Structure–mechanics relationship of hybrid polyvinyl alcohol-collagen composite by molecular dynamics simulations

Abstract Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer that can be used to make hydrogels for biomedical applications as well as biodegradable bags and films; however, compared to other plastics currently used for containers, it lacks mechanical strength, thermal stability, and can easily absorb water from humid environments. Although mechanical improvement has been observed by blending PVA with collagen in a hybrid hydrogel, there is a lack of fundamental understanding of the molecular mechanism, and it is not clear whether the improvement is limited to a hydrated state. Here, using classical molecular dynamics simulations based on fully atomistic models, we develop the equilibrated molecular structure of PVA with collagen and characterize its mechanics. We show that by interacting with a collagen molecule, PVA is equilibrated to a more ordered structure with each residue interacting with the near neighbors by forming more hydrogen bonds locally, making the structure stiffer than pure PVA. The structure shows higher thermal stability before melting, as well as higher rigidity in water. Our results provide the mechanism of the mechanical advantages of hybrid PVA-collagen polymer. The study demonstrates that the structure and mechanics of a synthetic polymer can be tuned by a tiny amount of a natural polymer at the molecular interface. Moreover, it may shed light on identifying a way to improve the mechanics of biodegradable polymer materials without adding much cost, which is crucial for environmental safety. Impact statement Blending natural and synthetic polymers (e.g., polyvinyl alcohol [PVA] and collagen in a hybrid hydrogel) has shown advantages in polymer mechanics, but there is a lack of fundamental understanding. Using molecular dynamics (MD) simulations based on fully atomistic models, we develop the equilibrated structure of the PVA with collagen and characterize its mechanics. We show that by interacting with a collagen molecule, PVA is equilibrated to a more ordered structure with each residue interacting with the near neighbors by forming more H-bonds locally and the structure is stiffer than pure PVA. Moreover, the structure shows a higher thermal stability before the melting point of PVA, as well as higher rigidity in water. Our results demonstrate that the structure and mechanics of a synthetic polymer can be tuned by a tiny amount of a natural polymer at the molecular interface. It provides the mechanism of the mechanical advantages as experimentally observed. This study paves the way for the multiscale modeling and mechanical design of the hybrid polymer material. It sheds light on identifying a way to improve the mechanics of biodegradable materials without adding much cost for both material functionality and environmental safety. Graphical abstract