Comparison of Static and Dynamic in Vitro Degradation of a Biodegradable Magnesium Implant Screw

Degradation of biodegradable metals and precipitation of apatite on their surfaces are commonly studied in vitro under static immersion conditions. Such static environments do not accurately replicate the dynamic conditions in vivo. This study aimed to develop an in vitro setup that introduces controlled fluid flow to better represent transport conditions than conventional static immersion experiments. Magnesium alloy screws were immersed in Hank’s Balanced Salt Solution (HBSS) or Simulated Body Fluid (SBF) either directly or after fixation in closed-cell or open-cell porous synthetic bone models. Screws were also studied in a dynamic flow-through system in which the solution flowed along the screw surface. The initial burst release of magnesium ions and the accompanying increase in pH demonstrated that fluid flow significantly affects the degradation behavior of magnesium screws. SBF accelerated degradation compared with HBSS in all experimental configurations. Dynamic flow conditions revealed an initial burst release of magnesium ions followed by stabilization of both magnesium concentration and pH. For mechanistic in vitro studies, HBSS may be advantageous because the slower degradation rate allows the underlying processes to be followed over longer periods. In contrast, SBF may be advantageous when shorter experimental durations are desired. Surface analyses further revealed the formation of magnesium-containing corrosion products and calcium- and phosphorus-containing precipitates. Overall, the findings demonstrate that both solution composition and fluid flow strongly influence the degradation behavior of biodegradable magnesium implants. Dynamic testing conditions provide valuable information not obtainable from conventional static immersion experiments and should, therefore, be considered when evaluating biodegradable magnesium implants in vitro.