A remaining challenge in tissue engineering approaches is the in vitro vascularization of engineered constructs or tissues. Current approaches in engineered vascularized constructs are often limited in the control of initial vascular network geometry, which is crucial to ensure full functionality of these constructs with regard to cell survival, metabolic activity, and potential differentiation ability. Herein, the combination of 3D-printed poly-ε-caprolactone scaffolds via melt electrospinning writing with the cell-accumulation technique to enable the formation and control of capillary-like network structures is reported. The cell-accumulation technique is already proven itself to be a powerful tool in obtaining thick (50 µm) tissues and its main advantage is the rapid production of tissues and its ease of performance. However, the applied combination yields tissue thicknesses that are doubled, which is of outstanding importance for an improved handling of the scaffolds and the generation of clinically relevant sample volumes. Moreover, a correlation of increasing vascular endothelial growth factor secretion to hypoxic conditions with increasing pore sizes and an assessment of the formation of neovascular like structures are included.

High-throughput screening of drug diffusion and cell transports from the blood-/lymph-capillary (BC/LC) networks to the peripheral cells in 3D engineered tissues using a microplate would make a powerful tool for in vitro pharmacokinetic assessments. Here, perfusable BC/LC networks embedded in 3D-tissues inside a 24-microplate using a cell-coating technology are reported which allows location control of cell layers. Arrangement of an endothelial cell layer at the top, middle, and bottom of dermal fibroblast tissues provides an interconnected BC/LC networks possessing open pores on both surfaces. When fluorescently labeled dextran, microparticles, and red blood cells are applied to the top surfaces, diffusion and penetration through the networks are observed depending on the size of the substances. Moreover, BC networks mimick a series of in vivo processes of cancer metastasis, extravasation, growth, and growth suppression with drug treatment. The perfusable networks existing in 3D-tissues show great potential for in vitro pharmacokinetic studies.

Caco-2, human colon carcinoma cell line, has been widely used as a model system for intestinal epithelial permeability because Caco-2 cells express tight-junctions, microvilli, and a number of enzymes and transporters characteristic of enterocytes. However, the functional differentiation and polarization of Caco-2 cells to express sufficient tight-junctions (a barrier) usually takes over 21 days in culture. This may be due to the cell culture environment, for example inflammation induced by plastic petri dishes. Three-dimensional (3D) sufficient cell microenvironments similar to in vivo natural conditions (proteins and cells), will promote rapid differentiation and higher functional expression of tight junctions. Herein we report for the first time an enhancement in tight-junction formation by 3D-cultures of Caco-2 cells on monolayered (1L) and eight layered (8L) normal human dermal fibroblasts (NHDF). Trans epithelial electric resistance (TEER) of Caco-2 cells was enhanced in the 3D-cultures, especially 8L-NHDF tissues, depending on culture times and only 10 days was enough to reach the same TEER value of Caco-2 monolayers after a 21 day incubation. Relative mRNA expression of tight-junction proteins of Caco-2 cells on 3D-cultures showed higher values than those in monolayer structures. Transporter gene expression patterns of Caco-2 cells on 3D-constructs were almost the same as those of Caco-2 monolayers, suggesting that there was no effect of 3D-cultures on transporter protein expression. The expression correlation between carboxylesterase 1 and 2 in 3D-cultures represented similar trends with human small intestines. The results of this study clearly represent a valuable application of 3D-Caco-2 tissues for pharmaceutical applications.

In article https://doi.org/10.1002/smll.201701521, Mitsuru Akashi, Jürgen Groll, and co‐workers use a cell‐accumulation technique for the controlled formation of tubular structures in cellular constructs. The image is a confocal laser scanning microscopy image showing HUVECs attached to polycaprolactone scaffolds with 100 μm pores produced by melt electrowriting after 1 day of incubation.