Droplet hardness for tissue engineering

In tissue engineering, it is important to examine the hardness of cultivated tissues for evaluating their vitality. This paper proposes a new index, “Droplet Hardness”, defined by the representative plastic deformation in depth of tissue caused by collision with a droplet whose initial diameter and speed are 80 μm and 4m/s, respectively. To understand the nature of physical phenomena of single droplet in collision with a tissue, we newly design and develop a dynamic active sensing system composed of a micro ink jet device for spouting out a micro water droplet and a high speed camera for capturing the dynamic behavior of the droplet after the collision. Through both computer simulation and experiments, we show that the Droplet Hardness is an essential parameter capable of nicely expressing a global hardness of tissue.