Indentation of poroviscoelastic vocal fold tissue using an atomic force microscope

Area of Science:

• Biomechanics
• Materials Science
• Vocal Fold Physiology

Background:

• Vocal fold (VF) elastic properties are crucial for voice production.
• Understanding VF biomechanics requires depth-dependent property characterization.
• Porcine VFs serve as a relevant model for human VF tissue.

Purpose of the Study:

• To measure the poroelastic anisotropic properties of porcine vocal folds (VFs) at various depths.
• To determine the optimal atomic force microscopy (AFM) tip size for accurate property measurement.
• To evaluate the influence of AFM tip dimensions and cantilever stiffness on results.

Main Methods:

• Atomic force microscopy (AFM)-based indentation was employed on porcine VF tissue.
• Nonlinear laser scanning microscopy and image analysis determined the minimum effective tip diameter (25µm).
• Indentation tests were conducted along sagittal and coronal planes to assess anisotropy, using Hertzian contact theory and poroelasticity equations.

Main Results:

• The study established a minimum AFM tip diameter of 25µm for accurate local property capture.
• Systematic investigation revealed the effects of AFM tip dimensions and cantilever stiffness.
• The permeability coefficient of porcine VF tissue was quantified as 1.80±0.32×10⁻¹⁵ m⁴/Ns.

Conclusions:

• Depth-dependent poroelastic anisotropic properties of VFs can be accurately measured using AFM.
• The determined permeability coefficient provides critical data for voice production models.
• This research enhances the understanding of VF biomechanics and tissue properties.