Rapid preparation of polydopamine coating as a multifunctional hair dye

Dyeing of hair is an interesting research field within the cosmetics industry due to the increasingly aging population worldwide. In order to reduce the toxicity of hair dye materials and improve the speed of hair dyeing, we developed an in situ polymerization of dopamine catalyzed by copper sulfate and hydrogen peroxide on the hair surface to form a polydopamine (PDA) coating for hair dyeing. The morphology and elements of polydopamine on hair were characterized. The durability, thermal insulation, and bacteriostasis performance of PDA hair dye were discussed. The results showed that human hair can be dyed by PDA in as little as 5 min with comparable dyeing results to those of commercial products. PDA-based hair dye displayed significant durability, and barely faded after continuous washing with shampoo (30 times). After PDA dyeing, the thermal insulation performance was enhanced, which could prevent external heat invasion in summer and local heat dissipation in winter, increasing the level of comfort. In addition, remarkable antibacterial properties were demonstrated, which could effectively prevent the occurrence of bacterial inflammation on the scalp. These results might push forward the evolution of nanomaterial-based hair dyes with promising green, healthy, and user-friendly advantages.


Experimental Section
Materials: Dopamine was purchased from Aladdin Chemical Co.Ltd, China.E. coli and S. aureus were purchased from Guangdong Microbial Culture Collection Center.
Phosphate buffer solution (PBS) was purchased from Sangon Biotechnology Co. Ltd, China.Blonde hair was purchased from Amazon (Emosa, #60 platinum blonde).

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Hair dyeing with polydopamine: The hair sample were first washed with water thoroughly to eliminate impurities on the surface.Then, add the fresh prepared mixture contained with dopamine (5 mg/mL), Cu 2+ (10 mM), and H 2 O 2 (15 mM).The entire dyeing process can be completed about 5 min.Then, the dyed hair was washed and dried in air.

Durability test of PDA hair dye:
The hair dyed with PDA was immersed in 5 vol% of shampoo in 40 mL of water in a 50 mL centrifugation tube.Then, the tube was vigorously shaken for 5 min on a vortex mixer.After washing, the hair was cleaned with water and dried in air.The PDA coating can endure over 30 washes without obvious decoloration.
Antibacterial test of PDA hair dye: First, the crude or PDA-dyed hair was placed into a 24-well culture plate.A 200 L of E. coli or S. aureus suspension in PBS (1×10 7 cfu/mL) was used to cover the substrate.Add 1800 L of PBS to dilute the bacterial solution after 2.5 h at 37 ℃ for agar plate incubation.Then, the bacterial suspension and each sample were transferred to a new tube for 5 min ultrasonic treatment to detach the adhered bacteria.Finally, the bacterial solution was diluted to 1000 times with PBS solution and 100 L of the bacterial solution was taken to measure the viability of bacterial by using agar plates.
Characterization: Morphology of the samples was observed by scanning electron microscope (SEM, QUANTA250, USA).X-ray photoelectron spectra were collected by a spectrometer (XPS, Perkin Elmer, USA) with Al Kα excitation radiation (1486.6 eV).UV-vis absorption was tested with an ultraviolet spectro-photometer (UV 2450, Shimadzu, Japan).MTT assays were performed on a BioTek Epoch2 microplate reader.Inductively coupled plasma mass spectroscopy (ICP-MS) were conducted on an ICPOES730 instrument (Agilent).Gel permeation chromatography (GPC) was carried out with a Shimadzu LC-10AD (column, TSKgel GMPWXL; solvent, water; flow rate 0.6 mL/min; 35 ℃).The digital images were taken on a shadow-less plate by a camera (5D Mark II, Canon) in a professional studio.

Fig. S2
Fig. S2 Reaction kinetics of PDA monitored by UV/Vis spectrophotometer at 465 nm.

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Fig. S3 (a) SEM micrographs of uncoated hair and PDA-coated hair.(b) SEM-EDS

Fig. S7
Fig. S7The diagram of changes of hair color responds to dyeing times.