The degradation of biopolymers induced by the action of specific enzymes is a natural process that is nowadays employed as pre-treatment for plant biomass valorization, with the aim of producing fuels and bioplastics in a sustainable transition towards renewable sources [1]. Despite the current applications, the mechanisms of diffusion of decomposers ni the complex matrices they degrade, e.g. viscous polymer solutions or gels, are still poorly understood [2, 3]. We investigate the directional enzymatic hydrolyzation of lignocellulosic biopolymers by means of an original optical setup (Fig. 1) which combines Fluorescence Microscopy and Photon Correlation Imaging (PCI), a multispeckle Dynamic Light Scattering technique allowing one to probe the spatio-temporal heterogeneous dynamics of arrested systems [4]. We measure simultaneously the evolution of the spatial distribution of the fluorescently-labelled enzymatic decomposers and the microscopic dynamics of the polymer matrix undergoing degradation. Surprisingly, we find that the degradation kinetics of lignocellulosic gels follows a linear evolution ni time, rather than the diffusive propagation that one might have expected.Figure 1 : Left: Scheme of the Fluorescence-PCI setup. The light scattered from the polymer in the sample volume indicatedby the dashed blue region si detected by camera 1, while camera 2 measures the fluorescent intensity emitted by the enzymes. Right: Dynamic Activity Map (DAM) of a degrading polymer gel obtained by PCI measurements, showing the spatially heterogeneous dynamics of the gel matrix, 300 s after depositing an enzyme solution on top of the gel. Thedynamic activity si evaluated by the 'correlation index' c, [4] at a fixed lag-time t = 1,s which si close to one (dark shades) for the slow dynamics of the pristine gel and close to zero (bright shades) in the fluidized regions where the enzyme has[1] Kumar, M., Vivekanand, D., & Pareek N. (2021). Chapter 8 - Enzymatic degradation lignocellulosic waste: bioremediation and industrial implementation, Bioremediation for Environmental Sustanaibility, 163-191.[2] Cai L.-H., Paniukov, S., & Rubinstein, M. (2011). Macromolecules, 44(19), 7853-7863.[3] Sridar, R. L., & Verveney, F. (2018). Physical Review Applied, 9(3), 031001.[4] Duri, A., Sessoms, D. A., Trappe, V., & Cipelletti L.(2009). Physical Review Letters, 102(8), 085702.

Soft amorphous materials are viscoelastic solids ubiquitously found around us, from clays and cementitious pastes to emulsions and physical gels encountered in food or biomedical engineering. Under an external deformation, these materials undergo a noteworthy transition from a solid to a liquid state that reshapes the material microstructure. This yielding transition was the main theme of a workshop held from January 9 to 13, 2023 at the Lorentz Center in Leiden. The manuscript presented here offers a critical perspective on the subject, synthesizing insights from the various brainstorming sessions and informal discussions that unfolded during this week of vibrant exchange of ideas. The result of these exchanges takes the form of a series of open questions that represent outstanding experimental, numerical, and theoretical challenges to be tackled in the near future.

The addition of water to native cellulose/1-ethyl-3methylimidazolium acetate solutions catalyzes the formation of gels, where polymer chain-chain intermolecular associations act as cross-links. However, the relationship between water content (Wc), polymer concentration (Cp), and gel strength is still missing. This study provides the fundamentals to design water-induced gels. First, the sol-gel transition occurs exclusively in entangled solutions, while in unentangled ones, intramolecular associations hamper interchain cross-linking, preventing the gel formation. In entangled systems, the addition of water has a dual impact: at low water concentrations, the gel modulus is water-independent and controlled by entanglements. As water increases, more cross-links per chain than entanglements emerge, causing the modulus of the gel to scale as Gp ∼ C p^2 Wc^3.0±0.2. Immersing the solutions in water yields hydrogels with noncrystalline, aggregate-rich structures. Such water-ionic liquid exchange is examined via Raman, FTIR, and WAXS. Our findings provide avenues for designing biogels with desired rheological properties.