Patch technology was developed taking as reference the transdermal patches developed by the pharmaceuticals industry for application in human medicine (oestrogens for treating menopause; nitroglycerine for chest pain (angina); or nicotine for treating smoking habit, contraceptives and analgesics).
The patches used in medicine release their compounds with regulation of both timing and dosage; in this context, the technology of IDP constitutes a revolutionary and unique system capable of transporting different beneficial molecules from the epidermis to the deepest layers of the dermis, thus allowing the active ingredients to act from inside to outside and maintaining the beneficial effects for longer periods of time.
The increase in oxygen demand and subsequent capillary expansion generates an absorption effect that facilitates transport of both water and the active ingredients contained in the inner surface of the patch; these substances are thus immediately absorbed by the roughest layers of the skin.
Transdermal Patches guarantee:
- Maximum penetration to the dermis
- Immediate and visible effects
- Programmable action: from 20 minutes to several days of continuous treatment
- Reasonable costs
WHAT ARE TRANSDERMAL PATCHES?
All you need to know about Transdermal Patches and Dermocosmetics
Introduction
A very important increase in the transdermal administration of pharmaceutical products was recorded during 1999 throughout the world. There are three reasons for this phenomenon:
1- The skin is the organ of easiest access in the human body.
2- The administration of active substances through the skin avoids first-step liver metabolisation and its risks.
3- The administration of active substances through the skin ensures the maintenance of therapeutic concentrations.
Some of the particularities of transdermal administration may be particularly advantageous in cosmetic applications.
In addition to protecting our organism, the skin possesses thermoregulatory and immune functions, and is responsible for the synthesis of vitamin D.
In the pharmaceutical and cosmetic context, the most interesting feature of the skin is its role in regulating water loss and its capacity to oppose the penetration of chemical and/or aggressive substances into the body.
This "chemical barrier" effect centres particularly on the outermost skin layer - preventing the progression of cosmetics even when these are destined to improve the physiological and biochemical conditions of the skin. On the other hand, the horny layer is composed of cells that have been dehydrated and are surrounded by lipids (20% water); this composition differs greatly from the hydrophilic medium (70% water) characterising the deeper-lying vital epidermis.
Taking these principles into account, it is possible to introduce cosmetic substances through the epidermis: firstly by developing lipophilic compositions to which vehicles or penetrative agents are added (to cross the horny layer), and secondly by including hydrophilic elements according to pre-established proportions and techniques (in order to penetrate the epidermis).
Transdermal Patch technology
The Transdermal and Epidermal Application systems can be classified as follows:
A- Transdermal or Intradermal Patches
B- Hydrogel Patches
C- Cosmetic Strips
D- Functional Strips
E- Aromatherapy Strips
A- Transdermal Patches - Hydrocolloid technology
The principal aim of this transdermal system is to control the percentage administration of active substance into the bloodstream; in this context, the skin plays an essential role in defining the pharmacokinetics of the active ingredients.
1- Controlled membrane permeation
This system consists of an impermeable posterior layer and a porous polymeric membrane containing a reservoir with the active substances (i.e., drug reservoir). The latter are delivered to the skin through the membrane at a predefined rate. An adhesive polymer layer ensures good contact between the patch and the skin.
2- Adhesive polymer dispersion system
This system, also known as a matrix technique, is fundamented on direct dispersion of the active substances within the adhesive component, with application to the skin under an impermeable film layer. Other layers lacking active ingredients can also be added beneath the active layer. In such cases, since the active substances must diffuse through the inactive adhesive layer in order to reach the skin, the components must be chemically and physically compatible.
3- Matrix controlled diffusion system
In this system the active substances are dispersed within a hydrophilic or lipophilic polymer, which is in turn located beneath an impermeable and occlusive disc. The adhesive component is distributed around the impermeable disc perimeter - unlike in the system described above. The release of the active ingredients is regulated by the polymeric matrix component.
4- Microreservoir-controlled diffusion system
In this system the active substance is suspended in a water-soluble solution. The suspension is then homogenized in a polymer that forms thousands of microscopic spheres. The lipophilic polymer is subsequently tailored to form an impregnated disc. The latter is applied under an occlusive and an impermeable lamina, beneath which lies the adhesive layer that keeps the device in contact with the skin. Active substances release is regulated via sedimentation within the fluid and polymer compartments, and by diffusion through the lipophilic polymer.
The Cosmetic Transdermal Patch designs detailed above do not include the protective layer, the function of which is simply to ensure preservation of the product. This protective layer is removed and discarded prior to use of the patch. Nevertheless, the choice of protective layer is very important, since an inadequate layer may adversely affect the stability (and therefore efficacy) of the patch.
Transdermal Patches in cosmetic practice
Although the therapeutic efficacy for cosmetic purposes of all the main transdermal application methods has been demonstrated, the design best suited to the practical requirements corresponds to the second dispersion system based on adhesive (matrix) polymers. This suitability is mainly due to the simplicity of use and to the relative ease with which the patch can be adapted to the needs in each case.
Unlike the traditional systems involving creams, oils, etc., Cosmetic Patches ensure total penetration into the skin and maximum biological availability of the active ingredients. These effects are the result of three defining features of Transdermal Patches:
1- Availability of the active ingredients in a lipophilic environment
As has been mentioned above, lipophilic compounds diffuse more easily through the outer horny layer of the skin.
2- Gradual (prolonged) release of the active ingredients
In the conventional formulations the active substance is immediately available and only a small portion effectively crosses the horny layer.
With the transdermal system, however, the active ingredients are released gradually (drop-by-drop), thus ensuring maximum absorption.
As an example, a cloth is wetted if a bucket of water is suddenly poured onto it - though the cloth only becomes thoroughly soaked if we empty the bucket slowly.
3- Occlusive application of the active substances
The polythene or PVC layer overlying the adhesive and active ingredients is impermeable and occlusive - a fact that increases perspiration in the zone, with opening of the skin pores and therefore easier access on the part of the substances. Another practical advantage of this layer is that it prevents evaporation and oxidation of the more delicate ingredients of the patch.
B - Hydrogel Patches
Hydrogel Patches are composed of a material (TNT) under which a sodium polyacrylate gel is applied (capable of retaining abundant water); the active substances are in turn dispersed within the gel component.
The main characteristic of these patches is the cold sensation they produce during application, as a result of their water content. As a result of this feature, Hydrogel Patches are widely used in antipyretic, freshening and hypothermal therapies.
As to their cosmetic applications, and although they are not Transdermal Patches, these devices are very useful as a vehicle for hydrating, firming and tensing substances. Hydrogel Patches are being used in application to delicate areas such as around the eyes - though they are also very popular for Facial and Body Patches.
C Cosmetic Strips
These are patches that have an essentially mechanical effect. The typical example is the Blackhead Patch for the nose.
In the case of these patches it is necessary to avoid synthetic polymers and use only natural substances: a mixture of casein and dextrin is a good choice. These patches must be moistened before use, and should then be allowed to dry. The keratinised zone becomes adhered to the patch, thus deep-cleansing the skin. The use of traditional glues is too aggressive and less effective in this sense.
The technical difficulty posed by these patches is keeping the layer beneath the TNT component humidified about 10%. Lower percentage humidities tend to dry the mixture excessively and thus reduce its efficacy. It is therefore essential to store the patch in a sachet to prevent evaporation of the water content.
D- Functional Strips
Other patches affording mechanical action are those applied to the nose to facilitate nostril dilatation and breathing.
These patches are used to limit snoring at night, and in sports activities to increase oxygen supply.
E- Aromatherapy Strips
Based on special manufacturing techniques, it is possible to produce aroma-containing microcapsules that are deposited onto a patch to facilitate adhesion to the skin. Specifically, microcapsules containing aromatic fluids are deposited onto an adhesive PVC, polythene or other support; gentle scratching of the patch surface releases the aromatic substances.
A classic example is the balsamic patch, the microcapsules of which contain essential eucalyptus and pine oils on a soft PVC support. Combinations with other essential oils can yield patches with relaxing, energizing or anti-nausea effects, or action against insect bites, etc.
If a nose clip such as those found in Functional Strips is used, the resulting strip can offer mechanical and aromatic properties - ensuring double efficacy by facilitating oxygen entry to the nostrils.
Conclusions
Patch technology offers extraordinary prospects for the future in both Pharmaceutics and in Cosmetics.
The manufacturers should be aware that Patch technology offers great efficacy at a reasonably low cost. A decisive factor is the choice of who is to produce their own patches - seeking true specialists in this technology and rejecting patches that do not meet the required quality and control standards. Their own credibility is at stake in this sense.
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