Nanoparticle-based drug delivery in the inner ear: current challenges, limitations and opportunities.

Hearing loss is the most common neurosensory impairment worldwide. While conductive hearing loss can be managed by surgery, the management of sensorineural hearing loss (SNHL), related to the damage of sensory cells of the inner ear is more challenging to manage medically. Many causes of SNHL such as sudden idiopathic SNHL, Meniere's disease, noise-induced hearing loss, autoimmune hearing loss or hearing loss from exposure to ototoxic substances can benefit from delivery of otoprotective drugs to the inner ear. However, systemic drug delivery through oral, intravenous and intramuscular methods leads to undesirable side effects due to the inner ear's limited blood supply and the relatively poor penetration of the blood-inner ear barrier (BLB). Therefore, there has been an increased interest for the targeted drug delivery to the inner ear using nanoparticles. Drug delivery through nanoparticles offers several advantages including drug stabilization for controlled release and surface modification for specific targeting. Understanding the biocompatibility of nanoparticles with cochlea and developing novel non-invasive delivery methods will promote the translation of nanoparticle-mediated drug delivery for auditory disorders from bench to bedside.