Planar Soft Functional Periodic Structures Exploiting Instabilities and Large Deformation

Soft materials can significantly change their shape and volume when subjected to various stimuli. Materials with deliberately designed periodic microstructure have long been proved to be characterized by properties that may exceed those of the corresponding bulk material. Though traditionally avoided as modes of failure, mechanical instabilities have recently been exploited to design systems with novel and tunable functionalities. Interestingly, the studies I conducted during my PhD show that the combination of soft materials, periodic structures, mechanical instabilities and large deformation give us the opportunity to design materials and structures with enhanced functionality. In this thesis, I present a systematic study on the response of planar sof୴ functional materials which use their large deformation and geometric rearrangements to dramatically change their properties. In particular, I used a combination of experiments and numerical simulations to investigate the effect of important parameters, such as pore shape, hole arrangement and loading conditions. With the fundamental understanding I gained, I developed a novel class of planar soft periodic materials with enhanced material functionalities such as tunable phononic band-gap, spontaneous symmetry breaking, chirality amplification and energy trapping. Remarkably, since the continuous 2D soft and porous structures I studied take advantage of reversible and scale-independent mechanisms, the proposed designs can be applied over a wide range of length scales. The studies presented here show that by mastering the interplay between the microstructure of soft periodic structures and their large deformation behavior, novel materials with enhanced funcEngineering and Applied Sciences - Engineering Science

Shape programmable structures

Shape programmable structures and devices are typically fabricated using shape memory materials and are attracting increasing interest because they can be designed to have multiple properties and functions. However, shape memory materials, such as NiTi-based metal alloys and block copolymers, suffer from severe structural -fatigue due to the microstructural changes occurring during each thermal cycle. Moreover, there is only a limited set of shape memory material systems, limiting the possible number of applications for reconfigurable structures and devices. To overcome all these issues and expand the range of applications of shape programmable structures, we designed a library of 2D elastic structures that can be programmed to retain multiple shapes simply by applying a force. The building block of our structure consists of a unit comprising interconnected elastic arches and we demonstrate both numerically and experimentally that geometric nonlinearity and snap-through instabilities can be effectively exploited to reconfigure the system into multiple shapes. Because our system exploits mechanical instability, our findings can be extended to different materials and length scales, outlining a general strategy to effectively design a new generation of shape programmable structures

Compaction through Buckling in 2D Periodic, Soft and Porous Structures: Effect of Pore Shape

Soft cellular structures that comprise a solid matrix with a square array of holes open avenues for the design of novel soft and foldable structures. Our results demonstrate that by simply changing the shape of the holes the response of porous structure can be easily tuned and soft structures with optimal compaction can be designed.Engineering and Applied Science

Harnessing instability to control wave propagation in phononic crystals and acoustic metamaterials

Artificially structured composite materials have the ability to manipulate the propagation of elastic waves due to the existence of band gaps, i.e., frequency ranges of strong wave attenuation. However, most configurations proposed to date cannot be tuned after the manufacturing process. We propose new strategies using elastic buckling mechanisms to design novel devices with in-situ adaptive properties that can be reversibly tuned. Buckling and large deformations can be effectively exploited to reversibly tune not only the width and location of band gaps, but also the directional preferences of the wave propagation, even for low-frequency elastic waves. Our proof-of-concept demonstrations also indicate that the proposed mechanisms work robustly over a wide range of length scales, opening avenues for the design of smart systems for applications, such as vibration/noise reduction, wave guiding, frequency modulation, and acoustic imaging

Dietary Isothiocyanates: Novel Insights into the Potential for Cancer Prevention and Therapy

Diet plays an important role in health. A high intake of plant chemicals such as glucosinolates/isothiocyanates can promote optimal health and decrease the risk of cancer. Recent research has discovered more novel mechanisms of action for the effects of isothiocyanates including the modulation of tumor microenvironment, the inhibition of the self-renewal of stem cells, the rearrangement of multiple pathways of energy metabolism, the modulation of microbiota, and protection against Helicobacter pylori. However, the hormetic/biphasic effects of isothiocyanates may make the recommendations complicated. Isothiocyanates possess potent anti-cancer activities based on up-to-date evidence from in vitro and in vivo studies. The nature of hormesis suggests that the benefits or risks of isothiocyanates largely depend on the dose and endpoint of interest. Isothiocyanates are a promising class of cancer-preventative phytochemicals, but researchers should be aware of the potential adverse (and hormetic) effects. In the authors’ opinion, dietary isothiocyanates are better used as adjunctive treatments in combination with known anti-cancer drugs. The application of nano-formulations and the delivery of isothiocyanates are also discussed in this review

Complex Ordered Patterns in Mechanical Instability Induced Geometrically Frustrated Triangular Cellular Structures

Geometrical frustration arises when a local order cannot propagate throughout the space because of geometrical constraints. This phenomenon plays a major role in many systems leading to disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that buckling induces complex ordered patterns which can be tuned by controlling the porosity of the structures. Our analysis reveals that the connected geometry of the cellular structure plays a crucial role in the generation of ordered states in this frustrated system.Engineering and Applied SciencesPhysic

Distinct small RNAs are expressed at different stages of Phytophthora capsici and play important roles in development and pathogenesis

Small RNAs (sRNAs) are important non-coding RNA regulators that play key roles in the development and pathogenesis of plant pathogens, as well as in other biological processes. However, whether these abundant and varying sRNAs are involved in Phytophthora development or infection remains enigmatic. In this study, sRNA sequencing of 4 asexual stages of Phytophthora capsici (P. capsici), namely, as mycelia (HY), sporangia (SP), zoospores (ZO), cysts (CY), and pepper infected with P. capsici (IN), were performed, followed by sRNA analysis, microRNA (miRNA) identification, and miRNA target prediction. sRNAs were mainly distributed at 25–26 nt in HY, SP, and ZO but distributed at 18–34 nt in CY and IN. 92, 42, 176, 39, and 148 known miRNAs and 15, 19, 54, 13, and 1 novel miRNA were identified in HY, SP, ZO, CY, and IN, respectively. It was found that the expression profiles of known miRNAs vary greatly at different stages and could be divided into 4 categories. Novel miRNAs mostly belong to part I. Gene ontology (GO) analysis of known miRNA-targeting genes showed that they are involved in the catalytic activity pathway, binding function, and other biological processes. Kyoto Encyclopedia of Gene and Genome (KEGG) analysis of novel miRNA-targeting genes showed that they are involved in the lysine degradation pathway. The expression of candidate miRNAs was validated using quantitative reverse transcription–polymerase chain reaction (qRT–PCR), and miRNAs were downregulated in PcDCL1 or PcAGO1 mutants. To further explore the function of the detected miRNAs, the precursor of a novel miRNA, miR91, was knockout by CRISPR-Cas9, the mutants displayed decreased mycelial growth, sporangia production, and zoospore production. It was found that 503142 (Inositol polyphosphate 5-phosphatase and related proteins) can be predicted as a target of miR91, and the interaction between miR91 and 503142 was verified using the tobacco transient expression system. Overall, our results indicate that the diverse and differentially expressed sRNAs are involved in the development and pathogenesis of P. capsici

Multi-Patterned Dynamics of Mitochondrial Fission and Fusion in a Living Cell

Mitochondria are highly-dynamic organelles, but it is challenging to monitor quantitatively their dynamics in a living cell. Here we developed a novel approach to determine the global occurrence of mitochondrial fission and fusion events in living human epithelial cells (Hela) and mouse embryonic fibroblast cells (MEF). Distinct patterns of sequential events including fusion followed by fission (Fu-Fi), the so-called “kiss and run” model previously described, fission followed by fusion (Fi-Fu), fusion followed by fusion (Fu-Fu), and fission followed by fission (Fi-Fi) were observed concurrently. The paired events appeared in high frequencies with short lifetimes and large sizes of individual mitochondria, as compared to those for unpaired events. The high frequencies of paired events were found to be biologically significant. The presence of membrane uncoupler CCCP enhanced the frequency of paired events (from both Fu-Fi and Fi-Fu patterns) with a reduced mitochondrial size. Knock-out of mitofusin protein Mfn1 increased the frequency of fission with increased lifetime of unpaired events whereas deletion of both Mfn1 and Mfn2 resulted in an instable dynamics. These results indicated that the paired events were dominant but unpaired events were not negligible, which provided a new insight into mitochondrial dynamics. In addition to kiss and run model of action, our data suggest that, from a global visualization over an entire cell, multiple patterns of action appeared in mitochondrial fusion and fission

N6-methyloxyadenine-mediated detoxification and ferroptosis confer a trade-off between multi-fungicide resistance and fitness

ABSTRACTMulti-fungicide resistance (MFR) is a serious environmental problem, which results in the excessive use of fungicides. Fitness penalty, as a common phenomenon in MFR, can partially counteract the issue of resistance due to the weakened vigor of MFR pathogens. Their underlying mechanism and relationship remain unexplained. By Oxford Nanopore Technologies sequencing and dot blot, we found that N6-methyloxyadenine (6mA) modification, the dominate epigenetic marker in Phytophthora capsici, was significantly altered after MFR emerged. Among the differently methylated genes, PcGSTZ1 could efficiently detoxify SYP-14288, a novel uncoupler, through complexing the fungicide with glutathione and induce MFR. Interestingly, PcGSTZ1 overexpression was induced by elevated 6mA levels and chromatin accessibility to its genomic loci. Moreover, the overexpression led to reactive oxygen species burst and ferroptosis in SYP-14288-resistant mutants, which enhanced the resistance and induced fitness penalty in P. capsici through triggering low energy shock adaptive response. Furthermore, this study revealed that the 6mA-PcGSTZ1-ferroptosis axis could mediate intergenerational resistance memory transmission and enabled adaptive advantage to P. capsici. In conclusion, the findings provide new insights into the biological role of 6mA as well as the mechanisms underlying the trade-off between MFR and fitness. These could also benefit disease control through the blockade of the epigenetic axis to resensitize resistant isolates.IMPORTANCEN6-methyloxyadenine (6mA) modification on DNA is correlated with tolerance under different stress in prokaryotes. However, the role of 6mA in eukaryotes remains poorly understood. Our current study reveals that DNA adenine methyltransferase 1 (DAMT1)-mediated 6mA modification at the upstream region of GST zeta 1 (GSTZ1) is elevated in the resistant strain. This elevation promotes the detoxification uncoupler and induces multifungicide resistance (MFR). Moreover, the overexpression led to reactive oxygen species burst and ferroptosis in SYP-14288-resistant mutants, which enhanced the resistance and induced fitness penalty in Phytophthora capsici through triggering low energy shock adaptive response. Furthermore, this study revealed that the 6mA-PcGSTZ1-ferroptosis axis could mediate intergenerational resistance memory transmission and enabled adaptive advantage to P. capsici. Overall, our findings uncover an innovative mechanism underlying 6mA modification in regulating PcGSTZ1 transcription and the ferroptosis pathway in P. capsici

Human Theta Burst Stimulation Combined with Subsequent Electroacupuncture Increases Corticospinal Excitability

Objective. Intermittent theta burst stimulation (iTBS) is a widely used noninvasive brain stimulation for the facilitation of corticospinal excitability (CSE). Previous studies have shown that acupuncture applied to acupoints associated with motor function in healthy people can reduce the amplitude of the motor-evoked potentials (MEPs), which reflects the inhibition of CSE. In our work, we wanted to test whether the combination of iTBS and electroacupuncture (EA) would have different effects on CSE in humans. Methods. A single-blind sham-controlled crossover design study was conducted on 20 healthy subjects. Subjects received 20 minutes’ sham or real EA stimulation immediately after sham or real iTBS. MEPs, short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), cortical silent period (CSP), and central motor conduction time (CMCT) were recorded before each trial, and immediately, 20 minutes, and 40 minutes after the end of stimulation. Results. In the sham iTBS group, EA produced a reduction in MEPs amplitude, lasting approximately 40 minutes, while in the real iTBS group, EA significantly increased MEPs amplitude beyond 40 minutes after the end of stimulation. In sham EA group, the recorded MEPs amplitude showed no significant trend over time compared to baseline. Among all experiments, there were no significant changes in SICI, ICF, CSP, CMCT, etc. Conclusion. These data indicate that immediate application of EA after iTBS significantly increased corticospinal excitability. This trial was registered in the Chinese Clinical Trial Registry (registration no. ChiCTR1900025348)