How subcutaneous fluid injection stretches and shapes the skin

We evaluate three mathematical models of skin surface deformation and subsurface fluid flow due to subcutaneous injection of fluid. We focus on a regime where the fluid volume injected is large enough to create a visible bleb on the skin surface whose lateral dimensions are significantly larger than the depth of the injection. The goal of the modeling is to improve our understanding of the mechanisms of bleb formation that might contribute to patient discomfort. The models considered are: (1) a poroelastic model, (2) pressurized void in an elastic half space, and (3) a blister model based on a membrane / plate supported by an inelastic foundation and overlying a pool of fluid. The bleb height, area, and area stretch ratios predicted by the mathematical models are compared to the authors' recent measurements on high volume injections into ex vivo porcine tissue over various viscosities and flow rates.