X-ray-Induced Photodegradation of Hydrogels by the Incorporation of X-ray-Activated Long Persistent Luminescent Nanoparticles

The development of on-demand degradable hydrogels remains an important challenge. Even though photodegradable hydrogels offer spatiotemporal control over degradation, it is difficult to use ultraviolet, visible, or near-infrared light as a tool for noninvasive triggering in vivo due to the poor tissue-penetration capacity. In contrast, X-ray irradiation can penetrate deep tissue and has virtually no penetration limitations for biological soft tissues. In this study, we propose an X-ray-photodegradation cascade system for hydrogel degradation by incorporating X-ray-activated persistent luminescence nanoparticles (X-PLNPs) into photodegradable hydrogels. A photodegradable 9,10-dialkoxyanthracene-based cross-linker was synthesized and used to prepare photodegradable hydrogels, of which the degradation behavior can be triggered by visible green light. Next, Tb³⁺-doped β-NaLuF₄ was introduced as an X-PLNP that can convert X-rays into visible light centered at 544 nm. The afterglow can even be detected for 4 × 10³ s after switching off the X-ray irradiation. The X-ray-induced green light emission was demonstrated to trigger photodegradation of the hydrogel. This proof-of-concept system for X-ray irradiation-induced on-demand hydrogel degradation was used to demonstrate X-ray-sensitive drug delivery inside a chicken breast as the in vitro tissue model. As this X-ray-induced cascade degradation of hydrogels can penetrate deep tissues, it is a promising platform for future in vivo applications requiring on-demand triggered hydrogel degradation, such as drug delivery or removal of hydrogel patches, hydrogel adhesives, or hydrogel tissue engineering scaffolds. It should, however, be noted that the hydrogel's X-ray and photoresponsiveness should be further improved to enable future in vivo use.