Flexible electronic systems for bioimplants that offer long-term (multidecade) stability and safety in operation require thin, biocompatible layers that can prevent biofluid penetration. Recent work shows that ultrathin films of silicon dioxide thermally grown (TG-SiO2) on device-grade silicon wafers and then released as transferrable barriers offer a remarkable set of attributes in this context. This paper examines the chemical stability of these materials in aqueous solutions with different combinations of chemistries that are present in biofluids. Systematic measurements reveal the dependence of the dissolution rate of TG-SiO2 on concentrations of cations (Na+, K+, Mg2+, Ca2+) and anions (Cl-, HPO42-) at near-neutral pH. Certain results are consistent with previous studies on bulk samples of quartz and nanoparticles of amorphous silica; others reveal significant catalyzing effects associated with divalent cations at high pH and with specific anions at high ionic strength. In particular, Ca2+ and HPO42- greatly enhance and silicic acid greatly reduces the rates. These findings establish foundational data of relevance to predicting lifetimes of implantable devices that use TG-SiO2 as biofluid barriers, and of other classes of systems, such as environmental monitors, where encapsulation against water penetration is important.
Bibliographical noteFunding Information:
Y. K. Lee is thankful for the support from Kwanjeong Educational Foundation. K. J. Yu acknowledges the support from the National Research Foundation of Korea (NRF 2017M1A2A2048904). Z.X. and X.F. acknowledge the support from the National Basic Research Program of China (Grant No. 2015CB351900) and National Natural Science Foundation of China (Grant Nos. 11402134 and 11320101001). Y.H.
acknowledges the support from NSF (Grant Nos. 1400169, 1534120, and 1635443) and NIH (Grant No. R01EB019337).
© 2017 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Materials Science(all)