Delivery of light to the skin through ablated conduits

Abstract

Background and objectives: Non-invasive laser skin treatment modalities are generally designed to protect the epidermis by cooling and limiting the laser energy deposition in accordance with skin type. We explore a treatment modality that uses a 2,940 nm Er:YAG laser with high tissue absorption to ablate an array of channels through the epidermis and upper dermis, and then deliver laser energy from a 1,320 nm Nd:YAG laser with lower tissue absorption through the ablated channels. Treatment through ablated conduits offers a unique capability to deliver laser radiation to a deeper level in the dermis or beyond the dermis and the delivered energy to be deposited in a nearly uniform distribution. The ablated channels represent a relatively small surface and volume fraction of the epidermis and upper dermis, and heal very fast. A pilot study was performed to explore the benefits of treatments through ablated conduits for skin tightening, cellulite, and acne scarring.

Materials and methods: A custom-built laser from Cynosure Inc. was designed to deliver to the epidermis up to 3 J/cm² at 2,940 nm from an Er:YAG laser followed in less than 10 ms by up to 20 J/cm² at 1,320 nm from a Nd:YAG laser. Both laser sources were delivered to the skin through a diffractive lens array. The spatial intensity modulation created by the diffractive lens array on the skin surface consisted of a low energy density background that did not damage the epidermis and a superimposed array of much higher energy density regions where the Er:YAG laser ablated the channels, and most of the 1,320 nm laser energy was delivered through the channels. Various fluence combinations of the ablative and non-ablative lasers were tested on ex vivo human skin samples to evaluate tissue effects and parameters for a clinical test. A limited clinical study was performed to evaluate tissue response and healing effects.

Results: Histology confirmed the presence of ablative channels through the epidermis and upper dermis as well as the absence of epidermal damage apart from the channels. Three days posttreatment there was complete skin healing with no evidence of channel ablation or coagulation in the skin biopsies. Limited clinical testing for facial treatments showed mild improvement for acne scarring and skin laxity.

Conclusions: Laser skin treatment through ablated conduits can be performed safely with fast subsequent healing of the channels ablated through the skin. Further refinement of the treatment parameters and variation of the wavelength of the non-ablative laser source may bring improved treatment efficacy. Lasers Surg. Med. 49:69-77, 2017. © 2016 Wiley Periodicals, Inc.

Keywords: ablative channels; diffractive lens array; fractional energy delivery.