The skin is the largest organ of the body and our primary barrier against microbes and the elements. It can be affected by diseases and disorders with very different pathophysiology, as well as suffering from the effects of aging. The potential for photonics applications in dermatology includes diagnosis, imaging and treatment for different conditions, as well as to enhance the properties of the skin for aesthetic appeal. Some well-known photonics technologies such as Optical Coherence Tomography (OCT) and confocal microscopy have been widely applied to the characterisation and analysis of skin samples. On one side, an evaluation of different features in the skin can be performed to decide when a treatment is necessary; on the other hand, they can also be used to monitor the evolution of a potential disease.

Another interesting example are the light therapies used to target tissues and achieve clinically useful effects without resulting in unintended heat or damage. Different wavelengths and power levels have been explored in order to get the best results in terms of efficiency and penetration in the internal layers of the skin.

Spectroscopy for skin analysis and characterisation

Spectroscopy is a very well-known set of techniques used in very different medical and healthcare applications. In particular, Raman spectroscopy is the perfect technique for in vivo measurements because it is non-destructive and does not require sample preparation, reagents, dyes, labels or other contrast enhancing agents. The technology is based on the scattering of light by molecules, where the sample under investigation is illuminated with low power laser light and part of the energy from the incoming light is transferred to a molecule, exciting one of its vibrational modes. Because every molecule of a cell or tissue contributes to the overall Raman spectrum, the data obtained is a direct representation of the overall molecular composition and can be used as a highly specific fingerprint of the specimen under analysis.

A good example is the gen2-SCA confocal Raman system that is made for in vivo skin analysis and developed by RiverD. It can be used to determine molecular concentration profiles from the skin’s surface into the dermis with high spatial resolution; to measure the distribution of intrinsic skin constituents – amino acids, sweat constituents, lipids, proteins and water, to name a few; to perform noninvasive quantitative analysis of dynamic processes such as skin penetration and permeation of topical formulations; or see the difference between volar forearm skin, cheek, forehead, scalp, axilla and other areas.

Advanced infrared spectroscopy

Infrared spectroscopy is another widely used technology due to the possibility of identifying free-living organisms, analysing the composition of biological fluids and tissues or understanding in vivo processes. Traditional infrared spectroscopy is now being enhanced by quantum cascade lasers (QCLs). Their increased power allows the penetration of thicker samples and their stability, spectral range and tunability make them a great tool to integrate in different clinical settings and medical devices. The company Alpes Lasers have been working in different applications for their QCLs, including mid-infrared imaging of thin tissue sections and pathogen detection. Another very interesting application of the Alpes Lasers sources are the non-invasive detection of glucose, in skin (back scattered radiation), in human epidermis (photo-acoustic detection) and in skin (photothermal deflection technique).

Diagnosis of skin cancer

The incidence of skin cancers has increased over the past decades, which has by necessity led to growing interest in the development of new diagnostic techniques. A typical dermatologic diagnosis relies primarily on the expertise of the dermatologist, followed by the histologic examination of a skin biopsy. As this is quite a slow and invasive method, different options have been studied to overcome its disadvantages, and photonics technologies have been the preeminent choice.

Confocal microscopy, multispectral imaging or optical coherence tomography are some of the imaging techniques most commonly used. Each show different advantages in the analysis of skin samples and can be used to detect different features. This diversity in the available techniques led the Universitat Politecnica de Catalunya to launch the EU project DIAGNOPTICS to evaluate different biophotonics-based tools in a pilot diagnostic workflow. The idea of the project was to use the different techniques as a set of consecutive filters to discard benign lesions and confirm the malignant ones, in order to guide the patient to surgery only when required. As a result of the project, a multiphotonic diagnostic platform was developed, including multispectral and 3D techniques, blood flow analysis based on self-mixing and confocal microscopy for in vivo imaging of skin cancer lesions.

New lasers for treatment of diseases and disorders

The development of diode lasers with new and improved specifications have significantly impacted the treatment of vascular lesions. Telangiectasia and Rosacea are two conditions that have been targeted using the technology. The first one, also known as spider veins, are small, dilated blood vessels that can occur near the surface of the skin or mucous membranes, measuring between 0.5– 1mm in diameter. They are commonly seen around the nose, cheeks and chin. Rosacea is a long-term skin condition that also affects the face, resulting in redness, pimples, swelling and small and superficial dilated blood vessels.

Lumics has been very active in this field and its diode lasers, Mini4 and Mini8, have emerged as game-changers in this domain. The company offers a versatile solution for medical device manufacturers that want to offer laser-based solutions for dermatologists, including different customisable options and an efficient cooling system to ensure reliable and consistent performance during treatments. Due to the capability of being equipped with the specific wavelengths absorbed by haemoglobin (up to four different wavelengths in one unit), they are a highly effective source in the treatment of vascular lesions. When directed at the affected area, Lumics’ diode laser precisely targets the blood vessels, causing them to coagulate and eventually fade from view. This targeted approach minimises damage to surrounding tissues, making diode lasers a safe and efficient choice for telangiectasia treatment.

Aesthetics applications

Photonics technologies and devices have developed not just to treat disease, but also as a way to enhance the skin, applications typically characterised as ‘cosmetic dermatology’. One example is body contouring or body sculpting, a treatment focused on the elimination of fat, shaping areas of the body and tightening the skin. Lumics’ diode lasers are used in this application due to their capability to deliver controlled and consistent energy to specific areas of the body.

“The light can penetrate deep into the skin to target fat cells, causing them to break down and stimulating collagen production and leading to firmer and tighter skin.”

The light can penetrate deep into the skin to target fat cells, causing them to break down and stimulating collagen production and leading to firmer and tighter skin. This dual-action approach makes diode lasers an ideal choice for body contouring procedures, allowing patients to achieve a more sculpted and youthful appearance.

Another example is laser blepharoplasty, also known as laser eyelid surgery. This procedure uses an infrared laser to tighten the skin and remove excess skin and fat. CO2 lasers replaced cold-steel scalpels in surgical dermatology procedures a few years ago. They were selected as the best suited surgical laser for this application because both cutting and haemostasis are achieved photothermally. Nevertheless, efforts have been focused on finding alternatives to avoid the surgical process altogether. One of the technologies that arose as alternative is the plasma fibroblast therapy, which presents some interesting benefits: there is no need to cut the skin, it is a pain-free treatment – although there can be some discomfort – no injectable anaesthetic is needed and it requires minimal recovery time. The treatment is performed using a plasma fibroblast pen that discharges a high frequency electric current just above the skin, causing micro injuries in the epidermal and upper dermal layers of the skin. The target of the treatment are the fibroblasts – collagen and protein producing cells that play an important role in maintaining skin firmness and helping skin heal. The heat damage breaks down proteins and stimulates fibroblast activity, encouraging tissue to regenerate and tighten the skin. The company Monocrom has developed a specific CW, fibercoupled laser source to integrate in these plasma fibroblast pens, with a peak wavelength at 1,478nm and operating power of 2W.

Er: glass fibre lasers for facial cosmetic treatments

Staying on the theme of facial rejuvenation, recent studies have looked at the results with newly developed Er: glass fibre lasers. These create microscopic thermal treatment zones within the stratum corneum and epidermis. These new sources allow for cosmetic treatment without the need of topical analgesics, and also reduce pain, discomfort and recovery time when compared with other laser-based techniques. The company LumIR is developing these novel Er:glass lasers to replace two main legacy technologies, Er:YAG lasers and CO2 lasers. The company offers single mode beam quality and single mode delivery fibre, allowing greater flexibility for scanners or diffractive optics and greater depth of field for a specific beam size, a benefit when used around the nose area; low lasing threshold, meaning a high dynamic range; and high repetition rates, in the range of kHz, allowing faster scanning speeds. One of the key characteristics is the possibility of using wavelengths in the range from 2,780– 2,910nm, very close to the water absorption peak and allowing for the right balance between ablation and coagulation. ­