Multilayered Blood Capillary Analogs in Biodegradable Hydrogels for In Vitro Drug Permeability Assays

Blood capillaries are crucial for the biological evaluation of drug diffusion to target tissues, and the penetration of cancer cells or viruses. Since most capillaries have a bilayered structure consisting of a monolayer of endothelial cells (ECs) and surrounding smooth muscle cells (SMCs), the in vitro reconstruction of this bilayered structure is a key challenge for pharmaceutical and biomedical applications. Here, a unique technology to construct size, length, orientation, and layer-number controllable blood capillary networks in biodegradable hydrogels is reported. Uniaxial microchannels are prepared inside biodegradable hydrogels by the simple extraction of silica capillary tubes. The channel size, length, and distance of the uniaxial channels are easily controlled by altering these parameters of the silica tubes. The inner surfaces of the channels are successfully covered by bilayered structures consisting of ECs and SMCs by a hierarchical cell manipulation technique. Notably, serum albumin, which has an approximately 8 nm size, cannot penetrate this capillary wall during several hours of incubation due to the high blood vessel wall barrier property. This suggests a successful reconstruction of multilayered blood capillary networks possessing similar barrier function as native blood capillaries. Moreover, these capillary networks can be completely collected by the selective degradation of the surrounding hydrogels. This technique will be an innovative and versatile approach for in vitro permeability assays of drugs, drug delivery carriers, and cancer cells.