[POSTECH research team develops photochemical tissue bonding technology using controlled afterglow luminescent particles]

In a scene in the movie Avatar, the Tree of Souls treats injured Na’vi people with light. However, it seems that the Na’vi in the film are not the only ones who can treat wounds with light. It is said that during ancient Egyptian times, leukoplakia was cured with sunlight and in 1903, the Nobel Prize was awarded for treatment of tubercular skin disease with light. In modern days, light therapy is used to treat various diseases, such as skin diseases and cancer.

It has become a norm to blow on the wound after applying an ointment on it. However, a POSTECH research team has recently developed an innovative way to treat wounds with light as opposed to the application of topical ointments. The work of the research team led by Professor Sei Kwang Hahn (Department of Materials Science and Engineering) was published in Light: Science and Applications, one of the prestigious international journals in the field of optics.

Ointments and other bio-binding agents that we commonly apply on wounds are still limited in their application due to their weak bonding power. Photochemical tissue bonding (PTB)^*1 is a newly emerging technique for closing wounds. PTB demonstrates a comparable level of wound healing efficiency to sutures, while overcoming some of the downsides, namely secondary inflammation and needle puncturing.
The technology utilizes light and photosensitizers to reduce inflammation and scarring by promoting collagen crosslinking. Rose Bengal (RB)^*2 dye is one of the most commonly used photosensitizers that absorbs energy from green light and interacts with collagen to produce collagen-free radicals. These radicals start to create covalent bonding between collagen molecules. However, light transmission efficiency decreases when the incision closes as the green light attenuates following the depth of tissue penetration. A new material is required to effectively activate RB in the deep tissue and induce collagen crosslinking for efficient PTB.

To this end, materials that allow the upconversion of near-infrared with high skin permeability into visible light have been explored. However, one disadvantage of upconversion materials is that they demonstrate limited effectiveness in light therapies due to their low energy conversion efficiency.

In that regard, the research team has developed a controlled ZnS:Ag,Co afterglow luminescent particle (ALP) that has the powerful and sustained green light required for photochemical tissue bonding. The ALPs developed by the research team have the optic property of emitting the stored energy as light by trapping irradiated photoenergy in defect states, resulting in the high intensity of luminescence and long-term afterglow.

The research team has also confirmed that ZnS:Ag,Co particles are rapidly recharged under short ultraviolet irradiation, which effectively activates RB in hyaluronate-RB (HA-RB) conjugates for the crosslinking of dissected collagen layers without additional light irradiation.

Professor Sei Kwang Hahn who led the research stated, “This study is the first application of afterglow luminescent particles to biochemical tissue bonding.“ He added, “It is anticipated that the use of light in healing wounds could be expanded to the treatments of the brain and other body tissues going forward.“

1. PTB
Photochemical tissue bonding technology

2. RB
Rose Bengal, xanthene dye and food coloring agents