Biopharmaceutical manufacturers usually apply resin-based affinity- chromatography media for monoclonal-antibody (MAb) capture. Such materials are costly, and their biophysical limitations can create operational difficulties. In an October 2022 webinar, Volkmar Thom (director of membrane chromatography R&D at Sartorius) spoke about his company’s development of a “convecdiff” affinity membrane. He described how the technology can help users to intensify capture processes, reducing downstream manufacturing costs.

The Presentation
Protein A resins contain porous beads of 50–100 μm in diameter. MAbs must diffuse into the pores for a resin to maximize its dynamic binding capacity (DBC). But such spaces have diffusional pathlengths (25–50 μm), and MAbs have relatively large hydrodynamic diameters (~10 nm). Thus, MAb solutions must undergo long residence times for a resin to achieve reasonable binding capacity, resulting in low process productivity (e.g., 10–20 g MAb/L resin/h). Lengthy processes prevent operators from running more than a few cycles per batch. After each batch, multiuse columns must be sanitized, requiring cleaning validation and bioburden management. Thom said that resins also tend to be underused over their lifetimes, begetting further inefficiency.

Sartorius sought to overcome such limitations by developing a rapid-cycling chromatography (RCC) approach. Such a platform, Thom said, would need to reduce cycling times from hours to minutes, provide significant binding capacity, and enable full use over a single batch. The technology also would require scalable device formats and an RCC system capable of rapid valve action and operation with low holdup volumes.

Thom said that hollow fibers, monoliths, membranes, and other convective materials exhibit fast mass-transfer characteristics, but their binding capacity “scales directly with the amount of inner surface area that is accessible to convective flow.” Thus, convective materials must have small nominal pore sizes (e.g., 3 μm) to ensure sufficiently high capacity (e.g., 35 g/L). The reduced permeability creates significant pressure drops and increases susceptibility to fouling. Applying low bed heights helps with such problems but limits scalability.

The convecdiff Sartobind Rapid A membrane combines the productivity of convective materials with the scalability of resin-based media. Antibody binding occurs within a structured hydrogel phase bearing convective and diffusive pores. Diffusion pathlengths of ~3 μm enable rapid mass transfer without need for reduced pore sizes. Thus, the technology exhibits excellent binding capacity, performs robustly, and presents significant scalability potential.

Thom presented data from internal evaluation of Sartobind Rapid A membrane DBC with 10% breakthrough (DBC10%) at residence times of
12 seconds for 14 Fc molecules. DBC10% measured 30–58 g/L. He also described a study in which Sartorius compared DBC10% as a function of residence time for different separation approaches, including protein A resins, convective fibers, and the Sartobind Rapid A membrane. Even at brief residence times, the convecdiff material exhibited high binding capacity.

In head-to-head studies with MabSelect SuRe protein A resin (Cytiva), the membrane achieved similar product recoveries and comparable impurity clearance but at much shorter residence times (0.2 min rather than 4.0 min) and with 15× the productivity (204 g/L/h rather than 14 g/L/h).

Thom stated that the Sartobind Rapid A membrane also enables users to leverage its entire lifetime capacity in a single batch. He noted that Sartorius has worked with industry partners to test convecdiff-material performance over 200 cycles. A clarified MAb solution was loaded onto a membrane through a 0.2-µm prefilter. Cleaning in place (CIP) was performed after each cycle. Impurity clearance remained robust throughout testing, and pressure cycles were performed reproducibly.

Sartorius has incorporated the convecdiff material into Sartobind Q 96-well plates and Sartobind Q Pico membrane-adsorber screening systems. In September 2022, the company introduced a portfolio of Sartobind Rapid A products, with formats ranging from nanoscale (1.2-mL bed volume) to five-inch capsule (75-mL) assemblies. Thom reported that 10-inch and cassette formats representing bed volumes of 200 mL and 800 mL, respectively, will be available soon.

Questions and Answers
Are convecdiff membranes available with ligands besides protein A? The platform certainly is capable of different functionalities. Sartorius continues to test alternative ligand chemistries.

How should convecdiff membranes be cleaned? Sartorius recommends a half-hour of sanitation in 0.5 M NaOH before initial application. Although the membrane can run for multiple cycles without CIP, it is advisable to perform one minute of cleaning in 0.1–0.2 M NaOH after each cycle.

Find the full webinar online at www.bioprocessintl.com/category/webinars.