  Healthy articular cartilage has excellent lubricating properties, with
friction coefficients reaching extremely low values at physiological pressures.
Such high-performing lubricating layer in joints is attributed to the surface
hydration arising from the interplay between multiple hydrophilic biopolymers
(such as hyaluronic acid, proteoglycans, and lubricin) and phospholipids in the
cartilage matrix. Mimicking such molecular structure, hydrogels, composed of a
hydrophilic polymer network, have the potential to replicate the lubricating
feature and possibly replace natural cartilages. In this study, we have
synthesized a poly(2-methacryloyloxyethyl
phosphorylcholine-co-N-isopropylacrylamide) (PMPC-co-PNIPAM, PMN)random
copolymer with highly-hydrated lubricious 2-methacryloyloxyethyl
phosphorylcholine moieties and less hydrated N-isopropylacrylamide moieties.
Incorporation of PMN copolymers within various hydrogels significantly reduces
the gels sliding surface friction, resulting in low friction coefficients
against different counter surfaces, including stainless steel (hard metal
surface), polyethylene (hydrophobic surface), and polyHEMA (soft hydrogel
surface). Additionally, hydrogels containing PMN are shown to be biocompatible
and have excellent antifouling properties, making them an ideal coating for
commercially available stents. With these qualities, hydrogels containing PMN
stand out as a promising new material with numerous possible applications.
