[show abstract][hide abstract] ABSTRACT: The impact and spreading of a compound viscous droplet on a flat surface are studied computationally using a front-tracking method as a model for the single cell epitaxy. This is a technology developed to create two-dimensional and three-dimensional tissue constructs cell by cell by printing cell-encapsulating droplets precisely on a substrate using an existing ink-jet printing method. The success of cell printing mainly depends on the cell viability during the printing process, which requires a deeper understanding of the impact dynamics of encapsulated cells onto a solid surface. The present study is a first step in developing a model for deposition of cell-encapsulating droplets. The inner droplet representing the cell, the encapsulating droplet, and the ambient fluid are all assumed to be Newtonian. Simulations are performed for a range of dimensionless parameters to probe the deformation and rate of deformation of the encapsulated cell, which are both hypothesized to be related to cell damage. The deformation of the inner droplet consistently increases: as the Reynolds number increases; as the diameter ratio of the encapsulating droplet to the cell decreases; as the ratio of surface tensions of the air-solution interface to the solution-cell interface increases; as the viscosity ratio of the cell to encapsulating droplet decreases; or as the equilibrium contact angle decreases. It is observed that maximum deformation for a range of Weber numbers has (at least) one local minimum at We=2. Thereafter, the effects of cell deformation on viability are estimated by employing a correlation based on the experimental data of compression of cells between parallel plates. These results provide insight into achieving optimal parameter ranges for maximal cell viability during cell printing.
Physics of Fluids 08/2010; 22(8). · 1.94 Impact Factor
[show abstract][hide abstract] ABSTRACT: In recent years, there has been a growing interest in generating compound droplets mainly due to their potential commercial value  and applications in emerging technologies such as single cell epitaxi . Ejecting encapsulated cells on a rigid surface is a promising way to produce 2D/3D tissues . However, this gained experimental capability requires a true understanding of the impact dynamics of the encapsulated cells on solid surfaces for further development. In the present study, a finite-volume/front-tracking method is used to model the impact and spreading of a viscous compound droplet on a flat solid surface as a first step in developing a model for the single cell epitaxi. The cell, the encapsulating droplet and ambient fluid are all assumed to be Newtonian. Simulations are performed for a range of dimensionless parameters and their effects on deformation of inner droplet are investigated. These results provide initial insight about the optimum parameter ranges for highest viability of cells.  Utada, Lorenceau, Link, et al., Science, 308(5721), (2005).  Demirci and Montesano, Lab Chip, 7, (2007).