Melt electrowriting (MEW) is an emerging high‐resolution additive manufacturing technique based on the electrohydrodynamic processing of polymers. MEW is predominantly used to fabricate scaffolds for biomedical applications, where the microscale fiber positioning has substantial implications in its macroscopic mechanical properties. This review gives an update on the increasing number of polymers processed via MEW and different commercial sources of the gold standard poly(ε‐caprolactone) (PCL). A description of MEW‐processed polymers beyond PCL is introduced, including blends and coated fibers to provide specific advantages in biomedical applications. Furthermore, a perspective on printer designs and developments is highlighted, to keep expanding the variety of processable polymers for MEW.

Melt electrospun fibers, in general, have larger diameters than normally achieved with solution electrospinning. This study uses a modified nozzle to direct‐write melt electrospun medical‐grade poly(ε‐caprolactone) onto a collector resulting in fibers with the smallest average diameter being 275 ± 86 nm under certain processing conditions. Within a flat‐tipped nozzle is a small acupuncture needle positioned so that reduces the flow rate to ≈0.1 µL h−1 and has the sharp tip protruding beyond the nozzle, into the Taylor cone. The investigations indicate that 1‐mm needle protrusion coupled with a heating temperature of 120 °C produce the most consistent, small diameter nanofibers. Using different protrusion distances for the acupuncture needle results in an unstable jet that deposited poor quality fibers that, in turn, affects the next adjacent path. The material quality is notably affected by the direct‐writing speed, which became unstable above 10 mm min−1. Coupled with a dual head printer, first melt electrospinning, then melt electrowriting could be performed in a single, automated process for the first time. Overall, the approach used here resulted in some of the smallest melt electrospun fibers reported to date and the smallest diameter fibers from a medical‐grade degradable polymer using a melt processing technology.

As scaffolds approach dimensions that are of clinical relevance, mechanical integrity and distribution becomes an important factor to the overall success of the implant. Hydrogels often lack the structural integrity and mechanical properties for use in vivo or handling. The inclusion of a structural support during the printing process, referred to as hybrid printing, allows the implant to retain structure and protect cells during maturation without needing to compromise its biological performance. In this study, scaffolds for the purpose of auricular cartilage reconstruction were evaluated via a hybrid printing approach using methacrylated Gelatin (GelMA) and Hyaluronic acid (HAMA) as the cellladen hydrogel, Polycaprolactone (PCL) as structural support and Lutrol F-127 as sacrificial material. Furthermore, printing parameters such as nozzle diameter, strand spacing and filament orientation scaffolds were investigated. Compression and bending tests showed that increasing nozzle sizes decrease the compressive modulus of printed scaffolds, with up to 82% decrease in modulus when comparing between a 400 μm and 200 μm sized nozzle tip at the same strand spacing. On the contrary, strand spacing and orientation influences mainly the bending modulus due to the greater porosity and changes in pore size area. Using a 400 μm sized nozzle, scaffolds fabricated have a measured compression and bending modulus in the range similar to the native cartilage. The viability and proliferation of human mesenchymal stem cells delivered within the bioink was not affected by the printing process. Using results obtained from mechanical testing, a scaffold with matching mechanical properties across six distinct regions mimicking the human auricular cartilage can be completed in one single print process. The use of PCL and GelMA-HAMA as structural support and cell-laden hydrogel respectively are an excellent combination to provide tailored mechanical integrity, while maintaining porosity and protection to cells during differentiation.

Three acceptor-π-bridge-acceptor (A-π-A) molecules derived from 2-(3-boryl-2-thienyl)thiazole have been synthesized and thoroughly characterized. Incorporation of a B-N unit into thienylthiazole and attachment of suitable acceptor moieties allowed to obtain ambient-stable A-π-A molecules with low-lying LUMO levels. Their potential for applications in organic electronics was tested in vacuum-deposited organic thin film transistors (OTFT). The OTFT device based on boryl-thienylthiazole and 1,1-dicyanomethylene-3-indanone (DCIND) acceptor moieties showed an electron mobility of ≈1.4×10 cm V s in air, which is the highest electron mobility reported to date for organoboron small molecules. Conversely, the device employing the malononitrile (MAL) derivative as an active layer did not show any charge transport behavior. As suggested by single crystal X-ray analysis of indandione (IND) and MAL derivatives, the enhanced mobility of IND (and DCIND) in comparison to the MAL molecule can be attributed to the effective two-dimensional π-stacking in the solid state imparted by the acceptor moieties with an extended π-surface.

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.

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.

The need to search for biomaterials that can promote tissue regeneration and easy to replicate and manufacture is a major driving force for research and development in the area of reconstructive surgery and regenerative medicine. It is of great importance to otolaryngologists to find alternate solutions that require harvesting large amounts of autologous cartilage in patients needing cartilage grafts. Due to its very limited self-regeneration capacity, cartilage repair and reconstruction is extremely challenging. Microtia is a congenital condition of abnormal development of the outer and/ or the middle ear and can range from mild to complete absence of the ear. Current treatment methods such as autologous, alloplastic and prosthetic reconstruction have limitations such as donor site morbidity, long-term complications and implant failure. 3D printing is an exciting solution to address the challenges of microtia and create customised implants. The ability to deposit cells and biomaterials in a controlled and precise manner, allows the fabrication of implants with complex internal architecture and functional properties not achievable through traditional manufacturing methods. Despite the ability to mimic native properties and structure of tissue, 3D printed constructs using pristine inks lack the structural integrity and adequate mechanical properties for use in vivo or handling. These requirements highlight the importance of ink development and selection, which is a continuing challenge in the bioprinting process. This review will address the current treatment options for patients with microtia and the potential of 3D bioprinting in area of auricular cartilage regeneration. In particular, the use of hybrid printing to better mimic the practical and functional requirements of an ear scaffold will be discussed.

Melt electrowriting (MEW) is an additive manufacturing technology enabling the production of highly porous microfiber scaffolds, suggested in particular for use in biomedical applications, including drug delivery. Indomethacin (IND) is a nonselective anti-inflammatory drug, for which sublingual delivery could offer advantages such as rapid absorption by the veins in the mouth floor while overcoming the side effects of peroral delivery such as damage to the gastrointestinal mucosa barrier. This study introduces MEW as a processing method to obtain rapid-dissolving drug-releasing scaffolds, containing IND as a model drug, for sublingual drug delivery applications. For this, an amorphous solid dispersion (ASD) of IND in combination with a poly(2-oxazoline)-based amphiphilic triblock copolymer excipient is introduced, enabling ultra-high drug loading. We prepared highly porous, melt electrowritten drug-loaded scaffolds with different polymer/IND w/w ratios up to 1:2 and assessed their morphology, amorphicity, and IND release rate. The results show completely amorphous dispersion of the polymer and drug after MEW processing resulting in smooth and uniform fibers and rapid dissolution of the drugloaded scaffold. These first water-soluble melt electrowritten IND-loaded microfiber scaffolds break ground as a model for rapid sublingual delivery of ultra-high drug-loaded ASDs.