Validation of Estimators for Weight-Bearing and Shoulder Joint Loads Using Instrumented Crutches

This research paper aimed to validate two methods for measuring loads during walking with instrumented crutches: one method to estimate partial weight-bearing on the lower limbs and another to estimate shoulder joint reactions. Currently, gait laboratories, instrumented with high-end measurement systems, are used to extract kinematic and kinetic data, but such facilities are expensive and not accessible to all patients. The proposed method uses instrumented crutches to measure ground reaction forces and does not require any motion capture devices or force platforms. The load on the lower limbs is estimated by subtracting the forces measured by the crutches from the subject’s total weight. Since the model does not consider inertia contribution in dynamic conditions, the estimation improves with low walking cadence when walking with the two-point contralateral and the three-point partial weight-bearing patterns considered for the validation tests. The shoulder joint reactions are estimated using linear regression, providing accurate values for the forces but less accurate torque estimates. The crutches data are acquired and processed in real-time, allowing for immediate feedback, and the system can be used outdoors in real-world walking conditions. The validation of this method could lead to better monitoring of partial weight-bearing and shoulder joint reactions, which could improve patient outcomes and reduce complications

Effects of indenter geometry on micro‐scale fracture toughness measurement by Pillar splitting

In this presentation, we will show the improvements to a recently developed pillar splitting technique that can be used to characterize the fracture toughness of materials at the micrometer scale. Micro-pillars with different aspect ratios were milled from bulk Si (100) and TiN and CrN thin films, and pillar splitting tests were carried out using four different triangular pyramidal indenters with centerline-to-face angles varying from 35.3° to 65.3°. Cohesive zone finite element modelling (CZ-FEM) was to evaluate the effect of different material parameters and indenter geometries on the splitting behavior. Pillar splitting experiments revealed a linear relationship between the splitting load and the indenter angle, while CZ-FEM simulations provided the dimensionless coefficients needed to estimate the fracture toughness from the splitting load. The results provide novel insights into the fracture toughness of small-scale materials using the pillar spitting technique and provide a simple and reliable way to measure fracture toughness over a broad range of material properties. Please click Additional Files below to see the full abstract

Biomechanics in crutch assisted walking

Crutch-assisted walking is very common among patients with a temporary or permanent impairment affecting lower limb biomechanics. Correct crutches’ handling is the way to avoid undesired side effects in lower limbs recovery or, in chronic users, upper limbs joints diseases. Active exoskeletons for spinal cord injured patients are commonly crutch assisted. In such cases, in which upper limbs must be preserved, specific training in crutch use is mandatory. A walking test setup was prepared to monitor healthy volunteers during crunch use as a first step. Measurements were performed by using both a motion capture system and instrumented crutches measuring load distribution. In this paper, we present preliminary tests results based on different subjects - having a variety of anthropometrical characteristics - during walking with parallel or alternate crutches, the so-called three and two-points strategies. Tests results present inter and intra subject variabilities and, as a first goal, influencing factors affecting crutch loads have been identified. In the future we aim to address crutch use errors that could lead to delayed recovery or upper limbs suffering in patients, giving valuable information to physicians and therapists to improve user’s training

Drug-perturbation-based stratification of blood cancer

As new generations of targeted therapies emerge and tumor genome sequencing discovers increasingly comprehensive mutation repertoires, the functional relationships of mutations to tumor phenotypes remain largely unknown. Here, we measured ex vivo sensitivity of 246 blood cancers to 63 drugs alongside genome, transcriptome, and DNA methylome analysis to understand determinants of drug response. We assembled a primary blood cancer cell encyclopedia data set that revealed disease-specific sensitivities for each cancer. Within chronic lymphocytic leukemia (CLL), responses to 62% of drugs were associated with 2 or more mutations, and linked the B cell receptor (BCR) pathway to trisomy 12, an important driver of CLL. Based on drug responses, the disease could be organized into phenotypic subgroups characterized by exploitable dependencies on BCR, mTOR, or MEK signaling and associated with mutations, gene expression, and DNA methylation. Fourteen percent of CLLs were driven by mTOR signaling in a non-BCR-dependent manner. Multivariate modeling revealed immunoglobulin heavy chain variable gene (IGHV) mutation status and trisomy 12 as the most important modulators of response to kinase inhibitors in CLL. Ex vivo drug responses were associated with outcome. This study overcomes the perception that most mutations do not influence drug response of cancer, and points to an updated approach to understanding tumor biology, with implications for biomarker discovery and cancer care.Peer reviewe

Determination of the elastic moduli and residual stresses of freestanding Au-TiW bilayer thin films by nanoindentation

International audienceIn this paper, we present a detailed mechanical characterization of freestanding bilayer (Au-TiW) micro-cantilevers and double clamped beams, for applications as Radio Frequency (RF)-switches Micro-Electromechanical Systems (MEMS). The testing structures have been characterized by an optical profilometer and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS), in order to acquire information about their geometries, composition, and the gap between the substrate underneath. Then, the micro-beams are deflected by using a specifically designed nanoindentation procedure based dynamic stiffness measurement during bending in order to extract the elastic modulus and the residual stresses of both layers. Firstly, the classic beam theory has been implemented for bilayer cantilevers enabling the extraction of elastic moduli. Then, residual stresses are estimated by deflecting double clamped beams, while implementing new analytical models for a bilayer system. The obtained elastic moduli are consistent with the average ones obtained for a single layer micro-cantilever and with nanoindentation results for TiW and Au homogeneous films. The residual stresses are in agreement with the values obtained from the double slot Focused Ion Beam (FIB) and Digital Image Correlation (DIC) procedure, providing an alternative and portable way for the assessment of residual stresses on composite double clamped micro-beams

Effects of indenter angle on micro-scale fracture toughness measurement by pillar splitting

We present improvements to a recently developed pillar splitting technique that can be used to characterize the fracture toughness of materials at the micrometer scale. Micro-pillars with different aspect ratios were milled from bulk Si (100) and TiN and CrN thin films, and pillar splitting tests were carried out using four different triangular pyramidal indenters with centerline-to-face angles varying from 35.3° to 65.3°. Cohesive zone finite element modeling (CZ-FEM) was used to evaluate the effect of different material parameters and indenter geometries on the splitting behavior. Pillar splitting experiments revealed a linear relationship between the splitting load and the indenter angle, while CZ-FEM simulations provided the dimensionless coefficients needed to estimate the fracture toughness from the splitting load. The results provide novel insights into the fracture toughness of materials at small-scales using the pillar spitting technique and provide a simple and reliable way to measure fracture toughness over a broad range of material properties

Validation of Contact Measurement System for Wheelchair Tennis Propulsion Using Marker-Less Vision System

This study investigates the reliability of marker-less vision systems for contact detection between hand and hand-rim during wheelchair propulsion. The measurement system uses a camera collecting RGB and depth images. The hand is detected through Mediapipe, a software able to recognize the key points of the hand on the RGB image. Hand position is expressed with respect to the wheel. A classifier is used to determine if there is contact between hand and hand-rim. To validate this procedure, 17 able-bodied participants pushed the wheelchair on an ergometer during six tests, given by the combinations of holding a tennis racket in their right hand while propelling at three different speeds: 4 km/h, 5.4 km/h and maximal sprint. Since validated contact detection methods are lacking in literature, experts provided a reference by manually evaluating video recordings and force signals frame-by-frame. The results showed that the hand identification by Mediapipe is not influenced by the presence of the racket but by the speed. Contact events were detected in the 99.5% of the cases. The mean error in contact time detection was -5 ms for the starts and 18 ms for the ends, the standard deviation was 48 ms for both and the combined root mean square error (RMSE) was 48 ms for the starts and 50 ms for the ends. These values, once corrected the systematic effects, lead to a standard uncertainty of approximately 0.05 s, corresponding to 15 % of the average contact duration. The study highlights the potential use of marker-less vision systems for contact detection in wheelchair propulsion

Effect of annealing treatment on mechanical properties of nanostructured metallic films deposited by pulsed laser deposition

International audienceThe design of metallic thin film with controlled composition and microstructure has become increasingly important for industry applications, involving strong mechanical solicitations. Specifically, metallic glasses (MGTFs) and high entropy alloys thin films (HEATFs) have shown a great potential due to their unique combination of large mechanical properties such as yield strength (3 GPa) and ductility (10%) [1,2]. However, the relationship microstructure-mechanical properties are not fully understood since the morphological control is often limited by the most employed sputtering deposition. In this field, Pulsed Laser Deposition (PLD) offers the possibility to widely control the morphology of the films by simply changing the process parameters, affecting the growth mechanisms from atom-by-atom to cluster-assembled growth regimes. Recently, PLD has shown a large potential for the deposition ZrCu MGTFs and CoCrCuFeNi HEATFs reporting large and tunable mechanical properties such as an elastic modulus and hardness of 175 and 11 GPa [2].Here, we explore the possibility to further nanostructuring PLD deposited ZrCu compact and nanogranular MGTFs by performing annealing treatments from 300 up to 550°C, while investigating the devitrification process and the evolution of the mechanical properties.Structural characterization shows that compact films remain amorphous up to 420°C, while the crystallization process of nanogranular films is completed at 420°C due to the combination of high interface density, free volume and O content [3]. We show that the mechanical properties increase with the annealing temperature due to the progressive crystallization reaching a plateau upon complete crystallization with elastic modulus and hardness up to 180 and 14 GPa, respectively. Furthermore, we show that compact films have residual tensile stress from 169 to 691 MPa whose magnitude increase as a function of the temperature due to nanocrystalline phase nucleation followed by grain growth. On the other hand, nanogranular films show a maximum residual stress of 1.1 GPa at 420°C followed by a decrease at higher annealing temperatures, indicating a complete crystallization.Overall, we show that PLD in combination with post-thermal annealing can generate different families of metallic films with varying nanoscale morphologies, resulting in tunable mechanical properties and thermal stability with potential as structural coatings.References:1. Y. Zou et al., Nat. Commun., 6, 7748, 2015.2. M. Ghidelli et al., Acta Mater., 213, 116955, 2021.3. F. Bignoli et al., Mater. Des., 221, 110972, 2022

A workaround for recruitment issues in preliminary WR studies: audio feedback and instrumented crutches to train test subjects

One of the main problems in studies involving exoskeletons for assisting gait of Spinal Cord Injury (SCI) users is recruitment of a suitable number of subjects, especially when age, gender, and pathologies are considered. Studies involving able-bodied subjects could instead rely on a considerable number of subjects, but the reliability of the results when transferred to real exoskeleton users is limited. This limitation could be partially solved using able-bodied subjects for preliminary tests. In this paper, we describe a first approach to train able-bodied subjects to behave as SCI subjects during walking. An audio feedback driven by a pair of instrumented crutches has been used to train healthy subjects during exoskeleton walking. To test the system, 22 able-bodied subjects have been analyzed during a straight walk with and without the audio feedback. Results show that the audio feedback induces a learning effect and a persistency effect in the participants.The authors would thank Marcello Domenighini for the preliminary tests and Technaid srl for the logistic support. This work was supported by COST Action CA16116, and by European project EUROBENCH (grant 779963)