Comparing the endothelialisation of extracellular matrix bioscaffolds with coated synthetic vascular graft materials.

INTRODUCTION: Existing synthetic vascular grafts have unacceptably high failure rates when replacing below knee arteries. In vitro endothelialisation is a technique, which has been shown to enhance the patency rates of below knee vascular grafts. Synthetic materials are however poor cellular substrates and must be combined with coatings to promote cellular growth and attachment. The most common coating clinically is fibrin-coated ePTFE. The aim of our study was to compare the endothelialisation of fibrin-coated ePTFE with novel extracellular matrix (ECM) biomaterials that we hypothesise will provide a superior substrate for cell growth. METHODS: Human endothelial cells were cultured on ECM scaffolds and fibrin-coated ePTFE. Uncoated Dacron and ePTFE acted as controls. The cells were examined for viability, phenotype, adhesion and proliferation. Cell morphology was accessed using scanning electron microscopy. RESULTS: Cells remained viable and produced von Willebrand factor on all substrates tested. ECM scaffolds and fibrin-modified ePTFE achieved statistically higher attachment efficiency when compared to both uncoated synthetic graft materials (p ≤ 0.001). At 90 min 80 ± 3.6% of cells had attached to the ECM scaffold compared to Dacron (30 ± 4.5%, n = 3) and ePTFE (33 ± 2.5%, n = 3). There was no difference in adhesion rates between ECM scaffolds and fibrin-coated ePTFE (p = 1.00). Endothelial cells proliferated fastest on ECM scaffolds when compared to all other materials tested (p < 0.001) and reached confluency on day seven. CONCLUSION: ECM bioscaffolds offer an improved substrate for promoting rapid endothelialisation compared to fibrin-coated ePTFE by combining firm cellular anchorage and superior cell expansion.

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.

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.

Development of a rotational cell-seeding system for tubularized extracellular matrix (ECM) scaffolds in vascular surgery.

Tubularized porcine extracellular matrices (ECMs) are under investigation as adjuvant scaffolds for endovascular aneurismal repair (EVAR). Limitations with tubularized ECMs in this setting include difficulties in achieving a confluent endothelium on the scaffold's luminal surface prior to in vivo implantation. In this in vitro study a rotational "cell-seeding rig" (RCR) was constructed to assess the potential for endothelialization of tubular ECM constructs. Human aortic endothelial cells (HAECs) were cultured onto the luminal surfaces of tubular porcine urinary bladder matrix (UBM) scaffolds and rotated in the RCR at experimental rotational speeds. Results showed that endothelial attachment occurred at a rotation speed of six revolutions per hour. HAECs continued to proliferate after the initial attachment period of 24 h and formed a confluent endothelial monolayer after 14 days of growth. Our results demonstrate that RCRs facilitate attachment of HAECs in vitro at a speed of six revolutions per hour. The endothelialization technique presented in the current study may be important for advancing tissue-engineering approaches to address some of the current limitations in endovascular treatments of abdominal aortic aneurysms.

Influence of implant design on the method of failure for three implants designed for use in the treatment of intertrochanteric fractures: the dynamic hip screw (DHS), DHS blade and X-BOLT.

BACKGROUND: The dynamic hip screw (DHS) has been widely adopted as the implant of choice in the treatment of intertrochanteric fractures. There have been attempts over the years to improve on the DHS lag screw design in order to reduce failure in the form of "cut out". The purpose of this study was to investigate how two new design variations of the DHS, the DHS blade and the X-BOLT, behave within bone, and if these design modifications do indeed improve the fixation achieved and lead to a reduction in failure due to cut out. METHODS: "Pushout" tests were chosen as the means of investigating the failure modes and patterns for these implants that lead to cut out. These pushout studies were performed in artificial bone substrate in the form of polyurethane foam blocks and in cadaveric femoral heads. RESULTS: The results demonstrated that each individual implant produces its own specific distinct force-displacement curve or pattern of failure, and that despite the very different implant designs and methods of fixation, all of the implants tested reached very similar peak forces in each of the test materials used. CONCLUSION: The results demonstrated that implant design only influences the pattern of failure, and that the peak forces reached by each implant are determined by the quality of the bone or test material into which they are placed. However, altering the force-displacement curve or pattern of failure may be enough to improve the fixation achieved and to provide an increased resistance to cut out.

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

INTRODUCTION: The 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. METHODS: Pushout 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. RESULTS: The 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. CONCLUSION: This 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.

Dynamic hip screw versus DHS blade: a biomechanical comparison of the fixation achieved by each implant in bone.

We biomechanically investigated whether the standard dynamic hip screw (DHS) or the DHS blade achieves better fixation in bone with regard to resistance to pushout, pullout and torsional stability. The experiments were undertaken in an artificial bone substrate in the form of polyurethane foam blocks with predefined mechanical properties. Pushout tests were also repeated in cadaveric femoral heads. The results showed that the DHS blade outperformed the DHS with regard to the two most important characteristics of implant fixation, namely resistance to pushout and rotational stability. We concluded that the DHS blade was the superior implant in this study.

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.

Porcine extracellular matrix scaffolds in reconstructive urology: An ex vivo comparative study of their biomechanical properties.

Functional reconstruction of the human urinary bladder has been attempted by replacing defective bladder tissue with tissue-engineered xenogenic extracellular matrix (ECM) scaffolds. However, experimental studies that demonstrate the effects of implanted ECMs on important biomechanical properties such as total bladder capacity (TBC) and compliance (C) are lacking. In the current study, the effects of ECM scaffold surface area (SA) on TBC and C was assessed, ex vivo, in an ovine model (n=5). TBC and C were measured at pressures (P) of 5, 10, 15 and 20 mm Hg prior to performing a 3×3 cm (9 cm(2)) partial cystectomy defect. Equal-sized 3×3 cm (9 cm(2)) and larger 6×6 cm (36 cm(2)) urinary bladder matrix (UBM) scaffolds of porcine origin replaced the 3×3 cm cystectomy defect, and TBC and C were re-recorded for comparative analysis. The results showed that TBC decreased by 39.6%±0.005% (122.9 ml±15 ml, p<0.05) and C by 38.9%±0.51%, (ΔP=0-5mmHg, p<0.05) in ovine bladders reconstructed with 3×3 cm UBM scaffolds compared to their native values. It was also found that TBC increased by 25.6±0.64% (64.2 ml ± 8.8 ml, p>0.05) and C by 24.5±0.43% (ΔP=0-5mmHg, p>0.05) in the 6×6 cm UBM scaffold group compared to the 3×3 cm UBM scaffold group; however, these values were not statistically significant. The present work demonstrates that a fourfold increase in ECM scaffold SA relative to its intended defect does not lead to a significant improvement in TBC and C values.

The effect of vessel material properties and pulsatile wall motion on the fixation of a proximal stent of an endovascular graft.

Migration is a serious failure mechanism associated with endovascular abdominal aortic aneurysm (AAA) repair (EVAR). The effect of vessel material properties and pulsatile wall motion on stent fixation has not been previously investigated. A proximal stent from a commercially available stent graft was implanted into the proximal neck of silicone rubber abdominal aortic aneurysm models of varying proximal neck stiffness (ß=25.39 and 20.44). The stent was then dislodged by placing distal force on the stent struts. The peak force to completely dislodge the stent was measured using a loadcell. Dislodgment was performed at ambient pressure with no flow (NF) and during pulsatile flow (PF) at pressures of 120/80 mmHg and 140/100 mmHg to determine if pulsatile wall motions affected the dislodgement force. An imaging analysis was performed at ambient pressure and at pressures of 120 mmHg and 140 mmHg to investigate diameter changes on the model due to the radial force of the stent and internal pressurisation. Stent displacement forces were ~50% higher in the stiffer model (7.16-8.4 N) than in the more compliant model (3.67-4.21 N). The mean displacement force was significantly reduced by 10.95-12.83% from the case of NF to the case of PF at 120/80 mmHg. A further increase in pressure to 140/120 mmHg had no significant effect on the displacement force. The imaging analysis showed that the diameter in the region of the stent was 0.37 mm greater in the less stiff model at all the pressures which could reduce the fixation of the stent. The results suggest that the fixation of passively fixated aortic stents could be comprised in more compliant walls and that pulsatile motions of the wall can reduce the maximum stent fixation.

Xenogenic extracellular matrices as potential biomaterials for interposition grafting in urological surgery.

PURPOSE: The field of tissue engineering focuses on developing strategies for reconstructing injured, diseased, and congenitally absent tissues and organs. During the last decade urologists have benefited from remodeling and regenerative properties of bioscaffolds derived from xenogenic extracellular matrices. We comprehensively reviewed the current literature on structural and functional characteristics of xenogenic extracellular matrix grafting since it was first described in urological surgery. We also reviewed the clinical limitations, and assessed the potential for safe and effective urological application of extracellular matrix grafting in place of autogenous tissue. MATERIALS AND METHODS: We performed literature searches for English language publications using the PubMed® and MEDLINE® databases. Keywords included "xenogenic," "extracellular matrix" and "genitourinary tract applications." A total of 112 articles were scrutinized, of which 50 were suitable for review based on clinical relevance and importance of content. RESULTS: Since the mid 1990s xenogenic extracellular matrices have been used to successfully treat a number of pathological conditions that affect the upper and lower genitourinary tract. They are typically prepared from porcine organs such as small intestine and bladder. These organs are harvested and subjected to decellularization and sterilization techniques before surgical implantation. Bioinductive growth factors that are retained during the preparation process induce constructive tissue remodeling as the extracellular matrix is simultaneously degraded and excreted. However, recent documented concerns over durability, decreased mechanical strength and residual porcine DNA after preparation techniques have temporarily hampered the potential of extracellular matrices as a reliable replacement for genitourinary tract structures. CONCLUSIONS: Extracellular matrices are a useful alternative for successfully treating a number of urological conditions that affect the genitourinary tract. However, clinical concerns regarding mechanical limitations and biosafety need to be addressed before their long-term role in reconstructive urological surgery can be clearly established.

A computational study of the magnitude and direction of migration forces in patient-specific abdominal aortic aneurysm stent-grafts.

OBJECTIVES: Endovascular aneurysm repair for abdominal aortic aneurysm (AAA) is now a widely adopted treatment. Several complications remain to be fully resolved and perhaps the most significant of these is graft migration. Haemodynamic drag forces are believed to be partly responsible for migration of the device. The objective of this work was to investigate the drag forces in patient-specific AAA stent-grafts. METHODS: CT scan data was obtained from 10 post-operative AAA patients treated with stent-grafts. 3D models of the aneurysm, intraluminal thrombus and stent-graft were created. The drag forces were determined by fluid-structure interaction simulations. A worst case scenario was investigated by altering the aortic waveforms. RESULTS: The median resultant drag force was 5.46 N (range: 2.53-10.84). An increase in proximal neck angulation resulted in an increase in the resultant drag force (p = 0.009). The primary force vector was found to act in an anterior caudal direction for most patients. The worst case scenario simulation resulted in a greatest drag force of 16 N. CONCLUSIONS: Numerical methods can be used to determine patient-specific drag forces which may help determine the likelihood of stent-graft migration. Anterior-posterior neck angulation appears to be the greatest determinant of drag force magnitude. Graft dislodgement may occur anteriorally as well as caudally.

Engineering silicone rubbers for in vitro studies: creating AAA models and ILT analogues with physiological properties.

In vitro studies of abdominal aortic aneurysm (AAA) have been widely reported. Frequently mock artery models with intraluminal thrombus (ILT) analogs are used to mimic the in vivo AAA. While the models used may be physiological, their properties are frequently either not reported or investigated. This study is concerned with the testing and characterization of previously used vessel analog materials and the development of new materials for the manufacture of AAA models. These materials were used in conjunction with a previously validated injection molding technique to manufacture AAA models of ideal geometry. To determine the model properties (stiffness (beta) and compliance), the diameter change of each AAA model was investigated under incrementally increasing internal pressures and compared with published in vivo studies to determine if the models behaved physiologically. A FEA study was implemented to determine if the pressure-diameter change behavior of the models could be predicted numerically. ILT analogs were also manufactured and characterized. Ideal models were manufactured with ILT analog internal to the aneurysm region, and the effect of the ILT analog on the model compliance and stiffness was investigated. The wall materials had similar properties (E(init) 2.22 MPa and 1.57 MPa) to aortic tissue at physiological pressures (1.8 MPa (from literature)). ILT analogs had a similar Young's modulus (0.24 MPa and 0.33 MPa) to the medial layer of ILT (0.28 MPa (from literature)). All models had aneurysm sac compliance (2.62-8.01 x 10(-4)/mm Hg) in the physiological range (1.8-9.4 x 10(-4)/mm Hg (from literature)). The necks of the AAA models had similar stiffness (20.44-29.83) to healthy aortas (17.5+/-5.5 (from literature)). Good agreement was seen between the diameter changes due to pressurization in the experimental and FEA wall models with a maximum difference of 7.3% at 120 mm Hg. It was also determined that the inclusion of ILT analog in the sac of the models could have an effect on the compliance of the model neck. Ideal AAA models with physiological properties were manufactured. The behavior of these models due to pressurization was predicted using finite element analysis, validating this technique for the future design of realistic physiological AAA models. Addition of ILT analogs in the aneurysm sac was shown to affect neck behavior. This could have implications for endovascular AAA repair due to the importance of the neck for stent-graft fixation.

Improved assessment and treatment of abdominal aortic aneurysms: the use of 3D reconstructions as a surgical guidance tool in endovascular repair.

BACKGROUND: Endovascular repair is fast becoming the treatment of choice for abdominal aortic aneurysms in anatomically suitable patients. 3D reconstructions not only aid conventional 2D measurements but also allow further analyses of the vessel anatomy. METHODS: Computed tomography scan data for four male patients awaiting endovascular repair were obtained. 3D reconstructions were performed to determine measurements. Wall stress was determined on one particular case using finite element analysis. RESULTS: 3D reconstruction allows measurements to be obtained that can be difficult to determine using 2D images. This method complements traditional 2D approaches. Reconstructions also provided imaging of potential anatomical problems. Wall stress results showed key regions that may be possible rupture sites. CONCLUSION: 3D reconstructions greatly aid surgical planning. As stent-graft devices evolve, anatomical difficulties previously considered contraindications to endovascular repair can now be overcome with careful planning. 3D reconstruction is a useful adjunct to assessment and planning of endovascular repair.

Extracellular matrices as advanced scaffolds for vascular tissue engineering.

An alternative non-vascular extracellular material was obtained by decellularisation of porcine urinary bladder and examined for its potential as scaffold for vascular tissue engineering. Analysis using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Laser Scanning Microscopy (LSCM) showed a porous interconnective microarchitecture, an abundance of well preserved fibers on the abluminal side and a micropatterned flat luminal surface. Uniaxial tensile testing revealed a strength of 1.9+/-0.3 MPa for the rehydrated material in a phosphate buffered saline medium for the ECM-UBM sheet and these results comparable to those of native artery of a middle aged human. Multilamination of the UBM increases the tensile properties in general (9+/-0.45 MPa for 2 layer, 30+/-0.6 MPa for 4 layers construct), with no effect on elongation capacities (38-40%) of the material. Contact-angle measurements indicated that the ECM-UBM surface exhibited a hydrophylic characteristic and better wettability than any vascular synthetic materials. Comparison of the initial adhesion in the multiplayer ECM constructs was evaluated and was found not to be altered by the preparation. The HAECs and HSMC shown an excellent adherence, spread and proliferation on the ECM-UBM material with the preservation of the cell phenotype. The level of MMP-1 and MMP-9 produced by endothelial cells was evaluated in this study and provides some data on the remodelling capacity of the scaffold. Vascular cell seeded-UBM constructs may also provide a suitable and affordable in vitro model for cell-physiology and drug development studies, which may elucidate to the mechanisms of vascular disease formation, and its prevention and treatment.

Use of finite element analysis in presurgical planning: treatment of mandibular fractures.

BACKGROUND: The current clinical procedure for mandible fracture fixation is plate application. 3D reconstructions are used to validate procedures numerically preceding experimental analysis. This study outlines the methods used to reconstruct a numerical model of the mandible. METHODS: A CT scan from a 22-year-old male patient with a healthy unfractured mandible was obtained. A 3D reconstruction was carried out using Mimics via thresholding and segmentation techniques. Boundary conditions and muscle forces were applied, and simulations were performed using ABAQUS. RESULTS: 3D reconstruction allows for precise anatomical dimensions, which can be used for further engineering analysis. Using the surgical Champy technique as an example, results showed that the mandible model returned to normal function post-plating. CONCLUSIONS: The study shows the clinical relevance of 3D reconstructions to plan surgical procedures. Results illustrate the benefit of carrying out numerical validations as a prerequisite to experimental modelling and as a method of pre-validating surgical procedures.

3D reconstruction and manufacture of real abdominal aortic aneurysms: from CT scan to silicone model.

Abdominal aortic aneurysm (AAA) can be defined as a permanent and irreversible dilation of the infrarenal aorta. AAAs are often considered to be an aorta with a diameter 1.5 times the normal infrarenal aorta diameter. This paper describes a technique to manufacture realistic silicone AAA models for use with experimental studies. This paper is concerned with the reconstruction and manufacturing process of patient-specific AAAs. 3D reconstruction from computed tomography scan data allows the AAA to be created. Mould sets are then designed for these AAA models utilizing computer aided designcomputer aided manufacture techniques and combined with the injection-moulding method. Silicone rubber forms the basis of the resulting AAA model. Assessment of wall thickness and overall percentage difference from the final silicone model to that of the computer-generated model was performed. In these realistic AAA models, wall thickness was found to vary by an average of 9.21%. The percentage difference in wall thickness recorded can be attributed to the contraction of the casting wax and the expansion of the silicone during model manufacture. This method may be used in conjunction with wall stress studies using the photoelastic method or in fluid dynamic studies using a laser-Doppler anemometry. In conclusion, these patient-specific rubber AAA models can be used in experimental investigations, but should be assessed for wall thickness variability once manufactured.

Evidence suggests rigid aortic grafts increase systolic blood pressure: results of a preliminary study.

Abdominal aortic aneurysm (AAA) is a serious complication of the aorta and is treated using vascular bypass grafts. Two main classes of graft are available to treat AAA; grafts implanted by open surgery and stent-grafts implanted using minimally invasive endovascular techniques. Both classes of graft consist of an aortic section which bifurcates into two iliac sections. It has been hypothesized that implantation of aortic grafts and stent-grafts serve to significantly increase abdominal aortic pressures. In this study, an open-loop computer-controlled pumping system was built to produce physiologically realistic pressure and flow-rates. Models of a compliant abdominal aortic aneurysm, a compliant walled graft and a tapered graft were manufactured using an injection moulding technique and fused deposition modelling was used to create a rigid walled graft. A specific transient flow-rate waveform was then applied at the inlet of each model and the resulting pressure waveforms 30 mm upstream from the bifurcation was recorded. Peak pressure measurements were recorded over the course of the pulse for each model. The compliant aneurysm model was found to have a systolic pressure of 107 mmHg while the complaint graft model was 153 mmHg. The rigid graft model had a peak systolic pressure of 199 mmHg. In the tapered graft, the peak pressure dropped to 142 mmHg. The data suggests that implanting a graft model in place of an aneurysm model in an in vitro flow circuit can increase the pressures recorded upstream from the iliac bifurcation and that tapered grafts may alleviate this problem.

Surgical feasibility study of a novel polytetrafluoroethylene graft design for the treatment of peripheral arterial disease.

Disturbed flow patterns, material mismatch, and surgical injury are often cited as being significant contributors to failure at the distal end of femoropopliteal bypass grafts. The objective of this research is to propose a novel bypass graft design concept which seeks to reduce the incidence of disturbed flow in the bypass junction and to establish the surgical feasibility of the proposed device. A preliminary evaluation of the hemodynamic benefit associated with the proposed device was made using computational fluid dynamics. A prototype of the device was then constructed from commercially available materials, and it was prepared for implantation into the aorta of a pig. The computational model of the proposed device showed that significant flow correction was occurring in the in vitro model due to the geometric configuration of the design. The magnitude of the peak wall shear stress in the recirculation region was noted to decrease by 78%. Surgical feasibility of the proposed device was verified by successful implantation into the aorta of the pig. The pig was sacrificed after 7 weeks, the graft and host artery were excised, and histological examination downstream from the distal junction showed that intimal hyperplasia had developed in the host artery. The proposed device is surgically feasible and may offer a significant hemodynamic advantage over current graft designs.