Research Papers

Mechanical Characterization of Microcapsules With Membrane Permeability by Using Indentation Analysis

[+] Author and Article Information
Kiyoshi Bando

Department of Mechanical Engineering,
Kansai University,
3-3-35 Yamate-cho,
Suita, Osaka 564-8680, Japan
e-mail: bando@kansai-u.ac.jp

Manuscript received September 22, 2013; final manuscript received July 13, 2014; accepted manuscript posted July 18, 2014; published online August 6, 2014. Assoc. Editor: Mohammad Mofrad.

J Biomech Eng 136(10), 101003 (Aug 06, 2014) (7 pages) Paper No: BIO-13-1440; doi: 10.1115/1.4028036 History: Received September 22, 2013; Revised July 13, 2014; Accepted July 18, 2014

Mechanical modeling of the deformation of a liquid-filled spherical microcapsule indented by a sharp truncated-cone indenter was proposed, in which membrane permeability was taken into account. The change in the internal volume of the microcapsule due to fluid permeation was calculated on the basis of Kedem and Katchalsky equations (1958, “Thermodynamic Analysis of the Permeability of Biological Membranes to Non-electrolytes,” Biochim. Biophys. Acta, 27, pp. 229–246). The membrane hydraulic permeability, membrane initial stretch, and effective osmotic pressure difference across the membrane of an alginate–poly(l)lysine–alginate (APA) microcapsule were identified by fitting calculated and measured force–displacement curves. The difference between deformed shapes with and without membrane permeability was shown, suggesting the spatial resolution of image analysis performed to measure the membrane permeability from the volume loss. The influences of changes in permeability, initial stretch, and a parameter β, used for determining the effective osmotic pressure difference, on the force–displacement relationship were examined, and mechanisms causing changes in the force–displacement relationship were discussed.

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Fig. 2

Geometries of microcapsules before and after deformation by an indenter. F is the indentation force, δ is the displacement of the indenter tip from the contact inception position, and d0 is the inflated initial diameter of a microcapsule.

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Fig. 1

A sharp truncated-cone indenter made from optical fiber

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Fig. 3

Calculated and experimentally measured force–displacement relationships for the indentation of a microcapsule. The identified values of Lp,λi, and β (shown in the figure) are determined by fitting the calculated curve to the experimental data.

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Fig. 4

The initial and deformed shapes of a microcapsule. The influence of membrane permeability on the deformed shape is shown at the maximum displacement of δ/d0= 0.279, as shown in Fig. 3.

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Fig. 5

The influence of the change in hydraulic permeability Lp on the force–displacement curve

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Fig. 6

The influence of the change in β on the force–displacement curve. The effective osmotic pressure difference is calculated by the value of β and Eqs. (2) and (3).

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Fig. 7

The influence of the change in the initial stretch λi on the force–displacement curve




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