Methods:

• A detailed mathematical model to define the design criteria was completed to

produce relevant ex-vivo flow behaviour (3).

• The tissue samples were prepared by a surgical procedure to ensure simulation of

the AVF geometry was comparable to clinical samples. The system includes a

peristaltic pump and silicone tubing, culture media supplemented Xanthan gum to

increase the viscosity of culture medium to 3.5 mPa∙s to replicate the viscosity of the

average haematocrit blood, pressure transducer and flow meter to ensure

physiological flow conditions.

• The tissue was perfused for periods of one, two and three weeks to characterise the

biological and geometrical changes at various time points.

• Haematoxylin and Eosin staining (H&E) technique provided an evaluation of

structural components of the tissue along with the tissue’s viability post-

experimentation. Finally, a MTT assay was completed by incubation for 1 hr to

evaluate the cell viability both pre and post experiment to compare the change after

exposure to new hemodynamics.

Introduction:Hemodynamics is strongly correlated with vascular remodeling, especially within arteriovenous fistulas (AVF) due to the untypical arterial flow conditions presented at the vascular

access site. Previous studies have analysed the effects on coronary by-pass graft models in vitro, the measurability of the systems prove to be a difficult aspect which reduces the

clinical relevance of these models (4). Many in vitro models have exposed the tissue to steady flow and hemodynamics such as wall shear stress (WSS) which are not representative of

the physiological parameters present in an in vivo environment (3). An attempt needs to be made to produce an ex-vivo system capable of controlling the key hemodynamics

parameters which are driving the cell mechanotransduction process during fistula maturation. To correlate the cell response to the altered shear stress and pressure drop across the

anastomosis region and development of intimal hyperplasia, it requires a living tissue sample to be maintained in a controlled environment due to the complex nature of fistula

maturation. The perfusion system can produce varied and controlled waveforms and expose a surgical constructed ex-vivo AVF for up to two weeks. A critical component of this system

development is the ability to maintain tissue viability to understand the maturation process at various timepoints from a biological standpoint. Post-analysis of the tissue samples using

biological techniques to identify the presence of inflammatory cytokines related to the hemodynamic parameters can provide vessel remodeling predictors.

Results:

Summary and Future Work:

The results allow for the system to be used as an ex-vivo AVF simulation to evaluate the

varied hemodynamics parameters that can be controlled individually by the components

within the system. Further biological techniques are required to understand the definitive

cellular mechanotransduction occurring due to this altered environment which will be

examined by comparing the immunofluorescence inflammatory cytokines present in the

sample post exposure. We show tissue and cell viability at a two-week period leading to

confirmation that the system currently can provide a platform for AVF ex-vivo simulation.

With further system adjustment, it is desirable to get up to four weeks to have a clinically

relevant comparison with fistula maturation process

THE DEVELOPMENT OF A PERFUSION DEVICE TO APPLY VARYING HEMODYNAMIC PARAMETERS TO BOVINE ARTERIOVENOUS TISSUE

O’Connor, D.T., Franzoni, M, Walsh, MT.Biomaterials Cluster, Health Research Institute (HRI), Bernal Institute, School of Engineering, University of Limerick.

email: david.t.oconnor@ul.ie

References:[1] Allen, J. W. and Bhatia, S. N. (2003) ‘Formation of steady-state oxygen gradients in vitro: Application to liver zonation’, Biotechnology and Bioengineering, 82(3), pp. 253–262. [2]. Foy, B. D. et al. (1994) ‘A device to measure the oxygen uptake rate of attached cells: importance in bioartificial organ design.’, Cell transplantation, 3(6), pp. 515–27.[3] Orr, D. E. and Burg, K. J. L. (2008) ‘Design of a Modular Bioreactor to Incorporate Both Perfusion Flow and Hydrostatic Compression for Tissue Engineering Applications’, Annals of Biomedical Engineering, 36(7), pp. 1228–1241.[4] Piola, M. et al. (2016) ‘Human saphenous vein response to trans-wall oxygen gradients in a novel ex vivo conditioning platform’, Annals of biomedical.

Results: