3D Plotting of Calcium Phosphate Cement and Melt Electrowriting of Polycaprolactone Microfibers in One Scaffold: A Hybrid Additive Manufacturing Process

Abstract

The fabrication of patient-specific scaffolds for bone substitutes is possible through extrusion-based 3D printing of calcium phosphate cements (CPC) which allows the generation of structures with a high degree of customization and interconnected porosity. Given the brittleness of this clinically approved material, the stability of open-porous scaffolds cannot always be secured. Herein, a multi-technological approach allowed the simultaneous combination of CPC printing with melt electrowriting (MEW) of polycaprolactone (PCL) microfibers in an alternating, tunable design in one automated fabrication process. The hybrid CPC+PCL scaffolds with varying CPC strand distance (800–2000 µm) and integrated PCL fibers featured a strong CPC to PCL interface. While no adverse effect on mechanical stiffness was detected by the PCL-supported scaffold design; the microfiber integration led to an improved integrity. The pore distance between CPC strands was gradually increased to identify at which critical CPC porosity the microfibers would have a significant impact on pore bridging behavior and growth of seeded cells. At a CPC strand distance of 1600 µm, after 2 weeks of cultivation, the incorporation of PCL fibers led to pore coverage by a human mesenchymal stem cell line and an elevated proliferation level of murine pre-osteoblasts. The integrated fabrication approach allows versatile design adjustments on different levels.

Materials Design Innovations in Optimizing Cellular Behavior on Melt Electrowritten (MEW) Scaffolds

“…The MEW fibers provided additional structural integrity and generally improved the infiltration of cells within the larger pores of the CP structure, providing an increased density of anchor points for cell attachment and stimulating rapid cell proliferation whilst only minimally impacting overall scaffold porosity (Figure 4A). [134] Staples et al (2022) utilized a gradient of pore sizes to mimic the periodontal ligament and bone respectively, and demonstrated precision control over cellular alignment using parallel fibers spaced 100 μm apart compared to the random orientation of cells on larger pore scaffolds (Figure 4B). [135] Ye et al (2020) vastly improved the cell seeding efficiency and structural integrity of MEW scaffolds by electrospinning a gelatin methacrylate (GelMA) hydrogel fiber membrane to create a multi-layer composite construct (Figure 4C).…”

Definition, measurement, and function of pore structure dimensions of bioengineered porous bone tissue materials based on additive manufacturing: A review

“…This technique is mainly used to extrude solid or slurry materials in 2D planes according to a specific scanning path and form a planar structure with pore morphology. It is followed by superimposing multiple planar structures with a certain thickness in the Z axis sequentially to finally build pore structures of porous materials ( Cubo-Mateo and Rodriguez-Lorenzo, 2020 ; Sakthiabirami et al, 2021 ; Yang et al, 2021 ; Kilian et al, 2022 ). Considering this molding technology’s characteristics, the prepared material’s structure in the 2D plane can be controlled.…”

“…Therefore, the literature continues to use pore size as a specific parameter to define the pore structure dimension, defining it as the spacing of two parallel rods in a 2D plane ( Shanjani et al, 2017 ; Gupta et al, 2021 ). However, some literature ignores the rod diameter size and uses the scan spacing directly as the pore size ( Kilian et al, 2022 ). Nevertheless, according to the original definition of pore size and pore throat size, such parameters should be defined as the pore throat size in the 2D plane, not pore size in 3D space.…”

“…Currently, the pore structure design used for bioengineered porous bone tissue materials mainly includes two approaches: regular and irregular pore structures. In this line, there are two main technical solutions to constructing a regular pore structure: through the regular arrangement of rod structures in 2D planes and through the superposition of 2D planes in the Z axis ( Cubo-Mateo and Rodriguez-Lorenzo, 2020 ; Sakthiabirami et al, 2021 ; Kilian et al, 2022 ). On the other hand, rod structures form the unit cells in 3D spaces through angular connections, and then the whole structure is formed by stacking the unit cells in the X/Y/ Z axes ( Li et al, 2018a ; Li et al, 2018b ).…”

Generation of Controlled Micrometric Fibers inside Printed Scaffolds Using Standard FDM 3D Printers

“…Recently, a multi-technological approach allowed for the simultaneous combination of calcium phosphate cement (CPC) printing with MEW of polycaprolactone (PCL) microfibers in an alternating, tuneable design in one automated fabrication process [ 15 ]. The hybrid CPC+PCL scaffolds featured a strong interface and the microfiber integration led to an improvement in integrity.…”