Robotic Postural Training With Epidural Stimulation for the Recovery of Upright Postural Control in Individuals With Motor Complete Spinal Cord Injury: A Pilot Study.

Activity-based training and lumbosacral spinal cord epidural stimulation (scES) have the potential to restore standing and walking with self-balance assistance after motor complete spinal cord injury (SCI). However, improvements in upright postural control have not previously been addressed in this population. Here, we implemented a novel robotic postural training with scES, performed with free hands, to restore upright postural control in individuals with chronic, cervical (n = 5) or high-thoracic (n = 1) motor complete SCI, who had previously undergone stand training with scES using a walker or a standing frame for self-balance assistance. Robotic postural training re-enabled and/or largely improved the participants' ability to control steady standing, self-initiated trunk movements and upper limb reaching movements while standing with free hands, receiving only external assistance for pelvic control. These improvements were associated with neuromuscular activation pattern adaptations above and below the lesion. These findings suggest that the human spinal cord below the level of injury can generate meaningful postural responses when its excitability is modulated by scES, and can learn to improve these responses. Upright postural control improvements can enhance functional motor recovery promoted by scES after severe SCI.

Infant Sitting and Multi-Directional Reaching Skill.

We tested twenty-one 6- to 10-month-old infants with a wide range of sitting experience in forward and rightward reaching during unsupported sitting on the floor. Sessions were video-recorded for further behavioral and machine learning-based kinematic analyses. All infants, including novice sitters, successfully touched and grasped toys in both directions. Infant falls, hand support, and base of support changes were rare. Infants with more sitting experience showed better upright posture than novice sitters. However, we found no differences in trunk displacement or reaching kinematics between directions or across sitting experience. Thus, multi-directional reaching is functional in both novice and experienced infant sitters. We suggest that trunk and arm stability in sagittal and frontal planes is integral to learning to sit.

Training Postural Balance Control with Pelvic Force Field at the Boundary of Stability.

This study characterizes the effects of a postural training program on balance and muscle control strategies in a virtual reality (VR) environment. The Robotic Upright Stand Trainer (RobUST), which applies perturbative forces on the trunk and assistive forces on the pelvis, was used to deliver perturbation-based balance training (PBT) in a sample of 10 healthy participants. The VR task consisted of catching, aiming, and throwing a ball at a target. All participants received trunk perturbations during the VR task with forces tailored to the participant's maximum tolerance. A subgroup of these participants additionally received assistive forces at the pelvis during training. Postural kinematics were calculated before and after RobUST training, including (i) maximum perturbation force tolerated, (ii) center of pressure (COP) and pelvic excursions, (iii) postural muscle activations (EMG), and (iv) postural control strategies (the ankle and hip strategies). We observed an improvement in the maximum perturbation force and postural stability area in both groups and decreases in muscle activity. The behavior of the two groups differed for perturbations in the posterior direction where the unassisted group moved towards greater use of the hip strategy. In addition, the assisted group changed towards a lower margin of stability and higher pelvic excursion. We show that training with force assistance leads to a reactive balance strategy that permits pelvic excursion but that is efficient at restoring balance from displaced positions while training without assistance leads to reactive balance strategies that restrain pelvic excursion. Patient populations can benefit from a platform that encourages greater use of their range of motion.

Study protocol for a randomised controlled trial to determine the efficacy of an intensive seated postural intervention delivered with robotic and rigid trunk support systems.

INTRODUCTION: Children with cerebral palsy (CP) classified as gross motor function classification system (GMFCS) levels III-IV demonstrate impaired sitting and reaching control abilities that hamper their overall functional performance. Yet, efficacious interventions for improving sitting-related activities are scarce. We recently designed a motor learning-based intervention delivered with a robotic Trunk-Support-Trainer (TruST-intervention), in which we apply force field technology to individualise sitting balance support. We propose a randomised controlled trial to test the efficacy of the motor intervention delivered with robotic TruST compared with a static trunk support system. METHODS AND ANALYSIS: We will recruit 82 participants with CP, GMFCS III-IV, and aged 6-17 years. Randomisation using concealed allocation to either the TruST-support or static trunk-support intervention will be conducted using opaque-sealed envelopes prepared by someone unrelated to the study. We will apply an intention-to-treat protocol. The interventions will consist of 2 hours/sessions, 3/week, for 4 weeks. Participants will start both interventions with pelvic strapping. In the TruST-intervention, postural task progression will be implemented by a progressive increase of the force field boundaries and then by removing the pelvic straps. In the static trunk support-intervention, we will progressively lower the trunk support and remove pelvic strapping. Outcomes will be assessed at baseline, training midpoint, 1-week postintervention, and 3-month follow-up. Primary outcomes will include the modified functional reach test, a kinematic evaluation of sitting workspace, and the Box and Block test. Secondary outcomes will include The Segmental Assessment of Trunk Control test, Seated Postural & Reaching Control test, Gross Motor Function Measure-Item Set, Canadian Occupational Performance Outcome, The Participation and Environment Measure and Youth, and postural and reaching kinematics. ETHICS AND DISSEMINATION: The study was approved by the Columbia University Institutional Review Board (AAAS7804). This study is funded by the National Institutes of Health (1R01HD101903-01) and is registered at clinicaltrials.gov. TRIAL REGISTRATION NUMBER: NCT04897347; clinicaltrials.gov.

Assessing engagement in rehabilitation: development, validity, reliability, and responsiveness to change of the Rehabilitation Observation Measure of Engagement (ROME).

Purpose: We describe the development of an observational video coding tool, the Rehabilitation Observation Measure of Engagement (ROME), to quantify engagement in rehabilitative settings at the person (internal state of an individual) and between-system (interaction between individuals) level.Methods: Forty-nine children with unilateral spastic cerebral palsy (29 males; Age: M = 9.28 yrs, SD = 3.08 yrs) and their interventionists were videotaped during different activities. Construct validity was examined by correlating the ROME with the Engagement vs. Disaffection with Learning Survey and the Pediatric Rehabilitation Intervention Measure of Engagement - Observation questionnaire. Inter- and intra-rater reliability were examined using two independent raters. The ROME's responsiveness to change was examined by comparing scores across activities.Results: For construct validity, results showed a positive correlation for person-level engagement (r = 0.444, p = 0.003). No relationship was found between-system-level engagement. High intrarater (91.8%) and interrater (96.1%) reliability was found. The ROME's responsiveness to change was supported by children exhibiting lower engagement scores during repetitive shaping activities.Conclusion: These findings provide evidence that the ROME is a reliable tool to objectively examine the construct of engagement within rehabilitation and is valid for quantifying person-level engagement. It provides information that cannot be extracted from questionnaires and can help guide intervention decisions.

Implications for rehabilitationBehavioral characteristics, including engagement, of the agents involved in rehabilitation are largely unstudied, although engagement is expected to benefit motor learning.The Rehabilitation Observation Measure of Engagement (ROME) is an observation measure that uses predefined codes and can be used universally, as it is not limited to specific language or cognitive levels.The ROME is a reliable tool for objectively measuring the role of the construct of behavioral engagement during rehabilitation and valid for examining person-level engagement.The ROME may be used as a measure of client and service provider process, of intervention quality, or as a decision guide.

Effects of Boundary-Based Assist-as-Needed Force Field on Lower Limb Muscle Synergies During Standing Posture Training.

The boundary-based assist-as-needed (BAAN) force field is widely used in robotic rehabilitation and has shown promising results in improving trunk control and postural stability. However, the fundamental understanding of how the BAAN force field affects the neuromuscular control remains unclear. In this study, we investigate how the BAAN force field impacts muscle synergy in the lower limbs during standing posture training. We integrated virtual reality (VR) into a cable-driven Robotic Upright Stand Trainer (RobUST) to define a complex standing task that requires both reactive and voluntary dynamic postural control. Ten healthy subjects were randomly assigned to two groups. Each subject performed 100 trials of the standing task with or without assistance from the BAAN force field provided by RobUST. The BAAN force field significantly improved balance control and motor task performance. Our results also indicate that the BAAN force field reduced the total number of lower limb muscle synergies while concurrently increasing the synergy density (i.e., number of muscles recruited in each synergy) during both reactive and voluntary dynamic posture training. This pilot study provides fundamental insights into understanding the neuromuscular basis of the BAAN robotic rehabilitation strategy and its potential for clinical applications. In addition, we expanded the repertoire of training with RobUST that integrates both perturbation training and goal-oriented functional motor training within a single task. This approach can be extended to other rehabilitation robots and training approaches with them.

Dynamic sitting in infants: Limits of stability.

BACKGROUND: Limits of stability-defined by the maximum distances a person is willing to reach without falling or changing the base of support-are measures of dynamic balance. RESEARCH QUESTION: What are infants' sitting stability limits in the forward and right directions? METHODS: Twenty-one 6- to 10-month old infants participated in this cross-sectional study. To incentivize infants to reach beyond arm's length, caregivers began by holding a toy close to their infants at shoulder height. Caregivers then moved the toy farther away as infants tried to reach for it until infants lost balance, placed their hands on the floor, or transitioned out of sitting. All sessions were conducted via Zoom™ and video-recorded for further analyses using DeepLabCut for 2D pose estimation and Datavyu to determine timings of the reach and to code infants' postural behaviors. RESULTS: Infants' trunk excursions in the anterior-posterior plane (for forward reaches) and medio-lateral plane (for rightward reaches) represented their stability limits. Most infants ended the reach by returning to their original sitting position; however, infants with higher Alberta Infant Motor Scale (AIMS) scores transitioned out of sitting and infants with lower AIMS scores sometimes fell (mostly during rightward reaching). Trunk excursions were correlated with months of sitting experience. Rightward trunk excursions were also correlated with AIMS scores and age. Overall, infants' trunk excursions were larger in the forward than in the right direction, and such discrepancy was consistent across infants. Lastly, the more often infants adopted movement strategies with their legs (e.g., bending the knees), the greater the trunk excursion they attained. SIGNIFICANCE: Sitting control entails learning to perceive the boundaries of stability limits and acquiring anticipatory postures to suit the needs of the task. Tests and interventions that target sitting stability limits could be beneficial for infants with or at risk of motor delays.

Robotic upright stand trainer (RobUST) and postural control in individuals with spinal cord injury.

CONTEXT/OBJECTIVE: Assessed feasibility and potential effectiveness of using a novel robotic upright stand trainer (RobUST) to deliver postural perturbations or provide assistance-as-needed at the trunk while individuals with spinal cord injury (SCI) performed stable standing and self-initiated trunk movements. These tasks were assessed with research participants' hands on handlebars for self-balance assistance (hands on) and with hands off (free hands). DESIGN: Proof of concept study. PARTICIPANTS: Four individuals with motor complete (n = 3) or incomplete (n = 1) SCI who were not able to achieve independent standing and presented a neurological lesion level ranging from cervical 4 to thoracic 2. OUTCOME MEASURES: Ground reaction forces, trunk displacement, and electromyography activity of trunk and lower limb muscles. RESULTS: Research participants received continuous pelvic assistance via RobUST, and manual trainer assistance at the knees to maintain standing. Participants were able to attempt all tasks. Free hands trunk perturbations resulted in greater load bearing-related sensory information (73% ipsilateral vertical loading), trunk displacement (57%), and muscle activation compared to hands on. Similarly, free hands stable standing with RobUST assistance-as-needed resulted in 8.5% larger bodyweight bearing, 112% larger trunk movement velocity, and higher trunk muscles activation compared to standing with hands on. Self-initiated trunk movements controlled by hands on showed 116% greater trunk displacement, 10% greater vertical ground reaction force, and greater ankle muscle activation compared to free hands. CONCLUSION: RobUST established a safe and challenging standing environment for individuals with SCI and has the potential to improve training paradigms and assessments of standing postural control.

A Deep-Learning Based Real-Time Prediction of Seated Postural Limits and Its Application in Trunk Rehabilitation.

Seated postural limit defines the boundary of a region such that for any excursions made outside this boundary a subject cannot return the trunk to the neutral position without additional external support. The seated postural limits can be used as a reference to provide assistive support to the torso by the Trunk Support Trainer (TruST). However, fixed boundary representations of seated postural limits are inadequate to capture dynamically changing seated postural limits during training. In this study, we propose a conceptual model of dynamic boundary of the trunk center by assigning a vector that tracks the postural-goal direction and trunk movement amplitude during a sitting task. We experimented with 20 healthy subjects. The results support our hypothesis that TruST intervention with an assist-as-needed force controller based on dynamic boundary representation could achieve more significant sitting postural control improvements than a fixed boundary representation. The second contribution of this paper is that we provide an effective approach to embed deep learning into TruST's real-time controller design. We have compiled a 3D trunk movement dataset which is currently the largest in the literature. We designed a loss function capable of solving the gate-controlled regression problem. We have proposed a novel deep-learning roadmap for the exploration study. Following the roadmap, we developed a deep learning architecture, modified the widely used Inception module, and then obtained a deep learning model capable of accurately predicting the dynamic boundary in real-time. We believe that this approach can be extended to other rehabilitation robots towards designing intelligent dynamic boundary-based assist-as-needed controllers.

Redistributing Ground Reaction Forces During Squatting Using a Cable-Driven Robotic Device.

Squatting is a dynamic task that is often done for strengthening and improving balance. Most squat training systems partially support body weight. However, one of the benefits of a squat exercise is efficiently distributing the body weight among the feet while maintaining stability. Several studies have shown how squatting and redistributing body weight among the feet can improve balance. The goals of this study are: (i) to show a robotic device that is transparent for studying human behavior during the squatting task, (ii) to investigate how ground reaction forces can be altered among the feet by applying a pelvic force during squatting. Seven able bodied adults underwent three squat conditions, squatting eight times per test. The first two conditions are a baseline set of squats followed by the third condition where participants received a constant lateral force on their pelvis. We use a cable-driven Robotic Upright Stand Trainer, RobUST, to deliver the lateral force on a pelvic belt. The lateral force was 5% of participants' body weight. Results show that a lateral force on the pelvis can significantly redistribute participants' ground reaction forces by increasing the symmetry index from 11.2% to 35.7% and increasing the lateral center of pressure amplitude from.07 to 0.18. The results also show that the pelvic lateral force did not add variability to the natural squat motion between repetitions, as measured by the coefficient of variability. These results are promising for future squat training paradigms to redistribute ground reaction forces and encourage specific weight distribution patterns.

Postural Control Strategies in Standing With Handrail Support and Active Assistance From Robotic Upright Stand Trainer (RobUST).

In people with severe neuromotor deficits of trunk and lower extremities, regaining balance in standing is often performed in rehabilitation with manual assistance, rigid body supports or by the use of handrails. To investigate and further expand postural control training in standing, we developed a Robotic Upright Stand Trainer (RobUST). In this study, we used RobUST to deliver trunk perturbations while simultaneously providing postural assistive forces on the pelvis in 10 able-bodied adults. Posture control responses with 'pelvic support' was then compared to 'no support' and 'hand supported' standing, with and without assistance from RobUST. We characterize postural imbalance with kinematic displacements and center of pressure (COP) outcomes, such as amplitude and root mean square of the excursions of COP. Surface electromyography (sEMG) was also applied to investigate muscle control. We additionally investigated ground reaction and handrail forces during standing to analyze how postural strategies and muscle mechanisms with 'pelvic support' via RobUST would differ from standing with 'no support' and with the 'handrail support'. Our results show that during perturbations, pelvic assistive support decreased kinematic and COP excursions compared to standing with no support. The pelvic assistance from RobUST showed similar level of COP changes as the use of handrail support but without reducing muscle activity or ground reaction forces. As expected, the maximum level of postural stability was observed when participants used the handrail and received pelvic assistive forces. In conclusion, RobUST demonstrates potential as a training device since it enhances postural balance without significantly removing muscular control mechanisms that are of interest in re-training postural control strategies in standing.

Continuous inter-limb coordination deficits in children with unilateral spastic cerebral palsy.

BACKGROUND: Continuous inter-limb coordination and the ability to offset perturbations to a movement pattern (i.e., stability) are important factors in efficient motor performance. Patients with movement disorders often show deficits in coordination and stability, although little is known about these features in children with cerebral palsy. The purpose of this study was to identify the continuous inter-limb coordination and stability deficits in children with cerebral palsy and determine if improvement occurs with upper extremity intervention. METHODS: Children with cerebral palsy participated in bimanual or unimanual intensive therapy. Continuous inter-limb coordination between the arms and between the more-affected arm and leg was evaluated using relative phase analysis during four gross motor tasks, including in-place marching and standing with asymmetric and symmetric arm swing. A control group of children with cerebral palsy and a group of typically developing children were also evaluated. FINDINGS: Children with cerebral palsy displayed coordination deficits compared to typically developing children (p<0.01), yet both groups presented similarly poor levels of stability (p=0.39). Compared to standing, adding legs to the task negatively impacted the coordination (p<0.01) and stability (p<0.01) of all children. Both groups improved coordination between the arms post-intervention (p<0.05 for all cases), however neither group improved stability (p>0.05 for all cases). INTERPRETATION: Relative phase analysis successfully provided a sensitive measurement of coordination and stability in pathologic and non-pathologic populations. Findings indicate that all children have difficulty producing consistent movement patterns and suggest that both bimanual and unimanual interventions can improve continuous coordination in children with cerebral palsy.

Exploring New Potential Applications for Hand Exoskeletons: Power Grip to Assist Human Standing.

Hand exoskeleton potential applications reach further than grasping or assistance during manipulation. In this paper, we present a preliminary study of how this technology can be applied in order to improve performance during standing to help the user to keep balance under perturbations. Non-impaired users wearing a hand exoskeleton gripping a hand rail were pushed by a cable-driven robot, so that their standing equilibrium was perturbed. The center of pressure, surface electromyography, and interaction force data were recorded in order to assess the performance of users and their postural strategy. The results showed that users could keep their balance with the same outcomes using their bare hands and the hand exoskeleton. However, when wearing the exoskeleton, a higher muscular activity was registered in hand flexor muscles. This is also supported by the grasping force, which shows that users stretched their hand more than expected when wearing the hand exoskeleton. This paper concludes that it is possible that the lack of tactile feedback could lead to over compensation in the grasping. Therefore, the next studies will aim to check whether this effect can be reversed by training users to wear the exoskeleton.

Promoting Functional and Independent Sitting in Children With Cerebral Palsy Using the Robotic Trunk Support Trainer.

Seated postural abilities are critical to functional independence and participation in children with cerebral palsy, Gross Motor Functional Classification System (GMFCS) levels III-IV. In this proof-of-concept study, we investigated the feasibility of a motor learning-based seated postural training with a robotic Trunk-Support-Trainer (TruST) in a longitudinal single-subject-design (13y, GMFCS IV), and its potential effectiveness in a group of 3 children (6-14y, GMFCS III-IV). TruST is a motorized-cable driven belt placed on the child's trunk to exert active-assistive forces when the trunk moves beyond stability limits. TruST-intervention addresses postural-task progression by tailoring the assistive-force fields to the child's sitting balance to train trunk control during independent short-sitting posture. TruST-intervention consisted of 2 training blocks of six 2hour-sessions per block (3 sessions per week). Pelvic strapping was required in the 1st block to prevent falls. As primary outcomes, we used the modified functional reach test, gross motor function measure-item set (GMFM-IS), Box & Blocks, and postural kinematics. After TruST-intervention children did not require pelvic strapping to prevent a fall, improved trunk stability during reaching (baseline = 5.49cm, 1week post-training = 16.38cm, 3mos follow-up = 14.63cm, ) and increased their sitting workspace (baseline = 127.55cm2, 1week post-training, = 409.92cm2, 3mos follow-up = 270.03cm2, ). Three children also improved in the GMFM-IS. In summary, our novel robotic TruST-intervention is feasible and can effectively maximize functional independent sitting in children with CP GMFCS III-IV.

Multimodality Imaging-Based Characterization of Regional Material Properties in a Murine Model of Aortic Dissection.

Chronic infusion of angiotensin-II in atheroprone (ApoE-/-) mice provides a reproducible model of dissection in the suprarenal abdominal aorta, often with a false lumen and intramural thrombus that thickens the wall. Such lesions exhibit complex morphologies, with different regions characterized by localized changes in wall composition, microstructure, and properties. We sought to quantify the multiaxial mechanical properties of murine dissecting aneurysm samples by combining in vitro extension-distension data with full-field multimodality measurements of wall strain and thickness to inform an inverse material characterization using the virtual fields method. A key advance is the use of a digital volume correlation approach that allows for characterization of properties not only along and around the lesion, but also across its wall. Specifically, deformations are measured at the adventitial surface by tracking motions of a speckle pattern using a custom panoramic digital image correlation technique while deformations throughout the wall and thrombus are inferred from optical coherence tomography. These measurements are registered and combined in 3D to reconstruct the reference geometry and compute the 3D finite strain fields in response to pressurization. Results reveal dramatic regional variations in material stiffness and strain energy, which reflect local changes in constituent area fractions obtained from histology but emphasize the complexity of lesion morphology and damage within the dissected wall. This is the first point-wise biomechanical characterization of such complex, heterogeneous arterial segments. Because matrix remodeling is critical to the formation and growth of these lesions, we submit that quantification of regional material properties will increase the understanding of pathological mechanical mechanisms underlying aortic dissection.

The robotic Trunk-Support-Trainer (TruST) to measure and increase postural workspace during sitting in people with spinal cord injury.

Study design: Cross-sectional study. Objectives: To measure and expand the sitting workspace of participants with spinal cord injury (SCI) with the Trunk-Support-Trainer (TruST). Setting: Columbia University. Methods: TruST is a motorized-cable belt placed around the torso. Participants performed maximal trunk excursions along eight directions, radiating in a star-shape, to define their seated postural limits and workspace area (cm2). TruST was configured to apply "assist-as-needed" forces when the trunk moved beyond these postural limits. Kinematics were collected to examine trunk control. The clinical features of the sample (n = 5) were documented by neurological injury, dynamometry, the American Spinal Injury Association Impairment Scale, and Spinal Cord Independence Measure-III. Results: Statistical significance was examined with paired t-tests. TruST successfully recreated the postural limits of participants and expanded their active sitting workspace (Mean: 123.3 ± SE: 42.8 cm2, p < 0.05). Furthermore, participants improved their trunk excursions to posterior (Mean: 5.1 ± SE: 0.8 cm, p < 0.01), right (Mean: 3.1 ± SE: 1.1 cm, p < 0.05), and left (Mean: 5.0 ± SE: 1.7 cm, p = 0.05) directions with TruST-force field. Conclusions: TruST can accurately define and expand the active seated workspace of people with SCI during volitional trunk movements. The capacity of TruST to deliver continuous force-feedback at the user's postural limits opens new frontiers to implement motor learning-based paradigms to retrain functional sitting in people with SCI.

The Seated Postural & Reaching Control Test in Cerebral Palsy: A Validation Study.

Aim: Children with moderate-severe cerebral palsy (CP) show postural control deficits that affect their daily activities, like reaching. The Seated Postural and Reaching Control test (SP&R-co) was developed to address the need for clinical measures that objectively identify dimensions of postural imbalance and corresponding reaching limitations in children with CP.Methods: SP&R-co documentation was designed for test validity and rater training. Rater and internal consistency were examined using Cronbach's α. Reference SP&R-co score sheets of children and rater's scores were used for absolute item-by-item, average inter-rater, and intra-rater reliability. Motor classification systems and performance tests were used for construct and concurrent validity.Results: The SP&R-co scoring showed acceptable-good consistency (α = 0.76-0.84). Interrelatedness of SP&R-co items was good-excellent (α = 0.82-0.97). The raters demonstrated fair, good, and excellent item-by-item reliability (ICC = 0.41-0.92). Inter-rater and intra-rater reliability of SP&R-co dimensions were good-excellent (ICC = 0.68-0.86 and ICC = 0.64-0.95, respectively). Construct and concurrent validity showed moderate-excellent correlations (r = 0.49-0.88).Conclusions: Results provide evidence that the SP&R-co is a reliable and valid test for therapists to objectively examine and quantify seated postural and reaching control in children with CP.

Characterization of chemoelastic effects in arteries using digital volume correlation and optical coherence tomography.

Understanding stress-strain relationships in arteries is important for fundamental investigations in mechanobiology. Here we demonstrate the essential role of chemoelasticity in determining the mechanical properties of arterial tissues. Stepwise stress-relaxation uniaxial tensile tests were carried out on samples of porcine thoracic aortas immersed in a hyperosmotic solution. The tissue deformations were tracked using optical coherence tomography (OCT) during the tensile tests and digital volume correlation (DVC) was used to obtain measurements of depth-resolved strains across the whole thickness of the tested aortas. The hyperosmotic solution exacerbated chemoelastic effects, and we were able to measure different manifestations of these chemoelastic effects: swelling of the media inducing a modification of its optical properties, and existence of a transverse tensile strain. For the first time ever to our best knowledge, 3D strains induced by chemoelastic effects in soft tissues were quantified thanks to the OCT-DVC method. Without doubt, chemoelasticity plays an essential role in arterial mechanobiology in vivo and future work should focus on characterizing chemoelastic effects in arterial walls under physiological and disease conditions. STATEMENT OF SIGNIFICANCE: Chemoelasticity, coupling osmotic phenomena and mechanical stresses, is essential in soft tissue mechanobiology. For the first time ever, we measure and analyze 3D strain fields induced by these chemoelastic effects thanks to the unique combination of OCT imaging and digital volume correlation.

Stand Trainer With Applied Forces at the Pelvis and Trunk: Response to Perturbations and Assist-As-Needed Support.

Functional rehabilitation of patients with spinal cord injury remains a current challenge. Training these patients to successfully stand is the first step towards restoring advanced skills such as walking. To address this need, we have developed a novel robotic stand trainer that can apply controlled forces on the trunk and the pelvis of a user, while controlling the knee angle. The stand trainer utilizes cables to apply assistive, resistive, or perturbation forces at the trunk, pelvis, and the knees, simultaneously. We have conducted a human study to validate the system. In this study, we applied multi-direction perturbation forces either at the pelvis or the trunk while assist-as-needed forces were applied to the other segment to keep balance. This study characterizes the human kinematics and measures of balance under the perturbations and assistive forces on the human body. Results shows that the level of force-field assistance (trunk or pelvis) directly affects the motion of the trunk, pelvis, and center of pressure. This provides a quantitative framework to restore balance in patients while providing assistance only when needed. This stand trainer can potentially free up therapists to attend to higher level rehabilitation goals and objectively assist patients to engage in interventions that challenge both their musculoskeletal and sensorimotor impairments.