  The corrosion, mechanical degradation and biological performance of
cold-drawn WE43 Mg wires were analyzed as a function of thermo-mechanical
processing and the presence of a protective oxide layer created by continuous
plasma electrolytic oxidation (PEO). It was found that the corrosion properties
of the non-surface-treated wire could be optimized by means of thermal
treatment within certain limits, but the corrosion rate remained very high.
Hence, strength and ductility of these wires vanished after 24 h of immersion
in simulated body fluid at 37$^\circ$C and, as a result of that rather quick
degradation, direct tests did not show any MC3T3-E1 preosteoblast cell
attachment on the surface of the Mg wires. In contrast, surface modification of
the annealed WE43 Mg wires by a continuous PEO process led to the formation of
a homogeneous oxide layer of $\approx$ 8$\mu$m and significantly improved the
corrosion resistance and hence the biocompatibility of the WE43 Mg wires. It
was found that a dense layer of Ca/P was formed at the early stages of
degradation on top of the Mg(OH)2 layer and hindered the diffusion of the
Cl-ions which dissolve Mg(OH)2 and accelerate the corrosion of Mg alloys. As a
result, pitting corrosion was suppressed and the strength of the Mg wires was
above 100 MPa after 96 h of immersion in simulated body fluid at 37$^\circ$C.
Moreover, many cells were able to attach on the surface of the PEO
surface-modified wires during cell culture testing. These results demonstrate
the potential of thin Mg wires surface-modified by continuous PEO in terms of
mechanical, degradation and biological performance for bioabsorbable wire-based
devices.
