1,827 research outputs found
Viscoelastic monitoring of starch-based biomaterials in simulated physiological conditions
Dynamic mechanical analysis (DMA) was used to investigate the solid-state rheological behaviour in a starch-based thermoplastic aimed to be used in different biomedical applications. The tested samples were processed by different injection moulding procedures. The dry samples were immersed in a simulated physiological solution and the relevant viscoelastic parameters were monitored against time. The decrease
of stiffness due to swelling can be followed in real time, being less pronounced for the composite sample with hydroxyapatite (HA). The temperature control of the liquid bath was found to be very good. Frequency scans were also performed in wet conditions in samples previously immersed during different times, indicating that DMA is a suitable method to control in-vitro the changes on the viscoelastic properties of biomaterials during degradation
Analysing protein competition on self-assembled mono-layers studied with quartz crystal microbalance
The mechanisms by which proteins adsorb to surfaces of biomaterials have long been of interest. The
present work started with the premise that small/hard and large/soft proteins will yield different sets
of normalized frequency shift and dissipation signals when studied with a quartz crystal microbalance.
The aim was to evaluate the usefulness of these raw data to study protein competition using protein incubations
in sequence and from mixtures of albumin (BSA) and gamma-globulin (BGG) at various ratios.
Increasing the concentration of BSA decreases the adsorption of subsequently incubated BGG. For BSA/
BGG mixtures the dissipation is similar for all logarithmic molar ratios BGG/BSA below 1 but soon
decreases when the molar ratio of BSA/BGG (and opposite for the normalized frequency shift) is above
1, indicating preferential binding of BGG. Modelling indicated that differences in the film shear modulus
and viscosity depend more on the properties of the self-assembling mono-layers (SAMs) than on the proteins.
Films high in BSA tentatively differ in film shear modulus and viscosity from that of films high in
BGG but only on the hydrophobic surfaces. The results were encouraging as the raw data were deemed to
be able to point at protein adsorption competition.The authors thank the Portuguese National Science and Technology Foundation (FCT) for the Project Grants PTDC/FIS/68517/2006 and PTDC/FIS/68209/2006, and personal Grant BPD/39331/2007 for J.B
Chemistry and applications of phosphorylated chitin and chitosan
Chitin and chitosan are natural based non-toxic,
biodegradable and biocompatible polymers and have been used in
biomedical areas in the form of sutures, wound healing materials and
artificial skin, and for the sustained release of drugs as well as in various
industrial applications. However, practical use of these polymers has
been mainly confined to the unmodified forms. Recently, there has been
a growing interest in chemical modification of chitin and chitosan to
improve their solubility and widen their applications. Among them,
phosphorylated chitin and chitosan have attracted considerable interest
because of their various advantages: anti-inflammatory property, ability
to form metal complexes, blood compatibility and formation of anionic
polyelectrolyte hydrogels. The purpose of this review is to take a closer
look of different synthetic methods of phosphorylated chitin and chitosan
and their potential applications in environmental, food, fuel cell, and
biomedical fields. Based on current research and existing products,
some new and futuristic approaches in this context area are discussed.R. Jayakumar acknowledges the Portuguese Foundation for Science and Technology for providing him a Post-Doc scholarship (SFRH/BPD/14670/2003). This work was partially supported by FCT Foundation for Science and Technology, through funds from the POCTI and/or FEDER program. This work was partially supported by the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758)
Synthesis and characterization of N-methylenephenyl phosphonic chitosan
Chitosan is a natural based polymer obtained by alkaline deacetylation of chitin, exhibiting excellent properties such as nonâtoxicity, biocompatibility and biodegradability. NâMethylenephenyl phosphonic chitosan (NMPPC) is synthesized from chitosan by reacting with phenyl phosphonic acid using formaldehyde. The NMPPC was characterized by FTIR, 31PâNMR, Xâray diffraction, scanning electron microscopy, thermogravimeteric analysis and solubility studies. A significant decrease of molecular weight was observed in the NMPPC. The TGA studies suggested that NMPPC has less thermal stability than chitosan. The Xâray diffraction analysis showed that NMPPC was amorphous in nature. The solubility property of the polymer was improved after the incorporation of a phenyl phosphonic grou
Preparation and in vitro characterization of scaffolds of poly(L-lactic acid) containing bioactive glass ceramic nanoparticles
Porous nanocomposite scaffolds of poly(L-lactic acid) (PLLA) containing different quantities of bioactive glass ceramic (BGC) nanoparticles
(SiO2:CaO:P2O5 ! 55:40:5 (mol)) were prepared by a thermally induced phase-separation method. Dioxane was used as the solvent
for PLLA. Introduction of less than 20 wt.% of BGC nanoparticles did not remarkably affect the porosity of PLLA foam. However,
as the BGC content increased to 30 wt.%, the porosity of the composite was observed to decrease rapidly. The compressive modulus of
the scaffolds increased from 5.5 to 8.0 MPa, while the compressive strength increased from 0.28 to 0.35 MPa as the BGC content
increased from 0 to 30 wt.%. The in vitro bioactivity and biodegradability of nanocomposites were investigated by incubation in simulated
body fluid (SBF) and phosphate-buffered saline, respectively. Scanning electron microscopy, energy dispersive X-ray spectroscopy,
Fourier transform infrared spectroscopy and X-ray diffraction were employed to monitor the surface variation of neat PLLA and PLLA/
BGC porous scaffolds during incubation. PLLA/(20 wt.%)BGC composite exhibited the best mineralization property in SBF, while the
PLLA/(10 wt.%)BGC composite showed the highest water absorption ability.This work was financially supported by FCT Grant for postdoctoral research (SFRH/BPD/25828/2005), and by the Projects POCTI/FIS/61621/2004 and PTDC/QUI/69263/2006. The authors also would like to acknowledge Dr. Aixue Liu, Changchun Institute of Applied Chemistry, for his help in characterization of composite material
Carboxymethyl chitosan-graft-phosphatidylethanolamine: amphiphilic matrices for controlled drug delivery
Modified carboxymethyl chitosan (CMC) containing phosphatidylethanolamine (PEA) groups were synthesized by a 1-
ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)-mediated coupling reaction. The structure of the modified CMC
exhibiting an amphiphilic character was analysed by FT-IR and 1H NMR. CMC-g-PEA beads were prepared with sodium
tripolyphosphate (TPP) by ionic-crosslinking. The beads sizes were in range from 800 to 1200 lm and encapsulation efficiencies
of drug were more than 68%. The morphologies of CMC-g-PEA beads were examined with scanning electron
microscopy (SEM). The release experiments were performed using ketoprofen as an hydrophobic model drug. The drug
dissolution kinetics showed longer release times for CMC-g-PEA beads: 20 h (at pH 1.4) and 45 h (at pH 7.4). The amount
of the drug release was much higher in acidic solution than in basic solution due to the swelling properties of the matrix at
acidic pH. These results suggest that modified CMC with PEA may become a potential delivery system to control the
release of hydrophobic drugs
Study of the molecular mobility in polymers with the thermally stimulated recovery technique : a review
Thermally stimulated recovery (TSR) is a non-conventional mechanical spectroscopy
technique that allows to analyse in detail the relaxation processes of polymeric
systems in the low frequency region. This work reviews the main aspects and potentialities
of this technique. The different kinds of TSR experiments that can be performed,
global and thermal sampling (TS) experiments, are described and illustrated with
several examples. Also, the different methods for the determination of the thermokinetic
parameters (activation energy and pre-exponential factor) of the thermal sampling
(TS) procedure are explained and compared. In this context, the compensation
phenomenon, which always appears in TSR results when the studies are performed
in the glass transition region of a given system, is discussed. Examples of the application
of this technique to different polymeric systems during the last 20 years are
provided. An emphasis will be made on the analysis of the effect of crystallinity
degree and crosslink density on the TSR response. A comparison between the results
(characteristic times and activation energies) obtained by different techniques,
namely TSR, dynamic mechanical analysis (DMA), and differential scanning calorimetry
(DSC), is made
Analysis of the thermal environment inside the furnace of a dynamic mechanical analyser
In this work, the thermal environment inside the furnace of a dynamic mechanical analyser was investigated by
putting a standard sample in distinct positions inside the furnace. Penetration experiments were carried out in order to
compare the measured melting temperature of the sample with the theoretical melting temperature. The thermal gradients
were investigated for three distinct modes: compression, three-point bending and extension. In the compression mode
a small variation of the measured melting point was found as a function of the radial distance. However, for both
extension and three-point bending modes quite important variations were measured along the relevant directions. In
the former case the bottom clamp was found to be warmer than the upper one and in the latter mode higher temperatures
are found in the extremities of the samples (closer to the furnace wall). Other factors, such as the influence of the
heating rate and the purge gas flow rate, were also investigated. In the particular case of the extension mode, it was
found that the measured melting temperature decreased with increasing scanning rate. A simple model was used in
order to investigate the influence of the temperature gradients on DMA measurements. For temperature gradients along
the sample length below 10°C the differences in the viscoelastic parameters (tan d, Dâ and Eâ) from the homogeneous
case are small when compared with typical experimental errors
Enthalpy relaxation studies in polymethyl methacrylate networks with different crosslinking degrees
Structural relaxation of PMMA networks with distinct crosslink density has been studied by differential scanning calorimetry (DSC). The
crosslinking agent used was ethylene glycol dimethacrylate (EGDMA). The experiments were carried out on heating after the samples have
been subjected to distinct thermal histories, namely isothermal stages at different temperatures below the glass transition temperature for
distinct times and cooling at different rates. These studies revealed a broadening of the glass transition with increasing crosslinking degree
due to the constraints imposed by the crosslinks and suggested the presence of crosslink heterogeneity in the networks. A phenomenological
model based on the configurational entropy concept was used to simulate the structural relaxation phenomenon and to evaluate the
temperature dependence and distribution of the relaxation times of the conformational rearrangements for these networks. The agreement
between the experimental results and the simulated thermograms was quite satisfactory.
In addition, the kinetic fragility of the networks was evaluated from the results corresponding to the thermal treatments at distinct cooling
rates. It was found an increase of the fragility index m with increasing crosslinking degree
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