Open Access Publications - Department of Mechanical Engineering
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Open access publications by faculty, postdocs, and graduate students in the Department of Mechanical Engineering.
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Item Raman Evidence for the Mechanism of Enhanced C–C Coupling during CO2RR on CuSnx Bimetallic Electrocatalysts at Dilute Sn Levels(Journal of The Electrochemical Society, 2025-12-01) Mishra, Mritunjay; Obetta, Emmanuel; Dauda, Monsuru Olatunji; Flake, John; Yao, Koffi P. C.The electrochemical carbon dioxide reduction reaction (CO2RR) presents a promising method for converting CO2 into valuable fuels and chemicals, but requires electrocatalysts with high selectivity. Here, we investigate CuSnx catalysts with systematically varied Sn contents to elucidate composition-selectivity relationships. Electrolyzer testing reveals that 3%Sn-doped Cu electrocatalyst selectively produces C2 products, primarily ethanol and ethylene, whereas higher Sn contents (>3%) shift selectivity toward C1 products, predominantly formic acid. X-ray photoelectron spectroscopy suggests the coexistence in similar proportions of near neutral (Cu) and partial positive (Cuδ+) sites at low Sn contents. On the other hand, at high Sn contents, surface Cu skews towards monolithically Cu2+ states. From In-situ surface-enhanced Raman spectroscopy, at 3%Sn, abundant *COOH absorbed via carbon is detected that leads to detected high *CO coverage with electrophilicity imbalance from absorbing at Cu and Cuδ+. Two electronically dissimilar *COs then promote *CO*CO dimerization favoring C2 products. At 50% and 80% Sn, HCOO* intermediate adsorbed via oxygen is detected instead, leading to formic acid as the major product upon proton transfer. The findings experimentally validate prior computational density functional theory conclusions and provide empirical insight into the role of Sn doping in tuning the catalytic behavior of Cu for CO2RR.Item Vibration-Mediated Recovery of Irradiated Osteocytes and Their Regulatory Role in Breast Cancer Bone Metastasis(Advanced Healthcare Materials, 2025-10-15) Song, Xin; Seaman, Kimberly; Sassi, Amel; Lin, Chun-Yu; Chu, Tiankuo; Wang, Liyun; Sun, Yu; You, LidanRadiotherapy is a cornerstone of breast cancer treatment, but it can unintentionally damage bone, causing bone loss and pain, with no currently effective therapeutic strategy available. While chemically mediated radioprotection is extensively studied, mechanically mediated radioprotection remains underexplored. Given its safety and efficacy, this work examines the potential of low-magnitude, high-frequency (LMHF) vibration as a non-invasive intervention to protect irradiated bone, focusing on osteocytes—the primary mechanosensors and regulators whose functions extend to modulating breast cancer bone metastasis. These results demonstrate that LMHF vibration (0.3 g, 60 Hz, 1 h) mitigates osteocyte apoptosis and upregulates cytoskeletal markers following 8 Gy irradiation. LMHF vibration applied 1 h per day over 3 days restores the regulatory function of irradiated osteocytes in controlling breast cancer extravasation in a microfluidic platform. A combined approach integrating vibration with radiotherapy further reduces cancer invasion and extravasation, demonstrating a compound effect. RNA sequencing (RNA-seq) analysis reveals that this osteocyte-mediated regulation is possibly driven by the Wnt signaling pathway. These findings highlight the potential of LMHF vibration in enhancing radiotherapy efficacy by protecting osteocytes and reducing breast cancer metastasis, underscoring the promise of a non-invasive mechanical intervention in preserving bone health and optimizing cancer treatment outcomes.Item Structure–property relationships of flexible, non-isocyanate polyurethane foams from lignin and castor oil-based reagents(RSC Advances, 2025-10-13) Evancho, Kathryn; Reiner, Richard S; Bujanovic, Biljana M; Pilla, Srikanth; Sternberg, JamesPolyurethane foam is a valuable material with applications across the automotive, packaging, construction, appliance, and furniture industries. However, traditional polyurethane foams are made from petroleumbased precursors including harmful isocyanates. Isocyanates are the leading cause of workplace asthma and are made from toxic phosgene gas, representing a challenge to green chemistry principles. To address these concerns, non-isocyanate polyurethane (NIPU) foams replace the traditional polyurethane reaction with a safer, non-isocyanate process most often employing cyclic carbonates and diamines. Current approaches to NIPU foams struggle to meet the low-density and flexibility of commercial foams and also employ many petroleum-derived and toxic agents. This work demonstrates the use of kraft lignin, a crosslinked aromatic polymer produced by the dominant kraft pulping process, as an effective raw material for flexible NIPU foams, reaching densities below 100 kg m−3 while displaying flexible compression properties. A biobased, aliphatic agent was added in various amounts to introduce flexibility to the polymer structure while modifying the viscosity of the reaction mixture to enable increased rise height of foams containing over 30% lignin. The thermal, mechanical, and burn testing results of a series of NIPU foams are compared to a conventional PU reference foam and the structure–property relationships of the novel materials are explored based on the lignin-to-aliphatic carbon content. The results show a fully biobased, flexible, NIPU foam from lignin that can approach commercial properties, helping to demonstrate the relevance of NIPU foams for many applications.Item Biobased chemical recycling: aminolysis of PET using renewable reagents and monomers to synthesize new semi-aromatic polyamides(RSC Sustainability, 2025-09-30) Kaumadi, Sathiska; Sternberg, James; Simmons, Kevin; Pilla, SrikanthChemical recycling of PET is a method of depolymerizing polymer chains to monomeric components enabling the synthesis of second-generation materials with virgin-like quality. Commercial chemical recycling techniques rely upon high pressure methanolysis to create precursors capable of synthesizing a second-generation PET resin. However, despite the circular approach of methanolysis, a product with a very short lifespan and similar value is created. The approach of the current study is to utilize aminolysis as an ambient pressure technique to create precursors for higher value materials with longer lifespans to address the current crisis in plastic waste. Semi-aromatic polyamides (SAP) are desired in this circumstance because of their high melting point and heat resistance combined with good meltprocessability similar to aliphatic polyamides. In this study SAPs were synthesized using precursors recovered from the aminolysis of PET employing biobased diamines and dicarboxylic acids. While aminolysis has been explored in previous studies, this work investigated the use of biobased components from castor oil: decamethylene diamine during recycling and sebacic acid during polymerization. Polymer synthesis resulted in the formation of SAPs similar to polyphthalamides (PPA) with novel structures given the aromatic portion from terephthalic acid (TPA) and aliphatic portion from the diamines and diacids. The synthesized materials exhibited excellent thermal stability with high glass transition temperatures. Novel polymers were created with varying aliphatic chain length to understand fundamental parameters needed to produce a valuable polymer from post-consumer waste.Item In-situ Visual Microdamage Detection in Lead-based Perovskite Solar Cells(Science China Chemistry, 2025-09-22) Zhang, Youzi; Wang, Tong; Chen, Hui; Yang, Jiabao; Wang, Yijin; Yin, Ranhao; Chen, Weizhe; Su, Jie; Hu, Xiaotian; Zhong, Wencheng; Shang, Li; Yan, Feng; Titirici, Maria-Magdalena; Wei, Bingqing; Li, XuanhuaAlthough Lead (Pb)-based perovskite solar cells (PSCs) have garnered intense attention for their remarkable photovoltaic conversion efficiency, their commercial process is urgently in need of an effective damage-evaluation system for the early diagnosis of faulty PSCs. The main cause of microdamage in perovskite films is the outflow of Pb, which significantly impacts device performance. However, no reliable correlation has been established between classical damage detection techniques and Pb detection, resulting in limited detection sensitivity. Here, we report an in-situ visual microdamage evaluation method of PSCs by coating the device surface with a silica gel encapsulation layer containing porphyrin molecules. This detection technology enables high selectivity and sensitivity based on the strong complexation between the porphyrin ring and trace Pb outflow from degraded PSCs. By establishing the linear relationship between the fluorescence intensity and Pb concentration in PSCs, trace Pb outflow is pinpointed and quantified with a low detection limit of 0.65 μg cm−2. An applet is developed for the in-situ visual fluorescence detection method to facilitate the continuous real-time monitoring of series-type PSCs, thereby enabling the prompt identification and replacement of damaged PSCs and ensuring the swift restoration of high efficiency.Item Force-Induced Selective Carbon-Carbon Bond Cleavage inMechanoresponsive Topochemical Polymers(Advanced Materials, 2025-09-18) Wei, Zitang; Kim, Hanul; Haque, Nazmul; Hu, Qixuan; Ma, Ke; Wang, Kang; Zhang, Shuchen; Luo, Xuyi; Lee, Yoon Ho; Choi, Siyoung Q.; Davis, Chelsea S; Savoie, Brett M.; Dou, LetianMechanoresponsive polymeric materials that respond to mechanical deformation are highly valued for their potential in sensors, degradation studies, and optoelectronics. However, direct visualization and detection of these responses remain significant obstacles. In this study, novel mechanoresponsive polybiidenedionediyl (PBIT) derivative topochemical polymers are developed that depolymerize under mechanical forces, exhibiting a distinct and irreversible color change in response to grinding, milling, and compression. This color change is attributed to the alteration of polymer backbone conjugation during elongated Carbon-Carbon (C─C) single bond cleavage. Quantum chemical pulling simulations on PBIT polymers reveals a force range of 4.3–5.0 nN associated with the selective cleavage of elongated C─C single bonds. This force range is comparable to that observed for typical homolytic mechanophores, supporting the mechanistic interpretation of homolytic bond scission under mechanical stress. C─C bond cleavage kinetic studies of PBIT under compression indicates that strong interchain interactions significantly increase the pressure needed to cleave the elongated C─C bonds. Additionally, PBIT polymer thin films are composited with polydimethylsiloxane to create free-standing and robust thin films, which can serve as ink-free and rewritable paper for writing and stress visualization applications. This advancement opens new possibilities for utilizing crystalline and brittle topochemical polymers in practical applications.Item Electrochemical Hydrogen Separation and Compression(Journal of Applied Electrochemistry, 2025-04-22) Aziz, Majid; Amrite, Archis; Raj Aryal, Ustav; Prasad, Ajay KThe potential benefits of hydrogen as an energy carrier can only be realized when its production, storage, and distribution are accomplished in a sustainable, safe, and efficient manner. For numerous end-user applications, a convenient solution is to separate hydrogen from a mixture containing hydrogen and store it as a compressed gas. Electrochemical hydrogen separation and compression (ECHSC) represents a promising alternative to conventional hydrogen separators and compressors because it can purify and compress hydrogen simultaneously in a single step. Furthermore, ECHSC offers additional advantages such as higher efficiency, lack of moving parts, noiseless operation, and modularity. Here, experimental results on ECHSC performance are presented in three modes, viz. electrochemical hydrogen pumping, separation, and compression. Gas mixtures containing various volume fractions (75%:25%; 50%:50%; 25%:75%) of hydrogen in nitrogen, methane, and carbon dioxide were employed for separation and compression studies. Various operating parameters were explored to investigate ECHSC performance. The ECHSC outlet hydrogen purity exceeded 99% for all three H2–N2 and H2–CH4 inlet mixtures and 95% for all three H2–CO2 inlet mixtures. The study also revealed the effect of CO poisoning for the case of the H2–CO2 inlet mixture. The results suggest that ECHSC is a viable alternative to conventional technologies for hydrogen separation and compression.Item Nanotechnology-enabled energy efficiency in semiconductors: plasmon-induced super-semiconductors and ballistic transport devices(Frontiers in Nanotechnology, 2025-08-21) Li, Zhigang; Wei BingqingThe semiconductor industry consumes staggering amounts of electricity annually, surpassing the energy usage of over 100 nations. This immense consumption not only underscores the environmental impact but also generates substantial heat within semiconductor devices, adversely affecting their performance, lifespan, and reliability, posing significant challenges to the advancement of nanodevices. To address these challenges, reducing energy consumption through the use of advanced, energy-efficient technologies has become a priority. Energy-efficient electronics (EEE), enabled by nanotechnology, have the potential to drastically reduce energy consumption in semiconductor devices while simultaneously enhancing their performance. From this perspective, this discussion focuses on two nano-semiconductor technologies poised to advance EEEs: plasmon-induced metal-based semiconductors and ballistic transport in nanostructured semiconductors. For example, p-n junction diodes constructed with the metal-based semiconductors can reduce power consumption by 3-4 orders of magnitude compared with silicon-based devices due to their low resistivity; similarly, the excellent ballistic transport property of InSe FETs enables an energy-delay product of ∼4.32*10−29 Js/μm of the devices, one order of magnitude lower than the Si counterparts. This perspective examines the offerings of each of these disciplines and explores how nanotechnology can be utilized to conserve energy and enhance performance. Differences from traditional technologies and limitations in existing research will also be assessed.Item Prognostic assessment of osteolytic lesions and mechanical properties of bones bearing breast cancer using neural network and finite element analysis(Mechanobiology in Medicine, 2025-04-10) Wang, Shubo; Chu, Tiankuo; Wasi, Murtaza; Guerra, Rosa M.; Yuan, Xu; Wang, LiyunThe management of skeletal-related events (SREs), particularly the prevention of pathological fractures, is crucial for cancer patients. Current clinical assessment of fracture risk is mostly based on medical images, but incorporating sequential images in the assessment remains challenging. This study addressed this issue by leveraging a comprehensive dataset consisting of 260 longitudinal micro-computed tomography (μCT) scans acquired in normal and breast cancer bearing mice. A machine learning (ML) model based on a spatial–temporal neural network was built to forecast bone structures from previous μCT scans, which were found to have an overall similarity coefficient (Dice) of 0.814 with ground truths. Despite the predicted lesion volumes (18.5 % ± 15.3 %) being underestimated by ∼21 % than the ground truths’ (22.1 % ± 14.8 %), the time course of the lesion growth was better represented in the predicted images than the preceding scans (10.8 % ± 6.5 %). Under virtual biomechanical testing using finite element analysis (FEA), the predicted bone structures recapitulated the loading carrying behaviors of the ground truth structures with a positive correlation (y = 0.863x) and a high coefficient of determination (R2 = 0.955). Interestingly, the compliances of the predicted and ground truth structures demonstrated nearly identical linear relationships with the lesion volumes. In summary, we have demonstrated that bone deterioration could be proficiently predicted using machine learning in our preclinical dataset, suggesting the importance of large longitudinal clinical imaging datasets in fracture risk assessment for cancer bone metastasis. Graphical abstract available at: https://doi.org/10.1016/j.mbm.2025.100130 Highlights • Fracture risk assessment is critical in managing bone cancer metastasis. • Utilized 260 longitudinal μCT scans of both normal mice and cancer-bearing mice. • Bone lesion progression predicted from μCT scans using machine learning (ML). • Finite element analysis (FEA) revealed the rigidity of the predicted bone structures. • Predictive modeling of bone deterioration is a valuable tool to assess fracture risk.Item Life Cycle Assessment of Thermoelectrics: Ecological Viability in Intermittent Waste Heat Scenarios(ACS Omega, 2025-04-01) Iyer, Rakesh Krishnamoorthy; Sabet, Morteza; Pilla, SrikanthThis study evaluates the ecological impacts of thermoelectrics (TEs) in stationary applications that periodically generate waste heat using life cycle assessment (LCA) methodology, a first of its kind. Six TE modules are analyzed for a periodic heat-emitting application: a natural gas-based power plant that meets only peak electricity demand. The analysis uses detailed inventories from an earlier study regarding the production and end-of-life stages of the TEs. The results show that while TEs are effective in conserving fossil fuels and lowering greenhouse gas emissions, they do not exhibit significant positive effects on other environmental impacts. These findings persist even when accounting for variations in TE conversion efficiency and lifetime and the implementation of a circular economy approach for recycling and repurposing TE modules. This suggests that the environmental suitability of TEs is predominantly influenced by the type of fossil energy source they replace, making current TEs unsuitable for stationary applications that periodically generate waste heat. The study also highlights the need for further research on the development of new, practical TEs that utilize nontoxic, abundant elements and are produced through less energy-intensive techniques.Item Modeling of periodical shearing flow in a fibrous space with applications in shear-induced brain injury(Physics of Fluids, 2024-06-04) Lang, Ji; Wang, Liyun; Wu, QianhongThis paper presents a theoretical model examining the interaction between a fibrous network and viscous fluid flow driven by an oscillating boundary. The aim is to understand how oscillating impacts are transmitted from the skull, through the arachnoid trabeculae network filled with cerebrospinal fluid, as observed in shaken baby syndrome. The model uses an effective medium approach to determine the fluid velocity field while each fiber is treated as a soft string undergoing deformation. Results indicate that the frequency of oscillation, fiber stiffness, and porous structure resistance significantly influence the oscillating shearing flow, as indicated by the Womersley (Wo), Brinkman (a), and Bingham (Bm ) numbers. Application of the model to shaken baby syndrome suggests that oscillations in the cerebrospinal fluid and arachnoid trabeculae can significantly surpass those on the skull, leading to intense shear stress penetration to the brain. This model is the first study to integrate the dynamic response of string-like fibrous networks in fluid flows with oscillating boundaries and offers a quantitative framework for predicting the transmission of shearing forces from the skull to the brain matter.Item Quadrupole Magnetic Tweezers for Precise Cell Transportation(IEEE Transactions on Biomedical Engineering, 2024-12-09) Yang, Yanda; Sokolich, Max; Mallick, Sudipta; Das, SambeetaThis research introduces a quadrupole magnetic tweezers which can be used for precise cell transportation by actuating magnetic spherical microrobots. The focus of the system is on navigating and manipulating cells within environments characterized by high cellular density. Demonstrating efficacy in moving cells through densely packed cell samples, the system underscores its potential to overcome common obstacles such as inaccurate target delivery and inefficiency. The findings from this study highlight the significant promise that microrobotic technologies hold in advancing medical applications, particularly in precise cell delivery mechanisms, setting a foundation for the future exploration and utilization of medical microrobots.Item Electrochemo-Mechanical Degradation and Failure of Active Particles in High Energy Density Batteries: A Review(Small, 2025-01-07) Li, Dawei; Shen, Chenhao; Zheng, Yuejiu; Xu, JunFailure of the active particles is inherently electrochemo-mechanics dominated. This review comprehensively examines the electrochemo-mechanical degradation and failure mechanisms of active particles in high-energy density lithium-ion batteries. The study delves into the growth of passivating layers, such as the solid electrolyte interphase (SEI), and their impact on battery performance. It highlights the role of elevated temperatures in accelerating degradation reactions, such as the dissolution of transition metals and the formation of new SEI layers, leading to capacity fade and increased internal resistance. The review also discusses the mechanical degradation of electrode materials, including the fracture of active particles and the impact of stress on electrode performance. Advanced characterization techniques, such as cryogenic scanning transmission electron microscopy and 3D tomography, are explored to provide insights into the structural and chemical evolution of battery materials. By addressing the interplay between chemical, mechanical, and thermal factors, this review aims to provide guidelines for the chemistry development, material selection, structural design as well as recycling of next-generation batteries with high safety, durability, and high energy density.Item Detailed computational modeling of crack patterns of silicon-based anode sheet in lithium-ion batteries upon mechanical stress(Energy Materials and Devices, 2025-02-17) Kawashima,Yuzuki; Ogata, Kazuma; Shibayama, Yuto; Takagi, Aoi; Yonezu, Akio; Xu, JunSilicon (Si)-based anodes, where Si serves as the active material, have garnered significant attention due to their potential to achieve high electric capacity in lithium-ion batteries (LIBs). A key challenge with Si-based anodes is their susceptibility to create in-plane cracks caused by stresses from the manufacturing process and cyclic charging, which ultimately shortens battery life and reduces the overall electrochemical capacity. To address this issue, a refined microstructural design of the active material layer is in pressing need to enhance both the performance and longevity of LIBs. We successfully applied the Oyane failure criterion, which models ductile failure under stress triaxiality, to simulate crack initiation and propagation in the binder matrix containing Si particles in the finite element modeling. Given the non-linear plastic deformation of the binder, this criterion was formulated based on cumulative strain increments. The computational results of microcrack formation within the active material layer under uniaxial tension were then validated by the experimental observations. Furthermore, we developed several models with varied particle arrangements, comparing each simulated crack path to actual microstructural images obtained via scanning electron microscopy. The findings confirm the accuracy of the model, underlying its promising application in optimizing the microstructure of Si-based anodes for enhanced LIB performance and durability. Graphical Abstract available at: https://doi.org/10.26599/EMD.2025.9370054.Item Osteocyte Dendrites: How Do They Grow, Mature, and Degenerate in Mineralized Bone?(Cytoskeleton, 2024-12-09) Guerra, Rosa M.; Fowler, Velia M.; Wang, LiyunOsteocytes, the most abundant bone cells, form an extensive cellular network via interconnecting dendrites. Like neurons in the brain, the long-lived osteocytes perceive mechanical and biological inputs and signal to other effector cells, leading to the homeostasis and turnover of bone tissues. Despite the appreciation of osteocytes' vital roles in bone biology, the initiation, growth, maintenance, and eventual degradation of osteocyte dendrites are poorly understood due to their full encasement by mineralized matrix. With the advancement of imaging modalities and genetic models, the architectural organization and molecular composition of the osteocyte dendrites, as well as their morphological changes with aging and diseases, have begun to be revealed. However, several long-standing mysteries remain unsolved, including (1) how the dendrites are initiated and elongated when a surface osteoblast becomes embedded as an osteocyte; (2) how the dendrites maintain a relatively stable morphology during their decades-long life span; (3) what biological processes control the dendrite morphology, connectivity, and stability; and (4) if these processes are influenced by age, sex, hormones, and mechanical loading. Our review of long, thin actin filament (F-actin)-containing processes extending from other cells leads to a working model that serves as a starting point to investigate the formation and maintenance of osteocyte dendrites and their degradation with aging and diseases.Item Mechanical Properties of the Cortex in Older Adults and Relationships With Personality Traits(Human Brain Mapping, 2025-02-06) Twohy, Kyra E.; Kramer, Mary K.; Diano, Alexa M.; Bailey, Olivia M.; Delgorio, Peyton L.; McIlvain, Grace; McGarry, Matthew D. J.; Martens, Christopher R.; Schwarb, Hillary; Hiscox, Lucy V.; Johnson, Curtis L.Aging and neurodegeneration impact structural brain integrity and can result in changes to behavior and cognition. Personality, a relatively stable trait in adults as compared to behavior, in part relies on normative individual differences in cellular organization of the cerebral cortex, but links between brain structure and personality expression have been mixed. One key finding is that personality has been shown to be a risk factor in the development of Alzheimer's disease, highlighting a structure–trait relationship. Magnetic resonance elastography (MRE) has been used to noninvasively study age-related changes in tissue mechanical properties because of its high sensitivity to both the microstructural health and the structure–function relationship of the tissue. Recent advancements in MRE methodology have allowed for reliable property recovery of cortical subregions, which had previously presented challenges due to the complex geometry and overall thin structure. This study aimed to quantify age-related changes in cortical mechanical properties and the relationship of these properties to measures of personality in an older adult population (N = 57; age 60–85 years) for the first time. Mechanical properties including shear stiffness and damping ratio were calculated for 30 bilateral regions of the cortex across all four lobes, and the NEO Personality Inventory (NEO-PI) was used to measure neuroticism and conscientiousness in all participants. Shear stiffness and damping ratio were found to vary widely across regions of the cortex, upward of 1 kPa in stiffness and by 0.3 in damping ratio. Shear stiffness changed regionally with age, with some regions experiencing accelerated degradation compared to neighboring regions. Greater neuroticism (i.e., the tendency to experience negative emotions and vulnerability to stress) was associated with high damping ratio, indicative of poorer tissue integrity, in the rostral middle frontal cortex and the precentral gyrus. This study provides evidence of structure–trait correlates between physical mechanical properties and measures of personality in older adults and adds to the supporting literature that neurotic traits may impact brain health in cognitively normal aging.Item Kinematics, kinetics, and muscle activations during human locomotion over compliant terrains(Scientific Data, 2025-01-16) Angelidou, Charikleia; Chambers, Vaughn; Hobbs, Bradley; Karakasis, Chrysostomos; Artemiadis, PanagiotisWalking on compliant terrains, like carpets, grass, and soil, presents a unique challenge, especially for individuals with mobility impairments. In contrast to rigid-ground walking, compliant surfaces alter movement dynamics and increase the risk of falls. Understanding and modeling gait control across such soft and deformable surfaces is thus crucial for maintaining daily mobility. However, access to the necessary equipment for modeling compliant surface walking is limited. Therefore, in this paper, we present the first publicly available biomechanics dataset of 20 individuals walking on terrains of varying compliance, using a unique robotic device, the Variable Stiffness Treadmill 2 (VST 2), designed to simulate walking on adjustable compliant terrain. VST 2 provides a consistent and reproducible environment for studying the biomechanics of walking on such surfaces within laboratory settings. The goal of this dataset is to provide insights into the muscular, kinematic, and kinetic adaptations that occur when humans walk on compliant terrain in order to design better controllers for prosthetic limbs, improve rehabilitation protocols, and develop adaptive assistive devices that can enhance mobility on compliant surfaces.Item Behavior of chemically powered Janus colloids in lyotropic chromonic liquid crystal(Physical Review E, 2024-11-21) Sudha, Devika Gireesan; Baza, Hend; Rivas, David P.; Das, Sambeeta; Lavrentovich, Oleg D.; Hirst, Linda S.Platinum-coated Janus colloids exhibit self-propelled motion in aqueous solution via the catalytic decomposition of hydrogen peroxide. Here, we report their motion in a uniformly aligned nematic phase of lyotropic chromonic liquid crystal, disodium cromoglycate (DSCG). When active Janus colloids are placed in DSCG, we find that the anisotropy of the liquid crystal imposes a strong sense of direction to their motion; the Janus colloids tend to move parallel to the nematic director. Motion analysis over a range of timescales reveals a crossover from ballistic to anomalous diffusive behavior on timescales below the relaxation time for liquid crystal elastic distortions. Surprisingly we observe that smaller particles roll during ballistic motion, whereas larger particles do not. This result highlights the complexity of phoretically-driven particle motion, especially in an anisotropic fluid environment.Item Muscular, temporal, and spatial responses to shoulder exosuit assistance during functional tasks(Journal of Neurophysiology, 2024-11-01) Burch, Kaleb; Higginson, JillShoulder exosuits are a promising new technology that could enable individuals with neuromuscular impairments to independently perform activities of daily living, however, scarce evidence exists to evaluate their ability to support such activities. Consequently, it is not understood how humans adapt motion in response to assistance from a shoulder exosuit. In this study, we developed a cable-driven shoulder exosuit and evaluated its effect on reaching and drinking tasks within a cohort of 18 healthy subjects to quantify changes to muscle activity and kinematics as well as trial-to-trial learning in duration and actuator switch timing. The exosuit successfully reduced mean muscle activity in the middle (reaching: 23.4 ± 26.3%, drinking: 20.0 ± 25.1%) and posterior (reaching: 12.8 ± 10.3%, drinking: 4.0 ± 7.2%) deltoid across both functional tasks. Likewise, the exosuit reduced integrated muscle activity in the middle deltoid (reaching: 22.2 ± 22.7%, drinking: 14.9 ± 27.0%). Exosuit assistance also altered kinematics such that individuals allowed their arms to follow forces applied by the exosuit. In terms of learning, subjects reduced movement duration by 15.6 ± 11.9% as they practiced using the exosuit. Reducing movement duration allowed subjects to reduce integrated muscle activity in the anterior (15.2 ± 10.3%), middle (14.7 ± 9.7%), and posterior (14.8 ± 9.7%) deltoids. Similarly, subjects activated the actuator switch earlier over the course of many assisted trials. The muscle activity reductions during both reaching and drinking demonstrate the promise of shoulder exosuits to enable independent function among individuals with neuromuscular impairments. The kinematic response to assistance and learning features observed in movement duration provide insight into human-exosuit interaction principles that could inform future exosuit development. NEW & NOTEWORTHY Shoulder exosuits assist arm function, but it is not understood how assistance affects motion. We evaluated spatiotemporal movement features and muscle activity during assisted and unassisted arm motions. Introducing the exosuit caused individuals to let their arms follow assistive forces. Furthermore, individuals learned to use the exosuit with practice by moving more quickly to reduce cumulative effort and by activating assistance earlier. These results demonstrate that individuals adapt exosuit-assisted motion to reduce effort.Item Individual closed-loop control of micromotors by selective light actuation(Soft Matter, 2024-11-11) Rivas, David P.; Sokolich, Max; Das, SambeetaControl of individual micromotors within a group would allow for improved efficiency, greater ability to accomplish complex tasks, higher throughput, and increased adaptability. However, independent control of micromotors remains a significant challenge. Typical actuation techniques, such as chemical and magnetic, are uniform over the workspace and therefore cannot control one micromotor independently of the others. To address this challenge, we demonstrate a novel control method of applying a localized region of UV light that activates a single light-responsive TiO2 micromotor at a time. To achieve this, a digital micromirror device (DMD) was employed which is capable of highly precise localized illumination. To demonstrate this precise user-defined control, patterns of micromotors were created via selective actuation and magnetic steering. In addition, a closed-loop system was also developed which automates the guidance of individual micromotors to specified locations, illustrating the potential for more efficient and precise control of the micromotors.