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Photodynamic therapy (PDT) uses a light-sensitive drug and a specific wavelength of light to destroy cancer cells. The treatment has become an important option for certain skin cancers because it can target diseased tissue while limiting damage to surrounding skin. But PDT has a fundamental challenge: both the drug and the light must reach the same area of tissue. While drugs applied to the skin often struggle to penetrate deeply, light also loses intensity as it passes through tissue, limiting treatment to relatively shallow lesions.
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Scientists have developed a potential solution that addresses both problems at once. In a study published in the Journal of Biomedical Optics, a team from Texas A&M University Biomedical Engineering and the São Carlos Institute of Physics at the University of São Paulo showed that dissolving microneedles, already known for improving drug delivery through the skin, can also help spread light more effectively within tissue.
Microneedles are tiny structures, less than a millimeter (0.04 inches) in length, that painlessly pierce the skin's outer barrier. Made from biodegradable polymers, they gradually dissolve after insertion.
Previous studies by the research group showed that microneedles loaded with aminolevulinic acid (ALA), a drug commonly used in PDT, delivered the treatment more deeply and evenly into skin tumors than traditional creams. This led to a more uniform production of the light-activated compound responsible for killing cancer cells upon light exposure.
This study asked a different question: Could the microneedles themselves improve the delivery of light?
How the needles reshape light
To find out, the researchers fabricated arrays containing hundreds of pyramid-shaped microneedles and illuminated them with a green laser. By photographing the light emerging from the arrays at different angles and analyzing the images, they mapped how the microneedles changed the path of the incoming light.
The experiments revealed that the tiny structures acted almost like miniature light spreaders. Instead of allowing light to travel only in a straight line, the microneedles redirected it in many directions through a combination of internal reflections and scattering.
As a result, light emerging from the needle tips was distributed much more evenly than light passing through the spaces between them.
Measurements showed that light coming from the microneedle tips maintained similar intensity across a range of viewing angles, indicating that the structures produced a nearly uniform, multidirectional pattern of illumination.
According to the researchers, this type of light distribution could be especially useful in biological tissues, where conventional surface illumination often leaves some regions underexposed.
What broader scattering could change
The team also developed a mathematical model to examine how thousands of microneedle tips might distribute light inside tissue. Their analysis suggests that this broader scattering pattern could reduce the rapid loss of light intensity typically seen with standard directed illumination. In practical terms, more of the treatment light may reach areas that are difficult to illuminate using conventional approaches.
For PDT, that could be important. Successful treatment depends not only on the amount of light delivered but also on how evenly that light activates the photosensitive drug throughout the lesion. Uneven illumination can leave pockets of tissue insufficiently treated, increasing the likelihood that cancer cells remain. By helping light spread more uniformly, microneedles may improve activation of the therapy across a larger volume of tissue.
Two possible treatment designs
The technology could potentially be used in two ways. One option is to use drug-loaded microneedles first and then apply a second microneedle array designed specifically to improve light delivery.
Another possibility is a single microneedle system that performs both functions simultaneously, delivering the drug while also guiding and redistributing light. Such an approach could simplify treatment and improve precision by ensuring that drug release and light exposure occur in the same location.
Lab results still need testing
The researchers caution that their optical measurements were performed in a simplified laboratory setup rather than in living tissue. Additional studies in tissue models and preclinical systems will be needed to determine how much the light-redistribution effect improves treatment in real-world conditions.
Still, the findings suggest that dissolving microneedles could do more than deliver drugs. By combining drug administration with improved light distribution in a single biodegradable device, they may help extend the reach of photodynamic therapy and improve treatment of skin cancers that are currently difficult to treat with light alone.
More information: Michelle B. Requena et al, Composing drug delivery with light distribution improvement: the use of dissolving microneedles in skin cancer with photodynamic therapy, Journal of Biomedical Optics (2026). DOI: 10.1117/1.jbo.31.5.058001
Provided by SPIE
This story was originally published on Medical Xpress.
