Effect of Li+/Na+ exchange on mechanical behavior and biological activity of lithium disilicate glass-ceramic

Lithium disilicate (LD) glass-ceramics with a stoichiometric composition were ion-exchanged in pure NaNO3 or mixed NaNO3 + KNO3 molten salt baths below the glass transition temperature (T-g). The microstructures, surface morphologies, mechanical properties and bioactivities of the ion-exchanged glass-ceramics were studied in detail. It was found that the strength and toughness of LD glass-ceramic could be enhanced from 175 MPa to 0.96 MPa m(1/2) before ion-exchange to 546 MPa and 4.31 MPa m(1/2) respectively under a lowered ion-exchange temperature because the less stress relaxation. In addition, a gradient of Na+ rich layer in the surface of glass-ceramic was induced by Li+/Na+ exchange, which could be beneficial to the formation of HA (Hydroxyapatite) with nano-size porous after soaking in SBF (Simulated Body Fluid) solution and exhibited better bioactivity compared with the original LD glass-ceramic. The results might provide a reference for the strengthening and biological activation of LD glass-ceramics in bone restoration applications.

Automated summary

Ion-exchange can significantly enhance the strength and toughness of LD glass-ceramics, while inducing a Na+-rich layer on the surface that promotes the growth of HA in solution, improving bioactivity.