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Research Papers

Engineered Airway Models to Study Liquid Plug Splitting at Bifurcations: Effects of Orientation and Airway Size

[+] Author and Article Information
Antonio Copploe, Rouzbeh Amini

Department of Biomedical Engineering,
The University of Akron,
Akron, OH 44325

Morteza Vatani, Jae-Won Choi

Department of Mechanical Engineering,
The University of Akron,
Akron, OH 44325

Hossein Tavana

Department of Biomedical Engineering,
The University of Akron,
260 S. Forge St.,
Akron, OH 44325
e-mail: tavana@uakron.edu

1Corresponding author.

Manuscript received November 26, 2017; final manuscript received May 23, 2018; published online June 26, 2018. Assoc. Editor: Ching-Long Lin.

J Biomech Eng 140(9), 091012 (Jun 26, 2018) (8 pages) Paper No: BIO-17-1548; doi: 10.1115/1.4040456 History: Received November 26, 2017; Revised May 23, 2018

Delivery of biological fluids, such as surfactant solutions, into lungs is a major strategy to treat respiratory disorders including respiratory distress syndrome that is caused by insufficient or dysfunctional natural lung surfactant. The instilled solution forms liquid plugs in lung airways. The plugs propagate downstream in airways by inspired air or ventilation, continuously split at airway bifurcations to smaller daughter plugs, simultaneously lose mass from their trailing menisci, and eventually rupture. A uniform distribution of the instilled biofluid in lung airways is expected to increase the treatments success. The uniformity of distribution of instilled liquid in the lungs greatly depends on the splitting of liquid plugs between daughter airways, especially in the first few generations from which airways of different lobes of lungs emerge. To mechanistically understand this process, we developed a bioengineering approach to computationally design three-dimensional bifurcating airway models using morphometric data of human lungs, fabricate physical models, and examine dynamics of liquid plug splitting. We found that orientation of bifurcating airways has a major effect on the splitting of liquid plugs between daughter airways. Changing the relative gravitational orientation of daughter tubes with respect to the horizontal plane caused a more asymmetric splitting of liquid plugs. Increasing the propagation speed of plugs partially counteracted this effect. Using airway models of smaller dimensions reduced the asymmetry of plug splitting. This work provides a step toward developing delivery strategies for uniform distribution of therapeutic fluids in the lungs.

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Figures

Grahic Jump Location
Fig. 1

A computational model of a single bifurcating airway unit of the z = 1–2 generation shown at (a) front, (b) oblique, (c) top, and (d) bottom views

Grahic Jump Location
Fig. 2

Fabricated model of a single bifurcating airway unit of the z = 1–2 generation shown at (a) front, (b) top, and (c) bottom views

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Fig. 3

The fabricated models are hydrophobic and show a water contact angle of 87.9 deg. Plasma oxidation makes the models hydrophilic and reduces the contact angle to zero.

Grahic Jump Location
Fig. 4

(a) Schematic of the test bed showing the roll angle (α) and the pitch angle (φ) and a liquid plug splitting at the bifurcation. A split ratio is defined as the ratio of the length of the plug in the upper daughter tube (plug B) to the length of the plug in the lower daughter tube (plug A), after splitting is complete. (b) The experimental setup at α= 60deg and φ=0deg.

Grahic Jump Location
Fig. 5

((a)–(c)) Effect of orientation through varying the roll angle (30deg, 60deg, 90deg) on splitting of plugs at three different bifurcating airways representing the z = 0–1, z = 1–2, and z = 2–3 airway models. Error bars represent standard deviations. Asterisks in panels a–c denote results of statistical significance tests on split ratios between roll angles of 30deg and 60deg, and between roll angles of 60deg and 90deg (*p < 0.05 and n.s. indicates nonsignificant). (d)–(f) Representative images right after splitting of a Tween solution plug in the z = 0–1, z = 1–2, and z = 2–3 airway models. A food coloring dye was added to the surfactant solution just for a better visualization in these images. In each image, the lengths of plugs A (LA) and B (LB) used to calculate the split ratio are also shown.

Grahic Jump Location
Fig. 7

(a)–(c) The effect of orientation of bifurcating airways through the pitch angle (0deg, 15deg, 30deg) at a constant roll angle of 30 deg on the splitting of liquid plugs at three different bifurcating airway models representing z = 0–1, z = 1–2, and z = 2–3. Error bars represent standard deviations.

Grahic Jump Location
Fig. 6

(a)–(c) The split ratio at three different bifurcating airways representing the z = 0–1, z = 1–2, and z = 2–3 airway models is shown as a function of Fr number. Airway units were oriented at three different roll angles (30deg, 60deg, 90deg) and a pitch angle of 0deg. Airways error bars represent standard deviations.

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