Single-walled carbon nanotubes loaded hydroxyapatite-alginate beads with enhanced mechanical properties and sustained drug release ability

Abstract

Single-walled carbon nanotubes (SWCNTs) containing biomaterial with enhanced mechanical properties for the potential orthopedic application were synthesized and investigated. X-ray diffraction and X-ray fluorescence analysis were indications of the formation of calcium-deficient (Ca/P = 1.65) hydroxyapatite (HA) with a small carbonate content under influence of microwave irradiation. The investigated mechanical properties (maximal relative deformation, compressive strength and Young's modulus) of SWCNT loaded HA-alginate composites confirm their dependence on SWCNTs content. The compressive strength of HA-alginate-SWCNT and the HA-alginate control (202 and 159 MPa, respectively) lies within the values characteristic for the cortical bone. The addition of 0.5% SWCNT, in relation to the content of HA, increases the Young's modulus of the HA-alginate-SWCNT (645 MPa) compared to the SWCNT-free HA-alginate sample (563 MPa), and enhances the material shape stability in simulated physiological conditions. Structural modeling of HA-alginate-SWCNT system showed, that physical adsorption of SWCNT into HA-alginate occurs by forming triple complexes stabilized by solvophobic/van der Waals interactions and H-bonds. The high-performance liquid chromatography demonstrated the influence of SWCNTs on the sustained anaesthesinum drug (used as a model drug) release (456 h against 408 h for SWCNT-free sample). Cell culture assay confirmed biocompatibility and stimulation of osteoblast proliferation of 0.05% and 0.5% SWCNT-containing composites during a 3-day cultivation. All these facts may suggest the potential possibility of using the SWCNT-containing materials, based on HA and alginate, for bone tissue engineering.

Keywords: Alginate; Drug release; Hydroxyapatite; Mechanical properties; Single-walled carbon nanotubes.

Fig. 1

TEM image of fabricated SWCNTs

Fig. 2

SEM images of the samples surface: HA-alginate (a), HA-alginate-0.05SWCNT (b) and HA-alginate-0.5SWCNT (c) at different magnifications

Fig. 3

FTIR spectra of the prepared samples

Fig. 4

Calculated spatial structures of HA-alginate-SWCNT triple complex (a, b—different views)

Fig. 5

Water uptake (swelling; S_w) and water retention (E_r) ability of HA-alginate, HA-alginate-0.05SWCNT and HA-alginate-0.5SWCNT composites after 24 h (p ≤ 0.05)

Fig. 6

Strength (σ_c) of the experimental composites (a); ‘loading–unloading’ diagrams during three loading cycles (b, c, d), measured at uniaxial compression

Fig. 7

HPLC pattern from test samples: release of AnS from HA-alginate-0.5SWCNT (a); release of the degradation products in 408 h of sample exposure (b)

Fig. 8

Concentration of AnS in PBS (µg/mL), released from the experimental samples for 480 h (p ≤ 0.05)

Fig. 9

Optical images of cell human primary osteoblasts on day 3 after cultivation on tissue culture plastic (a), HA-alginate (b) and HA-alginate-0.5SWCNT (c) and Resazurin reduction data on day 1 and day 3 (d) (p ≤ 0.05). Red arrows show the degradation products