Rheometry and associated techniques for blood coagulation studies

Blood Clot Dynamics and Fibrinolysis Impairment in Cancer: The Role of Plasma Histones and DNA

BACKGROUND

Blood viscoelasticity and plasma protein levels can play an important role in the diagnosis and prognosis of cancer. However, the role of histones and DNA in modulating blood clot properties remains to be investigated. This study investigates the differences in blood viscoelasticity and plasma protein levels among cancer patients, individuals with other diseases, and healthy individuals.

METHODS

Blood samples were collected from 101 participants, including 45 cancer patients, 22 healthy individuals, and 34 individuals with other diseases. Rheological properties of clots formed in vitro by reconstituted elements of fibrinogen or plasma were analyzed with an Anton Paar Rheometer, USA. Plasma protein levels of D-dimer, TPA, EPCR, fibrinogen, and histone H3 were measured through ELISA. Blood clots were formed with or without DNA and histones (H3) by adding thrombin and calcium to plasma samples, and were evaluated for viscoelasticity, permeability, and degradation.

RESULTS

Cancer patients show higher blood viscoelasticity and plasma D-dimer levels compared to healthy individuals and individuals with other diseases. Our in vitro analysis showed that the addition of histone to the plasma results in a significant decrease in viscoelasticity and mean fiber thickness of the clot formed thereafter. In parallel studies, using plasma from patients, DNA and histones were detected in fibrin clots and were associated with less degradation by t-PA. Moreover, our results show that the presence of DNA and histones not only increases clots' permeability, but also makes them more prone to degradation.

CONCLUSIONS

Plasma histones and DNA affect the structure of the clot formed and induce defective fibrinolysis. Moreover, the increased viscoelastic properties of plasma from cancer patients can be used as potential biomarkers in cancer prognosis.

A Multichannel Portable Platform With Embedded Thermal Management for Miniaturized Dielectric Blood Coagulometry

This article presents a standalone, multichannel, miniaturized impedance analyzer (MIA) system for dielectric blood coagulometry measurements with a microfluidic sensor termed ClotChip. The system incorporates a front-end interface board for 4-channel impedance measurements at an excitation frequency of 1 MHz, an integrated resistive heater formed by a pair of printed-circuit board (PCB) traces to keep the blood sample near a physiologic temperature of 37 °C, a software-defined instrument module for signal generation and data acquisition, and a Raspberry Pi-based embedded computer with 7-inch touchscreen display for signal processing and user interface. When measuring fixed test impedances across all four channels, the MIA system exhibits an excellent agreement with a benchtop impedance analyzer, with rms errors of ≤0.30% over a capacitance range of 47-330 pF and ≤0.35% over a conductance range of 2.13-10 mS. Using in vitro-modified human whole blood samples, the two ClotChip output parameters, namely, the time to reach a permittivity peak (Tpeak) and maximum change in permittivity after the peak (Δϵr,max) are assessed by the MIA system and benchmarked against the corresponding parameters of a rotational thromboelastometry (ROTEM) assay. Tpeak exhibits a very strong positive correlation (r = 0.98, p < 10-6, n = 20) with the ROTEM clotting time (CT) parameter, while Δϵr,max exhibits a very strong positive correlation (r = 0.92, p < 10-6, n = 20) with the ROTEM maximum clot firmness (MCF) parameter. This work shows the potential of the MIA system as a standalone, multichannel, portable platform for comprehensive assessment of hemostasis at the point-of-care/point-of-injury (POC/POI).

A comparative study into the effects of venous and arterial blood on clot microstructure in critically unwell patients. Assessment of the diagnostic potential of a biomarker of haemostasis

Blood for coagulation analysis can be sampled from the arterial or venous system in intensive care units (ICU). The determination of clot microstructure and strength by fractal analysis (df) gives valuable information in a range of vascular haemostatic disease and sepsis. We aimed to determine if df could be measured equally and comparatively in arterial or venous blood, and 45 critically ill patients in an ICU were recruited. df was found to be readily measured in arterial blood with results comparable to those in venous blood and that add value of df as a potential marker of haemostasis in these patients.

Evaluation of Blood Coagulation by Optical Vortex Tracking

Blood coagulation is a complicated dynamic process that maintains the blood's fluid state and prevents uncontrollable bleeding. The real-time monitoring of coagulation dynamics is critical for blood transfusion guidance, emergency management of trauma-induced coagulopathy, perioperative bleeding, and targeted hemostatic therapy. Here, we utilize optical vortex dynamics to detect the blood coagulation dynamic process in a rapid and non-contact manner. To characterize the temporal changes in viscoelastic properties of blood during coagulation, we track the stochastic motion of optical vortices in the time-varying speckles reflected from 100 blood samples with varied coagulation profiles. The mean square displacement (MSD) of the vortices increases nonlinearly with time lag during blood coagulation reminiscent of the particles in viscoelastic fluids. The MSD curves with coagulation time are similar to the tracings of thromboelastography (TEG) during the blood coagulation. The retrieved coagulation parameters, such as reaction time and activated clotting time measured using the optical vortex method, exhibit a close correlation to those parameters acquired from TEG. These results demonstrate the feasibility of the optical vortex method for monitoring blood coagulation at the point of care. Our method is also applicable to measuring the viscoelasticity of complex fluids and turbid soft matters.

In Vivo Effects of Balanced Crystalloid or Gelatine Infusions on Functional Parameters of Coagulation and Fibrinolysis: A Prospective Randomized Crossover Study

Prudent administration of fluids helps restore or maintain hemodynamic stability in the setting of perioperative blood loss. However, fluids may arguably exacerbate the existing coagulopathy. We sought to investigate the influence of balanced crystalloid and synthetic gelatine infusions on coagulation and fibrinolysis in healthy volunteers. This prospective randomized crossover study included 25 males aged 18–30 years. Infusions performed included 20 mL/kg of a balanced crystalloid solution (Optilyte^®) or 20 mL/kg of gelatine 26.500 Da (Geloplasma^®) in a random order over a period of 2 weeks. Laboratory analysis included conventional coagulation parameters and rotational thromboelastometry (ROTEM) assays. We confirmed a decrease in fibrinogen concentration and the number of platelets, and prolongation of PT after infusions. Compared to baseline values, differences in the ROTEM assays’ results after infusions signified the decrease in coagulation factors and fibrinogen concentration, causing impaired fibrin polymerization and clot structure. The ROTEM indicator of clot lysis remained unaffected. In the case of both Optilyte^® and Geloplasma^®, the results suggested relevant dilution. Gelatine disrupted the process of clot formation more than balanced crystalloid. Infusions of both crystalloid and saline-free colloid solutions causing up to 30% blood dilution cause significant dilution of the coagulation factors, platelets, and fibrinogen. However, balanced crystalloid infusion provides less infusion-induced coagulopathy compared to gelatine.

Passive high-frequency microrheology of blood

Indicative of various pathologies, blood properties are under intense scrutiny. The hemorheological characteristics are traditionally gauged by bulk, low-frequency indicators that average out critical information about the complex, multi-scale, and multi-component structure. In particular, one cannot discriminate between the erythrocytes contribution to global rheology and the impact of plasma. Nevertheless, in their fast stochastic movement, before they encounter each other, the erythrocytes probe the subtle viscoelasticity of their protein-rich environment. Thus, if these short time scales can be resolved experimentally, the plasma properties could be determined without having to separate the blood components; the blood is practically testing itself. This microrheological description of blood plasma provides a direct link between the composition of whole blood and its coagulability status. We present a parametric model for the viscoelasticity of plasma, which is probed by the erythrocytes over frequency ranges of kilohertz in a picoliter-sized volume. The model is validated both in vitro, using artificial hemo-systems where the composition is controlled, as well as on whole blood where continuous measurements provide real-time information. We also discuss the possibility of using this passive microrheology as an in vivo assay for clinically relevant situations where the blood clotting condition must be observed and managed continuously for diagnosis or during therapeutic procedures at different stages of hemostatic and thrombotic processes.

TEG® and ROTEM® Traces: Clinical Applications of Viscoelastic Coagulation Monitoring in Neonatal Intensive Care Unit

The concentration of the majority of hemostatic proteins differs considerably in early life, especially in neonates compared to adulthood. Knowledge of the concept of developmental hemostasis is an essential prerequisite for the proper interpretation of conventional coagulation tests (CCT) and is critical to ensure the optimal diagnosis and treatment of hemorrhagic and thrombotic diseases in neonatal age. Viscoelastic tests (VETs) provide a point-of-care, real-time, global, and dynamic assessment of the mechanical properties of the coagulation system with the examination of both cellular and plasma protein contributions to the initiation, formation, and lysis of clots. In this work, we provide a narrative review of the basic principles of VETs and summarize current evidence regarding the two most studied point-of-care VETs, thromboelastography (TEG^®) and rotational thromboelastometry (ROTEM^®), in the field of neonatal care. A literature analysis shows that viscoelastic hemostatic monitoring appears to be a useful additive technique to CCT, allowing targeted therapy to be delivered quickly. These tools may allow researchers to determine the neonatal coagulation profile and detect neonatal patients at risk for postoperative bleeding, coagulation abnormalities in neonatal sepsis, and other bleeding events in a timely manner, guiding transfusion therapies using the goal-oriented transfusion algorithm. However, diagnosis and treatment algorithms incorporating VETs for neonatal patients in a variety of clinical situations should be developed and applied to improve clinical outcomes. Further studies should be performed to make routinary diagnostic and therapeutic application possible for the neonatal population.

Dynamic assessment of plasma clotting in samples with distinct fibrinogen concentrations using impulsive acoustic radiation force

While some diseases reduce fibrinogen concentration, others increase the amount of this clotting factor in the blood. Some studies have shown that the fibrinogen concentration in the blood is related to the stiffness of the formed clot. Hence, the aim of this study was to employ an ultrasonic method based on impulsive acoustic radiation force (IARF) to identify the fibrinogen concentration (coagulation factor I) in a plasma sample by means of peak-displacement (PD), time of peak-displacement (TPD), and shear modulus (μ) as well as to identify the change of plasma samples during the clot formation process. The IARF-based ultrasonic system transmitted bursts with a frequency of 2.03 MHz, duration of 246.31 µs, amplitude of 118 VPP, and pulse with 1.25 Hz repetition frequency to generate an IARF on a glass sphere (2.99 mm in diameter and 2500 kg/m3 in density) embedded in a plasma sample, causing a displacement that was monitored by a pulse-echo system with a center frequency of 4.89 MHz. The values of the shear moduli were 124.14 ± 3.02, 556.99 ± 11.76, and 670.39 ± 9.77 Pa, for fibrinogen concentrations of 1.2, 2.4, and 3.6 g/L 20 to 36 min after the beginning of the coagulation process. The TPD values obtained in the same period were 5.28 ± 0.09, 3.03 ± 0.02, and 2.83 ± 0.01 s. The results indicate that an IARF-based ultrasonic system can be used clinically because it uses small amounts of plasma and has the ability to detect differences in PD, TPD, and μ as a function of fibrinogen concentrations.

The effect of diabetic ketoacidosis (DKA) and its treatment on clot microstructure: Are they thrombogenic?

BACKGROUND

Diabetic ketoacidosis (DKA) is a medical emergency with a high mortality rate and is associated with severe metabolic acidosis and dehydration. DKA patients have an increased risk of arterial and venous thromboembolism, however little is known about this metabolic derangement in the first 24 hours of admission and to assess its effect on coagulation. We therefore utilised a novel functional marker of clot microstructure (fractal dimension - df) to assess these changes within the first 24 hours.

METHODS

Prospective single centre observational study to demonstrate whether the tendency of blood clot formation differs in DKA patients.

RESULTS

15 DKA patients and 15 healthy matched controls were recruited. Mean df in the healthy control group was 1.74±0.03. An elevated df of 1.78±0.07 was observed in patients with DKA on admission. The mean pH on admission was 7.14±0.13 and the lactate was 3.6±2.0. df changed significantly in response to standard treatment and was significantly reduced to 1.68±0.09 (2-6& h) and to 1.66±0.08 at 24& h (p < 0.01 One-way ANOVA). df also correlated significantly with lactate and pH (Pearson correlation coefficient 0.479 and -0.675 respectively, p < 0.05).

CONCLUSIONS

DKA patients at presentation have a densely organising less permeable thrombogenic clot microstructure as evidenced by high df. These structural changes are due to a combination of dehydration and a profound metabolic acidosis, which was reversed with treatment. These changes were not mirrored in standard clinical markers of thromboge-nicity.

The treatment effect of rivaroxaban on clot characteristics in patients who present acutely with first time deep vein thrombosis

BACKGROUND

The acute vascular disease deep vein thrombosis (DVT) requires oral anticoagulants to prevent progression. Monitoring therapeutic efficacy of direct oral anticoagulants (DOAC), including rivaroxaban, is problematic as no reliable test is available. Advances in rheometry have led to the development of a functional coagulation biomarker using Gel Point (GP) analysis which assesses clot structure formation. The biomarker measures incipient clot formation time (TGP) and quantifies fibrin clot structure in terms of fractal dimension (df).

OBJECTIVE

This study aimed to investigate clot structure formation in first time DVT and the effect of rivaroxaban treatment.

METHODS

This prospective observational cohort study measured the GP and standard laboratory markers at three sample points: pre-treatment and at 20 and 60 days following 15 mg BD and 20 mg OD rivaroxaban respectively.

RESULTS

Forty DVT patients (mean age 64 years [SD±14.8]; 23 males, 17 female) were recruited. The results show that DVT vs non-DVT patients did not have a significantly different GP profile (df: 1.72±0.06 vs 1.70±0.06 and TGP: 267±68 sec vs 262±73 sec) with both within the defined healthy index. In addition, rivaroxaban therapy increased TGP to 392 s (±135 s) after 20 days, and subsequently increased to 395 s (±194 s) at 60 days but did not significantly increase df (from 1.69±0.05 to 1.71±0.06).

CONCLUSIONS

The results indicate in this cohort of DVT patients there was no underlying hypercoagulable effect as determined by gel point analysis. Furthermore, the anticoagulant effect of rivaroxaban prolonged clotting, suggesting a protective effect against clot formation, without significantly reducing clot microstructural properties.

Evaluation of real-time thrombus detection method in a magnetically levitated centrifugal blood pump using a porcine left ventricular assist circulation model

Pump thrombosis induces significant complications and requires timely detection. We proposed real-time monitoring of pump thrombus in a magnetically levitated centrifugal blood pump (mag-lev pump) without using additional sensors, by focusing on the changes in the displacement of the pump impeller. The phase difference between the current and displacement of the impeller increases with pump thrombus. This thrombus detection method was previously evaluated through simulated circuit experiments using porcine blood. Evaluation of real-time thrombus detection in a mag-lev blood pump was performed using a porcine left ventricular assist circulation model in this study. Acute animal experiments were performed five times using five Japanese domestic pigs. To create thrombogenic conditions, fibrinogen coating that induces thrombus formation in a short time was applied to the inner surfaces of the pump. An inflow and an outflow cannula were inserted into the apex of the left ventricle and the carotid artery, respectively, by a minimally invasive surgical procedure that allowed minimal bleeding and hypothermia. Pump flow was maintained at 1 L/min without anticoagulation. The vibrational frequency of the impeller (70 Hz) and its vibrational amplitude (30 μm) were kept constant. The thrombus was detected based on the fact that the phase difference between the impeller displacement and input current to the magnetic bearing increases when a thrombus is formed inside a pump. The experiment was terminated when the phase difference increased by over 1° from the lowest value or when the phase difference was at the lowest value 12 hours after commencing measurements. The phase difference increased by over 1° in three cases. The pump was stopped after 12 hours in two cases. Pump thrombi were found in the pump in three cases in which the phase difference increased by over 1°. No pump thrombus was found in the other two cases in which the phase difference did not increase. We succeeded in real-time thrombus monitoring of a mag-lev pump in acute animal experiments.

A nondestructive contactless technique to assess the viscoelasticity of blood clots in real-time

There is a need for reliable and quantitative real-time assessment of blood properties to study and treat a broad spectrum of disorders and cardiovascular diseases as well as to test the efficacy of hemostatic agents. In this study, the real-time changes in viscoelastic/rheological properties of bovine whole blood during coagulation induced by different concentrations of calcium chloride (CaCl₂; 15, 25, 35 and 45 mM) was investigated. For this purpose, a novel, contactless technique was used to accurately measure the clotting characteristics under controlled and sterile conditions. It was demonstrated that, increasing the calcium concentration from low values (i.e., 15 and 25 mM), led to shorter reaction time; however, a further increase in calcium concentration (i.e., 35 and 45 mM) favored longer reaction times. Additionally, increasing the CaCl₂ concentration resulted in higher shear storage modulus (i.e., stiffer clots). These results were also comparable to those generated by thromboelastrograph, a clinically established technique, as well as a conventional rheometer, which quantitatively verified the high correlation of the shear storage modulus data. In sum, the non-destructive testing technique used in this study is reproducible and sensitive in measuring clot formation kinetics, which could be applied to assess the efficacy of hemostatic agents, and may also contribute to better diagnosing relevant circulatory system diseases and conditions.

Electrowetting based local sensing of liquid properties using relaxation dynamics of stretched liquid interface

HYPOTHESIS

Monitoring progression of biochemical processes is required for medical and industrial applications. Spatiotemporal changes in fluid properties can be measured to determine progress of biochemical processes like blood coagulation. Localised electrowetting-on-dielectric (EWOD) actuates a part of droplet contact line, allowing local measurement of fluid properties without inducing bulk fluid motion, which is unlike full droplet oscillation-based techniques.

EXPERIMENTS

In this work, narrow electrodes (50-450 μm) were used to actuate a portion of drop interface. Dynamics of interface actuation and relaxation was used to estimate the local visco-elastic properties of the droplet.

FINDINGS

For local interface motion, theory predicts a generic dispersion relation ω=cqⁿ. In agreement with theory, decay time was found to be proportional to viscosity and inversely proportional to surface tension. Interface displacement remained almost constant for different viscosities, but it decreased with increase in surface tension. Capability to measure spatiotemporal dynamics of chemical process was demonstrated for sugar dissolution in a droplet of water. For full droplet oscillation-based techniques, the induced bulk flows adversely affect the monitored process. Localised EWOD reduces bulk flows in the sample. So, this technique was applied to study blood coagulation dynamics, enlightening the future prospect of developing biomedical sensors.

Microfluidics in Haemostasis: A Review

Haemostatic disorders are both complex and costly in relation to both their treatment and subsequent management. As leading causes of mortality worldwide, there is an ever-increasing drive to improve the diagnosis and prevention of haemostatic disorders. The field of microfluidic and Lab on a Chip (LOC) technologies is rapidly advancing and the important role of miniaturised diagnostics is becoming more evident in the healthcare system, with particular importance in near patient testing (NPT) and point of care (POC) settings. Microfluidic technologies present innovative solutions to diagnostic and clinical challenges which have the knock-on effect of improving health care and quality of life. In this review, both advanced microfluidic devices (R&D) and commercially available devices for the diagnosis and monitoring of haemostasis-related disorders and antithrombotic therapies, respectively, are discussed. Innovative design specifications, fabrication techniques, and modes of detection in addition to the materials used in developing micro-channels are reviewed in the context of application to the field of haemostasis.

A droplet-based microfluidic viscometer for the measurement of blood coagulation

A continuous microfluidic viscometer is used to measure blood coagulation. The viscometer operates by flowing oil and blood into a cross section where droplets are generated. At a set pressure, the length of the droplets is inversely proportional to the viscosity of the blood sample being delivered. Because blood viscosity increases during coagulation as the blood changes from a liquid to a solid gel, the device allows to monitor coagulation by simply measuring the drop length. Experiments with swine blood were carried out in its native state and with the addition of coagulation activators and inhibitors. The microfluidic viscometer detected an earlier initiation of the coagulation process with the activator and a later initiation with the inhibitor compared to their corresponding controls. The results from the viscometer were also compared with the clinical method of thromboelastography (TEG), which was performed concurrently for the same samples. The time to initiation of coagulation in the microfluidic viscometer was correlated with the reaction time in TEG. Additionally, the total time for the measurement of clot strengthening in TEG correlated with the time for the maximum viscosity observed in the microfluidic viscometer. The microfluidic viscometer measured changes in viscosity due to coagulation faster than TEG detected the clot formation. The present viscometer is a simple technology that can be used to further study the entire coagulation process.

Monitoring of blood coagulation with non-contact drop oscillation rheometry

BACKGROUND

Thromboelastography is widely used as a tool to assess the coagulation status of critical-care patients. It allows observation of changes in the material properties of whole blood brought about by clot formation and clot lysis. However, contact activation of the coagulation cascade at surfaces of thromboelastographic systems leads to inherent variability and unreliability in predicting bleeding or thrombosis risks, while also requiring large sample volumes.

OBJECTIVES

To develop a non-contact drop oscillation rheometry (DOR) method to measure the viscoelastic properties of blood clots and to compare the results with current laboratory standard measurements.

METHODS

Drops of human blood and plasma (5-10 μL) were acoustically levitated. Acoustic field modulation induced drop shape oscillations, and the viscoelastic properties of the sample were calculated by measuring the resonance frequency and damping ratio.

RESULTS

DOR showed sensitivity to coagulation parameters. An increase in platelet count resulted in an increase in the maximum clot stiffness. An increase in the calcium ion level enhanced the coagulation rate prior to saturation. An increase in hematocrit resulted in a higher rate of clot formation and increased clot stiffness. Comparison of the results with those obtained with thromboelastography showed that coagulation started sooner with DOR, but with a lower rate and lower maximum stiffness.

CONCLUSIONS

DOR can be used as a monitoring tool to assess blood coagulation status. The advantages of small sample size, the lack of contact and small strain (linear viscoelasticity) makes this technique unique for real-time monitoring of blood coagulation.

Comprehensive Coagulation Profiling at the Point-of-Care Using a Novel Laser-Based Approach

Delays in identifying internal bleeding are life-threatening, thus underscoring the need for rapid and comprehensive coagulation profiling at the bedside. The authors review a novel optical coagulation profiler that measures several coagulation metrics including prothrombin time, activated clotting time, clot polymerization rate (α-angle), clot stiffness (maximum amplitude), fibrinolysis (LY), and platelet function, using a single multifunctional instrument. The optical profiler is based on the principles of Laser Speckle Rheology that quantifies tissue viscoelasticity from light scattering patterns called laser speckle. To operate the optical profiler, whole blood (40 μL) is loaded into a disposable cartridge, laser speckle patterns are recorded via a camera, and the viscoelasticity of clotting blood is estimated from speckle intensity fluctuations. By monitoring alterations in viscoelastic moduli over time during clot initiation, thrombin generation, fibrin crosslinking, clot stabilization, and LY, global coagulation parameters are obtained within 10 minutes using a drop of whole blood. Clinical testing in over 500 patients to date has confirmed the accuracy of the optical profiler for comprehensively assessing coagulation status against conventional coagulation tests and thromboelastography. Recent studies have further demonstrated the capability to quantify platelet aggregation induced by adenosine diphosphate in a drop of platelet-rich-plasma in the absence of applied shear stress. Together, these studies demonstrate that global coagulation profiling in addition to platelet function may be accomplished using a single multifunctional device. Thus, by enabling rapid and comprehensive coagulation and platelet function profiling at the bedside, the optical profiler will likely advance the capability to identify and manage patients with an elevated risk for hemorrhage.

Structure, Mechanics, and Instability of Fibrin Clot Infected with Staphylococcus epidermidis

Health care-associated infection, over half of which can be attributed to indwelling medical devices, is a strong risk factor for thromboembolism. Although most experimental models of medical device infection draw upon isolated bacterial biofilms, in fact there is no infection without host protein contribution. Here we study, to our knowledge, a new model for medical device infection-that of an infected fibrin clot-and show that the common blood-borne pathogen Staphylococcus epidermidis influences this in vitro model of a blood clot mechanically and structurally on both microscopic and macroscopic scales. Bacteria present during clot formation produce a visibly disorganized microstructure that increases clot stiffness and triggers mechanical instability over time. Our results provide insight into the observed correlation between medical device infection and thromboembolism; the increase in model clot heterogeneity shows that S. epidermidis can rupture a fibrin clot. The resultant embolization of the infected clot can contribute to the systemic dissemination of the pathogen.

A Novel Device for the Evaluation of Hemostatic Function in Critical Care Settings

Major surgical procedures often result in significant intra- and postoperative bleeding. The ability to identify the cause of the bleeding has the potential to reduce the transfusion of blood products and improve patient care. We present a novel device, the Quantra Hemostasis Analyzer, which has been designed for automated, rapid, near-patient monitoring of hemostasis. The Quantra is based on Sonic Estimation of Elasticity via Resonance Sonorheometry, a proprietary technology that uses ultrasound to measure clot time and clot stiffness from changes in viscoelastic properties of whole blood during coagulation. We present results of internal validation and analytical performance testing of the technology and demonstrate the ability to characterize the key functional components of hemostasis.

Prothrombotic Fibrin Clot Phenotype in Patients with Deep Vein Thrombosis and Pulmonary Embolism: A New Risk Factor for Recurrence

Prothrombotic fibrin clot phenotype, involving faster formation of dense meshwork composed of thinner and highly branched fibers that are relatively resistant to plasmin-induced lysis, has been reported in patients with not only myocardial infarction or stroke, but also venous thromboembolism (VTE), encompassing deep vein thrombosis (DVT), and/or pulmonary embolism (PE). Prothrombotic fibrin clot phenotype, in particular prolonged clot lysis time, is considered a novel risk factor for VTE as well as venous thrombosis at unusual location, for example, cerebral sinus venous thrombosis, retinal vein obstruction, and Budd-Chiari syndrome. Growing evidence from observational studies indicates that abnormal fibrin clot properties can predict recurrent DVT and PE and they are involved in serious complications of VTE, for example, thromboembolic pulmonary hypertension and postthrombotic syndrome. The purpose of this article is to review our current understanding of the role of fibrin clot structure and function in venous thrombosis with emphasis on clinical issues ranging from prognosis to therapy.

Platelets stored at 4°C contribute to superior clot properties compared to current standard-of-care through fibrin-crosslinking

Currently, platelets for transfusion are stored at room temperature (RT) for 5-7 days with gentle agitation, but this is less than optimal because of loss of function and risk of bacterial contamination. We have previously demonstrated that cold (4°C) storage is an attractive alternative because it preserves platelet metabolic reserves, in vitro responses to agonists of activation, aggregation and physiological inhibitors, as well as adhesion to thrombogenic surfaces better than RT storage. Recently, the US Food and Drug Administration clarified that apheresis platelets stored at 4°C for up to 72 h may be used for treating active haemorrhage. In this work, we tested the hypothesis that cold-stored platelets contribute to generating clots with superior mechanical properties compared to RT-stored platelets. Rheological studies demonstrate that the clots formed from platelets stored at 4°C for 5 days are significantly stiffer (higher elastic modulus) and stronger (higher critical stress) than those formed from RT-stored platelets. Morphological analysis shows that clot fibres from cold-stored platelets were denser, thinner, straighter and with more branch points or crosslinks than those from RT-stored platelets. Our results also show that the enhanced clot strength and packed structure is due to cold-induced plasma factor XIII binding to platelet surfaces, and the consequent increase in crosslinking.

Hemostatic kaolin-polyurethane foam composites for multifunctional wound dressing applications

There are numerous challenges associated with the acute care of traumatic limb injuries in forward military settings. A lack of immediate medical facilities necessitates that the wound dressing perform multiple tasks including exudate control, infection prevention, and physical protection of the wound for extended periods of time. Here, kaolin was incorporated into recently developed robust polyurethane (PU) hydrogel foams at 1-10wt% in an effort to impart hemostatic character. ATR-IR and gel fraction analysis demonstrated that the facile, one-pot synthesis of the PU hydrogel was unaffected by kaolin loading, as well as the use of a non-toxic catalyst, which significantly improved cytocompatibility of the materials. Kaolin was generally well dispersed throughout the PU matrix, though higher loadings exhibited minor evidence of aggregation. Kaolin-PU composites exhibited burst release of ciprofloxacin over 2h, the initial release rates of which increased with kaolin loading. Kaolin loading imparted excellent hemostatic character to the PU foams at relatively low loading levels (5wt%). This work demonstrates the simple and inexpensive synthesis of robust, hemostatic, and absorptive kaolin-PU foams that have promising potential as multifunctional wound dressing materials.

Micro-electromechanical film bulk acoustic sensor for plasma and whole blood coagulation monitoring

Monitoring blood coagulation is an important issue in the surgeries and the treatment of cardiovascular diseases. In this work, we reported a novel strategy for the blood coagulation monitoring based on a micro-electromechanical film bulk acoustic resonator. The resonator was excited by a lateral electric field and operated under the shear mode with a frequency of 1.9GHz. According to the apparent step-ladder curves of the frequency response to the change of blood viscoelasticity, the coagulation time (prothrombin time) and the coagulation kinetics were measured with the sample consumption of only 1μl. The procoagulant activity of thromboplastin and the anticoagulant effect of heparin on the blood coagulation process were illustrated exemplarily. The measured prothrombin times showed a good linear correlation with R²=0.99969 and a consistency with the coefficient of variation less than 5% compared with the commercial coagulometer. The proposed film bulk acoustic sensor, which has the advantages of small size, light weight, low cost, simple operation and little sample consumption, is a promising device for miniaturized, online and automated analytical system for routine diagnostics of hemostatic status and personal health monitoring.

Effects of unidirectional flow shear stresses on the formation, fractal microstructure and rigidity of incipient whole blood clots and fibrin gels

Incipient clot formation in whole blood and fibrin gels was studied by the rheometric techniques of controlled stress parallel superposition (CSPS) and small amplitude oscillatory shear (SAOS). The effects of unidirectional shear stress on incipient clot microstructure, formation kinetics and elasticity are reported in terms of the fractal dimension (d_f) of the fibrin network, the gel network formation time (T_GP) and the shear elastic modulus, respectively. The results of this first haemorheological application of CSPS reveal the marked sensitivity of incipient clot microstructure to physiologically relevant levels of shear stress, these being an order of magnitude lower than have previously been studied by SAOS. CSPS tests revealed that exposure of forming clots to increasing levels of shear stress produces a corresponding elevation in d_f, consistent with the formation of tighter, more compact clot microstructures under unidirectional flow. A corresponding increase in shear elasticity was recorded. The scaling relationship established between shear elasticity and d_f for fibrin clots and whole blood confirms the fibrin network as the dominant microstructural component of the incipient clot in terms of its response to imposed stress. Supplementary studies of fibrin clot formation by rheometry and microscopy revealed the substantial additional network mass required to increase d_f and provide evidence to support the hypothesis that microstructural changes in blood clotted under unidirectional shear may be attributed to flow enhanced thrombin generation and activation. CSPS also identified a threshold value of unidirectional shear stress above which no incipient clot formation could be detected. CSPS was shown to be a valuable haemorheological tool for the study of the effects of physiological and pathological levels of shear on clot properties.

Altered clot microstructure detected in obstructive sleep apnoea hypopnoea syndrome

Abnormal clot microstructure plays a pivotal role in the pathophysiology of thromboembolic diseases. Assessing the viscoelastic properties of clot microstructure using novel parameters, Time to Gel Point (T_GP), Fractal Dimension (d_f) and clot elasticity (G׳_GP) could explain the increased cardiovascular and thromboembolic events in patients with Obstructive Sleep Apnoea Hypopnea Syndrome (OSAHS). We wanted to compare T_GP, d_f, and G׳_GP and their diurnal variation in OSAHS and symptomatic comparators. thirty six patients attending a sleep disturbed breathing clinic with symptoms of OSAHS were recruited. T_GP, d_f and G׳_GP were measured alongside standard coagulation screening, thrombin generation assays, and platelet aggregometry at 16:00 h and immediately after an in-patient sleep study at 07:30 h. OSAHS group had significantly lower afternoon d_f than comparators (1.705±0.033 vs. 1.731±0.031, p<0.05). d_f showed diurnal variation and only in the OSAHS group, being significantly lower in the afternoon than morning (p<0.05). Diurnal changes in d_f correlated with 4% DR, even after controlling for BMI (r=0.37, p=0.02). The lower d_f in the afternoon in OSAHS suggests a partial compensatory change that may make up for other pro-clotting abnormalities/hypertension during the night. The change to the thrombotic tendency in the afternoon is biggest in severe OSAHS. d_f Shows promise as a new microstructural indicator for abnormal haemostasis in OSAHS.

Simultaneous measurement of thrombin generation and fibrin formation in whole blood under flow conditions

Assays based on the formation of thrombin and fibrin are frequently used, and results are considered exchangeable in research/clinical settings. However, thrombin generation and fibrin formation do not always go hand in hand and flow profoundly influences thrombus formation. We describe the technical/clinical evaluation of an assay to simultaneously measure thrombin generation and fibrin formation under conditions of flow. Introduction of a fluorometer into a 'cone and base principle'-based rheometer allowed the measurement of thrombin generation (using a thrombin-sensitive substrate) and fibrin formation (changes in viscosity), while applying a linear shear flow. Increasing shear rates inversely related with thrombin generation and fibrin formation. Increasing fibrinogen concentrations in defibrinated plasma resulted in increased thrombin generation and fibrin formation. In pre-operative samples of 70 patients undergoing cardiothoracic surgery, fibrin formation and thrombin generation parameters correlated with fibrinogen content, rotational thromboelastometry (ROTEM) and whole blood Calibrated Automated Thrombinography (CAT) parameters, respectively. Upon dividing patients into two groups based on the median clot strength, a significant difference in perioperative/total blood loss was established. In conclusion, we clinically evaluated a method capable of simultaneously measuring thrombin generation and fibrin formation in plasma/whole blood under continuous flow, rendering our method one step closer to physiology. Importantly, our test proved to be indicative for the amount of blood loss during/after cardiothoracic surgery.

Thromboelastometry versus free-oscillation rheometry and enoxaparin versus tinzaparin: an in-vitro study comparing two viscoelastic haemostatic tests' dose-responses to two low molecular weight heparins at the time of withdrawing epidural catheters from ten patients after major surgery

Background

Monitoring low molecular weight heparins (LMWH’s) in the perioperative period is prudent in patients at high risk of coagulative complications, especially when the patient has an epidural catheter requiring withdrawal, which is associated with the risk of spinal haematoma. The aim of this study was to evaluate the in vitro dose-responses of two different LMWH’s on two different viscoelastic haemostatic tests, using blood sampled from patients with normal routine coagulation parameters, on the day after major surgery when their epidural catheters were due to be withdrawn.

Methods

Enoxaparin or tinzaparin were added in vitro to blood from ten patients who had undergone oesophageal resection, to obtain plasma concentrations of approximately 0, 0.5, 1.0 and 1.5 IU/mL. Coagulation was monitored using thromboelastometry (ROTEM®) using the InTEM® activating reagent; and free oscillation rheometry (FOR: ReoRox®), activated using thromboplastin. Clot initiation was measured using ROTEM-CT, ReoRox-COT1 and ReoRox–COT2. Clot propagation was measured using ROTEM-CFT, ROTEM-Alpha Angle and ReoRox-Slope. Clot stability was measured using ROTEM-MCF and ReoRox-G’max, and clot lysis was measured using ROTEM-ML and ReoRox-ClotSR.

Results

Clot initiation time assessed by thromboelastometry and FOR was prolonged by increasing concentrations of both LMWH’s (P < 0.01). Equivalent doses of tinzaparin in international units (anti-FXa units) per millilitre prolonged clot initiation more than enoxaparin (P < 0.05). There was significant inter-individual variation – the ranges of CT and COT1 at LMWH-concentrations of 0 and 1.5 IU/mL overlapped. None of the tests reflecting clot formation rate or stability showed a dose–response to either LMWH but clot lysis showed a tentative negative dose–response to the LMWH’s.

Conclusions

Clot initiation time’s dose-dependent prolongation by LMWH’s in this study agrees with previous research, as does tinzaparin’s stronger anti-coagulative effect than enoxaparin at equivalent levels of anti-FXa activity. This casts doubt on the validity of using anti-FXa assays alone to guide dosage of LMWH’s. The significant inter-individual variation in dose–response suggests that the relationship between dose and effect in the postoperative period is complicated. While both ROTEM and FOR may have some role in postoperative monitoring, more research is needed before any conclusion can be made about their clinical usefulness.

Electronic supplementary material

The online version of this article (doi:10.1186/s12871-015-0145-2) contains supplementary material, which is available to authorized users.

A constitutive model for a maturing fibrin network

Blood clot formation is crucial to maintain normal physiological conditions but at the same time involved in many diseases. The mechanical properties of the blood clot are important for its functioning but complicated due to the many processes involved. The main structural component of the blood clot is fibrin, a fibrous network that forms within the blood clot, thereby increasing its mechanical rigidity. A constitutive model for the maturing fibrin network is developed that captures the evolving mechanical properties. The model describes the fibrin network as a network of fibers that become thicker in time. Model parameters are related to the structural properties of the network, being the fiber length, bending stiffness, and mass-length ratio. Results are compared with rheometry experiments in which the network maturation is followed in time for various loading frequencies and fibrinogen concentrations. Three parameters are used to capture the mechanical behavior including the mass-length ratio. This parameter agrees with values determined using turbidimetry experiments and is subsequently used to derive the number of protofibrils and fiber radius. The strength of the model is that it describes the mechanical properties of the maturing fibrin network based on it structural quantities. At the same time the model is relatively simple, which makes it suitable for advanced numerical simulations of blood clot formation during flow in blood vessels.

Global Tests in Evaluation of the Function of Pro-and Anticoagulant Systems: Present and Future

Comparative analysis of the effectiveness of global tests for evaluation of the blood coagulation systems demonstrated the possibility of obtaining express data on hemostasis stages I-II and III when working with native substrate (whole blood). Changes in viscous characteristics of the whole blood recorded ex vivo during hemocoagulation allowed us to propose the concept of permanency of fibrinogenesis as the obligatory in vivo process determining the hemostatic potential, an integral characteristic of the hemocoagulation cycle providing sufficient blood fluidity and limiting extravasation of blood components under conditions of permeability disturbances and damage to the vascular wall.

Integration of acoustic radiation force and optical imaging for blood plasma clot stiffness measurement

Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood's transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 μm) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties.

Optical Thromboelastography to evaluate whole blood coagulation

Measurement of blood viscoelasticity during clotting provides a direct metric of haemostatic conditions. Therefore, technologies that quantify blood viscoelasticity at the point-of-care are invaluable for diagnosing coagulopathies. We present a new approach, Optical Thromboelastography (OTEG) that measures the viscoelastic properties of coagulating blood by evaluating temporal laser speckle fluctuations, reflected from a few blood drops. During coagulation, platelet-fibrin clot formation restricts the mean square displacements (MSD) of scatterers and decelerates speckle fluctuations. Cross-correlation analysis of speckle frames provides the speckle intensity temporal autocorrelation, g2 (t), from which MSD is deduced and the viscoelastic modulus of blood is estimated. Our results demonstrate a close correspondence between blood viscoelasticity evaluated by OTEG and mechanical rheometry. Spatio-temporal speckle analyses yield 2-dimensional maps of clot viscoelasticity, enabling the identification of micro-clot formation at distinct rates in normal and coagulopathic specimens. These findings confirm the unique capability of OTEG for the rapid evaluation of patients' coagulation status and highlight the potential for point-of-care use.

Global assays of hemostasis in the diagnostics of hypercoagulation and evaluation of thrombosis risk

Thrombosis is a deadly malfunctioning of the hemostatic system occurring in numerous conditions and states, from surgery and pregnancy to cancer, sepsis and infarction. Despite availability of antithrombotic agents and vast clinical experience justifying their use, thrombosis is still responsible for a lion’s share of mortality and morbidity in the modern world. One of the key reasons behind this is notorious insensitivity of traditional coagulation assays to hypercoagulation and their inability to evaluate thrombotic risks; specific molecular markers are more successful but suffer from numerous disadvantages. A possible solution is proposed by use of global, or integral, assays that aim to mimic and reflect the major physiological aspects of hemostasis process in vitro. Here we review the existing evidence regarding the ability of both established and novel global assays (thrombin generation, thrombelastography, thrombodynamics, flow perfusion chambers) to evaluate thrombotic risk in specific disorders. The biochemical nature of this risk and its detectability by analysis of blood state in principle are also discussed. We conclude that existing global assays have a potential to be an important tool of hypercoagulation diagnostics. However, their lack of standardization currently impedes their application: different assays and different modifications of each assay vary in their sensitivity and specificity for each specific pathology. In addition, it remains to be seen how their sensitivity to hypercoagulation (even when they can reliably detect groups with different risk of thrombosis) can be used for clinical decisions: the risk difference between such groups is statistically significant, but not large.

Ultra-sensitive detection of heparin via aPTT using plastic antibodies on QCM-D platform

One of the challenges faced by today's clinics is unavailability of practical, precise and accurate determination of the most commonly used anti-coagulant ‘heparin’ in human blood/plasma in surgery.

Revisiting Hartert's 1962 Calculation of the Physical Constants of Thrombelastography

Thrombelastography (TEG)/thromboelastometry (ROTEM) devices measure viscoelastic clot strength as clot amplitude (A). Transformation of clot amplitude into clot elasticity (E with TEG; CE with ROTEM) is sometimes necessary (eg, when calculating platelet component of the clot). With TEG, clot amplitude is commonly transformed into shear modulus (G; expressed in Pa or dyn/cm²) as follows: G = (5000 × A)/(100 – A). Use of the constant “5000” stems from Hartert's 50-year-old calculation of G for a normal blood clot. We question the value of calculating G as follows: (1) It may be questioned whether TEG/ROTEM analysis enable measurement of elasticity because viscosity may also contribute to clot amplitude. (2) It has been suggested that absolute properties of a blood clot cannot be measured with TEG/ROTEM analysis because the strain amplitude applied by the device is uncontrolled and changes during the course of coagulation. (3) A review of the calculation of G using Hartert's methods and some updated assumptions suggests that the value of 5000 is unreliable. (4) Recalculation of G for the ROTEM device yields a different value from that with Hartert TEG, indicating a degree of inaccuracy with the calculations. (5) Shear modulus is simply a multiple of E/CE and, because of the unreliability of G in absolute terms, it provides no additional value versus E/CE. The TEG and ROTEM are valuable coagulation assessment tools that provide an evaluation of the viscoelastic properties of a clot, not through measuring absolute viscoelastic forces but through continuous reading of the clot amplitude relative to an arbitrary, preset scale.

Correction of hypothermic and dilutional coagulopathy with concentrates of fibrinogen and factor XIII: an in vitro study with ROTEM

BACKGROUND

Fibrinogen concentrate treatment can improve coagulation during massive traumatic bleeding. The aim of this in vitro study was to determine whether fibrinogen concentrate, or a combination of factor XIII and fibrinogen concentrates, could reverse a haemodilution-induced coagulopathy during hypothermia.

METHODS

Citrated venous blood from 10 healthy volunteers was diluted in vitro by 33% with 130/0.42 hydroxyethyl starch (HES) or Ringer's acetate (RAc). The effects of fibrinogen concentrate corresponding to 4 gram per 70 kg, or a combination of the same dose of fibrinogen with factor XIII (20 IU per kg), were measured using rotational thromboelastometry (ROTEM). The blood was analysed at 33°C or 37°C with ROTEM EXTEM and FIBTEM reagents. Clotting time (CT), clot formation time (CFT), alpha angle (AA) and maximal clot formation (MCF) were recorded.

RESULTS

Fibrinogen with or without factor XIII improved all ROTEM parameters in either solution irrespective of temperature, with the exception of EXTEM-AA and EXTEM-CFT in HES haemodilution. Fibrinogen increased FIBTEM-MCF more in the samples diluted with RAc than HES, particularly in presence of factor XIII.

CONCLUSIONS

Fibrinogen improved in vitro haemodilution-induced coagulopathy at both 33°C and 37°C, though more efficiently after crystalloid than HES haemodilution. Factor XIII had an additional effect on FIBTEM-MCF, but only after crystalloid dilution.

Effect of cold storage on shear-induced platelet aggregation and clot strength

BACKGROUND

Platelets (PLTs) participate in hemostasis and save lives following trauma. PLTs for transfusion are maintained at room temperature (RT, 22°C), limiting viability to 5 days because of metabolic compromise and high risk of bacterial contamination. RT storage may result in weaker clots, delaying hemorrhage control, whereas cold storage (4°C) could permit longer PLT shelf life and result in a more hemostatic product. In this study, we characterized the effect of storage temperature on shear-induced PLT aggregation, clot formation, and strength.

METHODS

PLTs obtained from phlebotomized blood or by apheresis were stored at RT or 4°C for 5 days, and PLT aggregation and clot strength were assessed at 37°C. We studied PLT aggregation at steady and complex patterns of shear rates (500-2,500 per second) by flow cytometry, and the kinetics of clot formation and strength were measured using turbidity and dynamic mechanical analysis, respectively.

RESULTS

PLT aggregation was higher in 4°C-stored samples on Day 5 compared with fresh or RT-stored samples at all shear rates tested (fresh vs. 4°C and RT vs. 4°C, p < 0.05). PLTs stored at 4°C for 5 days formed significantly stronger clots compared with fresh or RT-stored samples as quantified by turbidity and elastic moduli measurements (fresh vs. 4°C and RT vs. 4°C, p < 0.05).

CONCLUSION

Our results show that cold-stored PLTs are more responsive to aggregation stimuli and form stronger clots, presumably because of thicker fibrin strands. These data suggest that the superior functionality of cold-stored PLTs may support faster hemostasis for acutely bleeding in trauma patients compared with RT-stored PLTs.

QCM-D providing new horizon in the domain of sensitivity range and information for haemostasis of human plasma

Monitoring of the haemostasis status is significant for proper therapeutic directions and decisions in surgery and innate coagulation disorders. In this regard, to gain a general overview of the plasmatic coagulation, prothrombin time (PT) tests are frequently combined with tests for activated partial thromboplastin time (aPTT). For aPTT we report for the first time that a QCM-D (Quartz Crystal Microbalances with Dissipation) based technique offers a better alternative to the standard coagulometer method in the perspective of range and information. We used heparin as anticoagulant to generate different coagulation times for human plasma. QCM-D astonishingly proved to be more sensitive and reliable than the standard coagulometer for aPTT range of upper limits of coagulation times. The established platform can monitor the fibrinogen concentration ranging from 1-6g/L (yielding R(2)=0.98 in calibration curves) along with aPTT from frequency and dissipation shifts together in a single set of measurements. Additionally the sensor layers have been tested for reusability, demonstrating no loss in sensor characteristics up to ten times measurements.

Blood viscosity during coagulation at different shear rates

During the coagulation process, blood changes from a liquid to a solid gel phase. These changes are reflected by changes in blood viscosity; however, blood viscosity at different shear rates (SR) has not been previously explored during the coagulation process. In this study, we investigated the viscosity changes of whole blood in 10 subjects with a normal coagulation profile, using a cone-on-plate viscosimeter. For each subject, three consecutive measurements were performed, at a SR of 20, 40, 80 sec(-1). On the basis of the time-dependent changes in blood viscosity, we identified the gel point (GP), the time-to-gel point (TGP), the maximum clot viscosity (MCV), and the clot lysis half-time (CLH). The TGP significantly (P = 0.0023) shortened for increasing SR, and was significantly associated with the activated partial thromboplastin time at a SR of 20 sec(-1) (P = 0.038) and 80 sec(-1) (P = 0.019). The MCV was significantly lower at a SR of 80 sec(-1) versus 40 sec(-1) (P = 0.027) and the CLH significantly (P = 0.048) increased for increasing SR. These results demonstrate that measurement of blood viscosity during the coagulation process offers a number of potentially useful parameters. In particular, the association between the TGP and the activated partial thromboplastin time is an expression of the clotting time (intrinsic and common pathway), and its shortening for increasing SR may be interpreted the well-known activating effects of SR on platelet activation and thrombin generation. Further studies focused on the TGP under conditions of hypo- or hypercoagulability are required to confirm its role in the clinical practice.

Detection of fibrinogen and coagulation factor VIII in plasma by a quartz crystal microbalance biosensor

A quartz crystal microbalance (QCM) biosensor with nanogram sensitivity has been constructed through a reasonable designing and biological processing of the piezoelectric quartz crystals. Due to its highly sensitivity, real time detection and low cost, the proposed QCM biosensor has a promising potential in blood coagulation research. In the current study, the QCM biosensor was used to determine the activated partial thromboplastin time (APTT) for 120 anticoagulated plasma specimens. A good linear relationship was found in a double-logarithmic plot of APTT versus fibrinogen concentration in the range of 1.58–6.30 g/L. For factor VIII, the detection range by the QCM biosensor is 0.0185–0.111 mg/L. The QCM biosensor results were compared with those obtained by commercial optical coagulometry and a good agreement (correlation coefficient is 0.949 for fibrinogen, and 0.948 for factor VIII) was reached. Furthermore, the QCM determination can be completed within 10 min. Our study suggested that the proposed QCM biosensor could provide for more convenient and time saving operations, which may be useful in clinical situations for rapid monitoring of anticoagulant therapy using small volume (20 μL) plasma specimens.

Virtual treatment of basilar aneurysms using shape memory polymer foam

Numerical simulations are performed on patient-specific basilar aneurysms that are treated with shape memory polymer (SMP) foam. In order to assess the post-treatment hemodynamics, two modeling approaches are employed. In the first, the foam geometry is obtained from a micro-CT scan and the pulsatile blood flow within the foam is simulated for both Newtonian and non-Newtonian viscosity models. In the second, the foam is represented as a porous media continuum, which has permeability properties that are determined by computing the pressure gradient through the foam geometry over a range of flow speeds comparable to those of in vivo conditions. Virtual angiography and additional post-processing demonstrate that the SMP foam significantly reduces the blood flow speed within the treated aneurysms, while eliminating the high-frequency velocity fluctuations that are present within the pre-treatment aneurysms. An estimation of the initial locations of thrombus formation throughout the SMP foam is obtained by means of a low fidelity thrombosis model that is based upon the residence time and shear rate of blood. The Newtonian viscosity model and the porous media model capture similar qualitative trends, though both yield a smaller volume of thrombus within the SMP foam.

"Ta panta rhei"

In this issue of Blood, Evans et al report that fractal analysis of the mechanical properties of whole-blood clots defines a unique property of the incipient clot that can be used as a functional biomarker of hemostasis.