The corpus is anchored by a mix of Chinese universities — including Zhejiang University of Technology, Tianjin Polytechnic University and Nanjing Tech University — and European industrial and academic filers such as Agfa-Gevaert and Katholieke Universiteit Leuven. No single assignee dominates the full 537-family corpus; filing is distributed across a long list of institutional filers rather than concentrated in one company. Recent-year filing counts for these same named assignees have flattened or dropped, which suggests the current filing wave is not led by any one dominant actor.

China received 448 of the 537 total records in this dataset, far ahead of the United States (28), the EPO (15) and WIPO PCT filings (15). This reflects both the volume of domestic Chinese university research activity in separation membranes and the practice of filing first or exclusively domestically before considering international protection. Anyone assessing competitive risk or freedom to operate in this space needs to screen CNIPA filings directly rather than relying on US or European patent databases alone.

Phase inversion is a casting technique where a polymer solution is precipitated into a porous solid, directly setting the pore structure of the resulting membrane in a single layer. Thin-film-composite (TFC) construction instead builds a thin selective layer, typically via interfacial polymerization, on top of a separately optimized porous support — decoupling selectivity from mechanical strength. Representative filings like US9808768B2 combine both: using phase inversion to form and crosslink the porous support while depositing a thin film for the selective layer, which is a common pattern in solvent-resistant membrane claims.

Filing volume grew substantially from 14 records in 2017 to a peak of 73 in 2025, passing through 48 at the 2022 midpoint. However, growth from the midpoint to the peak has flattened rather than accelerated, and several of the most active named assignees show flat or negative year-over-year filing counts in the latest tracked year. The 2026 count should be read as understated, since publication typically lags actual filing by around 18 months, but the overall trajectory looks like a maturing filing wave rather than one still accelerating.

Compared to the dense core of phase-inversion and thin-film-composite casting claims, sub-areas such as solvent-resistant TFC membranes for organic separations, antifouling surface-grafting chemistries and charged porous membrane variants carry comparatively thinner filing density. Casting-solution additive formulations and membrane use in body-fluid medical devices (13 records under A61M) also sit outside the main filing cluster. These are the branches worth screening first for a first-claim opportunity, since the core pore-structure and interfacial-polymerization claim space is already densely occupied.