Size-based separation of pharmaceutical oligonucleotides via polymer brush coatings

Abstract: Downstream separation and cleaning dominate the material intensity of oligonucleotide manufacturing. Conventional solid-phase synthesis exhibits a process mass intensity of ~4,000–5,000 kg per kg product, largely due to purification and wash solvents. Reducing chromatographic steps and developing regenerable separation platforms is therefore essential to lower solvent use and waste generation. Polymer brush–based affinity materials offer a promising alternative by providing high loading capacities and stimulus-responsive release. Polymer brushes consist of densely grafted polymer chains that create a confined, highly functionalized environment capable of capturing and releasing biomolecules in response to pH. Here, we report the fabrication and characterization of pH-responsive polymer brush coatings based on poly(2-(diethylamino)ethyl methacrylate) (PDEAMA) and PDEAMA/poly(methacrylic acid) (PMAA) copolymers grafted from gold or glass substrates. A modified surface-initiated polymerization eliminates the need for an inert atmosphere and significantly reduces solvent consumption, enabling synthesis in volumes as low as 3 mL or within a confined droplet between two glass slides. Interactions with oligonucleotides (10-, 20-, 30-, and 40-mers) were studied as a function of brush composition, thickness, oligonucleotide length, and pH using surface plasmon resonance, quartz crystal microbalance, and fluorescence microscopy. Binding capacity normalized to brush thickness was independent of copolymer composition up to 20% PMAA. In contrast, release behavior depended on oligonucleotide length and brush composition, with an 80:20 PDEAMA:PMAA brush enabling complete release at pH 10 and a pH window of 8–9 identified as optimal for size-based separation.