| MICRONEEDLING | PEER-REVIEW
microneedling treatment and is, therefore, a penetration enhancer. The topical needle massage leads to cell activation in the epidermis and stimulates the metabolism and absorbability in the upper cell layers. During the non-invasive microneedling treatment the
so-called Fakir effect prevents the penetration of the needles into the epidermis. The needles are very densely arranged during the non-invasive microneedle massage. The pressure ‘p’ depends on the force ‘F’ and the area ‘A’, on which the force is applied perpendicularly. Generally, it applies that how deep, or rather if, the microneedle penetrates the skin at all depends on the pressure as well as on the needle friction. With a few needles in the treatment area, slight pressure is enough to penetrate the skin. The friction increases with the increase in the number of needles and at a certain needle number the friction prevents the penetration of the skin completely. The material, the diameter, and the shape of the tip of the needle are further important influencing factors. Plastic needles have a higher friction coefficient than metal because the metal surface can be produced smoother.
Mode of action of minimally-invasive microneedling The minimally-invasive microneedling treatment is predominantly an application method for compounds to be applied onto the skin. The penetration depth of the needles is restricted to the epidermis during a minimally- invasive microneedling treatment. The stratum basale as the border layer to the dermis is not penetrated. Furthermore, the epidermis between the approximately 250 needles per cm2
stays intact, so that no structural
impairment occurs to the epidermal and dermal skin layers. Thereby, the non- and minimally-invasive microneedling treatments comply with the requirements of the cosmetic act 1223/2009/EC for a combined application with cosmetic products, as these may only be applied to the skin topically. The minimally-invasive microneedling treatment of
the epidermal barrier improves the absorbability of the skin for the topically applied compounds. In particular, the dead skin layer (stratum corneum) is perforated by the needle treatment. The cell layers below the epidermis (stratum granulosum, stratum spinosum, stratum basale) as well as the upper cell layer of the dermis (stratum papillare) are activated by the irritation of the needle. This cell activation leads to better circulation and stimulates the metabolism in the upper skin layers. Thus, the cosmetic product can more effectively cross the epidermal barrier increasing the uptake of the substance. To safely limit the penetration depth of the epidermis,
needling devices (for example needle rollers or powered devices with needle cartridges) with very short needles are used for the minimally-invasive microneedling treatment. The needle length amounts to between 0.2 and 0.5 mm. The actual penetration depth of the needle is dependent on the number of needles per area, performance of the needle tip, needling pressure, acceleration of the needle swing, and the flexibility of the skin.
The
conventional microneedling instrument is the so-called needle roller. Needle rollers are manual instruments with a handle and a cylinder, on which sharp needles with a diameter of 0.3 mm to 0.4 mm are fixed.
Definition of cosmetic non-invasive and minimally-invasive microneedling A non- or minimally-invasive microneedling treatment on healthy or damaged skin in combination with a cosmetic product according to the cosmetic act 1223/2009/EC for the purpose of cosmetic skin care is regarded as a cosmetic application. As far as the authors are aware, the execution of such a treatment, for example for the purpose of accelerated skin renewal or for the purpose of moisturizing psoriasis, can be performed by a qualified beauty therapist across the EU.
Definition for medical non-invasive and minimally-invasive microneedling A non- or minimally invasive microneedling treatment on diseased skin without, or in combination with, a topical medical compound to cure or to mitigate the pathological condition of the skin (for example pharmaceuticals according to the European pharmaceutical directive 2001/83/EC or medical devices according to the European medical device directive 93/42/EEC) is regarded as a medical application. In accordance to the nature of the skin area as well as to the medical compound the execution of the treatment is performed either by a physician or by a medical specialist delegated by a physician.
Mode of action of invasive microneedling During invasive microneedling treatments, thousands of tight adjacent micro-lesions are introduced into the dermis by fine needles, leading to the synthesis of collagen through the initiation of the wound healing cascade4
. This effect is called percutaneous collagen
induction (PCI). Through PCI it is possible to effectively treat wrinkles and scars without the risk of hyper- or hypopigmentation or a dysfunction in the wound healing process due to infections. To ensure the required penetration depth of the
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