Halloysite nanotubes loaded with nano silver for the sustained-release of antibacterial polymer nanocomposite scaffolds

doi:10.1016/j.jmst.2019.11.019

Abstract

Abstract:

It is challenging for antibacterial polymer scaffolds to achieve the drug sustained-release through directly coating or blending. In this work, halloysite nanotubes (HNTs), a natural aluminosilicate nanotube, were utilized as a nano container to load nano silver (Ag) into the lumen through vacuum negative-pressure suction & injection and thermal decomposition of silver acetate. Then, the nano Ag loaded HNTs (HNTs@Ag) were introduced to poly-l-lactic acidide) (PLLA) scaffolds prepared by additive manufacturing for the sustained-release of Ag⁺. Acting like a 'shield', the tube walls of HNTs not only retarded the erosion of external aqueous solution on internal nano Ag to generate Ag⁺ but also postponed the generated Ag⁺ to diffuse outward. The results indicated the PLLA-HNTs@Ag nanocomposite scaffolds achieved a sustained-release of Ag⁺ over 28 days without obvious initial burst release. Moreover, the scaffolds exhibited a long-lasting antibacterial property without compromising the cytocompatibility. Besides, the degradation properties, biomineralization ability and mechanical properties of the scaffolds were increased. This study suggests the potential application of inorganic nanotubes as drug carrier for the sustained-release of functional polymer nanocomposite scaffolds.

Key words: Halloysite nanotubes, Nano silver, Sustained-release, Antibacterial properties, Polymer nanocomposite scaffolds

Wang Guo, Wei Liu, Li Xu, Pei Feng, Yanru Zhang, Wenjing Yang, Cijun Shuai. Halloysite nanotubes loaded with nano silver for the sustained-release of antibacterial polymer nanocomposite scaffolds[J]. J. Mater. Sci. Technol., 2020, 46: 237-247.

Figures/Tables 9

Fig. 1. A schematic diagram illustrating the loading of nano Ag into the lumen of HNTs to construct a shell@core structured HNTs@Ag nanosystem through vacuum negative-pressure suction & injection and thermal decomposition of CH3COOAg. (a) HNTs are suspended in the CH3COOAg solution; (b) the vacuum removes air bubbles from the lumen of HNTs; (c) the CH3COOAg solution enters into the lumen of HNTs when the vacuum is broken; (d) washing, centrifuging and drying; and (e) thermal decomposition at 380 ℃ to produce nano Ag loaded HNTs.

Fig. 2. (a) The XRD patterns and (b) FTIR of HNTs and HNTs@Ag powders. (c, g) STEM, (d, h) TEM, (e, i) HRTEM and (f, j) SAED of (c?f) HNTs and (g?j) HNTs@Ag powders.

Fig. 3. (a) The preparation of PLLA-HNTs@Ag powders and the SEM morphology of powders; (b) a schematic diagram describing the preparation of PLLA-HNTs@Ag scaffolds by SLS and photographs of a representative porous scaffold; (c) the XRD patterns and (d) FTIR of PLLA-HNTs@Ag scaffolds. Note: HNTs@Ag was detected in the scaffolds.

Fig. 4. (a) The cumulative release concentration of Ag+ after soaking in deionized water for different time; (b) the average release concentration of Ag+ during different soaking periods; note: the result indicated Ag+ showed a sustained-release for 28 days and its release concentration can be adjusted by changing the content of HNTs@Ag; (c) a schematic diagram illustrating a possible mechanism of sustained-release of Ag+ from the scaffolds with a five-stage process, as discussed in the text.

Table 1 Release kinetic parameters of Ag+ from PLLA/HNTs@Ag scaffolds from fitting with the Ritger-Peppas model.

Samples	n	k	R²
PLLA-2%HNTs@Ag	0.35425	10.22581	0.98419
PLLA-4%HNTs@Ag	0.36839	7.44011	0.9819
PLLA-6%HNTs@Ag	0.34746	8.15246	0.98111
PLLA-8%HNTs@Ag	0.33022	9.52626	0.97514

Fig. 5. (a?c) Photographs of the PLLA-HNTs@Ag scaffolds after disk diffusion test for 3, 7, and 14 days; (d) the diameter of the inhibition zones; (e?i) the adhesion morphology of E. coil on the scaffolds after culture for one day. Note: the results indicated that HNTs@Ag endowed the scaffolds with a long-lasting and strong antibacterial property.

Fig. 6. The cytocompatibility of the PLLA/HNTs@Ag scaffolds tested by MG63 cells. (a?j) fluorescence staining images of MG63 cells after culture on the scaffolds for 1 and 3 days; (k) the CCK-8 assay of MG63 cells after culture on the scaffolds for 1, 3 and 5 days; (l?o) ALP staining images of MG63 cells after culture on the scaffolds for 5 days. Note: the results indicated the scaffolds supported the cell proliferation and osteogenic differentiation.

Fig. 7. (a) The mass loss of PLLA-HNTs@Ag scaffolds and (b) the pH of PBS after soaking test for different days; (c?h) the surface morphology of the scaffolds after soaking in SBF for 28 days. Note: the results indicated that HNTs@Ag improved the degradability and biomineralization ability of the scaffolds.

Fig. 8. (a?e) The distribution of HNTs@Ag in the PLLA matrix of the scaffolds with 0 to 8 wt% HNTs@Ag; (f) EDS spectra of S1, S2, and S3; (g) the compressive strength and modulus and (h) hardness of PLLA-HNTs@Ag scaffolds. Note: HNTs@Ag achieved a relatively uniform distribution in the PLLA matrix at relatively low contents, thereby keeping increase of the compressive strength and modulus and hardness with increasing its content; nevertheless, excessive HNT@Ag resulted in obvious aggregates and weakened the reinforcing effects.

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