Dynamic nanomechanical analysis of the vocal fold structure in excised larynges

Objectives/hypothesis: Quantification of clinical outcomes after vocal fold (VF) interventions is challenging with current technology. High-speed digital imaging and optical coherence tomography (OCT) of excised larynges assess intact laryngeal function, but do not provide critical biomechanical information. We developed a protocol to quantify tissue properties in intact, excised VFs using dynamic nanomechanical analysis (nano-DMA) to obtain precise biomechanical properties in the micrometer scale.

Study design: Experimental animal study.

Methods: Three pig larynges were bisected in the sagittal plane, maintaining an intact anterior commissure, and subjected to nano-DMA at nine locations with a 250-μm flat-tip punch and frequency sweep load profile (10-105 Hz, 1,000 μN peak force) across the free edge of the VF and inferiorly along the conus elasticus.

Results: Storage, loss, and complex moduli increased inferiorly from the free edge. Storage moduli increased from a mean of 32.3 kPa (range, 6.5-55.38 kPa) at the free edge to 46.3kPa (range, 7.4-71.6) 5 mm below the free edge, and 71.4 kPa (range, 33.7-112 kPa) 1 cm below the free edge. Comparable values were 11.6 kPa (range, 5.0-20.0 kPa), 16.7 kPa (range, 5.7-26.8 kPa), and 22.6 kPa (range, 9.7-38.0 kPa) for loss modulus, and 35.7 kPa (range, 14.4-56.4 kPa), 50.1 kPa (range, 18.7-72.8 kPa), and 75.4 kPa (range, 42.0-116.0 kPa) for complex modulus. Another larynx repeatedly frozen and thawed during technique development had similarly increased storage, loss, and complex modulus trends across locations.

Conclusions: Nano-DMA of the intact hemilarynx provides a platform for quantification of biomechanical responses to a myriad of therapeutic interventions to complement data from high-speed imaging and OCT.

Level of evidence: NA Laryngoscope, 127:E225-E230, 2017.