Titanium Scaffolds by Direct Ink Writing: Fabrication and Functionalization to Guide Osteoblast Behavior

Abstract

Titanium (Ti) and Ti alloys have been used for decades for bone prostheses due to its mechanical reliability and good biocompatibility. However, the high stiffness of Ti implants and the lack of bioactivity are pending issues that should be improved to minimize implant failure. The stress shielding effect, a result of the stiffness mismatch between titanium and bone, can be reduced by introducing a tailored structural porosity in the implant. In this work, porous titanium structures were produced by direct ink writing (DIW), using a new Ti ink formulation containing a thermosensitive hydrogel. A thermal treatment was optimized to ensure the complete elimination of the binder before the sintering process, in order to avoid contamination of the titanium structures. The samples were sintered in argon atmosphere at 1200 °C, 1300 °C or 1400 °C, resulting in total porosities ranging between 72.3% and 77.7%. A correlation was found between the total porosity and the elastic modulus of the scaffolds. The stiffness and yield strength were similar to those of cancellous bone. The functionalization of the scaffold surface with a cell adhesion fibronectin recombinant fragment resulted in enhanced adhesion and spreading of osteoblastic-like cells, together with increased alkaline phosphatase expression and mineralization.

Multifunctional homogeneous calcium phosphate coatings: Toward antibacterial and cell adhesive titanium scaffolds

“…An EDX mapping of a cryofractured Ti scaffold (Fig. 2A), showed mostly the presence of titanium on both the external surface and the freshly created fractured surface, with only a minor presence of C in the surface on the strut, as reported in a previous characterization of these type of scaffolds [9]. In contrast, the EDX mapping of a cryofractured coated scaffold (Fig.…”

“…Concerning to ultimate strength results, the measured values were closer to those described in the literature for human cancellous bone (~40MPa) than to cortical bone (~190MPa) [48,49]. Therefore, the tested scaffolds, with a porosity of 73.9%, may be considered as potential substitutes for human cancellous bone [9].…”

“…5). Besides, Young's modulus values are higher than those measured in previous studies (0.63 ± 0.01 GPa) [9]. The differences may be attributed to differences in the sintering process.…”

“…Ti ink was prepared by mixing irregular Ti powder (~325 mesh, 99.5% purity, Alfa Aesar, USA) with Pluronic® F127 hydrogel 30% w/v. The development of the Ti ink and the posterior thermal treatment was previously optimized [9]. Briefly, 69% w/w of Ti powder was mixed with 31% w/w of Pluronic® hydrogel in a centrifuge (Speedmixer, DAC 150.1 FVZ-K) for 5 min at 3500 rpm.…”

“…Furthermore, the coating thickness was analyzed by studying cross-sectional SEM images of three samples that were previously immersed in liquid nitrogen and fractured. Energy-dispersive Xray spectroscopy (EDX) analyses of cryofractured samples were acquired with a FE-SEM JEOL JSM-7001F (Jeol, Tokyo, Japan) complemented fabrication parameters were discussed [9]. The main advantage of this technique compared to powder-bed processes rests on the fact that no depowering process is needed.…”