Surface Energy Changes Involved in Apatite Formation in Copper-Containing Bioactive Glasses

Camila Miranda Fonseca Duarte,Luana Barbosa Da Cruz,Wilson Acchar,Euler Araujo Dos Santos,Silmara Caldas Santos

doi:10.1590/1980-5373-mr-2021-0436

Camila Miranda Fonseca Duarte, Luana Barbosa Da Cruz + Show 3 more

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https://doi.org/10.1590/1980-5373-mr-2021-0436

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Abstract

The aim of this work was to use the Washburn capillary rise method to evaluate changes in surface energy promoted by the insertion of CuO in a 58S glass and its implication in bioactivity. The presence of CuO decreased the surface wettability by decreasing the Lewis acid-base component γSAB and increasing the Lifshitz-van der Waals component γSLW. The insertion of CuO also diminished the value of the electron donor parameter γS-; i.e., the number of negative groups. This was accompanied by a nonuniform apatite formation on the surface, likely because the presence of CuO-rich regions with lower electron donor values impaired the adsorption of Ca2+, preventing uniform apatite precipitation. Therefore, surface energy was extremely sensitive to small physical and chemical changes in the glass structure and the behavior of the electron donor parameter could be used as an adequate probe to predict glass bioactivity.

Highlights

Upon implantation into the body, a biomaterial surface will undergo important transformations promoted by direct contact with biological fluids
The aim of this research was to employ the Washburn capillary rise method to measure the changes in the surface energy of CuO-containing 58S bioactive glasses (58% SiO2 - (33% - x) calcium oxide (CaO) - x% CuO - 9% P2O5, wt. %) during a bioactivity assay
The Lifshitz-van der Waals component γSLW was higher than the Lewis acid-base component γSAB in the glasses before the simulated body fluid (SBF) assay, regardless of the presence of CuO (Figure 1)

Summary

Introduction

Upon implantation into the body, a biomaterial surface will undergo important transformations promoted by direct contact with biological fluids. These transformations are associated with dissolution, precipitation, ion exchange, and the adsorption of ions, proteins, and several other organic molecules present in the extracellular medium[1,2]. When in contact with biological fluids, the siloxane groups (Si-O-Si) on the glass surface undergo hydrolysis, forming negatively charged silanol groups (Si-OH) at alkaline pH. These negative groups attract Ca2+ ions, leading to the precipitation of a positively charged Ca2+-rich layer. The apatite layer formed on the glass surface is responsible for the high biocompatibility associated with bioactive glasses[3]

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