Mesoporous Bioactive Glass Functionalized 3D Ti-6Al-4V Scaffolds with Improved Surface Bioactivity

Abstract

Porous Ti-6Al-4V scaffolds fabricated by means of selective laser melting (SLM), having controllable geometrical features and preferable mechanical properties, have been developed as a class of biomaterials that hold promising potential for bone repair. However, the inherent bio-inertness of the Ti-6Al-4V alloy as the matrix of the scaffolds results in a lack in the ability to stimulate bone ingrowth and regeneration. The aim of the present study was to develop a bioactive coating on the struts of SLM Ti-6Al-4V scaffolds in order to add the desired surface osteogenesis ability. Mesoporous bioactive glasses (MBGs) coating was applied on the strut surfaces of the SLM Ti-6Al-4V scaffolds through spin coating, followed by a heat treatment. It was found that the coating could maintain the characteristic mesoporous structure and chemical composition of MBG, and establish good interfacial adhesion to the Ti-6Al-4V substrate. The compressive strength and pore interconnectivity of the scaffolds were not affected by the coating. Moreover, the results obtained from in vitro cell culture experiments demonstrated that the attachment, proliferation, and differentiation of human bone marrow stromal cells (hBMSCs) on the MBG-coated Ti-6Al-4V scaffolds were improved as compared with those on the conventional bioactive glass (BG)-coated Ti-6Al-4V scaffolds and bare-metal Ti-6Al-4V scaffolds. Our results demonstrated that the MBG coating by using the spinning coating method could be an effective approach to achieving enhanced surface biofunctionalization for SLM Ti-6Al-4V scaffolds.

Keywords: in vitro bioactivity; mesoporous bioactive glass; scaffold; selective laser melting; spin coating; titanium.

Figure 1

Overview of Ti-6Al-4V scaffolds (a); low-magnification view of scaffold struts showing macro pore sizes around 0.5 mm (b) together with an inserted high-magnification SEM image of the surface morphology of Ti-6Al-4V scaffold struts (c); BG-coated Ti-6Al-4V scaffold struts (d) and MBG-coated Ti-6Al-4V scaffold struts (e).

Figure 2

Cross-section morphology (a) of MBG-coated Ti-6Al-4V scaffold strut showing an interlayer and the MBG coating layer with a thickness of about 1 μm and EDS line scan analysis (from the red dot to the blue dot) showing interdiffusion of Si (b) and Ti (c) across the interlayer between the coating layer and substrate.

Figure 3

Grazing incidence X-ray diffraction (GIXRD) pattern of the MBG-coated Ti-6Al-4V scaffolds (a); nitrogen adsorption−desorption isotherms of the MBG powder (b); pore size distribution extracted from the N2 adsorption isotherms of the MBG powder (c); and TEM images for the MBG-coated Ti-6Al-4V scaffolds (d,e) with a well-ordered mesopore channel structure.

Figure 4

Compressive strengths (a) and porosity values (b) of the bare-metal Ti-6Al-4V scaffolds, BG-coated, and MBG-coated Ti-6Al-4V scaffolds.

Figure 5

SEM surface morphology (a,b) of the MBG-coated Ti-6Al-4V scaffolds soaked in SBF for seven days and EDS analysis (c) of the flaky structure.

Figure 6

Ion concentrations of (a) Si and (b) Ca in the Tris-HCl solution after soaking of the scaffolds for one, three, five, and seven days.

Figure 7

Confocal images showing the morphology and cytoskeleton of hBMSCs attached to the strut surfaces of the bare-metal Ti-6Al-4V, BG-coated Ti-6Al-4V and MBG-coated Ti-6Al-4V scaffolds at day 1 and day 7 (scale bar: 50 µm).

Figure 8

Viability of hBMSCs after culturing with the three groups of scaffolds for one, three, and seven days. (* p < 0.05, significant difference compared to the blank control).

Figure 9

Osteogenesis-related gene expression ALP of hBMSCs after culturing with the three groups of scaffolds on day 7 (* p < 0.05, significant difference compared to the blank control).