Advancing a real-time image-based jet lag tracking methodology for optimizing print parameters and assessing melt electrowritten fiber quality

Melt electrowriting (MEW) has emerged as an important additive manufacturing process to fabricate high-resolution microscale fibrous scaffolds for engineered tissue applications. However, the complex interplay between the numerous process variables renders parametric optimization of this additive manufacturing technique a challenging task. In order to facilitate the optimization of MEW-jetted fiber fabrication, this study adopts a real-time jet lag tracking methodology. Specifically, this methodology is implemented to determine the optimum conditions to improve the fiber quality featured by a prescribed mean diameter and an enhanced uniformity. Firstly, a serpentine toolpath is designed, and the real-time jet lag length signal is recorded, exhibiting multiple successive peaks. The coefficient of variance CV_pv correlated with these peak values is first identified as an indicator of the jet lag stability. Second, for a given pressure (P) and translational stage speed (v), as the applied voltage (U) increases, CV_pv is found to initially decrease before reaching a minimum point at U=U_c, followed by an increase at higher U values. U_c represents an inflection point on the graph of CV_pv as a function of U, whereby fiber pulsing is observed when U < U_c. Otherwise, an enhanced fiber uniformity is achieved at the expense of detectable current leakage when U > U_c. Moreover, at a given P, as v decreases, U_c deceases and plateaus at a value U_b. Furthermore, U_b is found to increase as P increases. These aforementioned dependencies are closely related to the mass equilibrium around the Taylor cone. Finally, based on these results, a systematic protocol is advanced to determine the appropriate P-U-v settings that enable an enhanced printed fiber quality.