Dissolving Microneedles Show Dual Potential to Enhance Drug and Light Delivery in Photodynamic Therapy for Skin Cancer
Key Insights
Dissolving microneedles can act as miniature light spreaders, redirecting laser light in multiple directions for more uniform tissue illumination during photodynamic therapy.
A Texas A&M and University of São Paulo team demonstrated that microneedle arrays produce nearly uniform, multidirectional light patterns that could reduce underexposed regions in treated lesions.
Previous research showed ALA-loaded microneedles deliver the photosensitizing drug more deeply and evenly into skin tumors compared to traditional creams.
A team of researchers from Texas A&M University Biomedical Engineering (search) and the Sao Carlos Institute of Physics at the University of São Paulo has demonstrated that dissolving microneedles can serve a dual purpose in photodynamic therapy (PDT) for skin cancer (search)—not only delivering the light-sensitive drug more effectively but also redistributing treatment light more uniformly within tissue. The findings, published in the Journal of Biomedical Optics, address a fundamental challenge in PDT: ensuring that both the drug and the activating light reach the same tissue at sufficient and even levels.
The Challenge of Light and Drug Penetration
Photodynamic therapy 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. However, PDT faces a persistent obstacle: drugs applied to the skin often struggle to penetrate deeply, and light simultaneously loses intensity as it passes through tissue, restricting treatment to relatively shallow lesions.
Previous studies by the same research group had already shown 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.
Microneedles as Miniature Light Spreaders
The new study asked a different question: could the microneedles themselves improve the delivery of light? To investigate, 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—smaller than a millimeter in length and made from biodegradable polymers—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.
Mathematical Modeling Supports Broader Light Distribution
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, this could be clinically significant. 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 Potential Clinical Approaches
The technology could potentially be deployed 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.
The researchers note that "such systems may be particularly advantageous in resource-limited settings or outpatient care, where ease of use and effectiveness are essential," adding that "this strategy offers an approach to overcoming the limitations of conventional light-based therapies, supporting the development of more effective and accessible treatments for skin cancer (search) and other dermatological conditions."
Study Limitations and Next Steps
The researchers caution that their optical measurements were performed in a simplified laboratory setup rather than 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. Nevertheless, 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.