Nanotechnology in cosmetics as seen by a “nanocook” (part II)

[Qui trovate la versione italiana di questo articolo]

In the previous article we learned what is nanotechnology and why is it a hot topic in pharmaceutical and cosmetic research. 

Now let’s take a closer look to some nanomaterials that are actually used in cosmetics. 

Previously, I mentioned that nanomaterials used in cosmetics can have in most cases one of the following roles: functional ingredients, formulation aids and nanocarriers.

Nanomaterials in cosmetics

Functional ingredients

Inorganic nanoparticles as UV-filters: nano-titanium dioxide and zinc oxide. 

Titanium dioxide (TiO2) and zinc oxide (ZnO) are used in sunscreens since many years, because of their UV-attenuation capability. When formulated together, they provide protection against both UVA and UVB radiation. Sunscreens formulated with micro-sized TiO2 and ZnO have however the drawback of leaving a consistent white trace, resulting in the typical “vampire effect” of many mineral-based sunscreens. The reduction of the particle size to the nano range makes the particle appear transparent and avoids this drawback, improving the compliance of the product while still providing UV-protection. 

There is however some controversy related to the safety of TiO2 and ZnO nanoparticles, and as a result many companies claim that their products are free from nanoparticles. This message, like many of the “free from” claims, can be a bit misleading: actually TiO2 and ZnO nanoparticles are considered as safe by EU and American authorities, provided that they follow the regulation concerning nanomaterials. On the other hand, one aspect that would deserve a deeper investigation is for sure the effect of such ingredients (both in nano- and in micro-versions) on the environment (1-5).

Silver and gold nanoparticles (nanosilver and nanogold)

Nanosilver and nanogold are nanoparticles made either of silver or of gold. They are known since decades and they found application in topical products and cosmetics because of their antibacterial properties. For example, nanosilver shampoos are sometimes prescribed as treatment of dandruff, whereas antiperspirants often contain silver nanoparticles as coadiuvants for the deodorant activity. As with other metallic nanomaterials, there is of course great concern about the safety of nanosilver and nanogold, and there is to-date no agreement on this point among researchers (10,11).

Formulation aids and nanocarriers

Nanoemulsions

Remember when we talked about emulsions? Back then, we said that emulsions are colloidal systems in which one liquid is dispersed into another liquid, in which it is immiscible. The dispersed liquid is then in form of little droplets, and the smaller the droplets, the highest the stability. If the droplets are nano-sized (smaller than 100 nm), we talk about nanoemulsions. 

One of the things that immediately distinguish a nanoemulsion from a microemulsion is the appearance: the smaller the droplets, the more transparent is the emulsion. A nanoemulsion is typically a transparent or slightly opalescent fluid; an emulsion with big droplets is white (that’s the case of our creams). They find application in cosmetics mainly because of their high hydration power, higher product compliance and better skin penetration compared to microemulsions (6).

Nanocapsules

Nanocapsules are nanosized particles made of a capsule (typically polymeric) that surrounds an inner aqueous or oily core, where the functional ingredient is hosted. They can be used to enhance the penetration of functional ingredients and their delivery to the stratum corneum, or as formulation aids to improve the stability of certain ingredients (7,8).

We often hear or read of nanoparticles, nanocapsules and nanospheres in the same context: for pharmaceutical technologists, nanoparticles is the term for the big family of nanosized spheres used in drug delivery; nanocapsules are (typically polymeric) nanoparticles where the drug is hosted into an inner core, surrounded by a sort of shell – the capsule; nanospheres are (also typically polymeric) nanoparticles where the drug is distribute uniformly in all its volume. They are also known as matrices. The truth is, that in many cases it is very difficult to selectively synthesise nanospheres or nanocapsules and to distinguish them in the characterisation.

Solid Lipid Nanoparticles

Solid lipid nanoparticles (SLN) are nanosized spheres made of lipids that are solid at room and body temperature. The incorporation of functional ingredients into the solid matrix or the inner core of a SLN provides similar advantages as in the polymeric nanocapsules and nanospheres, like protection against degradation. In addition, the materials used in the production of SLN are often excipient that are already present in traditional formulation, i.e. already established as safe. More and specific information about the topical use of SLN can be found in reference (9). 

Dendrimers

Dendrimers consist of branched monomers that extend radially from a central core, with the most commonly used being polyamidoamine (PAMAM) dendrimers. Their interior is empty and can host functional ingredients. Dendrimers found application in cosmetics in for example in the design of low-viscosity formulations thanks to their rheology properties, as nanocarriers for salicylic acid and as delivery systems for transdermal administration (12).

Liposomes

And finally we talk about them: the only ones that we can actually find in the suppliers’ shops if we are hobbyist formulators. Liposomes are the grandfathers of all the nanothings that I mentioned above. They are around since decades and they found their way even in the pharmaceutical market. And we can use liposomal formulation of some functional ingredients also in our homemade cosmetics, because the suppliers sell them.

Liposomes are vesicles formed by a bilayer of phospholipids that enclose an inner aqueous core, where functional ingredients can be hosted.

They have been extensively studied in pharmaceutical research as drug delivery systems because of their numerous advantages, including the excellent biocompatibility and interaction with cell membranes. Indeed, the phospholipid bilayer of liposomes resembles a lot the one of our cells, with whom liposomes can interact very well, and most phospholipids used for their synthesis are completely biodegradable and non-toxic.

In cosmetics, just like the other nanocarriers mentioned above, they are used to enhance the penetration of functional ingredients to the stratum corneum (13).

Maybe in the future I will do some more extensive research and tell you something more about the penetration of functional ingredients and of the nanocarriers, but for now, just know that under certain experimental circumstances and application doses, liposomes can deliver functional ingredients to the stratum corneum. But like I mentioned in the previous article, we always speak of skin delivery and not to the systemic circulation. Whatever is delivered by liposomes and nanomaterials is not meant to reach the rest of the organism: it must stay in the skin!

In the next article, we will focus on liposomes, as they are basically the only nanomaterial that we can get as hobbyist formulators from the suppliers to add in our wonderful creams, and I will tell you my unsolicited opinion on the meaningfulness of using them in our homemade (non professional) creams.

References

(1) Nohynek and Dufour, Nano-sized cosmetic formulations or solid nanoparticles in sunscreens: A risk to human health?, Archives of Toxicology, 2012, 86, 1063-1075
(2) Newman et al., The safety of nanosized particles in titanium dioxide- and zinc oxide-based sunscreens, Journal of the American Academy of Dermatology, 2009, 61(4), 685-692
(3) Smijs and Pavel, Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness, Nanotechnology, Science and Applications, 2011, 4, 95-112
(4) Schilling et al., Human safety review of “nano” titanium dioxide and zinc oxide, Photochemical & Photobiological Sciences, 2010, 0, 495-509
(5) EWG – Environmental Working Group, Nanoparticles in Sunscreens website, accessed April 23, 2020
(6) Sonneville-Aubrun et al., Nanoemulsions: a new vehicle for skincare products, Advances in Colloid and Interface Science, 2004, 108-109, 145-149
(7) Guterres et al., Polymeric Nanoparticles, Nanospheres and Nanocapsules, for Cutaneous Applications, Drug Target Insights, 2007, 2
(8) Sukhorukov et al., Intelligent micro- and nanocapsules, Progress in Polymer Science, 2005, 30 (8-9), 885-897
(9) Müller et al., Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) in cosmetic and dermatological preparations, Advanced Drug Delivery Reviews, 2002, 54, S131-S155
(10) Pulit-Prociak et al., Safety of the application of nanosilver and nanogold in topical cosmetic preparations, Colloids and Surfaces B: Biointerfaces, 2019, 183, 110416
(11) Wiechers and Musee, Engineered Inorganic Nanoparticles and Cosmetics: Facts, Issues, Knowledge Gaps and Challenges, Journal of Biomedical Nanotechnology, 2010, 6, 408-431
(12) Ammala, Biodegradable polymers as encapsulation materials for cosmetics and personal care markets, International Journal of Cosmetic Science, 2013, 35, 113-124
(13) Egbaria and Wagner, Liposomes as a topical drug delivery system, Advanced Drug Delivery Reviews, 1990, 5(3), 287-300

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