Adapting the Pore Size of Individual, 3D-Printed CPC Scaffolds in Maxillofacial Surgery

Abstract

Three dimensional (3D) printing allows additive manufacturing of patient specific scaffolds with varying pore size and geometry. Such porous scaffolds, made of 3D-printable bone-like calcium phosphate cement (CPC), are suitable for bone augmentation due to their benefit for osteogenesis. Their pores allow blood-, bone- and stem cells to migrate, colonize and finally integrate into the adjacent tissue. Furthermore, the pore size affects the scaffold’s stability. Since scaffolds in maxillofacial surgery have to withstand high forces within the jaw, adequate mechanical properties are of high clinical importance. Although many studies have investigated CPC for bone augmentation, the ideal porosity for specific indications has not been defined yet. We investigated 3D printed CPC cubes with increasing pore sizes and different printing orientations regarding cell migration and mechanical properties in comparison to commercially available bone substitutes. Furthermore, by investigating clinical cases, the scaffolds’ designs were adapted to resemble the in vivo conditions as accurately as possible. Our findings suggest that the pore size of CPC scaffolds for bone augmentation in maxillofacial surgery necessarily needs to be adapted to the surgical site. Scaffolds for sites that are not exposed to high forces, such as the sinus floor, should be printed with a pore size of 750 µm to benefit from enhanced cell infiltration. In contrast, for areas exposed to high pressures, such as the lateral mandible, scaffolds should be manufactured with a pore size of 490 µm to guarantee adequate cell migration and in order to withstand the high forces during the chewing process.

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

“…Ahlfeld et al [ 25 ] incubated their biphasic scaffolds in CaCl 2 and achieved an increase in compressive strength from 0.5 to 0.7 MPa compared to the untreated specimens. Compared to this, the compressive strengths of our scaffolds were in a similar range to Mullah et al [ 17 ] between 5 and 25 MPa. In our other works [ 27 ], we also investigated the compressive strength of PCL scaffolds with different inner and outer geometries.…”

“…Depending on the pore size (in µm), the scaffolds broke at 543.6 ± 35 N (500 µm), 243.4 ± 34.1 N (700 µm), and 117.5 ± 43.4 N (1000 µm). Compared to the inversely printed scaffolds, we reached similar values, with maximum failure loads between 500 and 1400 N. Muallah et al [ 17 ] achieved compressive strengths of 5.2 ± 0.6 to 31.3 ± 6.8 MPa for square scaffolds, depending on the strand spacing and pore sizes. Ahlfeld et al [ 25 ] incubated their biphasic scaffolds in CaCl 2 and achieved an increase in compressive strength from 0.5 to 0.7 MPa compared to the untreated specimens.…”

“…In previous works [ 16 , 17 ], cube-shaped geometries were printed using patterns from the Visual Machines software (EnvisionTec, Gladbeck, Germany). The goal was to print round structures and avoid 90° angles.…”

Physicochemical properties of bone marrow mesenchymal stem cells encapsulated in microcapsules combined with calcium phosphate cement and their ectopic bone formation

“…A notable limitation of high porosity is a decrease in CPC compressive strength. However, in nonload-bearing areas, such as the craniomaxillofacial region, new bone formation at the expense of mechanical strength is acceptable ( Muallah et al, 2021 ).…”

Investigation of Patient-Specific Maxillofacial Implant Prototype Development by Metal Fused Filament Fabrication (MF3) of Ti-6Al-4V

“…The printed samples were characterized for density using the Archimedes method, refer Table 3 The optical micrographs revealed considerable porosities with sizes of 50 µm as shown in Figure 10a. A porosity of 750 µm seems to be the best for cell infiltration while smaller pores provide higher mechanical properties [39]. Using 3D printing, the size of the pores can be adapted to a specific purpose.…”