Team:Franconia/Project/Beam
Method 1
Protein Building Blocks
Protein building Blocks (without additional Streptavidin) . The single building blocks contain N- and C-terminal catcher-tag elements to form a permanent lock-key system. The polymer is build of two different building blocks as one single building block cannot be handled without instant polymerization. Mixing of the two building blocks start the polymerization via condensation reaction leading to a biopolymer tissue.
Pilis/Carbon Nano Tubes
Carbon Nanotubes (CNTs) are tubular architectures made of pure carbon. Every single carbon atom is sp2 hybridized and arranged in a hexagonal pattern. One can distinguish between Single Walled Carbon Nanotubes (SWCNTs) and Multi Walled Carbon Nanotubes (MWCNTs). The fabrication of the tubes can either be achieved by laser ablation of graphite or with a catalyst in a carbon rich gas phase. As pure carbon material, they are light-weight and flexible and robust. Further their thermal and electric conductivity is highly remarkable.
Artificial Muscle
Dielectric Elastomer Actuators (DEAs) are made of alternating layers of elastic and conductive material e.g. CNTs forming a stacked capacitor. The top and bottom contacts are metallic electrodes. By application of a voltage the elastomer between the cathodes and anodes is compressed in z-dimension and expands in the x,y-plane. This leads to a muscle-like contraction of the whole system.
Method 2
Protein Building Blocks
Protein building Blocks (with additional Streptavidin). The single building blocks contain N- and C-terminal catcher-tag elements with a streptavidin in the center of the protein. The catcher-tag system binds a permanent lock-key system to each other. The streptavidin unit can bind to the biotin functionalized azo dye to integrate the molecules into the polymer tissue.
Azo Dye
Molecular Machines (Azo dyes) can fulfill motion on a molecular length scale. The contraction of the dye is driven by light, which changes the conformation of the -N=N- bond from trans to cis. Implemented in high number in a tissue they can lead to contraction of the whole tissue. The invention of such small motors was awarded the nobel prize in chemistry in 2016.
Artificial Muscle
Muscle tissue with molecular machines can be obtained by combining biopolymeric tissue with an integrated streptavidin moiety. The streptavidin can bind a biotin functionalized azo dye leading to a further cross-linking. Via light-irradiation the azo dye molecules change their conformation and contract the tissue. Thermal or irradiation with a longer wavelength restores the position of the azo dye and the tissue relaxes to the original state.
The work, which is and can be done by robots is continuously increasing as well as the number of steps where complex shaped matter has to be handled. For this purpose, soft robotics are essential to prevent damage from the material. Current materials for soft robotics are based on silicones and related polymeric materials. Combined with electrically conductive materials in alternating layers, they form dielectric elastomer actuators (DEAs), which serve as muscle in robot arms. Silicones and elastic polymers can be counted to rather cost-efficient materials. However, considering the production of the material a high amount of electricity and chemical effort must be applied. This can be circumvented by a production from E. coli, where the organism produces a economically friendly biopolymer with the desired properties. The biosynthesis of the polymer building blocks, safes a significant amount of resources and energy.
The fabrication of the silicones to a device is carried out under elevated temperatures, where high accuracy at a micrometer scale is a crucial factor. This accuracy must also be maintained for the device made of biopolymer, which can be realized with modern 3D printers. Further, the 3D-printer is operating under ambient conditions, which safes money in the fabrication process.
Due to the material properties, a special issue is the degradation of the biopolymer in dependence of time. A degradation of the material can mainly be circumvented by using the cell-free peptides, which prevents the consumption of the peptides by the cells. However, oxygen and mechanic stress are main issues, which have to be tackled. Oxygen can be excluded by instant packing of the material, whereas the mechanic durability of this material is still unknown. However, a comparison with a hydrogel polyacrylate based or a disposable DEA implies a lifetime of 100 to 2960 cycles.[1,2]
| Biopolymer based DEA | Silicone based DEA | |
|---|---|---|
| Raw materials (price) | 6 € /g ink [3,4] | Av. 0,10 € /g ink[5] |
| Fabrication | 3D printing | 3D aerosol jet printing @ 80°C[6] |
| Solvent | water | Isopropanol/terpineol[6] |
| Weight | est. 1 g/mL (density of water) | 1.1-1.3 g/mL [7] |
| Waste | Biodegradable polymer; Simple regain of conductive material | Recycling of silicone possible, regain of conductive material complex to achieve |
The term “molecular machine” refers to a system that is able to perform mechanical movement on a nanoscopic scale by application of an external stimulus. In order to do so, such systems only consist of a small number of molecules. Depending on the nature of the used molecules, possible stimuli can be electrical energy (redox changes), electromagnetic energy (light) or chemical energy (change of pH value or addition of specific ions). Being an exceptionally novel field of science, starting in the mid 1980’s and just being rewarded with the Nobel prize of chemistry in 2016, the current applications of molecular machines are still rather few. However, a multitude of possible applications are being explored by the minute. Many mechanical devices can be mimicked, including rotors, oscillators, gears, paddle wheels, turnstiles, brakes, ratchets and gyroscopes.[1] One example of a more sophisticated system is a molecular motor[2] that can perform a 360° rotation by subsequent application of light and temperature, as can be seen in Figure 1. In another research group, four similar rotary systems have been combined on a larger molecule in order to create a four-wheeled nano-car that was able to move over a surface upon irradiation.[3]
In this project, azo dyes are used as molecular machines. Upon irradiation, the -N=N- azo group changes from a trans configuration to a cis configuration. As a consequence, the distance between the substituents R is shortened, resulting in a muscle-like contraction. The working principle of azo dyes as molecular machines can be seen in Figure 2.
[1] V. Balzani, A. Credi, M. Venturi: Molecular Devices and Machines – A Journey into the Nano World, Wiley-VCH, Weinheim, 2003.
[2] N. Koumura, R. W. J. Zijlstra, R. A. van Delden, N. Harada, B. L. Feringa, Nature, 1999, 401, 152-155.
[3] T. Kudernac, N. Ruangsupapichat, M. Parschau, B. Maciá, N. Katsonis, S. R. Harutyunyan, K.-H. Ernst, B. L. Feringa, Nature, 2011, 479, 208-211.
DEAs, or dielectric elastomer actuators, generally consist of thin elastic films coated with compliant electrode material on two opposing phases. That makes them flexible plate capacitors that deform due to Maxwell stress when applying a voltage across the electrodes. Since the elastic material is incompressible, applying said voltage causes the reduction of the film in thickness to result in an expansion in area. Stacking and bundling of multiple DEAs allows an actuation system to be adapted to different loading scenarios.Several materials are suitable for manufacturing DEAs. Electrodes can be made e.g. of metals, polymers, graphite or carbon nano tubes. Elastic dielectric materials in use for industrial applications are Polyacryl, Polyurethane or Polysiloxane. This project however focusses on the synthesis of a catcher-tag polymer as dielectric medium while using carbon nano tubes for the electrodes.
Manufacturing DEAs is possible in multiple ways. Thereby dipping, spin-coating and casting techniques are widely spread. For biomaterials, cartridges are more suitable for handling and dispensing the dielectric material. For the application of electrodes onto the elastomer, sputter and spraying techniques are widely used within the industry. Another option is the selective wetting process based on water-based solutions for when the polymer material is hydrophobic.
Source: F. Nendel, S. Reitelshöfer: Conception of an infrastructure for the volumetric flow rate controlled supply of process gases and for the dynamic diversion of aerosol-flows for manufacturing flexible graphene electrodes. Institute for Factory Automation and Production Systems, (06/2017)
