Journey of water in pine cones

Poroelastic plant-inspired structures & materials to sense, regulate flow, and move

Despite their lack of a nervous system and muscles, plants are able to feel, regulate flow, and move. Such abilities are achieved through complex multi-scale couplings between biology, chemistry, and physics, making them difficult to decipher. A promising approach is to decompose plant responses in different blocks that can be modeled independently, and combined later on for a more holistic view. In this perspective, we examine the most recent strategies for designing plant-inspired soft devices that leverage poroelastic principles to sense, manipulate flow, and even generate motion. We will start at the organism scale, and study how plants can use poroelasticity to carry informationin-lieuof a nervous system. Then, we will go down in size and look at how plants manage to passively regulate flow at the microscopic scale using valves with encoded geometric non-linearities. Lastly, we will see at an even smaller scale, at the nanoscopic scale, how fibers orientation in plants' tissues allow them to induce motion using water instead of muscles.

Optimization of the process of seed extraction from the Larix decidua Mill. cones including evaluation of seed quantity and quality

The objective of this study was to determine the number of stages of cone drying and immersion that yield the maximum number of high quality seeds. Nine variants of the process were conducted; they differed in terms of dwell time in the drying chamber and water immersion time. Each extraction variant consisted of five drying steps (lasting 10, 8 or 6 h) and four immersion steps (5, 10 or 15 min). Each drying step was followed by cone shaking in a purpose-made laboratory drum. The process variants were evaluated and compared in terms of cone moisture content as well as the dynamics of seed yield and the quality of seeds obtained in the various steps. The seed yield coefficient, α, and the cone mass yield coefficient, β, were calculated. The studied process of seed extraction can be described using the Lewis empirical model for the second stage of drying with the b coefficient ranging from 0.34 to 0.60. Relatively higher initial and final moisture content was found for cones immersed for 15 min (more than 0.45 kg_water·kg_d.w.^-1), while the lowest moisture content was found for those immersed for 5 min (less than 0.4 kg_water·kg_d.w.^-1). The highest seed yield at the first and second steps was obtained in the 8 h_10 min variant (53% and 32%, respectively). In all five-step variants, the mean cone yield amounted to 65% of total seeds in the cones; seeds obtained from all variants were classified in quality class I. The procedure recommended for commercial seed extraction facilities consists of three 8 h drying steps and two 10 min immersion steps, with cone shaking in a drum to maximize seed yield. A shorter cone extraction process maintaining an acceptable level of seed extraction may reduce energy consumption by nearly 50%.

Bidirectional Actuation of Silk Fibroin Films: Role of Water and Alcohol Vapors

Three-dimensional (3D) shape morphism observed in nature inspires the development of stimuli-responsive soft actuators. Vapor-responsive actuators are promising among the different stimuli-responsive materials due to their capability to produce macroscale movements in response to a minuscule amount of specific chemical vapor. Here, we report unusual multiple vapor-responsive bidirectional macroscale actuation behaviors of single-layer regenerated silk fibroin films. The vapor-responsive silk fibroin actuator exhibits antagonistic actuation characteristics in a reversible manner to both water and ethanol vapors. For instance, it produces an upward bending in the presence of water vapor and downward bending in ethanol vapor, which demonstrates the chemical vapor-specific actuation. However, the actuation characteristics remain largely invariant upon changing the polarity of alcohol molecules. The silk fibroin actuators effectively utilize the vapor-induced minuscule expansion and contraction of the film surface to produce large-scale actuation, which is fully reversible. The intrinsic water content of the films and the vapor pressure of the stimulants are exploited to control the actuation performance. Further, we demonstrated the 3D shape morphing ability of the actuator by generating an undulating wavelike motion via preprogrammed water and ethanol vapor exposure conditions. The change in the actuation direction is instantaneous, which ensures the sensitivity and rapid response of the fabricated actuators.

The Kinematics of Scale Deflection in the Course of Multi-Step Seed Extraction from European Larch Cones (Larix decidua Mill.) Taking into Account Their Cellular Structure

The objective of the study was to elucidate the kinematics of cone opening in the European larch (Larix decidua Mill.) during a four-step seed extraction process and to determine optimum process time on that basis. Each step lasted 8 h with 10 min of water immersion between the steps. The study also described the microscopic cellular structure of scales in cones with a moisture content of 5% and 20%, as well as evaluated changes in cell wall thickness. The obtained results were compared with the structural investigations of scales conducted using scanning electron microscopy (SEM) of characteristic sites on the inner and outer sides of the scales. The greatest increment in the scale opening angle was noted on the first day of the process (34°) and in scales from the middle cone segment (39°). In scales with a moisture content of 5% and 20%, the greatest changes in cell wall thickness were recorded for large cells (57%). The inner and outer structure of scales differed in terms of the presence and size of cells depending on the moisture content of the cones (5%, 10%, or 20%). The study demonstrated that the moisture content of cones was the crucial determinant of the cellular structure and opening of scales in larch cones. The scale opening angle increased with decreasing moisture content but did not differ significantly for various segments of cones or various hours of the consecutive days of the process. This finding may lead to reducing the seed extraction time for larch cones. The internal and external structure of scales differed depending on moisture content, which also determined the size and wall thickness of cells.

Hydration-induced reversible deformation of the pine cone

The scales of pine cones undergo reversible deformation due to hydration changes in order to optimize seed dispersal. This improves the survivability of the pine. The reversible flexing of the scales is caused by two tissue layers arranged in a sandwich configuration: a layer composed of sclereid cells and a sclerenchyma layer. They expand differentially upon hydration (and contract upon dehydration) due to differences in the structure that are analyzed here for Torrey pine (Pinustorreyana) cones. In addition to this well-known mechanism by which the cellulose microfibrils in the scales vary their angle with the wood cell axis, we confirm the presence of a porosity gradient in the sclereid cells and calculate, using a model consisting of three layers, the stresses generated upon dehydration taking into account the effect of hydration on the elastic modulus. Our quantitative analysis reveals that this gradient structure can significantly decrease the stress concentrations due to the mismatch between the two layers, and show that this is an ingenious design to increase the interfacial toughness to improve the robustness of pine cone scales. We also show that each individual layer of sclereid cells and sclerenchyma fibers undergoes bending when hydrated separately, and suggest that the two layers operate synergistically to effect the required deformation for seed release. A synthetic bioinspired analog consisting of hydrogels with different porosities is used to confirm this principal actuation mechanism. These findings may inspire the materials science and mechanical engineering communities to develop more robust, biocompatible and energy-efficient actuation systems. STATEMENT OF SIGNIFICANCE: Some biological structures can exhibit reversible deformation enabled by water inflow and outflow of their structure. We analyse the reversible motion of pine cone scales. The dehydration produces their flexure and opening, resulting in the release of seeds and their dispersal, when conditions are right. This process is reversible, and rehydration of the pine cone recloses the scales. The processes of flexing and straightening are governed by shrinking and swelling which are directed by differences in the arrangement of cellulose microfibrils in a bilayer construct. We demonstrate that the scales are more complex than a simple bilayer structure and that they actually have gradients, which significantly reduce the internal stresses and ensure their integrity. We analyse the process of opening and closing of the scales for a gradient structure in the Torrey pine cone using a simple idealized trilayer model. The results demonstrate a significant decrease in internal stresses produced by the gradient structure. Using the lessons learned from the pine cone, we produce a bilayer junction using hydrogels with different porosities which exhibit the same reversible bending response.

Functional Principles of Morphological and Anatomical Structures in Pinecones

In order to better understand the functions of plants, it is important to analyze the internal structure of plants with a complex structure, as well as to efficiently monitor the morphology of plants altered by their external environment. This anatomical study investigated structural characteristics of pinecones to provide detailed descriptions of morphological specifications of complex cone scales. We analyzed cross-sectional image data and internal movement patterns in the opening and closing motions of pinecones, which change according to the moisture content of its external environment. It is possible to propose a scientific system for the deformation of complex pinecone for the variable structures due to changes in relative humidity, as well as the application of technology. This study provided a functional principle for a multidisciplinary approach by exploring the morphological properties and anatomical structures of pinecones. Therefore, the results suggest a potential application for use in energy-efficient materials by incorporating hygroscopic principles into engineering technology and also providing basic data for biomimicry research.

Pine cone mold: a toolbox for fabricating unique metal/carbon nanohybrid electrocatalysts

Nature presents delicate and complex materials systems beyond those fathomable by humans, and therefore, extensive effort has been made to utilize or mimic bio-materials and bio-systems in various fields. Biomass, an inexhaustible natural materials source, can also present good opportunities for the development of unprecedented, advanced materials and processing systems. Herein, we demonstrate the use of pine cones as a biomass mold for creating new and useful metal/carbon nanohybrids (MCNHs). The inherent water-induced folding actuation of the cone scales allows the casting of an aqueous solution of a single metal precursor or a binary metal mixture into the cone mold by simply immersing the cone in the solution. The cone actively absorbs aqueous-phase metal precursors through the bract scales and the precursor ions introduced into the cone are anchored to the functional groups of the interior tissues of the cone. Subsequent heat treatment successfully led to the formation of unique MCNHs. Iron, manganese, and cobalt were employed as model metals, binary mixtures of which were also cast into the cone mold to create further versatile MCNHs. Nanoparticulate metals were formed on the carbon supports, where the size, size distribution, and crystallinity of the nanoparticles were highly dependent on the identity of the single-component precursor and the combination of precursors. Consequently, the electrochemical activity of the MCNHs also depended on which metal precursors were cast into the cone mold. The MCNH prepared from the mixture of iron and manganese precursors (M_FeMnCNH) showed the best electrochemical activity. As model applications, M_FeMnCNH was applied to electrode materials for electrochemical charge storage and the oxygen evolution reaction. An electrochemical capacitor cell based on the M_FeMnCNH electrodes showed excellent performance with energy densities of 38.7-54.2 W h kg^-1 at power densities of 16 000-160 kW kg^-1. In addition, M_FeMnCNH demonstrated a low overpotential of 464 mV and fast kinetics with a Tafel slope of 64.6 mV dec^-1 as an electrocatalyst for the oxygen evolution reaction in 1.0 M KOH. These results substantiate that pine cones as a biomass mold show great promise for creating versatile MCNHs through further combination of various precursors.

Review of Polymeric Materials in 4D Printing Biomedical Applications

The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as temperature, pressure, humidity, pH, wind, or light. Simply put, 4D printing is a continuum of 3D printing technology that is now able to print objects which change over time. In previous studies, many smart materials were shown to have 4D printing characteristics. In this paper, we specifically review the current application, respective activation methods, characteristics, and future prospects of various polymeric materials in 4D printing, which are expected to contribute to the development of 4D printing polymeric materials and technology.

3D and 4D Printing of Polymers for Tissue Engineering Applications

Three-dimensional (3D) and Four-dimensional (4D) printing emerged as the next generation of fabrication techniques, spanning across various research areas, such as engineering, chemistry, biology, computer science, and materials science. Three-dimensional printing enables the fabrication of complex forms with high precision, through a layer-by-layer addition of different materials. Use of intelligent materials which change shape or color, produce an electrical current, become bioactive, or perform an intended function in response to an external stimulus, paves the way for the production of dynamic 3D structures, which is now called 4D printing. 3D and 4D printing techniques have great potential in the production of scaffolds to be applied in tissue engineering, especially in constructing patient specific scaffolds. Furthermore, physical and chemical guidance cues can be printed with these methods to improve the extent and rate of targeted tissue regeneration. This review presents a comprehensive survey of 3D and 4D printing methods, and the advantage of their use in tissue regeneration over other scaffold production approaches.

Bioinspired Smart Moisture Actuators Based on Nanoscale Cellulose Materials and Porous, Hydrophilic EVOH Nanofibrous Membranes

Biomimetic actuators with rapid response speed, high sensitivity, and selectivity to external stimulus have found potential applications in smart switches, artificial muscles, and soft robots. The nanoscale structures of actuators enhance the exposed area to stimulus as well as enable versatile control of the actuation behaviors. Freestanding, flexible, and porous water-driven actuators with poly(vinyl alcohol- co-ethylene) (EVOH) nanofibers as the substrate and super hydrophilic nanoscale cellulose materials (cellulose nanofibers, cellulose nanocrystals, bacterial cellulose) as the active substance via uniform mixing or surface depositing were fabricated. The effects of the EVOH nanofiber substrate, the structures and concentrations of nanoscale cellulose materials, as well as the different environmental stimuli like humidity and temperature on the performance of actuators were studied. The water-driven actuation mechanism was proposed from the macroscopic and molecular aspects and the analysis of Gibbs free energy and mechanical energy. The actuator could bend to an angle of 180° and recovered less than 1 s for more than 100 circles without compromising properties when the environmental moisture changed. Furthermore, the multidimensional deformation behaviors of the water-stimulated actuators could also be well tuned by varying the orientations of the nanoscale materials. Additionally, the applications of the prepared actuator were demonstrated.

Cellulose-Based Biomimetics and Their Applications

Nature has been producing cellulose since long before man walked the surface of the earth. Millions of years of natural design and testing have resulted in cellulose-based structures that are an inspiration for the production of synthetic materials based on cellulose with properties that can mimic natural designs, functions, and properties. Here, five sections describe cellulose-based materials with characteristics that are inspired by gratings that exist on the petals of the plants, structurally colored materials, helical filaments produced by plants, water-responsive materials in plants, and environmental stimuli-responsive tissues found in insects and plants. The synthetic cellulose-based materials described herein are in the form of fibers and films. Fascinating multifunctional materials are prepared from cellulose-based liquid crystals and from composite cellulosic materials that combine functionality with structural performance. Future and recent applications are outlined.

How the pine seeds attach to/detach from the pine cone scale?

One of the primary purposes of pine cones is the protection and distant dispersal of pine seeds. Pine cones open and release their embedded seeds on dry and windy days for long-distance dispersal. In this study, how the pine seed attach to/ detach from the pine cone scale for efficient seed dispersal were experimentally investigated by using X-ray micro-imaging technique. The cone and seeds adhere to one another in the presence of water, which could be explained by the surface tension and the contact angle hysteresis. Otherwise, without water, the waterproof seed wing surface permits rapid drying for detach and dispersion. On the other hand, during wildfires, pine cones open their seed racks and detach the pine seeds from pine cones for rapid seed dispersal. Due to these structural advantages, pine seeds are released safely and efficiently on adjust condition. These advantageous structure could be mimicked in practical applications.

A Biologically-Inspired Symmetric Bidirectional Switch

Stimuli-sensitive hydrogels have been intensively studied because of their potential applications in drug delivery, cell culture, and actuator design. Although hydrogels with directed unidirectional response, i.e. capable of bending actuated by different chemical components reaction in response to several stimuli including water and electric fields, these hydrogels are capable of being actuated in one direction only by the stimulus. By contrast the challenge of building a device that is capable of responding to the same cue (in this case a temperature gradient) to bend in either direction remains unmet. Here, inspired by the structure of pine cone scales, we design a temperature-sensitive hydrogel with bending directed an imposed fishing line. The layers with same PNIPAAm always shrinks in response to the heat. Even the layers made with different chemical property, bends away from a warm surface, whether the warm surface is applied at its upper or lower boundary. To design the bending hydrogel we exploited the coupled responses of the hydrogel; a fishing line intercalating structure and change its construction. In addition to revealing a new capability of stimulus sensitive hydrogels, our study gives insight into the structural features of pine cone bending.

On the shape transformation of cone scales

The shape-morphing behaviours of some biological systems have drawn considerable interest over many years. This paper divulges that the opening and closing mechanism of pine cones is attributed to the self-bending of their scales, which undergo three states of humidity-driven deformation in terms of Föppl-von Kármán plate theory. Both numerical simulation and experimental measurement support the theoretical analysis, showing that the longitudinal principal curvature and the transverse principal curvature bifurcate at a critical humidity level according to the thickness and shape of scales. These findings help us understand the shape transformation of bilayer or multi-layer natural structures and gain insights into the design of transformable devices/materials with great potential in numerous applications.

Programmable shape transformation of elastic spherical domes

We investigate mismatch strain driven programmable shape transformation of spherical domes and report the effects of different geometric and structural characteristics on dome behavior in response to applied mismatch strain. We envision a bilayer dome design where the differential swelling of the inner layer with respect to the passive outer layer in response to changes in dome surroundings (such as the introduction of an organic solvent) introduces mismatch strain within the bilayer system and causes dome shape transformation. Finite element analysis reveals that, in addition to snap-through, spherical domes undergo bifurcation buckling and eventually gradual bending to morph into cylinders with increasing mismatch strain. Besides demonstrating how the snap-through energy barrier depends on the spherical dome shape, our analysis identifies three distinct groups of dome geometries based on their mismatch strain-transformed configuration relationships. Our experiments with polymer-based elastic bilayer domes that exhibit differential swelling in organic solvents qualitatively confirm the finite element predictions. We establish that, in addition to externally applied stimuli (mismatch strain), bilayer spherical dome morphing can be tuned and hence programmed through its geometry and structural characteristics. Incorporation of an elastic instability mechanism such as snap-through within the framework of stimuli-responsive functional devices can improve their response time which is otherwise controlled by diffusion. Hence, our proposed design guidelines can be used to realize deployable, multi-functional, reconfigurable, and therefore, adaptive structures responsive to a diverse set of stimuli across multiple length scales.