Biomedical subjects

João F Mano

Publications and source records attributed to João F Mano.

8 recordsLinked to original sources

PubMed2006

Stimuli-responsive hydrogels based on polysaccharides incorporated with thermo-responsive polymers as novel biomaterials.

In recent years, intelligent hydrogels which can change their swelling behavior and other properties in response to environmental stimuli such as temperature, pH, solvent composition and electric fields, have attracted great interest. The hydrogels based on polysaccharides incorporated with thermo-responsive polymers have shown unique properties such as biocompatibility, biodegradability, and biological functions in addition to the stimuli-responsive characters. These "smart" hydrogels exhibit single or multiple stimuli-responsive characters which could be used in biomedical applications, including controlled drug delivery, bioengineering or tissue engineering. This review focuses on the recent developments and future trends dealing with stimuli-responsive hydrogels based on grafting/blending of polysaccharides such as chitosan, alginate, cellulose, dextran and their derivatives with thermo-sensitive polymers. This review also screens the current applications of these hydrogels in the fields of drug delivery, tissue engineering and wound healing.

Biocompatible Materials↗

PubMed2006

Novel hydroxyapatite/chitosan bilayered scaffold for osteochondral tissue-engineering applications: Scaffold design and its performance when seeded with goat bone marrow stromal cells.

Recent studies suggest that bone marrow stromal cells are a potential source of osteoblasts and chondrocytes and can be used to regenerate damaged tissues using a tissue-engineering (TE) approach. However, these strategies require the use of an appropriate scaffold architecture that can support the formation de novo of either bone and cartilage tissue, or both, as in the case of osteochondral defects. The later has been attracting a great deal of attention since it is considered a difficult goal to achieve. This work consisted on developing novel hydroxyapatite/chitosan (HA/CS) bilayered scaffold by combining a sintering and a freeze-drying technique, and aims to show the potential of such type of scaffolds for being used in TE of osteochondral defects. The developed HA/CS bilayered scaffolds were characterized by Fourier transform infra-red spectroscopy, X-ray diffraction analysis, micro-computed tomography, and scanning electron microscopy (SEM). Additionally, the mechanical properties of HA/CS bilayered scaffolds were assessed under compression. In vitro tests were also carried out, in order to study the water-uptake and weight loss profile of the HA/CS bilayered scaffolds. This was done by means of soaking the scaffolds into a phosphate buffered saline for 1 up to 30 days. The intrinsic cytotoxicity of the HA scaffolds and HA/CS bilayered scaffolds extract fluids was investigated by carrying out a cellular viability assay (MTS test) using Mouse fibroblastic-like cells. Results have shown that materials do not exert any cytotoxic effect. Complementarily, in vitro (phase I) cell culture studies were carried out to evaluate the capacity of HA and CS layers to separately, support the growth and differentiation of goat marrow stromal cells (GBMCs) into osteoblasts and chondrocytes, respectively. Cell adhesion and morphology were analysed by SEM while the cell viability and proliferation were assessed by MTS test and DNA quantification. The chondrogenic differentiation of GBMCs was evaluated measuring the glucosaminoglycans synthesis. Data showed that GBMCs were able to adhere, proliferate and osteogenic differentiation was evaluated by alkaline phosphatase activity and immunocytochemistry assays after 14 days in osteogenic medium and into chondrocytes after 21 days in culture with chondrogenic medium. The obtained results concerning the physicochemical and biological properties of the developed HA/CS bilayered scaffolds, show that these constructs exhibit great potential for their use in TE strategies leading to the formation of adequate tissue substitutes for the regeneration of osteochondral defects.

Animals↗

PubMed2006

Drug release of pH/temperature-responsive calcium alginate/poly(N-isopropylacrylamide) semi-IPN beads.

A series of semi-interpenetrating, polymer network (semi-IPN), hydrogel beads, composed of calcium alginate (Ca-alginate) and poly(N-isopropylacrylamide) (PNIPAAM), were prepared for a pH/temperature-sensitive drug delivery study. The equilibrium swelling showed the independent pH- and thermo- responsive nature of the developed materials. At pH=2.1, the release amount of indomethacin incorporated into these beads was about 10% within 400 min, while this value approached to 95% at pH=7.4. The release rate of the drug was higher at 37 degrees C than that at 25 degrees C and increased slightly with increasing PNIPAAM content. These results suggest that the Ca-alginate/PNIPAAM beads have the potential to be used as an effective pH/temperature sustainable delivery system of bioactive agents. [GRAPHS: SEE TEXT] A summary of the temperature- and pH-dependence on the release of the drug over a period of 450 min. The effect of the temperature on the swelling of the beads is shown in the inset.

Acrylic Resins↗

PubMed2005

Hydroxypropyl chitosan bearing beta-cyclodextrin cavities: synthesis and slow release of its inclusion complex with a model hydrophobic drug.

Hydroxypropyl chitosan-graft-carboxymethyl beta-cyclodextrin (HPCH-g-CM beta-CD) was synthesized by grafting CM beta-CD onto HPCH using water soluble 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as the condensing agent. Due to the presence of hydrophobic beta-CD rings onto the HPCH backbone, this polymer can be used as a matrix for controlled drug release. The adsorption of a hydrophobic model drug, ketoprofen, by HPCH-g-CM beta-CD microparticles (using tripolyphosphate as an ionic crosslinking agent) fitted well in the Langmuir isotherm equation. The drug dissolution profile showed that HPCH-g-CM beta-CD microparticles provided a slower release of the entrapped ketoprofen than chitosan, and the release behavior was influenced by the pH value of the medium. These results suggest that beta-CD grafted with chitosan derivatives may become a potential biodegradable delivery system to control the release of hydrophobic drugs with pH-responsive capability.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed2005

Study of the segmental dynamics in semi-crystalline poly(lactic acid) using mechanical spectroscopies.

The glass transition of poly(L-lactic acid) (PLLA) occurs not far above typical service temperatures (room or body temperatures) which has consequences on the material properties during its use, such as damping or the occurrence of structural relaxation. This work aims at characterising the glass transition dynamics of a semi-crystalline PLLA using both dynamic mechanical analysis (DMA) and thermally stimulated recovery (TSR). The main viscoelastic parameters have been characterised at 1 Hz using DMA and the master curve obtained after isothermal experiments at different temperatures provided a full picture of the solid-state rheological behaviour throughout a wide frequency range. The activation energies calculated from the shift factors agree with the TSR ones, exhibiting a maximum near the T(g). Above the T(g), the results can be described with the WLF model. In the glassy state, the activation energy decreases with decreasing temperatures being always higher than the prediction of the Adam and Gibbs theory, at least down to temperatures 30 degrees C below the T(g). This suggests the existence of non-arrested degrees of freedom in the glassy state, being consistent with the existence of a significant degree of cooperativity in the TSR results.

Glass↗

PubMed2004

Fibers and 3D mesh scaffolds from biodegradable starch-based blends: production and characterization.

The aim of this work is the production of fibers from biodegradable polymers to obtain 3D scaffolds for tissue engineering of hard tissues. The scaffolds required for this highly demanding application need to have, as well as the biological and mechanical characteristics, a high degree of porosity with suitable dimensions for cell seeding and proliferation. Furthermore, the open cell porosity should have adequate interconnectivity for a continuous flow of nutrients and outflow of cell metabolic residues as well as to allow cell growth into confluent layers. Blends of corn starch, a natural biodegradable polymer, with other synthetic polymers (poly(ethylene vinyl alcohol), poly(epsilon-caprolactone), poly(lactic acid)) were selected for this work because of their good balance of properties, namely biocompatibility, processability and mechanical properties. Melt spinning was used to produce fibers from all the blends and 3D meshes from one of the starch-poly(lactic acid) blends. The experimental characterization included the evaluation of the tensile mechanical properties and thermal properties of the fibers and the compression stiffness, porosity and degradation behavior of the 3D meshes. Light microscopy picture of 3D meshes.

Absorption↗

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↗

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↗