A holistic model for melt electrowritten three-dimensional structured materials based on residual charge.

The printing accuracy of polymer melt electrowriting is adversely affected by the residual charge entrapped within the fibers, especially for three-dimensional (3D) structured materials or multilayered scaffolds with small interfiber distances. To clarify this effect, an analytical charge-based model is proposed herein. The electric potential energy of the jet segment is calculated considering the amount and distribution of the residual charge in the jet segment and the deposited fibers. As the jet deposition proceeds, the energy surface assumes different patterns, which constitute different modes of evolution. The manner in which the various identified parameters affect the mode of evolution are represented by three charge effects, including the global, local, and polarization effect. Based on these representations, typical modes of energy surface evolution are identified. Moreover, the lateral characteristic curve and characteristic surface are advanced to analyze the complex interplay between fiber morphologies and residual charge. Different parameters contribute to this interplay either by affecting residual charge, fiber morphologies, or the three charge effects. To validate this model, the effects of lateral location and grid number (i.e., number of fibers printed in each direction) on the fiber morphologies are investigated. Moreover, the "fiber bridging" phenomenon in parallel fiber printing is successfully explained. These results help to comprehensively understand the complex interplay between the fiber morphologies and the residual charge, thus furnishing a systematic workflow to improve printing accuracy.