Embodiments described herein generally provide for the expansion of cells in a cell expansion system using an active promotion of a coating agent(s) to a cell growth surface. A coating agent may be applied to a surface, such as the cell growth surface of a hollow fiber, by controlling the movement of a fluid in which a coating agent is suspended. Using ultrafiltration, the fluid may be pushed through the pores of a hollow fiber from a first side, e.g., an intracapillary (IC) side, of the hollow fiber to a second side, e.g., an extracapillary (EC) side, while the coating agent is actively promoted to the surface of the hollow fiber. In so doing, the coating agent may be hydrostatically deposited onto a wall, e.g., inner wall, of the hollow fiber.