Bioinspired materials by programming with classical conditioning algorithms
Olli Ikkala(1), Hang Zhang(1), Hao Zeng(2), Arri Priimagi(2)
1. Department of Applied Physics, Aalto University, P.O. Box 15100, FI-02150 Espoo, Finland.
2. Tampere University, Faculty of Natural Science and Engineering, FI-33014 Tampere, Finland
In bioinspired materials there is a search for ever more complex functionalities. Could one mimic classical conditioning from behavioral psychology, which is an elementary form of learning, originally shown by Pavlov in his dog experiments. Here we demonstrate two soft matter systems where the materials were originally responsive to heating and not to light irradiation, but upon simultaneous conditioning by heating and irradiation, they became responsive to specific light irradiation. To allow Pavlovian conditioning, triggerable memories are needed. In the Pavlovian hydrogel, the response is hydrogel melting and the memory consists of self-assembly of pH-sensitive Au-nanoparticles triggered by merocyanine photoacid (Zhang et al, Nat. Commun. 2019 10 3267). Forgetting is achieved by pushing the system out-of-equilibrium using systems chemistry. In splay-aligned liquid crystalline networks the unconditioned response is bending by heating, and the memory is the redistribution of light responsive laser dyes upon conditioning (Zeng at al, Matter; in press). By conditioning, the actuator learns to bend by light irradiation. We foresee a wealth of further materials, combinations of stimuli and different memory concepts for classically conditioned functional materials towards mimicking associative learning.