The robustness of a dynamical sliding mode control strategy with respect to unmatched perturbation inputs and modelling errors is examined for robotic manipulators equipped with an arrangement of antagonistic artificial muscles, acting as actuators. Differential flatness, which in the case of single-input manipulators coincides with exact linearizability of the system, is exploited to obtain a discontinuous feedback control strategy. The approach naturally allows for the introduction of a first order servovalve-artificial muscle actuator model for sliding mode controller design purposes.