Unit Operations
Formulation
Formulation is a critical step in bioprocessing that transforms a purified biologic into a stable, patient-ready drug substance. By concentrating the product to the target dose and exchanging into the optimal buffer and excipient system, formulation helps reduce aggregation risk and preserve potency.
What is formulation in bioprocessing?
In biopharmaceutical manufacturing, formulation is the downstream unit operation that prepares a purified biologic drug substance such as a monoclonal antibody, vaccine, or recombinant protein for final dosage. Following chromatographic purification and viral clearance steps, the product is in a process buffer at a concentration that is typically far below the therapeutic dose and in an excipient environment incompatible with long-term product stability or patient safety.
Formulation resolves both issues simultaneously. Using tangential flow filtration (TFF), specifically the sequential processes of ultrafiltration (UF) and diafiltration (DF), the biologic is:
- Concentrated to its target dose by removing water and small-molecule solutes across a semi-permeable membrane
- Buffer-exchanged as fresh formulation buffer is added in a continuous or stepwise diafiltration process, replacing process salts, residual host-cell proteins, and other impurities with stabilizing excipients
This step transforms the active pharmaceutical ingredient (API) into a form suitable for storage, transport, and administration. The output of the formulation step, the drug substance, is the material that enters fill-finish manufacturing. Its concentration, buffer composition, osmolality, and pH are the parameters that directly determine dosage accuracy and shelf-life stability.
Common challenges in biopharmaceutical formulation
Formulation development is technically demanding. Many of the most significant challenges arise not from basic filtration principles, but from the intersection of high product concentrations, sensitive biomolecules, regulatory scrutiny, and the need to scale reliably from bench to manufacturing.
High-concentration formulation
Subcutaneous (SC) dosage forms for mAbs and bispecifics increasingly require product concentrations above 150 g/L and sometimes exceeding 200 g/L. At these concentrations, solution viscosity rises sharply, membrane flux declines, and aggregation risk increases significantly, making endpoint control extremely difficult.
Product aggregation & degradation
Shear stress generated at the membrane surface, pressure differentials across the pump, and prolonged exposure to sub-optimal excipient conditions can all induce protein aggregation or degradation. For example, with lipid nanoparticles (LNPs) and gene therapy vectors, aggressive UF/DF conditions can directly compromise product potency and safety.
Lack of real-time process visibility
Traditional UF/DF processes rely on off-line UV absorbance measurements or refractive index readings to track concentration. These manual, off-line sampling methods interrupt the process, introduce dilution errors, and leave operators "flying blind" between sample pulls, increasing the risk of under- or over-concentration of the drug substance.
Solutions for formulation development and scale-up
Addressing the challenges of modern biopharmaceutical formulation requires an integrated approach that combines robust TFF systems, membranes, and real-time analytical control. Below are the foundational solutions that underpin successful formulation processes.
KrosFlo® TFF systems: Scalable precision from process development to GMP manufacturing
The KrosFlo TFF system portfolio is one of the most comprehensive tangential flow filtration platforms available for biopharmaceutical formulation. Built on decades of UF/DF expertise, KrosFlo systems deliver consistent fluid dynamics, broad membrane compatibility, and seamless scalability, from 35 mL bench-scale runs to 2,000 L manufacturing campaigns.
- End-to-end automation with cGMP-compliant electronic batch records on the KrosFlo® RS TFF System, purpose-built for GMP production with true closed-system operation
- Gentle low-shear processing for shear-sensitive biologics including lipid nanoparticles (LNPs) and viral gene therapy vectors
- Single-use ProConnex® flow paths that enable ready-to-run operation, eliminate cleaning validation, and support rapid product changeovers
- Compatibility with both flat-sheet cassettes (including TangenX® SC, SIUS®, and PRO reusable cassettes) and hollow-fiber filters for maximum formulation flexibility
- Minimal system hold-up volumes that maximize product recovery, critical for high-value drug substances and early-phase programs with limited material
PATsmart™ PAT Technologies: Real-time formulation control that eliminates off-line sampling
Repligen's PATsmart™ Process Analytical Technology portfolio delivers the real-time process insight needed to move from endpoint guesswork to fully automated, data-driven formulation control. At the heart of the formulation PAT strategy is the FlowVPX® in-line UV-Vis spectrophotometer— the only in-line, variable path length management system that is purpose-built for integration with KrosFlo TFF systems in GMP environments.
- Continuous, real-time protein concentration measurement directly in the TFF process stream. No sample pulls, no dilution errors, no process interruptions.
- Variable pathlength technology (VPT) extends the measurable concentration range far beyond conventional fixed-pathlength UV instruments, making it the only in-line tool capable of tracking concentration from dilute process streams all the way to high-concentration mAbs.
- PAT-driven automated endpoint control: the KrosFlo® RPM® (Real-time Process Management) System series integrates PATsmart FlowVPX® directly into KrosFlo® TFF systems, enabling the system to automatically stop the UF step when the target concentration is reached—eliminating over-concentration and product loss.
- Validated GMP deployment: FlowVPX® technology has been implemented in commercial GMP manufacturing at leading biopharmaceutical companies, including Janssen® and Bristol Myers Squibb® and has available software features designed for GMP use.
Spectrum® Hollow Fiber Filters: Gentle, high-flux UF/DF for formulation of sensitive biologics
Hollow fiber modules feed product through the fiber lumen in a highly laminar flow, generating lower shear than flat-sheet cassette formats, making them a natural fit for formulation of shear-sensitive modalities. This makes hollow fiber an ideal option for enveloped viruses like lentivirus and other fragile biologics where minimizing mechanical stress during concentration and buffer exchange is critical.
- Two membrane chemistries, ten ultrafiltration pore sizes, and five effective lengths to match the retention, flux, and scale requirements of each product class and formulation target concentration.
- Scalable from MicroKros and MidiKros modules for small-volume process development through large production-scale modules; adding fibers to process larger volumes while maintaining consistency in flow path length to increase surface area preserves scale-up predictability.
Reliable UF/DF performance for final drug substance formulation
In the final formulation stage of biotherapeutic manufacturing, precise control over concentration, buffer exchange, and product recovery is critical to ensuring stability, efficacy, and regulatory compliance. TangenX® tangential flow filtration (TFF) cassettes provide a robust and scalable platform for ultrafiltration and diafiltration (UF/DF), enabling efficient formulation of drug substances across a wide range of modalities.
- Precise concentration and buffer exchange
Achieve tight control over target concentration and final buffer composition, supporting optimal product stability and downstream fill-finish requirements.
- High product recovery and yield
Engineered membrane performance and flow path design minimize product loss and maximize recovery of high-value biologics, including sensitive proteins and advanced modalities.
- Scalable, predictable performance
From process development to GMP manufacturing, TangenX cassette formats enable linear scale-up, reducing risk and ensuring consistent process outcomes at every stage.
- Operational flexibility and efficiency
Available in both single-use (SIUS®, SIUS® Gamma) and reusable (SC and PRO) formats, TangenX cassettes support diverse manufacturing strategies while improving turnaround times and reducing cleaning validation burdens.
Biopharmaceutical formulation is the process of preparing a purified biologic for storage, transport, and administration. It typically involves concentrating the product, exchanging process buffers for formulation buffers, and optimizing conditions to maintain stability, potency, and product quality throughout its shelf life.
Formulation helps ensure that biologic drug products remain stable, effective, and safe from manufacturing through patient administration. An optimized formulation can reduce aggregation, improve shelf life, maintain activity, and support successful regulatory submission and commercialization.
Formulation focuses on creating a stable drug substance by optimizing concentration, buffer composition, and product stability. Fill-finish is the subsequent process of filling the formulated drug product into final containers such as vials, syringes, bags, or cartridges under sterile conditions.
UF/DF is commonly used to concentrate biologics and exchange process buffers for formulation buffers as the final formulation operation. These steps help achieve target concentrations, improve product stability, and prepare the drug substance for storage or final fill.
Concentrating biologics can help achieve target dosage requirements determined by the final delivery method such as intravenous (IV) or subcutaneous administration. This is also used to reduce volumes for storage and transportation efficiency. High-concentration formulations are increasingly common for monoclonal antibodies and other biologics.
Common formulation challenges include protein aggregation, increased viscosity at high concentrations, degradation, product loss, and limited process visibility. Effective process control and real-time monitoring can help mitigate these risks and improve consistency.
Protein aggregation can occur due to changes in concentration, pH, temperature, buffer composition, shear forces, or interactions between molecules. Aggregation can negatively impact product quality, efficacy, stability, and regulatory compliance.
Traditional formulation processes often rely on offline sampling, which provides limited and delayed insight into product attributes. Real-time monitoring can help reduce variability and processing time to support more consistent formulation outcomes.
Biologic stability can be affected by protein concentration, pH, buffer composition, temperature, excipient selection, and storage conditions. Formulation development aims to identify optimal conditions that preserve product quality through final fill, storage, transportation and administration.
A formulation buffer is the final solution that surrounds and stabilizes a biologic drug substance. It typically contains specific salts, pH-adjusting agents, and excipients designed to maintain stability, minimize degradation, and support product performance during storage and use.
As biologic concentrations increase, challenges such as viscosity, aggregation, and process complexity become more significant. Innovative solutions and process strategies help overcome these challenges while maintaining stability and patient-friendly dosing formats.
