Advancements of paper-based microfluidics and organ-on-a-chip models in cosmetics hazards

Abstract

Cosmetics have been used in society for centuries for beautification and personal hygiene maintenance. Modern cosmetics include various makeup, hair, and skincare products that range from moisturizers and shampoos to lipsticks and foundations and have become a quintessential part of our daily grooming activities. However, dangerous adulterants are added during the production of these cosmetics, which range from heavy metals to microbial contaminants. These adulterants not only reduce the quality and efficacy of cosmetic products but also pose a significant risk to human health. Detecting the presence of adulterants in cosmetics is crucial for regulating substandard cosmetic products in the industry. The conventional methods to detect such adulterants and quality testing are expensive and take a lot of effort, particularly when involving advanced analytical detection and clinical trials. Recently, efficient methods such as microfluidic methods have emerged to detect adulterants rapidly. In this review, we mainly focus on various adulterants present in cosmetics and their detection using paper-based microfluidic devices. In addition, this review also sheds light on the organ-on-a-chip model with the goal of developing a human tissue model for cosmetic testing. Combined, these approaches provide an efficient, inexpensive, and sustainable approach for quality testing in the cosmetics industry.

Fig. 1. A general schematic of the cosmetic adulterants and utility of μPADs and OOAC in their detection and safety testing.

Fig. 2. Fabrications, mechanism and application of microfluidic devices in detecting cosmetic adulterants. Microfluidic devices are designed and fabricated as according to the reaction principle of the reaction for detecting the adulterant. They may be fabricated using inkjet printing, electrode embedding in a chip, or polymer-based lithographic fabrication methods. The device contains loading site(s), to load samples and/or reagents. The samples will spread across the reaction site upon loading, through the capillary action. The target adulterant in the sample selectively reacts with specific reagent to give signal in terms of product. Different methods could be used for detection of the adulterants, including colorimetric, aptameric, fluorescence and luminescence-based approaches.

Fig. 3. Paper spray ionization and filter cone spray ionization working: the first part depicts paper spray ionization, which is used to identify nitrosamines in cosmetics; an electric current is applied to the sample directly on the paper substrate, causing the analytes within to ionize. After that, a mass spectrometer is used to analyse these charged ions. Paper spray ionization design modified and adapted from ref. , licensed under CC BY 4.0. In filter cone spray ionization, an additional ionization technique, charged droplets are formed on the application of electric fields, leading to the ionization of analytes, and these ions are subsequently analysed using a mass spectrometer. The sample is placed on the tip of the filter cone and an appropriate solvent is used to extract the analytes. Filter cone spray ionization modified and adapted from ref. , with permissions under Copyright ©2020, the American Chemical Society Publications. These methods were tested and adopted for nitrosamine detection using the same principle.

Fig. 4. Detection of various metals using paper-based microfluidics. (a) Aluminum hydrochloride in anti-perspirant samples using a colorimetric technique based on paper. The purple tint of Alizarin S was the colorimetric agent utilized. The figure design is modified and adapted from ref. , with permissions under Copyright ©2018, Elsevier. (b) Scheme showing using μPAD integrated colorimetric method based on aptamer, to detect lead in water samples. Due to differences in localized surface plasmon resonance (LSPR), the aptamers split apart when they bind to the target, accumulating AuNPs and changing color from red to blue or purple. Due to AuNP aggregation, the interaction of gold particles with NaCl causes a color shift from red to purple when lead is present. The figure design is modified and adapted from ref. , with permissions under Copyright © 2018, the Royal Society of Chemistry. (c) Scheme showing the design of a microfluidic device to detect zinc. The circular sample zone of the microfluidic paper-based device is surrounded by two similar arms, each of which has a circular pre-treatment zone and a circular detecting zone. Zinc and 1,2 naphthol reagent (PAN) react at room temperature and pH 6.0. Pink chelates are formed by zinc. Modified and adapted from ref. , licensed under CC BY 4.0.

Fig. 5. Eye-on-a-chip and skin-on-a-chip device structure: the first part depicts EOAC. The epithelium and endothelium cells derived from a human cornea are cultured on two scaffolds. There exists an extra-cellular membrane. There are inlet channels connected to both levels. The two cell layers interact with each other. The TEER (trans-epithelial electrical resistance) zone is connected to a computer to evaluate the corneal barrier function. Skin-on-a-chip (in the second part) consists of three layers: epidermis, dermis, and endothelium cells derived from the skin, which are grown one over the other, and are separated by an ECM. There are inlet channels which can be used for different treatments. Vertically stacked cell layers with ECM in between are used to study the interaction and inflammatory markers in between the layers. Eye on a chip modified and adapted from ref. , licensed under CC BY 4.0., and skin on a chip modified and adapted from ref. , licensed under CC BY 4.0.