Rheology as a monitoring tool for the biochemical parameters of insect cell-baculovirus system

Process Analytical Technology (PAT) tools are increasingly applied to improve monitoring of biopharmaceutical processes; however, few techniques have explored their use in liquid bioprocesses based on insect cell cultures. This work evaluated whether rheological parameters could be explored as monitoring indicators for biochemical variables during virus-like particle (VLP) production using the insect cell-baculovirus expression system.

Batch bioreactor cultivations of Spodoptera frugiperda (Sf9) cells were conducted under non-infected conditions and during rabies and SARS-CoV-2 VLP production. Rheological properties were determined by steady-shear cone-plate rheometry and correlated with viable and total cell densities, extracellular protein concentration, and viral titer. Empirical models were generated and ranked using Akaike's Information Criterion, and predictive performance was assessed by root mean square error. Statistical significance was evaluated using analysis of variance.

All cultures exhibited non-Newtonian, pseudoplastic behavior, with decreases in the flow behavior index associated with increasing cell density and protein concentration. Exponential functions were most frequently selected among the best-ranked empirical models, followed by rational, hyperbolic, logarithmic, and power equations. No statistically significant effect of rheological parameter or infection condition on prediction accuracy was observed (p > 0.05).

Rheological properties reflected compositional changes occurring during insect cell cultivations; however, under the conditions studied, rheology did not significantly improve quantitative monitoring of key biochemical parameters using other approaches. These findings indicate that while rheology may provide complementary process information, further investigation is required before its application as a robust PAT tool for VLP production.