Barrier membranes govern transport and mechanochemical coupling in lung-on-chip systems but typically exhibit low open porosity, limited pore interconnectivity, and diffusion distances exceeding native thin septal regions. An interstitium-mimicking, alveolus-shaped poly(ε-caprolactone) membrane is developed using dual-templated nonsolvent-induced phase separation followed by controlled enzymatic pore enlargement. The resulting architecture achieves ∼40% total porosity with 97% pore interconnectivity and a locally thinned dome region (∼2.5 µm). This structure sustains cyclic deformation while increasing oxygen diffusivity fivefold compared with conventional Transwell membranes under acellular and epithelial-endothelial co-culture conditions. Integrated into an air-liquid interface platform, the membrane enables aerosol deposition and quantitative interrogation of cross-barrier mass transfer. Using carbonaceous nanoscale particulate matter as a model aerosol, controlled exposure induces dose-dependent oxidative, inflammatory, and genotoxic responses. Matched cumulative dose studies reveal distinct biological trajectories: acute high-dose exposure produces rapid cytotoxic stress and barrier disruption, whereas chronic low-dose exposure preserves viability yet promotes sustained DNA repair and genome-maintenance programs. Compartment-resolved analysis and therapeutic intervention demonstrate the platform's utility for spatial and translational interrogation of lung injury. By restoring physiologically relevant diffusion distance, interconnectivity, and strain responsiveness, the interstitium-mimicking membrane advances lung-on-chip design toward functional replication of alveolar transport dynamics for studying lung injury and barrier dysfunction.