Impact of N-1 phase media optimization as a bioprocess intensification strategy on fed-batch production.

In the biopharmaceutical industry, improving process efficiency and reducing manufacturing costs remain major priorities. Conventional fed-batch processes are often limited by low initial cell densities, resulting in extended culture duration and reduced productivity. However, the combined effect of N-1 media optimization and high-cell-density (HCD) inoculation remains insufficiently characterized. This study systematically assessed the impacts of N-1 media optimization and initial seeding density utilizing a CHO-ZN cell line. During the N-1 phase, a media exchange strategy increased the cell density from approximately 3 × 10⁶ cells/mL to 15-22 × 10⁶ cells/mL, enabling direct production inoculation at 8 × 10⁶ cells/mL without an additional seed expansion step. Compared with low-cell-density (LCD; 1.2 × 10⁶ cells/mL) cultures, HCD cultures reduced production duration by approximately 36% and increased product concentration by about 89% (~ 3500 mg/L vs. ~1850 mg/L). Average interval-based specific productivity (qP), increased from approximately 17 to 31 pg/cell/day, suggesting that the gains in productivity were not solely attributable to increased biomass. Importantly, when the production-phase medium was standardized, differences in titer concentration, metabolite profiles, viability, and interval-based qP persisted among cells conditioned in different N-1 media. This indicates that N-1 medium composition influenced subsequent fed-batch behavior not only by affecting inoculum biomass, but also by modulating the physiological state of the cells prior to production inoculation. Overall, these findings emphasize the role of N-1 medium-dependent physiological conditioning in determining productivity, metabolic behavior, and product quality attributes under intensified fed-batch conditions.