Enhancement of Bone Regeneration on Calcium-Phosphate-Coated Magnesium Mesh: Using the Rat Calvarial Model

Abstract

Metallic biodegradable magnesium (Mg) is a promising material in the biomedical field owing to its excellent biocompatibility, bioabsorbability, and biomechanical characteristics. Calcium phosphates (CaPs) were coated on the surface of pure Mg through a simple alkali-hydrothermal treatment. The surface properties of CaP coatings formed on Mg were identified through wettability, direct cell seeding, and release tests since the surface properties of biomaterials can affect the reaction of the host tissue. The effect of CaP-coated Mg mesh on guided bone regeneration in rat calvaria with the critical-size defect was also evaluated in vivo using several comprehensive analyses in comparison with untreated Mg mesh. Following the application of protective CaP coating, the surface energy of Mg improved with higher hydrophilicity and cell affinity. At the same time, the CaP coating endowed Mg with higher Ca affinity and lower degradation. The Mg mesh with CaP coating had higher osteointegration and bone affinity than pristine Mg mesh.

Keywords: calcium phosphate; guided bone regeneration; magnesium mesh; rat calvarial defect; surface modification.

FIGURE 1

(A,B) Surface morphology and (C) cross-sectional elemental analysis of CaP-coated Mg after alkali-hydrothermal treatment for 2 h.

FIGURE 2

Contact angles of PM and CM were measured using Phoenix-300 Touch, representing the hydrophilicity of the sample surface. PM, pure magnesium; CM, calcium-phosphate-coated magnesium.

FIGURE 3

Scanning electron microscopy (SEM) analysis of MC3T3-E1 cells cultured on (A,C) pure magnesium (PM) and (B,D) calcium-phosphate-coated magnesium (CM) for 3 days. Red color box of A and B enlarged in C and D respectively.

FIGURE 4

Changes in the concentration of Mg and Ca ions in Earle’s balanced salt solution (EBSS) during the 6-week ion release test of pure magnesium (PM) and calcium-phosphate-coated magnesium (CM) (* indicates significant difference between PM and CM; a indicates significant differences compared to 1 week; b indicates significant differences compared to 2 weeks; c indicates significant differences compared to 4 weeks).

FIGURE 5

Quantitative analysis results of new bone volume and mineral density in the critical-size defects of rat calvaria obtained from micro-CT data (*p ≤ 0.05).

FIGURE 6

(A) Quantitative analysis results and (B) three-dimensional reconstruction images of the Mg meshes used in the rat calvarial model for guided bone regeneration obtained using micro-CT [* indicates significant difference between pure magnesium (PM) and calcium-phosphate-coated magnesium (CM)].

FIGURE 7

Micro-CT images of the morphology of degraded Mg mesh and newly formed bone in the rat calvaria. The degraded Mg mesh is highlighted in orange.

FIGURE 8

Histological cross-sectional images of bone formation in the pure magnesium (PM) and calcium-phosphate-coated magnesium (CM) groups after 4 and 8 weeks of implantation. Histomorphology is presented as 10× magnification of coronal slices and focal areas of the center and side points (30×).