Semidilute Polymer Scaling Controls PEG-induced Protein Phase Separation

PEG-induced phase separation of bovine serum albumin (BSA) shows binodals and tie lines that approximately collapse in PEG mass-concentration coordinates across PEG chain lengths from 4–100 kDa.

• Why it matters: A key gap is whether PEG mass concentration can serve as a transferable measure of depletion-driven crowding strength when polymer molecular weight changes.
• What they did: BSA was mixed with PEG (4–100 kDa) and coexisting phases were measured to map binodals, tie lines, and critical points; generalized free volume theory (GFVT) was used to fit them.
• The result: GFVT describes BSA binodals and tie lines and also approximately binodals for three other globular proteins in PEG 35K (7.2–66.4 kDa), implying PEG mass concentration (g/L) can be a common crowding metric for these systems.

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