A mosaic structure multi-level vascular network design for skull tissue engineering

Thermally reversible hydrogels printing of customizable bio-channels with curvature

Replicating intricate bio-channels, akin to expansive vascular networks, offers numerous advantages including self-repair, replacing damaged bio-channels, testing drugs, and biomedical devices. But, crafting multi-sized, editable bio-channels with specific curvatures, particularly using natural polymer-based bio-inks, poses a significant challenge. To address this, this study introduces a temperature-driven indirect printing method, exemplified by the diploic vein. Here, K-carrageenan (kca)-silk fiber (SF)-hyaluronic acid (HA)/hFOB 1.19 (SV40 transfection of human osteoblasts) and kca-collagen-HA/HUVECs (human umbilical vein endothelial cells) are employed to fabricate vascular-like walls and lumens, utilizing their thermoreversible properties to create multi-stage bifurcated lumens. Precise spatial curvature was generated by heating the vascular network wrapped in poly(N-isopropyl acrylamide) (PNIPAAm)-poly(ethylene glycol) diacrylate (PEGDA). Since temperature is specific to the thermal material carrying the cells, the rheological properties of bioinks, modeling temperature parameters, and their impact on printing size was explored. Additionally, mechanical properties and curvature response were characterized to determine the necessary process parameters for achieving the desired size. Ultimately, in vitro bioprinting experiments involving HUVECs and hFOB 1.19 demonstrate cell viability, adhesion, proliferation, and migration within the intraluminal hydrogel scaffold. This approach allows for customizing bio-channel content and controlling curvature programming, providing new prospects for in vitro biochannel production, with potential benefits for pathology research.

In silico analysis of a hierarchical microfluidic vascular network: Detecting the location of angiogenic sprouting

Lack of oxygen is one of the leading causes of failure in engineered tissue. Therefore, angiogenesis will be necessary for the survival of larger tissues in vivo. In addition, a proper lymphatic system that plays an essential role in relieving inflammation and maintaining tissue homeostasis is of great importance for tissue regeneration and repair. Many biomechanical parameters are involved in controlling angiogenesis and capillary network generation, which are challenging to study and control in experimental studies or in vitro. In the present study, using numerical modeling, the effect of various geometric and biomechanical parameters in creating suitable conditions for angiogenesis was investigated. Furthermore, sprouting points were predicted using flow dynamics. For this purpose, a porous scaffold, flow channels with parametric geometry that followed Murray's law, and a drainage channel were considered. Results suggested that the geometry of the microfluidic channels and the characteristics of the vessel wall and scaffold plays a complementary role in determining the transmural pressure. It was found that a twofold increase in the vascular hydraulic conductivity can reduce the minimum transmural pressure by up to 28% and increase the drainage flow rate by 44%. In addition, the minimum magnitude of transmural pressure tends to zero for scaffold's hydraulic conductivity values smaller than 10^-11  m³ s kg^-1 . The results of this study can be used in optimizing the design of the relevant microfluidic systems to induce angiogenesis and avoid leakage in the constructed implantable tissue.

Adjusting the accuracy of PEGDA-GelMA vascular network by dark pigments via digital light processing printing

Vascularization is one of the most important factors greatly influencing scaffold regeneration. In this study, a precise network of hollow vessels was printed by digital light processing (DLP) with poly(ethylene glycol) diacrylate (PEGDA)/gelatin-methacryloyl (GelMA), and dark pigmentation absorbers were added to ensure printing accuracy. First, the compound bio-inks of the PEGDA-GelMA hydrogel were prepared for direct vascular printing, and a high-precision DLP system was established. Second, the printing effects of three dark absorbers, namely, nigrosin, brilliant black, and brilliant blue, on the x-, y-, and z-axes were studied. By printing models with different densities, it was determined that 0.2% nigrosin, 0.1% brilliant black, and 0.3% brilliant blue had better effects on the x- and y-axes accuracy, and the absorbance of the absorbers played a decisive role in adjusting the accuracy. Additionally, to solve the problem of uneven curing on the upper and lower surfaces caused by the addition of an absorber with high absorbance, a model of the difference in curing width between the upper and lower surfaces of a unit-layer slice based on high-absorbance absorbers was established, and the reference value for the slice thickness was calculated. Third, the biological and mechanical properties of the bio-inks were verified with scanning electron microscopy and Fourier transform infrared, and by tensile, swelling, degradation, and cytotoxicity tests on different concentrations of PEGDA-GelMA hydrogel and absorbers. The results showed that 30% PEGDA-7% GelMA/0.1% brilliant black was the optimal preparation to print a hollow vascular network. The error of the printing tube wall and cavity was between 1% and 3%, which demonstrates the high precision of the method. Human umbilical vein endothelial cells were planted in the lumen, and the survival rate achieved 107% on the seventh day, demonstrating the good biocompatibility of the composite hydrogel.