Ashkan Shafiee1 Elham Ghadiri2 Warren Warren3 Anthony Atala1

1, Institute for Regenerative Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States
2, Chemistry, Wake Forest University, Winston-Salem, North Carolina, United States
3, Chemistry, Duke University, Durham, North Carolina, United States

Biocompatible electronic has become a focus of attention owing to the need in biomedical applications. Smart electronic devices capable of communicating with biological structures such as human tissues and organs are the requirement for many sophisticated purposes in medicine. Melanin is one of the most stable biopolymer, found in almost every live organism, versatile for application in the emerging field of bioelectronic devices. Melanin pigments are found in human skin, hair, eyes and the brain in different forms. For many years, it was viewed simply as a coloring agent with some photoprotective properties, but that view always ignored some obvious features. The functionality of melanin as a natural pigment is defined (although not fully understood) by its physical and chemical properties, such as its featureless broad UV-NIR optical absorption, antioxidant properties, and temperature/water dependent photoconductivity. Melanin also shows in vivo and in-vitro biocompatibility. All these properties identify melanin as a unique alternative for using as the functional material in the bioelectronic devices.

This paper report the inkjet printing of synthetic melanin nanoparticles with different size for electronic applications. Inkjet printing deposition with computer-assisted abilities can pattern different types of materials on various flexible or rigid substrates. Inkjet printing deposits patterns with Pico-liter size droplets of the functional materials with micrometer resolution. This economic consumption makes this technique much more affordable compared to other deposition techniques such as spin coating and dip coating.

Through solution-based chemical synthesis, we have prepared melanin nanoparticles with controlled size and chemical structures of melanin-like nanoparticles, pheomelanin and eumelanin. The active layer of the electronic device consists of melanin nanoparticles based film prepared with inkjet printing technique. Nanoparticles solutions with different sizes of 70 nm, 100 nm, and 250 nm were printed on transparent conductive electrode using Jetlab II Microfab, piezoelectric printer. The optoelectronic and photophysical processes in the films are studied using steady-state UV-NIR diffuse reflectance spectroscopy and ultrafast time-resolved broadband pump-probe spectroscopy technique. Using ultrafast broadband spectroscopy measurements, we identified the spectral signature of excited state formation and compared excited state relaxation in melanin nanoparticles with different sizes. This research can open up the new avenue of research toward biocompatible electronic manufacturing.