Novel 3D-printed hollow microneedles facilitate safe, reliable, and informative sampling of perilymph from guinea pigs

Abstract

BACKGROUND\nInner ear diagnostics is limited by the inability to atraumatically obtain samples of inner ear fluid. The round window membrane (RWM) is an attractive portal for accessing perilymph samples as it has been shown to heal within one week after the introduction of microperforations. A 1\xa0µL volume of perilymph is adequate for proteome analysis, yet the total volume of perilymph within the scala tympani of the guinea pig is limited to less than 5\xa0µL. This study investigates the safety and reliability of a novel hollow microneedle device to aspirate perilymph samples adequate for proteomic analysis.\n\n\nMETHODS\nThe guinea pig RWM was accessed via a postauricular surgical approach. 3D-printed hollow microneedles with an outer diameter of 100\xa0µm and an inner diameter of 35\xa0µm were used to perforate the RWM and aspirate 1\xa0µL of perilymph. Two perilymph samples were analyzed by liquid chromatography-mass spectrometry-based quantitative proteomics as part of a preliminary study. Hearing was assessed before and after aspiration using compound action potential (CAP) and distortion product otoacoustic emissions (DPOAE). RWMs were harvested 72\xa0h after aspiration and evaluated for healing using confocal microscopy.\n\n\nRESULTS\nThere was no permanent damage to hearing at 72\xa0h after perforation as assessed by CAP (n\xa0=\xa07) and DPOAE (n\xa0=\xa08), and all perforations healed completely within 72\xa0h (n\xa0=\xa08). In the two samples of perilymph analyzed, 620 proteins were detected, including the inner ear protein cochlin, widely recognized as a perilymph marker.\n\n\nCONCLUSION\nHollow microneedles can facilitate aspiration of perilymph across the RWM at a quality and volume adequate for proteomic analysis without causing permanent anatomic or physiologic dysfunction. Microneedles can mediate safe and effective intracochlear sampling and show great promise for inner ear diagnostics.