Suitable biomechanical properties, good biocompatibility,
and osteoconductivity
of a degradable magnesium (Mg) alloy make it a potential material
for orthopedic implants. The main limitation of Mg is its high corrosion
rate in the human body. Surface modification is necessary to improve
the Mg corrosion resistance. In this work, a polymeric layer of gelatin/nanohydroxyapatite
(Gel/nHA) was coated on a ZK60 Mg alloy by dip coating and spin coating
to test the corrosion resistance and biocompatibility in vitro and
in vivo. The results from the in vitro test revealed that the coated
groups reduced the corrosion rate with the corrosion current density
by 59 and 81%, from 31.22 to 12.83 μA/cm2 and 5.83
μA/cm2 in the spin coating and dip coating groups,
respectively. The dip coating group showed better corrosion resistance
than the spin coating group with the lowest released hydrogen content
(17.5 mL) and lowest pH value (8.23) and reducing the current density
by 45%. In vitro, the relative growth rate was over 75% in all groups
tested with MG63, demonstrating that the Mg substrate and coating
materials were within the safety range. The dip coating and spin coating
groups enhanced the cell proliferation with significantly higher OD
values (3.3, 3.0, and 2.5, respectively) and had better antihemolysis
and antiplatelet adhesion abilities than the uncoated group. The two
coating methods showed no difference in the cellular response, cell
migration, hemolysis, and platelet adhesion test. In in vivo tests
in rats, the dip coating group also showed a higher corrosion resistance
with a lower corrosion rate and mass loss than the spin coating group.
In addition, the blood biochemistry and histopathology results indicated
that all materials used in this study were biocompatible with living
subjects. The present research confirmed that the two methods have
no noticeable difference in cell and organ response but the corrosion
resistance of dip coating was higher than that of spin coating either
in vitro or in vivo.