Engineering in-plane mechanics of electrospun polyurethane scaffolds for cardiovascular tissue applications

Effective cardiovascular tissue surrogates require high control of scaffold structural and mechanical features to match native tissue properties, which are dependent on tissue-specific mechanics, function heterogenicity, and morphology. Bridging scaffold processing variables with native tissue properties is recognized as a priority for advancing biomechanical performance of biomedical materials and, when translated to the clinical practice, their efficacy. Accordingly, this study selected electrospinning on a rotating cylindrical target as an apparatus of broad application and mapped the relationship between key processing variables and scaffold mechanics and structure. This information was combined with mechanical anisotropy ranges of interest for the three main categories of tissue surrogated in cardiovascular tissue engineering: heart valve leaflets, ventricle wall, and large diameter blood vessels. Specifically, three processing variables have been considered: the rotational velocity and the rastering velocity of the mandrel and the dry (single nozzle - polymer only) vs wet (double nozzle - polymer plus phosphate buffer saline solution) fabrication configuration. While the dry configuration is generally utilized to obtain micro-fiber based polymeric mats, the wet fabrication is representative of processing conditions utilized to incorporate cells, growth factors, or micro-particles within the fibrous scaffold matrix. Dry and wet processed electrospun mats were fabricated with tangential and rastering velocities within the 0.3-9.0 m/s and 0.16-8 cm/s range respectively. Biaxial mechanics, fiber network, and pore micro-architectures were measured for each combination of velocities and for each fabrication modality (dry and wet). Results allowed identification of the precise combination of rotational and rastering velocities, for both dry and wet conditions, that is able to recapitulate the native cardiovascular tissue anisotropy ratio. By adopting a simple and broadly utilized electrospinning layout, this study is meant to provide a repeatable and easy to access methodology to improve biomimicry of the in plane-mechanics of heart valve leaflets, ventricular wall, and large diameter blood vessels.