{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"8017c287d521b6acc9e6ae0011f0251eacd4b3d7dc0d467471556fbaed11f476","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["8222004f4c0a29681ed24fe0acbc623c1b047355a40aca3bfc33dfe3281d7de5","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"71788d0ff9efa6a0f60bb2734cc754672c3edab9002b1e67502bc64069d5c593","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"bio.morphogenesis-mechanics.shape-index-fluidity","kind":"well-posed","literature_status":"contested","n":"2","parents":[],"plain":"Computer models of tightly packed cells predict that a tissue switches from solid-like to fluid-like once cells become elongated beyond a critical shape. Experiments disagree on whether this shape rule works in real tissues.","posed_since":"2015","precise":"The 2D vertex model with energy $E = \\sum_i [K_A (A_i - A_0)^2 + K_P (P_i - P_0)^2]$ ($A_i, P_i$ = cell area and perimeter) has a rigidity transition at target shape index $p_0 = P_0/\\sqrt{A_0} \\sim 3.81$. Determine whether the observed shape index $q = \\langle P/\\sqrt{A}\\rangle$ classifies fluid versus solid epithelia in vivo across tissues and species, or whether fluctuations, division and active tension remodeling set fluidity independently of q.","problem_ref":"8222004f4c0a29681ed24fe0acbc623c1b047355a40aca3bfc33dfe3281d7de5","references":"","settled_by":"Simultaneous in vivo measurement of q and of tissue rheology (cell rearrangement rate, stress relaxation) across several tissues and perturbations.","status_note":"Support from airway epithelia (2015) contrasts with 2026 reports of shape-independent fluidity in epithelial monolayers (arXiv 2603.05548).","title":"Does cell shape predict whether a tissue flows or holds?","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"3d83c99939403e9fb8d78c6f98415b738426e85f9c00e089cb97c6ccb31412c8","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"60041a8ac558eecd36fbee051519adbedd957f807c0a6a2a89d2701ff3b77f63","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"pZKJQ6V8cdl1fgfzIVdJQq5dL8uH7vjUVvM0Rn3Wo2pD9kWd9WcnTJq3beNiwKXfZHUp8vMNkbHHHnoJkfjzDQ"},"schema":"pubphys.envelope/1"},"record_hash":"3d83c99939403e9fb8d78c6f98415b738426e85f9c00e089cb97c6ccb31412c8","leaf_index":2596}