Is bamboo as strong as a human bone

What makes biological building materials so successful

Researchers are studying the skillful structure of biomaterials, especially the varying combinations of brittle minerals and soft biopolymers that make natural substances robust and tough. Bio-inspired materials are said to have similar properties.

Longhorn boxfish

From tear-resistant spider silk to hard bones and flexible quills: materials that nature has produced are superior to most man-made building materials and structures. This is mainly due to the variety of structures that cleverly combine hard minerals and flexible substances, summarizes a research team in the journal “Science”. The greatest advantage of biomaterials lies in their ability to heal themselves, according to the scientists, and in the fact that the internal structure usually serves several purposes at the same time.

“The application of modern methods from materials research is driving a new understanding of biological materials and guiding the design of biologically inspired materials and structures,” writes the team headed by Marc André Meyers from the University of California in San Diego.

Seahorses with bone plates

Together with colleague Joanna McKittrick and Po-Yu Chen from the National Tsing Hua University in Taiwan, the researcher evaluated and structured the results of worldwide studies. When analyzing the structure and function of the natural materials, the team paid particular attention to three points: tensile strength, breaking strength and buckling strength.

This is how the silk of silkworms stands (Bombyx mori) for high tensile and tear strength. The main reason for this lies in the collagen of the silk threads: The bioelastomer absorbs tensile energy by allowing reversible deformation by stretching and unrolling internal protein strands. Looking one level deeper, the hydrogen bonds also play a central role. The silk of various species of spiders, the wool of sheep and the egg cords of sea snails work in a similar way (Busycon carica)report the researchers.

Great hardness and breaking strength come about when elastic and hard components are cleverly combined and structured, such as in mussel shells and mother-of-pearl, in bones and teeth or in deer antlers. The headdress of elks (Cervus elaphus) is considered to be the hardest type of bone ever - achieved through an interplay of strongly mineralized regions and a very high collagen content, which catches and stops the beginning of cracks very quickly.

Shell of the abalone

The mother-of-pearl of the abalone snail (Haliotis rufescens) owes its hardness to countless tiny tiles made of calcium carbonate, which are connected by wafer-thin organic layers and tiny mineral bridges. The exoskeleton of crabs and lobsters, on the other hand, relies on mineralized chitin, also nested, between which stretchable tubes not only hold together but also transport moisture.

Bamboo stalks, but also feathers and the spines of the porcupine are used for the kink resistance with minimal weight (Hystrix cristata) known. The researchers working with Meyers explain this with structures such as hollow stems, the stability of which is achieved, for example, in bamboo by regular transverse discs or in the case of feather and spike by a kind of rigid foam filling. Birds' beaks made from a keratin shell and airy inner bracing also belong in this category, especially the toucan's beak (Ramphastos toco).

Meyers and colleagues list the enormous advantages of natural materials, which have arisen in the most varied of forms in the course of evolution and which have not been achieved technically for a long time, in seven points:

Toucan bill

  • Self-arrangement: The structures are built “bottom-up”, starting with the smallest elements.
  • Multifunctionality: Many components serve several purposes, feathers, for example, ensure flight, insulation and camouflage.
  • Hierarchy of structures: If you look into smaller dimensions with the microscope, you will always find other, even smaller functional structures.
  • Hydration or water storage: Above all, the elastic properties depend very much on the proportion of stored water.
  • Moderate production requirements: Nature usually succeeds in synthesizing materials at room temperature and normal pressure.
  • Adaptation to environmental requirements and evolution: Even with limited raw materials, meaningful structures succeed that are not optimal in every respect, but satisfactorily meet several requirements at the same time.
  • Self-healing properties: Living cell material and self-organizing structures can usually repair small damage independently.

Despite the superiority of natural synthesis, the researchers see good prospects for bio-inspired material and more energy-efficient design. The field is currently expanding rapidly.