This is the 2D cross-section counterpart of the 3D lipid-droplet simulator: the same population of droplets, the same three competing processes, viewed edge-on as circular profiles budding from a flat ER line instead of instanced spheres in a 3D box.
Ostwald ripening (Lifshitz–Slyozov–Wagner):
dr_i/dt = k_r · (1/r_c − 1/r_i)
r_c = Σr_i³ / Σr_i² (flux-weighted critical radius)
DGAT synthesis (adds TAG volume, spread by surface-area weight):
dV_i/dt += k_s · w_i, w_i ∝ r_i²
ATGL lipolysis (surface reaction, blocked by perilipin coat):
dr_i/dt −= k_l · (1 − coverage_i)
- DGAT synthesis rate — triacylglycerol production feeding droplet growth from the ER; the per-droplet volume share scales with surface area, which converts to an equal radial growth increment for every droplet regardless of size — larger droplets still gain more absolute lipid volume even though their radius grows at the same rate as a small one.
- ATGL lipolysis rate — the rate constant for adipose triglyceride lipase hydrolysing surface triglyceride to free fatty acid + diacylglycerol; a zero-order surface reaction, so shrink speed is independent of droplet size once uncoated.
- Perilipin coverage — PLIN-family proteins coating the droplet's phospholipid monolayer; higher coverage sterically blocks ATGL access, multiplying lipolysis by (1 − coverage).
- Seipin nucleation rate — how often new droplets bud from ER neutral-lipid lenses; new droplets start small and are the most vulnerable to ripening-driven shrinkage.
- Fasting pulse — briefly spikes lipolysis and strips perilipin coverage, mimicking hormone-sensitive PKA phosphorylation of perilipin during energy deficit that unmasks the droplet to ATGL/HSL.
Because r_c is the surface-weighted mean radius, droplets above it keep growing while smaller ones lose lipid to them and eventually vanish — the same coarsening dynamic (Ostwald ripening) seen in emulsions, alloys, and every lipid droplet population under active turnover. Drag to pan the cross-section and scroll to zoom in on individual droplets.