3.2 Examples of hierarchical structures in nature
4 min read•august 7, 2024
Nature's hierarchical structures are marvels of engineering. From bone to , these materials showcase intricate designs across multiple scales. This organization gives them unique properties like strength, flexibility, and toughness that far surpass their individual components.
Surface structures in nature are equally impressive. Gecko feet, lotus leaves, and butterfly wings demonstrate how micro and nanostructures can create amazing abilities. These examples inspire new materials with enhanced adhesion, self-cleaning, and optical properties.
Biological Materials
Bone Structure and Composition
Top images from around the web for Bone Structure and Composition
Module 5: Cartilage and Bone – Anatomy 337 eReader View original
Is this image relevant?
Bone Structure | Anatomy and Physiology I View original
Is this image relevant?
Bone Structure | Anatomy and Physiology I View original
Is this image relevant?
Module 5: Cartilage and Bone – Anatomy 337 eReader View original
Is this image relevant?
Bone Structure | Anatomy and Physiology I View original
Is this image relevant?
1 of 3
Top images from around the web for Bone Structure and Composition
Module 5: Cartilage and Bone – Anatomy 337 eReader View original
Is this image relevant?
Bone Structure | Anatomy and Physiology I View original
Is this image relevant?
Bone Structure | Anatomy and Physiology I View original
Is this image relevant?
Module 5: Cartilage and Bone – Anatomy 337 eReader View original
Is this image relevant?
Bone Structure | Anatomy and Physiology I View original
Is this image relevant?
1 of 3
- Bone is a hierarchical composite material consisting of organic and inorganic crystals
- Collagen fibers provide flexibility and while hydroxyapatite crystals contribute to bone's stiffness and compressive strength
- Bone's hierarchical structure spans multiple length scales from the nanoscale to the macroscale (collagen molecules, mineralized collagen fibrils, osteons, cortical and trabecular bone)
- Bone continuously remodels itself through the balanced actions of (bone-forming cells) and (bone-resorbing cells) to maintain its strength and adapt to mechanical loads
Spider Silk Properties and Production
- Spider silk is a protein-based fiber with exceptional mechanical properties including high tensile strength, extensibility, and toughness
- , used as a lifeline and for web construction, is composed of two main proteins: major ampullate 1 (MaSp1) and major ampullate spidroin 2 (MaSp2)
- These proteins contain repetitive amino acid sequences that form crystalline β-sheet structures (providing strength) and amorphous regions (providing elasticity)
- Spiders produce silk in specialized glands and spin it into fibers using a complex spinning process involving shear forces, pH changes, and ion exchange
Wood Anatomy and Mechanical Properties
- Wood is a hierarchical, anisotropic, and porous material composed of cellulose, , and
- are the main load-bearing components, providing tensile strength and stiffness along the grain direction
- Hemicellulose acts as a matrix material, binding cellulose microfibrils together, while lignin provides compressive strength and resistance to decay
- Wood's cellular structure, consisting of elongated cells (tracheids in softwoods and vessels and fibers in hardwoods), is optimized for water transport and mechanical support
Abalone Shell Structure and Toughness
- is a hierarchical composite of () platelets bound together by a small amount of organic material (proteins and polysaccharides)
- The aragonite platelets are arranged in a brick-and-mortar structure, with the organic material acting as the mortar, providing a tough and fracture-resistant material
- The platelets are organized into layers with alternating crystal orientations, further enhancing the shell's toughness and crack resistance
- Abalone shell's hierarchical structure and composition result in a material that is 3,000 times more fracture-resistant than pure calcium carbonate
Surface Structures
Nacre (Mother-of-Pearl) Formation and Properties
- is the iridescent inner layer of mollusk shells, composed of a hierarchical arrangement of aragonite platelets and organic material (similar to abalone shell)
- The aragonite platelets are organized into layers, with each layer rotated relative to the adjacent layers, creating a highly ordered, brick-and-mortar structure
- The organic material, consisting of proteins and polysaccharides, binds the platelets together and provides a ductile interface for stress dissipation and crack deflection
- Nacre's hierarchical structure and composition result in a material with high strength, toughness, and fracture resistance, making it a model for biomimetic materials design
Gecko Foot Adhesion Mechanism
- Geckos can adhere to and climb on various surfaces using specialized adhesive pads on their toes called
- Each lamella is covered with millions of microscopic, hair-like structures called , which further branch into nanoscale spatula-shaped structures
- The setae and spatulae make intimate contact with surfaces, creating a large surface area for van der Waals forces to act, enabling strong adhesion
- is reversible, allowing them to easily attach and detach their feet during climbing, and is self-cleaning, as dirt particles do not adhere as strongly as the spatulae
Lotus Leaf Surface Structure and Hydrophobicity
- Lotus leaves exhibit and self-cleaning properties due to their hierarchical surface structure and chemical composition
- The leaf surface is covered with microscale papillae (bumps) and nanoscale wax crystals, creating a highly rough, low-surface-energy surface
- Water droplets maintain a nearly spherical shape on the leaf surface, minimizing contact area and allowing them to easily roll off, picking up dirt particles in the process (self-cleaning effect)
- The combination of surface roughness and low surface energy (hydrophobicity) is known as the "" and has inspired the development of biomimetic self-cleaning surfaces
Butterfly Wing Scale Nanostructures and Optical Properties
- Butterfly wings display a wide range of colors and patterns, which are often produced by the micro- and nanostructures of the wing scales rather than pigments
- Wing scales are composed of and are arranged in a shingle-like pattern, with each scale having a complex hierarchical structure of ridges, cross-ribs, and lamellae
- The nanostructures on the wing scales interact with light through various mechanisms, such as thin-film interference, diffraction, and photonic crystals, producing iridescent and structural colors
- Examples of structural coloration in butterflies include the blue morpho butterfly (), whose wing scales have a multilayer structure that reflects blue light, and the glasswing butterfly (), whose transparent wings are due to nanopillars that minimize light reflection
Key Terms to Review (28)
Abalone Shell: The abalone shell is a hard, protective outer layer created by marine mollusks of the genus Haliotis, known for its iridescent inner surface. This unique structure not only serves to protect the animal from predators and environmental stressors but also demonstrates remarkable hierarchical organization, showcasing how biological materials can combine strength and beauty. The layered structure of the shell plays a critical role in its mechanical properties, allowing it to withstand significant stress while remaining lightweight.
Aragonite: Aragonite is a mineral form of calcium carbonate (CaCO₃) that is characterized by its orthorhombic crystal structure. This mineral is significant in nature as it forms the hard parts of various marine organisms, such as mollusk shells and coral skeletons, showcasing intricate hierarchical structures that are vital for their biological functions.
Bone structure: Bone structure refers to the complex organization of bone tissue, consisting of various components including cells, fibers, and minerals that contribute to its strength and function. This hierarchical arrangement allows bones to achieve optimal mechanical properties, providing support and protection to the body while facilitating movement. Understanding bone structure is crucial in recognizing how nature uses similar strategies for efficient designs in both biological and artificial systems.
Calcium Carbonate: Calcium carbonate is a chemical compound with the formula CaCO₃, commonly found in nature as minerals like calcite and aragonite. It plays a vital role in the formation of various hierarchical structures in organisms, such as shells, bones, and corals, showcasing the incredible ways life utilizes materials for strength and resilience. This compound is also central to biomineralization processes, where living organisms synthesize it through biochemical pathways to create robust structures.
Cellulose microfibrils: Cellulose microfibrils are microscopic, thread-like structures composed of cellulose, a polysaccharide that serves as a primary component of plant cell walls. These microfibrils provide structural support and strength to plants and contribute to the hierarchical organization found in natural materials, allowing for efficient load-bearing and flexibility in response to environmental changes.
Chitin: Chitin is a biopolymer made up of N-acetylglucosamine units, forming a structural component in the exoskeletons of arthropods and the cell walls of fungi. This polysaccharide not only contributes to the composition and structure of biological materials but also provides mechanical strength and protection, showcasing its significance in nature's designs.
Collagen fibers: Collagen fibers are structural proteins that provide strength and support to various tissues in the body, such as skin, tendons, ligaments, and cartilage. These fibers are crucial components of hierarchical structures in nature, allowing for complex arrangements that enhance mechanical properties and durability across different biological systems.
Dragline silk: Dragline silk is a type of silk produced by spiders, particularly used for constructing webs and creating safety lines during their movements. It is known for its remarkable strength and elasticity, making it an excellent example of a natural material that exhibits a hierarchical structure, where the molecular arrangement leads to impressive mechanical properties that outperform many synthetic materials.
Functionality over form: Functionality over form is the principle that emphasizes the importance of how something works rather than how it looks. This concept suggests that the effectiveness and utility of a structure or material are more critical than its aesthetic appeal, especially in design inspired by natural systems. This principle is particularly relevant in the context of hierarchical structures found in nature, where the organization and performance of these structures often take precedence over their outward appearance.
Gecko Adhesion: Gecko adhesion refers to the unique ability of geckos to stick to surfaces using specialized toe pads that employ millions of tiny hair-like structures called setae. This remarkable phenomenon highlights the complex interplay of hierarchical structures, material properties, and surface interactions, leading to innovations in various fields.
Greta oto: Greta oto, commonly known as the glasswing butterfly, is a species renowned for its unique wings that are transparent and allow light to pass through. This characteristic, combined with a delicate and colorful body, makes it an excellent example of how natural organisms have evolved to develop hierarchical structures, particularly in terms of their physical adaptations for survival in their environment.
Hemicellulose: Hemicellulose is a complex carbohydrate found in the cell walls of plants, serving as a key structural component alongside cellulose and lignin. It provides support and flexibility to plant cell walls, contributing to the hierarchical structures observed in natural systems. Hemicellulose is made up of various sugar monomers, making it more branched and less crystalline than cellulose, allowing for interactions that enhance the overall strength and integrity of plant materials.
Hydroxyapatite: Hydroxyapatite is a naturally occurring mineral form of calcium apatite with the chemical formula Ca₁₀(PO₄)₆(OH)₂. It plays a critical role in biological systems, particularly in forming and maintaining bone and teeth structures, and is also significant in various biomimetic materials applications, such as tissue engineering and regenerative medicine.
Lamellae: Lamellae are thin, plate-like structures that can be found in various biological systems. They play a crucial role in the organization and function of tissues, providing a hierarchical structure that enhances mechanical properties and biological functions. In nature, lamellae contribute to processes such as light absorption, mechanical support, and biochemical interactions.
Lignin: Lignin is a complex organic polymer found in the cell walls of many plants, particularly in wood and bark, that provides structural support and rigidity. It plays a crucial role in the hierarchical structure of plants by helping to form the vascular tissue, which is essential for water and nutrient transport, as well as providing resistance against decay and pathogens.
Load-Bearing Capacity: Load-bearing capacity refers to the maximum load or weight that a material or structure can support without experiencing failure or significant deformation. This concept is crucial in understanding how natural structures, such as bones, trees, and shells, achieve their strength and stability through a hierarchical organization of materials at different scales.
Lotus Effect: The lotus effect refers to the remarkable self-cleaning properties observed in the leaves of the lotus plant, where water droplets bead up and roll off, carrying dirt and contaminants with them. This phenomenon is attributed to the unique micro- and nanostructures on the leaf surface that create a superhydrophobic effect, inspiring the design of materials and surfaces that mimic this property.
Lotus Leaf: The lotus leaf is a large, flat leaf of the lotus plant, known for its unique surface properties that repel water and dirt. This remarkable characteristic is due to its hierarchical microstructure, which plays a significant role in both natural ecosystems and the development of bioinspired materials aimed at energy harvesting and storage. The lotus leaf's ability to maintain cleanliness while providing structural support is an example of how nature optimizes functionality through design.
Morpho peleides: Morpho peleides, commonly known as the Blue Morpho butterfly, is a striking species native to Central and South America, renowned for its vibrant blue wings that exhibit iridescence due to microscopic scales. The structure of its wings demonstrates a hierarchical design, with layers that manipulate light to create stunning visual effects, which play a role in both mate attraction and predator avoidance.
Nacre: Nacre, also known as mother of pearl, is a biocomposite material produced by mollusks, composed of aragonite and organic proteins arranged in a layered, brick-and-mortar structure. This unique arrangement gives nacre its remarkable mechanical properties and serves as an exemplary model for biomimetic materials that aim to replicate its lightweight yet strong characteristics.
Osteoblasts: Osteoblasts are specialized bone cells responsible for the formation of new bone tissue through the process of ossification. They play a crucial role in bone development and remodeling by synthesizing and secreting the bone matrix, which is primarily made up of collagen and other proteins that provide structure and strength to bones.
Osteoclasts: Osteoclasts are specialized cells responsible for the resorption of bone tissue, playing a critical role in the maintenance of bone health and homeostasis. These cells help break down old or damaged bone, which is essential for the remodeling process and ensuring that bone remains strong and adaptable. By functioning in a hierarchical manner with other bone cells, osteoclasts contribute significantly to the dynamic balance between bone formation and resorption.
Self-healing: Self-healing refers to the ability of a material or system to automatically repair damage without external intervention. This concept is crucial in understanding how biological materials maintain their integrity and functionality, as many living organisms possess mechanisms that allow them to heal after injury. The principles of self-healing can be applied in designing advanced materials that mimic these biological processes, showcasing potential in engineering and material science.
Setae: Setae are hair-like structures found on the surface of various organisms, particularly in arthropods and some annelids. These structures play important roles in locomotion, sensory perception, and sometimes even in defense. Setae can be made from chitin or other materials and often exhibit a hierarchical organization that contributes to their functional diversity in nature.
Spider silk: Spider silk is a natural fiber produced by spiders, known for its exceptional mechanical properties, including high tensile strength, elasticity, and lightweight nature. This remarkable material showcases the efficiency of biological materials, revealing intricate hierarchical structures and the relationship between their physical properties and molecular composition. Spider silk's unique characteristics make it a subject of interest in biomimetic applications, raising challenges in the large-scale production of synthetic alternatives.
Spidroin: Spidroins are a class of proteins that are the primary building blocks of spider silk, known for its extraordinary strength and elasticity. These proteins exhibit hierarchical structures that are organized at multiple scales, contributing to the unique mechanical properties of silk. The intricate arrangement of spidroins enables spiders to produce various types of silk, each tailored for specific functions such as web-building, prey capture, and ballooning.
Superhydrophobicity: Superhydrophobicity refers to the property of a surface to repel water, characterized by a water contact angle greater than 150 degrees. This unique trait allows surfaces to remain clean and dry by preventing water droplets from adhering, which can be observed in natural hierarchies such as lotus leaves. The micro- and nanostructures present in nature enhance this water-repelling ability, making it relevant for various applications, including water purification and advanced material integration.
Tensile Strength: Tensile strength is the maximum amount of tensile (pulling or stretching) stress that a material can withstand before failure or breaking. This property is crucial in understanding how biological materials function, as it reflects the material's ability to handle forces without deforming or breaking. The composition and structure of biological materials play a significant role in their tensile strength, while the mechanical properties of these materials provide insights into their performance under stress. Additionally, observing examples of hierarchical structures in nature reveals how biological systems optimize tensile strength through intricate designs.