Alternative Geometries for 3D Bioprinting of Calcium Phosphate Cement as Bone Substitute

Abstract

In the literature, many studies have described the 3D printing of ceramic-based scaffolds (e.g., printing with calcium phosphate cement) in the form of linear structures with layer rotations of 90°, although no right angles can be found in the human body. Therefore, this work focuses on the adaptation of biological shapes, including a layer rotation of only 1°. Sample shapes were printed with calcium phosphate cement using a 3D Bioplotter from EnvisionTec. Both straight and wavy spokes were printed in a round structure with 12 layers. Depending on the strand diameter (200 and 250 µm needle inner diameter) and strand arrangement, maximum failure loads of 444.86 ± 169.39 N for samples without subsequent setting in PBS up to 1280.88 ± 538.66 N after setting in PBS could be achieved.

About the Mechanical Strength of Calcium Phosphate Cement Scaffolds

“…Raymond et al [36] described a similar 3D plotting with 10% overlapping strands. As in Blankenburg et al [28], there were no significant differences in the surface roughness of the scaffolds regardless of whether the samples were incubated in PBS or not. There were also no significant differences in surface roughness between the two needles with a 200 and 250 µm inner diameter.…”

“…In previous works [33,34], cube-shaped geometries were printed using patterns from the Visual Machines software (EnvisionTec, Gladbeck, Germany). In one of our previous works [28], round structures with a layer rotation of 1 • showed good results regarding mechanical strength, but were limited to 12 layers. In addition, there were printing errors such as delamination of the layers.…”

“…This is due to the fact that water was sprayed every five to seven layers during 3D printing for intermediate consolidation of the green bodies in order to prevent the samples from slumping. In the work of Blankenburg et al [28], only 12 layers of maximum height could be achieved before printing defects such as delamination occurred. By spraying with water, more than 12 layers could be printed.…”

“…In this work, both systems, namely sintered ceramics and 3D-printed CPC scaffolds, were to be compared with regard to their mechanical properties [22,26] to determine if 3D-printed scaffolds exhibited similar mechanical properties to bone. To achieve this, we first focused on 3D printing more than 12 layers [27][28][29] so that we could produce comparably sized specimens. The working hypotheses were that (1) as the number of layers increased, the mechanical strength of the 3D-printed CPC scaffolds would increase and (2) the internal needle diameter would influence the mechanical strength, which would better mimic the mechanical strength of the bone than what is possible with sintered ceramics.…”

“…Thus, the first task was to determine the optimal printing parameters. In a previous work, these printing parameters were determined using the "Parameter Tuning" of the "Visual Machines" software [28]. For this purpose, several lines were printed where pressure and speed were varied.…”