Radiofrequency
RF energy has been used for more than a century in a variety of medical applications. Non-ablative RF (monopolar, bipolar, tripolar or multipolar and fractional) was described by different studies as an effective and safe approach for skin rejuvenation. Depending on the delivery system and frequency, superficial or deep heating can be produced. RF was approved by the FDA in 2002 for the non-ablative treatment of wrinkles and skin tightening and for full-face treatment in 2004.
Essentially, RF devices consist of a RF generator, automatic resistance test technology via computerized software, continuous cooling system, hand piece and different size treatment tips. The RF generator produces alternating current that creates an electric field through the skin. The electric field shifts the polarity millions of times per second, causing a change in the orientation of charged particles within the electric field. Thus, heat is generated by the skin's resistance to the flow of current within an electric field.
The mechanism of action of RF is dual in nature: i) an early instant collagen contraction and ii) a secondary wound-healing response, in the form of new collagen formation and remodeling with eventually tightening. The immediate skin contraction is attributed to the sparse pattern of collagen denaturation, while sufficient tissue is left healthy to ensure wound healing. Over time, as a thermally mediated healing response, heated fibroblast stimulation enhances formation of new collagen leading to further collagen tightening and overall increase in collagen deposition. Additionally, another mechanism of action for monopolar RF has been based on the fact that the delivered energy usually favors the least resistance path. As subcutaneous fat lobules are divided by interweaving network of collagen-based septa, these fibrous septa are preferentially heated resulting in collagen tightening. This gives the patient immediate, visible improvement the day of the procedure with subsequent lifting and remodeling of subcutaneous tissue, as well as the skin becomes tightly attached to the underlying structures.
Unlike most lasers, which target specific chromophores, the output energy of the RF is a chromophore-independent; it does not follow the principles of selective photothermolysis. Heat is generated as a result of tissue resistance to the movement of electrons within the RF field; allowing energy to be delivered to 3D levels of the dermis.
El-Domyati et al. analyzed the effect of monopolar RF on individuals who underwent treatment on the face every 2 weeks for 3 months for a total of six sessions. Punch biopsies of the facial skin were performed at baseline, end of treatment and 3 months after treatment. Noticeable clinical improvement, together with significant histologic findings including decreased dermal elastin as well as increased collagen types I and III was observed after treatment.
Bipolar RF devices pass electrical current only between two positioned electrodes applied to the skin. No grounding pad is necessary with these systems, as monopolar RF, because no current flows throughout the remainder of the body. It is claimed, however, that bipolar RF cannot produce a uniform volumetric heating comparable at all with monopolar RF.
The use of a tripolar (multipolar) device has been explored for the treatment of skin aging; the device has three probes that exploit the benefits of both unipolar and bipolar RF to treat tissue. Although bipolar devices rely on active integrated cooling devices to avoid damage to the epidermis, the tripolar device advertises simultaneous moderate deep and superficial heating of tissues that does not require protective cooling for the epidermis.
Newer RF technologies including devices with multigenerational sources and fractional RF system have emerged with more promising potential since then. Fractional RF has the non-invasive modes of known RF devices with the development of a minimally invasive bipolar microneedle delivery system. It generates localized coagulation zones within the reticular dermis characterized as RF thermal zones. This fractional RF system offers controlled dermal heating through pulse duration variance, allowing for fractional sparing of the epidermis and important adnexal structures. Studies showed that the treatment-generated RF thermal zone in the reticular dermis consists of denatured collagen separated by spared dermis. These zones were replaced by new dermal tissue within 10 weeks.
