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.

To enhance the viscoelastic properties of Feruloylated Water Extractable ArabinoXylan (F-WEAX) gels, F-WEAX were covalently linked by a laccase in the presence of cellulose nanocrystals (CNC). The CNC/ F-WEAX weight ratios varied from 0 to 1.5 at a constant F-WEAX concentration of 1 % (w/v). The resulting CNC/ F-WEAX gels became stiffer with increasing CNC content with the elastic modulus scaling as [CNC]3. CNC also altered the relaxation spectrum of the CNC/ F-WEAX gels: the loss factor increased at low frequencies while remaining constant at high frequencies. The strong affinity between F-WEAX and CNC was demonstrated by in situ QCM-D analysis which showed that F-WEAX adsorb spontaneously and irreversibly onto CNC. Following laccase oxidative gelation, the rate of recovered ferulic acid (FA) in di-and trimer forms was twice as high when oxidation occurred in the presence of CNC. Due their higher covalent cross-link density, the swelling capacity of F-WEAX-CNC gels slightly decreased. The increased elasticity of the F-WEAX-CNC gels can thus be attributed to 3 factors: a higher volume fraction of CNC leading to increased entanglement, a greater number of di- or tri-ferulic acid covalent cross-links between F-WEAX chains, and the formation of multiarm physical junctions between F-WEAX and CNC.

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.

Plastic pollution in the aquatic environment has been assessed for many years by ocean waste collection expeditions around the globe or by river sampling. While the total amount of plastic produced worldwide is well documented, the amount of plastic found in the ocean, the distribution of particles on its surface and its evolution over time are still the subject of much debate. In this article, we propose a general fragmentation model, postulating the existence of a critical size below which particle fragmentation becomes extremely unlikely. In the frame of this model, an abundance peak appears for sizes around 1mm, in agreement with real environmental data. Using, in addition, a realistic exponential waste feed to the ocean, we discuss the relative impact of fragmentation and feed rates, and the temporal evolution of microplastics (MP) distribution. New conclusions on the temporal trend of MP pollution are drawn.