Novel applications of bioelectrochemical systems (BES) are emerging constantly, but the majority still lacks economic viability. Especially the use of electrochemical system components without adaptation to BES requirements causes poor exploitation of the potential system performance. The electrode material is one central component that determines BES performance. While commercial carbon fiber (CF) fabrics are commonly used, their customizability as two-or three-dimensional electrode material for BES is rarely investigated. Using pure cultures of S. oneidensis MR-1, we identified CF properties impacting bacterial current generation: (1) The removal of the sizing (protective coating) is of great importance for all the fibers studied, as it acts as an electrical insulator. By desizing, the maximum current density (j max) is increased by up to 40-fold. (2) Alteration of the filament surface chemistry results in an accelerated initial development of current generation, but the maximum current density (j max) is hardly affected. (3) A specific yarn structure, the stretch-broken yarn, supports exceptionally high current densities. The good electrode performance is correlated to the presence of free filament ends (responsible for 41% current increase), which are characteristic for this yarn. (4) Moreover, a combination of these free filament ends with a high degree of graphitization enhances electrode performance of a commercial fabric by 100%. The results demonstrate that the CF selection can greatly influence the achievable electrode performance of CF fabrics, and thereby contributes to rational engineering of CF based electrodes that can be tailored for the many BES applications envisaged.

The technology of 3D printing is conquering the world and awakens the interest of many users in the most varying of applications. New formulation approaches for photo-sensitive thiol-ene resins in combination with various printing technologies, like stereolithography (SLA), projection based printing/digital light processing (DLP) or two-photon polymerization (TPP) are presented. Thiol-ene polymerizations are known for its fast and quantitative reaction and to form highly homogeneous polymer networks. As the resins are locally and temporally photo-curable the polymerization type is very promising for 3D-printing. By using suitable wavelengths, photoinitiator-free fabrication is feasible for single- and two photon induced polymerization. In this paper divinyl ethers of polyethylene glycols in combination with star-shaped tetrathiols were used to design a simple test-system for photo-curable thiol-ene resins. In order to control and improve curing depth and lateral resolution in 3D-polymerization processes, either additives in chemical formulation or process parameters can be changed. The achieved curing depth and resolution limits depend on the applied fabrication method. While two-/multiphoton induced lithography offers the possibility of micron- to sub-micron resolution it lacks in built-up speed. Hence single- photon polymerization is a fast alternative with optimization potential in sub-10-micron resolution. Absorber- and initiator free compositions were developed in order to avoid aging, yellowing and toxicity of resulting products. They can be cured with UV-laser radiation below 300 nm. The development at Fraunhofer ILT is focusing on new applications in the field of medical products and implants, technical products with respect to mechanical properties or optical properties of 3D-printed objects. Recent process results with model system (polyethylene glycol divinylether/Pentaerithrytol tetrakis (3-mercaptopropionat), Raman measurements of polymer conversion and surface modifications using bifunctional crosslinkers are presented with advantages, drawbacks and a general outlook

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