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. 2024 Jan 9;16(2):198.
doi: 10.3390/polym16020198.

Magnesium Hydroxide as a Versatile Nanofiller for 3D-Printed PLA Bone Scaffolds

Wang Guo  1   2 , Wenlang Bu  1   2 , Yufeng Mao  1   2 , Enyu Wang  1   2 , Yanjuan Yang  1   2 , Chao Liu  1   2 , Feng Guo  3   4 , Huaming Mai  3   4 , Hui You  1   2 , Yu Long  1   2
Affiliations

Magnesium Hydroxide as a Versatile Nanofiller for 3D-Printed PLA Bone Scaffolds

Wang Guo et al. Polymers (Basel). .

Abstract

Polylactic acid (PLA) has attracted much attention in bone tissue engineering due to its good biocompatibility and processability, but it still faces problems such as a slow degradation rate, acidic degradation product, weak biomineralization ability, and poor cell response, which limits its wider application in developing bone scaffolds. In this study, Mg(OH)2 nanoparticles were employed as a versatile nanofiller for developing PLA/Mg(OH)2 composite bone scaffolds using fused deposition modeling (FDM) 3D printing technology, and its mechanical, degradation, and biological properties were evaluated. The mechanical tests revealed that a 5 wt% addition of Mg(OH)2 improved the tensile and compressive strengths of the PLA scaffold by 20.50% and 63.97%, respectively. The soaking experiment in phosphate buffered solution (PBS) revealed that the alkaline degradation products of Mg(OH)2 neutralized the acidic degradation products of PLA, thus accelerating the degradation of PLA. The weight loss rate of the PLA/20Mg(OH)2 scaffold (15.40%) was significantly higher than that of PLA (0.15%) on day 28. Meanwhile, the composite scaffolds showed long-term Mg2+ release for more than 28 days. The simulated body fluid (SBF) immersion experiment indicated that Mg(OH)2 promoted the deposition of apatite and improved the biomineralization of PLA scaffolds. The cell culture of bone marrow mesenchymal stem cells (BMSCs) indicated that adding 5 wt% Mg(OH)2 effectively improved cell responses, including adhesion, proliferation, and osteogenic differentiation, due to the release of Mg2+. This study suggests that Mg(OH)2 can simultaneously address various issues related to polymer scaffolds, including degradation, mechanical properties, and cell interaction, having promising applications in tissue engineering.

Keywords: biological properties; bone scaffold; degradation properties; fused deposition modeling (FDM); magnesium hydroxide (Mg(OH)2); mechanical properties; polylactic acid (PLA).

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Morphology characterization of FDM 3D-printed PLA/Mg(OH)2 scaffolds: three-dimensional macroscopic appearance with digital camera (a1–a6); top view (b1–b6) and side view (c1–c6) with digital camera; the strut appearance with SEM (d1–d6). Notes: the prepared filaments have a good FDM printing quality, and the FDM 3D printed scaffolds show a well-ordered and interconnected three-dimensional porous structure.
Figure 2
Figure 2
XRD patterns (a) and FTIR spectra (b) of PLA/Mg(OH)2. Notes: the results indicate Mg(OH)2 was composited with PLA without impurity formation after screw extrusion and FDM 3D printing.
Figure 3
Figure 3
Water contact angle data (a) and images (b) of PLA/Mg(OH)2 composites. Notes: the hydrophilicity of PLA was effectively improved by Mg(OH)2.
Figure 4
Figure 4
Mechanical properties of PLA/Mg(OH)2: typical tensile stress-strain curves (a), tensile strength (b), tensile modulus (c); typical compressive stress-strain curves (d), compressive strength (e), compressive modulus (f). Notes: as the content of Mg(OH)2 increased, the strength and compressive modulus of PLA/Mg(OH)2 increased first and then decreased, with an optimal content at 5 wt%.
Figure 5
Figure 5
SEM images of liquid nitrogen fracture morphology for PLA/Mg(OH)2 composites: PLA (a), PLA/2.5Mg(OH)2 (b), PLA/5Mg(OH)2 (c), PLA/7.5Mg(OH)2 (d), PLA/10Mg(OH)2 (e), PLA/20Mg(OH)2 (f). Notes: at a low content (2.5 and 5 wt%), Mg(OH)2 particles can disperse relatively uniformly, thus exerting well mechanical strengthening effects; while at a high content (7.5–20 wt%), Mg(OH)2 particles tend to form obvious aggregates with poor bonding with PLA matrix.
Figure 6
Figure 6
The degradation properties of PLA/Mg(OH)2: water absorption (a), mass loss (b), pH value (c), Mg2+ release concentration from scaffolds (d), the schematic diagram illustrating the mechanism by which Mg(OH)2 accelerated the degradation of PLA scaffolds (e). Notes: Mg(OH)2 accelerated the degradation of PLA by adjusting the acidity and alkalinity in the aqueous environment.
Figure 7
Figure 7
Degradation morphology and product analysis of PLA/Mg(OH)2 scaffolds after immersing in PBS for 7, 14, and 28 days. SEM morphology of PLA (a1–a6); PLA/5Mg(OH)2 (b1–b6); PLA/20Mg(OH)2 (c1–c6); XRD patterns after degradation (d1–d3). Notes: With the increase in Mg(OH)2 content and experimental time, the mixed crystalline whisker-like substance of magnesium dihydrogen phosphate and magnesium hydroxide appeared on the surface of the scaffolds.
Figure 8
Figure 8
SEM surface morphology of PLA/Mg(OH)2 after immersion in SBF for 7, 14, and 28 days. SEM morphology of PLA (a1–a6); PLA/5Mg(OH)2 (b1–b6); PLA/20Mg(OH)2 (c1–c6). Notes: With the increase in Mg(OH)2 content and immersion time, the quantity and volume of white spherical mineral deposits on the surface of the scaffold gradually increased.
Figure 9
Figure 9
Element and phase analysis of mineral deposits on PLA/Mg(OH)2 after immersion in SBF for 7, 14, and 28 days: EDS spectra (a1–a3) and XRD patterns (b1–b3). Notes: EDS indicated the mineral deposits consisted mainly of Ca, P, and Mg elements, and XRD further indicated the mineral deposits consisted mainly of Ca3Mg3(PO4)4 (Mg-substituted apatite).
Figure 10
Figure 10
Fluorescence staining images of PLA and PLA/Mg(OH)2 scaffolds: DAPI (a1–a9), phalloidin (b1–b9), merged (c1–c9). Notes: Observations on the struts of the composite scaffold reveal a greater number of cell nuclei. The strut with PLA/5Mg(OH)2 shows the highest density of spread-out actin, while no actin is observed in PLA/20Mg(OH)2, indicating that the appropriate addition of Mg(OH)2 promotes cell proliferation and growth.
Figure 11
Figure 11
ALP staining images of BMSCs after culturing for 7 and 14 days: PLA (a,d), PLA/5Mg(OH)2 (b,e), PLA/20Mg(OH)2 (c,f). Notes: More cells with a higher degree of staining are observed in PLA/5Mg(OH)2, but only a large amount of whisker-like substances are seen in PLA/20Mg(OH)2, indicating that the appropriate addition of Mg(OH)2 is beneficial for enhancing the osteogenic differentiation ability of cells.
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