Karl Hawkins

• M.Eng, Ph.D.
• Professor at Swansea University

Background Exercise in healthy individuals is associated with a hypercoagulable phase, leading to a temporary increase in clot mass and strength, which are controlled by an effective fibrinolytic system. Conversely, people with cardiovascular diseases often have a reduced fibrinolytic pathway, increased clot mass and abnormal clot contraction, resu...

This study presents a numerical model for incipient fibrin-clot formation that captures characteristic rheological and microstructural features of the clot at the gel point. Using a mesoscale-clustering framework, we evaluate...

This study presents a numerical model for incipient fibrin-clot formation that captures characteristic rheological and microstructural features of the clot at the gel point. Using a mesoscale-clustering framework, we evaluate the effect of gel concentration or gel volume fraction and branching on the fractal dimension, the gel time, and the viscoel...

A hallmark of angiogenesis is the sprouting of endothelial cells. To replicate this event in vitro, biomaterial approaches can play an essential role in promoting cell migration. To study the capacity of a scaffold of fibrin (fibrinogen:thrombin mix) to support the movement of the endothelial cells, the migration area of spheroids formed with the H...

Background: Unfavourable clot microstructure is associated with adverse outcomes in ST elevation myocardial infarction (STEMI). We investigated the effect of comorbidities and anti-platelet treatment on clot microstructure in STEMI patients using fractal dimension (df), a novel biomarker of clot microstructure derived from the visco-elastic proper...

Background: A significant degree of mortality and morbidity in Covid-19 is through thromboembolic complications, only partially mitigated by anticoagulant therapy. Reliable markers of infection severity are not fully established. Objectives: This study investigated whether visco-elastic biomarkers predict disease severity on presentation to the...

Blood levels of the soluble receptor for advanced glycation end-products (sRAGE) are acutely elevated during the host inflammatory response to infection and predict mortality in COVID-19. However, the prognostic performance of this biomarker in the context of treatments to reduce inflammation is unclear. In this study we investigated the associatio...

Background: A significant degree of mortality and morbidity in Covid-19 is due to thromboembolic disease. Coagulopathy has been well described in critically unwell patients on ICU. There is less clear evidence regarding these changes at the time of presentation to the Emergency Department and the progression of disease over time. Objective: We s...

Purpose: Bioprinting is becoming an increasingly popular platform technology for engineering a variety of tissue types. Our aim was to identify biomaterials that have been found to be suitable for extrusion 3D bioprinting, outline their biomechanical properties and biocompatibility towards their application for bioprinting specific tissue types. Th...

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...

Introduction Thrombosis is a severe and frequent complication of heparin-induced thrombocytopenia (HIT). However, there is currently no knowledge of the effects of HIT-like antibodies on the resulting microstructure of the formed clot, despite such information being linked to thrombotic events. We evaluate the effect of the addition of pathogenic H...

Introduction: This aim of this study is to investigate the individual effects of varying concentrations of thrombin and fibrinogen on clot microstructure (characterised through the fractal dimension of the incipient clot network, df) and clot formation time (TGP) using a fibrin-thrombin clot model. df and TGP markers are measured using a haemorheo...

Background: One of the main challenges for extrusion 3D bioprinting is the identification of non-synthetic bioinks with suitable rheological properties and biocompatibility. Our aim was to optimize and compare the printability of crystal, fibril and blend formulations of novel pulp derived nanocellulose bioinks and assess biocompatibility with hum...

Medical devices, such as ventricular assist devices (VADs), introduce both foreign materials and artificial shear stress to the circulatory system. The effects these have on leukocytes and the immune response are not well understood. Understanding how these two elements combine to affect leukocytes may reveal why some patients are susceptible recur...

Bioinspiration from hierarchical structures found in natural environments has heralded a new age of advanced functional materials. Nanocellulose has received significant attention due to the demand for high-performance materials with tailored mechanical, physical and biological properties. In this study, nanocellulose fibrils, nanocrystals and a no...

The ability to control the mechanical properties of cell culture environments is known to influence cell morphology, motility, invasion and differentiation. The present work shows that it is possible to control the mechanical properties of collagen gels by manipulating gelation conditions near the sol gel transition. This manipulation is accomplish...

Background Antithrombotics are the mainstay of management in coronary artery disease (CAD). However, no biomarker is available to assess their global effect on clot formation and structure. We validated a novel biomarker that measures clot microstructure, fractal dimension of incipient blood clot (df), in healthy volunteers, stroke, lung cancer and...

The rheological characterisation of viscoelastic materials undergoing a sol-gel transition at the Gel Point (GP) has important applications in a wide range of industrial, biological, and clinical environments and can provide information regarding both kinetic and microstructural aspects of gelation. The most rigorous basis for identifying the GP in...

The suitability of controlled stress large amplitude oscillatory shear (LAOStress) for the characterisation of the nonlinear viscoelastic properties of fully formed fibrin clots is investigated. Capturing the rich nonlinear viscoelastic behaviour of the fibrin network is important for understanding the structural behaviour of clots formed in blood...

Background: The introduction of a foreign surface and the shear stress encountered by the blood moving through a rotary pump can affect both cells and proteins with leukocytes shown to be more vulnerable to shear than erythrocytes. At high shear, viability, counts, morphology, and function have been shown to be significantly impaired. As leukocytes...

Despite the increasing laboratory research in the growing field of 3D bioprinting there are few reports of successful translation into surgical practice. This review outlines the principles of 3D bioprinting including software and hardware processes, biocompatible technological platforms and suitable bioinks. The advantages of 3D bioprinting over t...

Background Coronary artery disease (CAD) is associated with an increased prothrombotic tendency and is also linked to unfavourably altered clot microstructure. We have previously described a biomarker of clot microstructure (df) that is unfavourably altered in acute myocardial infarction. The df biomarker assesses whether the blood will form denser...

Despite the interwoven nature of platelet activation and the coagulation system in thrombosis, few studies relate both analysis of protein and cellular parts of coagulation in the same population. In the present study, we use matched ex vivo samples to determine the influences of standard antiplatelet therapies on platelet function and use advanced...

Background: Balancing the beneficial effects of resuscitation fluids against their detrimental effect on hemostasis is an important clinical issue. We aim to compare the in vitro effects of 3 different colloid resuscitation fluids (4.5% albumin, hydroxyethyl starch [Voluven 6%], and gelatin [Geloplasma]) on clot microstructure formation using a no...

Aim: To use both a rheometer and the Calon shear device model to mimic the foreign surface and artificial shear introduced to the body by ventricular assist devices (VADs). Methods: For the rheometer model (AR-G2, TA Instruments), discs of biomaterial: diamond-like carbon coated stainless steel (DLC); single crystal sapphire (Sap); and titanium all...

We present a simple new analytical method for educing the materials' linear viscoelastic properties, over the widest range of experimentally accessible frequencies, from a simple step-strain measurement, without the need of preconceived models nor the idealization of real measurements. This is achieved by evaluating the Fourier transforms of raw ex...

We present a simple new analytical method for educing the materials' linear viscoelastic properties, over the widest range of experimentally accessible frequencies, from a simple step-strain measurement, without the need of preconceived models nor the idealization of real measurements. This is achieved by evaluating the Fourier transforms of raw ex...

To use a rheological model to mimic the foreign surface and artificial shear introduced to the body by ventricular assist devices (VADs) in order to evaluate the effect biomaterials have on leukocyte activation in this environment.

Background: Exercise is well established to lead to exercise-induced hypercoagulability, as demonstrated by kinetic coagulation markers. It remains unclear as to whether exercise-induces changes lead in clot development and increased polymerisation. Fractal dimension (df) has been shown to act as a marker of clot microstructure and mechanical prop...

The host- and bacteria-derived extracellular polysaccharide coating of the lung is a considerable challenge in chronic respiratory disease and is a powerful barrier to effective drug-delivery. A low molecular weight 12-15-mer alginate oligosaccharide (OligoG CF-5/20), derived from plant biopolymers, was shown to modulate the polyanionic components...

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 (TGP), Fractal Dimension (df) and clot elasticity (G׳GP) could explain the increased cardiovascular and thromboembolic events in patients with Obs...

Stroke is the second largest cause of death worldwide. Hypercoagulability is a key feature in ischaemic stroke due to the development of an abnormally dense clot structure but techniques assessing the mechanics and quality of clot microstructure have limited clinical use. We have previously validated a new haemorheological technique using three par...

Background: Anesthesia, critical illness, and trauma are known to alter thermoregulation, which can potentially affect coagulation and clinical outcome. This in vitro preclinical study explores the relationship between temperature change and hemostasis using a recently validated viscoelastic technique. We hypothesize that temperature change will c...

Aim: To evaluate the biocompatibility of materials used in ventricular assist devices (VADs) through their effect on cellular and protein behaviour. Results will be used to influence future designs. Methods: Highly polished discs of materials used in VAD designs – single-crystal sapphire (SAP), silicon nitride (SIN), zirconia toughened-alumina (ZTA...

Aim: To evaluate the effect of various biomaterials used in ventricular assist devices (VADs) on leukocyte behaviour to identify the most biocompatible. The results will impact future VAD designs to reduce common complications such as thromboembolism and infection. Methods: Discs of biomaterials used in VAD designs - single-crystal sapphire (SAP),...

Venous thromboembolism (VTE) is common in cancer patients, and is the second commonest cause of death associated with the disease. Patients with chronic inflammation, such as cancer, have been shown to have pathological clot structures with modulated mechanical properties. Fractal dimension (df) is a new technique which has been shown to act as a m...

Aim: To evaluate the effect of biomaterials used in ventricular assist devices (VADs) on leukocyte behaviour to identify the most biocompatible. The results will impact future VAD designs to reduce common complications such as thromboembolism and infection. Methods: Discs of biomaterials used in VAD designs - single-crystal sapphire (SAP), silicon...

Methods: PULVAD comprises a pneumatically-driven polyurethane pumping chamber with a valveless opening, which is implanted in the thoracic cavity and is connected to the ascending aorta. The pump is synchronized on the basis of the ECG and operates through inflation of the device air space during diastole (injecting blood into the aorta), and defla...

Changes in clot microstructure are increasingly implicated in the pathology of atherosclerosis although most data are from techniques in the remote laboratory using altered blood. We validate the novel biomarker Gel Point in STEMI patients and assess therapeutic interventions. Gel Point marks the transition of blood from a visco-elastic liquid to v...

Infections are frequent and very undesired occurrences after orthopedic procedures; furthermore, the growing concern caused by the rise in antibiotic resistance is progressively dwindling the efficacy of such drugs. Artificial bone graft materials could solve some of the problems associated with the gold standard use of natural bone graft such as l...

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 dimensio...

Rheological Gel Point measurements may incur errors in the case of rapid gelling systems due to the limitations of multiple frequency oscillatory shear techniques such as frequency sweeps and Fourier Transform Mechanical Spectroscopy, FTMS. These limitations are associated with sample mutation and data interpolation. In the present paper we conside...

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 dimensio...

Processes involving a unidirectional shear flow component are widespread in industrial manufacturing techniques such as printing and coating, or in physiological events such as blood coagulation. Standard rheometric techniques are usually employed under quiescent conditions and as such are inappropriate for the study of microstructural modification...

Stroke is the second largest cause of death worldwide. Abnormalities in hemostasis play an important role in the pathophysiology of ischemic stroke (IS). These hemostatic defects can be detected using rotational thromboelastometry (ROTEM) as a global method of measuring coagulation.This study assessed the effects of IS on blood hypercoagulability u...

This study compared patients with venous thromboembolism (VTE) to non-VTE patients using a biomarker of clot microstructure (df ) and clot formation time (TGP ). df was the only marker that identified a significant difference (P < 0·001) between the VTE (n = 60) and non-VTE cohorts (n = 69). The 'abnormal' clot microstructures in the VTE patients s...

Objective To assess the prognostic and diagnostic value of whole blood impedance aggregometry in patients with sepsis and SIRS and to compare with whole blood parameters (platelet count, haemoglobin, haematocrit and white cell count). Methods We performed an observational, prospective study in the acute setting. Platelet function was determined us...

Clinical outcomes from ventricular assist devices (VADs) have improved significantly during recent decades, but bleeding episodes remain a common complication of long-term VAD usage. Greater understanding of the effect of the shear stress in the VAD on platelet aggregation, which is influenced by the functional activity of high molecular weight (HM...

Introduction We investigated the effect of progressive haemodilution on the dynamics of fibrin clot formation and clot microstructure using a novel rheological method. The technique measures clotting time (TGP), clot strength (G`GP), and quantifies clot microstructure (df) at the incipient stages of fibrin formation. We use computational modelling...

Implantable ventricular assist devices (VADs) have proven efficient in advanced heart failure patients as a bridge-to-transplant or destination therapy. However, VAD usage often leads to infection, bleeding, and thrombosis, side effects attributable to the damage to blood cells and plasma proteins. Measuring hemolysis alone does not provide suffici...

The main focus of the present computational modelling work is to determine the extensional rheological response of some model biofluids, with a view to ultimately aiding experimentally based analyses and clinical practice. This is accomplished in the present study through model extensional flows and rheological investigation, addressing filament st...

More than 200 combinations of antiplatelet and anticoagulant drugs can be given during an acute cardiac event. However, no biomarker is available to assess their global effect on clot formation and structure. Fractal dimension (Df) and clot formation time (TGP) are global markers of haemostasis that have been validated in healthy and anticoagulated...

Introduction Untreated obstructive sleep apnoea syndrome (OSAS) increases cardiovascular risk and altered haemostasis is at least partly implicated. As previously reported using fractal analysis and a new biomarker called fractal dimension (Df) it is possible to assess the microstructure of incipient clot in whole blood (1). Df relates to the kinet...

Introduction Prevalence of OSAS in people with cardiovascular disease is much higher than in the general population. Many OSAS patients are prescribed Aspirin for secondary prevention of cardiovascular events but the effects of morning Aspirin might be attenuated by night of recurrent apnoeas and intermittent hypoxia. Therefore evening dosing might...

Objective: OligoG is a low molecular weight (ca. 2600) alginate oligomer, comprised of 90-95% guluronic acid, which potentiates biofilm disruption and the antibiotic treatment of multi-drug resistant (MDR) biofilm-related lung infections in vitro. Here the interaction between OligoG and the biopolymer mucin was studied in a range of model systems t...

Infection is a clinically relevant adverse event in patients with ventricular assist device (VAD) support. The risk of infection could be linked to a reduced immune response resulting from damage to leukocytes during VAD support. The purpose of this study was to develop an understanding of leukocyte responses during the in vitro testing of VADs by...

We report a study of the microstructural templating role of incipient fibrin–thrombin gels by analysis of rheological and confocal microscope measurements. Fractal analysis based on the spectral dimension is used, for the first time, to characterise fibrin gel microstructure in terms of the internal connectivity of gel networks. A significant corre...

The influence of a novel, safe antibiofilm therapy on the mechanical properties of Pseudomonas aeruginosa and Acinetobacter baumannii biofilms in vitro was characterized. A multiscale approach employing atomic force microscopy (AFM) and rheometry was used to quantify the mechanical disruption of the biofilms by a therapeutic polymer based on a low-...

A novel MEMS based drug delivery device has been developed, consisting of an array of metallic contacts on silicon and Pyrex glass wafers. The meander structured device creates a uniform electric field which stimulates drug release. An electro-active hydrogel based polymer matrix has also been developed, which responds to an electrical stimulus and...

The Harboe spectrophotometric assay is regarded as one of the safest and most reproducible methods for measuring plasma free hemoglobin (pfHb). However, there is still some ambiguity in the application of the assay when assessing the hemolytic performance of ventricular assist devices (VADs). The purpose of this study was to reexamine and compare v...

A recent rheological study has established that the fractal dimension, d(f), of an incipient clot, formed at the Gel Point (sol-gel transition) of coagulating blood is a significant new biomarker of haemostasis. In whole healthy blood, incipient clots show a clearly defined value of d(f) = 1.7 within a narrow range, which represents a new 'healthy...

This study investigates the potential use of rheometry to provide a structural biomarker for acute critical illness. Previous studies have reported an association of altered fibrin clot network architecture with several diseases including sepsis, bleeding or acute thromboembolic disease [1]. We investigate our biomarker by examining the relationshi...

A novel MEMS based drug delivery device has been developed, consisting of an array of metallic contacts. The meander structured device created a uniform electric field which stimulates drug releases. An electro-active hydrogel based polymer matrix responds to an electrical stimulus and shrinks or de-swells on application of an electric field from t...

Here we report the first application of a fractal analysis of the viscoelastic properties of incipient blood clots. We sought to ascertain whether the incipient clot's fractal dimension, D(f,) could be used as a functional biomarker of hemostasis. The incipient clot is formed at the gel point (GP) of coagulating blood, the GP demarcating a function...

This paper reports simulated sequential frequency sweep data which have been reconstructed from time resolved viscoelastic data obtained by Fourier transform mechanical spectroscopy. Comparisons of the results show that the recording of anomalous values of the stress relaxation power law exponent α at the Gel Point under ‘rapid’ gelling conditions...

This study reports an automated numerical method for the location of the gel point in oscillatory shear data and demonstrates its potential application in measurements on therapeutically modified (heparinised) samples of healthy coagulating blood. Heparin prolongs the onset of clot formation and has a significant effect on the microstructure of the...

We have investigated the hypothesis that in whole blood the incipient clot formed at the gel point (GP) is characterised by a fractal microstructure [1,2] and that this could be detected in healthy and anticoagulated blood. We compared the gel time (GT) required to form the incipient clot and the corresponding fractal dimension (df) against laborat...

We report studies of the coagulation of samples of whole human blood by oscillatory shear techniques, including Fourier Transform Mechanical Spectroscopy (FTMS). These techniques are used herein to identify the Gel Point of coagulating blood in terms of the Chambon-Winter Gel Point criterion which provides a rheometrical basis for detecting the est...

We report studies of the coagulation of samples of whole human blood by oscillatory shear techniques, including Fourier Transform Mechanical Spectroscopy (FTMS). These techniques are used herein to identify the Gel Point of coagulating blood in terms of the Chambon-Winter Gel Point criterion which provides a rheometrical basis for detecting the est...

This paper reports the results of experiments which were designed to test the hypothesis that the recording of anomalous values of rheological exponents in the gelation of gelatin may, under some circumstances, be due to inappropriate rheometry. Results obtained from stress relaxation tests and oscillatory shear frequency sweeps are compared with t...

We report a study of the coagulation of whole blood by oscillatory shear Fourier transform mechanical spectroscopy. The results include the first identification of the Gel Point of coagulating blood in terms of the Chambon–Winter Gel Point criterion and we show how this may be used as an appropriate basis for detecting the establishment of an incip...

This review considers various rheometrical approaches that have been adopted to study blood coagulation, with special reference to the rheological assessment of clotting time and studies of the evolution of viscoelasticity during the course of fibrin polymerization and cross-linking. The significance of the Gel Point in blood coagulation studies is...

The rheological behaviour of coagulating human blood has been measured using multiple strain wave frequencies. The results indicate that coagulating blood, prior to the point of incipient clot formation, can be modelled by a modified form of the Gross-Marvin 'ladder' model, and the benefits of such modeling for blood coagulation are discussed.

The rheological behaviour of coagulating human blood has been measured using a multiple frequency rheometrical technique known as Fourier Transform Mechanical Spectroscopy (FTMS). The results indicate that coagulating blood, prior to the point of incipient clot formation, can be modelled by a modified form of the Gross-Marvin ‘ladder’ model, and th...

The principal objectives of the work reported in this paper were two-fold. Firstly, to assess, by means of the numerical simulation of transverse wave propagation within a linear viscoelastic medium, the degree to which wavegroup propagation involving a finite frequency interval (2Δω) corresponds to an ‘ideal’ beat (i.e. one for which 2Δω → 0). Sec...

We report experimental work involving the rapid uniaxial elongation of jets of mobile (i.e. low shear viscosity) liquids formed by the collapse of a gas bubble under a cavitation-generated shockwave. The results of this work establish that the jets experience a significant degree of extensional deformation, at high rates of extension (typically > 1...