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The mechanism of action is thought to be a disruption of the epidermis and dermis. Micropunctures are created using microneedles, which produce a controlled skin injury without damaging the epidermis. The mechanical microinjury results in the classic wound‐healing cascade and stimulates cellular proliferation and migration through the stimulation of growth factors (see Figure 1.2).

These microinjuries lead to minimal superficial bleeding and set up a wound‐healing cascade with release of various growth factors, such as platelet‐derived growth factor (PDGF), transforming growth factor alpha and beta (TGFα and TGFβ), connective tissue activating protein, connective tissue growth factor, and fibroblast growth factor (FGF) [5]. The needles also break down the scar strands and allow them to revascularize. Neovascularization and neocollagenesis are initiated by migration and proliferation of fibroblasts and laying down of an intercellular matrix [6, 7]. A fibronectin matrix forms five days after injury and determines the deposition of collagen, resulting in skin tightening persisting for five to seven years in the form of collagen III. The depth of neocollagenesis has been found to be 5–600 μm with a 1.5 mm length needle. Histological examination of the skin treated with four microneedling sessions one month apart shows up to 400% increase in collagen and elastin deposition at six months postoperatively, with a thickened stratum spinosum and normal rete ridges at one year postoperatively [8]. Collagen fiber bundles appear to have a normal lattice pattern rather than parallel bundles as in scar tissue [9].

Figure 1.2 The electric pen‐shaped device has adjustable settings to control the speed and depth of needle penetration.

Source: skvalval/Shutterstock.

The devices used create transient epidermal and dermal openings ranging in size from 25 to 3000 um in depth as a microinjury, with the goal of stimulating the inherent skin repair mechanisms. These microwounds or microinjuries initiate the release of growth factors, which trigger and stimulate collagen and elastin formation in the dermis. That leads to healthier skin with improved texture. The microwounds are microchannels and heal following the classic wound‐healing cascade: inflammation, proliferation, and remodeling. This cascade is brought on by the needles’ disruption of the stratum corneum; the endothelial lining and the subendothelial matrix recruits platelets and neutrophils to the site of injury. Needling exposes thrombin and collagen fragments, which attract and activate platelets. The platelets form a plug and initiate the clotting cascade, which involves local platelet aggregation, inflammation, and blood coagulation through increased levels of thrombin and fibrin.

The needles carry an electric potential that stimulates fibroblast proliferation [10]. The mechanical injury triggers the release of potassium and proteins that alter intercellular resting potential, drawing in fibroblasts and stimulating neocollagenesis and revascularization [6].

Research has shown up‐regulation of TGFβ3, a cytokine that prevents aberrant scarring; increased gene expression for collagen type I; and elevated levels of vascular endothelial growth factor, fibroblast growth factor, and epidermal growth factor [11–13]. Histological studies have shown huge variation in epidermal thickness. Randomized murine studies have reported statistically significant epidermal thickening from 140% up to 685% after microneedling plus topical vitamins A and C when compared to control [13, 14]. This is thought to be one of the reasons microneedling is effective for scar therapy and notable skin rejuvenation.

A human study of 480 patients treated with microneedling plus topical vitamins A and C reported thickening of the stratum spinosum lasting up to one year [8, 15].

Increased collagen types I, III, and VII and tropoelastin in human biopsies were found after six sessions of microneedling, ten with elevated levels of collagen type I and elastin persisting at six months. The number of melanocytes was unchanged postprocedurally.

These results support the safe use of this modality in patients with darker skin types [8, 15]. Having a safe and effective treatment modality for all skin types is advantageous in an aesthetic practice.