Stereocomplexation Reinforced High Strength Poly(L-lactide)/Nanohydroxyapatite Composites for Potential Bone Repair Applications

Abstract

Composite materials composed of polylactide (PLA) and nano-hydroxyapatite (n-HA) have been recognized as excellent candidate material in bone repai The difference in hydrophilicity/hydrophobicity and poor interfacial compatibility between n-HA filler and PLA matrix leads to non-uniform dispersion of n-HA in PLA matrix and consequent poor reinforcement effect. In this study, an HA/PLA nanocomposite was designed based on the surface modification of n-HA with poly(D-lactide) (PDLA), which not only can improve the dispersion of n-HA in the poly(L-lactide) (PLLA) matrix but also could form a stereocomplex crystal with the matrix PLLA at the interface and ultimately lead to greatly enhanced mechanical performance The n-HA/PLA composites were characterized by means of scanning electron microscopy, Fourier transform infrared spectroscopy, X-Ray diffraction, thermal gravity analysis, differential scanning calorimetry, and a mechanical test; in vitro cytotoxicity of the composite material as well as its efficacy in inducing osteogenic differentiation of rat bone marrow stromal cells (rMSCs) were also evaluated. Compared with those of neat PLLA, the tensile strength, Young's modulus, interfacial shear strength, elongation at break and crystallinity of the composites increased by 34%, 53%, 26%, 70%, and 17%, respectively. The adhesion and proliferation as well as the osteogenic differentiation of rMSCs on HA/PLA composites were clearly evidenced. Therefore, the HA/PLA composites have great potential for bone repai.

Keywords: hydroxyapatite; mechanical property; nanocomposite; polylactide; stereocomplex.

Figure A1

SEM images of n-HA: (a,a’), acicular n-HA; (b,b’), clavate n-HA; (c,c’), schistose n-HA.

Figure 1

The basic physicochemical characterizations: (a) XRD pattern; (b) FTIR spectrum; and (c) TGA curv Particle size distributions of HA_1–3 and mHA_1–3: (d) HA₁ and mHA₁; (e) HA₂ and mHA₂; (f) HA₃ and mHA₃.

Figure 2

Stability of HA_1–3 and mHA_1–3 in chloroform. (a) Digital photos after 0 h and (b) after 12 h.

Figure 3

Mechanical properties of the mHA_1–3/PLA composites: (a,b), mHA₁/PLA; (c,d), mHA₂/PLA; (e,f), mHA₃/PLA.

Figure 4

Fractured surfaces of mHA_1–3/PLA nanocomposites: (a,a’), PLLA; (b,b’), mHA₁/PLA; (c,c’), mHA₂/PLA; (d,d’), mHA₃/PLA.

Figure 5

Polarized micrographs of mHA_1–3/PLA nanocomposites: (a/a’) PLLA; (b/b’) mHA₁/PLA; (c/c’) mHA₂/PLA; (d/d’) mHA₃/PLA.

Figure 6

DSC curves of mHA_1–3/PLA nanocomposites: (a) first cooling scan; (b) second heating scan.

Figure 7

XRD spectra of PLLA and the mHA_1–3/PLA composite.

Figure 8

Heat flux curves of PLLA and the mHA_1–3/PLA composites at various temperatures: (a) PLLA; (b) mHA₁(5%)/PLA; (c) mHA₂(5%)/PLA; (d) mHA₃(5%)/PLA.

Figure 9

Relative crystallinity curves of PLLA and the mHA_1–3/PLA composites at various temperatures: (a) PLLA; (b) mHA₁(5%)/PLA; (c) mHA₂(5%)/PLA; (d) mHA₃(5%)/PLA.

Figure 10

Relative crystallinity curves of PLLA and the mHA_1–3/PLA composites over time: (a) PLLA; (b) mHA₁ (5%)/PLA; (c) mHA₂ (5%)/PLA; (d) mHA₃ (5%)/PLA.

Figure 11

Biocompatibility of nanoparticles and nanocomposites: (a,b), hemolysis test; (c) cytotoxicity test; (d) the proliferation of rMSCs on composite surfac * refers to p < 0.05, ** refers to p < 0.01.

Figure 12

The expression of osteogenic markers of rMSCs on the surface of the composite: (a) AR-staining digital photos; (b) AR-staining light microscopy; (c) quantitative analysis by AR staining; (d) ALP activity; (e) the expression of osteocalcin (OCN: green fluorescence, nucleus: blue fluorescence). * refers to p < 0.05, ** refers to p < 0.01 and *** refers to p < 0.001.

Figure 13

Spreading of rMSCs on surface of nanocomposite film.