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RESEARCH PAPER

A practical approach for extracting mechanical properties of microcapsules using a hybrid numerical model A. Rahmat1   · J. Meng2 · D. R. Emerson2 · Chuan‑Yu Wu3 · M. Barigou1 · A. Alexiadis1 Received: 22 June 2020 / Accepted: 1 November 2020 © The Author(s) 2020

Abstract In this paper, the deformation of compliant microcapsules is studied in narrow constrictions using a hybrid particle-based model. The model combines the Smoothed Particle Hydrodynamic (SPH) method for modelling fluid flow and the Mass Spring Model (MSM) for simulating deformable membranes. The model is initially validated for the dynamics of microcapsules in shear flow. Then, several quantitative parameters such as the deformation index, frontal tip and rear tail curvatures and the passage time are introduced and their variations are studied with respect to capillary number and constriction size. Subsequently, a dependency analysis is performed on these quantitative parameters and some recommendations are made on fabrication of microfluidic devices and analysis of microcapsules for extracting their mechanical properties. It is revealed that the deformation index and frontal tip and rear tail curvatures are the most suitable parameters for correlating the elastic properties to the dynamics of microcapsules. Keywords  Discrete Multi-Physics (DMP)model · The Smoothed Particle Hydrodynamics (SPH)method · Fluid-Solid Interactions (FSI) · Microcapsules · Dependency analysis

1 Introduction Synthetic microcapsules consist of a viscous fluid covered by a thin polymeric membrane. They have been used in a broad range of applications such as protection and targeted release of active agents in cosmetic and pharmaceutical industries (Casanova and Santos 2016; Gombotz and Wee 1998), fermentation and flavor conservation in food processing units (Gharsallaoui et al. 2007), and anti-body production in biomedical applications (Murua et al. 2008). Thus, it is required to accurately determine mechanical properties of microcapsules to efficiently increase their performance.

* A. Rahmat [email protected] * A. Alexiadis [email protected] 1



School of Chemical Engineering, University of Birmingham, B15 2TT Birmingham, UK

2



STFC Daresbury Laboratory, WA4 4AD Daresbury, Warrington, UK

3

Department of Chemical and Process Engineering, University of Surrey, Guildford GU2 7XH, UK



For calculating mechanical properties of microcapsules, several experimental techniques are employed such as partial probing of membrane using (colloidal) Atomic Force Microscopy (AFM) (Fery and Weinkamer 2007; Dubreuil et al. 2003), suction of compliant microcapsules through micropipettes in Micropipette Aspiration (MA) (Hochmuth et al. 1982; Hochmuth 2000), and monitoring the deformation of microcapsules using optical tweezers (Helfer et al. 2001). However, these techniques are often cumbersome and time consuming especially for highly deformable microcapsules. An alternative approach is to investigate the deformation of compliant microcapsules in microfluidic