Characterizing Network Structure and Protein Separation in Lignin-Based Hydrogel Composites

Lignin-based hydrogels have recently garnered attention for use in a variety of biological applications involving proteins such as protein separation and delivery as lignin is a sustainable, naturally abundant biopolymer. However, to date, the use of these materials in protein related applications has been hindered by our limited understanding of how the addition of lignin, both as a crosslinker and ‘passive’ filler, affects the network (pore) structure of the crosslinked hydrogel. In this study, lignin-poly(vinyl alcohol) composites were synthesized using lignin of controlled, narrow molecular weights (MWs), allowing for the fabrication of membranes with more homogeneous network structures. The permeability of different proteins through the hydrated composites was measured via ultraviolet-visible spectroscopy, where protein permeability was found to depend on the MW and end group functionality of the lignin. In addition, poroelastic relaxation indentation was used to characterize both the mechanical (elastic modulus) and transport properties (diffusivity, effective pore size) of the composites. Results from this study illustrate how the incorporation of well-defined lignin into hydrogel composites can be used to directly tune the properties of the resultant membrane.