Detailed structure of a new bioactive glass composition for the design of bone repair materials

doi:10.1016/j.jnoncrysol.2017.07.027

Journal of Non-Crystalline Solids

Volume 475, 1 November 2017, Pages 10-14

https://doi.org/10.1016/j.jnoncrysol.2017.07.027 Get rights and content

Highlights

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Detailed structure of a new bioactive glass composition (PSC) was studied.
•
The structure information were obtained by HEXRD and solid NMR techniques.
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There is Si-O-P network formed for PSC samples but not for 45S5 and S70C30 samples.

Abstract

Detailed structure of a new bioactive glass composition (PSC, 54 mol% SiO₂, 35 mol% CaO and 11 mol% P₂O₅) was studied, and conventional glasses (45S5 and S70C30) were used as comparison. The structure information were obtained by HEXRD and solid NMR techniques. It was found that all the samples have different silicon and phosphorous coordination environment, there is Si-O-P network formed for PSC samples but not for 45S5 and S70C30 samples. These results may hopefully advance the design of new bioactive glasses.

Introduction

The life expectancy of the world population increased dramatically every year because of the developments of people's life. Plenty of bone implants are needed to maintain their quality of life after accidents or illnesses. However, current implants, e.g. metals and polymers, were biological inert triggering fibrous encapsulation after implantation and leading to a high rate of failure in the long time [1]. In order to avoid the flaw of bone implants, material scientists have been making great effort to develop synthetic bone materials. Among them, bioactive glasses (silicate-based glasses, phosphate-based glasses, borate-based glasses and borosilicate glasses) have provided many encouraging results [2], [3], [4], [5], [6], [7].

The first silicate-based bioactive glass (Bioglass®) were reported by Hench, which has a composition known as 45S5 corresponding to 45 wt%, SiO₂, 24.5 wt%, Na₂O, 24.5 wt% CaO, and 6 wt% P₂O₅, and has been widely used in clinical, e.g. dental and orthopaedic fields [8], [9]. However, these glasses need to be processed at very high temperatures. Sol-gel bioactive glasses processed at lower temperature were then explored. It was found that the gel-derived glasses had high surface area, porosity, and wider range of bioactive compositions (58S, 77S and S70C30, et al.), exhibiting higher bone bonding rates [10]. However, all these silicate-based glasses degrade slowly and usually take 1 to 2 years to disappear from the body [11].

Phosphate-based glasses (CaO-Na₂O-P₂O₅) have unique dissolution properties in body fluids, the degradation rates can be controlled from hours to several weeks by changing the glass composition. Furthermore, these glasses can be synthesized as particles, fibres and microtubes to include different dopants that are able to induce a specific biological function and enhance biocompatibility in soft tissue [3]. However, these glasses didn't not embody good bioactivity for bone regeneration. Because of these limitations, it is necessary to search for new bioactive glasses compositions for the repair of bone defects.

Since the silicate-based glasses with lower phosphate content (< 5 mol%) have higher bioactivity for bone defects, whereas phosphate glasses without silicate content have higher degradation rates, it may be possible to prepare a new phosphosilicate bioactive glass with higher phosphate content accelerating the degradation rates for bone defects. In previously, we used a non-toxic phytic acid as phosphorous precursor to prepare CaO-SiO₂-P₂O₅ glasses by sol-gel process, it was found that a much broader range of bioactive composition were obtained especially at high phosphate content [12]. In which, the composition of (CaO)_0.35(SiO₂)_0.54(P₂O₅)_0.11 (48.2 wt% SiO₂, 29.1 wt% CaO and 22.7 wt% P₂O₅, termed as PSC) has the best bioactivity, and the phosphate content is dramatically increased compared with conventional bioactive glasses. The PSC have also be found to have better cell proliferation, mRNA expression and osteocalcin and mineralization of hDPCs comparing with conventional 45S5 [13], and the released Si and P ions from PSC were larger than those released from 45S5, implying the higher degradation rate for PSC.

Detailed structural knowledge is a prerequisite for optimizing glasses design. The atomic-scale structure of bioactive glasses and its effect on bioactivity and chemical durability has attracted much attention, because of which is important to model and predict the behavior of bioactive glasses, and ultimately improve their design [14], [15], [16], [17]. In this paper, the detailed structure of this new bioactive glass composition (PSC) with higher phosphate content was studied by HEXRD and NMR techniques, which are possible to gain detailed insight into its structure. The linking between phosphate and silicate structural units will be answered, hopefully advancing the design of new bioactive glasses.

Section snippets

Sample preparation

Tetraethyl orthosilicate (TEOS, ≥ 99.0%) and Ca(NO₃)₂·4H₂O were purchased from Sinopharm Chemical Reagent Co., Ltd. Phytic acid (50 wt% aqueous solution) was purchased from Sigma Aldrich. All the precursors were used without further purification in the sol-gel preparation.

Bioactive glass (PSC: SiO₂-54 mol%, CaO-35 mol%, P₂O₅-11 mol%) was prepared as previously reported [12]. Phytic acid (1.6 mL) was firstly added in the mixture of ethanol and water at room temperature, then TEOS (5.82 mL) was added

TGA-DSC analysis

Fig. 1 shows TGA-DSC traces of representative PSC gels after dried at 120 °C. Three stages of weight loss are observed: the first one occur between 180 °C and 200 °C with an exothermic peak, which may be associated with the removal of trapped solvent (water, ethanol and nitrate etc.); the second one occur between 200 °C and 400 °C, which may because the further removal of nitrate and the loss of organic moieties by further condensation; the third stage of weight loss commence from the end of second

Discussion

It was reported that the silicate-based glasses degrade slowly and usually take much long time to disappear from the body [11], which may because the higher silica content in glass decreases the rate of dissolution [10]. Given the good biocompatibility and bioresorbability of phosphate materials, increasing P₂O₅ content in bioactive materials certainly has better control on dissolution rates [3]. Therefore, in previous study, we chose phytic acid as phosphorus precursor to produce different

Conclusion

A new bioactive glass composition (PSC, (CaO)_0.35(SiO₂)_0.54(P₂O₅)_0.11) with higher phosphate content have been characterized in detail by XRD, FTIR, MAS NMR and HEXRD. It was found that the calcium ions could be incorporated into the Si-O-P network even at low temperature (200 °C), and the nitrate ions could be removed fully by heating at 600 °C. It was also found that there was P-O-Si covalent bond formation and lower Ca-O bond length for PSC bioactive glass comparing with other composition

Acknowledgements

This work was supported by NSFC (Project 51603210, 51473004, 81470101 and U1232112) and a Royal Society/Natural Science Foundation of China international exchange grant (IE131323, 51411130151). We acknowledge the help from the station member at the beamline 13W at Shanghai Synchrontron Radiation Facility.

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Detailed structure of a new bioactive glass composition for the design of bone repair materials

Highlights

Abstract

Introduction

Section snippets

Sample preparation

TGA-DSC analysis

Discussion

Conclusion

Acknowledgements

Acta Biomater.

Acta Biomater.

J. Non-Cryst. Solids

Acta Biomater.

Chin. Chem. Lett.

J. Non-Cryst. Solids

Chin. Chem. Lett.

Biomaterials

Biomaterials

Acta Biomater.

Bioactive functional materials: a perspective on phosphate-based glasses

J. Mater. Chem.

Bioactive borosilicate glass scaffolds: improvement on the strength of glass-based scaffolds for tissue engineering

J. Mater. Sci. Mater. Med.

Kinetics and mechanisms of the conversion of silicate (45S5), borate, and borosilicate glasses to hydroxyapatite in dilute phosphate solutions

J. Mater. Sci. Mater. Med.

The story of Bioglass®

J. Mater. Sci. Mater. Med.