Increase of compressive strength and sustained ion release of ZIF-C under acidic conditions

Background and aim: The ZIF-C (ZIF-C, GC, Japan.) was developed as a novel encapsulated bioactive restorative. ZIF-C contains unique filler which release zinc ion (Zn2+) and fluoride ion (F-) and was named as “BioUnion”. Especially, Zn2+ has been focused on antimicrobial effects and inhibition of demineralization effect. In this study, compressive strength and ion release ability (Zn2＋/F-) of ZIF-C has been investigated for one month in acid environment. Methods: Cylindrical specimens (4 mm diameter, 6 mm height) were prepared by using following materials; ZIF-C, Fuji II CAPSULE (F2, a conventional glass ionomer, GC, Japan) and GRADIA DIRECT LoFlo(GDL, a resin-based composite, GC, Japan). These materials were filled into the metal mold. Then, light irradiation with G-Light Prima II (GC, Japan) was performed for 20 seconds for curing of GDL. The materials in the mold were clamped by metal plates and the assemblies were stored at 37℃/90% R.H. for 1 hour. This operation was repeated until 40 specimens of each materials were prepared. 40 specimens were divided into 5 groups as 1,3,7,14and 28days immersed group. Each group consists of 8 specimens. Each specimen was immersed in acid solution(pH4.5) under 37℃. Compressive strength was measured and concentration of Zn2+ and F- in acid solution was also analyzed with ICP-OES (AG-50kNG, SHIMADZU, japan) and F- ion selective electrode (n=4). Results: The compressive strength of ZIF-C was increased depending on immersed period as follows; 137.7(±13.8) MPa (1 day), 135.1(±16.0) MPa (3 days), 159.8(±26.9) MPa, (7 days), 156.0(±13.5) MPa (14 days) and 181.2(±10.6) MPa (28 days). Continuous Zn2+ release was monitored; 66.8(±0.7) μg/cm2 (1 day), 94.9(±7.8) μg/cm2 (3 days), 117.8(±6.3) μg/cm2 (7 days), 187.3(±19.7) μg/cm2 (14 days) and 170.2(±10.1) μg/cm2 (28 days). F- release was also monitored; 31.1(±0.76) μg/cm2 (1 day), 35.8(±2.46) μg/cm2 (3 days), 51.6(±0.74) μg/cm2, (7 days), 74.9(±1.98) μg/cm2 (14 days) and 76.2(±0.15) μg/cm2 (28 days). Conclusions: Sustained release of Zn2+ and F- was observed under the acidic condition. However, compressive strength of ZIF-C was increased. It indicates that release of ions are not due to dissolution or disintegration of the material. ZIF-C is a reliable material under acidic condition.