Fluid surface tension evaluation using capillary wave measurement with optical coherence tomography.

Hsiao-Chuan Liu,Piotr Kijanka,Matthew W Urban

doi:10.1063/1.5143935

Abstract

The surface tension of biological fluids is an important parameter because the mechanical properties of fluids are closely linked with hematological diseases and other pathophysiologies. Capillary waves are associated with fluid mechanical properties. Here, we propose a method that utilizes the acoustic radiation force (ARF) to generate propagating waves and optical coherence tomography (OCT) to measure the wave motion. This ARF-OCT method is capable of evaluating the surface tension of fluids, water and porcine whole blood in this study, based on the dispersion relation of capillary waves. Two-dimensional Fourier transforms were used to decompose frequency components of wave motion images to obtain a k-space representation and estimate the wave phase velocity. The phase velocity of capillary waves was obtained from the experimental results and compared to theoretical calculations. The surface tensions of water and porcine whole blood were determined from the experimental results. We first report that capillary waves measured with OCT can be a new promising modality for measuring the surface tension of fluids. The proposed method could be used to differentiate actual pathologic fluids or blood from those taken from healthy subjects and as a biomarker in future biomedical applications.

Highlights

The determination of the surface tension of biological fluids could be beneficial for understanding the pathological steps and physiological conditions
Could be a new modality to evaluate the mechanical property, surface tension, of liquids based on the characterization of the dispersion of capillary waves in frequency dependent rheology
Acoustic radiation forces were exerted on the fluid–air interface to generate a capillary wave, which can be imaged similar to watching ripples on a water surface created by dropping a stone in a pond, assuming that the depth of the water is smaller than half of a wavelength

Summary

Introduction

Surface tension is derived from cohesive forces of molecules pulled in every direction by neighboring liquid molecules so that the net force is zero (equilibrium).1 Surface tension properties, defined as energy per unit area (dyn/cm) or force per unit length (N/m),2 of biological liquids are closely linked with various physiological processes.3–5 Pathological processes such as lung carcinogenesis6 influence the surface tension of alveolar sacs,7 and blood clot formation is associated with the surface tension of blood.8 the determination of the surface tension of biological fluids could be beneficial for understanding the pathological steps and physiological conditions.3–5. Acoustic radiation forces were exerted on the fluid–air interface to generate a capillary wave, which can be imaged similar to watching ripples on a water surface created by dropping a stone in a pond, assuming that the depth of the water is smaller than half of a wavelength.25 The theoretical calculations of the surface tension were compared with our experimental results.

Results

Conclusion