Articular Cartilage-Inspired Hybrid Double-Network Hydrogels with a Layered Structure and Low Friction Properties

Biomimetic tough hydrogels composed of a biopolymer and a large amount of water, which show high mechanical and lubricating properties, are of great significance for articular cartilage application. In conventional tough hydrogel materials, there is a conflicting relationship between the lubricating capacity (hydration capacity) and the load-bearing capacity. Herein, inspired by the structure of articular cartilage, a layered hybrid double-network hydrogel (DN gel) was prepared by a two-step method; that is, the stiff and tough agar/poly (acrylamide-co- acrylic acid)-Fe3+ (Agar/PAMAAc-Fe3+) DN gel was first fabricated, and then a layer of soft and tough Agar/PAMAAc DN gel was formed on it by an alkali-induced network dissociation strategy. In the layered hybrid DN gel, physical agar gel served as the first network, while chemical PAMAAc gel or PAMAAc-Fe3+ gel acted as the second network. The coordination or dissociation between Fe3+ ions and carboxyl groups can render the high stiffness or a low modulus of the DN gels, and the soft and tough Agar/PAMAAc DN gel layer played a role in reducing friction and the stiff and tough Agar/PAMAAc-Fe3+ layer played a supporting role. As a result, a soft and tough lubricating layer on a stiff and tough load-bearing substrate provides an excellent balance of lubrication and load bearing, leading to a low coefficient of friction (COF) and wear-resistant biomimetic cartilage layered DN gel. The COF decreases from 0.024 to 0.001 as the compressive stress increases from 0.81 to 30.6 kPa. Because of their exceptional lubricating properties, layered hydrogels are attractive candidates for tissue engineering and medical devices.

Automated summary

This study develops a layered hybrid double-network hydrogel inspired by the structure of articular cartilage. The soft and tough layer on the stiff and tough substrate provides an excellent balance of lubrication and load-bearing, resulting in a low coefficient of friction and wear-resistant biomimetic cartilage.