradation characteristics of hydroxyapatite (HA) coatings on orthopaedic Ti-6Al-4V alloy while immersed in Ringer's salt solution, which were investigated by electrochemical impedance spectroscopy. Electrochemical impedance spectroscopy measurements were used to in situ characterize the electrochemical behavior of the passivated alloy covered with HA during aging in Ringer's solution. Comparison of the electrochemical data for the coated material with that for the uncoated metal substrate was also performed. The characteristic feature that describes the electrochemical behavior of the coated material is the coexistence of large areas of the coating itself with pores where the substrate is exposed to the aggressive media. The interpretation of results was thus performed in terms of a two-layer model of the film, in which the precipitation of hydrated oxide or phosphate compounds seals the pores left by the ceramic coating. The blocking effect due to salt precipitation inside the pores produces an enhancement of the resistance values, thus effectively diminishing the metal ion release in the system.

Alloys↗
PubMed2003

Plasma- and chemical-induced graft polymerization on the surface of starch-based biomaterials aimed at improving cell adhesion and proliferation.

Plasma and chemical induced graft polymerization of acrylic monomers on starch-based biomaterials has been performed with the aim to improve cell adhesion and proliferation on the surface of the polymers, in order to adequate their properties for bone tissue engineering scaffolding applications. Plasma and chemical surface activation was aimed to induce the polymerization of acrylic polar monomers being carried out by applying a radio frequency plasma and expose the samples to a mixture of Ar/O2, or by immersion in a H2O2/(NH4)2S2O8 solution with UV radiation, respectively. Both procedures were followed by the graft polymerization of the corresponding monomers. Polymer grafting was analyzed by Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) and by contact angle measurements. Properties such as mechanical performance, swelling degree, and degradation behavior, as well as bioactivity, have been studied and compared for the different activation methods. Finally, preliminary cell adhesion and proliferation tests were performed, using goat bone marrow cells, showing a remarkable improvement with respect to original non-surface modified starch-based biomaterials.

Journal Article↗
PubMed2003

Effect of crosslinking, thermal treatment and UV irradiation on the mechanical properties and in vitro degradation behavior of several natural proteins aimed to be used in the biomedical field.

Gelatine (GEL), soy (SI), casein (CAS) and sodium-caseinate (NaCAS) solutions were cast to produce protein films. All the proteins were chemically modified by adding glyoxal to the film-forming solutions in amounts varying from 0 to 0.9% (w/w based on the protein content). After casting, the same films were also submitted to a heat treatment performed at 80 degrees C or UV irradiation. The effect of those chemical/physical modifications on the mechanical properties and on the hydrolytic stability of the protein films was evaluated. As a result, a large variety of protein films with different mechanical properties and degradation profiles were developed. CAS and NaCAS even when chemically/physically modified do not resist to hydrolysis longer than 2 weeks. GEL, only when chemically modified with glyoxal, become water resistant. Due to its hydrolytic stability, SI become a very attractive material for biomedical applications where long term treatments are a requisite.

Journal Article↗
PubMed2002

New partially degradable and bioactive acrylic bone cements based on starch blends and ceramic fillers.

This work reports the development of new partially biodegradable acrylic bone cements based on corn starch/cellulose acetate blends (SCA), prepared by the free radical polymerization of methyl methacrylate and acrylic acid at low temperature. Amounts of biocompatible, osteoconductive and osteophilic mineral component such as hydroxylapatite (sintered and non-sintered), were incorporated in different percentages to confer a bone-bonding character to the bone cements in this type of applications. All cement formulations were characterized by 1H NMR spectroscopy. Curing parameters and mechanical properties were determined finding formulations which complete the ASTM legislation. Hydration degree, degradation studies, as well as bioactivity tests were performed in all prepared formulations. The developed systems show a range of properties that might allow for their application as self-curing bone cements, exhibiting several advantages with respect to other commercially available bone cements.

Bone Cements↗
PubMedDate not supplied

In vitro assessment of the enzymatic degradation of several starch based biomaterials.

The susceptibility of starch-based biomaterials to enzymatic degradation by amylolytic enzymes (glucoamylase and alpha-amylase) was investigated by means of incubating the materials with a buffer solution, containing enzymes at different concentrations and combinations, at 37 degrees C for 6 weeks. Two polymeric blends of corn starch with poly(ethylene-vinyl alcohol) copolymer and poly(epsilon-caprolactone), designated by SEVA-C and SPCL, respectively, were studied. The material degradation was characterized by gravimetry measurements, tensile mechanical testing, scanning electron microscopy (SEM), and Fourrier transform infrared-attenuated total reflectance (FTIR-ATR). The degradation liquors were analyzed for determination of reducing sugars, as a result of enzyme activity, and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to identify the degradation products. All of the analysis performed showed that starch polymeric blends are susceptible to enzymatic degradation, as detected by increased weight loss and reducing sugars in solution. alpha-Amylase caused significant changes on the overall mechanical properties of the materials, with a decrease of about 65% and 58% being observed in the moduli for SEVA-C and SPCL, respectively, when compared with the control (samples incubated in buffer only). SEM analysis detected the presence of fractures and pores at the material's surface as a result of starch degradation by amylolytic enzymes. FTIR spectra confirmed a decrease on the band corresponding to glycosidic linkage (-C-O-C-) of starch after incubation of the materials with alpha-amylase. In contrast, the incubation of the polymers in buffer only, did not cause significant changes on the material's properties and morphology. Comparing the two materials, SEVA-C exhibited a higher degradability, which is related to the physicochemical structure of the materials and also to the fact that the starch concentration is higher in SEVA-C. The identification of the degradation products by HPAEC-PAD revealed that glucose was the major product of the enzymatic degradation of starch-based polymers. alpha-Amylase, as expected, is the key enzyme involved in the starch degradation, contributing to major changes on the physicochemical properties of the materials. Nevertheless, it was also found that starch-based polymers can also be degraded by other amylolytic enzymes but in a smaller extent.

Bacteria↗
PubMedDate not supplied

Soy matrix drug delivery systems obtained by melt-processing techniques.

The aim of this study was to develop new soy protein drug delivery matrix systems by melt-processing techniques, namely, extrusion and injection moulding. The soy matrix systems with an encapsulated drug (theophylline, TH) were previously compounded by extrusion performed at two different pH values, (i) pH 4 (SIpDtp) and (ii) pH 7 (SIDtp), and further injection-moulded into a desired shape. During the extrusion process the matrixes SIDtp were also cross-linked with glyoxal (0.6X-SIDtp) and reinforced with a bioactive filler, hydroxylapatite (SI-HADtp). The obtained mouldings were used to study the drug-release mechanisms from the plastic soy-TH matrixes. In an isotonic saline solution (ISS) buffered at pH 5.0 (200 mM acetate buffer), the resulting release kinetics could be described using the Fick's second law of diffusion. Because the diffusion coefficients were found to be constant and the boundary conditions to be stationary, these systems are drug-diffusion controlled. Conversely, the dominant phenomena in an isotonic saline solution buffered at pH 7.4 (200 mM Tris/HCl buffer) are more complex. In fact, because of the higher polymer solubility, the resulting matrix is time-variant. So, the drug release is affected by swelling, drug diffusion, and polymer dissolution, being faster when compared to ISS-200 mM acetate buffer, pH 5.0. The changes in the formulation composition affecting the correspondent release rates were also investigated. At pH 7.4, increasing the cross-linking degree of the polymer matrix (via reaction with glyoxal or heat treatment) or decreasing the net charge (extruding at pH near its isoelectric point) led to lower release rates. The incorporation of ceramic filler caused the opposite effect. Because of the low solubility of the matrix at pH 5.0, no significant variations were detected with variations in the selected formulations. These systems, based on a nonstandard protein-based material, seem to be very promising to be used as carriers for drug delivery.

Biocompatible Materials↗