Biology subjects

Nasiri, R.

Publications and source records attributed to Nasiri, R..

6 recordsLinked to original sources

bioRxiv2025

Role of Speed Regulation and Speed Modulation in Velocity-Field Based Control

The velocity vector field (flow) controller is a well-established control strategy for lower limb exoskeletons. In this paper, we analyze this controller and propose modifications to improve its performance. We demonstrate that flow control acts as a variable proportional-derivative error regulator, where the parameter {Gamma} represents the desired norm of the hip-knee joint velocity vector (path speed). Based on this, we introduce two modifications to {Gamma}: (1) a constant {Gamma} set to the mean desired path speed, and (2) a variable {Gamma} that mimics natural path speed during unassisted walking. We compared the modified flow controllers with a slow-{Gamma} version in experiments involving seven participants walking on a treadmill at 0.6m/s, 0.8m/s, and 1.0m/s. Compared to the slow-{Gamma} controller, the RMS tracking error decreased by 30.7{+/-} 11.3% and the range of motion of the knee increased by 48.2 {+/-} 5.5% for the mean-{Gamma} controller, while the variable-{Gamma} controller had 32.4 {+/-} 14.7% smaller RMS error and 50.5 {+/-} 6.5% larger range of motion of the knee. Additionally, the slow-{Gamma} controller consistently applied resistive power, whereas participants reported more comfortable and natural gait with the modified controllers. We also compared them with the original tuning of flow controller, with results indicating superior performance from the proposed modifications. These findings demonstrate effectiveness across different walking speeds and offer a tuning strategy for future flow controller use.

bioengineering↗

bioRxiv2025

A Lung Tumor-on-a-Chip Model Recapitulates the Effect of Hypoxia on Radiotherapy Response and FDG-PET Imaging

Most solid tumors contain regions of hypoxia that pose a significant challenge to the efficacy of radiation therapy. This study introduces a novel 3D lung tumor-on-a-chip (ToC) model designed to replicate the hypoxic tumor microenvironment in vitro while also providing a platform for clinically relevant interventions such as radiotherapy and positron emission tomography (PET) imaging. To simulate the heterogeneous oxygen distribution found in tumors, the ToC model incorporates an oxygen gradient achieved through a straightforward chemical oxygen scavenging system. A unique innovation of this device is the integration of a thin scintillator plate, which enables high-resolution radioluminescence microscopy imaging of tumor metabolism under hypoxia and normoxia conditions using clinically approved PET tracers such as fluorodeoxyglucose (FDG). The response of this hypoxic model to radiation therapy (10 Gy X-ray) demonstrated [~]4-fold higher radioresistance compared to the normoxic ToC model, as assessed by colony formation potential. Additionally, DNA damage observed in the normoxic ToC model was [~]5-fold higher than that in the hypoxic model. Furthermore, the metabolic consumption of glucose was found to mirror the localization of hypoxia, validating the use of this biomarker for planning radiation therapy. The integration of high-resolution radionuclide imaging within ToC models enables on-chip PET imaging and facilitates oncology research and discovery, offering innovative capabilities for the preclinical testing of novel cancer therapies in a clinically relevant environment.

bioengineering↗

bioRxiv2023

Coordinated human-exoskeleton locomotion emerges from regulating virtual energy

Lower-limb exoskeletons showed great potential for the gait rehabilitation of individuals with motor impairments; however, maintaining human-exoskeleton coordination is still a challenge. Human-exoskeleton coordination problem, referred to as any mismatch or asynchrony between the users intended trajectories and exoskeleton desired trajectories, results in sub-optimal gait performance, particularly for the individuals with residual motor ability. Here, we investigate the virtual energy regulator (VER)s ability to generate coordinated locomotion in lower limb exoskeleton in a study on nine individuals. A comprehensive analysis of metrics obtained at three different speeds demonstrates the emergence of natural and coordinated locomotion as a result of a shared control between human and exoskeleton maintained with the VER. We also introduce a metric to measure the users contribution to gait and demonstrated that the resultant locomotion limit cycle is a linear combination of human-intended limit cycle and the VERs limit cycle. This results may have implications about how central nervous system controls our locomotion.

bioengineering↗

bioRxiv2021

Online Reference Trajectory Adaptation: A Personalized Control Strategy for Lower Limb Exoskeletons

This paper presents a novel method for reference trajectory adaptation in lower limb rehabilitation exoskeletons during walking. Our adaptation rule is extracted from a cost function that penalizes both interaction force and trajectory modification. By adding trajectory modification term into the cost function, we restrict the boundaries of the reference trajectory adaptation according to the patients motor capacity. The performance of the proposed adaptation method is studied analytically in terms of convergence and optimality. We also developed a realistic dynamic walking simulator and utilized it in performance analysis of the presented method. The proposed trajectory adaptation technique guarantees convergence to a stable, reliable, and rhythmic reference trajectory with no prior knowledge about the human intended motion. Our simulations demonstrate the convergence of exoskeleton trajectories to those of simulated healthy subjects while the exoskeleton trajectories adapt less to the trajectories of patients with reduced motor capacity (less reliable trajectories). Furthermore, the gait stability and spatiotemporal parameters such as step time symmetry and minimum toe off clearance enhanced by the adaptation in all subjects. The presented mathematical analysis and simulation results show the applicability and effectiveness of the proposed method and its potential to be applied for trajectory adaptation in lower limb rehabilitation exoskeletons.

bioengineering↗

bioRxiv2020

Human-in-the-Loop Weight Compensation and Mass Estimation in Upper Limb Wearable Robots Towards Muscles Effort Minimization

In this paper: (1) We present a novel human-in-the-loop adaptation method for whole arm muscles effort minimization by means of weight compensation in the face of an object with an unknown mass. (2) This adaptation rule can also be used as a cognitive model for the identification of mass value using EMG sensors. (3) This adaptation rule utilizes the activation (myoelectric) signal of only four muscles in the upper limb to minimize the whole muscles effort. We analytically discuss the stability, optimality, and convergence of the proposed method. The effectiveness of this method for whole muscles effort reduction is studied by simulations (OpenSim software) on a generic and realistic model of the human arm, a model with 7-DOF and 50 Hill-type-muscles. The simulation results show the presented methods performance and applicability for weight compensation and mass estimation in upper limb assistive robots. In addition, the simulations in OpenSim completely support that the suggested set of mono-articular muscles are sufficient for whole muscles effort reduction.

bioengineering↗

bioRxiv2020

A Kinematic Index for Estimation of Metabolic Rate Reduction in Running with I-RUN

In this paper, we target multiple goals related to our passive running assistive device, called I-RUN. The major goals are: (1) finding the main reason behind individual differences in benefiting from our assistive device at the muscles level, (2) devising a simple measure for on-line I-RUN stiffness tuning, and creating a lab-free simple kinematic measure for (3) estimating metabolic rate reduction as well as (4) training subjects to maximize their benefit from I-RUN. Our approach is using some extensive data-driven OpenSim simulation results employing a generic lower limb model with 92-muscles and 29-DOF. It is observed that there is a significant relation between the hip joints kinematic and changes in the metabolic rate in the presence of I-RUN. Accordingly, a simple kinematic index is devised to estimate metabolic rate reduction. This index not only explains individual differences in metabolic rate reduction but also provides a quantitative measure for training subjects to maximize their benefits from I-RUN. The simulation results also re-confirm our hypothesis that "reducing the forces of two antagonistic mono-articular muscles is sufficient for involved muscles total effort reduction". Consequently, we introduce a two-muscles EMG-based metric for the on-line tuning of I-RUN.

bioengineering↗