Digest — 2026-09-23

Curated America/New_York (ET). Prefer arXiv / open sources. Verified via arXiv Atom API and cond-mat.soft / active-matter keyword listings.
Focus: roughly since the 2026-09-22 digest. Prior items are not re-listed as “new today.”

At a glance

Diagram: original illustration of this digest’s key idea (not from the papers).

Highlights

1. Self-limited stacking of non-Euclidean colloidal shells: From saddles to caps

• Authors: Kyle T. Sullivan, Mark J. Stevens, Gregory M. Grason
• Submitted: 2026-09-21
• Link: https://arxiv.org/abs/2609.25399 
• Why newsworthy: Geometric frustration in curved colloidal “curvamers” extended from cylinders to spherical caps and saddles. Stretching vs bending (FvK-like thickness measure) sets how fast elastic energy grows with stack height; typical self-limiting sizes largest for cylinders, smallest for caps, intermediate for saddles — with thin saddles giving especially robust size selection.
• Beginner hook: Curved pieces that won’t tile flat space can still assemble towers that stop at a designed height — curvature as a built-in ruler.
• Caveat: Continuum + coarse-grained simulation; not a classroom chemistry kit.

2. Dense packing of tetrahedra in cylinders

• Authors: Gabrielle N. Jones, Adil Mughal, Philipp W. A. Schönhöfer, Sharon C. Glotzer
• Submitted: 2026-09-22
• Link: https://arxiv.org/abs/2609.26627 
• Why newsworthy: First systematic densest-packings map of regular tetrahedra in a circular cylinder: chiral Tetra Helices vs achiral Dimer Chains. Boerdijk–Coxeter helix emerges naturally under confinement; at a critical diameter the two families coexist at identical packing fraction.
• Beginner hook: Tube diameter alone can choose spiral vs paired stacks of the same sharp pieces — packing as programmable geometry.
• Caveat: Simulation + analytic packing theory.

3. Statistical signatures of microorganism motility under environmental stress

• Authors: Luiza Treichel Mossi, Nicole Mazzitelli Narvaz, Larissa da Silva Bento, Roger Modena, Bernardo Boatini, Amalia Garcez, Leonardo Gregory Brunnet, Alexandre Arenzon, Carolina Brito
• Submitted: 2026-09-21
• Link: https://arxiv.org/abs/2609.25403 
• Why newsworthy: Video microscopy of Paramecium and Artemia under baseline vs stress; trajectory metrics + data-fit run-and-tumble-style models. Path statistics proposed as physiological-stress indicators — an accessible active-matter experiment.
• Beginner hook: Living microscopic swimmers are active matter you can track — change the environment carefully and the path statistics change.
• Caveat: Experimental organisms; any classroom live-culture work needs adult supervision and ethical handling (no hazardous chemistry).

4. Mesoscale heterogeneity in protein hydrogels from dynamic unfolding

• Authors: Victoria Byelova, Lorna Dougan, David Head
• Submitted: 2026-09-22
• Link: https://arxiv.org/abs/2609.26681 
• Why newsworthy: Coarse-grained chemically crosslinked protein gels with one-step unfolding produce crowded high-density clusters linked by low-density stranded corridors; post-gelation relaxation shifts fractal metrics more than unfolding-barrier height.
• Beginner hook: Soft gels are not uniform Jell-O — after they set, dense clumps remain linked by stringy bridges.
• Caveat: Simulation only.

5. Linear and nonlinear active microrheology via fluid particle dynamics

• Authors: Muhammed Muhsin Abdul Azeez, Henning Reinken, Andreas M. Menzel
• Submitted: 2026-09-22
• Link: https://arxiv.org/abs/2609.26431 
• Why newsworthy: Microrheology method extended to viscoelastic/elastic media and nonlinear drive. Large forcing yields distorted stress–strain loops and net probe drift (near walls or between two probes) that vanishes in purely viscous or purely elastic limits — tweezers/magnetic-drive analogue.
• Beginner hook: Continues yesterday’s jammed-soft-matter theme — push a tiny bead hard enough and viscoelastic gels drift in ways linear rheology misses.
• Caveat: Simulation.

Stretch

• Endocytosis Onsager / cytoskeletal viscoelasticity (2026-09-22): https://arxiv.org/abs/2609.26734 
• Brownian gyrator probing scale (2026-09-21): https://arxiv.org/abs/2609.24748 
• Stratified-medium extended optical tweezers (2026-09-20): https://arxiv.org/abs/2609.23757 
• Modular robot calibration composition (2026-09-20): https://arxiv.org/abs/2609.23731 
• Equivariant Stokes resistance NN for microparticles (2026-09-19): https://arxiv.org/abs/2609.23105 

Safe classroom / discussion follow-ons

1. Curved-shell paper models: Cut paper saddles vs spherical-cap segments; stack identical pieces and ask which geometry “wants” to stop sooner as elastic cost grows (inspired by arXiv:2609.25399). Paper/scissors only; no chemistry.
2. Tetra-helix tube packing: Foam/wooden (or paper) tetrahedra in a clear tube of varying diameter — look for spiral vs paired arrangements (echo of arXiv:2609.26627). Supervise small parts; no chemistry.

Corpus mirror: /workspace/self-assembly-corpus/digests/2026-09-23.md.