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

Abstract 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.