Abstract
Multiscale models provide a powerful framework to link bioprocess operation conditions with polymer microstructure, yet their predictive capability for polymer attributes such as chain length distributions (CLDs) remains limited. In this work, an advanced multiscale modeling framework for the microbial production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in Cupriavidus necator is presented, targeting the quantitative prediction of polymer microstructure. The model consistently integrates a structured macroscopic kinetic description of substrate uptake, biomass growth, and copolymer accumulation with an explicitly formulated microscopic polymerization model resolving initiation, propagation, termination, and depolymerization reactions of living and dead chains. A central contribution of this study is the quantitative calibration of the polymerization kinetics based on experimental size-exclusion chromatography (SEC) data. Polymerization rate constants were identified by fitting simulated CLDs to measurements obtained at multiple diagnostic time points during fed-batch cultivations using fructose and propionic acid as carbon sources. Parameter estimation was performed using a hybrid multi-start optimization strategy combining simulated annealing with Gauss-Newton refinement. Compared to literature-based parameter sets, the optimized model accurately reproduces both the temporal evolution of the weight-average molecular weight and the full CLD shape, including the emergence of high-molecular-weight tails. The results demonstrate that explicit polymerization modeling combined with parameter identification is essential for quantitatively linking process dynamics to PHBV microstructure. The proposed framework provides a sophisticated basis for model-based optimization of feed strategies and supports quality-by-design approaches for sustainable biopolymer production.