Researchers have developed injectable, light-responsive nanoparticles that could offer a new route to restoring visual sensitivity in advanced retinal degeneration without genetic modification or conventional electronic implants.
The study, published in Nature Biomedical Engineering, describes hollow-sphere graphitic carbon nitride nanoparticles (hg-C3N4 NPs) inspired by the light-harvesting architecture of chloroplasts. The particles respond to illumination through photoelectrochemical and photothermal mechanisms and were designed to modulate biological electrical activity at cellular and tissue levels.
Although the team investigated applications ranging from intracellular calcium signaling to cardiac pacing, the ophthalmic experiments explored whether the nanoparticles could function as an injectable retinal prosthesis. Following intravitreal administration in wild-type mice, particles settled on the retinal surface close to retinal ganglion cells (RGCs). OCT imaging at 14 days showed preservation of retinal structure, with no significant changes in total retinal thickness or individual retinal layers.
Further analyses also provided encouraging preliminary safety data. Researchers observed no appreciable increase in retinal markers of glial activation, while RNA sequencing showed no statistically significant differences in pathways associated with retinal cell health, cell death or inflammatory responses between nanoparticle- and PBS-treated eyes.
The group then tested the approach in 12-week-old rd10 mice, a model of autosomal recessive retinitis pigmentosa in which electroretinographic responses are typically lost by around eight weeks. Four weeks after treatment, three of seven mice receiving hg-C3N4 nanoparticles spent more than 60 percent of their time in the dark compartment of a light-dark box – a preference not observed among animals receiving control nanoparticles.
Cortical measurements provided further evidence of a treatment-related response. Five of 14 nanoparticle-treated eyes met predefined criteria for a reproducible visual evoked potential (VEP), corresponding to a responder rate of 36 percent, compared with one of 14 eyes – 7 percent – among the pooled controls. However, the confidence interval for the resulting 29 percentage-point risk difference crossed zero, and responses remained substantially smaller and slower than those recorded in healthy mice.
Importantly, ERG responses remained absent in treated rd10 animals. The researchers therefore suggest that the recovered behavioral and cortical responses arose downstream of conventional photoreceptor-mediated signaling, rather than through restored photoreceptor function.
Experiments in ex vivo porcine retina strengthened the proposed mechanism. After hg-C3N4 nanoparticles settled onto the RGC layer, blue-light stimulation increased mean ganglion-cell firing from 5 to 29 Hz and raised peak-to-peak signal amplitudes from 12.0 to 39.1 µV. Blocking action potentials with tetrodotoxin substantially reduced these responses, supporting direct activation of RGCs.
The study authors acknowledge that the approach remains at an early preclinical stage. Relatively high light levels were needed to generate cortical responses, potentially because intravitreal injection produced limited nanoparticle contact with RGCs. Future work could therefore investigate alternative delivery approaches, cell-specific targeting and materials responsive to longer wavelengths with greater tissue penetration.
