A quantitative analysis of the environmental impact of hill farming in relation to vegetation, soil attributes and soil erosion: a land use perspective.

The research was carried out in conjunction with the commercially run Teagasc Hill Sheep Farm, Leenaun, Co. Mayo and with Met Éireann. The aim was to enhance habitat status and to maximise biodiversity conservation in the upland landscape of western Ireland through more evidence-based agricultural policies that are designed to maintain and improve agricultural productivity. Field data on vegetation frequency and composition over periods of 5 to 17 years, satellite tracking (GPS) of sheep and longterm trends in wind-driven rain were analysed. Vegetation frequency increased from a baseline of 64% in 1995 to 82% in 2008 at a mean annual stocking rate of 0.76 ewes/ha. Soil differences were responsible for most of the significant changes. Grazing reduced vegetation height by half, from 40 to 20 cm, thus opening the canopy and allowing an increase in species diversity in a number of instances. Long-term habitat exclosures revealed that grazing resulted in increased species diversity in acid grassland and lowland blanket bog and a significant increase in the frequency of sedges in all habitats. Winter grazing only, at 0.6 ewes/ha, which represents an annual stocking rate of 0.76 ewes/ha, was the most beneficial for total vegetation frequency and that of individual communities. Implementation of this management system would require substantial additional financial outlay. Restricted, temporary holding areas for animals resulted in substantial changes in vegetation composition but not in frequency. Average daily trekking by GPS tracked hill ewes varied from 2 to 3 km, which, at the present stocking rate, represented a mean daily trampling pressure of c. 2 km/ha. This pressure may be 5 to 10 times greater in areas preferred by sheep, which is why increasing trends, from 1950 to 2009, in aspects of wind-driven rain that are associated with peat erosion, are of serious concern. Regular monitoring of vegetation height by physiography and altitude is a key factor in appropriate grazing management. The development and introduction of wireless fencing together with sensors that attract rather than repel animals are necessary to achieve more even grazing pressure in a free-range grazing environment. Due to the likely synergy between increasing trends in certain aspects of wind-driven rain and peat erosion in areas of concentrated sheep activity, an early warning system similar to that for potato blight must be established

On the mechanical behaviour of carotid artery plaques:the influence of curve-fitting experimental data on numerical model results

Computational models of diseased arteries are advancing rapidly, and a need exists to develop more accurate material models of human atherosclerotic plaques. However, intact samples for in vitro mechanical testing are not readily available. Most plaque samples are harvested from carotid endarterectomies where the geometries are not suitable for the boundary parameters necessary for classical uniaxial tensile testing. Experimental studies of biological tissue, particularly human plaque tissue, have not specified the minimum width-to-length (WL) ratio necessary for appropriate tensile testing. This study proposes either tensile or planar shear testing on whole specimen samples depending on the WL ratio. However, a “grey-area” of WL ratios exists which are unsuitable for either test, between 0.5:1 and 4:1 WL ratio. Eighteen plaque samples are investigated in this study, and according to classical approaches, two of the plaque samples have WL ratios suitable for tensile testing and four are suitable for planar shear testing. The remaining twelve samples fall in the grey-area of WL ratio. The study analyses which test method is suitable for the samples in this grey-area and what effect using the incorrect test method has on results from a computational model. The study highlights that tissues above a WL ratio of 2:1 are suitable for planar shear testing, and samples below 1:1 are more suited for tensile testing. Therefore, the “grey-area” can be reduced with certain limitations applied by the minor strain assumption which need to be taken into account during experimental testing. This study also demonstrates the influence of curve-fitting experimental results using tensile- and planar shear–based boundary parameters from eighteen plaque samples

The advection of microparticles, MCF-7 and MDA-MB-231 breast cancer cells in response to very low Reynolds numbers

The lymphatic system is an extensive vascular network that serves as the primary route for the metastatic spread of breast cancer cells (BCCs). The dynamics by which BCCs travel in the lymphatics to distant sites, and eventually establish metastatic tumors, remain poorly understood. Particle tracking techniques were employed to analyze the behavior of MCF-7 and MDA-MB-231 BCCs which were exposed to lymphatic flow conditions in a 100 μm square microchannel. The behavior of the BCCs was compared to rigid particles of various diameters (η = dp/H= 0.05–0.32) that have been used to simulate cell flow in lymph. Parabolic velocity profiles were recorded for all particle sizes. All particles were found to lag the fluid velocity, the larger the particle the slower its velocity relative to the local flow (5%–15% velocity lag recorded). A distinct difference between the behavior of BCCs and particles was recorded. The BCCs travelled approximately 40% slower than the undisturbed flow, indicating that morphology and size affects their response to lymphatic flow conditions (Re < 1). BCCs adhered together, forming aggregates whose behavior was irregular. At lymphatic flow rates, MCF-7s were distributed uniformly across the channel in comparison to the MDA-MB-231 cells which travelled in the central region (88% of cells found within 0.35 ≤ W ≤ 0.64), indicating that metastatic MDA-MB-231 cells are subjected to a lower range of shear stresses in vivo. This suggests that both size and deformability need to be considered when modelling BCC behavior in the lymphatics. This finding will inform the development of in vitro lymphatic flow and metastasis models

The role of shear stress in arteriovenous fistula maturation and failure: a systematic review

Non-maturation and post-maturation venous stenosis are the primary causes of failure within arteriovenous fistulae (AVFs). Although the exact mechanisms triggering failure remain unclear, abnormal hemodynamic profiles are thought to mediate vascular remodelling and can adversely impact on fistula patency

Spherical indentation of free-standing acellular extracellular matrix membranes

Numerous scaffold materials have been developed for tissue engineering and regenerative medicine applications to replace or repair damaged tissues and organs. Naturally occurring scaffold materials derived from acellular xenogeneic and autologous extracellular matrix (ECM) are currently in clinical use. These biological scaffold materials possess inherent variations in mechanical properties. Spherical indentation or ball burst testing has commonly been used to evaluate ECM and harvested tissue due to its ease of use and simulation of physiological biaxial loading, but has been limited by complex material deformation profiles. An analytical methodology has been developed and applied to experimental load–deflection data of a model hyperelastic material and lyophilized ECM scaffolds. An optimum rehydration protocol was developed based on water absorption, hydration relaxation and dynamic mechanical analysis. The analytical methodology was compared with finite element simulations of the tests and excellent correlation was seen between the computed biaxial stress resultants and geometry deformations. A minimum rehydration period of 5 min at 37 °C was sufficient for the evaluated multilaminated ECM materials. The proposed approach may be implemented for convenient comparative analysis of ECM materials and source tissues, process optimization or during lot release testing

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 ± 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

Clinical evaluation of a safety-device to prevent urinary catheter inflation related injuries

OBJECTIVE: To evaluate the feasibility of a novel “safety-valve” device for preventing catheter related urethral trauma during urethral catheterization (UC). To assess the opinions of clinicians on the performance of the safety-valve device. MATERIALS AND METHODS A validated prototype “safety-valve” device for preventing catheter balloon inflation related urethral injuries was prospectively piloted in male patients requiring UC in a tertiary referral teaching hospital (n = 100). The device allows fluid in the catheter system to decant through an activated safety threshold pressure valve if the catheter anchoring balloon is misplaced. Users evaluated the “safety-valve” with an anonymous questionnaire. The primary outcome measurement was prevention of anchoring balloon inflation in the urethra. Secondary outcome measurement was successful inflation of urinary catheter anchoring balloon in the bladder. RESULTS: Patient age was 76 ± 12 years and American Society of Anaesthesiologists grade was 3 ± 1.4. The “safety-valve” was utilized by 34 clinicians and activated in 7% (n = 7/100) patients during attempted UC, indicating that the catheter anchoring balloon was incorrectly positioned in the patient’s urethra. In these 7 cases, the catheter was successfully manipulated into the urinary bladder and inflated. 31 of 34 (91%) clinicians completed the questionnaire. Ten percent (n = 3/31) of respondents had previously inflated a urinary catheter anchoring balloon in the urethra and 100% (n = 31) felt that a safety mechanism for preventing balloon inflation in the urethra should be compulsory for all UCs. CONCLUSION: The safety-valve device piloted in this clinical study offers an effective solution for preventing catheter balloon inflation related urethral injuries

The mesocolon a histological and electron microscopic characterization of the mesenteric attachment of the colon prior to and after surgical mobilization

Background: Colonic mobilization requires separation of mesocolon from underlying fascia. Despite the surgical importance of planes formed by these structures, no study has formally characterized their microscopic features. The aim of this study was to determine the histological and electron microscopic appearance of mesocolon, fascia, and retroperitoneum, prior to and after colonic mobilization.Methods: In 24 cadavers, samples were taken from right, transverse, descending, and sigmoid mesocolon. In 12 cadavers, specimens were stained with hematoxylin and eosin (3 sections) or Masson trichrome (3 sections). In the second 12 cadavers, lymphatic channels were identified by staining immunohistochemically for podoplanin. The ascending mesocolon was assessed with scanning electron microscopy. The above process was first conducted with the mesocolon in situ. The mesocolon was then surgically mobilized, and the process was repeated on remaining structures.Results: The microscopic structure of mesocolon and associated fascia was consistent from ileocecal to mesorectal level. A surface mesothelium and underlying connective tissue were evident throughout. Fibrous septae separated adipocyte lobules. Where apposed to retroperitoneum, 2 mesothelial layers separated mesocolon and underlying retroperitoneum. A connective tissue layer occurred between these (ie, Toldt's fascia). Lymphatic channels were evident both in mesocolic connective tissue and Toldt's fascia. After surgical separation of mesocolon and fascia both remained contiguous, the fascia remained in situ and the retroperitoneum undisturbed.Conclusions: The findings demonstrate that the contiguous mesocolon and retroperitoneum are separated by mesothelial and connective tissue layers. These properties generate the surgical planes (ie, meso-and retrofascial planes) exploited in colonic and mesocolic mobilization

Validity of synthetic bone as a substitute for osteoporotic cadaveric femoral heads in mechanical testing: a biomechanical study

IntroductionThe objective of this study was to determine if a synthetic bone substitute would provide results similar to bone from osteoporotic femoral heads during in vitro testing with orthopaedic implants. If the synthetic material could produce results similar to those of the osteoporotic bone, it could reduce or eliminate the need for testing of implants on bone.MethodsPushout studies were performed with the dynamic hip screw (DHS) and the DHS Blade in both cadaveric femoral heads and artificial bone substitutes in the form of polyurethane foam blocks of different density. The pushout studies were performed as a means of comparing the force displacement curves produced by each implant within each material.ResultsThe results demonstrated that test material with a density of 0.16 g/cm(3) (block A) produced qualitatively similar force displacement curves for the DHS and qualitatively and quantitatively similar force displacement curves for the DHS Blade, whereas the test material with a density of 0.08 g/cm(3) (block B) did not produce results that were predictive of those recorded within the osteoporotic cadaveric femoral heads.ConclusionThis study demonstrates that synthetic material with a density of 0.16 g/cm(3) can provide a good substitute for cadaveric osteoporotic femoral heads in the testing of implants. However we do recognise that no synthetic material can be considered as a definitive substitute for bone, therefore studies performed with artificial bone substrates may need to be validated by further testing with a small bone sample in order to produce conclusive results

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