Nanotechnology in cosmetic products might not be considered a new technology, as liposomes were introduced to the market in the 1980’s. Since then we’ve seen the rise of several trends, including peptides, proteomics, stem cells and epigenetics. Howsoever, cosmetic companies including L’Oreal, P&G, Henkel, Unilever, Dior and Johnson & Johnson publish several nanotechnology-related patents every year, which means that investments in this research area are relevant to this day.
What are cosmetic nanomaterials?
The EU Regulation 1223/2009 defines the term ‘nanomaterial’ as an “insoluble or biopersistant and intentionally manufactured material with one or more external dimensions, or an internal structure, on the scale from 1 to 100 nm”. Under this regulation, many biodegradable nanoparticle formulations used in cosmetic products are not considered nanomaterials and many suppliers are using this fact to name their ingredients ‘submicron particles’ instead of ‘nanoparticles’. Uncertainty and bias usually accompanies the surge of new technologies, which is the case with nanotechnology; many cosmetic companies are unclear in their communications about what technologies are used in their products.
More importantly, one should be reminded that nanotechnology includes the “understanding and control of matter and processes at the nanoscale, typically, but not exclusively, below 100 nanometres in one or more dimensions where the onset of size-dependent phenomena usually enables novel applications” as defined by the ISO/TC 229. Accordingly, submicron particles act as delivery systems and convey different properties to materials in that size range, hence they will be considered nanoparticles in the scope of this article.
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The size-dependent phenomena nanoparticles present are primarily linked to the higher surface area of particles in the nanoscale, which alter their optical properties (e.g. inorganic sunscreens will look transparent upon application on skin), and encapsulated fragrances can last longer and perform better. In addition, nanostructures can:
- Protect cosmetic actives from light or oxygen – especially advantageous for antioxidant molecules;
- Overcome insolubility problems;
- Control the release of substances;
- Perform better because of penetration into deeper skin layers through increase in skin permanence.
Many substances have been incorporated into nanostructures to benefit from these properties, including retinoids, antioxidants (e.g. resveratrol and curcumin), sunscreens (e.g. benzophenone-4 and avobenzone), peptides, depigmenting agents, among others. Particles in the nanometric size range have also the ability to scatter UV light, thus acting as physical UV filters.
In addition to these advantages, nanoparticles in general provide good hydration. This is due to an occlusion effect that is proportional to the decrease in size of nanoparticles and hence increase in particle number that form a protective thin film on the skin and reduce the trans-epidermal water loss (TEWL). Even though nanoparticles may be formed by solid or liquid lipids, the technology helps avoid the greasy appearance after application on the skin and the overall sensorial properties also improve.
Manufacturing nanocosmetics
The manufacture of a nanocosmetic requires some additional steps compared to other cosmetics. One must carefully analyse the need to incorporate an active substance into nanostructures and fully understand the purpose of encapsulation. Many suppliers of cosmetic ingredients produce nanotechnology-related formulations, ready to be incorporated into cosmetic bases. The advantage is that no internal development is needed, which requires specialized equipment and resources. Some examples of ingredients are listed below:
- NLT AdenoSphere 2.0 (liposomes with 2% adenosine) by BioSpectrum, Inc
- Nano-Lipobelle H-EQ10 (nanoemulsion with 5% coenzyme Q10 and 10% vitamin E acetate) by Mibelle AG Biochemistry
- LPD’s Lightening (liposomes with sodium ascorbyl phosphate) and LPD’s Slimming (liposomes with caffeine, Ivy extract and Laminaria digitata extract) by Infinitec
- Crystalide (lipid nanoparticles containing tripeptide) by Sederma
- BergaCare SmartCrystals Rutin (nanocrystals of rutin) by Berg + Schmidt
On the other hand, many companies choose to develop nanotechnology-based formulations internally to leverage the scientific knowledge of the company through patented formulations and exclusive products. See below for an overview of different types of nanoparticles that can be industrially produced.
Nanocrystals
The potential skin applications of plant-derived compounds such as astaxanthin, lutein, and curcumin is becoming well-known due to studies showing collagen and elastin production stimulation. The greatest issue with using these compounds in cosmetic formulations is their poor solubility in water and oil. In this way, nanocrystals of pure substances processed below 1000 nm (and stabilized by surfactants or polymers) solved this problem by increasing the saturation solubility of these compounds because of increased surface area of nanoparticles.
Milling, high-pressure homogenisation (HPH) and controlled precipitation/crystallization are common methods to produce nanocrystals in industrial scale.
Liposomes
Liposomes are composed of phospholipids such as phosphatidylcholine, phosphatidylserine, or phosphatidylethanolamine. Due to their amphipathic nature, they form bilayers in water that self-assemble into spherical vesicles with a hydrophilic core. Several methods are available to produce liposomes, and their size can be reduced with membrane extrusion techniques or HPH.
The main advantage of liposomes is that hydrophilic and lipophilic substances can be incorporated into the aqueous core and into the lipid bilayer, respectively. In addition, phospholipids naturally occur in the skin and for this reason they are considered biocompatible, biodegradable and non-immunogenic.
On the other hand, liposomes can be physically and chemically unstable, prone to aggregation and lipid peroxidation during storage.
Lipid nanoparticles
There are two generations of lipid nanoparticles: Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC). The first generation of lipid nanoparticles was made of solid lipids surrounded by an aqueous phase and stabilized by surfactants and/or emulsifiers. The main drawback found for the first generation was the crystallization of the solid lipids and consequent expulsion of the active substances from the nanoparticle.
This problem was overcome with the second generation of nanoparticles, in which the core is a mixture of solid and liquid lipids in varied proportions, hence keeping an amorphous structure and stabilizing the active substance within the nucleus.
Lipid nanoparticles improve the penetration of cosmetic actives by slowly releasing to the skin from the reservoir. In addition, lipid nanoparticles have an occlusive effect, thus reducing the TEWL and help maintaining a proper level of hydration. They are also known for their UV scattering effect, acting synergistically with chemical sunscreens to increase the SPF in cosmetic products.
The production of lipid nanoparticles requires high energy equipment to break down larger lipid droplets into nanoparticles. This is achieved with the use of HPH, available from laboratory to industrial scale. HPHs push a liquid formulation through a gap in the range of micrometres with high pressure (100 – 2000 bar). The production of formulations using HPH is cost-effective and suitable for large-scale production, and many products using this technology can be found in the market.
Polymeric nanocapsules
Nanocapsules are core-shell structures in the nanometric range. The core can be liquid, semi-solid or solid and it’s usually comprised of hydrophobic molecules. The shell is a polymeric membrane surrounding the core, typically made of polymers such as PCL, PLA, PLGA, PVP, among others. Natural polymers such as chitosan, sodium alginate, and albumin can also be used to formulate nanocapsules.
Because the active substance is usually confined within the core of the nanocapsule, the polymeric wall acts as a barrier to diffusion, which helps avoid a burst release and achieve controlled release. This reduces any irritability the active may present and also improves the chemical stability of the active. Moreover, the external coating of nanocapsules can be modified with other molecules so properties like adhesivity to the skin can be achieved.
One of the methods used to produce polymeric nanocapsules is nanoprecipitation. Industrial production can be achieved in different ways, based on the same principles of laboratory scale batches. The production involves solubilisation of the polymer and oil phase in an organic solvent, with consequent injection of that phase into an aqueous phase containing a surfactant – this is where the nanoprecipitation will occur. The organic solvent is removed through distillation. One can also perform spray-drying of the aqueous suspensions, and create a final powder formulation that is easily redispersed.
Other remarks
Nanotechnology-based formulations can provide great advantages to a cosmetic, but may pose some challenges during development. It is very important to consider the proper characterization of nanocosmetics as a fundamental step during development, since the stability and performance of the product will strongly relate to that. To develop a reliable, reproducible and effective product, it’s best to analyse multiple parameters. Characterization techniques include average size and size distribution, polydispersity index, zeta potential, and morphology.
Further reading
- When Small is Big: Nanomaterials EU Regulation 1223/2009 Update
- News Brief: “Green” Antimicrobial Nanoparticles Combine Lignin & Silver
- Oil in Water Nano-emulsions
References
Nanobiomaterials in Galenic Formulations and Cosmetics. DOI: http://dx.doi.org/10.1016/B978-0-323-42868-2.00001-2. Elsevier Inc. 2016.
Nanocosmetics and Nanomedicines – New Approaches for Skin Care. DOI 10.1007/978-3-642-19792-5. Springer 2011.
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Hello dear Gabriele. Thank you for providing such a thorough explanation. Could you possibly send me some advice on how to make nanostructured lipid carriers from soybean oil for cosmetic use? The goal is to make nanoparticles that are high content in oil and low in surfactant. I’m honoured to be able to rely on your advice.