MCIndustry filtration guide

Microbial Control in Biopharmaceutical Filtration

Selecting membrane materials, retention ratings and validation boundaries across critical process steps

01 / 05

Start with fluid compatibility, then define the control claim

Use PP primarily for prefiltration; PES and hydrophilic PVDF for aqueous biological liquids; hydrophobic PTFE for critical gases, tank venting and compatible solvents; hydrophilic PTFE for corrosive aqueous or solvent-containing drug solutions; and Nylon primarily for compatible solvents and small molecules, rather than by default for high-value proteins.

Three boundaries are non-negotiable: (1) 0.20/0.22 µm is a rated pore size, not an automatic sterile-grade claim; (2) 0.1 µm does not automatically establish a mycoplasma barrier; and (3) 0.2 µm microfiltration is not a general solution for virus removal, endotoxin removal, or final filtration of whole-cell or particle-containing drug products.

02 / 05

Microbial-control flow through biopharmaceutical processing

Filter duty changes by process step. Upstream operations focus on feed and culture-system risks, bioreactors require sterile-gas isolation, and purification and filling must balance product recovery, filter integrity and maintenance of sterility.

Critical process steps, typical streams, filter duties and preferred materials
Process step	Typical stream	Filter duty	Preferred material / format
Upstream solution preparation	Culture media, feeds, buffers, process water	Particle control and reduction of bacterial and mycoplasma risk	PP prefilter; PES/PVDF 0.1 or 0.2 µm; capsule or cartridge
Bioreaction	Inlet gas, exhaust gas, vessel vent	Sterile-gas filtration; isolation of the environment from the culture	Hydrophobic PTFE 0.2 µm; fixed cartridge or single-use capsule
Harvest and clarification	Cells, debris, DNA/HCP, product	Protect depth filtration, chromatography and UF; reduce particle loading	Centrifugation/depth filtration as the primary step; pleated PP as a guard filter
Purification intermediates	Chromatography pools; pre- and post-UF/DF streams	Protect resin, reduce bioburden and maintain a sterile state	PP/PES/PVDF; select against protein-recovery requirements
Formulation and filling	mAb, vaccines, viral vectors, LNP, small molecules	Final sterilizing filtration or sterilization of filterable components	PES/PVDF/hydrophilic PTFE; PTFE/Nylon for compatible solvents
Utilities	Sterile gases and WFI/PW points of use	Establish a local sterile barrier	Hydrophobic PTFE for gases; PES/PVDF/hydrophilic PTFE for liquids

03 / 05

Application ranges and boundaries of six membrane materials

Membrane selection must consider wettability, structure, target fluid, adsorption risk, chemical compatibility and sterilization tolerance together. Surface modification, support layers and morphology can differ within the same material family, so decisions must be based on the specific grade and representative-fluid testing.

Structure, preferred applications, retention ratings and limitations of common membrane materials
Membrane	Wetting / structure	Preferred application	Typical rating	Advantages	Main boundaries / notes
PP	Inherently hydrophobic; commonly nonwoven, depth or microporous media	Prefiltration, clarification, particle protection and upstream solvent filtration	0.6–50 µm is common; finer grades also exist	High dirt-holding capacity, low cost and broad chemical resistance	Do not describe 0.2 µm PP as a terminal sterilizing membrane unless the specific grade has completed sterile-grade validation
PES	Hydrophilic; commonly asymmetric or dual-layer membranes	Culture media, buffers, process intermediates, mAb and terminal liquid sterilization	0.1, 0.2/0.22 and 0.45 µm; dual-layer 0.8/0.2 configurations	High water flux, easy wetting and commonly low protein binding	Organic solvents, surfactants and concentrated proteins can change flux or adsorption; screen with the actual fluid
Hydrophobic PTFE	Inherently strongly hydrophobic; gases pass readily while aqueous phases do not	Sterile air, nitrogen, CO₂, tank/bioreactor venting and compatible solvent liquids	0.2 µm is common for critical gases; 0.45/1 µm for noncritical filtration or particle control	Chemical resistance, resistance to wetting and frequent suitability for steam duty	Condensate or surfactants can wet the membrane and block gas flow; liquid sterilization requires a liquid-challenge claim
Hydrophilic PTFE	Intrinsically or surface-modified hydrophilic; modification depends on the grade	Corrosive aqueous fluids, solvent mixtures, solvent-containing drug liquids, ozonated water and hot water	0.05–5 µm is available; only 0.2/0.22 µm may qualify as liquid sterilizing grade	Avoids alcohol prewetting while combining aqueous throughput with fluoropolymer chemical resistance	The hydrophilic layer, support, seals and sterilization tolerance must be validated together; hydrophobic-PTFE data cannot be transferred
PVDF	Hydrophilic-modified and hydrophobic grades; symmetric or asymmetric structures	Protein/biological fluids, vaccine or viral intermediates and terminal liquids; hydrophobic grades for gases	0.1, 0.22 and 0.45/0.22 µm are common	Commonly low-binding and low-extractables designs, with broad liquid and gas product families	Surface modification and morphology vary; published protein-recovery rankings are not consistent
Nylon	Inherently hydrophilic polyamide with amine, carboxyl and amide sites	Compatible water/organic solvents, small-molecule drug liquids and QC/HPLC samples	0.2/0.22, 0.45 and 0.65–5 µm are common	High mechanical strength, no prewetting and broad solvent applicability	Can adsorb proteins and some acidic/basic APIs; compatibility with strong acids/bases, oxidants and halogenated solvents is grade-dependent

04 / 05

A pore-size rating is not a performance claim

A pore-size rating describes a retention class but does not prove sterile-grade performance on its own. Nominal or absolute rating, microbial challenge, correlation to integrity testing, representative-fluid compatibility and process validation must support the application claim together.

Retention ratings, primary targets, common media and claim boundaries
Rating / grade	Primary target	Common media	Boundary / caution
5–50 µm	Visible particles, cell debris, precipitates and line debris	Pleated or depth PP	Does not control bacteria; used to protect downstream steps
0.6–3 µm	Fine particles, colloids/aggregates and membrane protection	PP, PES, PVDF, Nylon	Nominal or absolute rating must be stated clearly
0.45/0.65 µm	Clarification, load reduction and partial bioburden reduction	PES, PVDF, Nylon	Not normally used as the final sterilizing grade
0.20/0.22 µm	Validated liquid sterilization or sterile-gas filtration	PES, PVDF, PTFE; Nylon only for specific grades	The same pore size does not equal sterile grade; microbial challenge, integrity correlation and representative-fluid validation are required
0.10 µm	Improved control of small microorganisms and mycoplasma risk	Primarily PES/PVDF products	Some mycoplasma can penetrate 0.1 µm; a specific challenge claim, such as A. laidlawii, is required

05 / 05

Turn a filter specification into process control through validation

Final selection should use representative fluid to confirm flow, differential pressure, service life, product recovery, adsorption, extractables, chemical compatibility, sterilization cycles and integrity testing. Gas filtration also requires assessment of condensate risk and wet flow, while proteins and biological products require close attention to recovery and aggregation risk.

A reliable microbial-control strategy combines prefiltration, bioburden management, validated sterilizing filtration, sterile-gas barriers, integrity testing and process hygiene. No single pore size or membrane material replaces application-specific risk assessment and validation.