Abstract
Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol-gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid-base-catalyzed sol-gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic-inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO2-CaO BG were obtained using calcium hydroxide (CH), and we demonstrate its usability in the synthesis of promising BG-polycaprolactone hybrid scaffolds. BG and hybrids prepared with CH were able to form nanocrystalline nonstoichiometric apatite in simulated body fluid. The increased reliability of low-temperature syntheses associated with the use of a stable and inexpensive alkaline-earth precursor are major steps toward the translation of calcium silicate hybrids or other alkaline-earth silicates from bench to clinic.
Highlights
Since they were first developed by Hench in 1969, 1 bioactive glass (BG) have been the focus ofmuch research due to their remarkable properties: they strongly bond to bone,[2] they resorb as bone regenerates, and their dissolution products stimulate osteoblasts at the genetic level.[3]
We have deepened the understanding of the mechanism of calcium incorporation inside silicates during the acid−base catalyzed sol−gel synthesis of BG
The basic property of the calcium precursor plays an essential role in the mechanism of calcium incorporation as the increase of the pH above the IEP of silicic acid leads to the deprotonation of silanols
Summary
Since they were first developed by Hench in 1969, 1 bioactive glass (BG) have been the focus ofmuch research due to their remarkable properties: they strongly bond to bone,[2] they resorb as bone regenerates, and their dissolution products stimulate osteoblasts at the genetic level.[3] BG can be fabricated in various shapes such as monoliths, particulates, and scaffolds Their inherent brittleness prevents BG scaffolds from being viable in cyclic Joad bearing applications.[4] The toughness ofthe material can be greatly enhanced by combining BG with sasoopll--ogglyeemll hehyrybtbroirdidp. Calcium and its release is pknlaoyws na central role in the bioactivity ofBG9 to favor the adsorption of proteins involved in osteogenic processes and infiammatory response,[10] and to induce osteoblast proliferation and differentiation.[11]. TtCreraaa(dtNimtOieon3n)ta21lalbyb,osuvoetl-4t0hg0eels°eBCGctaaolrceaiulplmorwepsacoraeulcdricufermsomtroesqaeulntistreelrikteahCetahsGielirc2maotaerl network and to remove the counterion, as this has been well eInstatbhleishsyendtihnespisionoefehriynbgriwdso, rtkhsebyprLeisne,nYcue, and of a early stage of the sol-gel process forbids
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