On the shape transformation of cone scales

Orchestrated Movement Sequences and Shape-Memory-like Effects in Pine Cones

Hygroscopic seed-scale movement is responsible for the weather-adaptive opening and closing of pine cones and for facilitating seed dispersal under favorable environmental conditions. Although this phenomenon has long been investigated, many involved processes are still not fully understood. To gain a deeper mechanical and structural understanding of the cone and its functional units, namely the individual seed scales, we have investigated their desiccation- and wetting-induced movement processes in a series of analyses and manipulative experiments. We found, for example, that the abaxial scale surface is responsible for the evaporation of water from the closed cone and subsequent cone opening. Furthermore, we tested the capability of dry and deformed scales to restore their original shape and biomechanical properties by wetting. These results shed new light on the orchestration of scale movement in cones and the involved forces and provide information about the functional robustness and resilience of cones, leading to a better understanding of the mechanisms behind hygroscopic pine cone opening, the respective ecological framework, and, possibly, to the development of smart biomimetic actuators.

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%.

The cracking of Scots pine (Pinus sylvestris) cones

Pine cones show functionally highly resilient, hygroscopically actuated opening and closing movements, which are repeatable and function even in millions of years old, coalified cones. Although the functional morphology and biomechanics behind the individual seed scale motions are well understood, the initial opening of the cone, which is often accompanied by an audible cracking noise, is not. We therefore investigated the initial opening events of mature fresh cones of Scots pine (Pinus sylvestris) and their subsequent motion patterns. Using high-speed and time lapse videography, 3D digital image correlation techniques, force measurements, thermographic and chemical-rheological resin analyses, we are able to draw a holistic picture of the initial opening process involving the rupture of resin seals and very fast seed scale motion in the millisecond regime. The rapid cone opening was not accompanied by immediate seed release in our experiments and, therefore, cannot be assigned to ballistochory. As the involved passive hydraulic-elastic processes in cracking are very fine-tuned, we hypothesize that they are under tight mechanical-structural control to ensure an ecologically optimized seed release upon environmental conditions suitable for wind dispersal. In this context, we propose an interplay of humidity and temperature to be the external "drivers" for the initial cone opening, in which resin works as a crucial chemical-mechanical latch system.

Materials for Smart Soft Actuator Systems

In contrast to conventional hard actuators, soft actuators offer many vivid advantages, such as improved flexibility, adaptability, and reconfigurability, which are intrinsic to living systems. These properties make them particularly promising for different applications, including soft electronics, surgery, drug delivery, artificial organs, or prosthesis. The additional degree of freedom for soft actuatoric devices can be provided through the use of intelligent materials, which are able to change their structure, macroscopic properties, and shape under the influence of external signals. The use of such intelligent materials allows a substantial reduction of a device's size, which enables a number of applications that cannot be realized by externally powered systems. This review aims to provide an overview of the properties of intelligent synthetic and living/natural materials used for the fabrication of soft robotic devices. We discuss basic physical/chemical properties of the main kinds of materials (elastomers, gels, shape memory polymers and gels, liquid crystalline elastomers, semicrystalline ferroelectric polymers, gels and hydrogels, other swelling polymers, materials with volume change during melting/crystallization, materials with tunable mechanical properties, and living and naturally derived materials), how they are related to actuation and soft robotic application, and effects of micro/macro structures on shape transformation, fabrication methods, and we highlight selected applications.

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.

Progress in Bioinspired Dry and Wet Gradient Materials from Design Principles to Engineering Applications

Nature does nothing in vain. Through millions of years of revolution, living organisms have evolved hierarchical and anisotropic structures to maximize their survival in complex and dynamic environments. Many of these structures are intrinsically heterogeneous and often with functional gradient distributions. Understanding the convergent and divergent gradient designs in the natural material systems may lead to a new paradigm shift in the development of next-generation high-performance bio-/nano-materials and devices that are critically needed in energy, environmental remediation, and biomedical fields. Herein, we review the basic design principles and highlight some of the prominent examples of gradient biological materials/structures discovered over the past few decades. Interestingly, despite the anisotropic features in one direction (i.e., in terms of gradient compositions and properties), these natural structures retain certain levels of symmetry, including point symmetry, axial symmetry, mirror symmetry, and 3D symmetry. We further demonstrate the state-of-the-art fabrication techniques and procedures in making the biomimetic counterparts. Some prototypes showcase optimized properties surpassing those seen in the biological model systems. Finally, we summarize the latest applications of these synthetic functional gradient materials and structures in robotics, biomedical, energy, and environmental fields, along with their future perspectives. This review may stimulate scientists, engineers, and inventors to explore this emerging and disruptive research methodology and endeavors.

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.

4D pine scale: biomimetic 4D printed autonomous scale and flap structures capable of multi-phase movement

We developed biomimetic hygro-responsive composite polymer scales inspired by the reversible shape-changes of Bhutan pine (Pinus wallichiana) cone seed scales. The synthetic kinematic response is made possible through novel four-dimensional (4D) printing techniques with anisotropic material use, namely copolymers with embedded cellulose fibrils and ABS polymer. Multi-phase motion like the subsequent transversal and longitudinal bending deformation during desiccation of a natural pinecone scale can be structurally programmed into such printed hygromorphs. Both the natural concept generator (Bhutan pinecone scale) and the biomimetic technical structure (4D printed scale) were comparatively investigated as to their displacement and strain over time via three-dimensional digital image correlation methods. Our bioinspired prototypes can be the basis for tailored autonomous and self-sufficient flap and scale structures performing complex consecutive motions for technical applications, e.g. in architecture and soft robotics. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 3)'.

Humidity-Driven Soft Actuator Built up Layer-by-Layer and Theoretical Insight into Its Mechanism of Energy Conversion

An improved protocol is proposed for preparation of a humidity-sensitive soft actuator through the layer-by-layer assembling of weight-ratio-variable composites of sodium alginate (SA) and poly(vinyl alcohol) (PVA) into laminated structures. The design induces nonuniform hygroscopicity in the thickness direction and gives rise to strong interfacial interaction between layers, making the actuator have directional motility. A mathematical model reveals that the directional motion is driven by the chemical potential of humidity, and its energy conversion efficiency from humidity to mechanical work reaches 81.2% at 25 °C. By coating with CoCl₂, the composite film of SA@PVA/CoCl₂ can act as a warning sign that provides reminder information to prevent people from slipping or falling by a conspicuous red sign during a high-humidity environment. When the film is involved in a bidirectional switch, it is capable of turning on/off light-emitting diodes by humidity, showing promising potential in control over humidity-dependent devices.