Articular Cartilage-Inspired Robust Self-Lubricating Alginate Hydrogels

Abstract

The exceptional lubricity in living systems has stimulated wide scientific interest in the design of biomimetic lubricants. In this work, a sodium alginate hydrogel physically cross-linked with divalent cations (Ca2+), incorporating ~100 nm 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes in trace amounts (~0.004–0.08 wt% lipids), which we term “LipoGels”, was optimised to overcome gelation shrinkage to generate a homogeneous and smooth surface. Cryo-SEM revealed the compact porous gel structure with embedded liposomes, and confocal fluorescent microscopy revealed a uniform distribution of liposomes in the gel. The LipoGels demonstrated robust mechanical strength, with an elastic modulus G’ > 200 kPa and a Young’s modulus E ~1 MPa from rheology and micro-indentation measurements, respectively. Smallangle neutron scattering deduced a classic de Gennes’ mesh size of ξ ~3.8 nm for the polymer network, consistent with that estimated from the rheology results. The underwater friction
coefficient of liposome-alginate hybrid LipoGels, evaluated in the sphere-on-flat geometry with a tribometer, was as low as  ~0.02 at a maximum contact pressure of 0.45 MPa. Furthermore, comparison across five lipid types with distinct molecular structures revealed that lipids with cationic head groups and longer hydrophobic tails (DOTAP) exhibited the best lubrication performance. In addition, three newly synthesised bicephalous surfactants, structurally analogous to lipids, were characterised by SANS and XRR, showing lipid-like behaviours both in bulk and at interfaces. Collectively, these findings provide nano-structural insights into hybrid
liposome-alginate hydrogels, prepared via facile physical cross-linking, demonstrating their potential as biomimetic lubricants, also with encapsulation capacities for functional additives.

Date of Award	20 Jan 2026
Original language	English
Awarding Institution	University of Bristol
Sponsors	China Scholarship Council
Supervisor	Wuge H Briscoe (Supervisor) & Jeroen S Van Duijneveldt (Supervisor)