The development and mechanical characterisation of a novel reinforced venous conduit that mimics the mechanical properties of an arterial wall

Design and Verification of a Novel Perfusion Bioreactor to Evaluate the Performance of a Self-Expanding Stent for Peripheral Artery Applications

Endovascular stenting presents a promising approach to treat peripheral artery stenosis. However, a significant proportion of patients require secondary interventions due to complications such as in-stent restenosis and late stent thrombosis. Clinical failure of stents is not only attributed to patient factors but also on endothelial cell (EC) injury response, stent deployment techniques, and stent design. Three-dimensional in vitro bioreactor systems provide a valuable testbed for endovascular device assessment in a controlled environment replicating hemodynamic flow conditions found in vivo. To date, very few studies have verified the design of bioreactors based on applied flow conditions and their impact on wall shear stress, which plays a key role in the development of vascular pathologies. In this study, we develop a computationally informed bioreactor capable of capturing responses of human umbilical vein endothelial cells seeded on silicone tubes subjected to hemodynamic flow conditions and deployment of a self-expanding nitinol stents. Verification of bioreactor design through computational fluid dynamics analysis confirmed the application of pulsatile flow with minimum oscillations. EC responses based on morphology, nitric oxide (NO) release, metabolic activity, and cell count on day 1 and day 4 verified the presence of hemodynamic flow conditions. For the first time, it is also demonstrated that the designed bioreactor is capable of capturing EC responses to stent deployment beyond a 24-hour period with this testbed. A temporal investigation of EC responses to stent implantation from day 1 to day 4 showed significantly lower metabolic activity, EC proliferation, no significant changes to NO levels and EC's aligning locally to edges of stent struts, and random orientation in between the struts. These EC responses were indicative of stent-induced disturbances to local hemodynamics and sustained EC injury response contributing to neointimal growth and development of in-stent restenosis. This study presents a novel computationally informed 3D in vitro testbed to evaluate stent performance in presence of hemodynamic flow conditions found in native peripheral arteries and could help to bridge the gap between the current capabilities of 2D in vitro cell culture models and expensive pre-clinical in vivo models.

Mechanical and structural characterisation of the dural venous sinuses

The dural venous sinuses play an integral role in draining venous blood from the cranial cavity. As a result of the sinuses anatomical location, they are of significant importance when evaluating the mechanopathology of traumatic brain injury (TBI). Despite the importance of the dural venous sinuses in normal neurophysiology, no mechanical analyses have been conducted on the tissues. In this study, we conduct mechanical and structural analysis on porcine dural venous sinus tissue to help elucidate the tissues’ function in healthy and diseased conditions. With longitudinal elastic moduli values ranging from 33 to 58 MPa, we demonstrate that the sinuses exhibit higher mechanical stiffness than that of native dural tissue, which may be of interest to the field of TBI modelling. Furthermore, by employing histological staining and a colour deconvolution protocol, we show that the sinuses have a collagen-dominant extracellular matrix, with collagen area fractions ranging from 84 to 94%, which likely explains the tissue’s large mechanical stiffness. In summary, we provide the first investigation of the dural venous sinus mechanical behaviour with accompanying structural analysis, which may aid in understanding TBI mechanopathology.

Enhancing medial layer recellularization of tissue-engineered blood vessels using radial microchannels

Aim: Cell repopulation of tissue-engineered vascular grafts (TEVGs) from decellularized arterial scaffolds is limited by dense concentric tunica media layers which impede cells migrating radially between the layers. We aimed to develop and validate a new microneedle device to modify decellularized carotid arteries with radial microchannels to enhance medial layer repopulation. Material & methods: Modified decellularized porcine arteries were seeded with rat mesenchymal stem cells using either standard longitudinal injection, or a dual vacuum-perfusion bioreactor. Mechanical tests were used to assess the arterial integrity following modification. Results & conclusion: The method herein achieved radial recellularization of arteries in vitro without significant loss of mechanical integrity, Thus, we report a novel method for successful radial repopulation of decellularized carotid artery-based tissue-engineered vascular grafts.

Comparative mechanics of diverse mammalian carotid arteries

The prevalence of diverse animal models as surrogates for human vascular pathologies necessitate a comprehensive understanding of the differences that exist between species. Comparative passive mechanics are presented here for the common carotid arteries taken from bovine, porcine, ovine, leporine, murine-rat, and murine-mouse specimens. Data is generated using a scalable biaxial mechanical testing device following consistent circumferential (pressure-diameter) and axial (force-length) testing protocols. The structural mechanical response of carotids under equivalent loading, quantified by the deformed inner radius, deformed wall thickness, lumen area compliance and axial force, varies significantly among species but generally follows allometric scaling. Conversely, descriptors of the local mechanical response within the deformed arterial wall, including mean circumferential stress, mid-wall circumferential stretch, and mean axial stress, are relatively consistent across species. Unlike the larger animals studied, the diameter distensibility curves of murine specimens are non-monotonic and have a significantly higher value at 100 mmHg. Taken together, our results provide baseline structural and mechanical information for carotid arteries across a broad range of common animal models.