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1.
Vestn Oftalmol ; 136(5. Vyp. 2): 191-196, 2020.
Artigo em Russo | MEDLINE | ID: mdl-33063963

RESUMO

One of the research directions of the so-called non-motor manifestations of Parkinson's disease (PD) is associated with the assessment of structural and functional changes in the organ of vision. An assessment of the state of thin non-myelinated corneal nerve fibers (CNF) in Parkinson's disease seems to be promising considering the neurodegenerative nature of the disease, as well as the possibility of objective intravital assessment of both functional and structural changes in CNF. PURPOSE: To analyze the changes in the course and structure of corneal nerve fibers in the early stages of Parkinson's disease based on an objective algorithm of in vivo corneal confocal microscopy (CCM). MATERIAL AND METHODS: The study was conducted on a group of 16 patients aged 39 to 66 years with verified diagnosis of PD. In addition to standard neurological and ophthalmological examinations, all patients underwent IVCCM on a Heidelberg Retinal Tomograph device with special Rostock Cornea Module (HRT3 RCM), followed by processing of the obtained images using a uniquely designed analysis algorithm. RESULTS: A significant decrease in the directional anisotropy coefficient and an increase in the directional symmetry coefficient of the nerve fibers of the cornea were established (average values 3.15±1.08 and 0.92±0.04, respectively); in healthy individuals of the identical age range these indicators are 3.5±0.85 and 0.86±0.11, respectively. In addition, qualitative structural changes were noted, which consisted of an increase in the number of branches from the main nerve trunks, an increase in the tortuosity of CNF, multidirectionality, and "beaded" shape. In 9 cases, the presence of macrophages was revealed - dendritic Langerhans cells, which is an indirect sign of the inflammatory process. CONCLUSION: The preliminary nature of the results obtained in this study and the need for further research in this area are related, on the one hand, to a small sample of observations and, on the other hand, to the criterion used to assess the status of CNF based on a comparative analysis with conditionally normal indicators. In the future, in order to solve the problem of the uniqueness of changes in CNF and the possibility of using these changes as a marker for PD progression, longitudinal studies are required to reveal the presence or absence of a correlation between the stage of the disease, the results of known monitoring methods (e.g. electromyography) and quantitative indicators of the status of CNF.


Assuntos
Doença de Parkinson , Adulto , Idoso , Anisotropia , Córnea/diagnóstico por imagem , Humanos , Microscopia Confocal , Pessoa de Meia-Idade , Fibras Nervosas , Doença de Parkinson/diagnóstico por imagem
2.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 1692-1695, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018322

RESUMO

With several initiatives well underway towards amassing large and high-quality population-based neuroimaging datasets, deep learning is set to push the boundaries of what is possible in classification and prediction in neuroimaging studies. This includes those that derive increasingly popular structural connectomes, which map out the connections (and their relative strengths) between brain regions. Here, we test different Convolutional Neural Network (CNN) models in a benchmark sex prediction task in a large sample of N=3,152 structural connectomes acquired from the UK Biobank, and compare results across different connectome processing choices. The best results (76.5% test accuracy) were achieved using Fractional Anisotropy (FA) weighted connectomes, without sparsification, and with a simple weight normalisation through division by the maximum FA value. We also confirm that for structural connectomes, a Graph CNN approach, the recently proposed BrainNetCNN, outperforms an image-based CNN.


Assuntos
Conectoma , Anisotropia , Encéfalo/diagnóstico por imagem , Humanos , Redes Neurais de Computação
3.
Nat Commun ; 11(1): 4372, 2020 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-32873801

RESUMO

3D molecular structure determination is a challenge for organic compounds or natural products available in minute amounts. Proton/proton and proton/carbon correlations yield the constitution. J couplings and NOEs oftentimes supported by one-bond 1H,13C residual dipolar couplings (RDCs) or by 13C residual chemical shift anisotropies (RCSAs) provide the relative configuration. However, these RDCs or carbon RCSAs rely on 1% natural abundance of 13C preventing their use for compounds available only in quantities of a few 10's of µgs. By contrast, 1H RCSAs provide similar information on spatial orientation of structural moieties within a molecule, while using the abundant 1H spin. Herein, 1H RCSAs are accurately measured using constrained aligning gels or liquid crystals and applied to the 3D structural determination of molecules with varying complexities. Even more, deuterated alignment media allow the elucidation of the relative configuration of around 35 µg of a briarane compound isolated from Briareum asbestinum.


Assuntos
Antozoários/química , Produtos Biológicos/química , Diterpenos/química , Conformação Molecular , Prótons , Animais , Anisotropia , Espectroscopia de Prótons por Ressonância Magnética
4.
Nat Commun ; 11(1): 4902, 2020 09 29.
Artigo em Inglês | MEDLINE | ID: mdl-32994402

RESUMO

Living cells and tissues experience various complex modes of forces that are important in physiology and disease. However, how different force modes impact gene expression is elusive. Here we apply local forces of different modes via a magnetic bead bound to the integrins on a cell and quantified cell stiffness, chromatin deformation, and DHFR (dihydrofolate reductase) gene transcription. In-plane stresses result in lower cell stiffness than out-of-plane stresses that lead to bead rolling along the cell long axis (i.e., alignment of actin stress fibers) or at different angles (90° or 45°). However, chromatin stretching and ensuing DHFR gene upregulation by the in-plane mode are similar to those induced by the 45° stress mode. Disrupting stress fibers abolishes differences in cell stiffness, chromatin stretching, and DHFR gene upregulation under different force modes and inhibiting myosin II decreases cell stiffness, chromatin deformation, and gene upregulation. Theoretical modeling using discrete anisotropic stress fibers recapitulates experimental results and reveals underlying mechanisms of force-mode dependence. Our findings suggest that forces impact biological responses of living cells such as gene transcription via previously underappreciated means.


Assuntos
Cromatina/química , Fibras de Estresse/química , Tetra-Hidrofolato Desidrogenase/genética , Transcrição Genética/fisiologia , Regulação para Cima/fisiologia , Animais , Anisotropia , Fenômenos Biomecânicos/genética , Células CHO , Cromatina/metabolismo , Cricetulus , Compostos Heterocíclicos de 4 ou mais Anéis/farmacologia , Microscopia Intravital , Microscopia de Fluorescência , Miosina Tipo II/antagonistas & inibidores , Miosina Tipo II/metabolismo , Fibras de Estresse/efeitos dos fármacos , Fibras de Estresse/metabolismo , Estresse Mecânico , Transcrição Genética/efeitos dos fármacos , Regulação para Cima/efeitos dos fármacos
5.
Clin Imaging ; 67: 177-188, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32829150

RESUMO

OBJECTIVE: This study sought to assess the feasibility of diffusion tensor imaging (DTI) to noninvasively evaluate histological grade and lymph node metastasis in patients with rectal carcinoma (RC). METHODS: Thirty-seven consecutive patients with histologically confirmed RC were examined by 1.5-T MRI. DTI was performed using a single-shot echo-planar imaging sequence with b values of 0 and 1000 s/mm2 and motion-probing gradients in nine noncollinear directions. Fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) maps were compared with histopathological findings. RESULTS: The FA values (0.357 ±â€¯0.047) of the RCs were significantly lower than those of the normal rectal wall, muscle, prostate, and uterus (P < 0.001 for all), while the AD, MD, and RD values (1.221 ±â€¯0.131, 0.804 ±â€¯0.075, and 0.667 ±â€¯0.057 × 10-3 mm2/s, respectively) were also significantly lower than their respective normal values (P < 0.001 for all). The FA, AD, MD, and RD values for RC additionally showed significant inverse correlations with histological grades (r = -0.781, r = -0.750, r = -0.718, and r = -0.682, respectively; P < 0.001 for all). Further, the FA (0.430 vs. 0.611), AD (1.246 vs. 1.608 × 10-3 mm2/s), MD (0.776 vs. 1.036 × 10-3 mm2/s), and RD (0.651 vs. 0.824 × 10-3 mm2/s) (P < 0.001 for all) of the metastatic and nonmetastatic lymph nodes were significantly different. CONCLUSIONS: DTI may be clinically useful for the noninvasive evaluation of histological grade and lymph node metastasis in patients with RC.


Assuntos
Carcinoma/diagnóstico por imagem , Neoplasias Retais/diagnóstico por imagem , Anisotropia , Imagem de Difusão por Ressonância Magnética , Imagem de Tensor de Difusão/métodos , Imagem Ecoplanar , Feminino , Humanos , Linfonodos , Metástase Linfática , Imagem por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Útero
6.
Int J Mol Sci ; 21(15)2020 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-32751407

RESUMO

Enveloped viruses include the most dangerous human and animal pathogens, in particular coronavirus, influenza virus, and human immunodeficiency virus (HIV). For these viruses, receptor binding and entry are accomplished by a single viral envelope protein (termed the fusion protein), the structural changes of which trigger the remodeling and merger of the viral and target cellular membranes. The number of fusion proteins required for fusion activity is still under debate, and several studies report this value to range from 1 to 9 for type I fusion proteins. Here, we consider the earliest stage of viral fusion based on the continuum theory of membrane elasticity. We demonstrate that membrane deformations induced by the oblique insertion of amphipathic fusion peptides mediate the lateral interaction of these peptides and drive them to form into a symmetric fusion rosette. The pulling force produced by the structural rearrangements of the fusion protein ectodomains gives additional torque, which deforms the membrane and additionally stabilizes the symmetric fusion rosette, thus allowing a reduction in the number of fusion peptides needed for fusion. These findings can resolve the large range of published cooperativity indices for HIV, influenza, and other type I fusion proteins.


Assuntos
Infecções por HIV/virologia , HIV/fisiologia , Vírus da Influenza A/fisiologia , Influenza Humana/virologia , Peptídeos/química , Proteínas do Envelope Viral/química , Anisotropia , Membrana Celular/virologia , Humanos , Modelos Teóricos , Domínios Proteicos , Internalização do Vírus
7.
Exp Parasitol ; 217: 107959, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32795471

RESUMO

Helminths are parasitic worms that constitute a major public health problem. Conventional analytical techniques to evaluate helminth eggs in environmental samples rely on different steps, namely sedimentation, filtration, centrifugation, and flotation, to separate the eggs from a variety of particles and concentrate them in a pellet for direct observation under an optical microscope. To improve this process, a new approach was implemented in which various image processing algorithms were developed and implemented by a Helminth Egg Automatic Detector (HEAD). This allowed identification and quantification of pathogenic helminth eggs of global medical importance and it was found to be useful for relatively clean wastewater samples. After the initial version, two improvements were developed: first, a texture verification process that reduced the number of false positive results; and second, the establishment of the optimal thresholds (morphology and texture) for each helminth egg species. This second implementation, which was found to improve on the results of the former, was developed with the objective of using free software as a platform for the system. This does not require the purchase of a license, unlike the previous version that required a Mathworks® license to run. After an internal statistical verification of the system was carried out, trials in internationally recognized microbiology laboratories were performed with the aim of reinforcing software training and developing a web-based system able to receive images and perform the analysis throughout a web service. Once completed, these improvements represented a useful and cheap tool that could be used by environmental monitoring facilities and laboratories throughout the world; this tool is capable of identifying and quantifying different species of helminth eggs in otherwise difficult environmental samples: wastewater, soil, biosolids, excreta, and sludge, with a sensitivity and specificity for the TensorFlow (TF) model in the web service values of 96.82% and 97.96% respectively. Additionally, in the case of Ascaris, it may even differentiate between fertile and non-fertile eggs.


Assuntos
Helmintos/isolamento & purificação , Processamento de Imagem Assistida por Computador/métodos , Contagem de Ovos de Parasitas/instrumentação , Algoritmos , Animais , Anisotropia , Biossólidos/parasitologia , Fezes/parasitologia , Helmintos/classificação , Processamento de Imagem Assistida por Computador/normas , Distribuição Normal , Óvulo/classificação , Contagem de Ovos de Parasitas/normas , Sensibilidade e Especificidade , Esgotos/parasitologia , Solo/parasitologia , Águas Residuárias/parasitologia
8.
PLoS One ; 15(8): e0237654, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32797071

RESUMO

The present paper proposes a novel kernel adaptive filtering algorithm, where each Gaussian kernel is parameterized by a center vector and a symmetric positive definite (SPD) precision matrix, which is regarded as a generalization of scalar width parameter. In fact, different from conventional kernel adaptive systems, the proposed filter is structured as a superposition of non-isotropic Gaussian kernels, whose non-isotropy makes the filter more flexible. The adaptation algorithm will search for optimal parameters in a wider parameter space. This generalization brings the need of special treatment of parameters that have a geometric structure. In fact, the main contribution of this paper is to establish update rules for precision matrices on the Lie group of SPD matrices in order to ensure their symmetry and positive-definiteness. The parameters of this filter are adapted on the basis of a least-squares criterion to minimize the filtering error, together with an ℓ1-type regularization criterion to avoid overfitting and to prevent the increase of dimensionality of the dictionary. Experimental results confirm the validity of the proposed method.


Assuntos
Aprendizado de Máquina , Distribuição Normal , Algoritmos , Anisotropia , Dinâmica não Linear
9.
PLoS One ; 15(8): e0237909, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32853249

RESUMO

The influence of water content on mode I fracture toughness (KIc) of mudstones has been studied using semi-circular bend (SCB) specimens subject to three-point bendings. And the mudstone SCB specimens are divided into three types, including Type-A, Type-B and Type-C, corresponding to the three configurations of the bedding planes, including divider direction, arrester direction, and transverse direction, respectively. The test results show that the values of KIc for the three types of specimens are different due to the bedding structure, the Type-A specimens have the largest value of KIc for the same soak period, while the Type-C specimens possess the smallest value. As the soak period increases, the KIc of the three kinds of mudstone specimens decreases, and the fracture mechanisms of the specimens change gradually from the brittle failure form to the ductile failure form. Moreover, the standard deviation was used to quantify the anisotropy degree of the KIc of the mudstone samples. As the water content increases, the standard deviation increases from 0.057 to 0.139, which indicates a significant increase in anisotropy of the KIc of the mudstone specimens. In addition, the acoustic emission (AE) system was used to detect the AE events associated with the fracture initiation and propagation in the mudstone specimens for the different water content, with the raising water content, the cumulative AE events decrease, and the standard deviation of AE events increases, repesenting that the anisotropy of the AE events of the three types of specimens becomes more prominent. Further, the relationship between the tensile strength (σt) and the KIc of the three types of mudstone specimens for different water contents has been proved to be the linear relation.


Assuntos
Sedimentos Geológicos/química , Água/química , Acústica , Anisotropia , Difração de Raios X
10.
PLoS Comput Biol ; 16(7): e1008023, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32628719

RESUMO

In this study, we propose a new open-source simulation platform that comprises computer-aided design and computer-aided engineering tools for highly automated evaluation of electric field distribution and neural activation during Deep Brain Stimulation (DBS). It will be shown how a Volume Conductor Model (VCM) is constructed and examined using Python-controlled algorithms for generation, discretization and adaptive mesh refinement of the computational domain, as well as for incorporation of heterogeneous and anisotropic properties of the tissue and allocation of neuron models. The utilization of the platform is facilitated by a collection of predefined input setups and quick visualization routines. The accuracy of a VCM, created and optimized by the platform, was estimated by comparison with a commercial software. The results demonstrate no significant deviation between the models in the electric potential distribution. A qualitative estimation of different physics for the VCM shows an agreement with previous computational studies. The proposed computational platform is suitable for an accurate estimation of electric fields during DBS in scientific modeling studies. In future, we intend to acquire SDA and EMA approval. Successful incorporation of open-source software, controlled by in-house developed algorithms, provides a highly automated solution. The platform allows for optimization and uncertainty quantification (UQ) studies, while employment of the open-source software facilitates accessibility and reproducibility of simulations.


Assuntos
Encéfalo/fisiologia , Estimulação Encefálica Profunda , Reconhecimento Automatizado de Padrão , Software , Algoritmos , Anisotropia , Axônios/fisiologia , Mapeamento Encefálico , Simulação por Computador , Desenho Assistido por Computador , Análise de Fourier , Humanos , Processamento de Imagem Assistida por Computador , Modelos Neurológicos , Neurônios/fisiologia , Linguagens de Programação , Reprodutibilidade dos Testes
13.
PLoS One ; 15(7): e0235395, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32645032

RESUMO

There is increasing awareness that self-reported sleep abnormalities are negatively associated with brain structure and function in older adults. Less is known, however, about how objectively measured sleep associates with brain structure. We objectively measured at-home sleep to investigate how sleep architecture and sleep quality related to white matter microstructure in older adults. 43 cognitively normal, older adults underwent diffusion tensor imaging (DTI) and a sleep assessment within a six-month period. Participants completed the PSQI, a subjective measure of sleep quality, and used an at-home sleep recorder (Zeo, Inc.) to measure total sleep time (TST), sleep efficiency (SE), and percent time in light sleep (LS), deep sleep (DS), and REM sleep (RS). Multiple regressions predicted fractional anisotropy (FA) and mean diffusivity (MD) of the corpus callosum as a function of total PSQI score, TST, SE, and percent of time spent in each sleep stage, controlling for age and sex. Greater percent time spent in RS was significantly associated with higher FA (ß = 0.41, p = 0.007) and lower MD (ß = -0.30, p = 0.03). Total PSQI score, TST, SE, and time spent in LS or DS were not significantly associated with FA or MD (p>0.13). Percent time spent in REM sleep, but not quantity of light and deep sleep or subjective/objective measures of sleep quality, positively predicted white matter microstructure integrity. Our results highlight an important link between REM sleep and brain health that has the potential to improve sleep interventions in the elderly.


Assuntos
Cognição/fisiologia , Sono REM/fisiologia , Substância Branca/fisiologia , Idoso , Idoso de 80 Anos ou mais , Anisotropia , Difusão , Imagem de Difusão por Ressonância Magnética , Feminino , Humanos , Masculino , Análise de Regressão , Substância Branca/anatomia & histologia
14.
Zhongguo Dang Dai Er Ke Za Zhi ; 22(7): 711-715, 2020 Jul.
Artigo em Chinês | MEDLINE | ID: mdl-32669166

RESUMO

OBJECTIVE: To study the value of fractional anisotropy (FA) of regions of interest (ROI) on magnetic resonance diffusion tensor imaging (DTI) in bilirubin-induced neurological dysfunction in neonates. METHODS: A total of 91 neonates with hyperbilirubinemia who were hospitalized from January 2017 to January 2018 were enrolled. According to the peak level of total serum bilirubin, they were divided into three groups: mild/moderate increase (n=45), severe increase (n=35), and extremely severe increase (n=11). According to the presence or absence of abnormal neurological manifestations, they were divided into two groups: neurological dysfunction (n=20) and non-neurological dysfunction (n=71). Ten healthy full-term infants were enrolled as the control group. Head DTI was performed for all neonates to measure the FA values of the bilateral globus pallidus, the anterior limb of the internal capsule, the posterior limb of the internal capsule, and the cerebellar dentate nucleus. RESULTS: The extremely severe increase group had significantly lower FA values of the globus pallidus than the control, mild/moderate increase, and severe increase groups (P<0.05). The severe increase group had significantly lower FA values of the globus pallidus than the control group (P<0.05). The extremely severe increase group had significantly lower FA values of the posterior limb of the internal capsule than the control, mild/moderate increase, and severe increase groups (P<0.05). The neurological dysfunction group had significantly lower FA values of the globus pallidus and the posterior limb of the internal capsule than the non-neurological dysfunction group (P<0.05). CONCLUSIONS: Serum bilirubin level combined with the changes in the DTI FA values of the globus pallidus and the posterior limb of the internal capsule can be used to predict the injury of cerebral nuclei and white matter fibers.


Assuntos
Imagem de Tensor de Difusão , Substância Branca , Anisotropia , Bilirrubina , Encéfalo , Imagem de Difusão por Ressonância Magnética , Humanos , Recém-Nascido , Imagem por Ressonância Magnética , Espectroscopia de Ressonância Magnética
15.
Medicine (Baltimore) ; 99(24): e20411, 2020 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-32541463

RESUMO

OBJECTIVE: The aim of this systematic review and meta-analysis is to improve the understanding of the pathophysiology of tension-type headache (TTH), as well as propose avenues for future neuroimaging studies of TTH. METHODS: From the inception dates to May 1, 2020, a systematic literature will search in Medline (Ovid SP), Embase (Ovid SP), Cochrane Central Register of Controlled Trials, Web of Science, and 4 Chinese databases without limitation on language or publication. Additionally, International Clinical Trials Registry Platform , reference lists, and relevant gray literatures will be searched. After screening of eligible references, included studies will be determined according to included criteria, and then data extraction and a methodological quality assessment with a customized checklist will be conducted. Each process will be independently implemented by 2 reviewers, any disagreement will be resolved by consensus to the third researcher. If the extracted data is feasible, anisotropic effect-size version of signed differential mapping will be conducted to perform the meta-analysis of the structural and functional brain alterations in TTH patients.


Assuntos
Encéfalo/diagnóstico por imagem , Neuroimagem/métodos , Cefaleia do Tipo Tensional/fisiopatologia , Anisotropia , Encéfalo/irrigação sanguínea , Encéfalo/metabolismo , Mapeamento Encefálico/instrumentação , Lista de Checagem , Feminino , Humanos , Masculino , Neuroimagem/tendências , Avaliação de Resultados em Cuidados de Saúde , Prevalência , Cefaleia do Tipo Tensional/epidemiologia , Escala Visual Analógica
16.
Nat Commun ; 11(1): 2827, 2020 06 04.
Artigo em Inglês | MEDLINE | ID: mdl-32499507

RESUMO

Understanding the connection between the motion of the nuclei in a molecule and the rearrangement of its electrons lies at the heart of chemistry. While many experimental methods have been developed to probe either the electronic or the nuclear structure on the timescale of atomic motion, very few have been able to capture both these changes in concert. Here, we use time-resolved photoelectron imaging to probe the isomerisation coordinate on the excited state of an isolated model chromophore anion of the photoactive yellow protein. By probing both the electronic structure changes as well as nuclear dynamics, we are able to uniquely measure isomerisation about a specific bond. Our results demonstrate that the photoelectron signal dispersed in time, energy and angle combined with calculations can track the evolution of both electronic and geometric structure along the adiabatic state, which in turn defines that chemical transformation.


Assuntos
Proteínas de Bactérias/química , Elétrons , Fotorreceptores Microbianos/química , Anisotropia , Isomerismo , Fatores de Tempo
17.
Proc Natl Acad Sci U S A ; 117(27): 15650-15658, 2020 07 07.
Artigo em Inglês | MEDLINE | ID: mdl-32571937

RESUMO

Liquid-liquid phase separation of multivalent intrinsically disordered protein-RNA complexes is ubiquitous in both natural and biomimetic systems. So far, isotropic liquid droplets are the most commonly observed topology of RNA-protein condensates in experiments and simulations. Here, by systematically studying the phase behavior of RNA-protein complexes across varied mixture compositions, we report a hollow vesicle-like condensate phase of nucleoprotein assemblies that is distinct from RNA-protein droplets. We show that these vesicular condensates are stable at specific mixture compositions and concentration regimes within the phase diagram and are formed through the phase separation of anisotropic protein-RNA complexes. Similar to membranes composed of amphiphilic lipids, these nucleoprotein-RNA vesicular membranes exhibit local ordering, size-dependent permeability, and selective encapsulation capacity without sacrificing their dynamic formation and dissolution in response to physicochemical stimuli. Our findings suggest that protein-RNA complexes can robustly create lipid-free vesicle-like enclosures by phase separation.


Assuntos
Proteínas Intrinsicamente Desordenadas/química , Lipídeos/química , Nucleoproteínas/química , RNA/química , Anisotropia , Proteínas Intrinsicamente Desordenadas/genética , Lipídeos/genética , Complexos Multiproteicos/química , Complexos Multiproteicos/genética , Nucleoproteínas/genética , Pinças Ópticas , Transição de Fase , RNA/genética
18.
PLoS One ; 15(6): e0234340, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32579587

RESUMO

The experimental quantification and modeling of the multiaxial mechanical response of polymer membranes of coronary balloon catheters have not yet been carried out. Due to the lack of insights, it is not shown whether isotropic material models can describe the material response of balloon catheter membranes expanded with nominal or higher, supra-nominal pressures. Therefore, for the first time, specimens of commercial polyamide-12 balloon catheters membranes were investigated during uniaxial and biaxial loading scenarios. Furthermore, the influence of kinematic effects on the material response was observed by comparing results from quasi-static and dynamic biaxial extension tests. Novel clamping techniques are described, which allow to test even tiny specimens taken from the balloon membranes. The results of this study reveal the semi-compliant, nonlinear, and viscoelastic character of polyamide-12 balloon catheter membranes. Above nominal pressure, the membranes show a pronounced anisotropic mechanical behavior with a stiffer response in the circumferential direction. The anisotropic feature intensifies with an increasing strain-rate. A modified polynomial model was applied to represent the realistic mechanical response of the balloon catheter membranes during dynamic biaxial extension tests. This study also includes a compact set of constitutive model parameters for the use of the proposed model in future finite element analyses to perform more accurate simulations of expanding balloon catheters.


Assuntos
Angioplastia Coronária com Balão/instrumentação , Angioplastia Coronária com Balão/métodos , Nylons/química , Anisotropia , Fenômenos Biomecânicos/fisiologia , Cateteres Cardíacos/tendências , Análise de Elementos Finitos , Coração/fisiologia , Membranas/metabolismo , Modelos Biológicos , Miocárdio/metabolismo , Nylons/farmacologia , Estresse Mecânico , Resistência à Tração/fisiologia
19.
PLoS Comput Biol ; 16(6): e1007693, 2020 06.
Artigo em Inglês | MEDLINE | ID: mdl-32520928

RESUMO

Understanding cellular remodeling in response to mechanical stimuli is a critical step in elucidating mechanical activation of biochemical signaling pathways. Experimental evidence indicates that external stress-induced subcellular adaptation is accomplished through dynamic cytoskeletal reorganization. To study the interactions between subcellular structures involved in transducing mechanical signals, we combined experimental data and computational simulations to evaluate real-time mechanical adaptation of the actin cytoskeletal network. Actin cytoskeleton was imaged at the same time as an external tensile force was applied to live vascular smooth muscle cells using a fibronectin-functionalized atomic force microscope probe. Moreover, we performed computational simulations of active cytoskeletal networks under an external tensile force. The experimental data and simulation results suggest that mechanical structural adaptation occurs before chemical adaptation during filament bundle formation: actin filaments first align in the direction of the external force by initializing anisotropic filament orientations, then the chemical evolution of the network follows the anisotropic structures to further develop the bundle-like geometry. Our findings present an alternative two-step explanation for the formation of actin bundles due to mechanical stimulation and provide new insights into the mechanism of mechanotransduction.


Assuntos
Citoesqueleto de Actina/fisiologia , Resistência à Tração , Actinas/fisiologia , Animais , Anisotropia , Fenômenos Biomecânicos , Células Cultivadas , Simulação por Computador , Fibronectinas/fisiologia , Processamento de Imagem Assistida por Computador , Imageamento Tridimensional , Mecanotransdução Celular , Microscopia de Força Atômica , Miócitos de Músculo Liso/metabolismo , Miosinas/fisiologia , Ratos , Estresse Mecânico
20.
Nat Commun ; 11(1): 2924, 2020 06 10.
Artigo em Inglês | MEDLINE | ID: mdl-32522996

RESUMO

Biological membranes play pivotal roles in the cellular activities. Transmembrane proteins are the central molecules that conduct membrane-mediated biochemical functions such as signal transduction and substance transportation. Not only the molecular functions but also the supramolecular properties of the transmembrane proteins such as self-assembly, delocalization, orientation and signal response are essential for controlling cellular activities. Here we report anisotropic ligand responses of a synthetic multipass transmembrane ion channel. An unsymmetrical molecular structure allows for oriented insertion of the synthetic amphiphile to a bilayer by addition to a pre-formed membrane. Complexation with a ligand prompts ion transportation by forming a supramolecular channel, and removal of the ligand deactivates the transportation function. Biomimetic regulation of the synthetic channel by agonistic and antagonistic ligands is also demonstrated not only in an artificial membrane but also in a biological membrane of a living cell.


Assuntos
Transporte de Íons/fisiologia , Anisotropia , Biomimética , Bicamadas Lipídicas/química , Espectroscopia de Ressonância Magnética , Proteínas de Membrana/metabolismo , Microscopia de Fluorescência
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