Why Biologics Need Lyophilisation
Proteins, monoclonal antibodies, enzymes, and other biological molecules are inherently unstable in aqueous solution. In solution, they are subject to hydrolysis, oxidation, deamidation, aggregation, and physical denaturation, degradation pathways that can reduce potency, alter immunogenicity, and compromise the safety of the product. For biologics with an intended shelf life of two years or more, maintaining adequate chemical and physical stability in a liquid formulation is often not feasible without cold chain storage that is impractical for global distribution.
Lyophilisation, or freeze-drying, addresses this by removing water from the formulation while maintaining the structural integrity of the biologic molecule, converting the liquid drug product into a stable solid cake that can be stored at ambient or refrigerated temperature and reconstituted immediately before use. The process is technically demanding, time-consuming, and equipment-intensive, but for many biologics it is the only route to a commercially viable product.
The Three Phases of a Lyophilisation Cycle
Freezing
In the freezing phase, the liquid drug product in the vials is cooled to a temperature below the eutectic point or glass transition temperature of the formulation. The rate of freezing is critical. Slow freezing produces large ice crystals that create a coarser cake structure with good mass transfer properties during drying. Rapid freezing produces small ice crystals and a denser cake structure. Controlled nucleation, the induction of ice crystal formation at a defined temperature, is an emerging technique for improving freeze-drying cycle consistency and reducing vial-to-vial variability in cake structure.
Primary Drying
In primary drying, the chamber pressure is reduced and the shelf temperature is raised to supply the heat of sublimation, driving water directly from the frozen ice phase to vapour without passing through a liquid phase. The product temperature during primary drying must remain below the collapse temperature, which is typically close to the glass transition temperature of the maximally freeze-concentrated solution (Tg prime). Collapse, the loss of the porous cake structure, results in a product with reduced reconstitution performance and potentially altered potency.
Secondary Drying
After all ice has been sublimed, secondary drying removes the residual bound water from the amorphous matrix by desorption. The shelf temperature is raised to typically 20 to 40 degrees Celsius and held for several hours. The target residual moisture content for most lyophilised biologics is below 1%, as residual water acts as a plasticiser that reduces the Tg of the dried cake and increases molecular mobility, accelerating degradation.
Critical Formulation Components for Lyophilisation
| Excipient Role | Common Examples | Function in the Lyophilisate |
| Bulking agent | Mannitol, glycine, sucrose | Provides physical structure to the cake; prevents collapse of the matrix during drying |
| Cryoprotectant | Sucrose, trehalose, sorbitol | Protects the protein during freezing by replacing water in the protein hydration shell; reduces denaturation |
| Lyoprotectant | Sucrose, trehalose | Protects the protein during drying; glass-forming excipients that immobilise the protein in a rigid amorphous matrix |
| Buffer | Histidine, citrate, phosphate | Maintains pH during reconstitution; some buffers crystallise during freezing and can cause pH shift; histidine preferred for many biologics |
| Surfactant | Polysorbate 20 or 80, poloxamer 188 | Prevents protein aggregation at interfaces during freezing, drying, and reconstitution |
| Tonicity modifier | NaCl, mannitol, sucrose | Ensures reconstituted product is isotonic for injection |
Cycle Development and Scale-Up Considerations
Lyophilisation cycle development begins at laboratory scale using a small-scale freeze-dryer with full data logging capability. The critical parameters to establish are the collapse temperature or Tg prime of the formulation, the primary drying shelf temperature and chamber pressure that keep the product below collapse temperature while maximising sublimation rate, and the secondary drying conditions that achieve the target residual moisture.
Scale-up from laboratory to GMP manufacturing scale is not straightforward. Heat and mass transfer characteristics differ between dryers of different sizes and designs, and the cycle parameters optimised at lab scale rarely transfer directly to a larger dryer without modification. Computational modelling approaches and process analytical technology including temperature probes (thermocouples), pressure rise testing, and near-infrared spectroscopy for real-time endpoint detection are increasingly used to facilitate scale-up and cycle transfer between facilities.
Ardena’s Lyophilisation Capabilities at Ghent
Ardena’s sterile manufacturing facility in Ghent operates lyophilisation capacity for both development and GMP clinical batch manufacture. The lyophilisation team has experience with small molecule, peptide, and biologic lyophilised products, and can support cycle development from initial formulation characterisation through to GMP-validated cycle execution.
