LNP-mRNA Ultrafiltration Technology Showdown: TFF Cassette vs. Hollow Fiber Filter- A Case Study

In the biopharmaceutical, lipid nanoparticle (LNP) serve as the "golden carrier" for nucleic acid drug delivery. Their production efficiency and product quality directly impact drug efficacy and safety. However, large-scale LNP production faces a core challenge: achieving high-purity concentration and buffer exchange without compromising their structural integrity. This challenge, known as tangential flow filtration (TFF), is a key step in large-scale LNP production. With TFF cassette (Flat sheet ultrafiltration membrane) and hollow fiber ultrafiltration membrane being the two mainstream TFF technologies, how should we choose?

This article will introduce the selection and application cases in the LNP-mRNA ultrafiltration process, and examine its ultrafiltration application effects from multiple perspectives, including two different filter types: ultrafiltration membrane cassette and hollow fiber filter, multiple batches of liquid, and the reusability of the two filters.

TFF: Comparison of membrane materials and filter types

Tangential Flow Filtration (TFF) operates with the feed stream flowing parallel to the membrane surface, which continuously sweeps away retained particles and helps mitigate membrane fouling and concentration polarization. This cross-flow mechanism enables consistent filtration performance and extends membrane service life.

Common ultrafiltration (UF) membrane materials include polyethersulfone (PES) and regenerated cellulose (RC). Both membrane types offer high retention rates, high flux, and ease of cleaning. Among them, RC membranes are inherently hydrophilic, exhibiting lower protein binding and superior fouling resistance compared to PES membranes. These properties make RC membranes particularly suitable for processing high-concentration samples. Additionally, RC membranes demonstrate better compatibility with organic solvents.

Standard ultrafiltration filters primarily come in two formats: flat-sheet cassette and hollow fiber filter cartridges, each with distinct structural designs. Flat-sheet cassettes consist of multiple stacked membrane layers, creating a multilayer filtration system. The effective filtration area increases with the number of membrane layers. To enhance solute transfer, high-density screens are positioned between membrane layers, promoting turbulent tangential flow across the membrane surface. This turbulence effectively delays the development of a gel layer, maintaining optimal filtration performance.

Structure of flat-sheet ultrafiltration cassette

Hollow fiber filter cartridges are composed of multiple slender fiber filaments arranged in parallel. During operation, fluid flows axially through the lumen of each fiber, while filtration occurs via radial transmembrane permeation. Due to their open-channel design, hollow fibers generate relatively low shear forces. The shear intensity primarily follows laminar flow dynamics within the fiber lumen and can be quantitatively controlled by adjusting the flow rate (positively correlated) and selecting an appropriate fiber inner diameter (negatively correlated). This makes hollow fiber filters particularly suitable for processing shear-sensitive products.

In practical applications, hollow fiber filters and flat-sheet cassettes each offer distinct advantages due to their structural differences.

Hollow fiber filter, characterized by their low-shear flow paths, are particularly advantageous in processes such as perfusion cell culture, E. coli cell retention and lysate clarification, and virus particle concentration. Their open-channel design not only minimizes flow resistance but also maintains stable flux when handling high solid-content or viscous materials.

In contrast, flat-sheet cassettes exhibit superior mass transfer efficiency owing to their screen-layered structure, resulting in relatively higher flux performance. This makes them especially suitable for processing shear-tolerant materials. As a result, they are widely applied in downstream processes such as antibody purification, recombinant protein concentration, vaccine production, and plasma-derived product refinement.

Naturally, the selection of an optimal ultrafiltration strategy must take into account multiple factors, including fluid characteristics, production scale, and quality requirements. Therefore, the choice of ultrafiltration membrane material and filter format should be guided by comprehensive experimental comparison and multi-criteria evaluation, in order to enhance the overall efficiency of biologics manufacturing.

Case Study Data

Considering the unique characteristics of lipid nanoparticle (LNP), this case study compares the performance of RC (regenerated cellulose) flat-sheet cassettes and mPES (modified polyethersulfone) hollow fibers in mRNA-LNP ultrafiltration. The evaluation also includes validation of batch-to-batch consistency and reusability performance of both types of consumables.

Test Conditions:

① Two RC (regenerated cellulose) ultrafiltration cassettes with 300 kDa MWCO and a total membrane area of 0.11 m²each (model: UF-CLA0300010P) were used. The feed flow rate was maintained at 5 L/min/m² (LMM) with a transmembrane pressure (TMP) ≤ 5 psi.

② One mPES (modified polyethersulfone) hollow fiber filter with 500 kDa MWCO, 0.5 mm inner diameter, and a total membrane area of 0.24 m² (model: HFEPP0500530P) was used. The feed flow rate was similarly controlled at 5 LMM, with TMP ≤ 5 psi.

Ultrafiltration Cassette Application Diagram / Hollow Fiber Application Diagram

Experimental Results:

Table 1: Summary of Flux Results

Test Results:

Table 2 Test Results

Data Analysis:

Based on the data above, the filter application and the batch-to-batch variability of the materials remain relatively stable. The impact on key indicators of LNP, such as particle size, PDI, and encapsulation efficiency, is minimal. Moreover, the mRNA purity and integrity show slight improvements after ultrafiltration, indicating a certain degree of purification effect on the formulation.

Among the different types of ultrafiltration filters, RC ultrafiltration cassettes demonstrate a clear advantage in terms of flux, offering significant benefits in reducing process time and required membrane area. Under appropriate process conditions, the RC cassettes have minimal impact on the LNP system. Notably, in the early stages of LNP formulation development—when the system may still be relatively unstable—RC membranes offer additional advantages in terms of lower lipid adsorption and reduced impact on the material system.

Hollow fiber filter cartridge, on the other hand, feature an open-channel design that results in relatively low shear stress, but their membrane flux is typically slightly lower. Therefore, from the overall performance perspective in LNP-mRNA purification processes, UF RC cassette presents a more advantageous option and are recommended as a preferred filter selection.

In the field of LNP-mRNA purification, both ultrafiltration cassettes and hollow fiber filters represent viable technical approaches, each with distinct advantages. Users can flexibly select the appropriate solution based on the characteristics of their materials.

Cobetter, leveraging its extensive technical expertise, is capable of precisely matching membrane pore size with process parameters to not only purify LNP efficiently but also maintain critical quality attributes such as particle size uniformity (CV < 5%), encapsulation efficiency, and mRNA integrity. This enables a robust ultrafiltration process from laboratory scale to GMP production for LNP-based formulations.