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Pediatric gait rehabilitation and guidance strategies using robotic exoskeletons require a controller that encourages user volitional control and participation while guiding the wearer towards a stable gait cycle. Virtual constraint-based controllers have created stable gait cycles in bipedal robotic systems and have seen recent use in assistive exoskeletons. This paper evaluates a virtual constraint-based controller for pediatric gait guidance through comparison with a traditional time-dependent position tracking controller on a newly developed exoskeleton system. Walking experiments were performed with a healthy child subject wearing the exoskeleton under proportional-derivative control, virtual constraint-based control, and while unpowered. The participant questionnaires assessed the perceived exertion and controller usability measures, while sensors provided kinematic, control torque, and muscle activation data. The virtual constraint-based controller resulted in a gait similar to the proportional-derivative controlled gait but reduced the variability in the gait kinematics by 36.72% and 16.28% relative to unassisted gait in the hips and knees, respectively. The virtual constraint-based controller also used 35.89% and 4.44% less rms torque per gait cycle in the hips and knees, respectively. The user feedback indicated that the virtual constraint-based controller was intuitive and easy to utilize relative to the proportional-derivative controller. These results indicate that virtual constraint-based control has favorable characteristics for robot-assisted gait guidance.

This paper describes the development and evaluation of a novel, threshold-based gait event detection algorithm utilizing only one thigh inertial measurement unit (IMU) and unilateral, sagittal plane hip and knee joint angles. The algorithm was designed to detect heel strike (HS) and toe off (TO) gait events, with the eventual goal of detection in a real-time exoskeletal control system. The data used in the development and evaluation of the algorithm were obtained from two gait databases, each containing synchronized IMU and ground reaction force (GRF) data. All database subjects were healthy individuals walking in either a level-ground, urban environment or a treadmill lab environment. Inertial measurements used were three-dimensional thigh accelerations and three-dimensional thigh angular velocities. Parameters for the TO algorithm were identified on a per-subject basis. The GRF data were utilized to validate the algorithm's timing accuracy and quantify the fidelity of the algorithm, measured by the F1-Score. Across all participants, the algorithm reported a mean timing error of -41±20 ms with an F1-Score of 0.988 for HS. For TO, the algorithm reported a mean timing error of -1.4±21 ms with an F1-Score of 0.991. The results of this evaluation suggest that this algorithm is a promising solution to inertial based gait event detection; however, further refinement and real-time evaluation are required for use in exoskeletal control., (Copyright © 2024 by ASME.)

Exoskeleton technology has undergone significant developments for the adult population but is still lacking for the pediatric population. This paper presents the design of a hip-knee exoskeleton for children 6 to 11 years old with gait abnormalities. The actuators are housed in an adjustable exoskeleton frame where the thigh part can adjust in length and the hip cradle can adjust in the medial-lateral and posterior-anterior directions concurrently. Proper control of exoskeletons to follow nominal healthy gait patterns in a time-invariant manner is important for ease of use and user acceptance. In this paper, a hybrid zero dynamics (HZD) controller was designed for gait guidance by defining the zero dynamics manifold to resemble healthy gait patterns. HZD control utilizes a time-invariant feedback controller to create dynamically stable gaits in robotic systems with hybrid models containing both discrete and continuous dynamics. The effectiveness of the controller on the novel pediatric exoskeleton was demonstrated via simulation. The presented preliminary results suggest that HZD control provides a viable method to control the pediatric exoskeleton for gait guidance.

This paper presents an innovative design methodology for development of lower limb exoskeletons with the fabrication and experimental evaluation of prototype hardware. The proposed design approach is specifically conceived to be suitable for the pediatric population and uses additive manufacturing and a model parameterized in terms of subject anthropometrics to give a person-specific custom fit. The methodology is applied to create computer-aided design models using average anthropometrics of children 6-11 years old and using anthropometrics of an individual measured by the researchers. This demonstrates that the approach can scale to subject weight and height. A prototype exoskeleton is fabricated, which can actuate the hip and knee joints without restricting hip abduction-adduction motion. In order to test usability of the device and evaluate walking assistance, user effort is quantified in an assisted condition where the subject walks on a level treadmill with the exoskeleton powered. This is compared to an unassisted condition with the exoskeleton unpowered and a baseline condition with the subject not wearing the exoskeleton. Comparing assisted to baseline conditions, torque magnitudes increased at the hip and knee, mechanical energy generated increased at the hip but decreased at the knee, and muscle activations increased in the Vastus Lateralis but decreased in the Biceps Femoris. While the preliminary evidence for walking assistance is not entirely convincing for the tested conditions, the presented design methodology itself is promising as it has been successfully validated through the creation of computer-aided design models for children and fabrication of a serviceable exoskeleton prototype., (Copyright © 2021 by ASME.)

The nominal gait of each individual is unique and varies with the walking speed of the person. This poses a difficult problem for powered rehabilitative orthoses since control strategies often require a reference trajectory and give little control to the patient. This paper describes a simple control approach which applies torque resistive to joint movement that is unnatural for healthy individuals in the hip and knee joints during the swing phase of gait. The controller uses a configuration-dependent orthonormal basis to represent vectors in terms of components which are tangent and normal to healthy gait patterns for a continuum of gait speeds. The controller damps motion in the normal direction, thereby resisting movement which is unnatural for healthy individuals. With this control law, subjects are not restricted to a particular reference trajectory and have a large degree of volition over spatiotemporal gait parameters (e.g., stride length, swing time, and cadence). Experiments are conducted to check the feasibility of the control law in a provisional powered pediatric lower-limb orthosis. The gait guidance controller is used in conjunction with a human controller representing an individual with gait impairment. The main results compare gait shape quality when the gait guidance controller is enabled versus disabled, and show how the gait guidance controller is able to reshape gait to more closely resemble that of a healthy individual for various cadences.

7,12-Dimethylbenz(a)anthracene (DMBA):deoxyribonucleoside-adducts, from enzymatic hydrolysis of DNA from mouse skin exposed to [3H]DMBA in vivo, were analyzed by reverse-phase high-pressure liquid chromatography. Double-labeling studies showed that the adducts were qualitatively identical to those formed in mouse embryo cell cultures. These have been tentatively identified as bay-region anti-dihydrodiol epoxide: deoxyguanosine- and :deoxyadenosine adducts and a bay-region syn-dihydrodiol epoxide:deoxyadenosine-adduct (where the terms syn and anti define dihydrodiol-epoxides wherein the benzylic hydroxyl group and epoxide oxygen are cis or trans to one another, respectively). The relative amounts of individual adducts did not vary substantially with time or with the sex of the mice. However, the syn-dihydrodiol-epoxide:deoxyadenosine-adduct did increase with dose and constituted as much as 40% of the total DNA binding at high doses of DMBA. This is in contrast to the much lower (2 to 3%) levels of binding to deoxyadenosine residues in mouse skin reported for the less potent tumor initiator benzo(a)pyrene. The greater reactivity of DMBA with deoxyadenosine residues in mouse skin may play a role in determining its greater tumor initiating potential.

Neither butylated hydroxyanisole (BHA) nor butylated hydroxytoluene (BHT) significantly reduced overall 7,12-dimethylbenz[a]anthracene (DMBA)--DNA adduct formation in mouse embryo cell cultures. However, analysis of DMBA--DNA adducts by Servacel DHB chromatography and high-pressure liquid chromatography showed that treatment of cells with BHA, but not with BHT, resulted in a decreased contribution from the syn bay region dihydrodiol epoxide to overall binding.

The effect of butylated hydroxyanisole (BHA) administration on the hepatic monooxygenase system of nuclear and microsomal fraction was investigated in male mice. Addition of BHA to the diet significantly lowered the content of cytochrome P-450 in liver nuclei and increased the specific activity of NADPH-cytochrome c reductase and the content of cytochrome b5 in liver microsomes. Incubation of benzo[a]pyrene (BP) with liver nuclei from BHA-fed mice resulted in inhibition of binding of BP metabolites to nuclear macromolecules by 50% compared with control. However, there was no effect of BHA on the binding of BP metabolites to macromolecules when BP was incubated with added DNA and liver microsomes from BHA-fed mice. It has been postulated that modification of nuclear monooxygenases by BHA may play a role in the inhibitory effect of BHA on BP carcinogenesis.

7,12-Dimethylbenz(a)anthracene (DMBA):deoxyribonucleoside adducts, from enzymic hydrolyses of DNA from mouse embryo cells exposed in culture to [3H]DMBA, can be separated into two fractions on the basis of whether or not they bind to the phenyl boronic acid residues of Servacel DHB. This suggests that these two fractions of adducts are derived from anti and syn bay-region dihydrodiol-epoxides, respectively. The fluorescence spectra and interactions of the major components of these two fractions with borate ions substantiate this interpretation. These findings indicate that both syn- and anti-dihydrodiol-epoxides make a substantial contribution to DMBA binding to DNA in mouse embryo cells. For a given mouse embryo cell preparation, the relative contributions of each of these dihydrodiol-epoxides to DNA binding did not vary substantially with DMBA dose, with incubation time with DMBA, or in growing versus confluent cultures, although there were differences between one cell preparation and another.