Corrosion Controlling And Bio-Compability Of A Surface-immobilized Ultrathin 1-hydroxyethylidene-1,1-diphosphonic Acid (HEDP)Film On Biodegradable Magnesium

Biodegradable magnesium as well as its alloys have been widely investigated as biodegradable implants applications, because of its ease of corrosion, good mechanical properties, and unquestionable biosafety. However, the too fast corrosion rate leads usully to byproducts of hydrogen gas, locally increased pH valve and premature mechanical failure of the implants, both of which limited the use of magnesium in clinic. Therefore, a simple and efficient film was designed, not only to concroll the corrosion rate and behavior of magnesium, but also owns a good bio-compability.An ultrathin bisphosphonate film, 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), was deposited on magnesium for biodegradable implant applications. The small, bioactive HEDP molecule is supposed to be not only bio-safe, but also favorable for creating a highly protective layer for the control of the corrosion/degradation of Mg. In an in situ chemical sequence, the HEDP molecules were covalently surface-immobilized on the alkaline pretreated Mg and then spontaneously deposited by participation in a chelating reaction with Mg ions. An organometallic-like compound layer was thus formed, which was ascertained to be within the nanoscale and complied well with the substrate.The surface morphology, chemical composition(FTIR) and bonding energes(XPS) results showed a homogenious and compact HEDP coating formed on Mg surface by covalently surface-immobilizing and chelating reaction. The tape test showed that the HEDP film provides excellent adhesion strength. Electrochemical corrosion of Ecorr,icorr and EIS showed that HEDP coating can barrier the anion to attack the magnesium substrate, thus have a good protection of magnesium from electrode solution; the breakdowm potential Ebd got by the Tafel methord, surface morphology after PDP and EIS resulted that HEDP coating could control the corrosion behavior of magnesium and meliorate the localized corrosion/pitting corrosion. In vitro immersion degradation investigations demonstrated that the HEDP coated Mg exhibited significantly slower corrosion rate than untreated Mg in phosphate buffered saline (PBS) solution. Of particular significance is the observation that HEDP coated Mg presented a remarkably suppressed localized corrosion mode.The meliorated corrosion/degradation behavior is credited to both the nature of the organometallic-like HEDP derivative layer, as well as the high quality of the film, with respect to compactness and homogeneity. The controlled corrosion rate and behavior of magnesium not only could solve the problems caused by rappied corrosion of Mg, but also provide a good surface for the adhension, prolifation and grow of cells. Our HEDP modified Mg may bode well for application in biodegradable implants.The HEDP coated Mg also promotes osteoblast cells adhension and proliferation. The long-time in vitro osteoblast results also showed that a significantly larger number of viable (CCK-8) cells on the HEDP coated Ti both for 1,3, and 5 days culture as compared with bare Ti. For 3 days culuture, the cells on HEDP coating behaves vortex-like, and multilayer-like grow mode, showed our well-controlled biodegradable and biocompatible HEDP modified Mg might bode well for bone implant application.