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Mesoporous CeO2 with flowerlike and cottonlike hierarchical structures were prepared through a facile solvothermal strategy by using cerium glycolate as precursors. In the whole synthesis process, the solvothermal reaction time plays an important role in morphology control. Structure and composition information of the corresponding cerium glycolate were obtained and compared by using X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Oriented attachment/anisotropic crystal growth with Ostwald ripening/multistep splitting process mechanism was proposed for the formation of the cerium glycolate precursor. The catalytic test results show that the final CeO2 microparticles exhibit enhanced CO conversion performance and better reduction behavior than pure ceria. Furthermore, as a good support, the synthesized Au/CeO2 samples demonstrate higher catalytic activity in the oxidation of CO than pure ceria. [ABSTRACT FROM AUTHOR]

In this work, a facile one-step solvothermal method with the assistance of hydrochloric acid has been developed to prepare well-dispersed CeO2 hollow nanospheres with high surface areas. The effects of hydrochloric acid on the growth mechanism and the size distribution are investigated in detail. It is found that the hydrogen ions expedite the nucleation rate of the CeO2 nuclei in the nucleation course, while the chloride ions accelerate the Ostwald ripening in the acidic environment. Both the hydrogen ion (H+) and the chloride ion (Cl−) are confirmed to play a key role in the formation of hollow morphology. Based on our experiments, a HCl-assisted oxidation–nucleation with an Ostwald ripening process mechanism was proposed. Furthermore, Au nanoparticles with a size of 2.5–6 nm were uniformly deposited on the surface of the ceria support by a simplified reduction process with sodium borohydride (NaBH4). The synthesized Au/CeO2 nanospheres exhibit a higher catalytic activity in CO oxidation than pure ceria nanospheres due to the existence of different Au species (metallic Au0 and positively charged Auδ+) and the strengthened interfacial interactions between the Au NPs and the ceria support. [ABSTRACT FROM AUTHOR]

A series of transition-metal-doped (Cu, Co, Ni, Mn) hierarchically mesoporous CeO2 nanoparticles have been fabricated through a simple solvothermal strategy. The effect of these doping metals on the morphology and the phase transformation of the Ce(HCOO)3 precursor was investigated. The specific order in which the doping metal cations (except Cu2+) are added during the synthesis process has a remarkable influence on the precursor morphology. By introducing these different metal cations, the doping composition can be adjusted freely. The XRD, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) results show the high homogeneity of the doped ceria and demonstrate that the transition metal cations have been incorporated into the CeO2 lattice. All of the doped ceria nanoparticles, especially the Cu2+-doped ceria product, exhibit improved reduction behavior and enhanced CO conversion performance. [ABSTRACT FROM AUTHOR]

Uniform CeO 2 nanoparticles with diameter in the range of 13–17 nm were synthesized through a one-step rapid hydrothermal strategy. The characterization indicated that (2 2 0) surface is the majority of the exposed CeO 2 surfaces. The reaction conditions including reactant amounts, reaction time were studied and optimized. The addition of hexamethylenetetramine is the key to the formation of (2 2 0)-dominated surface structure. The product shows better catalytic performance on CO conversion corresponding to the result of temperature-programmed reduction under a H 2 environment. [ABSTRACT FROM AUTHOR]

Background: Advanced prosthetic hands may embed nanosensors and microelectronics in their cosmetic skin. Heat influx may cause damage to these delicate structures. Protecting the integrity of the prosthetic hand becomes critical and necessary to ensure sustainable function. This study aims to mimic the sensorimotor control strategy of the human hand in perceiving nociceptive stimuli and triggering self-protective mechanisms and to investigate how similar neuromorphic mechanisms implemented in prosthetic hand can allow amputees to both volitionally release a hot object upon a nociceptive warning and achieve reinforced release via a bionic withdrawal reflex., Methods: A steady-state temperature prediction algorithm was proposed to shorten the long response time of a thermosensitive temperature sensor. A hybrid sensory strategy for transmitting force and a nociceptive temperature warning using transcutaneous electrical nerve stimulation based on evoked tactile sensations was designed to reconstruct the nociceptive sensory loop for amputees. A bionic withdrawal reflex using neuromorphic muscle control technology was used so that the prosthetic hand reflexively opened when a harmful temperature was detected. Four able-bodied subjects and two forearm amputees randomly grasped a tube at the different temperatures based on these strategies., Results: The average prediction error of temperature prediction algorithm was 8.30 ± 6.00%. The average success rate of six subjects in perceiving force and nociceptive temperature warnings was 86.90 and 94.30%, respectively. Under the reinforcement control mode in Test 2, the median reaction time of all subjects was 1.39 s, which was significantly faster than the median reaction time of 1.93 s in Test 1, in which two able-bodied subjects and two amputees participated. Results demonstrated the effectiveness of the integration of nociceptive sensory strategy and withdrawal reflex control strategy in a closed loop and also showed that amputees restored the warning of nociceptive sensation while also being able to withdraw from thermal danger through both voluntary and reflexive protection., Conclusion: This study demonstrated that it is feasible to restore the sensorimotor ability of amputees to warn and react against thermal nociceptive stimuli. Results further showed that the voluntary release and withdrawal reflex can work together to reinforce heat protection. Nevertheless, fusing voluntary and reflex functions for prosthetic performance in activities of daily living awaits a more cogent strategy in sensorimotor control., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Xie, Li, Chou, Li, Dai and Lan.)

The ability of a novel biorealistic hand prosthesis for grasp force control reveals improved neural compatibility between the human-prosthetic interaction. The primary purpose here was to validate a virtual training platform for amputee subjects and evaluate the respective roles of visual and tactile information in fundamental force control tasks. We developed a digital twin of tendon-driven prosthetic hand in the MuJoCo environment. Biorealistic controllers emulated a pair of antagonistic muscles controlling the index finger of the virtual hand by surface electromyographic (sEMG) signals from amputees' residual forearm muscles. Grasp force information was transmitted to amputees through evoked tactile sensation (ETS) feedback. Six forearm amputees participated in force tracking and holding tasks under different feedback conditions or using their intact hands. Test results showed that visual feedback played a predominant role than ETS feedback in force tracking and holding tasks. However, in the absence of visual feedback during the force holding task, ETS feedback significantly enhanced motor performance compared to feedforward control alone. Thus, ETS feedback still supplied reliable sensory information to facilitate amputee's ability of stable grasp force control. The effects of tactile and visual feedback on force control were subject-specific when both types of feedback were provided simultaneously. Amputees were able to integrate visual and tactile information to the biorealistic controllers and achieve a good sensorimotor performance in grasp force regulation. The virtual platform may provide a training paradigm for amputees to adapt the biorealistic hand controller and ETS feedback optimally.

Sensory feedback provides critical interactive information for the effective use of hand prostheses. Non-invasive neural interfaces allow convenient access to the sensory system, but they communicate a limited amount of sensory information. This study examined a novel approach that leverages a direct and natural sensory afferent pathway, and enables an evoked tactile sensation (ETS) of multiple digits in the projected finger map (PFM) of participants with forearm amputation non-invasively. A bidirectional prosthetic interface was constructed by integrating the non-invasive ETS-based feedback system into a commercial prosthetic hand. The pressure information of five fingers was encoded linearly by the pulse width modulation range of the buzz sensation. We showed that simultaneous perception of multiple digits allowed participants with forearm amputation to identify object length and compliance by using information about contact patterns and force intensity. The ETS enhanced the grasp-and-transport performance of participants with and without prior experience of prosthetic use. The functional test of transport-and-identification further revealed improved execution in classifying object size and compliance using ETS-based feedback. Results demonstrated that the ETS is capable of communicating somatotopically compatible information to participants efficiently, and improves sensory discrimination and closed-loop prosthetic control. This non-invasive sensory interface may establish a viable way to restore sensory ability for prosthetic users who experience the phenomenon of PFM.

Grasping hot objects may be harmful, and a warning of nociceptive temperature should be provided to prevent prosthetic hands from damage. This study developed a fast algorithm to predict the steady state temperature of grasped objects based on a thermoresistant sensor, and verified a bi-state sensory encoding strategy to inform either contact force or nociceptive temperature at prosthetic finger. Below the threshold, a buzz percept was used to encode fingertip force, and above the threshold, a tingling pain sensation was induced to warn harmful temperature. This sensory encoding mechanism was tested in one able-bodied subject with a psychophysical experimental paradigm. Results indicated that fast identification of the steady state temperature could be achieved in 0.75±0.00 s with an error of 8.3±6.0%. The subject was able to recognize whether the object temperature was above or below the threshold of nociceptive temperature with an average success rate of 98.2% and 97.0%, respectively. The action to release the tube could be executed in 0.80±0.32 s. The reaction time of successful identification and execution was 1.55 ± 0.32 s. The probability that a release reaction was triggered at the threshold of 60.0°C was calculated with tube temperatures varying from 30.0°C to 80.0°C. The 50% percentile point on the fitted stimulus-response curve corresponded to a temperature of 59.5°C, nearly identical to the internally set threshold. The psychophysical behavior test verified the sensory function to recognize and notify unsafe temperatures in real time.Clinical Relevance-The method of identifying and alerting nociceptive temperatures may restore the sensory ability of amputees to avoid potential damage of grasping hot objects with a prosthetic hand in activities of daily life.

In this paper, the ability of precision control of fingertip forces was investigated in an antagonistic cable-driven prosthetic hand with neuromorphic twin of muscles. Surface electromyography (sEMG) signals collected from able-bodied subjects' forearm were processed and used as alpha motor commands to drive the neuromorphic muscle models. A pair of antagonistic muscles were cascaded by two servo motors to control the index finger. Force control performance was tested by pressing a spring with a fixed stiffness using the fingertip, where forces with varying target levels were regulated with visual feedback. Two able-bodied subjects performed the precision force control task with the prosthetic index finger by sEMG signals and the intact hand. One subject was tested with force level changes of 0.1N, and another subject with force level changes of 0.2N. The ability of force regulation by the prosthetic finger was compared to that of the intact finger. Results showed that the overall root-mean-squares (RMS) error of the prosthetic finger was low, although significantly higher than the intact finger, 75% higher in subject 1 and 57% in subject 2. However, the correlation coefficient between the forces of prosthetic finger and intact finger was high, 75% for subject 1 and 84% for subject 2, respectively. This preliminary study is encouraging, illustrating the feasibility of accurate and stable control of different levels of fingertip forces by the prosthetic finger, which is comparable to that of the intact finger. This capability may allow the prosthetic hand for fine manipulation tasks, such as grasping brittle objects, or response to object slip during grasp.Clinical Relevance-This work attempts to restore the ability of a prosthetic hand for precision fingertip force control that may enrich the functionality for users in activities of daily living.

In this paper, a novel prototype of a cable-driven prosthetic hand with biorealisitic muscle property was developed. A pair of antagonistic muscles controlled the flexion and extension of the prosthetic index finger. Biorealistic properties of muscle were emulated using a neuromorphic model of muscle reflex in real time. The model output was coupled to a servo motor that tracked the computed muscle force. The servo motor was able to track model output within a frequency range from 0 to 8.29 (Hz) with a phase shift from 2 to 205 (deg). Surface electromyography signals collected from the amputee's forearm were used as α commands to drive the muscle model. With this prototype system, we evaluated its characteristics for force and stiffness control. Results of the force variability test showed that the standard deviation of fingertip force was linear to the mean fingertip force, indicating that force variability was proportional to the background force. At different levels of antagonistic co-contraction, the index finger and muscles displayed different levels of stiffness corresponding to the degree of co-activation. This prototype system showed the similar compliant behaviors of human limbs actuated with biological muscles. In further studies, this prototype system would be thoroughly evaluated for its biorealistic properties, and integrated with sensors to investigate feedback strategies of various sensory information for individuals with amputation. Clinical Relevance- This article established an antagonistic control of a cable-driven prosthetic hand with biorealistic properties of muscle reflex for application to individuals with amputation.

In this paper, copper-doped ceria oxides with different hollowness and size are fabricated by changing the Cu(2+) doping concentration in the mixed water-glycol system. Results show that the copper-doped CeO₂ oxides undergo a morphology transformation from the solid nanospheres to core-shell, then to hollow nanospheres with the increase of the Cu(2+) doping concentration. The corresponding size becomes smaller during this transfer process. The Cu(2+) doping induced acceleration in the nucleation and growth process is further investigated. The resultant Cu(2+)-doped CeO2 oxides exhibit enhanced CO conversion performance and better reduction behaviors.