de Gennes’s mesh size in cartilage-inspired self-repairing alginate LipoGels

Inspired by the exceptional lubricity in living systems (e.g. knee joints and eye blinking), a physically cross-linked hydrogel film has been prepared from sodium alginate, an abundant green biopolymer derived from brown algae. Alginate hydrogels were cross-linked by divalent cations, Ca2+, and liposomes (or lipid vesicles) were embedded into the gel, aiming to generate a lubricious and self-repairing material, also with the potential for therapeutic encapsulation. The lubrication performance of the alginate hydrogels was evaluated with a tribometer (UMT Tribolab), and the results showed that the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) embedded alginate hydrogel exhibited excellent lubrication with a coefficient of friction (CoF) of 0.058 under water. However, to our best knowledge, no structural characterisation has been reported on such novel lubricious liposome-embedded hydrogels. Here, we propose a small angle neutron scattering (SANS) study of the hydrogel nanostructure, varying the alginate concentration, cross-linking conditions, type of lipids, and temperature. The unprecedented results offer structural insights into alginate hydrogels, enabling a correlation with the mechanical characterisation of the gel using nanoindenter and rheometer. Ultimately, this will underpin the rational design of robust hydrogels with tailored nanostructures for biomimetic lubrication.