Microgel Particle Collision with Smooth and Nanofiber Hydrophobic Surfaces during Three-Dimensional Printing of a Biopolymer Layer.

The impact of microgel particles onto a wall represents an elementary process that determines the one-stage production of a biopolymer layer on a nanofiber scaffold in the framework of tissue bioengineering. The formation of a microgel layer is experimentally examined on a hydrophobic uniform surface and a nonwoven polymer membrane made of vinylidene fluoride-tetrafluoroethylene copolymer. In-air microfluidics methods, namely, an external vibration disturbance on the microflow of a cross-linkable biopolymer, make it possible to form the microstructures of "beads-on-thread" with a uniform distance between microgel particles of identical size (340-480 μm, depending on the sample). The successive particle-surface and particle-particle collisions are explored to develop the concept of technology for depositing microgel particles on surfaces for mobile one-stage production of microgel layers with a thickness of one and two particles, respectively. A physical model of successive particle-surface and particle-particle interactions is proposed. Empirical expressions are derived for predicting the diameters of maximum spreading (deformation) and the minimum heights of microgel particles on smooth and nanofiber surfaces, as well as in particle-particle collisions using a dimensionless criterion of gelation degree. The effect of microgel viscosity and fluidity on the maximum particle spreading during successive particle-surface and particle-particle collisions is elucidated. The consistent findings have made it possible to develop a predictive method for determining the growth dynamics of microgel layer area with a thickness of one or two particles on a nanofiber scaffold within a few seconds. The specific behavior of a microgel with a given gelation degree is simulated to produce a layer.