Thromboembolic complications in critically ill COVID-19 patients are associated with impaired fibrinolysis.

BACKGROUND: There is emerging evidence for enhanced blood coagulation in coronavirus 2019 (COVID-19) patients, with thromboembolic complications contributing to morbidity and mortality. The mechanisms underlying this prothrombotic state remain enigmatic. Further data to guide anticoagulation strategies are urgently required. METHODS: We used viscoelastic rotational thromboelastometry (ROTEM) in a single-center cohort of 40 critically ill COVID-19 patients. RESULTS: Clear signs of a hypercoagulable state due to severe hypofibrinolysis were found. Maximum lysis, especially following stimulation of the extrinsic coagulation system, was inversely associated with an enhanced risk of thromboembolic complications. Combining values for maximum lysis with D-dimer concentrations revealed high sensitivity and specificity of thromboembolic risk prediction. CONCLUSIONS: The study identifies a reduction in fibrinolysis as an important mechanism in COVID-19-associated coagulopathy. The combination of ROTEM and D-dimer concentrations may prove valuable in identifying patients requiring higher intensity anticoagulation.

Physicochemical and emulsifying properties of mussel water-soluble proteins as affected by lecithin concentration.

The effects of lecithin addition at different concentrations (0-2.0%) on the physicochemical and emulsifying properties of mussel water-soluble proteins (MWP) were investigated. In solution system, low lecithin concentration (0.5%-1.0%) induced the aggregation and increased turbidity of composite particles. Lecithin addition caused changes in secondary structure and induced partial unfolding of MWP. Hydrophobic interactions between MWP and lecithin may contribute to the exposure of chromophores and hydrophobic groups of MWP. The interfacial tension decreased with lecithin addition. However, at a high lecithin concentration (1.5%-2.0%), the degree of aggregation and state of unfolding alleviated due to competitive adsorption. In emulsion system, with the low concentration of lecithin addition (0.5%-1.0%), droplet size and surface charge of emulsion decreased. The emulsion activity index, emulsion stability index, percentage of adsorbed protein increased. Both creaming stability and viscoelastic properties improved. At an intermediate lecithin concentration (1.0%), the emulsion showed the highest physical stability, while further addition of lecithin caused a slight deterioration in emulsifying properties. Overall, these results indicated the possibility that the lecithin-MWP mixed emulsifiers can be used to obtain emulsions with desirable properties.

Ovalbumin and guar gum foam and its surface properties as influenced by sucrose and sorbitol.

The surface properties and foaming of ovalbumin and guar gum aqueous solutions was investigated in the presence of sucrose or sorbitol. All solutions had a broad particle size distribution (395.60 at 1137.50 nm). Higher ovalbumin concentrations had lower equilibrium surface tension and higher absolute values of the zeta potential, regardless the presence of sucrose or sorbitol. Mixtures containing ovalbumin and guar gum resulted in a predominantly elastic character of the air-water interface probably due to the formation of a complex (hydrogen bonding and/or hydrophobic interactions) between ovalbumin and guar gum. Besides, the increase in guar gum concentration enhanced the elasticity of the surface film. Higher concentrations of both polymers were required to provide higher kinetic stability to the system, although the increase in guar gum concentration reduced foam capacity due to the increase in the apparent viscosity. Foams formed in the presence of sucrose or sorbitol showed similar half-lives.

Viscoelasticity of articular cartilage: Analysing the effect of induced stress and the restraint of bone in a dynamic environment.

The aim of this study was to determine the effect of the induced stress and restraint provided by the underlying bone on the frequency-dependent storage and loss stiffness (for bone restraint) or modulus (for induced stress) of articular cartilage, which characterise its viscoelasticity. Dynamic mechanical analysis has been used to determine the frequency-dependent viscoelastic properties of bovine femoral and humeral head articular cartilage. A sinusoidal load was applied to the specimens and out-of-phase displacement response was measured to determine the phase angle, the storage and loss stiffness or modulus. As induced stress increased, the storage modulus significantly increased (p < 0.05). The phase angle decreased significantly (p < 0.05) as the induced stress increased; reducing from 13.1° to 3.5°. The median storage stiffness ranged from 548N/mm to 707N/mm for cartilage tested on-bone and 544N/mm to 732N/mm for cartilage tested off-bone. On-bone articular cartilage loss stiffness was frequency independent (p > 0.05); however, off-bone, articular cartilage loss stiffness demonstrated a logarithmic frequency-dependency (p < 0.05). In conclusion, the frequency-dependent trends of storage and loss moduli of articular cartilage are dependent on the induced stress, while the restraint provided by the underlying bone removes the frequency-dependency of the loss stiffness.

Strain rate dependent hyperelastic stress-stretch behavior of a silica nanoparticle reinforced poly (ethylene glycol) diacrylate nanocomposite hydrogel.

Poly (ethylene glycol) diacrylate (PEGDA) derivatives are important biomedical materials. PEGDA based hydrogels have emerged as one of the popular regenerative orthopedic materials. This work aims to study the mechanical behavior of a PEGDA based silica nanoparticle (NP) reinforced nanocomposite (NC) hydrogel at physiological strain rates. The work combines materials fabrication, mechanical experiments, mathematical modeling and structural analysis. The strain rate dependent stress-stretch behaviors were observed, analyzed and quantified. Visco-hyperelasticity was identified as the deformation mechanism of the nano-silica/PEGDA NC hydrogel. NPs showed significant effect on both initial shear modulus and viscoelastic materials properties. A structure-based quasi-linear viscoelastic (QLV) model was constructed and capable to describe the visco-hyperelastic stress-stretch behavior of the NC hydrogel. A group of unified material parameters was extracted by the model from the stress-stretch curves obtained at different strain rates. Visco-hyperelastic behavior of NP/polymer interphase was not only identified but also quantified. The work could provide guidance to the structural design of next-generation NC hydrogel.

Dynamic analysis of bulk-fill composites: Effect of food-simulating liquids.

This study investigated the effect of food simulating liquids on visco-elastic properties of bulk-fill restoratives using dynamic mechanical analysis. One conventional composite (Filtek Z350 [FZ]), two bulk-fill composites (Filtek Bulk-fill [FB] and Tetric N Ceram [TN]) and a bulk-fill giomer (Beautifil-Bulk Restorative [BB]) were evaluated. Specimens (12 × 2 × 2mm) were fabricated using customized stainless steel molds. The specimens were light-cured, removed from their molds, finished, measured and randomly divided into six groups. The groups (n = 10) were conditioned in the following mediums for 7 days at 37°C: air (control), artificial saliva (SAGF), distilled water, 0.02N citric acid, heptane, 50% ethanol-water solution. Specimens were assessed using dynamic mechanical testing in flexural three-point bending mode and their respective mediums at 37°C and a frequency range of 0.1-10Hz. The distance between the supports were fixed at 10mm and an axial load of 5N was employed. Data for elastic modulus, viscous modulus and loss tangent were subjected to ANOVA/Tukey's tests at significance level p < 0.05. Significant differences in visco-elastic properties were observed between materials and mediums. Apart from bulk-fill giomer, elastic modulus was the highest after conditioning in heptane. No apparent trends were noted for viscous modulus. Generally, loss tangent was the highest after conditioning in ethanol. The effect of food-simulating liquids on the visco-elastic properties of bulk-fill composites was material and medium dependent.

Tromboelastometría: ¿determinación centralizada en el laboratorio o prueba a la cabecera del paciente? Experiencia en nuestro hospital como test centralizado / Thromboelastometry: centralized test in the laboratory or point of care testing? Experience in our hospital as centralized test

Introducción. La tromboelastografía es la herramienta que permite medir in vitro las propiedades viscoelásticas de la sangre de una manera dinámica y global, integrando las diferentes fases de la coagulación y fibrinólisis. Existen en el mercado dos dispositivos semiautomatizados: el tromboelastograma y el tromboelastómetro rotacional. Material y métodos. Se ha realizado un estudio observacional descriptivo retrospectivo de las solicitudes de tromboelastometría en nuestro hospital desde la implementación del protocolo con la técnica centralizada desde el laboratorio. Se ha evaluado el número de solicitudes, los servicios peticionarios y el grado de cumplimentación de la petición al laboratorio. Así mismo, hemos realizado una encuesta de satisfacción dirigida al personal facultativo del Servicio de Anestesia y Reanimación. El periodo estudiado fue de julio del 2012 a enero del 2016. Resultados. Desde el establecimiento del protocolo hasta la actualidad se ha producido un incremento y una consolidación de la técnica de tromboelastometría en nuestro hospital. La mayor parte de las solicitudes proceden de los Servicios de Anestesia y Reanimación (36,5%) y Angiología y Cirugía Cardiovascular (30,1%). En cuanto a la encuesta de satisfacción, los resultados obtenidos muestran una aceptación positiva por parte de los facultativos tanto con el protocolo como con los tiempos de respuesta obtenidos. Conclusiones. Estableciendo un protocolo elaborado y consensuado entre el laboratorio y los servicios solicitantes, podemos garantizar el estricto cumplimiento del mismo y que los tiempos de respuesta difieran poco de los obtenidos cuando esta técnica se realiza en la cabecera del paciente, permitiendo así dar un servicio global a todo el hospital (AU)

Introduction. Thromboelastography is the tool that allows in vitro measurement of the viscoelastic properties of the blood in a dynamic and comprehensive way, integrating the different phases of coagulation and fibrinolysis. There are two semi-automated devices on the market: the thromboelastogram and the rotational thromboelastometry analyzer. Material and methods. We have conducted a descriptive observatory retrospective study of the thromboelastography requests in our hospital after the implementation of the protocol. It has been evaluated the number of petitions, the petitioners services and the degree of filling of the application laboratory. Likewise, we have performed a satisfaction survey aimed at the medical staff of the Anesthesia and Resuscitation Service. The studied period was from July 2012 until January 2016. Results. From the protocol introduction in our hospital has been produced an increase and a consolidation of the thromboelastography. Most of the requests came from the Anesthesia and Resuscitation Service (36.5%) and Angiology and Cardiovascular Surgery Service (30.1%). As for the satisfaction survey, the results show a positive acceptance by the medical staff both of the protocol as of the response times obtained. Conclusions. By establishing a protocol elaborated and agreed between the laboratory and the requesting departments, we can guarantee the strict compliance of the same and that the response times only differ a little from the obtained ones when this technique is realized as point of care testing, providing a global service to the whole hospital (AU)

Importance of the PMMA viscoelastic rheology on the reduction of the leakage risk during osteoporotic bone augmentation: A numerical leakage model through a porous media.

Osteoporotic fractures poses one of the most problematic health issues that affects millions of people by weakening their bones (Osteoporosis). Polymethylmethacrylate (PMMA) cement is usually used to augment the bone and stabilize the fractures. Despite the benefit of using PMMA, it might cause a leakage where the cement undesirably access the surrounding tissues or vessels and lead to a serious complications. Consequently, it is important to study the leakage phenomenon and associated geometric and operation interactions. Although the experimental leakage models have been reported in many studies, a representative numerical leakage model is not exist. Therefore, the objectives of the present paper are to: (a) to develop and validate a representative numerical leakage model; and (b) to investigate numerically and analytically the importance of the rheological parameters (viscosity and relaxation time) on the cement flow to reduce the risk of leakage. ANSYS Polyflow was utilized to implement a 2D numerical leakage model to study the interaction of complex rheological parameters of the cement with the operational and geometrical structure of the representative porous media. In this model, the cement (represented by the upper-convected Maxwell model) flows from the entrance (tip of an 8 gauge cannula) through a porous media with a leakage path (blood vessels) toward the output (Bottom side). The verified and validated numerical leakage model showed the importance of the elastic and viscous part of the cement to control the uniformity of the distributed cement and augmentation pressure, respectively. Moreover, increasing the flow rate can lead to reduce the risk of leakage since the elastic effect will increase. Geometrical parameters of the porous media has a minor effect on changing the elasticity and subsequently on the uniformity of the distributed cement. In conclusion, Cement rheological parameters are found to be the most influential parameters to reduce the risk of leakage by controlling the uniformity of the distributed cement and the augmentation pressure.

Adhesion of bubbles and drops to solid surfaces, and anisotropic surface tensions studied by capillary meniscus dynamometry.

Here, we review the principle and applications of two recently developed methods: the capillary meniscus dynamometry (CMD) for measuring the surface tension of bubbles/drops, and the capillary bridge dynamometry (CBD) for quantifying the bubble/drop adhesion to solid surfaces. Both methods are based on a new data analysis protocol, which allows one to decouple the two components of non-isotropic surface tension. For an axisymmetric non-fluid interface (e.g. bubble or drop covered by a protein adsorption layer with shear elasticity), the CMD determines the two different components of the anisotropic surface tension, σs and σφ, which are acting along the "meridians" and "parallels", and vary throughout the interface. The method uses data for the instantaneous bubble (drop) profile and capillary pressure, but the procedure for data processing is essentially different from that of the conventional drop shape analysis (DSA) method. In the case of bubble or drop pressed against a substrate, which forms a capillary bridge, the CBD method allows one to determine also the capillary-bridge force for both isotropic (fluid) and anisotropic (solidified) adsorption layers. The experiments on bubble (drop) detachment from the substrate show the existence of a maximal pulling force, Fmax, that can be resisted by an adherent fluid particle. Fmax can be used to quantify the strength of adhesion of bubbles and drops to solid surfaces. Its value is determined by a competition of attractive transversal tension and repulsive disjoining pressure forces. The greatest Fmax values have been measured for bubbles adherent to glass substrates in pea-protein solutions. The bubble/wall adhesion is lower in solutions containing the protein HFBII hydrophobin, which could be explained with the effect of sandwiched protein aggregates. The applicability of the CBD method to emulsion systems is illustrated by experiments with soybean-oil drops adherent to hydrophilic and hydrophobic substrates in egg yolk solutions. The results reveal how the interfacial rigidity, as well as the bubble/wall and drop/wall adhesion forces, can be quantified and controlled in relation to optimizing the properties of foams and emulsions.

Viscoelastic and ultrastructural characteristics of whole blood and plasma in Alzheimer-type dementia, and the possible role of bacterial lipopolysaccharides (LPS).

Alzheimer-type dementia (AD) is a neurodegenerative disorder and the most common form of dementia. Patients typically present with neuro- and systemic inflammation and iron dysregulation, associated with oxidative damage that reflects in hypercoagulability. Hypercoagulability is closely associated with increased fibrinogen and in AD patients fibrinogen has been implicated in the development of neuroinflammation and memory deficits. There is still no clear reason precisely why (a) this hypercoagulable state, (b) iron dysregulation and (c) increased fibrinogen could together lead to the loss of neuronal structure and cognitive function. Here we suggest an alternative hypothesis based on previous ultrastructural evidence of the presence of a (dormant) blood microbiome in AD. Furthermore, we argue that bacterial cell wall components, such as the endotoxin lipopolysaccharide (LPS) of Gram-negative strains, might be the cause of the continuing and low-grade inflammation, characteristic of AD. Here, we follow an integrated approach, by studying the viscoelastic and ultrastructural properties of AD plasma and whole blood by using scanning electron microscopy, Thromboelastography (TEG®) and the Global Thrombosis Test (GTT®). Ultrastructural analysis confirmed the presence and close proximity of microbes to erythrocytes. TEG® analysis showed a hypercoagulable state in AD. TEG® results where LPS was added to naive blood showed the same trends as were found with the AD patients, while the GTT® results (where only platelet activity is measured), were not affected by the added LPS, suggesting that LPS does not directly impact platelet function. Our findings reinforce the importance of further investigating the role of LPS in AD.

Persistent corneal opacity after descemet stripping automated endothelial keratoplasty suggesting inert material deposits into the interface.

PURPOSE: To report a case of interface deposits after Descemet stripping automated endothelial keratoplasty (DSAEK) imaged by means of an electron microscope. METHODS: An 88-year-old man was referred with a history of corneal edema resulting from pseudophakic bullous keratopathy. A DSAEK was performed on his left eye without complications; however, the follow-up examination revealed a well-attached graft with persistent interface opacities at the donor-recipient interface. The DSAEK was repeated in this eye 1 year after the first surgery because of these corneal opacities that interfered with his vision. RESULTS: In the immediate postoperative period, the patient had adequate visual acuity with intact graft placement and a clear interface. Pathology and electron microscope analysis were performed on the removed endothelial graft, which revealed diffuse particles on the stromal surface of the endothelial graft. CONCLUSIONS: A repeated DSAEK procedure sufficiently removed this patient's corneal opacities and improved the visual acuity. The opacity is believed to have occurred because of residual viscoelastic material, which was used to maintain anterior chamber volume during surgery. This solution must be thoroughly removed to avoid similar complications.

Viscoelastic properties of fibrinogen adsorbed onto poly(ethylene terephthalate) surfaces by QCM-D.

In presented study a new approach using QCM-D for biocompatibility determination was introduced. The adsorption of fibrinogen on PET and modified PET surfaces was monitored in situ using QCM-D. Protein layer thicknesses were estimated on the basis of a Voight based viscoelastic model. The hydrophilicities and morphologies of the surfaces were investigated using a goniometer and AFM. The results showed that PET surfaces coated with sulphated polysaccharides are more hydrophilic and more fibrinogen-repulsive than non-modified PET surfaces. QCM-D equipped with QTools modelling software is well-applicable to the characterisation of surface properties and can be optimised for biocompatibility determination.

Tension-compression viscoelastic behaviors of the periodontal ligament.

BACKGROUND/PURPOSE: Although exhaustively studied, the mechanism responsible for tooth support and the mechanical properties of the periodontal ligament (PDL) remain a subject of considerable controversy. In the past, various experimental techniques and theoretical analyses have been employed to tackle this intricate problem. The aim of this study was to investigate the viscoelastic behaviors of the PDL using three-dimensional finite element analysis. METHODS: Three dentoalveolar complex models were established to simulate the tissue behaviors of the PDL: (1) deviatoric viscoelastic model; (2) volumetric viscoelastic model; and (3) tension-compression volumetric viscoelastic model. These modified models took into consideration the presence of tension and compression along the PDL during both loading and unloading. The inverse parameter identification process was developed to determine the mechanical properties of the PDL from the results of previously reported in vitro and in vivo experiments. RESULTS: The results suggest that the tension-compression volumetric viscoelastic model is a good approximation of normal PDL behavior during the loading-unloading process, and the deviatoric viscoelastic model is a good representation of how a damaged PDL behaves under loading conditions. Moreover, fluid appears to be the main creep source in the PDL. CONCLUSION: We believe that the biomechanical properties of the PDL established via retrograde calculation in this study can lead to the construction of more accurate extra-oral models and a comprehensive understanding of the biomechanical behavior of the PDL.

Layer-by-layer self-assembly of chitosan and poly(γ-glutamic acid) into polyelectrolyte complexes.

Chitosan (Ch) is a nontoxic and biocompatible polysaccharide extensively used in biomedical applications. Ch, as a polycation, can be combined with anionic polymers by layer-by-layer (LbL) self-assembly, giving rise to multilayered complexed architectures. These structures can be used in tissue engineering strategies, as drug delivery systems, or artificial matrices mimicking the extracellular microenvironment. In this work, Ch was combined with poly(γ-glutamic acid) (γ-PGA). γ-PGA is a polyanion, which was microbially produced, and is known for its low immunogenic reaction and low cytotoxicity. Multilayered ultrathin films were assembled by LbL, with a maximum of six layers. The interaction between both polymers was analyzed by: ellipsometry, quartz crystal microbalance with dissipation, Fourier transform infrared spectroscopy, atomic force microscopy, and zeta potential measurements. Ch/γ-PGA polyelectrolyte multilayers (PEMs) revealed no cytotoxicity according to ISO 10993-5. Overall, this study demonstrates that Ch can interact electrostatically with γ-PGA forming multilayered films. Furthermore, this study provides a comprehensive characterization of Ch/γ-PGA PEM structures, elucidating the contribution of each layer for the nanostructured films. These model surfaces can be useful substrates to study cell-biomaterial interactions in tissue regeneration.

Pathophysiology of osteoarthritis: evidence against the viscoelastic theory.

OBJECTIVES: Whether changes in the hyaluronan moiety of synovial fluid are associated with osteoarthritis (OA) is unresolved experimentally, notwithstanding frequent statements in the literature that the disease leads to degraded hyaluronan. We evaluated this hypothesis by comparing the molecular weight and concentration of hyaluronan in synovial fluid from patients with and without OA. METHODS: Synovial fluid was obtained by needle aspiration from patients with advanced OA (Kellgren-Lawrence Grade IV) and from patients with no radiological or arthroscopic evidence of OA. The distribution of the molecular weight of hyaluronan was measured using both gel electrophoresis and size-exclusion chromatography, and hyaluronan concentration was determined by immunosorbent assay and differential refractometry. RESULTS: The distributions of molecular weight were highly variable within each group of patients; the average distributions, however, were identical in the 2 groups. The average concentration of hyaluronan also did not differ statistically between the 2 groups. CONCLUSIONS: We found no evidence of hyaluronan degradation in synovial fluid of patients with OA. Commonly expressed opinion in the literature to the contrary may have resulted from a failure to adequately consider the limitations of previous experimental studies.