3D extrusion printing of density gradients by variation of sinusoidal printing paths for tissue engineering and beyond

During extrusion printing of pasty biomaterials, internal geometries are mainly adjusted by positioning of straightly deposited strands which does not allow realization of spatially adaptable density gradients in x-, y -and z-direction for anisotropic scaffolds or anatomically shaped constructs. Herein, an alternative concept for printing patterns based on sinusoidal curves was evaluated using a clinically approved cal-cium phosphate cement (CPC). Infill density in scaffolds was adjusted by varying wavelength and ampli-tude of a sinus curve. Both wavelength and amplitude factors were defined by multitudes of the applied nozzle diameter. For CPC as a biomaterial ink in bone application, porosity, mechanical stiffness and bi-ological response by seeded immortalized human mesenchymal stem cells - adhesion and pore bridging behavior - were investigated. The internal structure of a xyz-gradient scaffold was proven via X-ray based micro computed tomography (mu CT). Silicone was used as a model material to investigate the impact of printing velocity and strand distance on the shape fidelity of the sinus pattern for soft matter printing. The impact of different sinus patterns on mechanical properties was assessed. Density and mechanical properties of CPC scaffolds were successfully adjusted without an adverse effect on adhesion and cell number development. In a proof-of-concept experiment, a sinus-adjusted density gradient in an anatom-ically shaped construct (human vertebral body) defined via clinical computed tomography (CT) data was demonstrated. This fills a technological gap for extrusion-based printing of freely adjustable, continuously guidable infill density gradients in all spatial directions.Statement of significance 3D extrusion printing of biomaterials allows the generation of anatomically shaped, patient-specific im-plants or tissue engineering scaffolds. The density of such a structure is typically adjusted by the strand -to-strand distance of parallel, straight-meandered strands in each deposited layer. By printing in a si-nusoidal pattern, design of density gradients is possible with a free, spatial resolution in x-, y-and z -direction. We demonstrated that porosity and mechanical properties can be freely adapted in this way without an adverse effect on cell adhesion. With the example of a CT dataset of a human spine, the anisotropic pattern of a vertebral body was resembled by this printing technique that can be translated to various patterns, materials and application.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Printing patterns based on sinusoidal curves allows the adjustment of internal geometries and density gradients in biomaterials. The wavelength and amplitude of the sinus curve are varied to control the infill density in scaffolds, and the internal structure is confirmed by X-ray micro computed tomography. This technique fills a technological gap in extrusion printing for freely adjustable and continuously guidable density gradients in all spatial directions.