Studying mechanical load at body-seat interface during dynamic activities such as wheelchair propulsion: a scoping review.

BACKGROUND: The increasing number of wheelchair users and their risk of medical complications such as pressure ulcers (PU) make it important to have a better understanding of their seating characteristics. However, while most studies tackling this issue are based on static measurements, wheelchair users are active in their wheelchairs when performing daily life activities. This suggests the need to assess the mechanical loads at the wheelchair user's body-seat interface during dynamic activities. OBJECTIVES: A scoping review was conducted to explore the existing data (shear load and pressure) and highlight significant parameters, relevant conditions and methodological strategies when studying wheelchair users performing a dynamic task. MATERIALS AND METHODS: The literature search was performed by applying the PRISMA methodology. RESULTS: A total of 11 articles met the inclusion criteria. Differences between static and dynamic data were found in the literature for peak pressure values, pressure distribution and the location of peak pressure. None measured tangential load at the seat/body interface, although two studies measured the shift of the ischial region. A significant impact of the type of pathology has been quantified, showing the need to perform experimental studies on diverse populations. The protocol and the pressure parameters studied were very diverse. CONCLUSION: Further studies carefully choosing interface pressure mapping parameters and investigating a broader range of pathologies are required. Additionally, researchers should focus on finding a way to measure seated tangential load.

Development of an Innovative Surgical Navigation System for Sacrospinous Fixation in Pelvic Surgery.

STUDY OBJECTIVE: To validate the use of an innovative navigation method for sacrospinous fixation in surgery-like conditions as a new teaching tool and surgical method. DESIGN: Two-month experimental prospective pilot study between July and August 2021. SETTING: Biomechanics laboratory academic research. PATIENTS: A total of 29 participants took part in the study: 9 gynecological surgeons and 20 participants with no medical background. INTERVENTIONS: All participants used the 2 mocks-up. MEASUREMENTS AND MAIN RESULTS: The experiment was composed of 2 training phases dedicated to improving the hand-eye coordination and suture skills on a training mock-up and of a suturing phase on a pelvic mock-up designed to recreate the surgery-like conditions of a sacrospinous fixation. The surgeons provided qualitative feedback on the bio-accuracy of the mock-ups and evaluated the ease of use of the navigation software. Nonsurgeons were included to assess the progression of the suture performance between 2 experiments performed 1 week apart (session 1 and 2). The main objective for participants was to reach a virtual target and to stitch sacrospinous ligaments. For session 1, an overall comfort score of 7.2 of 10 was attributed to the tool; 14 (42%) surgeon suture attempts and 63 (65%) nonsurgeon suture attempts were accurate (i.e., below the 5-mm threshold). Twenty-two (67%) surgeon suture attempts and 28 (34%) nonsurgeon suture attempts were fast (i.e., in the first 2 quantiles of the duration dataset). An improvement in the nonsurgeon performance was observed between the 2 sessions in terms of duration (session 1: 46 ± 20 s; session 2: 37 ± 18 s; p = .047) and distance (session 1: 3.8 ± 1.3 mm; session 2: 3.2 ± 1.4 mm; p = 10-5) for the last suturing exercise. CONCLUSION: This new motion capture-based navigation method for sacrospinous fixation tested under surgery-like conditions seemed to be accurate and effective. The next step will be to design a pelvis model more adapted to the constraints of a sacrospinous fixation and to validate the benefits of this method compared with current techniques.

Cellular mechanosensitivity to substrate stiffness decreases with increasing dissimilarity to cell stiffness.

Computational modelling has received increasing attention to investigate multi-scale coupled problems in micro-heterogeneous biological structures such as cells. In the current study, we investigated for a single cell the effects of (1) different cell-substrate attachment (2) and different substrate modulus [Formula: see text] on intracellular deformations. A fibroblast was geometrically reconstructed from confocal micrographs. Finite element models of the cell on a planar substrate were developed. Intracellular deformations due to substrate stretch of [Formula: see text], were assessed for: (1) cell-substrate attachment implemented as full basal contact (FC) and 124 focal adhesions (FA), respectively, and [Formula: see text]140 KPa and (2) [Formula: see text], 140, 1000, and 10,000 KPa, respectively, and FA attachment. The largest strains in cytosol, nucleus and cell membrane were higher for FC (1.35[Formula: see text], 0.235[Formula: see text] and 0.6[Formula: see text]) than for FA attachment (0.0952[Formula: see text], 0.0472[Formula: see text] and 0.05[Formula: see text]). For increasing [Formula: see text], the largest maximum principal strain was 4.4[Formula: see text], 5[Formula: see text], 5.3[Formula: see text] and 5.3[Formula: see text] in the membrane, 9.5[Formula: see text], 1.1[Formula: see text], 1.2[Formula: see text] and 1.2[Formula: see text] in the cytosol, and 4.5[Formula: see text], 5.3[Formula: see text], 5.7[Formula: see text] and 5.7[Formula: see text] in the nucleus. The results show (1) the importance of representing FA in cell models and (2) higher cellular mechanical sensitivity for substrate stiffness changes in the range of cell stiffness. The latter indicates that matching substrate stiffness to cell stiffness, and moderate variation of the former is very effective for controlled variation of cell deformation. The developed methodology is useful for parametric studies on cellular mechanics to obtain quantitative data of subcellular strains and stresses that cannot easily be measured experimentally.

Excessive volume of hydrogel injectates may compromise the efficacy for the treatment of acute myocardial infarction.

Biomaterial injectates are promising as a therapy for myocardial infarction to inhibit the adverse ventricular remodeling. The current study explored interrelated effects of injectate volume and infarct size on treatment efficacy. A finite element model of a rat heart was utilized to represent ischemic infarcts of 10%, 20%, and 38% of left ventricular wall volume and polyethylene glycol hydrogel injectates of 25%, 50%, and 75% of the infarct volume. Ejection fraction was 49.7% in the healthy left ventricle and 44.9%, 46.4%, 47.4%, and 47.3% in the untreated 10% infarct and treated with 25%, 50%, and 75% injectate, respectively. Maximum end-systolic infarct fiber stress was 41.6, 53.4, 44.7, 44.0, and 45.3 kPa in the healthy heart, the untreated 10% infarct, and when treated with the three injectate volumes, respectively. Treating the 10% and 38% infarcts with the 25% injectate volume reduced the maximum end-systolic fiber stress by 16.3% and 34.7% and the associated strain by 30.2% and 9.8%, respectively. The results indicate the existence of a threshold for injectate volume above which efficacy does not further increase but may decrease. The efficacy of an injectate in reducing infarct stress and strain changes with infarct size. Copyright © 2016 John Wiley & Sons, Ltd.

Micro-structurally detailed model of a therapeutic hydrogel injectate in a rat biventricular cardiac geometry for computational simulations.

Biomaterial injection-based therapies have showed cautious success in restoration of cardiac function and prevention of adverse remodelling into heart failure after myocardial infarction (MI). However, the underlying mechanisms are not well understood. Computational studies utilised simplified representations of the therapeutic myocardial injectates. Wistar rats underwent experimental infarction followed by immediate injection of polyethylene glycol hydrogel in the infarct region. Hearts were explanted, cryo-sectioned and the region with the injectate histologically analysed. Histological micrographs were used to reconstruct the dispersed hydrogel injectate. Cardiac magnetic resonance imaging data from a healthy rat were used to obtain an end-diastolic biventricular geometry which was subsequently adjusted and combined with the injectate model. The computational geometry of the injectate exhibited microscopic structural details found the in situ. The combination of injectate and cardiac geometry provides realistic geometries for multiscale computational studies of intra-myocardial injectate therapies for the rat model that has been widely used for MI research.

Mixed experimental and numerical approach for characterizing the biomechanical response of the human leg under elastic compression.

Elastic compression is the process of applying an elastic garment around the leg, supposedly for enhancing the venous flow. However, the response of internal tissues to the external pressure is still partially unknown. In order to improve the scientific knowledge about this topic, a slice of a human leg wearing an elastic garment is modeled by the finite-element method. The elastic properties of the tissues inside the leg are identified thanks to a dedicated approach based on image processing. After calibrating the model with magnetic resonance imaging scans of a volunteer, the pressure transmitted through the internal tissues of the leg is computed. Discrepancies of more than 35% are found from one location to another, showing that the same compression garment cannot be applied for treating deficiencies of the deep venous system or deficiencies of the large superficial veins. Moreover, it is shown that the internal morphology of the human leg plays an important role. Accordingly, the approach presented in this paper may provide useful information for adapting compression garments to the specificity of each patient.