The Presence of a High Peak Feature Within Low-Average Shear Stimuli Induces Quiescence in Venous Endothelial Cells.

Wall shear stress (WSS) is an important stimulus in vascular remodelling and vascular lesion development. The current methods to assess and predict the risk associated with specific unsteady WSS consider the WSS mean values or the presence of reverse phases described by the oscillatory shear index. Recent evidence has shown that the accuracy of these methods is limited, especially with respect to the venous environment. Unsteady WSS are characterised by several features that may individually affect endothelial cells. Consequently, we assessed the effects of averaged WSS (TAWSS), temporal WSS gradient (TWSSG), maximum WSS (WSS peak) and reverse phase (OSI) by applying different WSS profiles to venous EC in-vitro, using a real-time controlled cone-and-plate cell-shearing device for 24 h. We found that TWSSG and WSS peak affect cell elongation and alignment respectively. We also found that the WSS waveforms with a peak of 1.5 Pa or higher significantly correlate with the induction of a protective phenotype. Cell phenotype induced by these high peak waveforms does not correlate to what is predicted by the hemodynamic indices currently used. The definition of reliable hemodynamic indices can be used to inform the computational models aimed at estimating the hemodynamic effects on vascular remodelling.

Long-term outcomes of urethral catheterisation injuries: a prospective multi-institutional study.

PURPOSE: There are no prospective data describing the incidence and spectrum of long-term complications associated with traumatic urethral catheterisation (UC). We prospectively monitored the long-term clinical outcomes and complications of patients with traumatic UC injuries. METHODS: A prospective study at two tertiary university hospitals was performed to record all referrals for iatrogenic urethral injuries caused by UC. Long-term follow-up was prospectively maintained by regular outpatient department visits and by monitoring all urological interventions and their outcomes from urinary catheter-related injuries. RESULTS: The incidence of traumatic UC was 13.4 per 1000 catheters inserted in male patients and 37 iatrogenic urethral injuries were recorded. The mean age was 74 ± 12 years and the mean length of follow-up was 37 ± 3.7 months. Urethral injuries were caused by inflating the catheter anchoring balloon in the urethra (n = 26) or by creating a false passage with the catheter tip (n = 11). In total, 29 patients (78%) developed urethral stricture disease during their follow-up; of which 11 have required at least one urethral dilation and two have required one urethrotomy. Three patients required long-term indwelling suprapubic catheter placement and seven patients opted for a long-term indwelling urethral catheter. There were eight patient mortalities; one of which was due to severe urosepsis resulting from catheter balloon inflation in the urethra. CONCLUSION: Catheter-related injuries are associated with significant long-term complications in this vulnerable patient cohort. In future, such injuries may be preventable if the safety profile of the urinary catheter is modified.

Serum Iron Analytes in Healthy and Diseased Florida Manatees (Trichechus manatus latirostris).

Serum iron concentration is usually decreased in true iron deficiency and with inflammatory disease in man and domestic animals. Serum total iron binding capacity (TIBC) may be increased in true iron deficiency and decreased with inflammatory disease. This prospective study was designed to measure serum iron analytes in healthy free-ranging and housed Florida manatees (Trichechus manatus latirostris) of both sexes and various ages and to evaluate the effects of diseases common to manatees on these analytes. Blood samples were collected without anticoagulant from 137 healthy free-ranging manatees, 90 healthy housed manatees and 74 free-ranging diseased manatees, and serum was prepared by centrifugation. Serum iron concentration and unsaturated iron binding capacity were measured colourimetrically, and TIBC and percent transferrin saturation with iron were calculated. Serum amyloid A (SAA) was measured to assist in the health assessment of manatees and provide evidence of inflammation in diseased manatees. Based on the serum iron analytes, iron availability was lower in immature manatees compared with adults, and it was lower in housed manatees compared with free-ranging manatees. In contrast to other mammals studied, serum iron concentration was elevated rather than depressed in late pregnancy. Serum iron concentrations and transferrin saturation with iron percentages were significantly lower, and SAA concentrations were significantly higher, in diseased (ill and injured) manatees compared with healthy manatees. Serum iron concentration and transferrin saturation with iron values were negatively correlated with SAA concentrations, and manatees with the highest SAA concentrations had lower serum TIBC values. These findings indicate that inflammation is the major factor responsible for alterations in iron analytes in diseased manatees. Consequently, hypoferraemia may be used as supportive evidence of inflammatory disease in manatees (unless haemorrhage is also present). A decision threshold of ≤13.8 µmol/l was determined for hypoferraemia using receiver operating curve analysis. Based on studies in man and domestic animals, iron therapy is unnecessary for manatees with hypoferraemia associated with inflammation and has the potential for causing tissue damage and increased susceptibility to bacterial infections.

Characterisation of human urethral rupture thresholds for urinary catheter inflation related injuries.

Data on urethral catheter related injuries is sparse. In this study we aimed to characterise urethral diametric strain and urinary catheter inflation pressure thresholds that precede human urethral trauma during urethral catheterisation (UC). Human urethras were obtained from patients undergoing male to female gender reassignment surgery [(n = 9; age 40 ±â€¯13.13 (range: 18-58)) years]. 12Fr urinary catheters were secured in the bulbar urethra and the catheter's anchoring balloon was inflated with a syringe pump apparatus. Urethral diametric strain and balloon pressure were characterised with video extensometry and a pressure transducer respectively. Immunohistochemistry, Masson's trichrome and Verhoeff-Van Gieson stains evaluated urethral trauma microscopically. Morphological characterisation of the urethral lumen was performed by examining non-traumatised histological sections of urethra and recording luminal area, perimeter and major/minor axis length. Tearing (n = 3) and rupture (n = 3) of the urethra were observed following catheter balloon inflation. The threshold for human urethral rupture occurred at an external urethral diametric strain ≥ 27% and balloon inflation pressure ≥ 120kPa. Significant relationships were identified between urethral wall thickness and the level of trauma induced during catheter balloon inflation (p = 0.001) and between the pressure required to inflate the catheter balloon and the length of the major axis of the urethral lumen (p = 0.004). Ruptured urethras demonstrated complete transection of collagen, elastin and muscle fibres. In conclusion, urethral rupture occurs at an external urethral diametric strain ≥ 27% or with balloon inflation pressures ≥ 120 kPa. Incorporation of these parameters may be useful for designing a safety mechanism for preventing catheter inflation related urethral injuries.

Biomaterials and Regenerative Medicine in Urology.

Autologous gastrointestinal tissue is the gold standard biomaterial for urinary tract reconstruction despite its long-term neuromechanical and metabolic complications. Regenerative biomaterials have been proposed as alternatives; however many are limited by a poor host derived regenerative response and deficient supportive elements for effective tissue regeneration in vivo. Urological biomaterials are sub-classified into xenogenic extracellular matrices (ECMs) or synthetic polymers. ECMs are decellularised, biocompatible, biodegradable biomaterials derived from animal organs. Synthetic polymers vary in chemical composition but may have the benefit of being reliably reproducible from a manufacturing perspective. Urological biomaterials can be 'seeded' with regenerative stem cells in vitro to create composite biomaterials for grafting in vivo. Mesenchymal stem cells are advantageous for regenerative purposes as they self-renew, have long-term viability and possess multilineage differentiation potential. Currently, tissue-engineered biomaterials are developing rapidly in regenerative urology with many important clinical milestones achieved. To truly translate from bench to bedside, regenerative biomaterials need to provide better clinical outcomes than current urological tissue replacement strategies.

Tissue engineered extracellular matrices (ECMs) in urology: Evolution and future directions.

Autologous gastrointestinal tissue has remained the gold-standard reconstructive biomaterial in urology for >100 years. Mucus-secreting epithelium is associated with lifelong metabolic and neuromechanical complications when implanted into the urinary tract. Therefore, the availability of biocompatible tissue-engineered biomaterials such as extracellular matrix (ECM) scaffolds may provide an attractive alternative for urologists. ECMs are decellularised, biodegradable membranes that have shown promise for repairing defective urinary tract segments in vitro and in vivo by inducing a host-derived tissue remodelling response after implantation. In urology, porcine small intestinal submucosa (SIS) and porcine urinary bladder matrix (UBM) are commonly selected as ECMs for tissue regeneration. Both ECMs support ingrowth of native tissue and differentiation of multi-layered urothelial and smooth muscle cells layers while providing mechanical support in vivo. In their native acellular state, ECM scaffolds can repair small urinary tract defects. Larger urinary tract segments can be repaired when ECMs are manipulated by seeding them with various cell types prior to in vivo implantation. In the present review, we evaluate and summarise the clinical potential of tissue engineered ECMs in reconstructive urology with emphasis on their long-term outcomes in urological clinical trials.

Urinary Bladder vs Gastrointestinal Tissue: A Comparative Study of Their Biomechanical Properties for Urinary Tract Reconstruction.

OBJECTIVE: To evaluate the mechanical properties of gastrointestinal (GI) tissue segments and to compare them with the urinary bladder for urinary tract reconstruction. METHODS: Urinary bladders and GI tissue segments were sourced from porcine models (n = 6, 7 months old [5 male; 1 female]). Uniaxial planar tension tests were performed on bladder tissue, and Cauchy stress-stretch ratio responses were compared with stomach, jejunum, ileum, and colonic GI tissue. RESULTS: The biomechanical properties of the bladder differed significantly from jejunum, ileum, and colonic GI tissue. Young modulus (kPa-measure of stiffness) of the GI tissue segments was on average 3.07-fold (±0.21 standard error) higher than bladder tissue (P < .01), and the strain at Cauchy stress of 50 kPa for bladder tissues was on average 2.27-fold (±0.20) higher than GI tissues. There were no significant differences between the averaged stretch ratio and Young modulus of the horizontal and vertical directions of bladder tissue (315.05 ± 49.64 kPa and 283.62 ± 57.04, respectively, P = .42). However, stomach tissues were 1.09- (±0.17) and 0.85- (±0.03) fold greater than bladder tissues for Young modulus and strain at 50 kPa, respectively. CONCLUSION: An ideal urinary bladder replacement biomaterial should demonstrate mechanical equivalence to native tissue. Our findings demonstrate that GI tissue does not meet these mechanical requirements. Knowledge on the biomechanical properties of bladder and GI tissue may improve development opportunities for more suitable urologic reconstructive biomaterials.

On the effect of computed tomography resolution to distinguish between abdominal aortic aneurysm wall tissue and calcification: A proof of concept.

PURPOSE: The purpose of this study is to determine the optimal target CT spatial resolution for accurately imaging abdominal aortic aneurysm (AAA) wall characteristics, distinguishing between tissue and calcification components, for an accurate assessment of rupture risk. MATERIALS AND METHODS: Ruptured and non-ruptured AAA-wall samples were acquired from eight patients undergoing open surgical aneurysm repair upon institutional review board approval and informed consent was obtained from all patients. Physical measurements of AAA-wall cross-section were made using scanning electron microscopy. Samples were scanned using high resolution micro-CT scanning. A resolution range of 15.5-155µm was used to quantify the influence of decreasing resolution on wall area measurements, in terms of tissue and calcification. A statistical comparison between the reference resolution (15.5µm) and multi-detector CT resolution (744µm) was also made. RESULTS: Electron microscopy examination of ruptured AAAs revealed extremely thin outer tissue structure <200µm in radial distribution which is supporting the aneurysm wall along with large areas of adjacent medial calcifications far greater in area than the tissue layer. The spatial resolution of 155µm is a significant predictor of the reference AAA-wall tissue and calcification area measurements (r=0.850; p<0.001; r=0.999; p<0.001 respectively). The tissue and calcification area at 155µm is correct within 8.8%±1.86 and 26.13%±9.40 respectively with sensitivity of 87.17% when compared to the reference. CONCLUSION: The inclusion of AAA-wall measurements, through the use of high resolution-CT will elucidate the variations in AAA-wall tissue and calcification distributions across the wall which may help to leverage an improved assessment of AAA rupture risk.

Calcification Volume Reduces Stretch Capability and Predisposes Plaque to Rupture in an in vitro Model of Carotid Artery Stenting.

OBJECTIVE/BACKGROUND: Carotid artery stenting (CAS) in calcified arteries carries a higher peri-operative risk. This study investigates the relationship between the stretching limits of carotid plaque samples and calcification in order to determine a stretch tolerance criterion for endovascular intervention. METHODS: Seventeen carotid plaque samples were acquired from standard endarterectomy procedures. The maximum stretch capability of the global plaque was determined by circumferentially extending the tissue to complete failure. Quantitative assessment of calcification was performed using high resolution computed tomography, including measures of percent calcification volume fraction (%CVF) and calcification configuration. Maximum stretch properties were then related to calcification measures in order to evaluate the predictive power of calcification for determining plaque stretching limits. RESULTS: A strong negative correlation was found between %CVF and stretch ratio with respect to specific calcification configuration types. All plaques with < 70% stenosis superseded the minimum required stretch threshold. Severe stenosis (> 70%) warrants a stretch of at least 2.33 during revascularisation and only plaques containing concentric calcifications with < 20% CVF successfully reached this minimum required stretch threshold. CONCLUSION: The addition of calcification measures to the stenosis classification may help in guiding endovascular intervention techniques to achieve a balance between an acceptable residual patency level while avoiding plaque rupture in calcified carotid plaques.

Towards the prediction of flow-induced shear stress distributions experienced by breast cancer cells in the lymphatics.

Tumour metastasis in the lymphatics is a crucial step in the progression of breast cancer. The dynamics by which breast cancer cells (BCCs) travel in the lymphatics remains poorly understood. The goal of this work is to develop a model capable of predicting the shear stresses metastasising BCCs experience using numerical and experimental techniques. This paper models the fluidic transport of large particles ([Formula: see text] where [Formula: see text] is the particle diameter and W is the channel width) subjected to lymphatic flow conditions ([Formula: see text]), in a [Formula: see text] microchannel. The feasibility of using the dynamic fluid body interaction (DFBI) method to predict particle motion was assessed, and particle tracking experiments were performed. The experiments found that particle translational velocity decreased from the undisturbed fluid velocity with increasing particle size (5-14% velocity lag for [Formula: see text]). DFBI simulations were found to better predict particle behaviour than theoretical predictions; however, mesh restrictions in the near-wall region ([Formula: see text]) result in computationally expensive models. The simulations were in good agreement with the experiments ([Formula: see text] difference) across the channel ([Formula: see text]), with differences up to 25% in the near-wall region. Particles experience a range of shear stresses (0.002-0.12 Pa) and spatial shear gradients ([Formula: see text]) depending on their size and radial position. The predicted shear gradients are far in excess of values associated with BCC apoptosis ([Formula: see text]). Increasing our understanding of the shear stress magnitudes and gradients experienced by BCCs could be leveraged to elucidate whether a particular BCC size or location exists that encourages metastasis within the lymphatics.

Dietary cation-anion difference may explain why ammonium urate nephrolithiasis occurs more frequently in common bottlenose dolphins () under human care than in free-ranging common bottlenose dolphins.

Ammonium urate nephrolithiasis frequently develops in common bottlenose dolphins () managed under human care but is rare in free-ranging common bottlenose dolphins. In other species, the dietary cation-anion difference (DCAD) can affect ammonium urate urolith formation by increasing proton excretion as ammonium ions. Therefore, differences in diet between the 2 dolphin populations could affect urolith formation, but the DCAD of most species consumed by free-ranging and managed dolphins is unknown. To compare the nutrient composition of diets consumed by free-ranging and managed bottlenose dolphins, samples ( = 5) of the 8 species of fish commonly consumed by free-ranging bottlenose dolphins in Sarasota Bay, FL, and the 7 species of fish and squid commonly fed to managed bottlenose dolphins were analyzed for nutrient content. Metabolizable energy was calculated using Atwater factors; the DCAD was calculated using 4 equations commonly used in people and animals that use different absorption coefficients. The nutrient composition of individual species was used to predict the DCAD of 2 model diets typically fed to managed common bottlenose dolphins and a model diet typically consumed by common bottlenose dolphins in Sarasota Bay. To mimic differences in postmortem handling of fish for the 2 populations of bottlenose dolphins, "free-ranging" samples were immediately frozen at -80°C and minimally thawed before analysis, whereas "managed" samples were frozen for 6 to 9 mo at -18°C and completely thawed. "Free-ranging" species contained more Ca and P and less Na and Cl than "managed" fish and squid species. As a consequence, the DCAD of both model managed dolphin diets obtained using 3 of the 4 equations was much more negative than the DCAD of the model free-ranging bottlenose dolphin diet ( < 0.05). The results imply that managed bottlenose dolphins must excrete more protons in urine than free-ranging bottlenose dolphins, which will promote nephrolith formation. The nutrient composition of the free-ranging bottlenose dolphin diet, determined for the first time here, can be used as a guide for feeding managed bottlenose dolphins, but research in vivo is warranted to determine whether adding more cations to the diet will prevent urolith formation in managed dolphins.

Towards the characterisation of carotid plaque tissue toughness: Linking mechanical properties to plaque composition.

UNLABELLED: The morphological manifestation of calcification within an atherosclerotic plaque is diverse and the response to cutting balloon angioplasty remains an elusive target to predict in the presence of extensive calcification. This study examines the resistance of plaque tissue to blade penetration by characterising the underlying toughness properties and stratifying the upper and lower scale toughness limits based on the strong mechanical influence of calcification. Mechanical toughness properties of the common, bifurcation and internal carotid artery (n=62) were determined using guillotine-cutting tests measuring the energy required to pass a surgical blade through a unit length of plaque tissue. The corresponding structural composition of the dissected plaque segments was characterised using Fourier transform infrared analysis, electron microscopy and energy dispersive x-ray spectroscopy. Mechanical results reveal a clear distinction in toughness properties within each region of the carotid vessel with significantly tougher properties localised in the bifurcation (p=0.004) and internal region (p=0.0003) compared to the common. The severity of the intra-plaque variance is highest in plaques with high toughness localised in the bifurcation region (p<0.05). Structural examination reveals that the diverse mechanical influence of the level of calcification present is characteristic of specific regions within the carotid plaque. The energy required to overcome the calcific resistance and propagate a controlled cut in the calcified tissue at each region varies further with the degree of plaque progression. The identification of the localised calcification characteristics is a key determinant in achieving successful dissection of the severely toughened plaque segments during cutting balloon angioplasty. STATEMENT OF SIGNIFICANCE: Calcification plays a fundamental role in plaque tissue mechanics and demonstrates a diverse range of material moduli properties. This work addresses the characterisation of the toughness properties in human carotid plaque tissue using a fracture mechanics approach. Toughness determines the energy required to propagate a controlled cut in the plaque material. This parameter is crucial for predicting the cutting forces required during endovascular cutting balloon angioplasty intervention. Results demonstrate that a strong relationship exists between the structural calcification configurations, fracture mechanisms and associated toughness properties that are characteristic of specific regions within the carotid artery plaque. The identification of the morphological characteristics of localised calcification may serve as a valuable quantitative measure for cutting balloon angioplasty treatment.

Incidence, Cost, Complications and Clinical Outcomes of Iatrogenic Urethral Catheterization Injuries: A Prospective Multi-Institutional Study.

PURPOSE: Data on urethral catheter related injuries are sparse. To highlight the dangers inherent in traumatic urethral catheterization we prospectively monitored the incidence, cost and clinical outcomes of urethral catheter related injuries. MATERIALS AND METHODS: This prospective study was performed during a 6-month period at 2 tertiary referral teaching hospitals. Recorded data included method and extent of urethral catheterization injury, setting and time of injury, number of catheterization attempts, urological management provided, additional bed days due to urethral injury and clinical outcomes after followup. The additional cost of managing urethral injuries was also calculated. RESULTS: A total of 37 iatrogenic urethral injuries were recorded during the 6-month period. The incidence of traumatic urethral catheterization was 6.7 per 1,000 catheters inserted. Thirty (81%) patients sustained a complication Clavien-Dindo grade 2 or greater. The additional length of inpatient hospital stay was 9.4 ± 10 days (range 2 to 53). Of these patients 9 (24%) required an indwelling suprapubic catheter and 8 (21%) have an indwelling transurethral catheter. In addition, 9 (24%) are performing self-urethral dilation once weekly and 4 (11%) have required at least 1 urethral dilation due to persistent urethral stricture disease. The additional cost of managing iatrogenic urethral injuries was €335,377 ($371,790). CONCLUSIONS: Iatrogenic urethral catheterization injuries represent a significant cost and cause of patient morbidity. Despite efforts to educate and train health care professionals on urethral catheterization insertion technique, iatrogenic urethral injuries will continue to occur unless urinary catheter safety mechanics are altered and improved.

On the effect of calcification volume and configuration on the mechanical behaviour of carotid plaque tissue.

Vascular calcification is a complex molecular process that exhibits a number of relatively characteristic morphology patterns in atherosclerotic plaques. Treatment of arterial stenosis by endovascular intervention, involving forceful circumferential expansion of the plaque, can be unpredictable in calcified lesions. The aim of this study was to determine the mechanical stretching mechanisms and define the mechanical limits for circumferentially expanding carotid plaque lesions under the influence of distinct calcification patterns. Mechanical and structural characterisation was performed on 17 human carotid plaques acquired from patients undergoing endarterectomy procedures. The mechanical properties were determined using uniaxial extension tests that stretch the lesions to complete failure along their circumferential axis. Calcification morphology of mechanically ruptured plaque lesions was characterised using high resolution micro computed tomography imaging. Scanning electron microscopy was used to examine the mechanically induced failure sites and to identify the interface boundary conditions between calcified and non-calcified tissue. The mechanical tests produced four distinct trends in mechanical behaviour which corresponded to the calcification patterns that structurally defined each mechanical group. Each calcification pattern produced unique mechanical restraining effects on the plaque tissue stretching properties evidenced by the variation in degree of stretch to failure. Resistance to failure appears to rely on interactions between calcification and non-calcified tissue. Scanning electron microscopy examination revealed structural gradations at interface boundary conditions to facilitate the transfer of stress. This study emphasises the mechanical influence of distinct calcification configurations on plaque expansion properties and highlights the importance of pre-operative lesion characterisation to optimise treatment outcomes.

The influence of composition and location on the toughness of human atherosclerotic femoral plaque tissue.

The toughness of femoral atherosclerotic tissue is of pivotal importance to understanding the mechanism of luminal expansion during cutting balloon angioplasty (CBA) in the peripheral vessels. Furthermore, the ability to relate this parameter to plaque composition, pathological inclusions and location within the femoral vessels would allow for the improvement of existing CBA technology and for the stratification of patient treatment based on the predicted fracture response of the plaque tissue to CBA. Such information may lead to a reduction in clinically observed complications, an improvement in trial results and an increased adoption of the CBA technique to reduce vessel trauma and further endovascular treatment uptake. This study characterises the toughness of atherosclerotic plaque extracted from the femoral arteries of ten patients using a lubricated guillotine cutting test to determine the critical energy release rate. This information is related to the location that the plaque section was removed from within the femoral vessels and the composition of the plaque tissue, determined using Fourier Transform InfraRed spectroscopy, to establish the influence of location and composition on the toughness of the plaque tissue. Scanning electron microscopy (SEM) is employed to examine the fracture surfaces of the sections to determine the contribution of tissue morphology to toughness. Toughness results exhibit large inter and intra patient and location variance with values ranging far above and below the toughness of healthy porcine arterial tissue (Range: 1330-3035 for location and 140-4560J/m(2) for patients). No significant difference in mean toughness is observed between patients or location. However, the composition parameter representing the calcified tissue content of the plaque correlates significantly with sample toughness (r=0.949, p<0.001). SEM reveals the presence of large calcified regions in the toughest sections that are absent from the least tough sections. Regression analysis highlights the potential of employing the calcified tissue content of the plaque as a preoperative tool for predicting the fracture response of a target lesion to CBA (R(2)=0.885, p<0.001). STATEMENT OF SIGNIFICANCE: This study addresses a gap in current knowledge regarding the influence of plaque location, composition and morphology on the toughness of human femoral plaque tissue. Such information is of great importance to the continued improvement of endovascular treatments, particularly cutting balloon angioplasty (CBA), which require experimentally derived data as a framework for assessing clinical cases and advancing medical devices. This study identifies that femoral plaque tissue exhibits large inter and intra patient and location variance regarding tissue toughness. Increasing calcified plaque content is demonstrated to correlate significantly with increasing toughness. This highlights the potential for predicting target lesion toughness which may lead to an increased adoption of the CBA technique and also further the uptake of endovascular treatment.

Mechanical, biological and structural characterization of human atherosclerotic femoral plaque tissue.

The failure of endovascular treatments of peripheral arterial disease represents a critical clinical issue. Specialized data are required to tailor such procedures to account for the mechanical response of the diseased femoral arterial tissue to medical device deployment. The purpose of this study is to characterize the mechanical response of atherosclerotic femoral arterial tissue to large deformation, the conditions typical of angioplasty and stenting, and also to determine the mechanically induced failure properties and to relate this behaviour to biological content and structural composition using uniaxial testing, Fourier transform infrared spectroscopy and scanning electron microscopy. Mechanical and biological characterization of 20 plaque samples obtained from femoral endarterectomy identified three distinct classifications. "Lightly calcified" samples display linear mechanical responses and fail at relatively high stretch. "Moderately calcified" samples undergo an increase in stiffness and ultimate strength coupled with a decrease in ductility. Structural characterization reveals calcified nodules within this group that may be acting to reinforce the tissue matrix, thus increasing the stiffness and ultimate strength. "Heavily calcified" samples account for the majority of samples tested and exhibit significantly reduced ultimate strength and ductility compared to the preceding groups. Structural characterization of this group reveals large areas of calcified tissue dominating the failure cross-sections of the samples. The frequency and structural dominance of these features solely within this group offers an explanation as to the reduced ultimate strength and ductility and highlights the need for modern peripheral endovascular devices to account for this behaviour during novel medical device design.

Attitudes among junior doctors towards improving the transurethral catheterisation process.

OBJECTIVES: To evaluate the subjective opinions of junior doctors on their adequacy of training and confidence levels for performing transurethral catheterisation (TUC) and to investigate their subjective interest in a 'safety mechanism' that would eliminate the potential for urethral trauma during TUC. METHODS: An anonymous online survey was emailed to all interns that had a documented email address on the Royal College of Surgeons Ireland registry (2012-2013). The survey consisted of eight questions pertaining to TUC of male patients. RESULTS: The survey was delivered to 252 email addresses and the response rate was 52% (130/252). The vast majority (99%; n = 128) of interns felt confident inserting a transurethral catheter independently and 73% (n = 95) subjectively received appropriate training for catheterising male patients. The incidence of trauma after mistakenly inflating the catheter's anchoring balloon in the urethra was 3% (n = 4). The majority (90%; n = 116) of respondents were interested in a safety mechanism for preventing urethral trauma and 71% (n = 92) felt that a safety mechanism for urethral trauma prevention should be compulsory for all transurethral catheterisation among male patients. CONCLUSION: Despite pre-emptive training programmes, it appears that iatrogenic urethral trauma secondary to TUC remains a persistent morbidity in healthcare settings. Designing a safer transurethral catheter may be necessary to eliminate the risk of unnecessary urethral trauma in patients.

The effects of stent interaction on porcine urinary bladder matrix employed as stent-graft materials.

Deployment of stent-grafts, derived from synthetic biomaterials, is an established minimally invasive approach for effectively treating abdominal aortic aneurysms (AAAs). However, a notable disadvantage associated with this surgical technique is migration of the deployed stent-graft due to poor biocompatibility and inadequate integration in vivo. Recently, tissue-engineered extracellular matrices (ECMs) have shown early promise as integrating stabilisation collars in this setting due to their ability to induce a constructive tissue remodelling response after in vivo implantation. In the present study the effects of stent loading on an ECM׳s mechanical properties were investigated by characterising the compression and loading effects of endovascular stents on porcine urinary bladder matrix (UBM) scaffolds. Results demonstrated that the maximum stress was induced when the stent force was 8-times higher than a standard commercially available stent-graft and this represented about 20% of the failure strength of the UBM material. In addition, the influence of stent shape was also investigated. Findings demonstrated that the stress induced was higher for circular stents at low forces and a higher stress was induced on square stents when increased force was applied. Our findings demonstrate that porcine UBM possesses sufficient mechanical strength to withstand the compression and loading effects of commercially available stent-grafts in the setting of endovascular aneurysm repair.

Uniaxial tensile testing approaches for characterisation of atherosclerotic plaques.

The pathological changes associated with the development of atherosclerotic plaques within arterial vessels result in significant alterations to the mechanical properties of the diseased arterial wall. There are several methods available to characterise the mechanical behaviour of atherosclerotic plaque tissue, and it is the aim of this paper to review the use of uniaxial mechanical testing. In the case of atherosclerotic plaques, there are nine studies that employ uniaxial testing to characterise mechanical behaviour. A primary concern regarding this limited cohort of published studies is the wide range of testing techniques that are employed. These differing techniques have resulted in a large variance in the reported data making comparison of the mechanical behaviour of plaques from different vasculatures, and even the same vasculature, difficult and sometimes impossible. In order to address this issue, this paper proposes a more standardised protocol for uniaxial testing of diseased arterial tissue that allows for better comparisons and firmer conclusions to be drawn between studies. To develop such a protocol, this paper reviews the acquisition and storage of the tissue, the testing approaches, the post-processing techniques and the stress-strain measures employed by each of the nine studies. Future trends are also outlined to establish the role that uniaxial testing can play in the future of arterial plaque mechanical characterisation.

On the potential of hydrated storage for naturally derived ECMs and associated effects on mechanical and cellular performance.

Tissue engineered acellular vascular grafts are an emerging concept in the development of vascular prostheses for the minimally invasive treatment of cardiovascular diseases. Extracellular matrix (ECM) scaffolds, such as small intestinal submucosa (SIS) and urinary bladder matrix (UBM), offer many advantages over currently available synthetic devices. However, storage of such biomaterials can unduly influence the scaffold properties. This study evaluated the effects of up to 16 weeks hydrated storage on the mechanical and cellular performance of stented and unstented tubular scaffolds. This study aimed to demonstrate the viability, mechanical integrity, and bioactive potential of xenogeneic ECMs as potential off-the-shelf vascular prosthetic devices. Rehydrated ECM samples versus the lyophilized controls showed an increase in UTS and stiffness. The mechanical strength of all samples evaluated was above the average reported aortic tissue failure strength and more compliant than current synthetic materials employed. Post-storage cellular bioactivity investigations indicated that both ECM scaffolds tested were unaffected by increased hydrated storage duration when compared with the controls. Overall, the results indicate that the biomechanical and biologic properties of ECMs are not negatively affected by long-term hydrated storage. Therefore, with further investigations, naturally derived ECM materials may offer potential as an off-the-shelf therapeutic treatment of cardiovascular diseases.