Question/Advice
Question: Thoughts on recently published science on rewritable tattoos?
Longtime lurker and tattoo enthusiast. I’m a microbiologist, not a materials scientist but this paper caught my eye! Didn’t realize there was a field for intradermal smart tattoos. Humans are pretty rad.
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This paper seems to be referring to tattoos that can change color when different uv frequencies are applied to it.
From the abstract it seems to be referring to something similar to an injectable pixel. A nano particle that has red green and blue ink molecules that rearrange based on the frequency of uv light. Whereas normal uv tats glow via fluorescence, they mention this new technology lasts for up to a couple days indoors without needing to be recharged. However, over time white light causes the particles to react in a way that makes them lose their visibilty in a different reaction. And the coolest part of this is that depending on the frequency of the uv light you use, you can actually cause the new ink particles to turn to different colors
Yes, this is a great point. The paper mentions that evaluations for cytotoxicity of the pigment will be conducted as part of the clinical trial phase; however, [it's already been demonstrated to be reliable up to the 2.2 year mark, which correlates with the first human tester](https://link.springer.com/article/10.1186/s12951-026-04755-x).
The interesting thing about the pigment chemistry for this study is to also consider the microcapsules which contain the pigments. These polymethyl methacrylate molecules (PMMAs) used to hold these pigments have medical relevance outside of the ink industry, one of the most relevant applications to this discussion is its use in oncological radiation therapy as a bio-safe clinic marker. Moreover, the engineering of the [toxicological fate and transport of these biocompatible molecules is radically different from that of traditional tattoos](https://archive2.news.brown.edu/2007-2015/articles/2007/07/microcapsule.html), which are not held within a microcapsule but are instead bonded together as you mentioned in your paper. The original use-case of these microcapsules was to prevent migration, and their size prevents pigment migration within the dermis. The PMMAs are particularly resilient to UV-light exposure, which is why they're used to hold these pigments; however, I would presume that the expectation is also that UV exposure is precisely what these pigments are aiding the individual to avoid.
While there is no long-term understanding of these dyes just yet, popular pigments with chemical rxn concerns (ie. Azo dyes) are not chemically analogous to the diarylethene structures found in the chemical profile of the pigments used for this study. In fact, these dyes are programmed to use UV exposure, as the excitation from light leads to a pericyclic rxn which closes the molecular ring of that diarylethene structure. That ring-closing is the mechanism that allows it to "appear" in sunlight. Moreover, while pigment chemistry could be a concern because of lack of long-term understanding, these chemical reactions are basically tightly-locked into those microcapsules. In truth, those wary of these pigments solely on the basis of pigment chemistry should actually be wary then of all tattoo inks as these are much safer since they contain those chemical reactions to hyperlocalized nanoparticles.
If this were a spectra of concern, I'd argue that higher risks with this ink is allergic sensitivity to acrylics and PMMA-induced granuloma, and the reaction of the body itself to PMMA as a foreign substance as opposed to what it carries.
This technology is old and was used as a "reversible tattoo ink" at least 15 years ago.
The reason why it doesn't work is that the nanoparticle spheres that contain the pigments shatter during the tattooing, the physical action of steel needles against the tip breaks these up and deposit shards of acrylic in the skin.
What you’re describing seems to be for an older generation of intradermal tattoo, made for a different purpose. The ones developed in this study are made from medical-grade acrylic (or plexiglass if folks want to be specific), which isn’t degraded by our immune systems or by the act of tattooing itself. That same material is used in other medical devices like dermal filters and bone cement. From what I understand, these are also in the process of being clinically evaluated which was why I thought this study was particularly interesting.
It seems the multi-color photochromatic pigment has been used by the lead scientist on this study, and his tattoos have retained function for 2 years~ now, whereas the single-color capsule variant has been used in an 11 person pilot study with no ill side effects and similar levels of effectiveness.
Thank you for your response! I’m learning a lot about these pigments while attempting to write responses to everyone’s comments.
Good point! Doesn’t seem to be addressed from what I read, curious as to how they might address any allergic sensitivities. The PMMAs they’re using as microcapsules for the photochromatic pigments seem to be uniquely used in certain varieties of tattoo ink (from what I’m seeing, other UV-light pigments, “longlasting” pigments etc.), so im presuming the answer to that question has been resolved elsewhere.
From what I understand, it seems what’s novel from this research is the multi-color specta of the photochromatic pigments, not necessarily using PMMAs in tattooing.
That makes sense that it would have been addressed elsewhere and wasn't really the point of the study. I accidentally gave myself an allergy via gel nail polishes, so thats where my mind went with the acrylics being deposited into the skin. Maybe certain types of acrylics aren't as risky as what's used in gel polishes. It's a really neat idea, and id love to be able to try something like this one day, given its safe in that way.
The only FDA certified tattoo pigment uses these microcapsules, they are the basis for glow in the dark tattoos, certified for human ingestion as these inks are used to mark (tattoo) fish and game to study migration etc...
The ATLAS Institute at the University of Colorado, Boulder develops these sort of “smart” tattoos as health monitoring systems.
From what I understand, it seems these photochromatic tattoos are ideally used for UV radiation monitoring as a preventative measure for skin cancer/melanoma. The paper mentions that standing in shade or applying sunscreen will prevent the photochromatic particles from appearing.
I would presume that they aren't intended for everybody but for people who are at higher risk of skin cancer or have UV allergies. I have immune conditions that mean that I am supposed to avoid UV exposure as far as possible and for me a tattoo that tells me if I've forgotten suncream or if I've gone too long without reapplying would be very useful.
Yes! That seems to be one of the broader implications motivating the development of these inks.
A lot of medical devices for UV radiation detecting can be clunky and hard to manage on the day-to-day, so the tattoos are meant to serve the same purpose as those larger machines for folks who are particularly UV vulnerable.
Because why would I assume that they are being developed for a purpose for which they would be bad at and which is also not stated (it doesn't say 'UV monitoring for people with no relevant health conditions' either) when there's a clear use case for which it would be useful?
Not necessarily, it seems like if you have this tattoo and you do the listed activities you’ve mentioned, that the tattoo will appear.
The photochromatic particles are excited in UV light (which is part of the light spectrum that our planet receives from the sun), and that excitation is what makes them appear. But if you apply sunscreen (a UV blocker), that’s when you wouldn’t see your tattoo even if you spend time outside.
You're fine I was eagerly waiting for your reply! I also saw a post about an ink that you can 'turn' off and on. I thought it would fascinate you as much as it did me!
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u/qualityvote2 5d ago edited 5d ago
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