Tuning Fiber Alignment to Achieve Mechanical Anisotropy on Polymeric Electrospun Scaffolds for Cardiovascular Tissue Engineering

Abstract

Background: Soft tissues are characterized by strong mechanical anisotropy, as a result of internal fiber architecture, matching the needs of mechanical function in each body part. Polymeric grafts, used for diseased tissues replacement, suffer from mechanical mismatch with the tissues replaced and the remaining healthy tissues to be connected. Electrospinning is an attractive technique by which we can produce biodegradable polymeric scaffolds for tissue engineering applications. Fiber characteristics and structural architecture has to be tuned to match mechanically the tissues to be replaced. Furthermore, for the design of fibrous scaffolds, other characteristics, like fiber diameter, porosity and hydrophilicity play an important role as far as cell atraction, function and tissue regeneration are concerned.Objective: In the present work, we aimed to produce polymeric membranous scaffolds with specific architecture, giving attention to fibers’ orientation and hence, controlling the final mechanical behavior to match that of the physiological tissues to be replaced.Methods: To this end, we used a specifically designed drum collector, with accurate velocity control, and tested different electrospinning parameters (polymeric solution concentrations, transfer rates, rotational speed, etc) to obtain design optimization.Results: Scanning Electron Microscopy on scaffolds showed a good morphology quality. Fiber orientation was directly related to the drum speed. Tensile testing showed mechanical anisotropy in higher speeds. Young’s modulus and Ultimate tensile strength demonstrated strong anisotropy (one order of magnitude larger) in parallel to transverse direction, with regard to drum speed, similar to that of physiologic soft cardiovascular tissues. Scaffold hydrophilicity, expressed by contact angle measurements remained high, although a relation to fiber architecture has been recorded. Conclusion: Enhancement of membranous anisotropy was attained, one order of magnitude greater for the parallel fibers’ direction compared to the transverse one. A similar anisotropy can be found in cardiovascular soft tissues, like human and porcine aortic heart valve leaflets.