Julian P. Hewitt – JPH SunCare Technologies, UK SUN CARE
Status of nanotechnology in sunscreens
The prefix ‘nano’ is one of those terms that polarises opinion. Advocates of nanoscale materials point to their many advantages and applications, while on the opposite side are those who feel that nanotechnology per se carries unknown risks to human health and should be avoided at all costs.
A number of different nano-sized components have applications in personal care, for example: Nanoemulsions: emulsions with a droplet size of typically 50 nm to 100 nm, which, because of this small droplet size, are usually transparent or at least translucent in appearance and also provide pleasant texture and/or skin feel.
Liposomes, niosomes, nanosomes and nanocapsules: liposomes and niosomes are globular vesicles which can vary from 25 nm to 5000 nm in size, and are used to encapsulate active ingredients in order to improve stability or skin delivery (and hence efficacy) of these ingredients. Nanocapsules represent a similar concept except that such capsules have rigid walls.
Fullerenes: a number of prestige cosmetic products have been developed which contain C60 fullerene molecules, which have unique anti-oxidant properties.
Inorganic particles: nanoscale forms of, for example, iron oxide, silica, and alumina have also found application in cosmetic products.
Of these, the nanoemulsions and the vesicles are designed to break down into their constituent ingredients when applied onto skin or hair, so in terms of assessing risk, these are no different to conventional cosmetic emulsions and delivery systems. Assessing the safety of such systems is simply a matter of considering the safety of the bulk constituents; the fact that they are in a nano form in the formulation is irrelevant. The current debate around nanotechnology in personal care is instead focused on ‘persistent’ nanoparticles, i.e. those that remain in a particulate form after the product has been applied.
Nano-object: an object having one or more external dimensions on the nanoscale.
Nanoparticle: an object having three external dimensions on the nanoscale.
Nanorod: an object having two external dimensions on the nanoscale.
Nanoplate: an object having one external dimension on the nanoscale...
The most common types of such nanoparticles in personal care products are the UV-attenuating grades of titanium dioxide and zinc oxide, in which a small particle size is required in order to give effective UV protection combined with transparency on skin. This article outlines current thinking regarding the definition and characterisation of nanomaterials in cosmetics, discusses the properties of inorganic sunscreens in relation to these definitions, and examines the safety and regulatory aspects of these materials.
What is ‘nano’?
Nanotechnology is one of those terms that we all think we understand (in the scientific community at least), but for which most of us would struggle to provide a precise definition. This may be because there is no ‘official’, globally-recognised definition of the term. However, it is now generally considered that nanoscale substances are those in the size range below 100 nm, where the physical and/or chemical properties of the material are significantly different from the larger size or bulk versions of the same material. A current draft definition from the German Standards Institute (DIN) and the International Standards Organisation defines the following:
...with ‘nanoscale’ being defined as approximately 1 nm to 100 nm. However, composing a precise definition of a nanoscale material is not as simple as just specifying a particle size range. It is important to recognise that some materials can exist as particles that have external dimensions outside the nanoscale, but which consist of aggregates or agglomerates of smaller particles or crystals, where these smaller particles are within the nanoscale range. The DIN/ISO proposal describes these as “nano- structured aggregates” or “nano-structured agglomerates”. The terms aggregate and agglomerate are often confused or used interchangeably, but they are in fact quite distinct and are defined as follows:1 Aggregate: particle comprising strongly bonded or fused particles where the resulting external surface area may be significantly smaller than the sum of calculated surface areas of the individual components.
Agglomerate: collection of loosely bound particles or aggregates or mixtures of the two where the resulting external surface area is similar to the sum of the surface areas of the individual components.
The situation is not helped by the plethora of particle sizing techniques available, and the different results given by these methods. Some techniques measure the component nanoparticles, while others measure the size of aggregates and/or agglomerates. Also, any measurement is dependent on how the samples are prepared. This is why the particle sizes quoted by manufacturers can vary so widely; in order to compare different
April 2012 PERSONAL CARE 129
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