Coaxial 3D Bioprinting Process Research and Performance Tests on Vascular Scaffolds

Abstract

Three-dimensionally printed vascularized tissue, which is suitable for treating human cardiovascular diseases, should possess excellent biocompatibility, mechanical performance, and the structure of complex vascular networks. In this paper, we propose a method for fabricating vascularized tissue based on coaxial 3D bioprinting technology combined with the mold method. Sodium alginate (SA) solution was chosen as the bioink material, while the cross-linking agent was a calcium chloride (CaCl₂) solution. To obtain the optimal parameters for the fabrication of vascular scaffolds, we first formulated theoretical models of a coaxial jet and a vascular network. Subsequently, we conducted a simulation analysis to obtain preliminary process parameters. Based on the aforementioned research, experiments of vascular scaffold fabrication based on the coaxial jet model and experiments of vascular network fabrication were carried out. Finally, we optimized various parameters, such as the flow rate of internal and external solutions, bioink concentration, and cross-linking agent concentration. The performance tests showed that the fabricated vascular scaffolds had levels of satisfactory degradability, water absorption, and mechanical properties that meet the requirements for practical applications. Cellular experiments with stained samples demonstrated satisfactory proliferation of human umbilical vein endothelial cells (HUVECs) within the vascular scaffold over a seven-day period, observed under a fluorescent inverted microscope. The cells showed good biocompatibility with the vascular scaffold. The above results indicate that the fabricated vascular structure initially meet the requirements of vascular scaffolds.

Keywords: 3D bioprinting; biological scaffold; coaxial jet; finite element analysis; vascular network.

Figure 1

Schematic diagram of the theoretical model for each stage of the coaxial jet process.

Figure 2

(a) Runner 3D model, (b) element quality statistics, and (c) overall and local meshing.

Figure 3

Feed speed of 2 mm/s: (a) runner axial section pressure overall distribution cloud; (c) runner axial section velocity overall distribution cloud; (e) runner outlet velocity cloud; and (g) runner axial section local wall shear stress distribution cloud. Different feed rate: (b) outer runner axial pressure distribution curve; (d) inner runner axial velocity distribution curve; (f) runner radial velocity distribution curve; and (h) outer runner local radial wall shear stress distribution curve.

Figure 4

(a) Bioink form, (b) three-phase flow form.

Figure 5

(a) Vascular network 3D model, (b) element quality statistics, (c) overall and local meshing, (d) vascular network axial section pressure distribution cloud, (e) tributary vascular pressure distribution curve, (f) vascular network axial section velocity distribution cloud, and (g) tributary vascular velocity distribution curve.

Figure 6

(a) Schematic of local coupling, (b) blood vessel total deformation cloud, (c) blood vessel axial section equivalent stress cloud, and (d) blood vessel axial section equivalent elastic strain cloud.

Figure 7

(a) Schematic of fabrication process based on coaxial jet, (b) peristaltic pump, (c) experimental platform, and (d) coaxial nozzle.

Figure 8

Schematic of fabrication process based on mold method.

Figure 9

(a) Linear extrudate, (b) perfusion experiment, (c) the printability of vascular scaffolds, (d) effect of bioink concentration on duct diameter, (e) effect of cross-linking agent concentration on duct diameter, (f) effect of the flow rate of bioink on duct diameter, and (g) effect of cross-linking agent to bioink flow rate ratio on the ratio of inner to outer duct diameter.

Figure 10

Schematic of the fabrication process of vascular network scaffold. (a–c) Bifurcation structure at all levels of vascular structures, (d,e) integration of bifurcated and single-through structures, and (f) vascular network structure.

Figure 11

(a) Degradation rate curve of vascular scaffolds, (b) water absorption rate of vascular scaffolds with different concentrations of bioink, (c) ultimate stress and elastic modulus of vascular scaffolds with different concentrations of bioink and cross-linking agents, and (d) number of living cells and cell culture observation.