74 TESTING
Figure 3: Punctual compression to determine structural strength of the nail.
close cooperation with Professor Paola Perugini and her team of the University of Pavia, Italy. The measuring parameters such as structural strength of the nail, hardness, firmness, thickness and flexibility of the distal edge before and after applying a product or cosmetic treatment on the nail, can precisely be evaluated by measuring the resistance against a compressive/bending force applied. The result is a curve in a force deflection diagram. Its slope is different depending on interesting mechanical properties of the nail.
Structural strength/firmness
This parameter describes the cohesion of the nail matrix. The nail is punctually compressed by a special adapter. The result is the slope of the force/deflection curve. The steeper the curve, the more pressure is needed to compress the nail and the higher
Figure 4: Different applicator tips, to assess a variety of mechanical nail parameters.
the structural strength/firmness. Firmness is positively related with nail density. The density is usually determined by dividing the membrane weight by its volume (in vitro).7
Flexibility and elasticity
Also the flexibility and elasticity of the nail can be successfully measured with the Nail StrainStress Meter by evaluating the force versus deflection curve of the nail using special adapters for transversal and longitudinal deformation. Both parameters are very interesting not only for brittle nails.
Thickness With the new measurement method described above, also the thickness of the nail is determined quite easily. It ranges roughly between 300-800 nm and increases with age, whereas the structural strength decreases when a person gets older.
Other nail parameters
Ultrasound images have also been used to investigate nail plate thickness and alterations. Optical parameters such as nail shape,
roughness, free edge length and curvature can be assessed by cameras or video microscopy.3
For the measurement of the nail colour
directly or of products applied to the nail (e.g. nail polish) a colorimeter can be used. There are also probes available to
measure the nail gloss. These come in extremely handy when you want to demonstrate the effect of nail gloss and finishers applied to the nails. The measurement time, same as for nail colour measurements is only one second. For the manufacturers, such measurements make it easy for them to compare the effects of their nail polish. Surprisingly, in general the evaporation
Figure 5: A special soft rubber tip makes colour measurements on the nail easily possible.
PERSONAL CARE EUROPE
rate from the nails (TransOnychial Water Loss - TOWL) is a lot higher than on the
skin. This indicates that the nails play an important role in the metabolism of the complete body. The better their structural strength, the lower the TOWL. Tests have been conducted using a modified Tewameter®
. Conclusion
So, altogether a number of claims for the nails can be objectively measured. The effect of nail hardeners, nail polish and the properties of various types of artificial nails can be easily demonstrated with the new Nail StrainStress Meter. Other claims could be restructuring and re-densifying of the nails by treatment with special nail care products or nail strengthening by certain food supplements. Protective products could be evaluated by measuring the evaporation rate of water. Also, the TOWL measurement could be used to show that nail polish remover, the glue from an artificial nail or other aesthetic nail treatments do not damage the nail. Fields of application for the assessment of nail gloss and colour are obvious, and not only restricted to the evaluation of applied nail polish. Such measurements can also be used to show the effects of whitening products and mechanical polish. Even in medical conditions like nail fungus, the measurement of nail thickness could give an indication of the effect of treatments with anti-fungal medication. As also other skin diseases can extend to the nails, the objective measurement of the nail condition can be used to offer additional information about the overall improvement by medical treatment.
And why not try to test whether my anti- ageing hand cream does not also improve the condition of my fingernails? There are no limits to new claims created around nail care that can be proven with these new methods.
September 2018
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