Development of the surface lighting red microLED based biomedical patch for skin phototherapy

Abstract

Non-invasive and non-thermal characteristics of phototherapy have achieved lots of research for many years. Currently, devices using laser and light emitting diodes are applied to various treatments such as skin diseases, wound healing, and hair growth. However, due to large size and high cost of lasers and light-emitting diode devices, space and time restrictions are imposed on the treatment. In addition, a constant distance between the device and the human skin must be maintained due to the high heat and limited form factor. This causes a light loss inversely proportional to the square of the distance. Accordingly, there has been a demand for a phototherapy device in the form of a patch capable of attaching to human skin. For a flexible patch type phototherapy device, phototherapy research using organic light emitting diodes or quantum dot light emitting diodes as a light source is underway, but it has limitations due to low light output and short life span. Accordingly, flexible inorganic light emitting diodes having high light output, high lifetime, and low heat generation characteristics have attracted a great deal of attention, but have limitations in non-uniform light irradiation due to the point light emission characteristics of inorganic light emitting diodes. In this study, we have developed a surface lighting flexible vertical light emitting diode (LED) by using silica particles to form a light diffusing layer. This surface-lighting vertical LED can be driven at a low voltage of 3V and exhibits constant electrical and optical characteristics even after a total bending fatigue test of 100,000 times at 5 mm bending. It was well driven on the skin with about 2 cm bending radius and showed a low heat generation less than 39 degree Celsius while applying current within 10 mA and did not cause any damage or burn to the skin. This device, which has a wavelength of about 630 nm, was irradiated to melanocytes, showing a 70% reduction in melanin synthesis and inhibiting the expression of microphthalmia-assisted transcription factor (MITF), a key factor in melanin synthesis, proving the feasibility of a wearable patch for phototherapy.