In a groundbreaking paper published in Nature, scientists have challenged the long-held belief that the properties of solid biological materials are solely determined by their atomic and molecular composition. Instead, they argue that the character of many biological materials is shaped by the water that permeates them. The authors introduce a new class of matter called “hydration solids,” which are defined as materials that derive their structural rigidity from the fluid within their pores.
According to Ozgur Sahin, a professor of Biological Sciences and Physics and one of the paper’s authors, this discovery represents a significant moment in science, as it unifies the complexity of diverse biological materials under a simple explanation. The researchers compare biological materials to skyscrapers, where the molecular building blocks act as steel frames and the water between them functions as the air inside the frames. In some cases, the solidity of the biological material is not supported by its molecular structure, but rather by the water within it.
The key factor at play is the hydration force, which was identified in the 1970s but was previously thought to have limited influence on biological matter. When water combines with the molecules in biological materials, it tips the balance between order and disorder, pushing the molecules apart and creating the hydration force. This force, responsible for defining the character of biological matter, determines its softness, hardness, and other mechanical properties.
While it has long been known that biological materials absorb ambient moisture, this research reveals that water plays a much more central role in defining their characteristics than previously understood. By placing water at the forefront, the scientists were able to develop simple mathematical formulas to describe the properties of organic materials. This simplicity indicates that the team is onto something significant.
For example, the equation E=Al/λ was found to accurately describe how a material’s elasticity changes based on factors such as humidity, temperature, and molecule size. E represents elasticity, A is a factor dependent on environmental conditions, l is the approximate size of biological molecules, and λ is the distance over which hydration forces weaken.
The new insights originated from Professor Sahin’s research on spores, dormant bacterial cells that exhibit peculiar behavior when exposed to water. The team’s experiments did not immediately provide answers, but they sparked curiosity and led to the realization that the hydration force might govern water movement in spores.
Hygroscopic biological materials, which allow water to enter and exit them, make up a substantial portion of the world around us, accounting for 50% to 90% of living organisms, including wood, bamboo, cotton, pine cones, wool, hair, fingernails, pollen grains, animal skin, and bacterial and fungal spores. The term “hydration solids” coined in the paper applies to any natural material responsive to ambient humidity.
The researchers’ equations enable the prediction of mechanical properties based on fundamental physics principles, expanding our understanding of materials beyond gases, which have been well-studied since the 19th century.
In essence, this groundbreaking research highlights the critical role of water in shaping the properties of biological materials, transforming our perception of the natural world and opening up new possibilities for scientific exploration.
Source: Columbia University