This presentation summarizes three contributions based on a second-gradient continuum framework, including uncertainty quantification, for the modeling of architectured metamaterials and other microscale materials when the underlying microstructure and interactions are unknown. First, a higher-order nonlocal elasticity continuum model integrating Piola peridynamics and Eringen nonlocal elasticity [1] is introduced, enabling the description of long-range interactions and complex external actions, while linking higher-order gradient effects to characteristic interaction lengths. Building on this framework, a stochastic second-gradient continuum model is then developed, with mechanical properties modeled by random fields and random matrices, enabling uncertainty quantification via mixed finite element methods and Monte Carlo simulations. This model is applied to colloidal crystals, revealing significant mechanical fluctuations and showing that second-gradient effects can either amplify or mitigate uncertainty depending on the chosen observable [2]. Finally, the same second-gradient framework is used to investigate wave propagation in unbounded particle-based materials [3], where a center-symmetric formulation and a novel acoustic tensor allow the extension of classical elasticity-based identification techniques. REFERENCES [1] G. La Valle and C. Soize. A higher-order nonlocal elasticity continuum model for deterministic and stochastic particle-based materials. Zeitschrift für angewandte Mathematik und Physik, Vol. 75, No. 2, 49, 2024. [2] G. La Valle and C. Soize. Stochastic second-gradient continuum theory for particle-based materials: part II. Zeitschrift für angewandte Mathematik und Physik, Vol. 75, No. 3, 93, 2024. [3] G. La Valle and C. Soize. Identifying second-gradient continuum models in particle-based materials with pairwise interactions using acoustic tensor methodology. Journal of Elasticity, Vol. 156, No. 2, pp. 623–639, 2024.