What Are Biological Materials? Composition and Examples

Biological materials are substances produced by or derived from living organisms, including a vast array of materials from plants, animals, and microbes. These materials form the structures of life, from the tissues and cells of an organism to the protective shells and supportive skeletons they create. Their defining characteristic is their origin in biological processes, which gives them unique and complex structures. Their biological origin also makes them biocompatible, capable of integrating with living systems.

The Fundamental Composition of Biological Materials

Most biological materials are polymers, which are large molecules made of repeating smaller units called monomers. These biopolymers are categorized based on their chemical makeup, and the specific arrangement of monomers dictates the material’s final properties. This molecular architecture is the foundation of their function, whether for structure, defense, or movement.

A significant class of these materials is protein-based. Proteins are constructed from amino acid chains and are responsible for many dynamic and structural components. Examples include collagen, which provides tensile strength in skin and bone; keratin, which assembles into tough structures like hair and nails; and silk, a fiber known for its strength and flexibility.

Another major group is built from polysaccharides, which are long chains of sugar molecules. In plants, cellulose is the primary structural component of cell walls, giving them rigidity. Lignin is another polymer often found with cellulose in wood, adding compressive strength. In fungi and arthropods, chitin serves a similar structural purpose, forming the hard exoskeletons of insects and the cell walls of fungi.

Many biological materials are composites, meaning they are made of two or more substances that create a material with enhanced properties. Bone and teeth are prime examples, blending soft organic components with hard inorganic minerals. This combination results in materials that are both strong and resistant to fracture.

Examples in the Natural World

Nature provides many examples of materials perfectly tailored to an organism’s survival needs. These materials exhibit properties that engineers strive to replicate. Their structures are often complex and hierarchical, meaning they are organized on multiple levels from the molecular to the macroscopic, which gives them their exceptional performance.

Bone is a lightweight, strong, and adaptive biological material that provides structural support and protects internal organs. It is a dynamic, living tissue capable of self-repair. Its composite structure consists of a flexible collagen framework intertwined with rigid hydroxyapatite mineral crystals. This combination allows it to resist both pulling and compressing forces without being overly dense or brittle.

Spider silk possesses a strength-to-weight ratio that surpasses steel. Different spiders produce various types of silk, each optimized for a specific function, such as a web’s framework or a protective egg sac. The material’s toughness comes from its molecular structure, which has crystalline regions for strength and flexible regions that allow it to stretch significantly before breaking. This elasticity enables a web to absorb the kinetic energy of a flying insect.

Nacre, the iridescent inner layer of mollusk shells, protects the soft-bodied animal inside. Nacre’s fracture resistance is derived from its microscopic “brick-and-mortar” arrangement. It is composed of thin platelets of aragonite (a form of calcium carbonate) that act as “bricks,” which are layered and held together by a thin film of elastic biopolymers that function as “mortar.” When a crack attempts to propagate, it is forced to follow a zigzag path around the hard platelets, dissipating energy.

Wood functions as the structural support for trees and other plants, enabling them to grow to great heights. It also contains a network of tubes that transport water and nutrients. Wood’s properties are anisotropic, meaning they differ depending on the direction. It is strong along the grain, where long cellulose fibers are aligned, but weaker across it.

Human Applications and Technology

Humans have used biological materials for millennia for shelter, clothing, tools, and fuel. The characteristics of these substances, perfected by evolution for specific biological roles, made them suitable for a wide range of human needs. The history of civilization is intertwined with the use of these traditional materials.

Wood has been a fundamental resource for construction and a primary source of energy. Fibers from plants and animals have been woven into textiles for thousands of years.

• Cotton, for its softness and breathability, became a staple of clothing.
• Wool, for its warmth and insulation, was used for clothing and domestic goods.
• Animal hides were processed into leather, a durable material for footwear and armor.
• Silk has long been prized for luxury textiles due to its strength and sheen.

In the modern era, the properties of biological materials have been leveraged for advanced technological and biomedical applications. Collagen is now widely used in medical procedures, serving as a scaffold for tissue engineering and in cosmetic treatments. Derivatives of chitin, known as chitosan, have found applications in advanced wound care, as chitosan dressings can promote clotting and have antimicrobial properties.

Hydroxyapatite, the mineral component of bone, is used to create synthetic bone grafts and coatings for orthopedic and dental implants. Because it mimics the body’s own mineral, it encourages bone cells to attach and grow. This leads to better integration of the implant into the surrounding skeletal tissue.

Bio-Inspired and Bio-Hybrid Innovations

Scientists also draw inspiration from nature to design entirely new substances. This field of materials science seeks to mimic the strategies that organisms use to create high-performance materials. This approach has led to the development of materials that solve complex engineering challenges.

A distinction exists between bio-inspired and bio-hybrid materials. Bio-inspired materials are fully synthetic, but their structure or function is based on a biological model. Bio-hybrid materials physically combine biological elements, such as cells or proteins, with synthetic components to create a new material with novel functionalities.

Examples of bio-inspiration are becoming more common. The invention of Velcro was inspired by the way burr seeds cling to fur using tiny hooks. Research is focused on creating synthetic spider silk that replicates the natural fiber’s properties for use in textiles and medical sutures. Engineers are also developing fracture-resistant ceramics by mimicking the brick-and-mortar microstructure of nacre.

Bio-hybrid materials represent a frontier where living systems are merged with man-made structures. Scientists are experimenting with “living concrete” that incorporates bacteria capable of producing calcium carbonate to heal cracks. In medicine, biosensors are being developed that embed enzymes or antibodies into a synthetic matrix. These biological molecules can detect specific substances, like glucose in the blood, with high precision.