Biomechanical characterization of MEW-manufactured synthetic scaffold structures for tissue-engineered vascular grafts

Abstract

The limitation of synthetic vascular implants as well as the frequent lack of transplantable tissue highlights the necessity for tissue-engineered constructs to provide safe, durable, and indefinite alternatives for tissue replacement. 3D printing methods like melt electrowriting (MEW) [1] provide a promising technique for the production of highly precise and reproduceable scaffold structures. MEW was optimized to produce tubular scaffolds on a custom-made rotating printing bed by using a 3D Printer R-Gen 200 (REGENHU, Villaz-St-Pierre, Switzerland) [2]. Printing parameters like pressure for material extrusion, voltage between collector and nozzle, nozzle offset to the collector and the printing speed, definable and even patient-specific structures were adjusted.

We present a biomechanical characterization of 3D-printed tubular scaffold designs (n= 5-15 per design) which approach those of native porcine blood vessels (n=36, and n=15 vessels decellularized according to [3]). Uniaxial testing at a zwickLine (ZwickRoell GmbH & Ko KG, Ulm, Germany) was performed. Increasing the winding angle of the fibers around the rotational printing bed (from 15 to 75°) showed an increasing effect on tensile strength and Young’s modulus in radial testing, whereas there was no effect in longitudinal testing. A bigger strand diameter (range 52-132 µm) and lowered strand distance (0.5 to 0.2 mm) led to an increased Young’s modulus in longitudinal testing. The degradation rate of ?-polycaprolactone (45 or 80 kg* mmol^-1) and poly-L-lactic acid (Sigma, Missouri, US) was observed over a three-month period in incubation assays favoring longer-chained polymers. Following this an intricate interdependency/synergy/interplay between the angle of the printed fibers and the strand diameter as well as the selection of a suitable polymer is crucial for the biomechanical characteristics of 3D-printed tubular scaffolds. The here presented mechanical adaptions of tubular scaffolds for cardiovascular grafts provide a deep insight into bioartificial blood vessel grafts with physiological stress strain behavior and further allow the adaptions of blood vessel scaffolds with patient specific properties.