20 research outputs found
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Delayed mechanical response to chemical kinetics in self- oscillating hydrogels driven by the BelousovâZhabotinsky reaction
We show experimentally that chemical and mechanical self-oscillations in
BelousovâZhabotinsky hydrogels are inherently asynchronous, that is, there is a detectable
delay in swellingâdeswelling response after a change in the chemical redox state. This
phenomenon is observable in many previous experimental studies and potentially has farreaching
implications for the functionality and response time of the material in future
applications; however, so far, it has not been quantified or reported systematically. Here,
we provide a comprehensive qualitative and quantitative description of the chemical-tomechanical
delay, and we propose to explain it as a consequence of the slow nonequilibrium swellingâdeswelling dynamics of the
polymer material. Specifically, standard hydrogel pieces are large enough that transport processes, for example, counterion migration
and water diffusion, cannot occur instantaneously throughout the entire gel piece, as opposed to previous theoretical considerations.
As a result, the volume response of the polymer to a chemical change may be governed by a characteristic response time, which leads
to the emergence of delay in mechanical oscillation. This is supported by our theoretical calculations
Annual report by The Japanese Association for Thoracic Surgery
All data regarding cardiovascular surgery and thoracic surgery were obtained from NCD, whereas data regarding esophageal surgery were collected from survey questionnaire by The Japanese Association for Thoracic Surgery forms because NCD of esophageal surgery does not include non-surgical cases (i.e., patients with adjuvant chemotherapy or radiation alone). Based on the change in data aggregation, there are several differences between this 2015 annual report and previous annual reports: the number of institutions decreased in each category from 578 (2014) to 568 (2015) in cardiovascular, from 762 to 714 in general thoracic and from 626 to 571 in esophageal surgery. Because more than two departments in the same institute registered their data to NCD individually, we cannot calculate correct number of institutes in this survey. Then, the response rate is not indicated in the category of cardiovascular surgery (Table 1), and the number of institutions classified by the operation number is also not calculated in the category of cardiovascular surgery (Table 2)
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Harmonic resonance and entrainment of propagating chemical waves by external mechanical stimulation in BZ self-oscillating hydrogels
Smart polymer materials that are non-living yet exhibit complex âlife-likeâ or biomimetic behaviours have been the focus of intensive research over the past decades, in the quest to broaden our understanding of how living systems function under nonequilibirum conditions. Discovery of how chemical and mechanical coupling can
generate resonance and entrainment with other cells or external environment is an important research question. We prepared Belousov-Zhabotinsky (BZ) self-oscillating hydrogels which convert chemical
energy to mechanical oscillation. By cyclically applying external mechanical stimulation to the BZ hydrogels, we found that when the
oscillation of a gel sample entered into harmonic resonance with the
applied oscillation during stimulation, the system kept a "memory"
of the resonant oscillation period and maintained it post stimulation,
demonstrating an entrainment effect. More surprisingly, by systematically varying the cycle length of the external stimulation, we revealed the discrete nature of the stimulation-induced resonance and
entrainment behaviours in chemical oscillations of BZ hydrogels, i.e.,
the hydrogels slow down their oscillation periods to the harmonics
of the cycle length of the external mechanical stimulation. Our theoretical model calculations suggest the important roles of the delayed mechanical response caused by reactant diffusion and solvent
migration in affecting the chemomechanical coupling in active hydrogels and consequently synchronising their chemical oscillations
with external mechanical oscillations