Biology subjects

Fletcher, D. F.

Publications and source records attributed to Fletcher, D. F..

3 recordsLinked to original sources

bioRxiv2024

Haemodynamic impact of implant materials and anastomotic angle in peripheral vascular grafts

End-to-side anastomoses are commonly utilised in peripheral arterial bypass surgery and are plagued by high rates of re-stenosis as a result of non-physiological blood flow impacting arterial and graft structures. Computational simulations can examine how patient-specific surgical decisions in bypass graft placement and material selection affect blood flow and future risk of graft restenosis. Despite graft geometry and compliance being key predictors of restenosis, current simulations do not consider the interaction of flowing blood with compliant vessel, graft, and suture structures. Utilising fluid-structure interaction simulations, this study examines the impact of surgical technique, such as anastomosis angle, graft material, and suture material, on blood flow and fluid-structure forces in patient-specific asymptomatic arterial tree versus side-to-end peripheral grafts for symptomatic atherosclerotic disease. To render these complex simulations numerically feasible, our pipeline uses regional suture mechanics and a pre-stress pipeline previously validated in small-scale idealised models. Our simulations found that higher anastomosis angles generate larger regions of slow and recirculating blood, characterised by non-physiologically low shear stress and high oscillatory shear index. The use of compliant graft materials reduces regions of non-physiologically high shear stress only when used in combination with compliant suture materials. Altogether, our fluid-structure interaction simulation provides patient-specific platforms for vascular surgery decisions concerning graft geometry and material. HighlightsO_LISimulating bypass graft haemodynamics with realistic fluid-structure interactions. C_LIO_LIBypass grafts generate large regions of slow blood flow and blood recirculation. C_LIO_LIGreater graft anastomosis angles correlate with larger blood recirculation regions. C_LIO_LINonphysiologically stiff graft and suture materials increase vessel shear stress. C_LI

bioengineering↗

bioRxiv2024

Simulating big mechanically-active culture systems (BigMACS) using paired biomechanics-histology FEA modelling to derive mechanobiology design relationships.

Big mechanically-active culture systems (BigMACS) are promising to stimulate, control, and pattern cell and tissue behaviours with less soluble factor requirements, however, it remains challenging to predict if and how distributed mechanical forces impact single-cell behaviours to pattern tissue. In this study, we introduce a centimetre, tissue-scale, finite element analysis (FEA) framework able to correlate sub-cellular quantitative histology with centimetre-scale biomechanics. Our framework is relevant to diverse bigMACS; media perfusion, tensile-stress, magnetic, and pneumatic tissue culture platforms. We apply our framework to understand how the design and operation of a multi-axial soft robotic bioreactor can spatially control mesenchymal stem cell (MSC) proliferation, orientation, differentiation to smooth muscle, and extracellular vascular matrix deposition. We find MSC proliferation and matrix deposition correlate positively with mechanical stimulation but cannot be locally patterned by soft robot mechanical stimulation within a centimetre scale tissue. In contrast, local stress distribution was able to locally pattern MSC orientation and differentiation to smooth muscle phenotypes, where MSCs aligned perpendicular to principal stress direction and expressed increased -SMA with increasing 3D Von Mises Stresses from 0 to 15 kPa. Altogether, our new biomechanical-histological simulation framework is a promising technique to derive the future mechanical design equations to control cell behaviours and engineer patterned tissue generation.

bioengineering↗

bioRxiv2023

Fluid-Structure Interactions of Peripheral Arteries Using a Coupled in silico and in vitro Approach

Vascular compliance is considered both a cause and a consequence of cardiovascular disease and a significant factor in the mid- and long-term patency of vascular grafts. However, the biomechanical effects of localised changes in compliance, such as during plaque development or after bypass grafting and stenting, cannot be satisfactorily studied with the available medical imaging technologies or surgical simulation materials. To address this unmet need, we developed a coupled silico-vitro platform which allows for the validation of numerical fluid-structure interaction (FSI) results as a numerical model and physical prototype. This numerical one-way and two-way FSI study is based on a three-dimensional computer model of an idealised femoral artery which is validated against patient measurements derived from the literature. The numerical results are then compared with experimental values collected from compliant arterial phantoms. Phantoms within a compliance range of 1.4 - 68.0%/100mmHg were fabricated via additive manufacturing and silicone casting, then mechanically characterised via ring tensile testing and optical analysis under direct pressurisation with differences in measured compliance ranging between 10 - 20% for the two methods. One-way FSI coupling underestimated arterial wall compliance by up to 14.71% compared to two-way FSI modelling. Overall, Smooth-On Solaris matched the compliance range of the numerical and in vivo patient models most closely out of the tested silicone materials. Our approach is promising for vascular applications where mechanical compliance is especially important, such as the study of diseases which commonly affect arterial wall stiffness, such as atherosclerosis, and the model-based design, surgical training, and optimisation of vascular prostheses.

bioengineering↗