Dissolving microneedles could help PDT reach deeper skin tumours

In photodynamic therapy, a light-sensitive drug accumulates in cancer cells and is then activated by light, producing cell-killing molecules. Microneedles can help deliver the drug and distribute light more effectively within non-melanoma skin cancer. Image by M. Requena et al.

A biodegradable microneedle patch designed to deliver treatment through the skin may also guide and scatter light, potentially allowing photodynamic therapy (PDT) to treat nonmelanoma skin cancers more uniformly, according to a study published in the Journal of Biomedical Optics.

The finding points to a possible solution for a central difficulty in PDT: a photosensitizing agent and activating light of a specific wavelength must reach the same tissue. Topically administered agents may penetrate incompletely, while light attenuates with depth, restricting treatment to comparatively superficial lesions and potentially leaving undertreated regions.

Researchers at Texas A&M University and the University of São Paulo fabricated arrays containing hundreds of pyramidal microneedles made from a biocompatible, dissolving polymer. They illuminated the arrays with a green laser, photographed emerging light at multiple angles and used image analysis to characterize its distribution.

The analysis showed light exiting the microneedle tips maintained similar intensity across the angles evaluated, producing a nearly uniform, multidirectional pattern. The investigators attributed the effect to internal reflection and scattering within the structures. By contrast, light passing through spaces between the needles remained more directionally constrained.

A mathematical model examining illumination from thousands of microneedle tips suggested that the broader distribution could reduce the steep loss of intensity associated with directed surface illumination. The study did not, however, test tumour clearance, recurrence, or other clinical outcomes.

The same group previously reported that microneedles with aminolevulinic acid, a PDT prodrug, delivered the agent more deeply and evenly into skin tumours than conventional topical creams, resulting in more uniform production of the photoactive compound.

The researchers proposed either a sequential approach—a drug-bearing patch followed by an optical microneedle array—or a single device combining localized drug release with light redistribution. This spatial colocalization could improve activation of photosensitizer throughout a lesion.

However, the researchers note tissue-model and preclinical studies will be needed to establish whether the apparent waveguiding effect translates into deeper or more complete tumour treatment.