Scalable membrane filtration system for bioprocessing concentration and buffer exchange
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Repligen TFF systems are the gold standard for used purchases because parts availability is excellent, the pump design is simple (easy rebuilds), and control systems use standard Siemens or Allen-Bradley components. The KR2i (2010-present) is nearly identical mechanically to current production, so you're not buying obsolete technology. Older KMPI models (2005-2010) use the same cassette holders but have less sophisticated controls—still excellent performers for non-GMP work. LabScale benchtop units can be found for $8,000-15,000 and work for small pilot batches under 20L.
Checklist: Run pump at maximum RPM for 30 minutes and listen for bearing noise or vibration—these are signs of imminent failure. Check tubing compression on peristaltic pump head: grooves worn into the raceway mean $1,200 pump head replacement. Test all pressure transducers by applying known pressure and comparing to gauge readings (±5% tolerance). Request service logs showing pump head and tubing change intervals. Verify touchscreen responsiveness and check for error codes in system diagnostics. Most importantly, run a water flush through all flow paths and inspect for leaks at cassette holder connections.
Sartorius equipment is built to German engineering standards with exceptional material quality and sanitary design. Their TFF skids hold value well because Sartocon cassettes remain the preferred choice for antibody manufacturing (mAbs, bispecifics). The challenge with used Sartorius is that many systems were custom-built for specific clients, so you may encounter non-standard configurations. Control systems on pre-2015 models can be proprietary and difficult to service without Sartorius technicians. That said, mechanical reliability is outstanding—pumps and valves last 2x longer than competitors.
Checklist: Verify cassette holder compatibility: older Sartocon models use discontinued Mini or Midi formats. Check that all documentation is in English (German-market units often have untranslated manuals and software). Test CIP functionality if reusable system: heat exchanger must reach 80°C and spray balls must provide complete coverage. Inspect all tri-clamp gaskets and ferrules for wear. Request electrical schematics and confirm you can source replacement control components locally.
GE/Cytiva dominated TFF in the 1990s-2000s with their Pellicon cassettes, which are still widely used despite Repligen's recent market gains. Used GE skids are plentiful because many pharma companies upgraded to single-use platforms. The main risk is parts availability: GE discontinued many pilot-scale models when they transitioned to ReadyToProcess single-use focus. That said, Pellicon 2 and 3 cassettes remain available and work in competitor holders with adapters. Control systems on older units are often proprietary iFIX or Wonderware SCADA, which require specialized service.
Checklist: Confirm Pellicon cassette availability for your MWCO and membrane chemistry: some specialty formats are discontinued. Test pump operation extensively: GE used both peristaltic (Watson Marlow) and centrifugal (Alfa Laval) pumps depending on model year. Check control system software version and ensure you can obtain licensing and updates. Inspect stainless tubing for crevice corrosion, especially on older acid-cleaned systems. Request validation data from previous owner if GMP-qualified.
Pall TFF systems are robust and well-engineered but less common in the used market than Repligen or Sartorius, which can make pricing unpredictable. Pall's strength is virus filtration integration: some pilot skids combine TFF with downstream virus filters in a single platform. Minimate cassettes are reliable and available but typically 15-20% more expensive per m² than competitors. Service network is smaller, so factor in potential shipping delays for parts. Best value in used Pall is finding systems from pharma companies doing facility consolidations—often low hours and well-maintained.
Checklist: Inspect cassette holder seal integrity: Pall uses O-ring compression seals that can develop leaks after repeated cycles. Test pressure hold test: pressurize system to maximum working pressure and monitor for 15 minutes (drop >2 psi indicates leak). Check control panel for error logs and alarm history. Verify availability of Minimate cassettes in your required MWCO. Request calibration certificates for all sensors and meters.
Millipore (now Merck) was an early TFF pioneer but has largely exited the pilot skid market to focus on benchtop and single-use devices. Used Millipore skids are typically 10-20 years old, which means obsolete control systems and pump technology. However, they're built like tanks and mechanical components last forever. The ProFlux M12 peristaltic systems are simple, reliable workhorses that can be purchased very cheaply ($5,000-12,000) and are perfect for academic labs with tight budgets. Not suitable for GMP without major upgrades.
Checklist: Expect to replace all tubing, pump heads, and gaskets immediately—budget $2,000-3,000 for consumables. Test pump motor and controller: many older units use proprietary motor drives that are impossible to replace. Check frame condition: welds and casters often show rust or damage. Verify cassette holder compatibility with modern membranes. Plan on manual operation: control systems are rarely functional after 15+ years of storage.
Budget new alternatives
Budget-conscious labs processing <100L batches who need GMP-ready documentation but don't require maximum scale-up capacity
Labs already using Pall chromatography or filtration who want single vendor integration and can leverage existing service contracts
Research-focused labs needing membrane flexibility and willing to trade automation for lower upfront cost, no GMP compliance required
Tangential flow filtration skids operate by pumping process fluid parallel to membrane surfaces rather than perpendicular through them (dead-end filtration). This tangential flow sweeps concentrated material across the membrane, minimizing fouling and allowing continuous operation at high recovery rates. The skid integrates pumps, pressure sensors, flow meters, membrane holders, and a control system into a mobile cart. During operation, feed pressure drives smaller molecules (buffer, water, small proteins) through membrane pores into the permeate stream while retaining larger molecules (target proteins, cells, viruses) in the retentate. Pilot TFF skids are critical for establishing filtration parameters (transmembrane pressure, crossflow rate, concentration factors) that scale linearly to manufacturing. They're used throughout bioprocess development: harvesting cell culture supernatant, concentrating monoclonal antibodies 10-50x, exchanging buffers before chromatography, removing endotoxins and viruses, and formulating final drug products. The ability to swap membrane cassettes with different molecular weight cutoffs (MWCO from 5 kDa to 0.2 µm) makes these systems versatile for proteins, plasmid DNA, exosomes, and gene therapy vectors. Modern skids feature single-use flow paths to eliminate cleaning validation, automated control of TMP and crossflow, real-time UV monitoring of permeate quality, and data logging for regulatory documentation.
The KR2i is the most widely adopted pilot TFF platform in biotech because it balances automation sophistication with operational simplicity. Its touchscreen interface allows technicians to set up filtration runs in minutes using pre-programmed recipes for concentration, diafiltration, or single-pass mode. The peristaltic pump delivers gentle handling for shear-sensitive products like AAV vectors while achieving flow rates up to 8 LPM. Critically, the system uses disposable KrosFlo Max cassette holders and single-use tubing sets, eliminating cleaning validation and preventing cross-contamination between campaigns. The automated TMP control maintains setpoints within ±1 psi by adjusting retentate valve position in real-time, producing reproducible results run-to-run. Built-in permeate UV monitoring lets you watch protein breakthrough in real-time, and data logging meets 21 CFR Part 11 requirements for GMP documentation. Repligen's extensive membrane portfolio (5 kDa to 750 kDa MWCO in mPES, UFP, and PS materials) fits directly into the cassette holders without adapters. Service and support are exceptional: replacement parts ship overnight and field service engineers can rebuild pumps on-site. The 18-month warranty on new systems and guaranteed parts availability for 10+ years make this a low-risk investment. Used KR2i systems retain 60-70% of their value because membrane technology hasn't changed significantly in 10 years.
What you lose: Budget TFF options sacrifice automation (manual valve adjustment vs PLC control), data logging capability (no 21 CFR Part 11 compliance), and modern single-use flow paths. You'll spend 2-3x more labor per run doing manual TMP adjustments, recording data on paper, and performing CIP/SIP validation. Older control systems lack recipe management, so operators must manually replicate conditions run-to-run. Pump technology on budget systems is often first-generation peristaltic with poor flow stability and high maintenance. You lose vendor support for parts, calibration, and qualification documentation.
What you keep: The core physics of TFF doesn't change: budget systems perform the same separation as premium skids if you manually maintain proper TMP, crossflow, and temperature. Membrane cassettes are interchangeable across vendors (with adapters), so you're not locked into expensive proprietary consumables. Stainless steel construction on even old systems lasts decades with proper passivation. Most importantly, you keep scalability: process parameters developed on a $10,000 used skid translate directly to manufacturing-scale systems. For research applications without GMP requirements, budget skids deliver 80% of premium performance at 20% of the cost.
TFF skids used in GMP manufacturing must meet strict design and documentation requirements. All wetted materials must be USP Class VI certified (316L stainless, platinum-cured silicone tubing, PVDF/PES membranes). Skid qualification requires Factory Acceptance Testing (FAT), Site Acceptance Testing (SAT), Installation Qualification (IQ), Operational Qualification (OQ), and Performance Qualification (PQ) protocols validated by quality assurance. The control system must support 21 CFR Part 11 electronic records with audit trails, user access controls, and electronic signatures. For viral clearance applications, the skid must demonstrate consistent log reduction values (LRV) across validation runs, requiring precise control of TMP (±1 psi), temperature (±2°C), and flux. Cleaning validation is required for reusable systems: prove that CIP removes >99% of protein residues and sanitization achieves <10 CFU/100cm² bioburden. Most companies now use single-use assemblies for GMP to avoid cleaning validation entirely. When buying used GMP skids, request complete equipment history files, previous validation reports, and change control documentation. A skid used for research can be GMP-retrofitted but expect $30,000-80,000 in re-qualification costs including new sensors, control system upgrades, and validation studies. The membrane holder design is critical: it must prevent bypass flow and provide uniform transmembrane pressure across all cassettes to ensure reproducible separation.