TY  - JOUR
A1  - Liashenko, Ievgenii
A1  - Hrynevich, Andrei
A1  - Dalton, Paul D.
T1  - Designing Outside the Box: Unlocking the Geometric Freedom of Melt Electrowriting using Microscale Layer Shifting
JF  - Advanced Materials
N2  - Melt electrowriting, a high‐resolution additive manufacturing technology, has so far been developed with vertical stacking of fiber layers, with a printing trajectory that is constant for each layer. In this work, microscale layer shifting is introduced through deliberately offsetting the printing trajectory for each printed layer. Inaccuracies during the printing of sinusoidal walls are corrected via layer shifting, resulting in accurate control of their geometry and mechanical properties. Furthermore, more substantial layer shifting allows stacking of fiber layers in a horizontal manner, overcoming the electrostatic autofocusing effect that favors vertical layer stacking. Novel nonlinear geometries, such as overhangs, wall texturing and branching, and smooth and abrupt changes in printing trajectory are presented, demonstrating the flexibility of the layer shifting approach beyond the state‐of‐the‐art. The practice of microscale layer shifting for melt electrowriting enables more complex geometries that promise to have a profound impact on the development of products in a broad range of applications.
KW  - 3D printing
KW  - additive manufacturing
KW  - biomaterials
KW  - electrohydrodynamics
KW  - melt electrospinning writing
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-217974
VL  - 32
IS  - 28
ER  - 
TY  - JOUR
A1  - Böhm, Christoph
A1  - Tandon, Biranche
A1  - Hrynevich, Andrei
A1  - Teßmar, Jörg
A1  - Dalton, Paul D.
T1  - Processing of Poly(lactic–co–glycolic acid) Microfibers via Melt Electrowriting
JF  - Macromolecular Chemistry and Physics
N2  - Polymers sensitive to thermal degradation include poly(lactic-co-glycolic acid) (PLGA), which is not yet processed via melt electrowriting (MEW). After an initial period of instability where mean fiber diameters increase from 20.56 to 27.37 µm in 3.5 h, processing stabilizes through to 24 h. The jet speed, determined using critical translation speed measurements, also reduces slightly in this 3.5 h period from 500 to 433 mm min\(^{−1}\) but generally remains constant. Acetyl triethyl citrate (ATEC) as an additive decreases the glass transition temperature of PLGA from 49 to 4 °C, and the printed ATEC/PLGA fibers exhibits elastomeric behavior upon handling. Fiber bundles tested in cyclic mechanical testing display increased elasticity with increasing ATEC concentration. The processing temperature of PLGA also reduces from 165 to 143 °C with increase in ATEC concentration. This initial window of unstable direct writing seen with neat PLGA can also be impacted through the addition of 10-wt% ATEC, producing fiber diameters of 14.13 ± 1.69 µm for the first 3.5 h of heating. The investigation shows that the initial changes to the PLGA direct-writing outcomes seen in the first 3.5 h are temporary and that longer times result in a more stable MEW process.
KW  - poly(lactide-co-glycolide)
KW  - 3D printing
KW  - additive manufacturing
KW  - electrohydrodynamics
KW  - melt electrospinning writing
KW  - plasticizers
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318444
VL  - 223
IS  - 5
ER  - 
TY  - JOUR
A1  - Böhm, Christoph
A1  - Stahlhut, Philipp
A1  - Weichhold, Jan
A1  - Hrynevich, Andrei
A1  - Teßmar, Jörg
A1  - Dalton, Paul D.
T1  - The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting
JF  - Small
N2  - Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75 °C and only increases with time for 85 and 95 °C. Fiber fusion at increased layer height is observed for 85 and 95 °C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95 °C. After the initial 5-d period, the MEW processing of PCL at 75 °C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µm over the entire 25-d period.
KW  - polycaprolactone
KW  - 3D printing
KW  - additive manufacturing
KW  - electrohydrodynamic
KW  - melt electrospinning writing
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257741
VL  - 18
IS  - 3
ER  -