A Structural Accessibility Hypothesis for Interpreting Negative Biodegradation Results in Crosslinked Photopolymer Networks

This perspective proposes a structural accessibility hypothesis for interpreting negative biodegradation results in crosslinked photopolymer additive-manufacturing materials. The hypothesis is deliberately non-exclusive: an observed low biodegradation fraction may reflect intrinsic chemical recalcitrance, limited accessibility created by specimen geometry or network transport, samplepreparation effects, the selected test conditions and time horizon, or a combination of these factors. OECD ready-biodegradability methods describe a solution or suspension of the test substance in mineral medium, while controlled-composting methods such as ISO 14855-2 and ASTM D5338 quantify aerobic biodegradation of plastics under specified composting conditions. None of these methods, by itself, separates intrinsic polymer chemistry from geometry-dependent transport in a macroscopic crosslinked specimen. For rigid photopolymer thermosets, the cured network can restrict dissolution and hinder transport of large biological catalysts, while a low surface-area-to-volume ratio reduces the amount of polymer directly exposed per unit mass. The perspective therefore proposes that specimen geometry and network accessibility should be treated as explicit experimental variables when negative results are interpreted. No quantitative accessibility index is claimed. A complementary four-element research outlook considers feedstock carbon origin, network deconstruction, enzymatic depolymerisation of accessible susceptible bonds, and carefully controlled weathering or oxidation as distinct research axes. The hypothesis remains conceptual and requires direct geometry-dependence studies, transport measurements and multi-laboratory validation. It is offered as an experimental design and interpretation framework, not as a replacement for standardised biodegradability or compostability methods.