Ultrastrong Poly(2-Oxazoline)/Poly(Acrylic Acid) Double-Network Hydrogels with Cartilage-Like Mechanical Properties

The exceptional stiffness and toughness of double-network hydrogels (DNHs) offer the possibility to mimic even complex biomaterials, such as cartilage. The latter has a limited regenerative capacity and thus needs to be substituted with an artificial material. DNHs composed of cross-linked poly(2-oxazoline)s (POx) and poly(acrylic acid) (PAA) are synthesized by free radical polymerization in a two-step process. The resulting DNHs are stabilized by hydrogen bridges even at pH 7.4 (physiological PBS buffer) due to the pK(a)-shifting effect of POx on PAA. DNHs based on poly(2-methyl-2-oxazoline), which have a water content (WC) of around 66 wt% and are not cytotoxic, show biomechanical properties that match those of cartilage in terms of WC, stiffness, toughness, coefficient of friction, compression in body relevant stress conditions and viscoelastic behavior. This material also has high strength in PBS pH 7.4 and in egg white as synovial liquid substitute. In particular, a compression strength of up to 60 MPa makes this material superior.

Automated summary

The exceptional properties of double-network hydrogels make them suitable for mimicking complex biomaterials, such as cartilage. The stability of these hydrogels is maintained even at physiological conditions. A specific type of double-network hydrogel based on poly(2-methyl-2-oxazoline) exhibits biomechanical properties similar to cartilage and high strength.