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Introduction: The design and development of a novel dynamic hand orthosis that allows individual and progressive adaptation to the patient’s condition require knowledge about the maximum voluntary contraction forces of the fingers. The following work presents a test setup and procedure for determination of isometric finger contraction forces during flexion depending on various finger positions and finger tasks. Methods: The test setup places hand and fingers in certain positions (position 0: grasping of a plate; position 1-3: circular grasping of cylinders of three different diameters). The force measurement is carried out using pressure sensing: A capacitive force sensor is placed on each fingertip. To perform various finger tasks, the subjects are asked for isometric contraction of defined finger groups and single fingers against the boundary system. For proof of the concept, measurements are performed with six subjects and compared with reference values from the literature. Results: The separated finger force of each finger can be captured during the finger tasks in varying positions. Furthermore, the total finger force of all active fingers can be determined. It is shown that the total finger force during contraction of all fingers (IMRLtask; 78.4N ± 25.8N, d2) is higher than during contraction of the index finger (25.8N ± 3.4N, d2). Furthermore, the single finger force of the index finger is higher than the index finger activity in IMRL-task. The results also show a tendency for the finger contraction force to increase with increasing flexion. Further investigations may require improvements to the method. In this proof of concept, this potential is revealed and discussed. However, the functionality of the test setup and procedure can be demonstrated.

As a viscous mycelium-substrate-composite, mycelia can be processed into more complex geometries in generative extrusion-based processes, even without molding tools. Biological transformation can also affect the properties of a printed object such that the mycelium still lives and grows after the 3D-build-process and changes the object over time. Depending on the substrate composition, type of fungus and growth conditions, different properties of the object can be manipulated. Different test geometries with corresponding preliminary characterization tests are shown. The present results demonstrate that test geometries could be successfully 3D printed with living mycelium material and manipulated during cultivation. [ABSTRACT FROM AUTHOR]

Cellulose-based biocomposites, such as Cottonid, are a promising class of materials to improve the carbon footprint of products during their service life. Cottonid has high technological potential due to its physical and mechanical similarities to engineering plastics and light metals. To replace traditional metallic materials in industry, cellulose-based semi-finished products need to be formed and cut. In particular, blanking is the most cost-effective and industrially common cutting method for metals. However, this study investigates the influence of various blanking process parameters on the quality and the fatigue strength of the resulting cutting edges of Cottonid. The presented results give insights on how the relationships between process parameters during cutting and resulting material properties known from conventional materials can be transferred to cellulose-based biocomposites like Cottonid. The relative clearance was varied between 4 and 10% and the cutting velocity between 0.05 and 10 m/s. It was evident that slower velocities and smaller clearances resulted in visibly better cutting edges. In order to relate this effect to the mechanical performance of Cottonid, new 3-point bend specimens were taken from the blanked strips for fatigue testing. It was found that the fatigue strength was significantly affected by the velocity and clearance. Further, similar to metallic materials, clean-cut (smooth area) and a fractured zone can be clearly distinguished. A good cutting edge quality results in a higher resistance of the Cottonid component against crack initiation at process-induced defects. The knowledge gained may enable an efficient cutting process for cellulose-based materials with higher fatigue strength in the future. [ABSTRACT FROM AUTHOR]

Exoskeletons have gained importance recently. In the case of musculoskeletal diseases, they can restore or support the mobility of injured body parts; in everyday life, they can relieve the musculoskeletal system and thus contributes to the preservation of health into old age. However, active systems face challenges due to the efficient and reliable actuators. In the following, the example of the hand will be used to investigate what influence the individuality of the hand under consideration has on the selection of a suitable actuator about force and stroke. The literature outlines that tendon-driven mechanism with a biomimetic design are a promising approach for hand exoskeletons: The finger is actively moved by an actuator using artificial tendons positioned along the finger to match anatomical structures. For this purpose, actuators based on electromagnetic or pneumatic principles, and smart materials are described. The requirements for force and stroke of the drive can be derived from the analysis of finger kinematics. In this study the finger kinematics of 13 subjects were analyzed. The results show a scatter in stroke and force depending on the finger considered. To select a suitable actuator for the biomimetic hand exoskeleton, these results are compared with the force and stroke characteristics of various actuating principles. The comparison reveals that the choice of the actuator depends on the intended primary support for the hand (movement, endurance, grip strength). Hence, it can be deduced that step drivers meet the force and stroke requirements and may be a suitable alternative. [ABSTRACT FROM AUTHOR]

Compared to sensible heat storage, latent heat storage provides higher energy density due to the enthalpy difference of the storage medium undergoing a phase change. However, the heat storage capability of phase change materials is opposed by low thermal conductivity. To enable sufficient heat transfer within a latent heat storage unit, phase change materials can be used in combination with a metallic matrix. One approach is the infiltration of phase change materials into additively manufactured metallic lattice structures. In this work, the fabrication of aluminum lattice structures through laser powder bed fusion is described. During fabrication, the cell size and the strut diameter were varied to obtain specimens of different geometries. To obtain the thermal conductivity of the fabricated lattices, measurements were conducted based on the transient plane source method. Additionally, finite element simulations were carried out to evaluate the effect of fabrication and measurement uncertainties. The thermal conductivity of the fabricated lattices was found to be between 3 W/(m·K) and 130 W/(m·K). The numerically and analytically performed calculations provide good estimations of the experimentally obtained data. [ABSTRACT FROM AUTHOR]

According to the European Medical Device Directive (MDR (EU) 2017/745), medical products of all risk classes are obliged to be labelled with Unique Device Identification Codes (UDI). In order to meet the requirements of the MDR, a novel method of identification for additively manufactured metallic products was developed at the Fraunhofer Institute for Machine Tools and Forming Technology (IWU). The method provides a product traceability within its production process and during the whole product lifespan, and also functions as a counterfeit protection. This paper shows the integration of a unique identification during an additive manufacturing process for a titanium part. The readout of the integrated identification was executed using ultrasonic and eddy current methods, as well as micro computed tomography. Obtained results are discussed in the paper.

To increase learning success in surgical training, physical simulators are supplemented by measurement technology to generate and record objective feedback and error detection. An opportunity to detect fractures following hip stem implantation early can be measurement of occurring strains on bone surface. These strains can be determined while using strain gauges, digital image correlation (DIC) or photoelasticity. In this research strain gauges and DIC were compared regarding their suitability as strain measurement tools for use in physical simulators. Therefore a testing method was described to replicate the implantation of a hip stem. Testing devices modelled on a realistic prosthesis were pressed into prepared porcine femora in a two-step procedure with a material testing machine. The local strains occurring on bone surface were determined using an optical measurement system for DIC and strain gauges. The initial fractures in the tested femora are located medial-anterior in most cases (73,6%). With increasing indentation depth of the test device, the strains on bone surface increase. Comparing the local strains determined by DIC and strain gauges consistencies in curves are noticeable. Maximal determined strains before fracturing amount to 0,69% with strain gauges and 0,75% with DIC. In the range of the fracture gap, strain gradients are determined by using DIC. However the detected surfaces are of low quality caused by gaps and motion artefacts. The results show strains on bone surfaces for early fracture detection are measurable with strain gauges and DIC. DIC is assessed as less suitable compared to strain gauges. Furthermore strain gauges have greater level of integration and economic efficiency, so they are preferred the use in surgical training simulators.