How do you identify a living organism? With scientific equipment, you would look for its cells under a microscope or sequence its DNA. But what if you had to tell whether something was alive just by looking at it? Intuitively, you'd search for clues about how its body changes over time. Does it move around or remain still? Does it grow into unique and increasingly complex forms, or simply break down with time?
The concept of how soft bodies evolve into new forms over time is summarized by the word "morphogenesis." Although it's a widespread concept in biology, it’s not commonly heard of in other fields of science, and almost never used in the context of technology. I often wonder how our vocabulary choices subtly influence our understanding of bodies, particularly those we classify as non-living. Morphogenesis, however, is a common phenomenon across a variety of material systems, both biological and non-biological, natural and artificial.
Back in 2019, researchers from the University of Pennsylvania discovered that carefully balanced, heterogeneous mixtures of liquid crystal molecules can form branched, coral-like structures that spontaneously blossom when the environment's temperature drops below a specific threshold. The process is reversible: as soon as the temperature rises again, the droplets contract back into spheres. The morphogenesis of these droplets is truly mesmerizing to watch.
Liquid crystals get their name from their ambivalent physical properties. Although they're fluid materials, their rod-shaped molecules tend to align into perfectly ordered patterns, similar to solid crystals. When liquid crystal molecules are dissolved in water, a delicate balance of forces regulates their behavior. These molecules are lipophilic, which means they spontaneously avoid water and tend to minimize their surface area, forming spherical droplets. However, as the temperature decreases, the tendency of liquid crystals to align parallel to each other prevails, driving the emergence of long, branched tendrils.
Liquid crystals have captivated scientists for centuries, and they are undeniably one of my favorite topics to talk about. Ever since their discovery in the late nineteenth century by German chemist Otto Lehmann, their remarkable ability to undergo morphogenesis has intrigued scientists, serving as a symbol of the potential connection between living and non-living matter. Philosopher and naturalist Ernst Haeckel even proposed that their growth and evolution stemmed from their own "crystalline soul." If you're interested in delving deeper into the cultural history of liquid crystals, from nineteenth-century vitalism to modern LCD displays, I highly recommend the fascinating book Liquid Crystals: The Science and Art of a Fluid Form by Esther Leslie.
In the realm of materials science and technology, the morphogenesis of liquid crystals is more than just a philosophical curiosity. One day, it may help us with the production of increasingly smart and responsive materials for applications such as sensing, drug delivery, and microrobotics. Besides these speculative technological developments, liquid crystals teach us that the interplay between structure and entropy is essential for generating complexity and evolution in both biological and non-biological materials. Despite being chemically different, liquid crystals share with our living bodies a delicate balance between order and chaos, determinism and freedom.
References:
Esther Leslie, Liquid Crystals: The Science and Art of a Fluid Form, Reaktion, London, 2016.