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Calcite incorporated in silica/collagen xerogels mediates calcium release and enhances osteoblast proliferation and differentiation
Multiphasic silica/collagen xerogels are biomaterials designed for bone regeneration. Biphasic silica/collagen xerogels (B30) and triphasic xerogels (B30H20 or B30CK20) additionally containing hydroxyapatite or calcite were demonstrated to exhibit several structural levels. On the first level, low fibrillar collagen serves as template for silica nanoparticle agglomerates. On second level, this silica-enriched matrix phase is fiber-reinforced by collagen fibrils. In case of hydroxyapatite incorporation in B30H20, resulting xerogels exhibit a hydroxyapatite-enriched phase consisting of hydroxyapatite particle agglomerates next to silica and low fibrillar collagen. Calcite in B30CK20 is incorporated as single non-agglomerated crystal into the silica/collagen matrix phase with embedded collagen fibrils. Both the structure of multiphasic xerogels and the manner of hydroxyapatite or calcite incorporation have an influence on the release of calcium from the xerogels. B30CK20 released a significantly higher amount of calcium into a calcium-free solution over a three-week period than B30H20. In calcium containing incubation media, all xerogels caused a decrease in calcium concentration as a result of their bioactivity, which was superimposed by the calcium release for B30CK20 and B30H20. Proliferation of human bone marrow stromal cells in direct contact to the materials was enhanced on B30CK20 compared to cells on both plain B30 and B30H20
ATR-FTIR in Kretschmann configuration integrated with electrochemical cell as in situ interfacial sensitive tool to study corrosion inhibitors for magnesium substrates
Integrated attenuated total reflection – Fourier transform infrared spectroscopy (ATR-FTIR) – Electrochemical impedance spectroscopy (EIS) measurements were used to simultaneously follow chemisorption mechanisms of organic inhibitors as well as their corrosion inhibition efficiency towards magnesium based substrates. Four carboxylic compounds, i.e. 2,5-pyridinedicarboxylic acid (PDC), 3-methylsalicylic acid (MSA), sodium salicylate (SS) and fumaric acid (FA), were selected based on their promising inhibiting capacities and were all shown to chemisorb at the MgO/Mg(OH)2 surface by carboxylate bond formation. Orientation analysis using polarized infrared light showed that carboxylate bonds established using aliphatic carboxylate compound aligned perpendicular to the magnesium surface, whereas carboxylate bonds with aromatic compounds were oriented in plane with the magnesium surface. This different orientation is associated to the involvement of π-interactions in the MgO/Mg(OH)2 – aromatic carboxylate adsorption. Additionally, DFT calculations revealed that the addition of hetero-atoms (i.e. N or OH) in the molecular structure contributes to increased adsorption energies, indicating that next to carboxylate groups also these hetero-atoms are involved in interfacial interactions. Integrating the ATR-FTIR setup with an electrochemical cell allowing for simultaneous EIS measurements lead to two surface phenomena determining the inhibition efficiency. Surface hydroxylation processes on one hand forming a MgO/Mg(OH)2 layer on one hand, and the chemisorption of carboxylate compounds on the other hand. The inhibition efficiency was found to increase in following order: FA < PDC < MSA and was mainly associated to the formation of a MgO/Mg(OH)2 layer. SS was shown to act as a corrosion accelerator rather than a corrosion inhibitor. Despite its high sensitivity for water, both surface processes could be followed in situ by means of ATR-FTIR. Simultaneously, protective properties of the formed films could be quantified by means of EIS. Consequently, integrated ATR-FTIR – EIS methodology has shown to be highly valuable for gaining in-situ insights in the inhibition mechanism, while quantifying the inhibition efficiency. This was even possible for highly active metal substrate as magnesium, although further developments are suggested if one aims to quantify electrochemical constants related to corrosion and other surface processes measured at the low frequencies (i.e. < 1 Hz).</p