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A self-optimising controller is designed for stabilisation of a class of bioreactor exploiting sliding-mode techniques. The stability analysis for the class of bioreactor, in open-loop configuration, suggests that the optimal behaviour, respect to maximal biomass production, occurs in an unstable region (structurally unstable). In this contribution, a variable-structure controller is designed, exploiting the inhibitory effect of substrate concentration under the biomass growth rate, such that the closed-loop system reaches the optimal manifold where the effect induced by the growth rate gradient is compensated (favouring the maximum growth rate). The self-optimising comprises an uncertainty estimator which computes the unknown terms for increasing the robustness issues of the sliding-mode scheme. Numerical experiments illustrate the performance and execution of the control strategy considering different parameter values …