In a recent study published in iScience, researchers developed a rapid, sterile, and painless method of tattooing using single-use microneedle tattoo patches, which can be used for cosmetic and veterinary applications and storing medical information.
Tattoos have long held cultural and religious significance and have been widely used for decorative and artistic purposes. Tattoos also have medical applications such as cosmetic reconstruction, pigmentation correction in conditions like vitiligo, and communicating emergency medical information about chronic or serious health conditions. Veterinary uses of tattoos include identification numbers or symbols on cattle and other animals.
While the technology and inks used in tattoos have significantly improved, the basic principle still involves depositing pigment into the skin using needles. Traditional tattoo technologies have associated risks such as infection, pruritis, and bleeding due to contaminated needles or ink and unsafe application methods.
Microneedle patches have been used as an alternative to injections in biomedical applications. The patches contain microneedles coated with drugs taken up via the dermal vasculature. These medical patches are easy to administer, cause very little trauma, and do not result in biohazardous waste. Single-use microneedle patches can provide safe and painless medical, cosmetic, or decorative tattoo options.
About the study
The present study used a carbon dioxide laser cutting machine to make conical cavities in a polydimethylsiloxane (PDMS) sheet to form the tattoo pattern. The microneedles were created using a mixture of tattoo ink and a water-soluble, biocompatible polymer called poly(acrylic acid) (PAA) that dissolves after application, leaving behind the patch backing. The tattoos were tested on rat and porcine skin.
The researchers designed tattoos in various shapes, numbers, and letters using blue and red visible ink and ultraviolet (UV)-fluorescent ink. Tattoos were also designed for blood-type codes and disease labels such as ‘T1D’ for type-1 diabetes.
Additionally, the team developed microneedle tattoo patches for vaccine delivery, which had two components — one carrying the inactivated polio vaccine (IPV) and the other carrying information such as the year of vaccination — to avoid negative interactions between the ink and the vaccine. Rat models were used to test the immunogenicity of the IPV vaccine delivered through the microneedle patch.
Tattoos that were sensitive to environmental changes were also explored. Thermochromic ink was used to design a tattoo that would change color in response to varying temperatures. A more complex tattoo carrying a quick response (QR) code was also designed and tested using various applications that read QR codes.
The results showed that the tattoos were visible for at least a year, with no distortion in color and only mild distortion in shape due to aging of the skin. There were no adverse reactions to the procedure, and no biohazardous waste was generated. The UV tattoos were visible only under UV illumination, which kept the tattoo private.
Immunogenicity tests revealed similar levels of neutralizing antibodies in rat models as intramuscular injections of the same vaccine, signifying the efficacy of a microneedle vaccine. The companion microneedle patch tattoo carrying the year of vaccination was visible clearly for at least a year after vaccination. Such tattoo-vaccine combination patches can be especially useful in areas where recordkeeping facilities are limited.
The tattoo with the thermochromic ink changed color when heated beyond 40°C. Such tattoos can monitor temperatures during illness or treatments that result in elevated body temperatures. Similar environment-sensitive tattoo patches can be developed for other stimuli of interest, such as pH, enzyme, and glucose, to monitor health conditions.
Overall, the study reports a sterile, painless, bloodless method to administer tattoos for decorative, cosmetic, and medical applications. While the design options have not yet attained the levels of complexity and artistry of traditional tattoos, these microneedle patch tattoos can effectively administer simple, medically informative, or cosmetically useful tattoos.
The QR tattoos designed in this study have a wide range of potential applications and the ability to carry large amounts of information that can be accessed through various easily available applications. The microneedle patch tattoos can also indicate animal identity and sterilization status without causing trauma. Furthermore, they can provide life-saving information on health conditions to emergency responders.
To conclude, the microneedle patch tattoos developed in this study provide access to safe, infection-free, painless, and possibly self-administrable tattoos that can be used for decorative, cosmetic, and medical applications.