A Spatial-Mechanistic Design Map for Microenvironment-Responsive Nanomaterials in Solid Tumors.

Solid tumors are organized pathophysiologic systems in which vascular dysfunction, stromal remodeling, and diffusion-consumption imbalance partition lesions into recurrent microenvironmental microdomains. These regions regulate not only whether agents enter tumors, but also where they localize and function within tissue. This review presents a microdomain-centered framework linking tumor biology and microenvironment heterogeneity to the behavior of microenvironment-responsive nanomaterials, with emphasis on clinically relevant tissue exposure rather than therapeutic outcome. We first distinguish trans-vascular entry from intratumoral transport, demonstrating why tumor-level accumulation does not ensure uniform cellular exposure. Vascular heterogeneity, including endothelial-mediated transport pathways and perfusion variability, is examined as a determinant of delivery efficiency across tumor types. We then analyze stromal and interstitial constraints-extracellular matrix organization, interstitial fluid pressure, solid stress, and cellular sequestration-that dominate postentry distribution and bias localization toward perivascular compartments. Hypoxic, acidic, protease-active, fibroblast-remodeled, and receptor-defined niches are interpreted as spatially structured metabolic and signaling environments whose clinical relevance depends on accessibility and residence time. We propose morphology-based evidence standards centered on compartment-resolved mapping of localization and in situ material state transitions, together with minimum reporting practices to improve reproducibility and cross-study translation. We identify recurring mismatches between tumor architecture and material design that contribute to heterogeneous distribution and variable response across lesions and patients. Standardized spatial metrics, including vessel-distance stratification and penetration-depth profiling, are recommended to support comparison across studies. Future work should prioritize 3D coregistration of microenvironmental markers, localization, and activation, and incorporate lesion-level heterogeneity as a measurable biological variable to improve clinical translation.