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The clinical utility of measuring pressure at the prosthetic socket-residual limb interface is currently unknown.This study aimed to identify whether measuring interface pressure during prosthetic design and fabrication results in closer agreement in pressure measurements between sockets made by different clinicians, and a reduction in pressure over areas of concern. It also investigated whether clinicians value knowing the interface pressure during the fabrication process.Mixed methods.Three prosthetists designed a complete prosthetic system for a transtibial residual limb surrogate. Standardised mechanical testing was performed on each prosthetic system to gain pressure measurements at four key anatomical locations. These measurements were provided to the clinicians, who subsequently modified their sockets as each saw fit. The pressure at each location was re-measured. Each prosthetist completed a survey that evaluated the usefulness of knowing interface pressures during the fabrication process.Feedback and subsequent socket modifications saw a reduction in the pressure measurements at three of the four anatomical locations. Furthermore, the pressure measurements between prosthetists converged. All three prosthetists found value in the pressure measurement system and felt they would use it clinically.Results suggest that sensors measuring pressure at the socket-limb interface has clinical utility in the context of informing prosthetic socket design and fabrication. If the technology is used at the check socket stage, iterative designs with repeated measurements can result in increased consistency between clinicians for the same residual limb, and reductions in the magnitudes of pressures over specific anatomical landmarks.This study provides new information on the value of pressure feedback to the prosthetic socket design process. It shows that with feedback, socket modifications can result in reduced limb pressures, and more consistent pressure distributions between prosthetists. It also justifies the use of pressure feedback in informing clinical decisions.

The interface between the residual limb and the socket of a person with an amputation experiences complex loading conditions during daily activities. Currently, the effect of such loading conditions on tissue health and comfort is poorly assessed. This is largely due to the lack of appropriate sensing technology to facilitate measurement of strains/stresses at this interface. This paper will outline a novel method to simultaneously measure the normal and shear strains using fiber Bragg grating sensors embedded into a foam liner that sits at the prosthetic interface. Furthermore, this method enables the measurement of normal and shear strains when the material properties of the embedding material are unknown. As a validation to the new technique, an application of this process using Pe-Lite foam is presented. A comparison of the derived load based on this process to an applied load measured using a material testing machine is performed. Results show a very good agreement of measured normal and shear strains/stresses for loads below 20 N. However, discrepancies were evident above this load. This paper has provided a proof of concept for using fiber Bragg grating sensors in materials with unknown or inconsistent properties. This method provides a pathway for embedding sensors in prosthetic and orthotic applications.

Myocardial bridging is a congenital anomaly wherein a segment of a coronary artery passes under a ‘bridge’ of heart muscle rather than resting upon the heart’s surface. Although it is usually benign, myocardial bridging has been associated with adverse clinical events including ischaemia, arrhythmia and sudden death. Moreover, there is a tendency for atherosclerotic lesions to develop upstream of the bridge. These lesions may be the result of adverse fluid dynamic phenomena induced by the periodic compression of the artery by the overlying myocardial bridge. It is not possible to visualise these phenomena in vivo, and in this study we present an in vitro model capable of replicating the bridging conditions. This model is comprised of a pressure-measuring guide wire and catheter, a piston pump, a scaled artery model, and a ‘myocardial bridging mechanism’ which periodically compresses the artery model. A proportional-integral-derivative (PID) controller allowed the piston pump to recreate a patient-specific aortic pressure waveform upstream of the occluded artery model segment for each study. Stationary occlusions—achieved by placing 3D printed ‘stenosis inserts’ within the artery model—induced globally reduced pressures downstream of the stenosis when compared against the upstream pressure waveform. Conversely, the pressures downstream of the dynamic stenoses generated by the bridging mechanism closely matched the upstream pressures at all stages of the cardiac cycle except at the end of systole. This divergent pressure behaviour at the end of systole was similarly observed in vivo within a patient with a myocardial bridge. Flow visualisation using a laser sheet enabled dynamic flow structures to be observed, including recirculating flow regions, which may be precursors to arterial dysfunction.

Arteriovenous fistula creation is the preferred vascular access for haemodialysis therapy, but has a large failure rate in the maturation period. This period generally lasts 6 to 8 weeks after surgical creation, in which the vein and artery undergo extensive vascular remodelling. In this review, we outline proposed mechanisms for both arteriovenous fistula maturation and arteriovenous fistula failure. Clinical, animal and computational studies have not yet shown a definitive link between any metric and disease development, although a number of theories based on wall shear stress metrics have been suggested. Recent work allowing patient-based longitudinal studies may hold the key to understanding arteriovenous fistula maturation processes.

Aim We sought to determine if a modification to the peri-anastomotic vein configuration during end-to-side arteriovenous fistula (AVF) creation would achieve a favourable haemodynamic environment compared with the standard acute-angle AVF. Methods Computational fluid dynamics (CFD) modelling of two end-to-side AVF geometries (smooth-vein-loop vs. acute-angle) allowed for haemodynamic modelling. Haemodynamic fields at various stages of the pulse cycle were observed and compared across both models. Results We found a significant reduction in flow disturbance in the modified shape at the peri-anastomotic vein region, a common site for stenosis. The acute anastomotic angle characteristic of a standard-end-to-side AVF was found to cause significant flow disturbance throughout the pulse cycle. Conclusion Computational modelling indicates that improvements in the haemodynamic environment of an AVF are achievable when a gentle change in direction is present in the vein segment. This may lead to improved maturation and AVF patency through reduction in disturbed flow patterns.

Stereoscopic particle image velocimetry (S-PIV) was used to quantify the dynamic flow field caused by the venous needle jet (VNJ) in an idealised model of hemodialysis cannulation. Scaling based on Reynolds number ensured dynamic similarity with physiological conditions. Measurements taken along the center plane indicate the presence of a steady secondary flow region, which develops downstream of the impingement region. Upon impingement, a wall jet forms on the floor of the vein and spreads along the curvature of the vessel. Circulating flow forms due to the interaction between the jet spreading and the wall jet. This secondary flow region represents a potential site of stenosis on the roof of the vein where flow is reversed. The effects of the circulating flows can be minimized by using shallow needle angles, low needle flow rates and placement of the needle away from the walls of the vein.

The jet of fluid returning to the patient through a hemodialysis venous needle has previously been reported as a potential source of endothelial damage which can lead to intimal hyperplasia (IH) in arteriovenous fistulae (AVF). Metal needles are the current standard practice for accessing the vascular system in hemodialysis. However, plastic cannulae have been used in Japan for 30 years. This study utilized computational fluid dynamics to analyze the hemodynamics of blood exiting a plastic cannula and determined the optimal placement and blood flow rate. Transient simulations were run using a 15G Argyle Safety Fistula Cannula with Anti-Reflux Valve inserted into an idealized cephalic vein. The cannula tip was fixed at three different locations within the vein (upper third, middle, and lower third) with blood flow rates of 200 mL/min, 300 mL/min, and 400 mL/min imposed. The high degree of jet break down immediately after exiting the cannula was attributed to the staggered side hole arrangement, position of the cannula in the vein, and the imposed blood flow rate. Elevated levels of wall shear stress which may lead to IH were identified at the site of jet impingement on the vein floor as well as regions of high residency time. The risk of IH may be minimized by enhancing the breakdown of the jet through the use of optimal blood flow rates between 300 and 400 mL/min and ensuring the cannula tip is placed away from the walls of the vein.

The creation of an arteriovenous fistula (AVF) is a common surgical procedure in hemodialysis patients suffering from end-stage renal disease (ESRD). However, several complications may occur after surgery, including thrombosis, stenosis, and aneurysm. These complications are attributed to hemodynamics perturbations including pathophysiological wall shear stress (WSS) and flow recirculation zones. In this study, we present a computational hemodynamic analysis in a model of a mature side-to-side AVF, which is then validated by experimental measurements. Both computational and experimental results confirmed the presence of complex flow patterns within the AVF with vortices initially developing at the center of the venous region and gradually moving downstream, such that at four characteristic anastomosis lengths downstream, the flow disturbances became minimum. A complex pattern was also observed in WSS distribution with regions of low and high WSS identified in proximal vein and feeding artery, respectively. In addition, the temporal distribution of WSS varied significantly along the venous wall where a large portion of it remained above normal levels of WSS during systole while the area was largely normal during diastole. Our findings support the hypothesis that high WSS is not detrimental to immediate patency of AVF; however, other factors including low WSS and temporal and spatial gradients of WSS increase the risk of vascular access complications.

Background and objective: The use of patient-specific CFD modelling for arteriovenous fistulae (AVF) has shown great clinical potential for improving surveillance, yet the use of imaging modes such as MRI and CT for the 3D geometry acquisition presents high costs and exposure risks, preventing regular use. We have developed an ultrasound based procedure to bypass these limitations. Methods: A scanning procedure and processing pipeline was developed specifically for CFD modelling of AVFs, using a freehand ultrasound setup combining B-mode scanning with 3D probe motion tracking. The scanning procedure involves sweeping along the vasculature to create a high density stack of B-mode frames containing the lumen geometry. This stack is converted into a continuous volume and transient flow waveforms are recorded at the boundaries, synchronised with ECG and automatically digitised, forming realistic boundary conditions for the CFD models. This is demonstrated on a diseased patient-specific AVF. Results: The three scans obtained using this procedure varied in geometry and flow behaviour, with regions of disease located in the first two scans. The outcome of the second procedure seen in the third scan indicated successful restoration with no sites of disease and higher flow. The models gave insight into the lumenal changes in diameter for both the artery and vein segments, as well as characterising hemodynamic behaviours in both the diseased and restored states. Vascular segment resistances obtained from the CFD models indicate a significant reduction once disease was removed, resulting in much higher flows enabling the patient to resume dialysis. Conclusion: The methodology described in this study allowed for a multifaceted analysis and high level tracking in terms of both geometry and flow behaviours for a patient case, demonstrating significant clinical utility and practicality, as well as enabling further research into vascular disease progression in AVFs through longitudinal analysis.

Abdominal aortic aneurysms (AAA) are seen in both suprarenal and infrarenal positions though infrarenal is more common. Initiation and development of thrombosis and atherosclerosis in abdominal aneurysms and renal arteries have previously been correlated to areas of adverse haemodynamic conditions such as flow recirculation, low shear stress and high temporal oscillation in shear. However, it is still unknown if the haemodynamic perturbations arisen from different types of aneurysms, suprarenal vs infrarenal, contribute to the formation of atherosclerosis within the renal branches. In this work, virtual models of symmetric and asymmetric AAAs located above and below renal branches were simulated under resting and exercise conditions to determine the influence of location of the aneurysm on important haemodynamic parameters. The results showed that the size of the recirculation zones and vortices inside the renal branches and aneurysm region is considerably smaller in the infrarenal AAAs than the suprarenal models. Furthermore, our data demonstrated that occurrence of the aneurysm below the renal level augments the magnitude of shear stress and reduces the oscillations in shear in renal branches. These results confirm that the suprarenal AAA promotes thrombosis initiation within the aneurysm and increases the risk of endothelial dysfunction and the development of atherosclerosis in renal arteries. The findings also showed that under exercise conditions the haemodynamic differences between the suprarenal and infrarenal AAAs become less important and the local unfavourable haemodynamic conditions are improved to some extent.

Lower-limb amputees commonly utilize non-articulating energy storage and return (ESAR) prostheses for high impact activities such as sprinting. Despite these prostheses lacking an articulating ankle joint, amputee gait analysis conventionally features a two-link segment model of the prosthetic foot. This paper investigated the effects of the selected link segment model׳s marker-set and geometry on a unilateral amputee sprinter׳s calculated lower-limb kinematics, kinetics and energetics. A total of five lower-limb models of the Ottobock® 1E90 Sprinter were developed, including two conventional shank-foot models that each used a different version of the Plug-in-Gait (PiG) marker-set to test the effect of prosthesis ankle marker location. Two Hybrid prosthesis-specific models were then developed, also using the PiG marker-sets, with the anatomical shank and foot replaced by prosthesis-specific geometry separated into two segments. Finally, a Multi-link segment (MLS) model was developed, consisting of six segments for the prosthesis as defined by a custom marker-set. All full-body musculoskeletal models were tested using four trials of experimental marker trajectories within OpenSim 3.2 (Stanford, California, USA) to find the affected and unaffected hip, knee and ankle kinematics, kinetics and energetics. The geometry of the selected lower-limb prosthesis model was found to significantly affect all variables on the affected leg (p < 0.05), and the marker-set also significantly affected all variables on the affected leg, and none of the unaffected leg variables. The results indicate that the omission of prosthesis-specific spatial, inertial and elastic properties from full-body models significantly affects the calculated amputee gait characteristics, and we therefore recommend the implementation of a MLS model.

Conventional lower-limb mechanical models were originally developed for gait analysis of ablebodied Conventional lower-limb mechanical models were originally developed for gait analysis of ablebodied subjects and therefore potentially misrepresent prosthetic foot behavior when applied to modern energy storage and return (ESAR) prostheses. This review investigates the limitations of current models of prosthetic foot dynamics and kinematics. The Scopus online database was used to identify 236 articles on prosthetic foot behavior during either experiments or simulations, categorized into three main types of models: 74% (n = 175) of studies featured a rigid-link model, 17% (n = 39) a lumped-parameter model and 10% (n = 23) finite element (FE) analysis. Notably, 64% (n = 152) of the studies used a conventional two-link segment model, yet only 8% (n = 20) featured the rigid, articulating prosthesis that satisfies this model's underlying rigid-body mechanics assumptions. Conversely, the available preliminary studies on multi-link segment, lumped-parameter and FE models present viable and more mechanically relevant alternatives to conventional techniques, particularly for ESAR prostheses. Expanding these alternative models to include inertial behavior, multiple-degrees of freedom and standardization of boundary conditions will lead towards both accurate and standardized prosthetic foot analysis.

Thrombus in a femoral artery may form under stagnant flow conditions which vary depending on the local arterial waveform. Four different physiological flow waveforms - poor (blunt) monophasic, sharp monophasic, biphasic and triphasic - can exist in the femoral artery as a result of different levels of peripheral arterial disease progression. This study aims to examine the effect of different physiological waveforms on femoral artery haemodynamics. In this regard, a fluid-structure interaction analysis was carried out in idealised models of bifurcated common femoral artery. The results showed that recirculation zones occur in almost all flow waveforms; however, the sites at where these vortices are initiated, the size and structure of vortices are highly dependent on the type of flow waveform being used. It was shown that the reverse diastolic flow in biphasic and triphasic waveforms leads to the occurrence of a retrograde flow which aids in 'washout' of the disturbed flow regions. This may limit the likelihood of thrombus formation, indicating the antithrombotic role of retrograde flow in femoral arteries. Furthermore, our data revealed that the flow particles experience considerably higher residence time under blunt and sharp monophasic waveforms than under biphasic and triphasic waveforms. This confirms that the risk of atherothrombotic plaque initiation and development in femoral arteries is higher under blunt and sharp monophasic waveforms than under biphasic and triphasic flow waveforms.

Maintaining the patency of vascular access is essential for performing efficient hemodialysis. Appropriate cannulation technique is critical in maintaining the integrity of vascular access. This study focused on analyzing the hemodynamic effect of needle rotation, which is performed to alleviate the pressure if the needle becomes attached to the blood vessel wall. The hemodynamic benefits (normal wall shear stress [WSS] and smooth flow with no oscillatory motion) of this technique are investigated in an idealized model of the cephalic vein in order to determine a needle position that will reduce conditions known to contribute to vascular access failure. A computational fluid dynamics study was conducted, with antegrade and retrograde orientations simulated on the arterial needle, whereas the venous needle is placed in the antegrade orientation. In every case, needle rotation offered no hemodynamic benefit in minimizing the conditions known to cause endothelial damage, a precursor to vascular access failure. Venous needle rotation reduced the maximum WSS by 30%. However, the WSS was above the range, which may damage the endothelial layer. The arterial needle in the antegrade orientation produced a large region of oscillatory shear, whereas a retrograde orientation produced a region of smooth flow in the vicinity of the needle with only a small region of oscillatory shear. The flow through the venous needle back eye was negligible, whereas the arterial needle back eye was more efficient in the retrograde orientation. Therefore, the venous needle should not be rotated, whereas the arterial needle may be rotated to alleviate pressure with consideration given to the orientation of the needle.

Microbubbles have previously been detected in the hemodialysis extracorporeal circuit and can enter the blood vessel leading to potential complications. A potential source of these microbubbles is highly pulsatile flow resulting in cavitation. This study quantified the pulsatility produced by the roller pump throughout the extracorporeal circuit. A Sonosite S-series ultrasound probe (FUJIFILM Sonosite Inc., Tokyo, Japan) was used on a single patient during normal hemodialysis treatment. The Doppler waveform showed highly pulsatile flow throughout the circuit with the greatest pulse occurring after the pump itself. The velocity pulse after the pump ranged from 57.6 ± 1.74 cm/s to -72 ± 4.13 cm/s. Flow reversal occurred when contact between the forward roller and tubing ended. The amplitude of the pulse was reduced from 129.6 cm/s to 16.25 cm/s and 6.87 cm/s following the dialyzer and venous air trap. This resulted in almost nonpulsatile, continuous flow returning to the patient through the venous needle. These results indicate that the roller pump may be a source of microbubble formation from cavitation due to the highly pulsatile blood flow. The venous air trap was identified as the most effective mechanism in reducing the pulsatility. The inclusion of multiple rollers is also recommended to offer an effective solution in dampening the pulse produced by the pump.

We sought to determine if a modification to the peri-anastomotic vein configuration during end-to-side arteriovenous fistula (AVF) creation would achieve a favourable haemodynamic environment compared with the standard acute-angle AVF.Computational fluid dynamics (CFD) modelling of two end-to-side AVF geometries (smooth-vein-loop vs. acute-angle) allowed for haemodynamic modelling. Haemodynamic fields at various stages of the pulse cycle were observed and compared across both models.We found a significant reduction in flow disturbance in the modified shape at the peri-anastomotic vein region, a common site for stenosis. The acute anastomotic angle characteristic of a standard-end-to-side AVF was found to cause significant flow disturbance throughout the pulse cycle.Computational modelling indicates that improvements in the haemodynamic environment of an AVF are achievable when a gentle change in direction is present in the vein segment. This may lead to improved maturation and AVF patency through reduction in disturbed flow patterns.

Surface modification is a flexible approach for manipulating blood-material interactions with the advantage that many different forms of devices can be modified without changing the bulk material properties. This study hypothesises that organic modifiers (OMs) used to prepare silicates for incorporation into polyurethane (PU) nanocomposites can migrate and be expressed on the PU surface and directly affect biological interactions. Two OMs of equivalent chain length with COOH or CH3 end groups were used, and their surface expression was measured. Results suggested that surface expression occurred only in nanocomposites with methyl modified silicates. Platelet adhesion to the CH3 and COOH modified nanocomposites showed significantly lower adhesion on the CH3 nanocomposites. Similarly, platelet activation was lower on CH3 nanocomposites as indicated by morphological differences in degree of spreading. Finally, surface roughness showed little correlation between material type and platelet adhesion, indicating that roughness was not a significant factor influencing platelet interactions. This study proposes that a nanocomposite approach with migrating OMs can provide an elegant platform for surface modification of polymers for biomedical applications. Refereed/Peer-reviewed

The source of micro bubbles within the haemodialysis extracorporeal circuit is currently unknown. If micro bubbles enter the body they may result in several health issues. Micro bubbles may be formed near the needles if the local pressure drops below the vapour pressure of blood, causing cavitation. Cavitation has been hypothesised to occur at the arterial needle due to the lower local pressures from the suction forces created by the peristaltic blood pump. A CFD model was developed to study the possible inception of cavitation from various options. Variations in needle flow rate and needle orientation were studied using a transient waveform, to determine the clinical conditions in which cavitation might occur. Cavitation may occur within the needle bore when the flow rates are temporarily elevated in the waveform. Needle orientation was also found to have no effect on cavitation potential.

Hemodialysis is an extracorporeal system which removes the waste product from kidneys for patients with kidney failure. Air bubbles within the system can cause several deficiencies to the system, and more importantly serious health issues to the patients. Therefore, different types of air traps (artery and venous side) are situated in the setup to prevent air bubbles passing through the system and being sent to the body. There have been evidence of the air trap deficiency. In order to understand these deficiencies the flow inside these air traps need to be understood. The investigation of the flow structures in air traps allow us to predict the efficiency of the air traps in capturing the air bubbles and preventing them from passing through. Computational fluid dynamic (CFD) has been used to compare the flow inside both these air traps. The results show interesting flow phenomena leading to explanations of the air bubble capturing effect.

The prediction of conditions that may result in thrombus formation is a useful application of computational fluid dynamics. A number of techniques exist, based on the consideration of wall shear stress and regions of low blood flow; however, no clear guideline exists for the best practice of their use. In this paper, the sensitivity of each parameter and the specific mechanical forces are explained, before the optimal indicator of thrombosis risk is outlined. An extracorporeal access device cavity provides a suitable geometry to test the methodology. The recommended method for thrombus prediction considers areas with a calculated residence time (RT) and shear strain rate (SSR) thresholds, here set to RT1 and SSR 10 s(- 1). Evidence of thrombosis was found for physiological waveforms with an absence of reverse flow, which is expected to 'wash out' the cavity. The predicted thrombosis sites compare well with evidence collected from explanted devices.

On average, an end-stage renal disease patient will undergo hemodialysis (HD) three or four times a week for 4-5 h per session. Any minor imperfection in the extracorporeal system may become significant in the treatment of these patients due to the cumulative exposure time. Recently, air traps (a safety feature of dialysis systems) have been reported to be inadequate in detecting microbubbles and may even create them. Microbubbles have been linked to lung injuries and damage to the brain in chronic HD patients; therefore the significance of microbubbles has been revisited. Bubbles may originate at the vascular access sites, sites of local turbulent blood flow, the air trap, or in the bloodlines after priming with saline prior to use. In this paper, computational fluid dynamics is used to model blood flow in the air trap to determine the likely mechanisms of microbubble dynamics. The results indicate that almost all bubbles with diameters less than 50 μm and most of the bubbles of 50-200 μm pass through the air trap. Consequently, the common air traps are not effective in removing bubbles less than 200 μm in diameter.

There are a range of factors proposed to perturb the release mechanisms in polymer nanocomposites (NCs) but little focus has been directed towards the understanding of interactions between the drug and NC which can also affect the drug release behaviour. A variety of model/active drugs of different size, surface charge and polarity were investigated for their impact on silicate dispersion and drug release of polyurethane nanocomposites (PUNC) composed of three components. Findings revealed that the addition of a fourth component, i.e. a drug, can disrupt the dispersion of silicates and the disruption is dependent on the strength of electrostatic interactions and hydrogen bonding with the silicates. As a result, the release rate and level of retardation were governed largely by the physical and chemical properties of the drug. Furthermore, due to these interactions, release of hydrophilic drugs is not necessarily at a higher rate than for hydrophobic drugs but is dependent on the host polymer interaction.

Arteriovenous fistulae (AVF) are the favored choice of vascular access but still have poor long-term success. Hemodynamic parameters play an important role in vascular health and have been linked to the development of intimal hyperplasia (IH), a pathological growth of the blood vessel initiated by injury. This study aimed to investigate the hemodynamics surrounding the arterial needle (AN) and venous needle (VN), using computational fluid dynamics. A range of blood flow rates, needle positions, and needle orientations were examined. Disturbed flows were found around AN tip in both antegrade and retrograde orientations, which result in regions of high residency time on the surface of the vein and may disrupt endothelial function. Conversely, a high speed jet exits the VN, which produced high wall shear stresses (WSSs) at the point of impingement which can damage the endothelium. The secondary flows produced by jet dissipation also resulted in regions of high residency time, which may influence endothelial structure, leading to IH. The use of shallow needle angles, a blood flow rate of approximately 300 ml/min, and placement of the needle tip away from the walls of the vein mitigates this risk.

The creation of an arteriovenous fistula (AVF) is a common surgical procedure in hemodialysis patients suffering from end-stage renal disease (ESRD). However, several complications may occur after surgery, including thrombosis, stenosis, and aneurysm. These complications are attributed to hemodynamics perturbations including pathophysiological wall shear stress (WSS) and flow recirculation zones. In this study, we present a computational hemodynamic analysis in a model of a mature side-to-side AVF, which is then validated by experimental measurements. Both computational and experimental results confirmed the presence of complex flow patterns within the AVF with vortices initially developing at the center of the venous region and gradually moving downstream, such that at four characteristic anastomosis lengths downstream, the flow disturbances became minimum. A complex pattern was also observed in WSS distribution with regions of low and high WSS identified in proximal vein and feeding artery, respectively. In addition, the temporal distribution of WSS varied significantly along the venous wall where a large portion of it remained above normal levels of WSS during systole while the area was largely normal during diastole. Our findings support the hypothesis that high WSS is not detrimental to immediate patency of AVF; however, other factors including low WSS and temporal and spatial gradients of WSS increase the risk of vascular access complications.

The jet of fluid returning to the patient through a hemodialysis venous needle has previously been reported as a potential source of endothelial damage which can lead to intimal hyperplasia (IH) in arteriovenous fistulae (AVF). Metal needles are the current standard practice for accessing the vascular system in hemodialysis. However, plastic cannulae have been used in Japan for 30 years. This study utilized computational fluid dynamics to analyze the hemodynamics of blood exiting a plastic cannula and determined the optimal placement and blood flow rate. Transient simulations were run using a 15G Argyle Safety Fistula Cannula with Anti-Reflux Valve inserted into an idealized cephalic vein. The cannula tip was fixed at three different locations within the vein (upper third, middle, and lower third) with blood flow rates of 200 mL/min, 300 mL/min, and 400 mL/min imposed. The high degree of jet break down immediately after exiting the cannula was attributed to the staggered side hole arrangement, position of the cannula in the vein, and the imposed blood flow rate. Elevated levels of wall shear stress which may lead to IH were identified at the site of jet impingement on the vein floor as well as regions of high residency time. The risk of IH may be minimized by enhancing the breakdown of the jet through the use of optimal blood flow rates between 300 and 400 mL/min and ensuring the cannula tip is placed away from the walls of the vein.

The suitability of finite element analysis (FEA) for standardizing the mechanical characterization of energy storage and return (ESAR) prostheses was investigated. A methodology consisting of both experimental and numerical analysis was proposed and trialed for the Vari-flex® ModularTM, Flex-foot Cheetah and Cheetah Xtreme by Ossur® and a 1E90 Sprinter by Ottobock®. Gait analysis was conducted to determine suitable orientation angles for non-destructive testing (NDT) of the ESAR prostheses followed by a quasi-static inverse FEA procedure within COMSOL Multiphysics®, where the NDT conditions were replicated to determine the homogenized material properties of the prostheses. The prostheses' loading response under bodyweight for an 80kg person was then simulated, using both Eigenfrequency and time-dependent analysis. The apparent stiffness under bodyweight was determined to be 94.7, 48.6, 57.4 and 65.0Nmm-1 for the Vari-flex® ModularTM, Flex-foot Cheetah, Cheetah Xtreme and 1E90 Sprinter, respectively. Both the energy stored and returned by the prostheses varied negatively with stiffness, yet the overall efficiency of the prostheses were similar, at 52.7, 52.0, 51.7 and 52.4% for the abovementioned prostheses. The proposed methodology allows the standardized assessment and comparison of ESAR prostheses without the confounding influences of subject-specific gait characteristics.

J Biomed Mater Res B Appl Biomater 2013; 101: 310–319. Urinary catheters are among the most frequently used medical devices in clinical practice. However, their use is associated with high rates of nosocomial infection. This study investigates the use of polyurethane nanocomposites (PUNCs) incorporating an antimicrobial agent, chlorhexidine diacetate (CHX), behaving as nanoparticle dispersant and model drug/active agent, as sustained-release antibacterial biomaterials in urinary devices. A range of PUNCs incorporating organically modified silicate (OMS) nanoparticles with CHX was fabricated using a solution-cast method. PUNCs with free CHX added into the bulk polymer were also made. Materials were assessed for antibacterial activity in an in vitro urinary tract (UT) model and release kinetics of CHX was studied. PUNCs demonstrated sustained antibacterial activity against Staphylococcus epidermidis in the UT model, reaching 50 days infection-free in materials with 2 wt % free CHX loading. Drug-release profiles demonstrated that, compared with microcomposite and unfilled polyurethane, the initial burst effect was significantly reduced in PUNCs. Prolonged drug release was achieved through incorporation of OMS, hypothesized to be due to a combination of barrier properties created by the nanoinclusions and strong interactions between CHX and MMT within the PUNCs. Use of PUNCs for sustained drug release in long-term urinary applications shows promise in addressing catheter-related nosocomial infections. Editorial Comment: This is the latest publication from this group in their efforts to build (engineer) a better mousetrap. Two obvious ways to decrease catheter associated infections are to 1) reduce the frequency and duration of catheterization, and 2) create a catheter resistant to bacteria. Various coatings have been used for catheters with mixed results. This group uses the antibacterial CHX incorporated into a polyurethane nanocomposite. They demonstrate sustained release of CHX with this composition and, in an in vitro staphylococcus epidermidis model, reduced bacterial counts compared to control material. How well this formulation would work at decreasing bacterial counts and, importantly, symptomatic infections in vivo compared to other catheters remains to be determined. However, the use of nanocomposites, in theory, is promising.

Organically modified layered silicates were incorporated into a polyether soft-segment polyurethane to form composites of at least delaminated morphology. The primary organic modifier was a quaternary ammonium compound; however, one composite included an alternative amino undecanoic acid-modified silicate. The composites' biostability was assessed in an in vivo ovine model over a period of 6 weeks. Attenuated total reflectance-Fourier transform infrared analysis and semi-quantitative scanning electron microscopy image rating indicate a significant enhancement of the base polyurethane biostability with the inclusion of silicate at 3 wt.%. The potential effect at 15 wt.% was confounded by probable leaching of the quaternary ammonium compound affecting the tissue response. The amino undecanoic acid composite compared favourably with the quaternary ammonium compound composite of equivalent silicate loading, and offers the promise of a more favourable tissue response.

Gait summary measures have been developed as a convenient method to communicate overall gait pathology. These measures are primarily used in the context of paediatric cerebral palsy and their use remains largely untested in other disability groups. This study assessed the suitability of gait summary measures for use with lower limb amputees. Modified (m) versions of three published gait summary measures were investigated - the Gillette Gait Index (mGGI), the Gait Deviation Index (mGDI) and the Gait Profile Score (mGPS) in conjunction with the Movement Analysis Profile (MAP). Twenty unilateral lower limb amputees underwent three-dimensional gait analysis. All measures reported significant differences between levels of amputation on the prosthetic limb. The mGGI and mGPS detected significant differences between the levels of amputation on the intact side, but the mGDI did not. All gait summary measures were moderately to strongly correlated with leg-length normalised self-selected walking speed and strong correlations were reported between all measures. The MAP exposed common strategies in amputee gait and showed that sagittal hip and knee kinematics contributed predominantly to overall gait deviation in this population group. The mGGI, mGDI and mGPS identified, quantified and stratified gait pathology, indicating that any of the gait measures investigated in this study can be applied as outcome measures in research and case management in lower limb amputees.

Computational fluid dynamics simulation of stenosed arteries allows the analysis of quantities including wall shear stress, velocity, and pressure; detailed in vivo measurement is difficult yet the analysis of the fluid dynamics related to stenosis is important in understanding the likely causes and ongoing effects on the integrity of the vessel. In this study, a three-dimensional Large Eddy Simulation is conducted of a 50% occluded vessel, with a typical femoral artery profile used as the transient inlet conditions. The fluid is assumed to be homogenous, Newtonian and incompressible and the walls are assumed rigid. The stenosis is axisymmetric, however the three-dimensional study allows for a flow field that is not axisymmetric and results show significant three-dimensionality. High values of wall shear stress and oscillatory values of wall shear stress (varying in both space time) are observed. The results of the study give insight into the time-varying flow structures for a mildly stenosed artery and indicate that three-dimensional simulations may be important to gain a complete understanding of the flow field.

The need to optimize therapeutic outcomes while minimizing side effects is a major driving force for research and development in the controlled drug delivery field. Polymer nanocomposites (NCs) are an emerging class of materials with remarkable potential for controlled drug delivery. There are a range of release mechanisms that characterize polymer NC systems, and these may be perturbed not only by the addition of nanofillers, but also by the type of drug and the interactions of the drug with the components of the system.The focus of this review is on non-degradable polymer NC systems. In particular, the types of drug delivery approach from these polymer NCs and the theoretical models developed to describe those approaches are discussed. The importance of component interactions and factors affecting drug delivery from polymer NCs is also addressed.Despite the remarkable potential and extensive research being conducted on polymer NCs for use in drug delivery, commercialization and large-scale production are limited by the cost and difficulty in consistently producing fully exfoliated NCs. A continuing challenge for the field is to understand better the key interactions and structure-property relationships arising from different polymer, filler and drug combinations.

There is a scarcity of investigation into the mechanical properties of subdermal fat. Recently, progress has been made in the determination of subdermal stress and strain distributions. This requires accurate constitutive modelling and consideration of the subdermal tissues. This paper reports the results of a study to estimate non-linear elastic and viscoelastic properties of porcine subdermal fat using a simple constitutive model. High-resolution magnetic resonance imaging (MRI) was used to acquire a time series of coincident images during a confined indentation experiment. Inverse finite element analysis was used to estimate the material parameters. The Neo Hookean model was used to represent the elastic behaviour (μ = 0.53 ± 0.31 kPa), while a single-element Prony series was used to model the viscoelastic response (α = 0.39 ± 0.03, τ = 700 ± 255 s).

National and international guidelines outlining ethical conduct in research involving humans and animals have evolved into large and complex documents making the process of gaining ethics approval a complicated task for researchers in the area. Researchers, in particular those who are relatively new to the ethics approval process, can struggle to understand the parts of an ethics guideline that apply to their research and the nature of their ethical obligations to trial participants. With the scope of medical research likely to continue to expand in the future, it is clear that ethics guidelines will only increase in complexity and number. This paper describes one possible solution to the problem: the use of an internet-based expert system to intelligently and interactively distribute the information stored in ethics guidelines to individual researchers. This paper also details how one such system was designed and tested with respect to Australian medical research ethics guidelines.

Polymer nanocomposites (NC) are fabricated by incorporating well dispersed nanoscale particles within a polymer matrix. This study focuses on elastomeric polyurethane (PU) based nanocomposites, containing organically modified silicates (OMS), as bioactive materials. Nanocomposites incorporating chlorhexidine diacetate as an organic modifier (OM) were demonstrated to be antibacterial with a dose dependence related to both the silicate loading and the loading of OM. When the non-antibacterial OM dodecylamine was used, both cell and platelet adhesion were decreased on the nanocomposite surface. These results suggest that OM is released from the polymer and can impact on cell behaviour at the interface. Nanocomposites have potential use as bioactive materials in a range of biomedical applications.

SUMMARY In spite of greater awareness of the need for action to reduce obesity, the evidence on sustainable community approaches to prevent childhood and adolescent obesity is surprisingly sparse. This paper describes the design and methodological components of the Sentinel Site for Obesity Prevention, a demonstration site in the BarwonSouth West region of Victoria, Australia, that aims to build the programs, skills and evidence necessary to attenuate and eventually reverse the obesity epidemic in children and adolescents. The Sentinel Site for Obesity Prevention is based on a partnership between the region’s university (Deakin University) and its health, education and local government agencies. The three basic foundations of the Sentinel Site are: multi-strategy, multi-setting interventions; building community capacity; and undertaking program evaluations and population monitoring. Three intervention projects have been supported that cover different age groups ( preschool: 2 –5 years, primary school: 5– 12 years, secondary school: 13– 17 years), but that have many characteristics in common including: community participation and ownership of the project; an intervention duration of at least 3 years; and full evaluations with impact (behaviours) and outcome measures (anthropometry) compared with regionally representative comparison populations. We recommend the Sentinel Site approach to others for successfully building evidence for childhood obesity prevention and stimulating action on reducing the epidemic.

Obstructive Sleep Apnoea (OSA), characterised by repeated collapse of the pharyngeal airway during sleep, causes cessation of breathing followed by arousal, restoring normality. Continuous Positive Airway Pressure (CPAP) is a non-invasive, effective treatment for OSA where positive pressure is applied to the airway through a mask, maintaining patency. Nasal masks are commonly used, contacting the face across the upper lip, sides of the nose and the nasal bridge. Despite health benefits, therapy compliance is sub-optimal, often due to poor mask fit and discomfort. Masks have been designed to conform to the facial profile, but have not taken into account facial deformations. The nature of facial deformations while undergoing CPAP therapy is unknown. This study investigates the facial deformations experienced by a patient while undergoing nasal CPAP therapy. Magnetic Resonance Imaging (MRI) scans of the face were acquired of participants in the reference configuration and while undergoing CPAP therapy. The CPAP scan volume was registered onto the reference volume prior to surface generation for each state. Perpendicular deformation was measured from the reference facial profile to the deformed profile. Large facial deformations were measured at the sides of the nose (4.6±1.6mm) and the upper lip (4.9±1.8mm) with much smaller deformations at the nasal bridge (2.4±0.2mm). When normalised by applied load and tissue thickness, no difference was found. These findings and techniques can be used to consider facial deformation in the development of future nasal CPAP masks to improve comfort and compliance to therapy.

The presence of a spiral arterial blood flow pattern in humans has been widely accepted. It is believed that this spiral component of the blood flow alters arterial haemodynamics in both positive and negative ways. The purpose of this study was to determine the effect of spiral flow on haemodynamic changes in aorta-renal bifurcations. In this regard, a computational fluid dynamics analysis of pulsatile blood flow was performed in two idealised models of aorta-renal bifurcations with and without flow diverter. The results show that the spirality effect causes a substantial variation in blood velocity distribution, while causing only slight changes in fluid shear stress patterns. The dominant observed effect of spiral flow is on turbulent kinetic energy and flow recirculation zones. As spiral flow intensity increases, the rate of turbulent kinetic energy production decreases, reducing the region of potential damage to red blood cells and endothelial cells. Furthermore, the recirculation zones which form on the cranial sides of the aorta and renal artery shrink in size in the presence of spirality effect; this may lower the rate of atherosclerosis development and progression in the aorta-renal bifurcation. These results indicate that the spiral nature of blood flow has atheroprotective effects in renal arteries and should be taken into consideration in analyses of the aorta and renal arteries.

Maintaining the patency of vascular access is essential for performing efficient hemodialysis. Appropriate cannulation technique is critical in maintaining the integrity of vascular access. This study focused on analyzing the hemodynamic effect of needle rotation, which is performed to alleviate the pressure if the needle becomes attached to the blood vessel wall. The hemodynamic benefits (normal wall shear stress [WSS] and smooth flow with no oscillatory motion) of this technique are investigated in an idealized model of the cephalic vein in order to determine a needle position that will reduce conditions known to contribute to vascular access failure. A computational fluid dynamics study was conducted, with antegrade and retrograde orientations simulated on the arterial needle, whereas the venous needle is placed in the antegrade orientation. In every case, needle rotation offered no hemodynamic benefit in minimizing the conditions known to cause endothelial damage, a precursor to vascular access failure. Venous needle rotation reduced the maximum WSS by 30%. However, the WSS was above the range, which may damage the endothelial layer. The arterial needle in the antegrade orientation produced a large region of oscillatory shear, whereas a retrograde orientation produced a region of smooth flow in the vicinity of the needle with only a small region of oscillatory shear. The flow through the venous needle back eye was negligible, whereas the arterial needle back eye was more efficient in the retrograde orientation. Therefore, the venous needle should not be rotated, whereas the arterial needle may be rotated to alleviate pressure with consideration given to the orientation of the needle.

Stent implantation is one of the most widely used interventional treatments for arterial stenosis which occurs predominantly due to atherosclerosis. Although stent placement can ensure very good patency of the lumen, stent-induced hemodynamic disturbance, which can lead to further stenosis, still remains a common clinical complication. This study investigates the degree of hemodynamic disturbance induced by stenting an idealized bifurcated popliteal artery, which branches into the anterior and posterior tibial arteries, and is known as a site prone to atherosclerosis. Both stent-free and stented bifurcated arteries were examined, and the local flow patterns analysed for the comparative disturbance through the use of Micro Particle Image Velocity (micro-PIV) system. A life-size model of the artery was reconstructed using dimensions obtained from a patient specific MRI scan. The experiments were conducted under steady flow conditions, and the flow rates across the bifurcation were visualized and measured using the micro-PIV system. It was shown that hemodynamic disturbances induced by the blood flow over the stent can further disrupt the arterial wall downstream of the stent causing further downstream vascular damage in addition to the in-stent restenosis. This downstream vascular disruption may require additional treatment depending on the type and severity of the damage. The results also support the hypothesis that links certain flow dynamic behaviour with the development of early intimal thickening, as the near wall low fluid momentum regions are found at locations where thickening was localized in bifurcated arteries in clinical studies.

The effect of various forms of sterilisation on a novel thermoplastic polyurethane elastomer synthesised using poly(hexamethylene oxide) (PHMO) and poly(dimethylsiloxane) (PDMS) macrodiols has been studied. The five sterilisation methods investigated were ethylene oxide (EtO) (single and multiple cycles), gas plasma, steam, vapour phase liquid chemical and gamma-irradiation (single and multiple cycles). Following sterilisation, scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to assess changes in the surface chemical structure and morphology, and gel permeation chromatography (GPC) and tensile testing were used to examine changes in bulk characteristics. Biostability was assessed using subcutaneous implantation of strained samples in sheep for 6 weeks. The results showed that the properties of the commercially available control material, Pellethane 2363-80A, were significantly affected by exposure to gamma-irradiation, steam and multiple cycles of EtO with aging and implantation compounding the effect. Exposure to a gas plasma sterilisation process resulted in significant degradation in both polyurethanes. A vapour phase liquid chemical sterilisation process caused minimal adverse effects. Sterilisation of the PDMS-based polyurethane using EtO, gamma-irradiation and autoclaving resulted in no significant changes in properties. The material's biostability was also unaffected by exposure to each of these sterilisation processes followed by short-term implantation suggesting that this material is a potential candidate for use in a wide range of implantable medical devices sterilised using commercially available processes. Further biostability studies should be performed to assess the longer-term in vivo biostability of the PDMS-based material sterilised using autoclaving and gamma-irradiation.

Lysozyme interaction with an acrylic-based hydrogel, poly(2-hydroxyethyl methacrylate) co-methacrylic acid (P(HEMA-MAA)), was investigated using a combination of quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR) and dual polarisation interferometry (DPI). This combination of techniques demonstrated that lysozyme initially absorbed into the hydrogel matrix and displaced water from the hydrogel while subsequent lysozyme additions were adsorbed onto the surface of the hydrogel material. QCM-D, being sensitive to bound water, showed an overall decrease in mass and stiffening of the layer after lysozyme addition. SPR, a water insensitive technique, showed a net mass increase after addition of lysozyme and buffer rinses. DPI showed that the first exposure of lysozyme to P(HEMA-MAA) was consistent with lysozyme absorption while subsequent lysozyme exposures were consistent with lysozyme adsorption. © 2005 Elsevier Ltd. All rights reserved.

The clinical effects of application of a permethrin acaricidal formulation, Provent-a-mite™, were studied on three species of reptiles by direct application to African spurred tortoises, Geochelone sulcata, and by application to the bedding of rosy boas, Lichanura trivirgata, and green iguanas, Iguana iguana, using on each occasion ten times the recommended dosage every fifth day for a total of six applications. No evidence of toxic reactions related to treatment with the permethrin formulation was found in any of the three species of reptiles treated, suggesting that Provent-a-mite™ is a safe product to use as an acaricide for control of ticks on other species of tortoises, snakes and lizards.

This is a report of the introduction of the exotic tick Amblyomma helvolum Koch into the United States on imported king cobras (Ophiophagus hannah). Information on the host range, geographical distribution and biology of A. helvolum is reviewed.