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.

Perioperative management of chronic anticoagulation therapy in urological patients: a cross-sectional survey of practice.

BACKGROUND: There has been a significant increase in the volume of urological patients on daily anticoagulation therapy requiring invasive elective urological procedures. AIMS: We sought to assess whether urologists are familiar with appropriate perioperative management strategies in this patient cohort. METHODS: Urologists completed a questionnaire on their current management strategy for warfarin during the perioperative period in patients undergoing elective urological surgery. Eleven urological procedures graded as minor, endoscopic and major were assessed in the study. In addition, respondents were also asked whether they administered bridging therapy with heparin when warfarin was discontinued perioperatively. RESULTS: The response rate was 52.5% (210/400). Procedure grade did not influence the duration warfarin was discontinued preoperatively with respondents discontinuing the agent 4.71 ± 1.52 days (range 2-10 days) prior to minor procedures, 4.74 ± 1.43 days (range 2-10 days) prior to endoscopic procedures and 4.88 ± 1.34 days (range 2-10 days) prior to major procedures (p > 0.05). Postoperatively, procedure grade significantly affected the day to recommencement with respondents recommencing warfarin 2.41 ± 2.31 days (range 1-14 days) after minor procedures, 3.07 ± 3.52 days (range 1-28 days) after endoscopic procedures and 4.38 ± 3.53 days (range 1-14 days) after major procedures (p < 0.0001). In total, 60 ± 0.52% of the respondents who discontinued warfarin routinely administered bridging therapy with heparin perioperatively. CONCLUSIONS: Our study demonstrates variations in perioperative management practices for patients on chronic anticoagulation therapy undergoing urological procedures. Urologists should familiarise themselves with standardised guidelines if this patient subgroup are to receive optimal perioperative management.

Wall shear stresses remain elevated in mature arteriovenous fistulas: a case study.

Maintaining vascular access (VA) patency continues to be the greatest challenge for dialysis patients. VA dysfunction, primarily due to venous neointimal hyperplasia development and stenotic lesion formation, is mainly attributed to complex hemodynamics within the arteriovenous fistula (AVF). The effect of VA creation and the subsequent geometrical remodeling on the hemodynamics and shear forces within a mature patient-specific AVF is investigated. A 3D reconstructed geometry of a healthy vein and a fully mature patient-specific AVF was developed from a series of 2D magnetic resonance image scans. A previously validated thresholding technique for region segmentation and lumen cross section contour creation was conducted in MIMICS 10.01, allowing for the creation of a 3D reconstructed geometry. The healthy vein and AVF computational models were built, subdivided, and meshed in GAMBIT 2.3. The computational fluid dynamic (CFD) code FLUENT 6.3.2 (Fluent Inc., Lebanon, NH) was employed as the finite volume solver to determine the hemodynamics and shear forces within the healthy vein and patient-specific AVF. Geometrical alterations were evaluated and a CFD analysis was conducted. Substantial geometrical remodeling was observed, following VA creation with an increase in cross-sectional area, out of plane curvature (maximum angle of curvature in AVF=30 deg), and angle of blood flow entry. The mean flow velocity entering the vein of the AVF is dramatically increased. These factors result in complex three-dimensional hemodynamics within VA junction (VAJ) and efferent vein of the AVF. Complex flow patterns were observed and the maximum and mean wall shear stress (WSS) magnitudes are significantly elevated. Flow reversal was found within the VAJ and efferent vein. Extensive geometrical remodeling during AVF maturation does not restore physiological hemodynamics to the VAJ and venous conduit of the AVF, and high WSS and WSS gradients, and flow reversal persist. It is theorized that the vessel remodelling and the continued non-physiological hemodynamics within the AVF compound to result in stenotic lesion development.