A characteristic lengthscale causes anomalous size effects and boundary programmability in mechanical metamaterials

The architecture of mechanical metamaterialsis designed to harness geometry, non-linearity and topology to obtain advanced functionalities such as shape morphing, programmability and one-way propagation. While a purely geometric framework successfully captures the physics of small systems under idealized conditions, large systems or heterogeneous driving conditions remain essentially unexplored. Here we uncover strong anomalies in the mechanics of a broad class of metamaterials, such as auxetics, shape-changers or topological insulators: a non-monotonic variation of their stiffness with system size, and the ability of textured boundaries to completely alter their properties. These striking features stem from the competition between rotation-based deformations---relevant for small systems---and ordinary elasticity, and are controlled by a characteristic length scale which is entirely tunable by the architectural details. Our study provides new vistas for designing, controlling and programming the mechanics of metamaterials in the thermodynamic limit.Comment: Main text has 4 pages, 4 figures + Methods and Supplementary Informatio

On the additive manufacturing, post-tensioning and testing of bi-material tensegrity structures

An investigation on the additive manufacturing and the experimental testing of 3D models of tensegrity prisms and columns is presented. An Electron Beam Melting facility (Arcam EBM S12) is employed to 3D print structures composed of tensegrity prisms endowed with rigid bases and temporary supports, which are made out of the titanium alloy Ti6Al4V. The temporary supports are removed after the additive manufacturing phase, when Spectra cross-strings are added to the 3D printed models, and a suitable state of internal prestress is applied to the structure. The experimental part of the study shows that the examined structures feature stiffening-type elastic response under large or moderately large axial strains induced by compressive loading. Such a geometrically nonlinear behavior confirms previous theoretical results available in the literature, and paves the way to the use of tensegrity prisms and columns as innovative mechanical metamaterials and smart devices

THE USE OF FLUORESCENCE SENSORSAS OPTICAL BIOSENSORS

The use of miniaturized fluorescence probes for on-line monitoring analytes in continuous- flow systems (automated clinical analysis, process control, e.g. in biotechnological processes, environmental control, etc.) has becomeincreasingly important. Wereport the application of a fiber-optic based fluorescence probe used as optrode for a novel optical biosensor system to monitor NAD(H) dependent enzymatic reactions based on the flow-injection analysis (FIA) principle. A miniaturized fiber-optic fluorimeter is combined with a small size membrane reactor (1 ml) (Fig. 1). In here, enzymes (dehydrogenases) for analyte conversion and coenzymeregeneration as well as the macromolecular coenzyme derivative polyethyleneglycol (PEG, M, = 20,000)-N°-(2-aminoethyl)-NAD(H) [1] are retained in the direct vicinity of the sensor tip of a concentric fiber-optic probe (fluorescence excitation 360 nm / emission 460 nm) by an ultrafiltration membrane (cutoff: 5000 Dalton) (Fig. 2). Only low molecular-weight compounds (analytes, products, etc.) can freely pass through thisultrafiltration membrane

Two Examples of Biosensor Systems Based on Flow Injection Analysis

Two optical biosensor systems will be presented in this paper: one uses immobilized enzymes and coenzymes, while the other employs immunoreagents. They can be used for eultivation monitoring of low and high molecular weight components in fermentation broth. Both sensors are based on the principles of flow injection analysis. The principles of these sensor systems, their characteristics, and their application will be discussed

Biosensor Systems for Process Control in Biotechnolgy

Three different types of biosensor systems will be presented in this paper: a microbial optrode (measuring the intracellular NAD(P)H-content in immobilized cells), an optrode with immobilized coenzymes and enzymes (measuring the fluorescence of molecular weight increased NADH/NADPH), an enzymethermistor system (measuring the heat evolved during enzymatic or microbial reactions) and a automized immunoanalysis system. The application of these sensor systemswill be discussed