Is HEPES suitable for the in vitro testing of inorganic biomaterials in SBF?

Recently, much work has focused on the development of inorganic materials in bone tissue engineering, such as glass and glass scaffolds. These inorganic materials classified as “bioactive” should first pass an in vitro test in simulated body fluid (SBF).In the test, an inert buffer to keep neutral pH is necessary to maintain conditions close to those in blood plasma. According to an international standard (ISO:23317:2014) for the test, Tris(hydroxymethyl)aminomethane is using to maintain neutral pH in SBF.

In 2011, Rohanova et al. found that TRIS buffer used with a highly reactive glass-ceramic scaffold accelerates the dissolution of the glass-ceramic crystalline phase and lead to the formation of hydroxyapatite. It demonstrates that TRIS buffer is not suitable for in vitro testing. So other alternatives must be sought.

Rohanova et al. evaluated whether would HEPES buffer be more suitable for SBF. They studied the interaction of HEPES buffer with the glass-ceramic scaffold (45S5 bioactive glass-based) through comparing SBF with HEPES and demineralized water with HEPES. The tested scaffold was exposed to the media under a static-dynamic arrangement for 15 days. Leachate samples were collected daily for analysis Ca²⁺ ions and Si, (PO₄)^3- ions, and to measure pH. The glass-ceramic scaffold was analyzed by SEM/EDS, XRD, and WD-XRF before and after 0.3,1,3,7,11,15 days of exposure. Their results confirmed the rapid selective dissolution of the glass-ceramic crystalline phase containing Ca²⁺ ions due to the presence of HEPES, hydroxyapatite supersaturation being reached within 24 h in both solutions. These results suggest that HEPES is also not suitable for the in vitro testing of highly reactive inorganic biomaterials (glass, glass-ceramics).

In a word, findings of Rohanova et al. show that TRIS and HEPES buffers are not suitable to maintain the neutral pH for the in vitro testing. Consequently, researcher will work further to test other buffers to find suitable alternatives.

Edited by Suzhou Yacoo Science Co., Ltd.