Lithography’s Journey: From Stone Printing to Tardigrade Tattoos
Lithography began over two centuries ago as a printing revolution and has since evolved into a key microfabrication technique that powers modern technology. Its name, from the Greek lithos (stone) and graphein (to write), hints at its origins. In 1796 German playwright Alois Senefelder accidentally discovered that drawing on limestone with a greasy crayon, then etching away the rest of the stone, created a flat-surface “master” that could repeatedly print images. This invention of “flat-surface printing” came to be called lithography, and by the 19th century it was the dominant method for book illustrations and posters. The classical process exploited the fact that oil-based inks stick to the greasy design on the stone but not to the wet background, allowing high-quality prints with a natural hand-drawn feel.
Over time, lithography shifted from the atelier to the laboratory. In the 20th century, engineers adapted the principle to semiconductor manufacturing. Instead of limestone, silicon wafers became the “canvas,” and instead of wax crayon, ultraviolet light would transfer a pattern from a photomask onto a light-sensitive photoresist. This photolithography process became the workhorse of the microelectronics revolution, fabricating the integrated circuits (chips) in our phones, computers and cameras. Modern photolithography “transfers geometric patterns to a film or substrate,” building the microscopic circuit elements on silicon. As one explanation puts it, lithography in chipmaking essentially means transferring a fine circuit design onto another surface using light. By carefully controlling masks, wavelengths and chemical develops, photolithographers etch features ever finer, driving Moore’s Law for decades.
Electron-beam lithography (EBL) is the next step in miniaturisation. Rather than using light and masks, EBL replaces photons with a focused beam of electrons. The beam “draws” patterns directly on an electron-sensitive resist film. Because electrons can be focused to very small spots, EBL can achieve feature sizes down to a few nanometres – orders of magnitude finer than optical lithography. However, this precision comes at the cost of speed. EBL is a maskless, serial process: it writes patterns pixel by pixel, which is slow and expensive. It is therefore typically used for photomask production, research prototypes and low-volume nanodevices In effect, if photolithography is the printing press of microchips, electron-beam lithography is a high-precision pen for making the finest doodles on silicon.
Despite these advances, applying lithography to living, irregular surfaces has remained a challenge. Traditional microfabrication prefers flat, clean substrates; biological tissues and cells are wet, soft and textured. As University of Missouri physicist Gavin King explains, e-beam lithography “is great for the relatively uniform surfaces of silicon wafers but not for highly textured and organic materials,” whereas the emerging technique of ice lithography “can be applied to the delicate and complex surfaces of biological systems”. This insight has motivated researchers to find gentler “printing” methods for biology.
Ice lithography extends the lithography concept into the cryogenics. In this process, a thin layer of ice (or frozen solvent) is deposited on a sample, and a focused electron beam carves patterns into the ice. The beam’s high energy induces chemical changes in the frozen layer where it strikes. When the sample is later warmed, any unreacted ice evaporates (sublimates), leaving behind only the reacted material as a stable micro-pattern. In essence, the ice acts as a temporary resist that protects the underlying surface while the beam does the writing.
The general idea of ice lithography has been explored for delicate nanofabrication. For example, a team at Missouri used frozen ethanol to coat fragile purple membranes of Halobacterium microbes. The ice layer protected these biological photosynthetic membranes from damage during exposure; the electron beam etched patterns into the ice, and then warming removed the ice. As King notes, “the frozen layer helps keep everything stable during the process and makes it possible for us to work with delicate biological materials that would normally be damaged”. In this way, the lab’s ice-based lithography bridged microelectronics and microbiology.
Ice lithography is still in its infancy, but it offers exciting possibilities. One could freeze volatile organic vapours or water to form a protective cloak over a sample, write patterns with an electron beam, and then sublime away the icing to reveal conductive or functional deposits. As Technology Networks explains, ice lithography “carves designs into a thin layer of ice” on a surface, and the beam-triggered chemistry “leaves behind a stable pattern once the ice sublimates”. This resolves the old problem of how to print on something that melts or moves at room temperature – simply keep it frozen until after you’ve written!
Tattooing Tardigrades: A Microfabrication Breakthrough
In April 2025, researchers published a striking demonstration of ice lithography on a living organism: a tardigrade. Tardigrades (also called water bears) are microscopic eight-legged animals famed for their extreme hardiness. As the American Chemical Society press release enthuses, “prepare to be wowed”: these half-millimetre critters can withstand freezing, near-starvation, crushing pressure, intense radiation and even the vacuum of space. In short, nothing, or no place seems to kill a tardigrade in its tracks.
Taking advantage of this resilience, Ding Zhao, Min Qiu and colleagues (Westlake University, China) devised a protocol to inscribe microscopic “tattoos” onto living tardigrades. The team reported their results in ACS Nano Letters under the title “Patterning on living tardigrades.” In other words, they used the tardigrade as a testbed for biocompatible microfabrication, aiming to “build microscopic, biocompatible devices” on the surface of a living creature.
Image Credit: Nano Letters 2025, DOI: 10.1021/acs.nanolett.5c00378
The key technique was ice lithography. The researchers first dehydrated the animals slowly, inducing a cryptobiotic state of suspended animation: in this state metabolism nearly stops and the tardigrade can survive extreme conditions. Each dehydrated tardigrade was then placed on a carbon-composite substrate and cooled to about –143 °C. A thin film of anisole – an aromatic organic compound – was introduced as a vapour and instantly froze into a smooth protective layer around the specimen. (Anisole, which smells faintly of anise, was chosen because it is reactive under electron beams and can readily sublimate).
Once the tardigrade lay encased in frozen anisole, a focused electron beam was scanned over selected regions. The high-energy electrons locally reacted the anisole, forming a novel biocompatible chemical coating wherever the beam hit. Crucially, this reaction-bound material adhered to the tardigrade’s surface at higher temperature, while the rest of the ice remained unmodified. The sample was then gently warmed in vacuum. Unreacted frozen anisole simply evaporated away, sublimating into gas and leaving behind only the reacted residue that constituted the micro-pattern. Finally, the cryogenically preserved tardigrade was rehydrated. Remarkably, it revived and continued moving – now sporting a microscopic tattoo on its back where the anisole had been patterned.
In practical terms, the result was astonishing. Under the scanning electron microscope, the team could see tidy arrays of dots, lines, squares and even a university logo (Wuhan University) imprinted on the tardigrade’s body. The smallest features were about 72 nanometres across (less than one-thousandth the width of a human hair). Out of dozens of try, roughly 40% of the tardigrades survived the entire process. Those that did survive showed no change in behaviour after revival: they crawled about and fed normally, apparently unbothered by their “tattoos”. This suggests the method is indeed biocompatible, at least for such rugged animals.
The laboratory “tattoo” of a water bear has profound implications. It shows that micro-scale electronic or sensor components could one day be written directly onto living tissues without killing them. In the words of Ding Zhao (co-author of the study): “Through this technology, we’re not just creating micro-tattoos on tardigrades – we’re extending this capability to various living organisms, including bacteria”. In other words, this proof-of-principle opens the door to patterning circuits on cells and other organisms as well as tiny animals.
Tardigrades: Nature’s Nano-Engineers
Why were tardigrades chosen? Their answer lies in their remarkable biology. Tardigrades routinely undergo anhydrobiosis: they can survive extreme desiccation by entering a glass-like inert state. During cryptobiosis, tardigrades retract their legs, lose almost all body water and turn into a “tun” which can withstand freezing or heating. When later rehydrated, they burst back to life. This ability to freeze and rehydrate is exactly what the experiment needed. Many microorganisms and some small animals share cryptobiotic abilities (nematodes, rotifers, etc.), but tardigrades are among the toughest – as one news release put it, they “can survive practically anything: freezing temperatures, near starvation, high pressure, radiation exposure, outer space and more”.
In biology, cryptobiosis is defined as “a reversible state of suspended metabolism that some organisms enter in response to adverse environmental conditions, such as dehydration or freezing”. Tardigrades exploit this to endure conditions that would kill most life. For the lithographers, this was a perfect feature: it let them subject the animal to vacuum, extreme cold and an electron beam, yet still expect revival. By contrast, human cells would instantly die under these conditions. The tardigrade, practically immortal under tough conditions, served as a living test substrate for micro-patterning on life forms.
After tattooing, the tardigrades indeed revived and behaved normally. “Most importantly, the tardigrades didn’t seem to mind their new tattoos: once rehydrated, they showed no changes in behaviour,” the researchers note. This indicates the micron-scale patterns did not physically harm or disturb them in any obvious way. Because the chemical ink was biocompatible (derived from reacted anisole), it didn’t dissolve away or toxify the creature. In essence, the tardigrade silently carried an onboard micro-circuit of sorts.
The scientific significance goes beyond a cute gimmick. It suggests that we could eventually print functional electronic or sensing elements onto cells, bacteria or even small organisms. For example, circuits could be written on bacterial biofilms to create “microbial cyborgs” that sense environments or produce energy. Patterning tissue scaffolds or plant leaves with conductive traces might one day allow integrated living electronics. This research demonstrates a convergence of nanofabrication and biology: taking the rigid processes of semiconductor making and stretching them to the living organisms.
Applications and Future Directions
The researchers themselves, Zhao and Qiu, envision “advancements such as microbial cyborgs and other biomedical applications” flowing from this first step. What might those look like? Some possibilities include:
- Biohybrid microsensors: Writing tiny electrodes or sensors onto living cells or tissues could yield implantable devices that monitor health parameters from the inside out.
- Living microchips: Embedding logic or memory circuits on bacteria (as molecular carriers) to create biological computing elements.
- Environmental biosensing: Printing responsive micro-patterns on soil microbes or plant roots to detect pollutants, pathogens or nutrient levels in real time.
- Tissue engineering: Patterning scaffolds with micro-electronics, perhaps to stimulate cell growth or deliver drugs at precise locations inside the body.
In all these scenarios, the goal is to integrate living organisms and electronic functions seamlessly. This work with tardigrades is a first demonstration that the feat is physically possible on a tiny scale. The fact that nearly half the animals survived such harsh processing is promising, and the survival rate could improve with refinements. For example, optimising the thickness of the ice layer, the beam energy, or the type of sublimating material might raise viability.
Moreover, the technique could be adapted to other “cryophiles” – organisms that tolerate low temperatures – or to cells and tissues by finding suitable cryo-protectants. (Interestingly, the Missouri team found that ethanol ice was gentler than water ice for some microbes) Future work could even aim to deposit conductive or semiconductive materials via the beam, not just organic patterns. For instance, metal salts frozen into ice could be reduced by the electron beam to form metal lines that become actual circuits on cells. In principle, one could imagine wiring up a living neuron network or building a wireless antenna on a plant leaf!
At this stage, however, such applications remain in the future, probably. Gavin King aptly remarks that this advance “portends a new generation of biomaterial devices and biophysical sensors that were previously only present in science fiction”. Indeed, the idea of “tattooing” living beings with microelectronics used to sound like science fiction. Now it is science fact – a small step, but a real one.
Conclusion
From Senefelder’s limestone prints in 1796 to nanoscale tattoos on tardigrades in 2025, lithography has undergone an extraordinary journey. The same basic idea – patterning a surface to build an image or device – has scaled down by a factor of millions, from the size of a book page to the width of a few dozen molecules. The latest chapter in this story is as surprising as it is visionary: using lithography not on chips or stone, but on a tiny, living animal.
This breakthrough microfabrication technique opens fascinating horizons. It suggests that the tools of electronics and photonics might one day work hand-in-hand with the tools of biology. Imagine a future where circuits literally grow on biological tissues, or microscopic robots made of cells carry built-in electronics. That future will require new interdisciplinary science.
For now, the image of a “water bear” with a university logo on its back is both a playful curiosity and a signal: nature, with a little human ingenuity, can carry the future of technology on its shoulders. It’s a small step for microelectronics, but perhaps a giant leap for microbioelectronics.
Sources
Yang et al., “Patterning on living tardigrades,” Nano Letters 25, 6168–6175 (2025), doi:10.1021/acs.nanolett.5c00378.
R. Cole, Lithography, Royal Collection Trust (Queen’s Gallery, Edinburgh)rct.uk.
Alois Senefelder, Encyclopædia Britannica britannica.com.
WaferWorld (2016), “Photolithography in Semiconductor Manufacturing” waferworld.com.
College of Arts & Science, University of Missouri (2024), Nanotech on ice coas.missouri.edu.
EurekAlert! (20 May 2025), “Cool science: Researchers craft tiny biological tools using frozen ethanol” eurekalert.org.
Technology Networks (23 Apr 2025), “Ice Lithography Tattoos Micro-Patterns on Living Organisms” technologynetworks.com
American Chemical Society (22 Apr 2025), Press Release: “Scientists have found a way to ‘tattoo’ tardigrades”acs.orgacs.org.
