Transition from continuous to microglobular shaped peptide assemblies through a Liesegang-like enzyme-assisted mechanism.

Enzyme-assisted self-assembly confined within host materials leads to Liesegang-like spatial structuration when precursor peptides are diffusing through an enzyme-functionalized hydrogel. It is shown here that playing on peptide and enzyme concentrations results in a transition from continuous self-assembled peptide areas to individual microglobules. Their morphology, location, size and buildup mechanism are described. Additionally, it is also found that the enzymes adsorb onto the peptide self-assemblies leading to co-localization of peptide self-assembled microglobules and enzymes. Finally, we find that large microglobules grow at the expense of smaller ones present in their vicinity in a kind of Ostwald ripening process, illustrating the dynamic nature of the peptide self-assembly process within host hydrogels.

Non-monotonous enzyme-assisted self-assembly profiles resulting from reaction-diffusion processes in host gels.

Reaction-diffusion (RD) processes are responsible for surface and in-depth micropatterning in inanimate and living matter. Here we show that enzyme-assisted self-assembly (EASA) of peptides is a valuable tool to functionnalize host gels. By using a phosphatase distributed in a host hydrogel, the diffusion of phosphorylated peptides from a liquid/host gel interface leads to the spontaneous formation of a pattern of dephosphorylated peptide self-assembly presenting at least two self-assembly maxima. Variation of enzyme and peptide concentrations change the pattern characteristics. When a peptide drop is deposited on a phosphatase functionalized gel, a self-assembly pattern is also formed both along the gel-solution interface and perpendicular to the interface. This self-assembly pattern induces a local change of the gel mechanical properties measured by nanoindentation. Its appearance relies on the formation of self-assembled structures by nucleation and growth processes which are static in the hydrogel. This process presents great similarities with the Liesegang pattern formation and must be taken into account for the functionalization of hydrogels by EASA. A mechanism based on RD is proposed leading to an effective mathematical model accounting for the pattern formation. This work highlights EASA as a tool to design organic Liesegang-like microstructured materials with potential applications in biomaterials and artificial living systems design.

Nanocellulose-based foam morphological, mechanical and thermal properties in relation to hydrogel precursor structure and rheology.

Foams were prepared from nanocellulose-based hydrogel precursors using a freeze-drying process. The work mainly aims at investigating the relationships between the mechanical and thermal properties of foams and the rheological properties of their hydrogel precursors, which were characterized in a previous paper. The structure of foams was characterized by SEM and confocal microscopy, their elasticity by compression tests, and their thermal conductivity by hot strip as well as transient pulsed techniques. A strong correlation was shown between the elastic properties of foams and those of their hydrogel precursors, and a minimum thermal conductivity was shown to appear at a cellulose volume fraction corresponding to a transition in viscoelastic properties of hydrogels. Results suggest that foams and hydrogels share common microstructural features, which makes it possible to tune the mechanical and thermal properties of foams by tuning the rheological properties of their hydrogel precursors.

Structure and rheology of aqueous suspensions and hydrogels of cellulose nanofibrils: Effect of volume fraction and ionic strength.

The structure and rheology of TEMPO-oxidized cellulose nanofibrils (CNF) suspensions and hydrogels, used as precursors in the elaboration of bio-based aerogels for thermal insulation applications, were studied as a function of CNF volume fraction and ionic strength. The CNF geometry and rigidity were evaluated using AFM observations. Viscometric measurements, performed at very low CNF concentrations, highlighted the prominent role played by electroviscous effects, which can be modulated by ionic strength. Oscillatory measurements on semi-dilute CNF suspensions revealed the formation of a three-dimensional hydrogel network above a percolation fraction, which was shown to depend on the ionic strength. The rheological properties of CNF hydrogels were shown to depend on CNF fraction and ionic strength. In deionized water, the existence of two different concentration regimes was discussed in terms of network structural characteristics and CNF interactions.