Parametric control of fiber morphology and tensile mechanics in scaffolds with high aspect ratio geometry produced via melt electrowriting for musculoskeletal soft tissue engineering

Melt electrowriting (MEW) is an additive manufacturing technique that has the potential to create fibrous scaffolds that reproduce the scale and organization of collagen fiber networks in musculoskeletal soft tissues. For musculoskeletal soft tissue engineering, it is useful for scaffolds to have a high aspect ratio (length to width ratio of 5:1 or higher). However, the relationship between MEW process variables and the structural and mechanical properties of such scaffolds is not well understood. In addition, prior studies have cut samples from larger MEW structures, resulting in test specimens with discontinuous fibers. In this study, MEW scaffolds with low (square, 12 mm x 12 mm) and high aspect ratio (rectangular, 35 mm x 5 mm) macroscale geometries were fabricated at varying stage translation speeds or melt extrusion temperatures. Fiber morphology in both geometries and mechanical properties of the continuous rectangular structures were then quantified. Fiber diameter in both square and rectangular scaffolds generally decreased with increasing stage speed, but increased with melt temperature, though the effect of the latter was greater in square scaffolds. Interfiber spacing in both geometries was closer to the intended value as stage speed increased. Spacing became less accurate in square scaffolds with increasing melt temperature but changed little in rectangular scaffolds. Transverse fiber angle in rectangular scaffolds improved with increasing stage speed and had a median value within 1.4% of the intended angle at all temperatures. Finally, apparent tensile modulus in rectangular scaffolds decreased with increasing speed and temperature. These findings highlight the need to tailor MEW process parameters in scaffolds with high aspect ratio geometry in order to consistently generate specific structural and mechanical properties. Because of the potential to reproduce the structural anisotropy, fiber size, and mechanical properties of collagenous extracellular matrix, MEW structures are promising as musculoskeletal soft tissue scaffolds.