Numerical Modeling and Simulation of Non-Invasive Acupuncture Therapy Utilizing Near-Infrared Light-Emitting Diode

Acupuncture is one of the most widely used complementary and alternative therapies worldwide, originating in traditional Chinese medicine more than 2,000 years ago. This non-pharmacologic and minimally invasive practice has become increasingly popular in the West, with more than 10,000 randomized controlled trials published since 1975 investigating its clinical efficacy and mechanisms of action. Modern acupuncture involves the insertion of very fine needles at specific points on the body (acupoints), followed by mechanical, electrical, or other physical forms of energy stimulation. A variation called moxibustion uses heat from burning mugwort (moxa) over acupoints, providing thermal stimulation rather than needle penetration.

Although moxibustion is non-invasive, it produces smoke and harmful odors similar to those found in tobacco smoke.

This study aimed to develop and validate a fully non-invasive alternative to traditional moxibustion, using light-emitting diodes (LEDs) in the near-infrared spectrum to deliver thermal stimulation to skin tissues. The researchers created a three-dimensional computational model of skin with three layers (epidermis, dermis, and subcutaneous tissue) to investigate how LED light interacts with tissue and generates heating. The model used the Pennes heat-transfer equations combined with the Beer-Lambert law to simulate the temperature distribution in time and space within skin tissues when exposed to LED irradiation.

The methodology first included the experimental characterization of the irradiation profile of two types of commercial LEDs operating at 850 nanometers, with 90° and 150° emission patterns. The LEDs were experimentally tested in agar gel to validate the numerical model, showing good agreement between the computationally predicted results and those obtained experimentally. Next, extensive parametric analyses were performed to quantify the effects of LED power, treatment duration, distance between the LED and the skin surface, and use of multiple LEDs on the resulting temperature distribution.

The main results demonstrated that LED heating can effectively deliver therapeutic thermal stimulation to depths of 4-5 millimeters in the skin, similar to traditional moxibustion. The safe operating power was identified as 200-300 mW for 90° LEDs and 300-500 mW for 150° LEDs to reach therapeutic temperatures between 43-48°C without causing tissue damage (maximum safe temperature below 50°C). The 90° LED showed deeper penetration due to its more focused beam, while the 150° LED warmed a larger area but with less penetration. Increasing the distance between the LED and the skin significantly reduced heating efficacy, with drops of 37.6% and 59% in maximum temperature for the 90° and 150° LEDs, respectively, when moved 2,000 micrometers from the skin surface.

The use of multiple LEDs substantially increased the volume of tissue heated, with 2, 3, 4, and 5 LEDs resulting in increases of 324%, 674%, 1,014%, and 1,338% in heated volume, respectively.

For patients and clinicians, these results suggest that LED-based therapy offers a promising and safe alternative to traditional acupuncture and moxibustion. LEDs are safer and more cost-effective than lasers, well tolerated by patients of all ages, and may potentially be incorporated into wearable devices for home use. The therapy eliminates risks of infection, pain from needle insertion, and the production of harmful smoke. The identified operating parameters can guide the development of safe and effective treatment protocols.

The ability to precisely control temperature and treatment area by adjusting power, distance, and multi-LED configuration offers significant therapeutic flexibility.

The main limitations of the study include experimental validation limited to agar gel rather than real human tissue, and ex vivo testing that does not fully account for the effects of microvascular blood perfusion under real physiological conditions. In addition, although the computational model is sophisticated, it still simplifies the complex vascular structure and heterogeneity of real biological tissues. Human clinical trials will be needed to confirm safety and therapeutic efficacy prior to clinical implementation.

The work represents a significant advance in the development of non-invasive acupuncture therapies based on modern technology. The authors are working on the clinical translation of these results and on the development of miniaturized devices that can be integrated into wearable textile products to provide physical stimulation on demand in the home setting, potentially revolutionizing access to and practicality of acupuncture therapies.