Chemo-mechanical modelling of swelling and crosslinking reaction kinetics in alginate hydrogels: A novel theory and its numerical implementation

Hydrogels are mechanically stabilized through the action of external agents which induce the formation of crosslinks in the polymer network as a consequence of transport and reactive mechanisms. Crosslinking increases the stiffness of the construct, produces inelastic deforma-tions in the polymer network and interacts with the swelling capacity of hydrogels. The control of this process is hence crucial for fulfilling functional criteria in several technological fields, like drug-delivery or bioprinting. Nevertheless, experimental approaches for monitoring the crosslinking kinetics with the required resolution are currently missing. The development of new computational models in the field might open the way to novel investigation tools. This paper presents a thermodynamically consistent chemo-mechanical model in large deformation for reactive-diffusive mechanisms occurring during crosslinking in alginate hydrogels. The system accounts for shrinking and swelling effects, fluid movements, as well as the reaction kinetics of calcium-induced crosslinking. Crosslinks alter mechanical and diffusive properties in the hydrogel. Moreover, on the basis of thermodynamic arguments, internal stresses directly affect the crosslinking kinetics, revealing a two-way coupling between mechanics and chemistry. The model is implemented in a finite element framework, considering a monolithic coupling between chemical transport and mechanics. The computational framework allows characterizing the (experimentally inaccessible) heterogeneous distribution of mechano-chemical quantities and properties in the hydrogel. Parametric campaigns of simulations are presented to investigate hydrogels' behaviour and compare numerical outcomes with available experimental evidence.