Biomimetic mineralized strontium-doped hydroxyapatite on porous poly(l-lactic acid) scaffolds for bone defect repair

Abstract

Introduction

poly(l-lactic acid) (PLLA) has been approved for clinical use by the US Food and Drug Administration (FDA); however, their stronger hydrophobicity and relatively fast degradation rate restricted their widespread application. In consideration of the composition of bone, the inorganic–organic composite has a great application prospect in bone tissue engineering. Many inorganic–organic composite scaffolds were prepared by directly mixing the active ingredient, but this method is uncontrolled and will lead to lack of homogeneity in the polymer matrix. Strontium (Sr) is an admirable addition to improve the bioactivity and bone induction of hydroxyapatite (HA). To our knowledge, the application of biomimetic mineralized strontium-doped hydroxyapatite on porous poly(l-lactic acid) (Sr-HA/PLLA) scaffolds for bone defect repair has never been reported till date. Biomimetic mineralized Sr-HA/PLLA porous scaffold was developed in this study. The results indicated that the Sr-HA/PLLA porous scaffold could improve the surface hydrophobicity, reduce the acidic environment of the degradation, and enhance the osteoinductivity; moreover, the ability of protein adsorption and the modulus of compression were increased. The results also clearly showed the effectiveness of the Sr-HA/PLLA porous scaffold in promoting cell adhesion, proliferation, and alkaline phosphatase (ALP) activity. The micro computed tomography (micro-CT) results showed that more new bones were formed by Sr-HA/PLLA porous scaffold treatment. The histological results confirmed the osteoinductivity of the Sr-HA/PLLA porous scaffold. The results suggested that the Sr-HA/PLLA porous scaffold has a good application prospect in bone tissue engineering in the future.

Purpose

The purpose of this study was to promote the bone repair.

Materials and methods

Surgical operation of rabbits was carried out in this study.

Results

The results showed that formation of a large number of new bones by the Sr-HA/PLLA porous scaffold treatment is possible.

Conclusion

Biomimetic mineralized Sr-HA/PLLA porous scaffold could effectively promote the restoration of bone defects in vivo.

Keywords:

• Sr-HA
• PLLA porous scaffold
• biomimetic mineralization
• bone repair

Supplementary materials

Methods

poly(l-lactic acid) (PLLA) with an inherent viscosity of 1.6 dL/g was purchased from Ji’nan Daigang (Ji Nan, China). d-Fructose (melting point [m.p.] 119°C–122°C) and Span 80 were purchased from Sigma-Aldrich Co (St Louis, MO, USA). Dioxane, cyclohexane, and hexane were purchased from Sigma-Aldrich Co.

Preparation of PLLA porous scaffolds

The PLLA porous scaffolds were fabricated according to our previous work. The details were reported.¹ Briefly, d-Fructose was melted and then emulsified into mineral oil with Span 80 as a surfactant under stirring. The resulting mixture was cooled down, and the sugar spheres were washed and sieved to desired sizes. The sieved sugar spheres were packed and heated to form a template. PLLA/dioxane solution was casted into the assembled sugar template under vacuum. The above system was phase separated at −20°C overnight. The resulting composites were freeze-dried, the sugar was leached out in distilled water, and then the scaffold was freeze-dried.

Subcutaneous implantation of the porous scaffolds

Twenty ICR mice were used for biocompatibility in vivo. The mice were anesthetized by chloral hydrate, and a 10 mm long skin incision was made in the back of the mice. After that, the scaffolds were placed subcutaneously. Mice were sacrificed with ether after 30 days of surgery. The scaffolds, together with surrounding tissues, were excised and immediately fixed in 10% formalin solution.

Figure S1 Histopathology of the heart, liver, spleen, lung, and kidney of mice.

Abbreviations: PLLA, poly(l-lactic acid); HA/PLLA, hydroxyapatite on porous poly(l-lactic acid); Sr-HA/PLLA, strontium-doped hydroxyapatite on porous poly(l-lactic acid).

Figure S2 Histological images of scaffolds and surrounding tissue in mice stained with H&E and Masson.

Abbreviations: H&E, hematoxylin and eosin; PLLA, poly(l-lactic acid); HA/PLLA, hydroxyapatite on porous poly(l-lactic acid); Sr-HA/PLLA, strontium-doped hydroxyapatite on porous poly(l-lactic acid).

Reference

• GeMXueLNieTMaHZhangJThe precision structural regulation of PLLA porous scaffold and its influence on the proliferation and differentiation of MC3T3-E1 cellsJ Biomater Sci Polym Ed201627171685169727569555
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Acknowledgments

This research was supported by the National Natural Science Foundations of China (31470961, 21271059, 21301046, and 51302062), Hebei Province “Hundred Talents Program” (BR2-202), Hebei Province “Three Three Three Talents Program” (A201401002), and Natural Science Foundation of Hebei Province (B2016201209).

Author contributions

All authors contributed toward data analysis, drafting, and revising the paper, and agreed to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.