@article{BakirciFrankGumbeletal.2021, author = {Bakirci, Ezgi and Frank, Andreas and Gumbel, Simon and Otto, Paul F. and F{\"u}rsattel, Eva and Tessmer, Ingrid and Schmidt, Hans-Werner and Dalton, Paul D.}, title = {Melt Electrowriting of Amphiphilic Physically Crosslinked Segmented Copolymers}, series = {Macromolecular Chemistry and Physics}, volume = {222}, journal = {Macromolecular Chemistry and Physics}, number = {22}, doi = {10.1002/macp.202100259}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257572}, year = {2021}, abstract = {Various (AB)\(_{n}\) and (ABAC)\(_{n}\) segmented copolymers with hydrophilic and hydrophobic segments are processed via melt electrowriting (MEW). Two different (AB)\(_{n}\) segmented copolymers composed of bisurea segments and hydrophobic poly(dimethyl siloxane) (PDMS) or hydrophilic poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEG-PPO) segments, while the amphiphilic (ABAC)\(_{n}\) segmented copolymers consist of bisurea segments in the combination of hydrophobic PDMS segments and hydrophilic PPO-PEG-PPO segments with different ratios, are explored. All copolymer compositions are processed using the same conditions, including nozzle temperature, applied voltage, and collector distance, while changes in applied pressure and collector speed altered the fiber diameter in the range of 7 and 60 µm. All copolymers showed excellent processability with MEW, well-controlled fiber stacking, and inter-layer bonding. Notably, the surfaces of all four copolymer fibers are very smooth when visualized using scanning electron microscopy. However, the fibers show different roughness demonstrated with atomic force microscopy. The non-cytotoxic copolymers increased L929 fibroblast attachment with increasing PDMS content while the different copolymer compositions result in a spectrum of physical properties.}, language = {en} } @article{BoehmStahlhutWeichholdetal.2022, author = {B{\"o}hm, Christoph and Stahlhut, Philipp and Weichhold, Jan and Hrynevich, Andrei and Teßmar, J{\"o}rg and Dalton, Paul D.}, title = {The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting}, series = {Small}, volume = {18}, journal = {Small}, number = {3}, doi = {10.1002/smll.202104193}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257741}, year = {2022}, abstract = {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.}, language = {en} } @article{BoehmTandonHrynevichetal.2022, author = {B{\"o}hm, Christoph and Tandon, Biranche and Hrynevich, Andrei and Teßmar, J{\"o}rg and Dalton, Paul D.}, title = {Processing of Poly(lactic-co-glycolic acid) Microfibers via Melt Electrowriting}, series = {Macromolecular Chemistry and Physics}, volume = {223}, journal = {Macromolecular Chemistry and Physics}, number = {5}, doi = {10.1002/macp.202100417}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318444}, year = {2022}, abstract = {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.}, language = {en} } @article{HochleitnerJuengstBrownetal.2015, author = {Hochleitner, Gernot and J{\"u}ngst, Tomasz and Brown, Toby D and Hahn, Kathrin and Moseke, Claus and Jakob, Franz and Dalton, Paul D and Groll, J{\"u}rgen}, title = {Additive manufacturing of scaffolds with sub-micron filaments via melt electrospinning writing}, series = {Biofabrication}, volume = {7}, journal = {Biofabrication}, number = {3}, doi = {10.1088/1758-5090/7/3/035002}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-254053}, year = {2015}, abstract = {The aim of this study was to explore the lower resolution limits of an electrohydrodynamic process combined with direct writing technology of polymer melts. Termed melt electrospinning writing, filaments are deposited layer-by-layer to produce discrete three-dimensional scaffolds for in vitro research. Through optimization of the parameters (flow rate, spinneret diameter, voltage, collector distance) for poly-ϵ-caprolactone, we could direct-write coherent scaffolds with ultrafine filaments, the smallest being 817 ± 165 nm. These low diameter filaments were deposited to form box-structures with a periodicity of 100.6 ± 5.1 μm and a height of 80 μm (50 stacked filaments; 100 overlap at intersections). We also observed oriented crystalline regions within such ultrafine filaments after annealing at 55 °C. The scaffolds were printed upon NCO-sP(EO-stat-PO)-coated glass slide surfaces and withstood frequent liquid exchanges with negligible scaffold detachment for at least 10 days in vitro.}, language = {en} } @article{HoehneDickhautSchmitter2020, author = {H{\"o}hne, Christian and Dickhaut, Nora and Schmitter, Marc}, title = {Introduction of a new teaching concept for dentin post preparation with 3D printed teeth}, series = {European Journal of Dental Education}, volume = {24}, journal = {European Journal of Dental Education}, number = {3}, doi = {10.1111/eje.12528}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-215586}, pages = {499 -- 506}, year = {2020}, abstract = {Introduction The preparation for dentin posts is difficult and hard to learn. There are currently no reproducible simulation models to train this clinical procedure. The purpose of this study was the design, feasibility and evaluation of a three-dimensional (3D) printed tooth model for the pre-clinical teaching of students. Materials and methods A printable tooth was designed and printed by a stereolithographic printer. A total of 48 fourth-year dental students in the first clinical course in prosthodontics were trained in a voluntary hands-on course on 4 similar printed teeth. The students used standard model teeth and real-teeth models during their education. They had experience in caries removement and root canal treatment on real patients. Root perforations were counted for every attempt. The different benefits of the 3D printed tooth were evaluated by a questionnaire using German school grades from 1 (best) to 6 (worst). Results The overall rating of the printed tooth was {\O}1.9 ± 0.3. The item "suitable exercise option" was rated {\O}2.0 ± 0.8, and the teeth were "easy to use" {\O}1.9 ± 0.9. The item "realistic approach to dentin post preparation" was rated {\O}2.1 ± 0.8, and the teeth showed the "shortcomings at a root perforation" {\O}1.5 ± 0.6. The students reported to have much more motivation and enthusiasm to improve their skills with the printed teeth {\O}2.1 ± 0.9. They had a strong desire to include these teeth in their pre-clinical education before the first patient treatment {\O}1.6 ± 0.8. The success rate of the dentin post preparation was significantly better for the second 25\% (P = .047) and fourth 48\% (P = .04) attempt. Conclusions The feasibility of this teaching concept was confirmed. The students had the possibility to learn a correct dentin post preparation on a printed tooth model. The learning effect with this tooth model was rated as good to very good by the questionnaire.}, language = {en} } @article{HoehneSchwarzbauerSchmitter2020, author = {H{\"o}hne, Christian and Schwarzbauer, Raphael and Schmitter, Marc}, title = {Introduction of a new teaching concept for crown preparation with 3D printed teeth}, series = {European Journal of Dental Education}, volume = {24}, journal = {European Journal of Dental Education}, number = {3}, doi = {10.1111/eje.12532}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218133}, pages = {526 -- 534}, year = {2020}, abstract = {Introduction For both students and teachers, it is challenging to learn and teach a correct crown preparation. The purpose of this study was the design, feasibility and evaluation of a 3D printed tooth model with internal preparation for dental education in crown preparation and to analyse the quality of the prepared printed teeth in comparison with prepared standard model teeth. Materials and methods A printable tooth was designed and printed by a stereolithographic printer. 38 fourth-year dental students in the first clinical course in prosthodontics were trained in a voluntary course using printed teeth. Different aspects of the printed tooth were evaluated by a questionnaire using German school grades (1 best to 5 worst). The quality of the preparation with the printed teeth and standard training teeth was also rated in an evaluation form done by an expert group consisting of five experienced dentists. Results The workflow was feasible and cost-effective for the production of the teeth. The overall rating of the printed tooth was {\O} 2.0 ± 0.34 in the questionnaire completed by the students. The students rated the printed tooth model ({\O} 2.1 ± 0.85) as significantly better than the standard model tooth ({\O} 3.3 ± 0.77; P = .000). The students reported great benefits in the use of this model tooth, for example valuable replacement of a standard model and real teeth, direct control of material loss. The quality of the preparation was evaluated by the expert group as significantly better with an overall mean grade of {\O} 2.6 ± 0.37 for the printed teeth compared to {\O} 2.9 ± 0.42 for the standard model teeth (P = .000). Conclusions The feasibility of this teaching concept was confirmed. The students favoured to work on the innovative 3D-teeth with internal preparation, emphasising the usefulness of this technique in dental education. The expert group confirmed also the significant training effect of this tooth model in contrast to a standard model tooth.}, language = {en} } @article{KadeBakirciTandonetal.2022, author = {Kade, Juliane C. and Bakirci, Ezgi and Tandon, Biranche and Gorgol, Danila and Mrlik, Miroslav and Luxenhofer, Robert and Dalton, Paul D.}, title = {The Impact of Including Carbonyl Iron Particles on the Melt Electrowriting Process}, series = {Macromolecular Materials and Engineering}, volume = {307}, journal = {Macromolecular Materials and Engineering}, number = {12}, issn = {1438-7492}, doi = {10.1002/mame.202200478}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318482}, year = {2022}, abstract = {Melt electrowriting, a high-resolution additive manufacturing technique, is used in this study to process a magnetic polymer-based blend for the first time. Carbonyl iron (CI) particles homogenously distribute into poly(vinylidene fluoride) (PVDF) melts to result in well-defined, highly porous structures or scaffolds comprised of fibers ranging from 30 to 50 µm in diameter. This study observes that CI particle incorporation is possible up to 30 wt\% without nozzle clogging, albeit that the highest concentration results in heterogeneous fiber morphologies. In contrast, the direct writing of homogeneous PVDF fibers with up to 15 wt\% CI is possible. The fibers can be readily displaced using magnets at concentrations of 1 wt\% and above. Combined with good viability of L929 CC1 cells using Live/Dead imaging on scaffolds for all CI concentrations indicates that these formulations have potential for the usage in stimuli-responsive applications such as 4D printing.}, language = {en} } @article{KadeOttoLuxenhoferetal.2021, author = {Kade, Juliane C. and Otto, Paul F. and Luxenhofer, Robert and Dalton, Paul D.}, title = {Melt electrowriting of poly(vinylidene difluoride) using a heated collector}, series = {Polymers for Advanced Technologies}, volume = {32}, journal = {Polymers for Advanced Technologies}, number = {12}, issn = {1042-7147}, doi = {10.1002/pat.5463}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318493}, pages = {4951 -- 4955}, year = {2021}, abstract = {Previous research on the melt electrowriting (MEW) of poly(vinylidene difluoride) (PVDF) resulted in electroactive fibers, however, printing more than five layers is challenging. Here, we investigate the influence of a heated collector to adjust the solidification rate of the PVDF jet so that it adheres sufficiently to each layer. A collector temperature of 110°C is required to improve fiber processing, resulting in a total of 20 fiber layers. For higher temperatures and higher layers, an interesting phenomenon occurred, where the intersection points of the fibers coalesced into periodic spheres of diameter 206 ± 52 μm (26G, 150°C collector temperature, 2000 mm/min, 10 layers in x- and y-direction).The heated collector is an important component of a MEW printer that allows polymers with a high melting point to be processable with increased layers.}, language = {en} } @article{KadeTandonWeichholdetal.2021, author = {Kade, Juliane C. and Tandon, Biranche and Weichhold, Jan and Pisignano, Dario and Persano, Luana and Luxenhofer, Robert and Dalton, Paul D.}, title = {Melt electrowriting of poly(vinylidene fluoride-co-trifluoroethylene)}, series = {Polymer International}, volume = {70}, journal = {Polymer International}, number = {12}, doi = {10.1002/pi.6272}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257654}, pages = {1725-1732}, year = {2021}, abstract = {Poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-co-TrFE)) is an electroactive polymer with growing interest for applications in biomedical materials and flexible electronics. In this study, a solvent-free additive manufacturing technique called melt electrowriting (MEW) has been utilized to fabricate well-defined microperiodic structures of the copolymer (P(VDF-co-TrFE)). MEW of the highly viscous polymer melt was initiated using a heated collector at temperatures above 120 °C and required remarkably slow collector speeds below 100 mm min\(^{-1}\). The fiber surface morphology was affected by the collector speed and an increase in β-phase was observed for scaffolds compared to the unprocessed powder. Videography shows vibrations of the P(VDF-co-TrFE) jet previously unseen during MEW, probably due to repeated charge buildup and discharge. Furthermore, piezo-force microscopy measurements demonstrated the electromechanical response of MEW-fabricated fibers. This research therefore achieves the melt electrohydrodynamic processing of fibers with micrometer resolution into defined structures with an important electroactive polymer.}, language = {en} } @article{LiashenkoHrynevichDalton2020, author = {Liashenko, Ievgenii and Hrynevich, Andrei and Dalton, Paul D.}, title = {Designing Outside the Box: Unlocking the Geometric Freedom of Melt Electrowriting using Microscale Layer Shifting}, series = {Advanced Materials}, volume = {32}, journal = {Advanced Materials}, number = {28}, doi = {10.1002/adma.202001874}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217974}, year = {2020}, abstract = {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.}, language = {en} }