Mathioudaki E. et al. - Photobiomodulation and cellular wound repair: a keratinocyte model

This study is an in vitro study conducted on cultured keratinocytes, not on patients. A low-power red laser at 661 nm accelerated the healing of a cellular abrasion in the study, but this did not demonstrate any effect in humans.

What this study measured

This study was conducted in the laboratory using a keratinocyte cell line—NCTC 2544 cells—that were scraped to create an empty area: this is known as the scratch assay. This model simply mimics a wound by measuring the rate at which cells repopulate the empty space. No animals or patients were involved.

The cells were then irradiated with a low-power red laser at 661 nm, using various power densities and exposure times. Images were acquired at 0, 24, 48, and 72 hours after treatment. Cell proliferation was assessed using the MTT assay, and the production of reactive oxygen species was measured at 0 and 24 hours using fluorescence microscopy. Image analysis was used to calculate scratch closure rates.

Key Findings

The results below describe cells in culture dishes—and nothing else.

• The tested energy range, from 0.18 to 7.2 J/cm², was not found to be phototoxic.
• Cell viability increased within this range.
• The closure of the scratch was promoted by irradiation.
• The power and duration of irradiation were more decisive factors than the total energy.
• Two thresholds—one for power and one for duration—must be exceeded to improve closure.
• An increase in reactive oxygen species was observed at midnight only in the group with the slowest closure rate.

The authors conclude that this laser stimulated the proliferation and migration of keratinocytes, and propose an in vivo effect as a hypothesis to be tested.

How Photobiomodulation Affects Skin Cells

The mechanism typically proposed remains hypothetical. Red light is thought to be absorbed by cytochrome c oxidase, a complex in the mitochondrial respiratory chain, which could alter ATP production and intracellular signaling. This additional energy would promote the migration and proliferation of keratinocytes, two key steps in wound healing. Oxidative stress appears to play a dual role: moderate production of reactive oxygen species serves as a signal, while an early and marked increase appears to inhibit proliferation. These explanations remain hypotheses, not established facts in this context.

Limits You Should Know

The main limitation lies in the model: cultured cells, not living skin or a patient. A scratch in a dish has no blood vessels, no immune cells, no supportive matrix, and no risk of infection. Therefore, no conclusions regarding the efficacy of photobiomodulation in humans can be drawn from this study. Compounding these issues are the use of a single cell line, a single wavelength, and a heavy reliance on specific settings, all of which make any extrapolation to human subjects highly uncertain.

What This Means in Practice

For a reader, this does not change anything about wound care. This type of research serves to explore mechanisms and guide the parameters to be evaluated next in animal studies and then in clinical trials. Its most concrete contribution is methodological: power and exposure time appear to matter more than the cumulative energy dose—a point often overlooked when only joules per square centimeter are reported. A wound that does not heal requires medical evaluation, not a light-emitting device.

Frequently Asked Questions

What is the difference between an in vitro study and a clinical trial?

An in vitro study examines isolated cells in an artificial, controlled environment. A clinical trial measures an effect in actual people, using a comparison group and predefined criteria. A result obtained in cells does not predict a benefit in humans; rather, it suggests a potential mechanism of action.

Does this study prove that red light helps wounds heal?

No. It shows that cultured keratinocytes recolonize a scratched area more quickly after irradiation. Nothing in the study was demonstrated on a human wound.

What lighting settings were used?

A low-power red laser at 661 nm, with varying power densities and pulse durations, delivering energy ranging from 0.18 to 7.2 J/cm².

Reference

Mathioudaki E, Rallis M, Politopoulos K, Alexandratou E. Photobiomodulation and Wound Healing: Low-Level Laser Therapy at 661 nm in a Scratch Assay Keratinocyte Model. Annals of Biomedical Engineering, 2023; 52(2): 376-385. PMID 37851144. DOI 10.1007/s10439-023-03384-x. https://pmc.ncbi.nlm.nih.gov/articles/PMC10808316/

This summary is provided for informational purposes only and does not constitute medical advice. Photobiomodulation is not a substitute for prescribed treatment. Consult a healthcare professional.