What do experimental cancer-fighting drugs, inkjet printing, and a small lineage of alpine plants have in common? Apparently, they share a rare and enigmatic mineral called vaterite.
In the past few years, scientists at Cambridge University have made an esoteric but potentially game-changing discovery: small crystal formations on the leaves of a certain plant species contain novel amounts of vaterite. Cambridge gardens have long been host to particularly tenacious group of plants in the genus Saxifraga, which in nature are most commonly found in the harsh upper altitudes of mountain ecosystems [1]. Researchers are interested in these plants due to their unique adaptations that allow them to survive the harsh winds and extreme temperatures in their natural habitats. One such trait, found in Saxifraga sempervivum, is a protective crystal crust that forms on the leaf surfaces. Although this calcium carbonate crust exists on multiple species of Saxifraga, only on S. sempervivum does the specific form (called a polymorph) of the carbonate exist as pure vaterite. The mineral forms from the chalky crust-producing glands on the edges of fleshy leaves of small alpine plants and may possibly benefit these leaves with thermal insulation [2].
Vaterite is notable for several reasons, the first being how rare it is to find in nature. It is seen occasionally in meteorites and can be produced in small quantities as a biomineral by certain crustaceans, birds, and fish [2]. This scarcity is unsurprising given that vaterite is also the most unstable of all calcium carbonate polymorphs – even minimal exposure to water is usually enough to transform it into another carbonate [3]. As such, its temperamental qualities, scattered occurrences, and miniscule volume when produced should have pushed the mineral to the wayside of current scientific research – but this isn't the case. Difficulties in procuring it aside, vaterite has proven to have several valuable and uncommon properties as a mineral. Unusual solubility, high loading capacity, and a high rate of uptake by cells have piqued interest in the polymorph from researchers and inventors alike[1].
Given the uniqueness of these properties in combination of one mineral, vaterite has the potential to be widely profitable in multiple industries. For instance, it can be used as a binding agent in cosmetic products, a template for biodegradable polymers, and a superior coating pigment for inkjet printing [3]. Yet, even more impressive is the potential of vaterite in medicine, especially as a tool for cancer-fighting pharmaceuticals. Here, its value lies in the ability of its nanoparticles to load up on anti-cancer drugs and then systematically offload those agents at targeted cancer sites – essentially a top-notch drug-delivery service [1].
Of course, all these hypothetical applications have been fruitless given the scarcity and instability of vaterite in nature, as well as the difficulties in mass-producing it in a lab. But the discovery of its pure form in Saxifraga could be a game-changer. Not only is this the first instance of the mineral appearing in plants, but it is also the largest quantity of vaterite production seen in nature yet [2]. As a result, many scientists are strongly optimistic about vaterite’s future in medical and industrial technology – all thanks to one unassuming alpine plant.
References:
[1] Grube, K. A rare mineral with potential industrial and medical applications has been discovered on alpine plants at Cambridge University Botanic Garden, 2018. University of Cambridge. https://www.cam.ac.uk/research/news/rare-mineral-discovered-in-plants-for-first-time (accessed November 1, 2020).
[2] Konopacka-Łyskawa, D. Synthesis Methods and Favorable Conditions for Spherical Vaterite Precipitation: A Review. Crystals 2019, 9, 223-241.
[3] Wightman, R.; Wallis, S.; Aston, P. Leaf margin organization and the existence of vaterite-producing hydathodes in the alpine plant Saxifraga scardica. Flora 2018, 241, 27-34.
Image: Pettinger, B. Saxifraga sempervivum; 2012. Flickr Creative Commons.