Provided herein are methods and related systems for controlling droplet spreading on a surface, including droplets in which a biological component is suspended. A biological solution is provided as a droplet to a surface. Interference fringes generated by the droplet on the surface are imaged, wherein the imaging is over a time course during which the droplet spreads on the surface. A droplet parameter is determined from the imaging step and a process parameter controlled to obtain an interference fringe pattern corresponding to a desired droplet parameter. In this manner, well-controlled droplet spreading is achieved, which is important in a range of applications, including assays that rely on good metaphase spreading.