This paper deals with robust gripping force control at the microscale for a safe manipulation of deformable soft materials. Since mechanical properties of micrometer sized objects are uncertain, instability often occurs during a gripping task. In this article, the design of an output feedback self-scheduled dynamic controller is proposed considering parametric uncertainties of a set of 65 soft and resilient microspheres. The degrees of freedom of the controller are managed by the design of a set of elementary observers. Robustness with respect to parametric uncertainties is satis_ed thanks to an iterative procedure based on an eigenstructure assignment methodology and a worst case analysis. The developed controller is of low order and can be implemented in real time. Simulations demonstrate the validity of the proposed control approach.