This paper proposes the relation between hardened nuclei and plastic peripheries as a model for sustaining living research systems. Long-duration corpora require two contrary capacities: they must remain stable enough to be cited, taught, reused and trusted, while remaining open enough to evolve. A hardened nucleus consists of durable reference-bearing objects such as DOI-anchored papers, indexes, definitions, protocols and datasets. A plastic periphery consists of drafts, fragments, speculative texts, provisional concepts and experimental materials. The paper argues that intellectual vitality depends on the designed relation between these zones: differential speeds of change, threshold closure, resistance to premature canonisation and distributed addressability.