Robocasting
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High-performance bioceramics such as zirconia, alumina, and their composites, are attractive materials for the fabrication of load-bearing bone implants because of their outstanding mechanical properties, biocompatibility, corrosion resistance, and aesthetic quality. A suitable level of porosity and pore sizes with a few hundred microns are required for a good bone integration of the scaffolds. This requirement can be achieved through additive manufacturing, like robocasting. For this purpose, the optimization of colloidal inks is one of paramount importance as the rheological properties of the inks determine the quality of the three-dimensional structures. This target has not been satisfactorily accomplished in previous research works. The present study aims at closing this gap by carrying out a systematic investigation about the influence of the most important parameters that determine the printing ability of zirconia inks. The dispersing ability of the zirconia powder was studied in order to maximize the solids loading while keeping a high degree of homogeneity of the starting suspensions. The viscoelastic properties of the suspensions were then altered by adding suitable doses of a coagulating agent to obtain easily extrudable pastes for the robocasting process. The green samples were dried and sintered at the heating rate of 1ºC/min up to 600ºC, an holding at this temperature for 1 h, followed by an heating rate of 5ºC/min up to 1350ºC and holding for 1 h at this temperature, and then cooling down to room temperature. Zirconia inks with high fraction of solids (48 vol.%) could be successfully prepared. The extruded cylinders exhibited an excellent shape retention in scaffolds with different macropore sizes (200, 300, 400 and 500 mm).
The purpose of this study is to analyze the mechanical enhancement provided by nanocomposite coatings deposited on robocast 45S5 bioglass (BG) scaffolds for bone tissue regeneration. In particular, a nanocomposite layer consisting of hydroxyapatite (HA) nanoparticles, as reinforcing phase, in a polycaprolactone (PCL) matrix was deposited onto the surface of the BG struts conforming the scaffold. Three different HA nanopowders were used in this study. The effect of particle size and morphology of these HA nanopowders on the mechanical performance of 45S5 BG scaffolds is evaluated.
Biphasic calcium phosphate (BCP) scaffolds were successfully produced by robocasting. The BCP powder was prepared by hydrothermal synthesis (150°C for 4 h) and calcined at 1000°C. The as-obtained powder was milled to obtain A suitable particle size distribution (PSD) for optimizing the rheological properties of the suspensions and pastes prepared thereof. Scaffolds with different pore dimensions (300x300, 500x500, 250x500 and 300x600 μm) were prepared by extruding the pastes through 410 μm diameter nozzles. The green scaffolds were dried and posteriorly sintered at 1100°C. The compressive strength of the sintered scaffolds was well within the range of the mechanical properties reported from cancellous bone, being intrinsically related with the particle size distribution. Moreover, the obtained scaffolds demonstrated to have good biomineralization ability. The obtained scaffolds by robocasting revealed to possess promising features for their applications in bone regeneration and tissue engineering.
