Enhanced cell attachment and hemocompatibility of titanium by nanoscale surface modification through severe plastic integration of magnesium-rich islands and porosification

Abstract

Besides the wide applications of titanium and its alloys for orthopedic and biomedical implants, the biocompatible nature of titanium has emerged various surface modification techniques to enhance its bioactivity and osteointegration with living tissues. In this work, we present a new procedure for nanoscale surface modification of titanium implants by integration of magnesium-rich islands combined with controlled formation of pores and refinement of the surface grain structure. Through severe plastic deformation of the titanium surface with fine magnesium hydride powder, Mg-rich islands with varying sizes ranging from 100 nm to 1000 nm can be integrated inside a thin surface layer (100-500 µm) of the implant. Selective etching of the surface forms a fine structure of surface pores which their average size varies in the range of 200-500 nm depending on the processing condition. In vitro biocompatibility and hemocompatibility assays show that the Mg-rich islands and the induced surface pores significantly enhance cell attachment and biocompatibility without an adverse effect on the cell viability. Therefore, severe plastic integration of Mg-rich islands on titanium surface accompanying with porosification is a new and promising procedure with high potential for nanoscale modification of biomedical implants.

Figure 1

Cross-sectional optical micrographs show the effect of MgH₂ preplacing and severe plastic integration on the microstructural features of titanium plates. (a) Ti surface before treatment. (b) Ti surface after plastic deformation at 1250 rpm for 15 s in the presence of MgH₂ powder. (c) Top-view SEM image indicates that the FSI process forms small pores on the surface. (d) Optical micrograph shows formation of different zones along the thickness of the titanium plate after FSI.

Figure 2

EDS elemental maps show the distribution of Mg (red dots) in the titanium matrix processed at rotational speeds of (a) 1250 rpm, (b) 800 rpm, and (c) 1600 rpm. The dwell time was 15 s. (d) XRD pattern indicates the formation of Mg islands inside the titanium matrix after FSI at 1250 rpm for 15 s. (e) XRD pattern determines that after chemical etching, Mg was etched out while characteristic peaks of MgH₂ are still visible.

Figure 3

Representative SEM images show porosification of the FSI-treated titanium plate after chemical etching for 30 s. The specimens were prepared at rotational speed of 1250 rpm with a dwell time of (a) 15 s, (b) 25 s, and (c) 35 s. (d) Pore coalescence forms large voids and cracks. (e) Histogram shows the distribution of pore sizes dependent on the dwell time (s)

Figure 4

Effect of surface treatment on the hardness of different zones for FSI-treated (1 and 3) Ti + MgH₂ and (2 and 4) Ti. The rotational speed and dwell time was (1 and 2) 800 rpm and 15 s and (3 and 4) 1250 rpm and 15 s.

Figure 5

Results of cell studies showing the effect of mechanical surface treatment and Mg-rich islands on the biocompatibility, cell attachment and hemocompatibility of examined titanium implants. (a) MTT assay incubation for 7 days indicates that cell viability is enhanced by the magnesium treatment. (b) Hemolysis reveals that the Mg-rich islands slightly improved blood compatibility of titanium. SEM images show L929 cell attchemt on the surface of FSI-treated titanium after 7 days of incubation. The processing condition was: (c) 1250 rpm for 15 s in the presence of MgH₂ and after 80 s chemical etching; (d) 1250 rpm for 15 s and after 80 s chemical etching; (e) 1250 rpm for 15 s in the presence of MgH₂; (f) 1250 rpm for 15 s.