Elsevier

Microporous and Mesoporous Materials

Volume 184, 15 January 2014, Pages 122-126
Microporous and Mesoporous Materials

Short Communication
Application of orthogonal experimental design in synthesis of mesoporous bioactive glass

https://doi.org/10.1016/j.micromeso.2013.10.007Get rights and content

Highlights

  • A method combining orthogonal design and quantitive analysis of SAXS was proposed.

  • An efficient method to evaluate the impact of multifactor to mesoporous structure.

  • The optimum formula of a MBG with complex components was revealed.

Abstract

An orthogonal experimental design method combining with quantitive analysis of small-angle X-ray scattering (SAXS) pattern was applied to optimize the synthesis of bioactive glasses with highly ordered mesoporous structure (MBGs). The quantitive analysis of SAXS pattern allows a quantified evaluation of the ordering of the mesoporous structure, which makes it possible to tailoring the mesoporous structure of the MBGs with complex component by a traditional orthogonal experimental design method. The number of trials for preparing MBGs can be greatly reduced and the primary factors affecting the formation of mesoporous structure and the properties of MBGs can be easily found out by this orthogonal experimental design method. MBGs containing SiO2, CaO, Fe2O3 were prepared as an example to present the way to obtain optimized ordered mesoporous structure. It confirmed that Fe2O3 was the primary factor influencing the mesoporous structure of the MBGs. The ordering of the mesopores increased in the first and then decreased with the increase of F127 content.

Graphical abstract

A novel method combining an orthogonal experiment (L16) and a quantitive analysis of SAXS patterns was proposed to reveal the impact degree of multifactor to pore ordering of mesoporous bioactive glasses and determine the optimum synthesis formula of the MBGs with complicated multicomponent. The verification experiment showing the highly ordered mesoporous structure of the optimum MBGs confirmed the rationality and validity of the method.

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Introduction

Since the first report of 45S5 [1], MBGs have exhibited more superior bone-forming bioactivities in vitro than solid bioactive glasses (BGs) [2], and have been proposed potential materials for making implants with local drug delivery function [3], [4], [5]. The ordered mesoporous structure within MBGs could be obtained by using nonionic block copolymers as structure-directing agents and through an evaporation-induced self-assembly (EISA) process. Synthesis of MBGs containing ions is becoming a frontier research of biomaterialists because it has been confirmed that the addition of some ions into solid BGs can improve the properties of BGs or enable them to have additional functions [6], [7], [8]. For instance, the addition of MgO in BGs has been confirmed inducing formation of whitelockite-like phase in the formed biomimetic layer on BGs, thus affecting cell behavior on the scaffold surface and bonding to natural tissues [9], [10], [11]. In another report, an ordered mesoporous calcium–magnesium silicate showed better bioactivity than calcium–magnesium silicate [12]. BGs scaffolds containing silver showed important local antibacterial property [13], [14]. Inducing Zn2+ and Sr2+ into BGs can improve the bioactive property significantly [15], [16], [17]. MBGs incorporated with Co2+ showed enhanced vascular endothelial growth factor secretion, HIF-1α expression and bone related gene expression of human bone marrow stromal cells [18]. However, because MBGs are complicated multicomponent systems, the species and contents of components composed of MBGs can strongly influence the formation of ordered mesoporous structure. For example, a decrease of a specific area and a progressive change of the mesoporous structure was observed when silver was added into a SiO2–CaO–P2O5 ternary system [19]. To prepare a highly ordered mesoporous structure, vast quantities of experiments could be necessary. In a typical case, in order to synthesize a MBG containing SiO2, CaO, P2O5 and Na2O with a triblock copolymer template F127, five factors in total, taking account of three levels of each factor, 243 (35) trials are necessary, which could be a tedious task difficult to be carried out.

The orthogonal experimental design method is a highly efficient way capable of dealing with multifactor experiments and screening optimum levels by using the orthogonal design table. Before making an orthogonal design table, reasonable and representative levels of all factors are determined at first according to theories or a few experimnents. And then experiments represent all the level groups of the experimental factors are performed. Positive and negative factors and their impact degrees (ID) to the objective of production are revealed by calculating the experimental results, e.g. conversion and yield. The possible optimum level can be concluded according to the impact of the factors. At last, a confirmatory experiment is performed following the concluded optimum level. For example, for an experiment with four factors and four levels of each factor, an orthogonal design table L16(44) could be used, and the experiment program only contains 16 level groups, reflecting the overall situation of the comprehensive experiment containing 256 level groups in all. Thus it is much easier to find out the optimum level group.

This paper is aiming at designing an efficient way to find out the primary factors influencing the formation of MBGs and determine the optimum synthesis formula of the MBGs with complicated multicomponent. We speculate that this aim could be easily realized through the combination of an orthogonal experimental design method and the quantitive analysis of SAXS patterns. MBGs containing SiO2, CaO, Fe2O3 were synthesized through an EISA process and as an example to present the way to obtain an optimized ordered mesoporous structure.

Section snippets

Materials

Most raw materials, tetraethyl orthosilicate (TEOS), calcium nitrate tetrahydrate (Ca(NO3)2·4H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), nitric acid (HNO3, 16M), anhydrous ethanol (EtOH), purchased from Sinopharm Chemical Reagent Co., Ltd., were all of analytical grade and used directly without further purification. Nonionic triblock copolymer PEO106PPO70PEO106 (F127, PEO is poly(ethylene oxide), PPO is poly(propylene oxide)) was purchased from Sigma–Aldrich. Deionized water was obtained

Results and discussion

As a complicated multicomponent system, both the species and component contents of MBGs can significantly influence the OD of pore arrangement. In order to evaluate and compare the IDs of multifactors to pore ordering (PO) of mesoporous structure prepared with different formulas in an orthogonal experiment, a quantitive evaluation to pore ordering is necessary. SAXS has been utilized as a powerful method to characterize the structure of mesoporous materials such as SBA-15 [20], [21], [22], [23]

Conclusions

In summary, this paper reports for the first time an efficient method for evaluating the ID of multifactor to PO of MBGs and determining the optimum synthesis formula of the MBGs with complicated multicomponent. This method combined an orthogonal experiment and a quantitive analysis of SAXS patterns. In the example experiment, the IDs of the factors were as follows: Fe(NO3)3·9H2O > TEOS > Ca(NO3)2·4H2O > F127. The optimum formula which was concluded and confirmed was TEOS(0.015)-Ca(NO3)2·4H2

Acknowledgements

LJ and XS were supported to work by the National Natural Science Foundation of China (No. 51273171 and No. 21201149) and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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