Non-invasive skin treatment device using r.f. electrical current with a treatment settings determiner (koninklijke philips n.v.) arkansas gas association

Various forms of electromagnetic radiation, particularly laser light beams, have been used for many years for a variety of therapeutic and non-therapeutic treatments of the skin, such as hair removal, skin rejuvenation to reduce wrinkles, and the treatment of conditions like acne, actinic keratosis, blemishes, scar tissue, discoloration, vascular lesions, cellulite and tattoo removal. Most of these treatments rely on photothermolysis, wherein a treatment location in the skin is targeted by the treatment radiation.

For example, to treat wrinkles, the dermis layer of the skin is damaged by heating (thermolysis) to induce a wound response, while minimizing damage to the epidermis layer of the skin. These microscopic photo-thermal lesions may be created by fractional non-ablative treatment using laser.

Radio-frequency (usually abbreviated as r.f.) energy has also been used for skin rejuvenation and skin tightening in both the professional and home-use aesthetic treatment devices market. Home-use devices are frequently used for non-therapeutic or cosmetic treatments. Compared to laser treatment devices, r.f. treatment devices have a substantially lower cost price and can provide larger-volume deep-tissue treatment. Additionally, r.f. energy dissipation does not rely on the absorption of light by chromophores, so that tissue pigmentation does not interfere with the delivery of energy. The advantages of r.f. treatments over laser treatments, and some embodiments of known r.f. treatment devices, are described in the article “Radio Frequency Energy for Non-invasive and Minimally Invasive Skin Tightening”, by R. Stephen Mulholland, Clin Plastic Surg 38 (2011) 437-448.

The basic principle of r.f. energy delivery at the skin surface to skin tissue is that an alternating current is applied in a closed circuit with the skin. The r.f. energy is dissipated as thermal energy primarily due to intramolecular vibrations. A broad range of thermal effects may be produced, including:

These effects may have different desired effects on the skin. Superficial skin damages are used for skin rejuvenation of the epidermis or to enhance the penetration of substances, while sub-epidermal tissue contraction is primarily used for skin tightening purposes and to stimulate new collagen synthesis.

Skin rejuvenation is generally achieved by intentionally heating an inner (or first) region of skin, proximate to the skin surface and the r.f. treatment electrode, to a temperature that is significantly above normal body temperature, typically to a temperature above 55 degrees C., so as to induce collagen denaturation and/or coagulation and/or full ablation of the epidermal skin tissue. This heating causes collagen and epidermal tissue re-modelling, resulting in a rejuvenated skin. To minimize downtime and side effects while maintaining sufficiently high efficacy levels, skin rejuvenation is often performed on a fractional area of the skin surface through the creation of distributed small lesions in inner regions of the skin close to the skin surface, typically 100-300 microns in size and usually by achieving a temperature of between 65-90 degrees C. An r.f. treatment device to generate a fractional pattern of such inner regions of the skin is disclosed in WO 2012/023129 A1.

Skin tightening is a non-ablative treatment based on thermolysis by heating an inner region of the skin, in particular the dermal skin layer. Typically, the target of the treatment is the dermis layer, which is at least 0.5 mm below the outer surface of the skin.

The thermal effects generated depend on the properties of the r.f. energy delivered, such as frequency, power, and duration, the treatment regime, the electrode configuration, such as size and inter-electrode distance, and the use of a conductive substance. An r.f. treatment of a certain condition may require more than one treatment to be performed at the same or proximal locations to generate the same, similar or different thermal effects.

To date, fractional skin treatments using r.f. energy are limited to professional use and are not considered suitable for home-use. A major reason is safety, because incorrect operation can result in undesired damage to the skin, which increases the healing time. Undesired ablative damage can easily occur, resulting in unnecessary pain for the person being treated. This is particularly challenging since the amount of RF energy deposited in the tissue depends on local tissue impedance, and since skin tissue has an inhomogeneous impedance distribution. This uncertainty relating to the skin impedance combined with the use of high current densities and voltages results in uncertainty relating to the achieved temperatures in the skin tissue during treatment.

U.S. Pat. No. 6,413,255 B1 discloses an apparatus to treat human skin by means of radio-frequency (RF) energy. The apparatus comprises a temperature and impedance feedback system used to control the delivery of the RF energy to the skin by the RF electrodes. The temperature of the skin tissue is measured by a temperature sensor. The skin impedance is calculated based on measurements of the current delivered through the RF electrodes and of the voltage between the RF electrodes. The delivery of the RF energy is interrupted when a maximum pre-set temperature or a set value of the impedance are exceeded. If the calculated impedance is within acceptable limits, RF energy continues to be applied to the skin.

WO 2015/040049 A1, KR-A-2012 0090007 and US 2011/0015687 A1 disclose similar examples of RF skin treatment devices comprising a sensor to measure the skin impedance during the application of the RF treatment energy, and comprising a controller to control the delivery of the RF treatment energy depending on the measured skin impedance. SUMMARY

An object of the invention is to improve a non-invasive skin treatment device using radio-frequency electrical current. In particular, an object of the invention is to provide an r.f. skin treatment device that provides better control over the heating during treatment.

wherein the skin treatment device further comprises a controller programmed such that, during operation, the controller, before activating the r.f. generator to apply the r.f. treatment signal, activates the impedance measurement circuit to measure an initial skin impedance (Z0) between the r.f. treatment electrode and the return electrode, wherein the treatment settings determiner is programmed such that, during operation, the treatment settings determiner determines the treatment settings depending on the measured initial skin impedance (ZO) and on a dimension of the r.f. treatment electrode in the contact plane, the treatment settings comprising at least the following:

an r.f. electrical parameter associated with the r.f. treatment signal; and wherein the controller is further programmed such that, after activating the impedance measurement circuit to measure the initial skin impedance, the controller consecutively: