Inspired by the iron gall ink that has been used since the Middle Ages, we formulated a hair-dyeing solution for blackening hair. The ingredients in the formulation have been approved as cosmetic ingredients, including tannic acid, gallic acid, and Fe(d-gluconate)₂. The formulation does not require any harmful oxidizing agents, such as hydrogen peroxide—the Fe(II) cations bound to tannins are oxidized spontaneously upon exposure to air and form the blackish Fe(III)-tannin nanocomplex that coats hair firmly. In our study, we show that the dyed color did not fade under sunlight exposure for at least three months and after shampooing. This natural formulation for black hair-dyeing can have great impact in the hair cosmetic industry.

One-step fabrication method for thin films and shells is developed with nature-derived eggshell membrane hydrolysates (ESMHs) and coffee melanoidins (CMs) that have been discarded as food waste. The nature-derived polymeric materials, ESMHs and CMs, prove highly biocompatible with living cells, and the one-step method enables cytocompatible construction of cell-in-shell nanobiohybrid structures. Nanometric ESMH-CM shells are formed on individual probiotic Lactobacillus acidophilus, without any noticeable decrease in viability, and the ESMH-CM shells effectively protected L. acidophilus in the simulated gastric fluid (SGF). The cytoprotection power is further enhanced by Fe³⁺-mediated shell augmentation. For example, after 2 h of incubation in SGF, the viability of native L. acidophilus is 30%, whereas nanoencapsulated L. acidophilus, armed with the Fe³⁺-fortified ESMH-CM shells, show 79% in viability. The simple, time-efficient, and easy-to-process method developed in this work would contribute to many technological developments, including microbial biotherapeutics, as well as waste upcycling.

Inspired by the redox reactions in the preparation of the iron gall ink that has been used in Europe since the Middle Ages, we developed a technology for forming the oil-in-water emulsions, without any surfactants and emulsifiers, by homogenizing a mixture of tannic acid, gallic acid, Fe(D-gluconate)₂, and natural oil, which are all approved as cosmetic ingredients. Various plant-derived oils, such as argan oil, olive oil, sunflower oil, grape seed oil, hemp seed oil, peppermint oil, rosemary oil, and ylang-ylang oil, were used as an oil phase for the emulsion formation, and all the fabricated emulsions exhibited the capability of black hair-dyeing. This surfactant-free emulsion technology for combining the hair-dyeing capability of Fe³⁺–tannin complex with the hair-fortifying property of natural oil would have great impact on the hair-cosmetic industry.