Ultrathin surface-attached hydrogel coating for potential reversible nanogluing of implants

A multifunctional copolymer of N-(2-Hydroxypropyl)methacrylamide (HPMA) and a phosphonate-containing monomer was developed with the aim of applying a hydrogel coating to implant surfaces. For this purpose, a copolymer was prepared that could bind to the implant surface (e.g. titanium) via a phosphonate group. A photocrosslinkable group (phenyl azide) and hydrophilic groups were also incorporated to form a hydrogel. Coatings of these polymers produced by spin coating and subsequent photocrosslinking were characterised by laser ellipsometry, which gave controlled dry layer thicknesses in the range 40 to 140 nm. Furthermore, the swelling ability was investigated by in-situ ellipsometry in different aqueous media. According to these measurements, the coatings can swell up to three times the initial dry film thickness, depending on their crosslinker content. We also validate long-term stability under physiological conditions. In addition, the hydrogel coatings can immobilise different types of silica nanoparticles (non-porous silica (15 nm), nanoporous silica (40 nm) and periodic mesoporous organosilica (100 nm), which makes them suitable for nanogluing. Preliminary tests have shown that a PDMA hydrogel can indeed adhere to the surface-bound hydrogels by way of nanoparticles.