The influence of microstructural characteristics and cell wall material properties on the mechanical behaviors of different tissues of sorghum stems.

Sorghum stems comprise different tissue components, i.e., rind, pith, and vascular bundles in the rind and pith regions, of different cell morphologies and cell wall characteristics. The overall responses of stems to mechanical loadings depend on the responses of these tissues themselves. Investigating how each tissue deforms to various loading conditions will inform us of the failure mechanisms in sorghum stems when exposed to wind loadings, which can guide the development of lodging-resistant variants. To this end, numerical analyses were implemented to investigate the effects of cell morphologies and cell wall properties on the overall mechanical responses of the above four tissues under tension and compression. Microstructures of different tissues were constructed from microscopic images of the tissues using computer-aided design (CAD), which were then used for finite element (FE) analyses. Shell finite elements were used to model the cell walls, and the classical lamination model was used to determine the overall mechanical responses of cell walls having different fiber composite arrangements. The results from the numerical analyses helped explain how the loading (boundary) conditions, the cell microstructures, the mechanical properties of cell walls of different tissues, the cell wall thickness, the microfibril angle (MFA) of fiber composites of the cell walls, and the turgor pressure affected the overall mechanical responses of the tissues. Tissue stiffening or softening behaviors were attributed to different microstructural deformations, i.e., local or global buckling of cell walls, cell collapse, densifications of cells, or reorientation and rearrangement of cells. The mechanical properties and thickness of cell walls only affected the stiffness and load-bearing ability of the tissues. The turgor pressure affected the compressive responses but its effect on tensile responses was negligible. The MFA had a significant influence on the stiffness and load-bearing ability when the tissues were loaded along their longitudinal axis, but it had an insignificant effect on loading in the transverse direction. Tissues with smaller cell sizes and denser cells were stronger and stiffer than those with larger cell sizes. The numerical simulations also revealed that rind and rind vascular bundles were stiffer and had higher load-bearing ability than pith and pith vascular bundles.

Mechanical stimulation reprograms the sorghum internode transcriptome and broadly alters hormone homeostasis.

Stem structural failure, or lodging, affects many crops including sorghum, and can cause large yield losses. Lodging is typically caused by mechanical forces associated with severe weather like high winds, but exposure to sub-catastrophic forces may strengthen stems and improve lodging resistance. The responses of sorghum internodes at different developmental stages were examined at 2 and 26 h after initiating moderate mechanical stimulation with an automated apparatus. Transcriptome profiling revealed that mechanical stimulation altered the expression of over 900 genes, including transcription factors, cell wall-related and hormone signaling-related genes. IAA, GA1 and ABA abundances generally declined following mechanical stimulation, while JA increased. Weighted Gene Co-expression Network Analysis (WGCNA) identified three modules significantly enriched in GO terms associated with cell wall biology, hormone signaling and general stress responses, which were highly correlated with mechanical stimulation and with biomechanical and geometrical traits documented in a separate study. Additionally, mechanical stimulation-triggered responses were dependent on the developmental stage of the internode and the duration of stimulation. This study provides insights into the underlying mechanisms of plant hormone-regulated thigmomorphogenesis in sorghum stems. The critical biological processes and hub genes described here may offer opportunities to improve lodging resistance in sorghum and other crops.

A hydraulic soft microgripper for biological studies.

We have developed a microscale hydraulic soft gripper and demonstrated the handling of an insect without damage. This gripper is built on Polydimethylsiloxane (PDMS) with the soft material casting technique to form three finger-like columns, which are placed on a circular membrane. The fingers have a length of 1.5 mm and a diameter of 300 µm each; the distance between the two fingers is 600 µm of center-to-center distance. A membrane as a 150 µm soft film is built on top of a cylindrical hollow space. Applying pressure to the interior space can bend the membrane. Bending the membrane causes the motion of opening/closing of the gripper, and as a result, the three fingers can grip an object or release it. The PDMS was characterized, and the experimental results were used later in Abaqus software to simulate the gripping motion. The range of deformation of the gripper was investigated by simulation and experiment. The result of the simulation agrees with the experiments. The maximum 543 µN force was measured for this microfluidic-compatible microgripper and it could lift a ball that weighs 168.4 mg and has a 0.5 mm diameter. Using this microgripper, an ant was manipulated successfully without any damage. Results showed fabricated device has great a potential as micro/bio manipulator.

Thigmostimulation alters anatomical and biomechanical properties of bioenergy sorghum stems.

Sorghum [Sorghum bicolor (L.) Moench] is a tropical grass that can be used as a bioenergy crop but commonly suffers from stem structural failure (lodging) when exposed to mechanical stimuli, such as rain and wind. Mechanical stimulation can trigger adaptive growth in plant stems (thigmomorphogenesis) by activating regulatory networks of hormones, proteins, transcription factors, and targeted genes, which ultimately alters their physiology, morphology, and biomechanical properties. The goals of this study are 1) to investigate differences in the morpho-anatomical-biomechanical properties of internodes from control and mechanically-stimulated plants and 2) to examine whether the changes also depend on the plant developmental stages at the time of stimulation. The sweet sorghum cultivar Della was grown in a greenhouse under two growth conditions: with and without mechanical stimulation. The mechanical stimulation involved periodic bending of the stems in one direction during a seven-week growth period. At maturity, the anatomical traits of the stimulated and non-stimulated stems were characterized, including internode lengths and diameters, and biomechanical properties, including elastic (instantaneous) modulus, flexural stiffness, strength, and time-dependent compliance under bending. The morpho-anatomical and biomechanical characteristics of two internodes of the stems that were at different stages of development at the time of mechanical stimulation were examined. Younger internodes were more responsive and experienced more pronounced changes in length due to the stimulation when compared to the older internodes. Statistical analyses showed differences between the stimulated and non-stimulated stems in terms of both their anatomical and biomechanical properties. Mechanical stimulation produced shorter internodes with slightly larger diameters, as well as softer (more compliant) and stronger stems.

Time-dependent mechanical behavior of sweet sorghum stems.

Grasses represent the most productive and widely grown crop family across the globe but are susceptible to structural failure (lodging) during growth (e.g., from wind). The mechanisms that contribute to structural failure in grass stems are poorly understood due to a lack of systematic studies of their biomechanical behavior. To this end, this study examines the biomechanical properties of sweet sorghum (Sorghum bicolor (L.) Moench), focusing on the time-dependent behavior of the stems. Specifically, we conducted uniaxial compression tests under ramp and creep loading on pith and stem specimens of the sorghum cultivar Della. The tests demonstrated significantly nonlinear and time-dependent stress-strain behavior in all samples. We surmise that this behavior arises from a combination of poroelasticity due to migration of water through the plant and viscoelasticity due to rearrangement of macromolecular networks, such as cellulose microfibrils and lignin matrices. Overall, our measurements demonstrate that sorghum is not a simple reversible elastic material. As such, a complete understanding of the conditions that lead to stem lodging will require knowledge of sorghum's time-dependent biomechanical properties. Of practical importance, the time-dependent biomechanical properties of the stem influence its mechanical stability under various loading conditions during growth in the field (e.g., different wind speeds).

High throughput phenotyping of morpho-anatomical stem properties using X-ray computed tomography in sorghum.

BACKGROUND: In bioenergy/forage sorghum, morpho-anatomical stem properties are major components affecting standability and juice yield. However, phenotyping these traits is low-throughput, and has been restricted by the lack of a high-throughput phenotyping platforms that can collect both morphological and anatomical stem properties. X-ray computed tomography (CT) offers a potential solution, but studies using this technology in plants have evaluated limited numbers of genotypes with limited throughput. Here we suggest that using a medical CT might overcome sample size limitations when higher resolution is not needed. Thus, the aim of this study was to develop a practical high-throughput phenotyping and image data processing pipeline that extracts stem morpho-anatomical traits faster, more efficiently and on a larger number of samples. RESULTS: A medical CT was used to image morpho-anatomical stem properties in sorghum. The platform and image analysis pipeline revealed extensive phenotypic variation for important morpho-anatomical traits in well-characterized sorghum genotypes at suitable repeatability rates. CT estimates were highly predictive of morphological traits and moderately predictive of anatomical traits. The image analysis pipeline also identified genotypes with superior morpho-anatomical traits that were consistent with ground-truth based classification in previous studies. In addition, stem cross section intensity measured by the CT was highly correlated with stem dry-weight density, and can potentially serve as a high-throughput approach to measure stem density in grass stems. CONCLUSIONS: The use of CT on a diverse set of sorghum genotypes with a defined platform and image analysis pipeline was effective at predicting traits such as stem length, diameter, and pithiness ratio at the internode level. High-throughput phenotyping of stem traits using CT appears to be useful and feasible for use in an applied breeding program.

Pneumatically Actuated Soft Micromold Device for Fabricating Collagen and Matrigel Microparticles.

Collagen microparticles have recently gained more attention as viable cell confinement blocks in many biomedical research fields. Small volume and high surface area of collagen structure improve cell confinement, viability, and proliferation. Moreover, dense collagen fiber structure can protect cells from immune destruction. The ability to produce collagen microparticles in an accurate and reliable way is of upmost importance to the advancement of many biomedical researches, especially cancer research and tissue engineering. Currently, no such fabrication technique exists due to inherent fragility of collagen. Herein, we report the very first platform, pneumatically actuated soft micromold (PASMO) device, which addresses challenges in collagen microparticle production. Our new platform uses a soft micromold with a pneumatic actuator that can produce arbitrary shapes of collagen microstructures precisely from 100 µm to over 2 mm in range and can encapsulate cells inside without damaging the shape. The duplication accuracy of more than 96% in dimensions and 90% in depth has been demonstrated. The density of collagen fiber distribution is determined to be 86.57%, which is higher than that of collagen microparticles produced by other methods. We have confirmed cell viability in collagen microparticles. We also produce Matrigel™ particles as tool to develop a xenograft cancer model. The results demonstrate that Matrigel particles created by the PASMO device can reduce cell scattering for the xenograft model and the uniformity of tumors developed in mice is 12-fold improved, which can lead to an increased accuracy of cancer metastasis studies and drug screening research. These breakthroughs in the production of modular microparticles will push the boundaries of cancer research in the near future.

Mechanical reinforcement of epoxy with self-assembled synthetic clay in smectic order.

Epoxy films containing self-assembled 2D colloidal α-zirconium phosphate nanoplatelets (ZrP) in smectic order were prepared using a simple, energy-efficient fabrication process suitable to industrial processing. The ZrP nanoplatelets form a chiral smectic mesophase with simultaneous lamellar order and helical arrangements in epoxy. The epoxy nanocomposite films are transparent and flexible and exhibit exceptionally high tensile modulus and strength. The findings have broad implications for development of multifunctional materials for engineering applications.