Laboratoire Matière et Systèmes Complexes

There will be a live diffusion with Zoom :

Exceptional Schedule. Tuesday February 7th, 11h00 in room 454 A.

Please contact Jean-Baptiste Manneville or Michael Berhanu to attend the visio-seminar.

Biopolymer Hydrogels, from the Cradle to the Grave

Olivier Ronsin & Tristan Baumberger

Université Paris-Cité Institut des nanosciences de Paris, Sorbonne Université.

Biopolymers (proteins, polysaccharides...), can (self-)assemble into networks via a wealth of processes. A fascinating class of soft materials are the “physical” hydrogels that involve non-covalent cross-links and are used extensively in drug delivery, cell encapsulation, cell transplantation and tissue engineering applications. In the course of our studying the dynamics of these versatile systems, from the first stage of their assembly to the last instant of their rupture, we have identified numerous issues amenable to physical investigation and modelling. This involved connecting fields at the interface between mechanics and physics : non-Newtonian fluid mechanics, non-Hookean elasticity, poro-elasticity, solid friction, fracture mechanics, slow glass-like dynamics of soft amorphous solids... After a brief presentation of some specific methodological and technical tools, we will focus on two representative recent topics and the perspectives they open :

1. Syneresis of extruded alginate fibers : an original closed-loop aging process [1] Alginate gelation is usually accompanied by syneresis, or expulsion of solvent out of the network as it gets increasingly cross-linked by calcium ions. In self-crowded, stiff gels the dynamics of syneresis exhibits the attributes of glass-like aging, usually ascribed to activated barrier jumps in a complex energy landscape. Experiments tells us that such is not the case. We propose an alternate scenario in which the deterministic exploration of the frozen structural disorder of the network by the global deswelling flow mimics the “glassy” relaxation spectrum. Accordingly the gel can be fully rejuvenated by osmotic swelling.

2. Environmental control of crack growth in gelatin gels : clogging the tip with nanoparticles [2, 3] A non-covalently cross-linked hydrogel can sustain large deformations before breaking. When ultimately a crack grows in such a soft and tough material, its blunted tip becomes an active zone of exchange with the fluid environment. Small environmental perturbations may have strong effects on the dissipative mechanisms in the near-tip process zone where the network disrupts. What happens in this mesoscopic, moving zone is readily revealed by the crack velocity variations. As an illustration, we will discuss the effect of wetting the tip with a drop of solvent containing nanoparticles which, depending on their concentration, size and electric charge can slow down or even pin the crack on the spot.

[1] B. Da Silva Pinto, O. Ronsin, and T. Baumberger, Syneresis of self-crowded calcium-alginate hydrogels as a self-driven athermal aging process (2022), preprint 〈hal-03878062〉.

[2] O. Ronsin, I. Naassaoui, A. Marcellan, and T. Baumberger, Environmental nanoparticle-induced toughening and pinning of a growing crack in a biopolymer hydrogel, Physical Review Letters 123, 158002 (2019).

[3] T. Baumberger and O. Ronsin, Environmental control of crack propagation in polymer hydrogels, Mechanics of Soft Materials 2, 1 (2020).