1,808 research outputs found
Functionalization of different polymers with sulfonic groups as a way to coat them with a biomimetic apatite layer
Covalent coupling of sulfonic group (–SO3H)
was attempted on different polymers to evaluate efficacy of
this functional group in inducing nucleation of apatite in
body environment, and thereupon to design a simple biomimetic
process for preparing bonelike apatite-polymer
composites. Substrates of polyethylene terephthalate
(PET), polycaprolactam (Nylon 6), high molecular weight
polyethylene (HMWPE) and ethylene-vinyl alcohol copolymer
(EVOH) were subjected to sulfonation by being
soaked in sulfuric acid (H2SO4) or chlorosulfonic acid
(ClSO3H) with different concentrations. In order to incorporate
calcium ions, the sulfonated substrates were soaked
in saturated solution of calcium hydroxide (Ca(OH)2). The
treated substrates were soaked in a simulated body fluid
(SBF). Fourier transformed infrared spectroscopy, thin-film
X-ray diffraction, and scanning electron microscopy
showed that the sulfonation and subsequent Ca(OH)2
treatments allowed formation of –SO3H groups binding
Ca2+ ions on the surface of HMWPE and EVOH, but not on
PET and Nylon 6. The HMWPE and EVOH could thus
form bonelike apatite layer on their surfaces in SBF within
7 d. These results indicate that the –SO3H groups are
effective for inducing apatite nucleation, and thereby that
surface sulfonation of polymers are effective pre-treatment
method for preparing biomimetic apatite on their surfaces
The dynamics of spiral arms in pure stellar disks
It has been believed that spirals in pure stellar disks, especially the ones
spontaneously formed, decay in several galactic rotations due to the increase
of stellar velocity dispersions. Therefore, some cooling mechanism, for example
dissipational effects of the interstellar medium, was assumed to be necessary
to keep the spiral arms. Here we show that stellar disks can maintain spiral
features for several tens of rotations without the help of cooling, using a
series of high-resolution three-dimensional -body simulations of pure
stellar disks. We found that if the number of particles is sufficiently large,
e.g., , multi-arm spirals developed in an isolated disk can
survive for more than 10 Gyrs. We confirmed that there is a self-regulating
mechanism that maintains the amplitude of the spiral arms. Spiral arms increase
Toomre's of the disk, and the heating rate correlates with the squared
amplitude of the spirals. Since the amplitude itself is limited by the value of
, this makes the dynamical heating less effective in the later phase of
evolution. A simple analytical argument suggests that the heating is caused by
gravitational scattering of stars by spiral arms, and that the self-regulating
mechanism in pure-stellar disks can effectively maintain spiral arms on a
cosmological timescale. In the case of a smaller number of particles, e.g.,
, spiral arms grow faster in the beginning of the simulation
(while is small) and they cause a rapid increase of . As a result, the
spiral arms become faint in several Gyrs.Comment: 18 pages, 19 figures, accepted for Ap
Dynamic ordering of driven vortex matter in the peak effect regime of amorphous MoGe films and 2H-NbSe2 crystals
Dynamic ordering of driven vortex matter has been investigated in the peak
effect regime of both amorphous MoGe films and 2H-NbSe2 crystals by mode
locking (ML) and dc transport measurements. ML features allow us to trace how
the shear rigidity of driven vortices evolves with the average velocity.
Determining the onset of ML resonance in different magnetic fields and/or
temperatures, we find that the dynamic ordering frequency (velocity) exhibits a
striking divergence in the higher part of the peak effect regime.
Interestingly, this phenomenon is accompanied by a pronounced peak of dynamic
critical current. Mapping out field-temperature phase diagrams, we find that
divergent points follow well the thermodynamic melting curve of the ideal
vortex lattice over wide field and/or temperature ranges. These findings
provide a link between the dynamic and static melting phenomena which can be
distinguished from the disorder induced peak effect.Comment: 9 pages, 6 figure
Growth of a bonelike apatite on chitosan microparticles after a calcium silicate treatment
Bioactive chitosan microparticles can be prepared successfully by treating them with a calcium silicate solution and then subsequently
soaking them in simulated body fluid (SBF). Such a combination enables the development of bioactive microparticles that can be used
for several applications in the medical field, including injectable biomaterial systems and tissue engineering carrier systems. Chitosan
microparticles, 0.6 lm in average size, were soaked either for 12 h in fresh calcium silicate solution (condition I) or for 1 h in calcium
silicate solution that had been aged for 24 h before use (condition II). Afterwards, they were dried in air at 60 !C for 24 h. The samples
were then soaked in SBF for 1, 3 and 7 days. After the condition I calcium silicate treatment and the subsequent soaking in SBF, the
microparticles formed a dense apatite layer after only 7 days of immersion, which is believed to be due to the formation of silanol (Si–
OH) groups effective for apatite formation. For condition II, the microparticles successfully formed an apatite layer on their surfaces in
SBF within only 1 day of immersion.I.B.L. thanks the Portuguese Foundation for Science and Technology (FCT), for providing her a PhD scholarship (SFRH/BD/9031/2002), the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758) and the European NoE EXPERTISSUES (NMP3-CT-2004-500283)
Biomimetic apatite formation on different polymeric microspheres modified with calcium silicate solutions
Proceedings of the 18th International Symposium on Ceramics in Medicine, The Annual Meeting of the International Society for Ceramics in Medicine (ISCM), Kyoto, Japan, 5-8 December 2005. Published in : Key Enggineering Materials, vol. 309 - 311Bioactive polymeric microspheres can be produced by pre-coating them with a calcium
silicate solution and the subsequent soaking in a simulated body fluid (SBF). Such combination
should allow for the development of bioactive microspheres for several applications in the medical
field including tissue engineering. In this work, three types of polymeric microspheres with different
sizes were used: (i) ethylene-vinyl alcohol co-polymer (20-30 'm), (ii) polyamide 12 (10-30 'm) and
(iii) polyamide 12 (300 'm). These microspheres were soaked in a calcium silicate solution at 36.5ºC
for different periods of time under several conditions. Afterwards, they were dried in air at 100ºC for
24 hrs. Then, the samples were soaked in SBF for 1, 3 and 7 days. Fourier transformed infrared
spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that after the
calcium silicate treatment and the subsequent soaking in SBF, the microspheres successfully formed a
bonelike apatite layer on their surfaces in SBF within 7 days due to the formation of silanol (Si-OH)
groups that are quite effective for apatite formation.I. B. Leonor thanks the Portuguese Foundation for Science and Technology (FCT) for providing her a PhD scholarship (SFRH/BD/9031/2002) and the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758) and the European NoE EXPERTISSUES (NMP3-CT-2004-500283)
Surface potential change in bioactive polymer during the process of biomimetic apatite formation in a simulated body fluid
A bioactive polyethylene substrate can be produced by incorporation of sulfonic functional groups (-SO3H) on its surface and by soaking in a calcium hydroxide saturated solution. Variation of the surface potential of the polyethylene modified with -SO3H groups with soaking in a simulated body fluid (SBF) was investigated using a laser electrophoresis zeta-potential analyzer. To complement the study using laser electrophoresis, the surface was examined by X-ray photoelectron spectroscopy (XPS), thin film X-ray diffraction (TF-XRD), field-emission scanning electron microscopy (FE-SEM) and energy-dispersive electron X-ray spectroscopy (EDS). Comparing the zeta potential of sulfonated and Ca(OH)2-treated polyethylene with its surface structure at each interval of these soaking times in SBF, it is apparent that the polymer has a negative surface potential when it forms -SO3H groups on its surface. The surface potential of the polymer increases when it forms amorphous calcium sulfate. The potential decreases when it forms amorphous calcium phosphate, revealing a constant negative value after forming apatite. The XPS and zeta potential analysis demonstrated that the surface potential of the polyethylene was highly negatively charged after soaking in SBF for 0.5 h, increased for higher soaking times (up to 48 h), and then decreased. The negative charge of the polymer at a soaking time of 0.5 h is attributed to the presence of -SO3H groups on the surface. The initial increase in the surface potential was attributed to the incorporation of positively charged calcium ions to form calcium sulfate, and then the subsequent decrease was assigned to the incorporation of negatively charged phosphate ions to form amorphous calcium phosphate, which eventually transformed into apatite. These results indicate that the formation of apatite on bioactive polyethylene in SBF is due to electrostatic interaction of the polymer surface and ions in the fluid
Effects of hydroxyapatite and PDGF concentrations on osteoblast growth in a nanohydroxyapatite-polylactic acid composite for guided tissue regeneration
The technique of guided tissue regeneration (GTR) has evolved over recent years in an attempt to achieve periodontal tissue regeneration by the use of a barrier membrane. However, there are significant limitations in the currently available membranes and overall outcomes may be limited. A degradable composite material was investigated as a potential GTR membrane material. Polylactic acid (PLA) and nanohydroxyapatite (nHA) composite was analysed, its bioactive potential and suitability as a carrier system for growth factors were assessed. The effect of nHA concentrations and the addition of platelet derived growth factor (PDGF) on osteoblast proliferation and differentiation was investigated. The bioactivity was dependent on the nHA concentration in the films, with more apatite deposited on films containing higher nHA content. Osteoblasts proliferated well on samples containing low nHA content and differentiated on films with higher nHA content. The composite films were able to deliver PDGF and cell proliferation increased on samples that were pre absorbed with the growth factor. nHA–PLA composite films are able to deliver active PDGF. In addition the bioactivity and cell differentiation was higher on films containing more nHA. The use of a nHA–PLA composite material containing a high concentration of nHA may be a useful material for GTR membrane as it will not only act as a barrier, but may also be able to enhance bone regeneration by delivery of biologically active molecules
Formation of bone-like apatite on polymeric surfaces modified with -SO3H groups
Sulfonic groups (-SO3H) were covalently attached on different polymeric surfaces
enabling them to induce apatite nucleation, for developing bioactive apatite-polymer composites with
a bonelike 3-dimensional structure. High molecular weight polyethylene (HMWPE) and
ethylene-co-vinyl alcohol co-polymer (EVOH) were used. The polymers were soaked in two types of
sulphate-containing solutions with different concentrations, sulphuric acid (H2SO4) and
chlorosulfonic acid (ClSO3H). To incorporate calcium ions into to the sulfonated polymers, the
samples were soaked in a saturated Ca(OH)2 solution for 24 hours. After soaking of the samples in a
simulated body fluid (SBF), formation of an apatite layer on both surfaces was observed. The results
obtained prove the validity of the proposed concept and show that the -SO3H groups are effective on
inducing apatite nucleation on the surface of these polymers.(undefined
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