Nanoscale modification of magnesium with highly textural lamellar nanosheets towards increasing the corrosion resistance and bioactivity

The present study aims to modify the surface of microarc oxidation (MAO) coated Mg using an alkaline fluoride solution so as to impart a nanoscale surface feature, which would be beneficial to improve the corrosion resistance and to promote a better bioactivity. The MAO coated Mg is modified with the formation of a highly textural lamellar nanosheet-like morphology after immersion in 0.1 M NaF (pH: 8.40) at 25 °C for 120 min, which completely covered the porous structure with the formation of nanosheets along with some agglomerated crystals. Thin film X-ray diffraction measurement, chemical composition analysis and Fourier transform infrared spectroscopy studies confirmed that the nanosheets are primarily Mg(OH)_2 − xF_x while the agglomerates are NaMgF₃. The complete coverage of the porous structure by the modified layer along with the formation of Mg(OH)_2 − xF_x and NaMgF₃ has enabled a better corrosion resistance for MAO coated Mg modified by NaF. The higher surface area of the nanosheets favoured nucleation of monocalcium phosphate anhydrous and newberyite, both of which are biologically relevant. The unique morphological feature of the modified surface helped to achieve an improved cell adhesion and proliferation of MC3T3-E1 osteoblast-like cells. The relative growth rate of both uncoated and coated Mg are > 75% on all the three days, fulfilled Grade 1 specification in terms of cytocompatibility as per ISO 10993-5 standard. The formation of nanoscale surface feature, improvement in corrosion resistance, better bioactivity and acceptable cytocompatibility point out that this methodology could be of immense help to modify the surface of Mg based absorbable implants.