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Depth filters play an essential role across both upstream and downstream bioprocessing. With their unique depth-based retention mechanism, they act not only as the first physical barrier for removing cells, cell debris, and various impurities, but also as a foundation for process robustness and cost efficiency.
Core Principle: Beyond Surface Filtration
Unlike membrane filters that rely primarily on surface sieving, depth filters operate through a three-dimensional filtration mechanism. The filter media are typically composed of materials such as cellulose, diatomaceous earth, and resins, processed into a porous matrix with large internal surface area and highly tortuous flow paths.
The depth filtration mechanism is a complex, synergistic process:
1. Depth Structure
The filter media are engineered with a gradient structure. The upper layer has relatively larger pores, while pore size gradually decreases along the depth, forming a tightening structure. Larger particles are retained at the surface, while smaller particles are captured at different depths depending on their size. This structure provides depth filters with high dirt-holding capacity.
2. Efficient Adsorption
As the process fluid flows through the complex pore network, particles are removed not only by size exclusion but also through mechanisms such as van der Waals forces and electrostatic interactions. This enables efficient capture of submicron particles, colloids (such as host cell proteins and nucleic acid fragments), and lipids, resulting in excellent clarification performance.
Combining size-based retention, adsorption, and application-driven design, new generations of depth filtration products continue to emerge, including fully synthetic series, functionalized synthetic media, and hybrid solutions that integrate depth filters with membrane layers.
PC Series
The PC series represents traditional depth filters composed of wood pulp fibers, diatomaceous earth, and resin binders. These filters provide both positively charged adsorption and the non-specific adsorption capability of diatomaceous earth.
The PE series, in contrast, offers negatively charged adsorption along with the same non-specific adsorption from diatomaceous earth, making it another type of conventional depth filter.
SA Series
Primarily used in the food and beverage industry, the SA series shares similar material characteristics with the PC series. Typical applications include wine, beer, syrups, juices, and other beverage products' clarification.
DE Series Filter Sheets
Manufactured through a specialized process combining high-purity cellulose and inorganic filter aids. The DE series features a three-dimensional cross-linked internal structure. This enables excellent filtration performance and high dirt-holding capacity. The filters also exhibit low extractables, low metal leaching, and low endotoxin levels.
CE Series Filter Sheets
Made from high-purity wood cellulose without mineral components. The CE series offers extremely low levels of extractables, metal leaching, and endotoxins. It is mainly used for the separation and clarification of plasma-derived products, especially coagulation factors.
AC Series
The AC series uses cellulose fibers combined with activated carbon and other filter aids as the filtration medium. Activated carbon provides a very large surface area, enabling efficient adsorption of particles, pigments, and impurities within its porous structure.
It is widely used for decolorization and endotoxin reduction across chemical pharmaceuticals, biopharmaceuticals, and food processing, as well as for small-molecule toxin removal in ADC processes.
CL Series Depth Filter Sheets
The CL series is composed of wood cellulose and binders, with a near-neutral charge. It does not rely on diatomaceous earth or charge-based adsorption, allowing for high product recovery, especially in virus-related applications. It is mainly used in vaccines, cell therapy, and gene therapy processes.
SP Series
The SP series consists of fully synthetic materials, produced by combining composite fibers with inorganic filter aids through a specialized process. Its three-dimensional internal structure enables efficient filtration and high dirt-holding capacity.
NY Series
The NY series is designed to provide enhanced protection for downstream sterile filtration. Selected application case studies demonstrate its strong performance in real-world processes.
Comparison Data of New Technology
Case 1:
Initial turbidity 2150 NTU
Cell density 22.1 M
Viability 98%
Case 2:
Centrifuged antibody feed
Initial turbidity 55 NTU
Conclusion:
H2NY02 provides strong protection for downstream sterile filtration, enabling up to a 3-fold increase in throughput capacity.
CH Series
The CH series combines depth filtration media with functionalized fully synthetic (polypropylene fiber) materials. It delivers both the impurity removal capability of depth filters and the adsorption functionality of ion exchange chromatography. Compared with conventional depth filters, it offers enhanced removal of host cell proteins (HCP) and DNA. Currently, the CH series is available in the M02 format only.
HCM Series
The HCM series consists of functionalized fully synthetic (polypropylene fiber) media in a depth filter format.
HCMO is designed for clarification of cell harvest fluids, achieving effective clarification in a single-stage filtration process.HCMC is mainly used for post-centrifugation cell broths, delivering lower filtrate turbidity and improved HCP removal compared to conventional depth filters. At present, the HCM series is also available in the M02 format only.
As biopharmaceutical manufacturing advances into the era of monoclonal antibodies, gene therapy, and vaccines, depth filtration technology continues to evolve. Its core strengths remain: high dirt-holding capacity, cost efficiency, enhanced process robustness, and broad impurity removal capability.
To better serve global pharmaceutical companies and strengthen supply capabilities, Cobetter has invested nearly RMB 100 million to introduce an 80-meter continuous depth filter sheet production line from Germany. The production line covers 1,500 m² and operates with a fully automated continuous manufacturing process, equipped with in-line monitoring systems for thickness, basis weight, and moisture, enabling real-time quality control and closed-loop management.
All filter sheets are manufactured in a Class 100,000 cleanroom environment, where key parameters such as airborne particles, temperature, humidity, pressure differentials, and microbial contamination are strictly controlled to meet the high standards of the pharmaceutical industry.
The production line now exceeds an annual capacity of 1 million m², significantly shortening lead times and providing customers with faster and more reliable supply.
