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An ankle-foot orthosis (AFO) constructed as a single piece of isotropic elastic material is a commonly used assistive device that provides stability to the ankle joint of patients with spastic diplegic cerebral palsy. The AFO has asymmetric stiffness that restricts plantarflexion during the swing phase while it is flexible to allow dorsiflexion during the stance phase with a large deflection, including buckling originating from geometric nonlinearity. However, its mechanical implications have not been sufficiently investigated. This study aims to develop a computational model of an AFO considering geometric nonlinearity and examine AFO stiffness asymmetry during plantarflexion and dorsiflexion using physical experiments. Three-dimensional AFO mechanics with geometric nonlinearities were expressed using corotational triangle-element formulations that obeyed Kirchhoff-Love plate theory. Computational load tests for plantarflexion and dorsiflexion, using idealised AFOs with two different ankle-region designs (covering or not covering the apexes of the malleoli), showed that plantarflexion moment-ankle angle relationships were linear and dorsiflexion moment-ankle angle relationships were nonlinear; increases in dorsiflexion led to negative apparent stiffness of the AFO. Both ankle-region designs resisted both plantarflexion and dorsiflexion, and out-of-plane elastic energy was locally concentrated on the lateral side, resulting in large deflections during dorsiflexion. These findings give insight into appropriate AFO design from a mechanical viewpoint by characterising three-dimensional structural asymmetry and geometric nonlinearity.

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BACKGROUND: Robotic surgery improves minimally invasive interventions. However, it is challenging to determine the best gain settings for control of the endoscope. Providing the surgeon with the ability to manipulate the endoscope at an appropriate speed will likely improve the surgery by reducing the surgeon's stress. In this study, we validated the feasibility of a gain-tuning method in which the operator's brain activity is measured and used to evaluate stress levels. METHODS: We developed an endoscope-manipulation simulator and used functional near-infrared spectroscopy to measure the prefrontal cortical activity, while participants controlled the simulator at different gain values. RESULTS: The brain activation levels in the prefrontal cortex exhibited significant differences under different viewpoint motion gain conditions. CONCLUSIONS: The stress-related brain activity was significantly reduced at specific gains, indicating that the brain activity evaluation would be useful to determine the parameters related to the operator's feelings.

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OBJECTIVE: To perform an effective and safe nerve block, the needle must be placed near the target nerve while avoiding nerve damage. Our objective was to conduct an animal study to determine whether changes in electrical impedance (EI) could be used to guide the needle and achieve a safe and accurate nerve block. METHODS: We measured the EI of rabbit tissues during ultrasound-guided sciatic nerve block using a bipolar needle via the in-plane needle approach. The EI values and needle track on the ultrasound monitor were video-recorded. When there was a change in the EI, the needle advancement was stopped, and a stained anesthetic was injected. Subsequently, the animals were euthanized, and the anesthetic-stained tissue was examined via dissection, while the other tissue was preserved at -80°C for microscopic analysis. RESULTS: The EI remained stable as the needle advanced through the muscle (extraneural); however, it markedly decreased when the needle tip contacted the nerve or slightly punctured the epineurium (paraneural). The mean extra- and paraneural EIs were 4.92 ± 1.31 kΩ (range, 2.39-9.67 kΩ) and 2.86 ± 0.96 kΩ (range, 1.66-5.13 kΩ), respectively. Examination of the dissections and cryostat sections showed anesthetic delivery around the nerve. CONCLUSIONS: EI values differed between extra- and paraneural sites, and monitoring these values allowed prediction of the needle tip location with respect to the target nerve. Real-time EI measurement could improve the nerve block.

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BACKGROUND: Age-related changes of human gait characteristics associated with muscle weakness have been reported in previous studies. Human gait is considered as a cyclic motion adapted to individual body-characteristics and the surrounding-environment based on motion criteria. Based on this hypothesis, elderly gait characteristics may be caused by an adaptation to muscle weakness. RESEARCH QUESTION: What role does gait adaptation to muscle weakness play in the development of elderly gait, and what criteria are used in elderly gait adaptation? METHODS: We examined the effects of gait adaptation to muscle weakness on steady gait characteristics using computational forward dynamics simulation with a two-dimensional neuro-musculo-skeletal model. For gait adaptation, we tested two motion criteria: (i) energy cost minimization, which is a widely used criterion for healthy adults; and (ii) energy rate minimization, based on existing measurements of elderly gait characteristics. RESULTS: Progression of muscle weakness enhanced the reduction of joint angle motion and minimum toe clearance, and finally resulted in falling. Gait adaptation to muscle weakness successfully formed stable walking patterns regardless of motion criteria, even at muscle weakness of 30 %, which represents a moderate degree of elderly muscle weakness. When criterion (i) was used, the time courses of joint motion were similar to those of healthy adults and a relatively high level of muscle activation was found in the whole gait cycle to compensate for muscle weakness. When criterion (ii) was used, the muscle activity level was lower than that of criterion (i) to minimize the energy rate, and the constructed gait successfully captured the characteristics of elderly gait reported in previous studies. SIGNIFICANCE: These findings suggest that gait adaptation to muscle weakness plays an essential role in the development of stable gait characteristics, whereas elderly people might use a different motion criterion compared with healthy adults in gait adaptation.

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In this study, we computationally assess the effects of the distributed fibre orientation in the periodontal ligament (PDL) on mechanical responses of the tooth-PDL complex. An idealised axial-symmetric geometry of a tooth-PDL complex was constructed. The fibre orientation in the PDL was modelled as a trigonometric function based on anatomical knowledge, and the PDL was modelled as a transversely isotropic hyperelastic material dependent on fibre orientations. Parametric studies of the fibre orientation on the mechanical responses of the tooth-PDL complex were conducted. Obtained results showed that the anatomically consistent fibre orientation functions as a supporting structure against not only vertical but also horizontal loads.

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Understanding the viscoelastic properties of biological tissues is important because they can reveal tissue structure. This study analyzes the viscoelastic properties of soft biological tissues using a fractional dynamics model. We conducted a dynamic viscoelastic test on several porcine samples, i.e., liver, breast, and skeletal muscle tissues, using a plate-plate rheometer. We found that some soft biological tissues have non-minimum phase properties, i.e., the relationship between compliance and phase delay is not uniquely related to the non-integer derivative order in the fractional dynamics model. The experimental results show that the actual phase delay is larger than that estimated from compliance. We propose an empirical model to represent these non-minimum phase properties; a fractional Maxwell model with the fractional Hilbert transform term is proposed. The model and experimental results were highly correlated in terms of compliance and phase diagrams, and complex mechanical impedance. We also show that the amount of additional phase delay, defined as the increase in actual phase delay compared to that estimated from compliance, differs with tissue type.

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The anterior cruciate ligament (ACL) comprises an anteromedial bundle (AMB) and posterolateral bundle (PLB). Cadaver studies showed that this double-bundle structure exhibits reciprocal function during passive knee flexion-extension, with the PLB taut in knee extension and the AMB taut in knee flexion. In vivo measurements indicated that straight-line lengths of both bundles decrease with increasing knee-flexion angle (KFA). To interpret these seemingly conflicting facts, we developed a computational ACL model simulating the kinematics of the double-bundle structure during passive knee flexion-extension. Tibial and femoral shapes were reconstructed from computed-tomography images of a cadaver knee and used to construct an idealized model of an ACL including its bundles at the tibiofemoral joint. The ACL deformations at various KFAs were computed by finite element analysis. Results showed that the PLB was stretched in knee extension (KFA = 0∘) and slackened with increasing KFA. The AMB was stretched in knee extension (KFA = 0∘) and remained stretched on the medial side when the knee flexed (KFA = 90∘), but its straight-line length decreased with increasing KFA. These findings are consistent with cadaver and in vivo experimental results and highlight the usefulness of a computational approach for understanding ACL functional anatomy.

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Caregivers hug their infants to express affection and joy. However, it remains unknown how infants react to being hugged. Here we examined heart rate responses in first-year infants during a hug, hold, and tight hug from parents. Infants older than four months showed an increased R-R interval (RRI) during a hug, indicating reduced heart rates and pronounced parasympathetic activity. Few head movements predicted a higher RRI increase in infants during a parental hug compared with that during a hold and tight hug. Infants did not show an increased RRI during a hug from a female stranger. Infants younger than four months did not show RRI increase during parental hug but exhibited a decreased RRI correlated with contact pressure. Parents showed an increased RRI during hugging their infants. These results suggest the parent-infant hug underlies the parent-infant bonding and psychophysiological development of infants.

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GOAL: To realize intuitive, minimally invasive surgery, surgical robots are often controlled using master-slave systems. However, the surgical robot's structure often differs from that of the human body, so the arrangement between the monitor and master must reflect this physical difference. In this study, we validate the feasibility of an embodiment evaluation method that determines the arrangement between the monitor and master. In our constructed cognitive model, the brain's intraparietal sulcus activates significantly when somatic and visual feedback match. Using this model, we validate a cognitively appropriate arrangement between the monitor and master. METHODS: In experiments, we measure participants' brain activation using an imaging device as they control the virtual surgical simulator. Two experiments are carried out that vary the monitor and hand positions. CONCLUSION: There are two common arrangements of the monitor and master at the brain activation's peak: One is placing the monitor behind the master, so the user feels that the system is an extension of his arms into the monitor; the other arranges the monitor in front of the master, so the user feels the correspondence between his own arm and the virtual arm in the monitor. SIGNIFICANCE: From these results, we conclude that the arrangement between the monitor and master impacts embodiment, enabling the participant to feel apparent posture matches in master-slave surgical robot systems.

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This paper presents a feasibility study of a brain-machine interface system to assist repetitive facilitation exercise. Repetitive facilitation exercise is an effective rehabilitation method for patients with hemiplegia. In repetitive facilitation exercise, a therapist stimulates the paralyzed part of the patient while motor commands run along the nerve pathway. However, successful repetitive facilitation exercise is difficult to achieve and even a skilled practitioner cannot detect when a motor command occurs in patient's brain. We proposed a brain-machine interface system for automatically detecting motor commands and stimulating the paralyzed part of a patient. To determine motor commands from patient electroencephalogram (EEG) data, we measured the movement-related cortical potential (MRCP) and constructed a support vector machine system. In this paper, we validated the prediction timing of the system at the highest accuracy by the system using EEG and MRCP. In the experiments, we measured the EEG when the participant bent their elbow when prompted to do so. We analyzed the EEG data using a cross-validation method. We found that the average accuracy was 72.9% and the highest at the prediction timing 280 ms. We conclude that 280 ms is the most suitable to predict the judgment that a patient intends to exercise or not.

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Gait training robots are useful for changing gait patterns and decreasing risk of trip. Previous research has reported that decreasing duration of the assistance or guidance of the robot is beneficial for efficient gait training. Although robotic intermittent control method for assisting joint motion has been established, the effect of the robot intervention timing on change of toe clearance is unclear. In this paper, we tested different timings of applying torque to the knee, employing the intermittent control of a gait training robot to increase toe clearance throughout the swing phase. We focused on knee flexion motion and designed a gait training robot that can apply flexion torque to the knee with a wire-driven system. We used a method of timing detecting for the robot conducting torque control based on information from the hip, knee, and ankle angles to establish a non-time dependent parameter that can be used to adapt to gait change, such as gait speed. We carried out an experiment in which the conditions were four time points: starting the swing phase, lifting the foot, maintaining knee flexion, and finishing knee flexion. The results show that applying flexion torque to the knee at the time point when people start lifting their toe is effective for increasing toe clearance in the whole swing phase.

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Static stretching is widely performed to decrease muscle tone as a part of rehabilitation protocols. Finding out the optimal duration of static stretching is important to minimize the time required for rehabilitation therapy and it would be helpful for maintaining the patient's motivation towards daily rehabilitation tasks. Several studies have been conducted for the evaluation of static stretching; however, the recommended duration of static stretching varies widely between 15-30 s in general, because the traditional methods for the assessment of muscle tone do not monitor the continuous change in the target muscle's state. We have developed a method to monitor the viscoelasticity of one muscle continuously during static stretching, using a wearable indentation tester. In this study, we investigated a suitable signal processing method to detect the time required to change the muscle tone, utilizing the data collected using a wearable indentation tester. By calculating a viscoelastic index with a certain time window, we confirmed that the stretching duration required to bring about a decrease in muscle tone could be obtained with an accuracy in the order of 1 s.

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PURPOSE: Our purpose is to develop a system based on image processing methods that can inform users of the angular relationship between the needle and the forceps. The user thereby adjusts their needle grasping posture according to the angle information, which leads to an improvement in suturing accuracy. METHODS: The system prototype consists of a camera and an image processing computer. The image captured by the camera is input to the computer, and then, the angular relationship between the forceps and needle is calculated via image processing. Then, the system informs the user of the calculated angular relationship between the needle and forceps in real time. To evaluate whether the system improves suturing accuracy, we invited 12 participants to enroll in an experiment based on a suturing task. RESULTS: The experimental results illustrate that the system allows participants to easily adjust the positional relationship between the needle and the forceps and that this adjusted angular relationship leads to higher suturing accuracy. CONCLUSIONS: Adjustment to holding the needle at a right angle before insertion has a critical effect on suturing quality. Therefore, we developed a system that informs the user of the angular relationship between the needle and the forceps. The results of the evaluation show that the system significantly improves the suturing accuracy of participants via informing them of the angle.

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Understanding the rheological properties of soft biological tissue is a key issue for mechanical systems used in the health care field. We propose a simple empirical model using fractional dynamics and exponential nonlinearity (FDEN) to identify the rheological properties of soft biological tissue. The model is derived from detailed material measurements using samples isolated from porcine liver. We conducted dynamic viscoelastic and creep tests on liver samples using a plate-plate rheometer. The experimental results indicated that biological tissue has specific properties: (i) power law increase in the storage elastic modulus and the loss elastic modulus of the same slope; (ii) power law compliance (gain) decrease and constant phase delay in the frequency domain; (iii) power law dependence between time and strain relationships in the time domain; and (iv) linear dependence in the low strain range and exponential law dependence in the high strain range between stress-strain relationships. Our simple FDEN model uses only three dependent parameters and represents the specific properties of soft biological tissue.

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PURPOSE: We developed and evaluated a visual compensation system that allows surgeons to visualize obscured regions in real time, such that the surgical instrument appears virtually transparent. METHODS: The system consists of two endoscopes: a main endoscope to observe the surgical environment, and a supporting endoscope to render the region hidden from view by surgical instruments. The view captured by the supporting endoscope is transformed to simulate the view from the main endoscope, segmented to the shape of the hidden regions, and superimposed to the main endoscope image so that the surgical instruments look transparent. A prototype device was benchmarked for processing time and superimposition rendering error. Then, it was evaluated in a training environment with 22 participants performing a backhand needle driving task with needle exit point error as the criterion. Lastly, we conducted an in vivo study. RESULTS: In the benchmark, the mean processing time was 62.4 ms, which was lower than the processing time accepted in remote surgeries. The mean superimposition error of the superimposed image was 1.4 mm. In the training environment, needle exit point error with the system decreased significantly for experts compared with the condition without the system. This change was not significant for novices. In the in vivo study, our prototype enabled visualization of needle exit points during anastomosis. CONCLUSION: The benchmark suggests that the implemented system had an acceptable performance, and evaluation in the training environment demonstrated improved surgical task outcomes in expert surgeons. We will conduct a more comprehensive in vivo study in the future.

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Elderly people are at risk of tripping because of their narrow range of articular motion. To avoid tripping, gait training that improves their range of articular motion would be beneficial. In this study we propose a gait-training robot that applies a torque during the pre-swing phase to achieve this goal. We investigated the relationship between magnitude of applied torque and change in the range of knee-articular motion while walking before and after the application of this torque. We developed a wearable robot and carried out an experiment on human participants in which a motor pulls a string embedded on the robotic frame, applying torque in the pre-swing phase for a period of 20 [s]. Before and after applying torque the participant walked normally for 15 [s] without interference from the robot. We found that knee flexion angle increased after applying the torque if the torque was within the range of approximately 6-8 [Nm]. Therefore, we were able to verify that a new range of knee articular motion can be learned through application of torque.

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PURPOSE: Endoscopic surgery is performed under a horizontal view in comparison to the vertical view that is associated with open surgery. We developed an endoscopic pseudo-viewpoint alternation system with out any scope action. We investigate the effect of this novel system on forceps manipulation among expert pediatric surgeons. METHODS: Six expert pediatric surgeons performed a Nissen wrap in a fundoplication simulator either with or without this system. The constructed Nissen wrap was evaluated. The total path length and the average velocity of the forceps were also analyzed. RESULTS: The times required either with or without this system were 587.5 ± 122.7 and 634.0 ± 212.4 s (p = 0.45), respectively. The total path lengths of right and left forceps either with or without this system were 12,309 ± 2495.5 and 15,726 ± 5649.6 mm (p = 0.07), 10,091 ± 2439.2 and 12,575 ± 5511.1 mm (p = 0.11), respectively. The average velocity of the right and left forceps with or without this system were 26.9 ± 5.29 and 31.6 ± 1.62 mm/s (p = 0.04), 21.6 ± 2.48 and 25.5 ± 6.48 mm/s (p = 0.15), respectively. There was no significance in the suture balance and suture interval. CONCLUSION: The endoscopic pseudo-viewpoint alternation system thus made it possible for expert pediatric surgeons to carry out slow and economical forceps manipulation. These effects make it possible for surgeons to perform safe and precise surgery, thus leading to a shortening of operation time.

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PURPOSE: we present an evaluation method to qualify the embodiment caused by the physical difference between master-slave surgical robots by measuring the activation of the intraparietal sulcus in the user's brain activity during surgical robot manipulation. We show the change of embodiment based on the change of the optical axis-to-target view angle in the surgical simulator to change the manipulator's appearance in the monitor in terms of hand-eye coordination. The objective is to explore the change of brain activation according to the change of the optical axis-to-target view angle. METHODS: In the experiments, we used a functional near-infrared spectroscopic topography (f-NIRS) brain imaging device to measure the brain activity of the seven subjects while they moved the hand controller to insert a curved needle into a target using the manipulator in a surgical simulator. The experiment was carried out several times with a variety of optical axis-to-target view angles. RESULTS: Some participants showed a significant peak (P value = 0.037, F-number = 2.841) when the optical axis-to-target view angle was 75°. CONCLUSIONS: The positional relationship between the manipulators and endoscope at 75° would be the closest to the human physical relationship between the hands and eyes.

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This paper presents a method to evaluate the hand-eye coordination of the master-slave surgical robot by measuring the activation of the intraparietal sulcus in users brain activity during controlling virtual manipulation. The objective is to examine the changes in activity of the intraparietal sulcus when the user's visual or somatic feedback is passed through or intercepted. The hypothesis is that the intraparietal sulcus activates significantly when both the visual and somatic sense pass feedback, but deactivates when either visual or somatic is intercepted. The brain activity of three subjects was measured by the functional near-infrared spectroscopic-topography brain imaging while they used a hand controller to move a virtual arm of a surgical simulator. The experiment was performed several times with three conditions: (i) the user controlled the virtual arm naturally under both visual and somatic feedback passed, (ii) the user moved with closed eyes under only somatic feedback passed, (iii) the user only gazed at the screen under only visual feedback passed. Brain activity showed significantly better control of the virtual arm naturally (p<;0.05) when compared with moving with closed eyes or only gazing among all participants. In conclusion, the brain can activate according to visual and somatic sensory feedback agreement.

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This paper presents a robotic gait training system for neuro-motor rehabilitation of hemiplegic stroke survivors. The system is composed of a treadmill consisting of two separated belts, footprint array sensor attached below each belt for gait data acquisition, and an electroencephalography (EEG) device for monitoring brain activities during gait training. The split belt treadmill allow physical therapists to set different treadmill belt velocities to modify physical workload of the patients during walking, thus being able to better improve the symmetry of gait phases between affected and unaffected (sound) legs in comparison with conventional treadmills where there is only one single belt. In contrast to in-shoe pressure sensors, the under-belt footprint sensor array designed in this study not only reduces the preparation complexity of gait training but also collects more gait data for motion analysis. Recorded EEG is segmented synchronously with gait-related events. The processed EEG data can be used for monitoring brain-activities during gait training, providing a neurological approach for motion assessment. One subject with simulated stroke using an ankle-foot orthosis participated in this study. Preliminary results indicate the feasibility of the proposed system to improve gait function and monitor neuro-motor recovery.

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