Anti-wrinkle peptide physical techniques follow two basic pathways: one is mechanical disruption of the epidermis (e.g., microdermabrasion, microneedling), and the other is cavitation or pore formation in the skin (e.g., sonophoresis and iontophoresis) effect). Despite all the advantages of physical methods, one of their limitations is the need for special equipment to apply these techniques to clinical skin. Only two physical techniques, microneedling and iontophoresis, have been used in research on anti-wrinkle treatments.
Microneedles are a hybrid of hypodermic needles and transdermal patches, in which micron-sized needles are arranged on a small patch. There are microneedles with different penetration depths, and their most important feature is that they allow drug/cosmetic molecules to pass through the stratum corneum, the most challenging skin barrier. The average thickness of the stratum corneum is between 10–30 micrometers, and the length of the drug delivery needle is between several hundreds of micrometers. That's why microneedles don't induce pain and can effectively deliver agents to their targets in the skin.
There was no statistically significant difference in the total amount of peptide captured in the skin among all treatment groups, except for the comparison between the special microneedle ophthalmic patch and the commercially available patch containing acetyl hexapeptide-3. Compared with flat microneedle patches, the skin penetration of the specially prepared microneedle patches was better, which underscores the importance of conforming the microneedle patches to the skin surface during use.
Iontophoresis is a physical technique in which a physiologically acceptable electrical current is used to transport molecules across the skin. Mechanisms of electrorepulsion (driving charged molecules across the skin) and electroosmosis (creating a mass flow of charged and uncharged molecules in the membrane) lead to the iontophoresis process being effective for both charged and uncharged molecules. This method of physical penetration enhancement of anti-wrinkle peptides may aid in the skin delivery of the peptides.
The application of anti-wrinkle peptides as active ingredients in skin care products is currently a field of concern in the cosmetic industry. Numerous published studies have demonstrated the anti-wrinkle properties of such peptides, but their skin penetration has not been demonstrated. Most anti-wrinkle peptides do not have the characteristics of ideal penetration for skin delivery, and enhancement methods must also be used to increase their penetration.
Of course, further research is needed to determine the strengths and weaknesses of each augmentation method. It should always be noted that anti-wrinkle products are used by cosmetic consumers, so methods to increase skin penetration of peptides must not detract from the attractiveness of the product. Although we would like anti-wrinkle peptides to have higher skin penetration, the possible skin side effects of applying enhancement methods cannot be ignored. There are still many unanswered questions about skin penetration enhancement of anti-wrinkle peptides, such as the effect of electroporation, ultrasound, multipolar radiofrequency, and most chemical enhancers on the permeability of these poorly soluble molecules. Therefore, further research is needed to find out the optimal penetration enhancement strategy of anti-wrinkle peptides.
