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Volume 2022, Issue 18, Additive manufacturing of thermoplastics and metals is a sustainable and established process in industry for the rapid production of individual technical components. For a long time, this technology was not accessible for the group of elastomers, or only to a limited extent in the form of thermoplastic elastomers or silicone rubbers. The development of the Additive Manufacturing of Elastomers (AME)-process has enabled the additive manufacturing of high viscosity rubbers. In future, additively manufactured rubber components may be used in technical logistics in particular. On the one hand, the supply of spare parts such as sealing and damping elements is possible, and on the other hand, the production of individual geometries for grippers in handling technology. For the additive manufacturing of rubber, an industrial 3D-printer was modified by a twin screw extruder, which can process rubber filament and deposit it on a printing plate in strand form, similar to the thermoplastic Fused Filament Fabrication (FFF)-process. The use of a screw extruder is necessary because the viscosity of the rubber does not decrease sufficiently with heating, making it impossible to guide the filament through conventional print heads for thermoplastic filaments. The AME-process is a two-step manufacturing process. First, the components are additively manufactured, followed by vulcanization in a high-pressure autoclave or heating oven. Single-part production is a particular challenge in this case, as the vulcanization time depends on the rubber compound and the component geometry. In order to avoid waste, it is therefore necessary to know the optimum vulcanization time before vulcanization. For this purpose, a simulation was developed and validated that outputs the degree of crosslinking in the component as a function of the vulcanization temperature and time., Die additive Fertigung von Thermoplasten und Metallen ist ein nachhaltiges und in der Industrie zur schnellen Herstellung von individuellen technischen Bauteilen bewährtes Verfahren. Lange Zeit war diese Technologie für die Werkstoffgruppe der Elastomere nicht oder nur eingeschränkt in Form von Thermoplastischen Elastomeren oder Silikonkautschuken zugänglich. Durch die Entwicklung des Additive Manufacturing of Elastomers (AME)-Verfahrens ist nun auch die additive Fertigung von hochviskosen Kautschuken möglich. Besonders in der technischen Logistik können zukünftig additiv gefertigte Kautschukbauteile Einsatz finden. Einerseits ist die Bereitstellung von Ersatzteilen wie Dichtungs- und Dämpferelementen möglich, aber auch die Fertigung individueller Geometrien für Greifer in der Handhabungstechnik. Zur additiven Fertigung von Kautschuk wurde ein industrieller 3D-Drucker um einen Zweischneckenextruder erweitert, der Kautschukfilament verarbeiten und ähnlich zum thermoplastischen Fused Filament Fabrication (FFF)-Verfahren strangförmig auf eine Druckplatte auftragen kann. Der Einsatz eines Schneckenextruders ist notwendig, da die Viskosität des Kautschuks nicht ausreichend durch Erwärmung abnimmt und somit eine Führung des Filaments durch konventionelle Druckköpfe für thermoplastische Filamente nicht möglich ist. Das AME-Verfahren ist ein zweistufiges Fertigungsverfahren. Zuerst werden die Bauteile additiv gefertigt, anschließend folgt die Vulkanisation in einem Hochdruckautoklav oder Wärmeschrank. Hierbei ist besonders die Einzelteilfertigung eine Herausforderung, da die Vulkanisationszeit abhängig von der Kautschukmischung und der Bauteilgeometrie ist. Um keinen Ausschuss zu produzieren ist es daher notwendig die optimale Vulkanisationszeit vor der Vulkanisation zu kennen. Hierfür wurde eine Simulation, die den Vernetzungsgrad im Bauteil in Abhängigkeit von der Vulkanisationstemperatur und -zeit ausgibt, entwickelt und validiert.

Additive manufacturing of thermoplastics or metals is a well-approved sustainable process for obtaining rapidly precise and individual technical components. Except for crosslinked silicone rubber or thermoplastic elastomers, there is no method of additive manufacturing of elastomers. Based on the development of the additive manufacturing of elastomers (AME) process, the material group of rubber-based cured elastomers may gain first access to the process field of three-dimensional (3D) printing. Printing and crosslinking of rubber is separated into two steps. In the first step, printing is realized by extrusion of the rubber by using a twin-screw extruder, which works according to the derived fused-filament-fabrication principle. In the second step, the component is vulcanized in a high-pressure hot-air autoclave. Because of the plastic flow behavior of non–crosslinked rubber materials, a thermoplastic shell is probably needed to maintain the geometry and position of the additively manufactured rubber. In this way, one layer of thermoplastic and one layer of rubber are printed alternatingly until the component is finished. Afterward, the manufactured binary component is placed in an autoclave to obtain the elastomer after vulcanization under a hot-air and high-pressure atmosphere. Then, the thermoplastic shell is removed from the elastomer and can subsequently be recycled. As compared with conventional thermoplastics, the high viscosity of rubber during processing and its instable shape after extrusion are challenging factors in the development of the AME. This contribution will show a modified 3D printer; explain the printing process from the designed component, via shell generation, to the vulcanized component; and show first printed components.

The blood-saliva barrier (BSB) consists of the sum of the epithelial cell layers of the oral mucosa and salivary glands. In vitro models of the BSB are inevitable to investigate and understand the transport of salivary biomarkers from blood to saliva. Up to now, standardized, cell line-based models of the epithelium of the submandibular salivary gland are still missing for this purpose. Therefore, we established epithelial barrier models of the submandibular gland derived from human cell line HTB-41 (A-253). Single clone isolation resulted in five different clones (B2, B4, B9, D3, and F11). Clones were compared to the parental cell line HTB-41 using measurements of the transepithelial electrical resistance (TEER), paracellular marker permeability assays and analysis of marker expression for acinar, ductal, and myoepithelial cells. Two clones (B9, D3) were characterized to be of acinar origin, one clone (F11) to be of myoepithelial origin and one isolation (B4) derived from two cells, to be presumably a mixture of acinar and ductal origin. Clone B2, presumably of ductal origin, showed a significantly higher paracellular barrier compared to other clones and parental HTB-41. The distinct molecular identity of clone B2 was confirmed by immunofluorescent staining, qPCR, and flow cytometry. Experiments with ferritin, a biomarker for iron storage, demonstrated the applicability of the selected model based on clone B2 for transport studies. In conclusion, five different clones originating from the submandibular gland cell line HTB-41 were successfully characterized and established as epithelial barrier models. Studies with the model based on the tightest clone B2 confirmed its suitability for transport studies in biomarker research.