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Rheological monitoring of tau protein polymerisation with acoustic waves sensor
Electronics Letters
Abstract
Among acoustic waves sensors, the thickness shear mode resonator presents high sensitivity for the measurement of liquid viscoelastic properties, enabling the monitoring of the shear moduli, G′ G″, by using a suitable physical model. The development of an instrumental system for detecting the tau protein involved in Alzheimer's disease is proposed which will aid in understanding the mechanisms of this disease. The tau protein is present in complex products such as blood and cerebrospinal fluid. The experimental results show that the acoustic wave system allows to differentiate between tau protein solutions with different states of polymerisation.
... Finalement, les différentes recherches sur l'effet de la taille des gouttelettes de la phase dispersée sur l'activité antimicrobienne montrent des résultats contradictoires. De nombreuses études utilisant la microrhéologie ont déjà été menées, notamment pour le suivi de la formation de biofilms bactériens dans un milieu de culture enrichi, mais aussi pour suivre la polymérisation de fibres amyloïdes de protéines impliquées dans des pathologies dites de conformation comme la maladie d'Alzheimer [127], ou encore pour suivre la formation d'un yaourt [128]. Pour les trois types de Carbopol, la formation d'un réseau tridimensionnel passe par une ionisation des fonctions carboxylates grâce à une neutralisation avec une base (ici, la soude) ; les fonctions carboxylates ainsi formées permettent de déployer le polymère par répulsions électrostatiques à travers toute la formulation. ...
... L'utilisation inédite de la microrhéologie pour la caractérisation d'émulsions cosmétiques, fait suite à différentes études menées par le laboratoire validant sa pertinence à la fois pour un suivi d'évolution structurale et pour un suivi de développement de microorganismes [127], [143], [154], [155]. Ainsi, l'un des objectifs de ce travail consistait à mettre en évidence l'intérêt de la microrhéologie en association avec d'autres techniques de l'utilisation de techniques connues telle que la mesure du potentiel zêta [5], [156] par exemple, apporterait un éclairage pertinent sur l'ensemble des interactions qui existent au sein des émulsions en lien avec les différentes organisations spatiales et instabilités [42], [43]. ...
... En pratique, ces informations sont accessibles à l'aide d'un analyseur de réseau (Agilent) qui mesure la variation d'impédance électrique du capteur piézoélectrique chargé (c'est-à-dire en contact avec le milieu). Le capteur est donc utilisé en émission/réception et l'on peut alors montrer que[127], un coefficient de transduction dépendant de la géométrie du capteur et de sespropriétés piézoléctriques, est la masse volumique du fluide étudié et G * est le module complexe de cisaillement du matériau représentatif des propriétés viscoélastiques du milieu à la fréquence considérée. Pour suivre l'évolution du matériau une mesure de l'impédance de charge est réalisée à intervalle de temps régulier (au minimum toutes les minutes). ...
Depuis plus de 20 ans, de nombreuses méthodes et techniques non invasives ont été développées en vue de mesurer le plus objectivement possible, les propriétés (physico-chimiques, sensorielles, etc.) des produits cosmétiques. Ces méthodes visent à évaluer leur innocuité et leur efficacité, et deviennent d’autant plus perfectionnées que les processus d’élaborations de ces produits deviennent complexes et innovants.Au cours de ces travaux de thèse, une étude multi-échelle, de l'évolution structurale d'émulsions cosmétiques représentatives des crèmes mises sur le marché a été menée, afin de prédire leur stabilité tant texturale que microbiologique.L’étude du lien entre l’organisation structurale de ces émulsions avec leur composition et leur stabilité a été un des premiers défis à relever. Grâce à une technique non destructive ultrasonore permettant d’accéder aux propriétés micro-rhéologiques (propriétés viscoélastiques observée lors d'une sollicitation harmonique de cisaillement à quelques MHz), en association à différentes techniques classiques de caractérisation (microscopie optique, rhéologie basse fréquence, etc.) ; il a été possible de corréler les paramètres micro-rhéologiques obtenus à des modèles physiques reliant structuration interne et stabilité dans les émulsions considérées. Les résultats ont montrés que les données micro-rhéologiques sont sensibles aux variations de compositions (concentration) et d’organisations microscopiques des micelles au sein des émulsions (floculation, coalescence, etc.).Ensuite, le suivi de l’évolution d’une bactérie type (Pseudomonas fluorescens) dans des émulsions possédant des structures internes différentes, a montré d’une part la sensibilité de la micro-rhéologie vis-à-vis de la présence de bactéries dans le milieu, et d’autre part, l’impact de la structure et l’organisation des micelles sur le développement de ces bactéries.Finalement, la micro-rhéologie apparait être une méthode de mesure innovante et adaptée à l’échelle industrielle apportant une valeur ajoutée lors du développement de formulations cosmétiques. D’un point de vue sécuritaire, le dépistage précoce de contaminations biologiques par la détection d’instabilités (de changements) structurales au sein des émulsions, pourrait représenter une avancée majeure lors des phases de production et de commercialisation des produits cosmétiques.
... This paper presents an ultrasonic set-up based on a thickness shear mode (TSM) quartz crystal transducer to monitor the viscoelastic properties of skin explants, consisting of human ex vivo tissue samples obtained from surgical residues, including the dermis and the epidermis. This transducer was used to study the viscoelasticity of organic and inorganic soft materials [39][40][41][42][43][44]. Moreover, measurements on thawed explants demonstrated over several hours the instrumental system ability to perform accurate monitoring of this kind of samples [45], and preliminary results on fresh skin explants have already been presented [46]. ...
// OPEN ACCESS -> MDPI Cosmetics. //
The investigation of the mechanical properties of skin is of great interest for monitoring physiological and pathological changes in the cutaneous barrier function for dermatological and cosmetic issues. Skin constitutes a complex tissue because of its multi-layered organisation. From a rheological point of view, it can be considered to be a soft tissue with viscoelastic properties. In order to characterise ex vivo mechanical properties of skin on the mesoscopic scale, a biosensor including a thickness shear mode transducer (TSM) in contact with a skin explant was used. A specific experimental set-up was developed to monitor continuously and in real-time human skin explants, including the dermis and the epidermis. These were kept alive for up to 8 days. Skin viscoelastic evolutions can be quantified with a multi-frequency impedance measurement (from 5 MHz to 45 MHz) combined with a dedicated fractional calculus model. Two relevant parameters for the non-destructive mesoscopic characterisation of skin explants were extracted: the structural parameter αapp and the apparent viscosity ηapp. In this study, the validity of the biosensor, including repeatability and viability, was controlled. A typical signature of the viscoelastic evolutions of the different cutaneous layers was identified. Finally, monitoring was carried out on stripped explants mimicking a weakened barrier function.
... Ce dispositif, développé par C. Ould Ehssein [181], a servi au suivi au cours du temps des propriétés viscoélastiques à l'échelle microscopique de différents types de fluides complexes sous forme de liquide (solutions aqueuses, huiles), d'émulsions (crèmes), ou de gels (polymères, vernis, matériaux hybrides organiques-inorganiques). Il a notamment été utilisé pour étudier le processus d'acidification lors de la fabrication de yaourt [200], la formation de film bactérien dans des émulsions cosmétiques [201] ou la polymérisation de la protéine Tau dans le cadre de la maladie d'Alzheimer [202]. ...
One of the main challenges for dermatology and cosmetics is to develop competitive tools for characterisation of skin intrinsic and extrinsic interactions. Our goal is to investigate two new competitive oscillatory techniques. On the one hand, micro rheology enables to dynamically measure the viscoelasticity at the mesoscopic scale. A sensor has been designed to monitor mechanical properties of skin explants kept alive, such as hydration or elasticity. On the other hand, an optical CARS spectroscopy bench has been set upped for a study at the molecular level. The goal is to improve the sensitivity and the resolution of the molecular vibrations measurements by a laser excitation. It is then possible to get information about the biochemical structures including lipids and proteins. In a context of well being increasing search, these two innovative devices should help for the evaluation of new ingredients, as an alternative to animal or clinical testing.
As an answer to alternative non-animal testing, biosensors dedicated to the ex vivo skin explants monitoring are a challenge to study physiological-like behavior and optimize new topical products. Because of the skin viscoelastic behavior, mechanical tests are commonly based on macroscopic measurement and give global descriptors of its state. Other techniques, including photoacoustic ones, are more focused on the molecular scale. There is a gap to fill in the mesoscopic range to get information about the microstructure of the skin. This article presents the proof-of-concept of a biosensor coupling a thickness shear-mode transducer with human skin explants kept in life-like state for a week. Thanks to a multifrequency analysis of the transducer impedance, this biosensor is able to monitor the viscoelastic properties of the skin. To extract the complex shear modulus and the microstructural evolutions, a mechanical model based on fractional calculus is used. As a preliminary results, the sensitivity of the sensor to probe the skin viscoelasticity in lifelike state and the impact of its culture medium are presented. A suitable microstructural coefficient is also extracted in order to identify mechanical breaches in the skin barrier after the application of peeling products.
The phenomenon of protein aggregation and amyloid formation has become the subject of rapidly increasing research activities across a wide range of scientific disciplines. Such activities have been stimulated by the association of amyloid deposition with a range of debilitating medical disorders, from Alzheimer's disease to type II diabetes, many of which are major threats to human health and welfare in the modern world. It has become clear, however, that the ability to form the amyloid state is more general than previously imagined, and that its study can provide unique insights into the nature of the functional forms of peptides and proteins, as well as understanding the means by which protein homeostasis can be maintained and protein metastasis avoided.
Alzheimer's disease (AD) is the most common form of dementia, with over 37 million sufferers worldwide and a global cost of over $600 billion. There is currently no cure for AD and no reliable method of diagnosis other than post-mortem brain examination. The development of a point-of-care test for AD is an urgent requirement in order to provide earlier diagnosis and, thus, useful therapeutic intervention. Here, we present a novel, label-free impedimetric biosensor for the specific detection of amyloid-beta oligomers (AβO), which are the primary neurotoxic species in AD. AβO have been proposed as the best biomarker for AD and levels of AβO in the blood have been found to correlate with cerebrospinal fluid load. The biorecognition element of our biosensor is a fragment of the cellular prion protein (PrP(C), residues 95-110), a highly expressed synaptic protein which mediates the neuronal binding and toxicity of AβO. During the layer-by-layer sensor construction, biotinylated PrP(C) (95-110) was attached via a biotin/NeutrAvidin bridge to polymer-functionalised gold screen-printed electrodes. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry and scanning electron microscopy were used to validate biosensor assembly and functionality. EIS was employed for biosensor interrogation in the presence of Aβ oligomers or monomers. The biosensor was specific for the detection of synthetic AβO and gave a linear response, without significant detection of monomeric Aβ, down to an equivalent AβO concentration of ~0.5pM. The biosensor was also able to detect natural, cell-derived AβO present in conditioned medium. The eventual commercialisation of this biosensor system could allow for the early diagnosis and disease monitoring of AD.
The aggregation of proteins or peptides in amyloid fibrils is associated with a number of clinical disorders, including Alzheimer's, Huntington's and prion diseases, medullary thyroid cancer, renal and cardiac amyloidosis. Despite extensive studies, the molecular mechanisms underlying the initiation of fibril formation remain largely unknown. Several lines of evidence revealed that short amino-acid segments (hot spots), located in amyloid precursor proteins act as seeds for fibril elongation. Therefore, hot spots are potential targets for diagnostic/therapeutic applications, and a current challenge in bioinformatics is the development of methods to accurately predict hot spots from protein sequences. In this paper, we combined existing methods into a meta-predictor for hot spots prediction, called MetAmyl for METapredictor for AMYLoid proteins. MetAmyl is based on a logistic regression model that aims at weighting predictions from a set of popular algorithms, statistically selected as being the most informative and complementary predictors. We evaluated the performances of MetAmyl through a large scale comparative study based on three independent datasets and thus demonstrated its ability to differentiate between amyloidogenic and non-amyloidogenic polypeptides. Compared to 9 other methods, MetAmyl provides significant improvement in prediction on studied datasets. We further show that MetAmyl is efficient to highlight the effect of point mutations involved in human amyloidosis, so we suggest this program should be a useful complementary tool for the diagnosis of these diseases.
The diagnostic guidelines of Alzheimer's disease (AD) have recently been updated to include brain imaging and cerebrospinal fluid (CSF) biomarkers, with the aim of increasing the certainty of whether a patient has an ongoing AD neuropathologic process or not. The CSF biomarkers total tau (T-tau), hyperphosphorylated tau (P-tau) and the 42 amino acid isoform of amyloid β (Aβ42) reflect the core pathologic features of AD, which are neuronal loss, intracellular neurofibrillary tangles and extracellular senile plaques. Since the pathologic processes of AD start decades before the first symptoms, these biomarkers may provide means of early disease detection. The updated guidelines identify three different stages of AD: preclinical AD, mild cognitive impairment (MCI) due to AD and AD with dementia. In this review, we aim to summarize the CSF biomarker data available for each of these stages. We also review results from blood biomarker studies. In summary, the core AD CSF biomarkers have high diagnostic accuracy both for AD with dementia and to predict incipient AD (MCI due to AD). Longitudinal studies on healthy elderly and recent cross-sectional studies on patients with dominantly inherited AD mutations have also found biomarker changes in cognitively normal at-risk individuals. This will be important if disease-modifying treatment becomes available, given that treatment will probably be most effective early in the disease. An important prerequisite for this is trustworthy analyses. Since measurements vary between studies and laboratories, standardization of analytical as well as pre-analytical procedures will be essential. This process is already initiated. Apart from filling diagnostic roles, biomarkers may also be utilized for prognosis, disease progression, development of new treatments, monitoring treatment effects and for increasing the knowledge about pathologic processes coupled to the disease. Hence, the search for new biomarkers continues. Several candidate biomarkers have been found in CSF, and although biomarkers in blood have been harder to find, some recent studies have presented encouraging results. But before drawing any major conclusions, these results need to be verified in independent studies.
We studied fibril formation in a family of peptides based on PHF6 (VQIVYK), a short peptide segment found in the microtubule binding region of tau protein. N-Acetylated peptides AcVYK-amide (AcVYK), AcIVYK-amide (AcPHF4), AcQIVYK-amide (AcPHF5), and AcV-QIVYK-amide (AcPHF6) rapidly formed straight filaments in the presence of 0.15 m NaCl, each composed of two laterally aligned protofilaments approximately 5 nm in width. X-ray fiber diffraction showed the omnipresent sharp 4.7-A reflection indicating that the scattering objects are likely elongated along the hydrogen-bonding direction in a cross-beta conformation, and Fourier transform IR suggested the peptide chains were in a parallel (AcVYK, AcPHF6) or antiparallel (AcPHF4, AcPHF5) beta-sheet configuration. The dipeptide N-acetyl-YK-amide (AcYK) formed globular structures approximately 200 nm to 1 microm in diameter. The polymerization rate, as measured by thioflavin S binding, increased with the length of the peptide going from AcYK --> AcPHF6, and peptides that aggregated most rapidly displayed CD spectra consistent with beta-sheet structure. There was a 3-fold decrease in rate when Val was substituted for Ile or Gln, nearly a 10-fold decrease when Ala was substituted for Tyr, and an increase in polymerization rate when Glu was substituted for Lys. Twisted filaments, composed of four laterally aligned protofilaments (9-19 nm width, approximately 90 nm half-periodicity), were formed by mixing AcPHF6 with AcVYK. Taken together these results suggest that the core of PHF6 is localized at VYK, and the interaction between small amphiphilic segments of tau may initiate nucleation and lead to filaments displaying paired helical filament morphology.
The Butterworth-Van Dyke equivalent circuit for description of the electrical behavior of piezoelectric bulk resonators is considered. The motional capacitance, C/sub 1/, in the circuit characterizes the strength of piezoelectric excitability of a vibration mode. For layered one-dimensional (1-D) structures this parameter can be calculated from the admittance given by the transfer matrix description of H. Nowotny and E. Benes (1987). Introducing the equivalent area of a vibration mode, the calculation is generalized for the three-dimensional (3-D) case of thickness-mode vibration amplitudes varying only slowly in the lateral directions. Detailed formulae are given for the case of singly rotated quartz crystals or ultrasonic transducers with additional layers on one or two sides. Good agreement of the calculated C/sub 1/ with experimental data is shown for mass-loaded planoconvex AT-cut quartz crystals.< >
This paper describes a one‐dimensional analysis of a piezoelectric resonator with multiple nonpiezoelectric layers of arbitrary thickness and complex shear modulus. This analysis shows under what conditions the simple Butterworth–Van Dyke (BVD) lumped‐element equivalent circuit can be used to extract the properties of these layers, and provides a theoretical basis for doing so under these conditions. The method presented here is based on the physics of wave propagation, but uses transmission line techniques to transform the equations and boundary conditions into a simple string of 2×2 matrix multiplications, which easily accommodate any number of layers. An analysis of the AT‐cut quartz/polymer/liquid composite resonator is presented in detail because of its importance in sensor and electrochemical quartz crystal microbalance applications. The analysis shows that adding the polymer and liquid impedances in the motional arm of a BVD circuit is not valid near the polymer film resonance, but is appropriate for a thin, rigid polymer film in contact with a liquid.
Clinical diagnosis for Alzheimer's disease (AD) is provided by the criteria of DSMIV and clinical progress in addition to imaging analysis with MRI after negative screening. The final exclusive diagnosis iis confirmed by the neuropathological findings of neurofibrillary tangles and senile plaques in autopsy brains. We developed a new ELISA system to measure the amount of tau in cerebrospinal fluids (CSF) using phosphorylation-independent and sequence-specific antibodies. The present ELISA was sensitive enough to detect tau in CSF of normal subjects. The amount of tau was significantly elevated in CSF of AD subjects compared with those of normal subjects and subjects with dementia of cerebrovascular disease, suggesting that tau in CSF reflects the massive and continuous neuronal cell death in the AD brain. In conclusion, we established an ELISA system which enabled us to detect tau in CSF and demonstrated that tau was significantly and specifically elevated in CSF of AD subjects. The assay system can provide us with a potent diagnostic tool for clinical AD.
The physicochemical parameters of biomolecules are the key determinants of the multitude of processes that govern the normal and aberrant behavior of living systems. A particularly important aspect of such behavior is the role it plays in the self-association of proteins to form organized aggregates such as the amyloid or amyloid-like fibrils that are associated with pathological conditions including Alzheimer's disease and Type II diabetes. In this study we describe quantitative quartz crystal microbalance measurements of the kinetics of the growth of amyloid fibrils in a range of crowded environments and in conjunction with theoretical predictions demonstrate the existence of general relationships that link the propensities of protein molecules to aggregate with fundamental parameters that describe their specific structures and local environments.
Uncontrolled fibrous protein aggregation is implicated in a range of aberrant biological phenomena. Much effort has consequently been directed towards establishing quantitative in vitro assays of this process with the aim of probing amyloid growth in molecular detail as well as elucidating the effect of additional species on this reaction. In this paper, we discuss some recent approaches based on label-free technologies focussed on achieving these objectives. Several biosensor techniques have been developed to monitor biomolecular assembly without the requirement for fluorophore marker molecules; in particular quartz crystal microbalance and surface plasmon resonance measurements provide advantageous alternatives to traditional spectroscopic methods and are currently receiving increasing attention in the context of amyloid growth assays.
The last decades have seen the development of sol-gel (SG) process currently used to develop new materials in a wide range of scientific applications. The SG process leads to an oxide macromolecular network through a sol (liquid phase) to gel transition. To optimize this process, the control of the kinetic of the chemical reaction is required. This kinetic can be deduced from the temporal evolution of the viscoelastic parameters. Upto date no complete investigation during the SG formation can be achieved by a unique non-destructive technique. In this paper, we present an ultrasonic technique to measure the viscoelastic parameters (storage G' and loss G'' shear moduli) of the gel material during its formation. By using a suitable model which takes into account the mass loading on the surface, the viscoelastic parameters of these materials are accurately deduced. In order to study the efficiency of this technique, silica gels transition is monitored at various formation temperatures and for different initial hydrolysis molar ratio (h). In addition, the monitoring is performed at different oscillatory shear measurements in the 6-54 MHz frequency range to determine a new characteristic time t(vs) corresponding to the moment when the material is no more a newtonian liquid. This characteristic time is then compared to the gelation time t(g) determined by rheological or acoustic audible range methods. Thus the new characteristic time is also a good criterion to characterize earlier the SG matrix transition. Our AT-cut quartz technique using our model can also be used as a high frequency rheometer for the sol-gel materials.
The behavior of weak gels during their formation singularly attracts attention of dairy products factories. In our study we investigate acidified pre-heated milk gels formation that are fairly often used to product yoghurts. The gel formation requires a tight control of the first step of micelles modification process and the kinetics reaction parameters. The most current rheological parameters used to achieve the monitoring are the storage G' and the loss G'' shear moduli and the gelation time. The study of these parameters is commonly performed at very low frequencies (1 Hz). Our technique uses a 6 MHz AT-cut quartz crystal immersed in an acidified milk solution kept at a constant temperature. This method is singularly effective to ensure a complete and a reliable follow-up of the viscoelastic parameters of casein gels. A suitable new model enables a complete follow-up of the micelles evolution from the viscoelastic properties. The experimental results of the G' and G'' moduli versus temperature and versus glucono-delta-lactone (GDL) added to milk are analyzed. In order to understand the micelles modifications, an analysis of the viscoelastic evolution try to explain the validity of the various models of micelles modification. In addition a new accurate kinetics characteristic time is proposed. This time corresponds to the moment for which the elastic effect of material becomes significant. From the kinetics study of casein gels at various temperatures, the Arrhenius relationship and a modified Flory-Stockmayer relationship give us access to the activation energy. By using the proposed technique and the suitable models developed, the structure thus quality of dairy products may be better controlled.
Amyloid fibrillation has been intensively studied because of its association with various neurological disorders. While extensive time-dependent fibrillation experimental data are available and appear similar, few mechanistic models have been developed to unify those results. The aim of this work was to interpret these experimental results via a rigorous mathematical model that incorporates the physical chemistry of nucleation and fibril growth dynamics. A three-stage mechanism consisting of protein misfolding, nucleation, and fibril elongation is proposed and supported by the features of homogeneous fibrillation responses. Estimated by nonlinear least-squares algorithms, the rate constants for nucleation were approximately 10,000,000 times smaller than those for fibril growth. These results, coupled with the positive feedback characteristics of the elongation process, account for the typical sigmoidal behavior during fibrillation. In addition, experiments with different proteins, various initial concentrations, seeding versus nonseeding, and several agitation rates were analyzed with respect to fibrillation using our new model. The wide applicability of the model confirms that fibrillation kinetics may be fairly similar among amyloid proteins and for different environmental factors. Recommendations on further experiments and on the possible use of molecular simulations to determine the desired properties of potential fibrillation inhibitors are offered.
Although it remains unclear whether they are related to one another, tau aggregation and phosphorylation are the main pathological hallmarks of the neuronal disorders known as tauopathies. The capacity to aggregate is impaired in a variant of the tau 3R isoform that lacks residues 306-311 (nomenclature for the largest CNS tau isoform) and hence, we have taken advantage of this feature to study how phosphorylation and aggregation may be related as well as the role of this six amino acid peptide (VQIVYK). Through these analyses, we found that the phosphorylation of the tau variant was higher than that of the complete tau protein and that not only the deletion of these residues, but also the interaction of these residues, in tau 3R, with thioflavin-S augmented tau phosphorylation by glycogen synthase kinase 3. In addition, the binding of the peptide containing the residues 306-311 to the whole tau protein provoked an increase in tau phosphorylation. This observation could be physiologically relevant as may suggest that tau-tau interactions, through those residues, facilitate tau phosphorylation. In summary, our data indicate that deletion of residues VQIVYK, in tau protein produces an increase in tau phosphorylation, without tau aggregation, because the VQIVYK peptide, that favors aggregation, is missing. On the other hand, when the whole tau protein interacts with thioflavin-S or the peptide VQIVYK, an increase in both aggregation and phosphorylation occurs.
Evidence linking soluble aggregation intermediates of the amyloid-beta protein (A beta), as well as the ongoing growth of A beta aggregates, to physiological responses characteristic of Alzheimer's disease (AD) indicates that a kinetic description A beta aggregation intermediate growth may be fundamental to understanding disease progression. Although the growth of mature A beta fibrils has been investigated using several experimental platforms, the growth of A beta aggregation intermediates has been less thoroughly explored. In the current study, a quartz crystal microbalance (QCM) was employed to analyze the real-time growth of A beta(1-40) aggregation intermediates selectively immobilized on the crystal surface. Immobilization permitted quantitative evaluation of A beta(1-40) aggregation intermediate growth under controlled solution conditions. Elongation of A beta(1-40) aggregation intermediates via monomer addition proceeded in a nonsaturable and reversible fashion. The rate of elongation was observed to vary linearly with both monomer concentration and immobilized aggregate density, to be elevated by increases in solution ionic strength, and to increase as solution pH became more acidic. Elongation was consistent with a first-order kinetic model for the single growth phase observed. These findings extend previous kinetic studies involving the growth of mature A beta fibrils to describe the growth of A beta(1-40) aggregation intermediates via monomer addition.
The nanostructure evolution of gels, biomaterials or porous media can be characterized by its mechanical properties. Few nondestructive techniques are developed to investigate the viscosity evolution. This paper present a new electromagnetic-acoustic technique using a wireless thickness shear mode transducer. A suitable model of the measurement is also presented to characterize the viscosity of the nanostructure in contact with the transducer. This transducer is a double copper-clad PVDF substrate resonator, designed to operate over a wide radiofrequency range without lumped tuning capacitors. This architecture constitutes an alternative solution to design a high-Q ultrasonic microbalance. To characterize the material at the surface of the transducer, the evolution of the induced complex impedance is measured. From this evolution, the mechanical energy storage and dissipation in the material can be extracted. In order to validate the lumped element model used, a series of glycerolwater mixtures is studied. We show that the resonant frequency shift and damping follow an accurate linear shape (<5%) according to the square root of the liquid viscosity and density product. This result is in good agreement with the classical prediction of Martin and Kanazawa obtained with a quartz crystal microbalance.
Système instrumental pour la rhéologie ultrasonore
- C Ould Ehssein
C. Ould Ehssein, "Système instrumental pour la rhéologie ultrasonore," Université Cergy
Pontoise, 2006.
Gelation monitoring by quartz microbalance in pulse mode
- E Caplain
- C O Ehssein
- L Martinez
- S Serfaty
- P Griesmar
- M Gindre
E. Caplain, C. O. Ehssein, L. Martinez, S. Serfaty, P. Griesmar, and M. Gindre, "Gelation
monitoring by quartz microbalance in pulse mode," in Ultrasonics Symposium, 2004 IEEE,
2004, vol. 1, pp. 323-324.
Piezoelectric sensor for the detection and characterization of at least one biochemical element
- S Serfaty
- P Griesmar
- J.-Y. Le Huerou
- E Caplain
S. SERFATY, P. GRIESMAR, J.-Y. LE HUEROU, E. CAPLAIN, and Others, "Piezoelectric
sensor for the detection and characterization of at least one biochemical element." 2012.
Chaperons moléculaires et tauopathies : effet de Hsp90 sur la fibrillation in vitro du peptide VQIVYK issu de la protéine tau
- C Schirmer
C. Schirmer, "Chaperons moléculaires et tauopathies : effet de Hsp90 sur la fibrillation in vitro
du peptide VQIVYK issu de la protéine tau.," Université de Rennes 1, 2014.