CNN-Based Self-Attention Weight Extraction for Fall Event Prediction Using Balance Test Score.

Injury, hospitalization, and even death are common consequences of falling for elderly people. Therefore, early and robust identification of people at risk of recurrent falling is crucial from a preventive point of view. This study aims to evaluate the effectiveness of an interpretable semi-supervised approach in identifying individuals at risk of falls by using the data provided by ankle-mounted IMU sensors. Our method benefits from the cause-effect link between a fall event and balance ability to pinpoint the moments with the highest fall probability. This framework also has the advantage of training on unlabeled data, and one can exploit its interpretation capacities to detect the target while only using patient metadata, especially those in relation to balance characteristics. This study shows that a visual-based self-attention model is able to infer the relationship between a fall event and loss of balance by attributing high values of weight to moments where the vertical acceleration component of the IMU sensors exceeds 5 m/s² during an especially short period. This semi-supervised approach uses interpretable features to highlight the moments of the recording that may explain the score of balance, thus revealing the moments with the highest risk of falling. Our model allows for the detection of 71% of the possible falling risk events in a window of 1 s (500 ms before and after the target) when compared with threshold-based approaches. This type of framework plays a paramount role in reducing the costs of annotation in the case of fall prevention when using wearable devices. Overall, this adaptive tool can provide valuable data to healthcare professionals, and it can assist them in enhancing fall prevention efforts on a larger scale with lower costs.

The social Simon effect in the tactile sensory modality: a negative finding.

This study seeks to investigate whether users activate cognitive representations of their partner's action when they are involved in tactile collaborative tasks. The social Simon effect is a spatial stimulus-response interference induced by the mere presence of a partner in a go/nogo task. It has been extensively studied in the visual and auditory sensory modalities, but never before in the tactile modality. We compared the performances of 28 participants in three tasks: (1) a standard Simon task where participants responded to two different tactile stimuli applied to their fingertips with either their left or right foot, (2) an individual go/nogo task where participants responded to only one stimulus and (3) a social go/nogo task where they again responded to only one stimulus, but were partnered with another person who responded to the complementary stimulus. The interference effect due to spatial incongruence between the side where participants received the stimulus and the foot used to answer increased significantly in the standard Simon task compared to the social go/nogo task. Such a difference was not observed between the social and individual go/nogo tasks. Performances were nevertheless enhanced in the social go/nogo task, but irrespectively of the stimulus-response congruency. This study is the first to report a negative result for the social Simon effect in the tactile modality. Results suggest that cognitive representation of the co-actor is weaker in this modality.

Design and Study of a Smart Cup for Monitoring the Arm and Hand Activity of Stroke Patients.

This paper presents a new platform to monitor the arm and hand activity of stroke patients during rehabilitation exercises in the hospital and at home during their daily living activities. The platform provides relevant data to the therapist in order to assess the patients physical state and adapt the rehabilitation program if necessary. The platform consists of a self-contained smart cup that can be used to perform exercises that are similar to everyday tasks such as drinking. The first smart cup prototype, the design of which was based on interviews regarding the needs of therapists, contains various sensors that collect information about its orientation, the liquid level, its position compared to a reference target and tremors. The prototype also includes audio and visual displays that provide feedback to patients about their movements. Two studies were carried out in conjunction with healthcare professionals and patients. The first study focused on collecting feedback from healthcare professionals to assess the functionalities of the cup and to improve the prototype. Based on this paper, we designed an improved prototype and created a visualization tool for therapists. Finally, we carried out a preliminary study involving nine patients who had experienced an ischemic or hemorrhagic stroke in the previous 24 months. This preliminary study focused on assessing the usability and acceptability of the cup to the patients. The results showed that the cup was very well accepted by eight of the nine patients in monitoring their activity within a rehabilitation center or at home. Moreover, these eight patients had almost no concerns about the design of the cup and its usability.

Actuation means for the mechanical stimulation of living cells via microelectromechanical systems: A critical review.

Within a living body, cells are constantly exposed to various mechanical constraints. As a matter of fact, these mechanical factors play a vital role in the regulation of the cell state. It is widely recognized that cells can sense, react and adapt themselves to mechanical stimulation. However, investigations aimed at studying cell mechanics directly in vivo remain elusive. An alternative solution is to study cell mechanics via in vitro experiments. Nevertheless, this requires implementing means to mimic the stresses that cells naturally undergo in their physiological environment. In this paper, we survey various microelectromechanical systems (MEMS) dedicated to the mechanical stimulation of living cells. In particular, we focus on their actuation means as well as their inherent capabilities to stimulate a given amount of cells. Thereby, we report actuation means dependent upon the fact they can provide stimulation to a single cell, target a maximum of a hundred cells, or deal with thousands of cells. Intrinsic performances, strengths and limitations are summarized for each type of actuator. We also discuss recent achievements as well as future challenges of cell mechanostimulation.

A planar structure sensitive to out-of-plane forces for the force-controlled injection of suspended and adherent cells.

We present a novel force sensor for the injection of both suspended and adherent cells. Unlike most configurations, this force sensor is independent of the tool interacting with the cells. It is a planar structure that provides a surface sensitive to out-of-plane forces where living cells can be placed for manipulation. It also integrates two beam resonators. Forces perpendicular to the sensor's plane are estimated via frequency shifts of the resonators. In this paper, we develop a theoretical study for predicting and optimizing the structure's sensitivity. As a proof of concept, we report the fabrication and characterization of a first prototype designed for the injection of spherical cells with a diameter of ~100-600 µm. In air, our prototype presently offers a quality factor of 700, and a linear force sensitivity of ~2.6 Hz/mN. The measurement of forces applied upon lobster eggs is also experimentally demonstrated.

Characterization of cellular mechanical behavior at the microscale level by a hybrid force sensing device.

This paper deals with the development of an open design platform for characterization of mechanical cellular behavior. The resulting setup combines Scanning Probe Microscopy (SPM) techniques and advanced robotic approaches in order to carry out both prolonged observations and spatial measurements on biological samples. Visual and force feedback is controlled to achieve automatic data acquisition and to monitor process when high skills are required. The issue of the spring constant calibration is addressed using an accurate dynamic vibration approach. Experimentation on the mechanical cell characterization under in vitro conditions on human adherent Epithelial Hela cells demonstrates the viability and effectiveness of the proposed setup. Finally, the JKR (Johnson, Kendall and Roberts), the DMT (Derjaguin, Muller and Toporov) and Hertz contact theories are used to estimate the contact area between the cantilever and the biological sample.

Calibration of lateral force measurements in atomic force microscopy with a piezoresistive force sensor.

We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092 to 1.24 N/m and lateral stiffness from 10.34 to 101.06 N/m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to +/-12.4% or better. This standard has less error than the commonly used method based on the cantilever's beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.

The force sensing bio-microscope: an efficient tool for cells mechanotransduction studies.

This paper deals with the development of an open design platform for explorative cells mechanotransduction investigation. The produced setup combines SPM techniques and advanced robotics approaches allowing to carry out both prolonged observations and spatial measurements on biological samples. As a result, enhanced force probing method based on scanning microscopy techniques and advanced robotics/automation approaches are integrated in this device. Visual and force feedback control are used to achieve automatic data acquisition and monitoring process when high skills are required. Preliminary in vitro experiments on human promyelocytic leukemia cells (NB4) are conducted in order to demonstrate the viability of the proposed design. Some relevant mechanical cell properties are extracted such as elasticity and viscosity parameters.