Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration

A ubiquitous biological material, keratin represents a group of insoluble, usually high-sulfur content and filament-forming proteins, constituting the bulk of epidermal appendages such as hair, nails, claws, turtle scutes, horns, whale baleen, beaks, and feathers. These keratinous materials are formed by cells filled with keratin and are considered 'dead tissues'. Nevertheless, they are among the toughest biological materials, serving as a wide variety of interesting functions, e.g. scales to armor body, horns to combat aggressors, hagfish slime as defense against predators, nails and claws to increase prehension, hair and fur to protect against the environment. The vivid inspiring examples can offer useful solutions to design new structural and functional materials. Keratins can be classified as α- and β-types. Both show a characteristic filament-matrix structure: 7 nm diameter intermediate filaments for α-keratin, and 3 nm diameter filaments for β-keratin. Both are embedded in an amorphous keratin matrix. The molecular unit of intermediate filaments is a coiled-coil heterodimer and that of β-keratin filament is a pleated sheet. The mechanical response of α-keratin has been extensively studied and shows linear Hookean, yield and post-yield regions, and in some cases, a high reversible elastic deformation. Thus, they can be also be considered 'biopolymers'. On the other hand, β-keratin has not been investigated as comprehensively. Keratinous materials are strain-rate sensitive, and the effect of hydration is significant. Keratinous materials exhibit a complex hierarchical structure: polypeptide chains and filament-matrix structures at the nanoscale, organization of keratinized cells into lamellar, tubular-intertubular, fiber or layered structures at the microscale, and solid, compact sheaths over porous core, sandwich or threads at the macroscale. These produce a wide range of mechanical properties: the Young's modulus ranges from 10 MPa in stratum corneum to about 2.5 GPa in feathers, and the tensile strength varies from 2 MPa in stratum corneum to 530 MPa in dry hagfish slime threads. Therefore, they are able to serve various functions including diffusion barrier, buffering external attack, energy-absorption, impact-resistance, piercing opponents, withstanding repeated stress and aerodynamic forces, and resisting buckling and penetration. A fascinating part of the new frontier of materials study is the development of bioinspired materials and designs. A comprehensive understanding of the biochemistry, structure and mechanical properties of keratins and keratinous materials is of great importance for keratin-based bioinspired materials and designs. Current bioinspired efforts including the manufacturing of quill-inspired aluminum composites, animal horn-inspired SiC composites, and feather-inspired interlayered composites are presented and novel avenues for research are discussed. The first inroads into molecular-based biomimicry are being currently made, and it is hoped that this approach will yield novel biopolymers through recombinant DNA and self-assembly. We also identify areas of research where knowledge development is still needed to elucidate structures and deformation/failure mechanisms

Case-studies: lasergebaseerde matrijzenbouw

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Industrial results for laser sintered injection moulds

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Rapid manufacturing tool related products

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Vision system based 2D quality control of micro aerosol jet printed tracks

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Mobile measurement techniques for the dimensional analyses and control of large objects by measuring indidvidual points

There is a significantly growing market of flexible and portable measurement systems. This is due to the development of different technologies. The increasing industrial requirements for accuracy, speed, robustness and ease of use of these systems together with a demand for the highest possible degree of automation have forced universities and system manufacturers to develop hard- and software solutions to meet these requirements. The paper will show the latest trends in hardware development and explain the principle of the different technology’s which can measure individual points.status: publishe

An initial study into Aerosol Jet® printed interconnections on extrusion based 3d printed substrates

The combination of different additive manufacturing techniques to produce freeform products with multifunctional properties is gaining increasing popularity. In the research presented, Aerosol Jet® Printing (AJP) is combined with extrusion-based 3D printing. AJP starts with an ink to create micro-tracks. These tracks commonly have widths ranging from a few micrometers up to several millimeters and track heights ranging from a few tenths of a micrometer up to several micrometers, unlike extrusion-based 3D printers with which the extruded material usually has a resolution of tenths of millimeters. AJP can therefore be a complementary technique for extrusion-based 3D printing; in this manner, fine high resolution features can be added onto relatively rapidly produced extrusion-based 3D printed parts. Furthermore, AJP can be used to produce electrically conductive tracks to create interconnections, inductors, capacitors, strain gauges, etc. In this paper, the creation of AJP-manufactured interconnects on extrusion-based 3D printed substrates is investigated. The relevant AJP process parameters to take into account are the flow rates of the aerosol, the flow rate of the sheath gas, the temperature settings of the ink and substrate, and the platform speed and nozzle-to-substrate distance. To obtain reliable results, the AJP process parameters are optimized for printing single-layered and multilayered silver ink tracks on extrusion-based 3D-printed surfaces. Important quality output parameters include the dimensions and the electrical properties of the printed interconnects.status: publishe

Aerosol Jet® printed interconnections on extrusion based 3D printed substrates

The combination of different additive manufacturing techniques to produce freeform products with multifunctional properties is gaining more and more popularity. In the presented research Aerosol Jet® Printing (AJP) is combined with extrusion based 3D printing. AJP starts from an ink to create micro tracks, unlike extrusion based 3D printers where the extruded material usually has a resolution of tenths of millime-ters. AJP can therefore be a complementary technique for extrusion based 3D printing, in this manner fine high resolution features can be added onto relatively fast produced extrusion based 3D printed parts. Further-more, AJP can be used to produce electrically conductive tracks to create interconnects, inductors, capacitors, strain gauges, etc… In this paper the creation of AJP manufactured interconnects on extrusion based 3D print-ed substrates is investigated. Important AJP process parameters to take into account are flow rates of the aero-sol, flow rate of the sheath gas, temperature settings of the ink and substrate, platform speed and nozzle to substrate distance. To obtain reliable results, the AJP process parameters are optimized for printing single lay-ered and multilayered silver ink tracks on extrusion based 3D printed surfaces. Important quality output pa-rameters include the dimensions and the electrical properties of the printed interconnectsstatus: publishe

Additive manufacturing of thermoplastic composites

Ever since composite materials where first introduced, they have been pushing the boundaries of high performance, lightweight designs in all branches of engineering. The demand for sustainable lightweight structures results in an augmented use of thermoplastic composites. Depending on the type of matrix and reinforcement, there are various manufacturing options for the fabrication of composite parts. Composite manufacturing processes are in essence additive processes. In order to reduce the labor-intensive manual operations, and the need for a flexible automated composite process, researchers are investigating the feasibility of implementing Additive Manufacturing (AM) techniques to aid the fabrication of composite parts. AM techniques are able to produce parts directly from CAD data sources. As opposed to classical subtractive fabrication methods, parts are created layer upon layer. The geometric freedom provided by the additive process unlocks a wide variety of designs, which would be impossible to create via subtractive methods. Furthermore, AM processes have no direct need of tooling. The flexibility of this manufacturing approach gives rise to the development of application-oriented parts. Given the flexibility of the additive process, these techniques can be used in the design and manufacturing of composite parts. There are several options for which AM can be implemented in the composite production process. This paper highlights the potential of AM in the design and manufacturing of composite parts, gives a review on the application of composite AM, and identifies the technological challenges associated with the direct production of thermoplastic AM composites.status: publishe