290 spray dryer

Lactose monohydrate (DFE Pharma, Goch, Germany) and L-leucine (Sigma-Aldrich, NSW, Australia) were co-spray dried with a cocktail of phages comprising PEV1, PEV2 and PEV20. The excipient composition used in this study was 80% (wt/wt) lactose and 20% (wt/wt) leucine as our group has previously demonstrated individual phage stability and powder dispersibility with long shelf-life with this formulation (Chang et al., 2019 (link)). The liquid feed consisted of 100 mL of excipient solution (25 mg/mL) in ultra-pure water and 1 mL of phage cocktail suspension (of the three phages at ratio of 1:1:1, each with a titre of 10⁹ PFU/mL) with pH adjusted to 7.4. The phage-excipient suspension was tested for phage viability. A Büchi 290 spray dryer coupled with a conventional two-fluid nozzle as an atomizer was used. The solution was loaded at a constant feed rate of 1.8 mL/min, atomizing air flow rate of 742 L/hr, an aspiration rate of 35 m³/h and inlet temperature of 60°C. The samples passing through the cyclone were collected in a glass vial. A small amount of powders was dissolved in PBS with a final concentration of 25 mg/mL. Plaque assay was performed to test the phage viability after spray drying process. An aliquot of powder was stored at 20°C/15% RH to assess storage stability.

The phage and excipient mixtures were prepared as above and spray dried using a Büchi 290 spray dryer coupled with a conventional two-fluid nozzle for droplet atomization. The mixture was fed at a flow rate of 1.8 ml/min and atomized with compressed dry air at 742 l/hr, and a small sample of the atomized droplets was collected to confirm the phage titer. Then the spray drier was run at an aspiration rate of 35 m³/hr and inlet temperature of 60 °C. The outlet temperature was recorded to be 40–45 °C. Low outlet temperatures were used to minimize phage inactivation during the drying process [39 (link)]. The SD powders were collected inside a relative humidity controlled chamber (RH < 20%) and stored in a desiccator at 4°C before use.

The liquid feed was composed of 30 mL of excipient solution in ultra-pure water and 0.3 mL of phage suspension (10⁹ pfu/mL) with pH adjusted to 7.4. The phage viability in the feed solution was assessed prior to spray drying using plaque assay. The resulting phage-excipient suspension was spray dried using a Büchi 290 spray dryer coupled with a conventional two-fluid nozzle for atomisation. The suspension was fed at a constant feed rate 1.8 mL/min and an atomising airflow of 742 L/h with an aspiration rate of 35 m³/h. The drying inlet air was heated to 60 °C and the outlet temperature ranged between 40–41 °C. Dried powder after passing through the cyclone was collected in a vial. A small amount of powder was resuspended in PBS to give a concentration of 50 mg/ml and the phage titre was assessed using plaque assay. Spray dried powders were stored over silica beads at 20 °C before use.