Creating vascular networks in tissues is crucial for tissue engineering. Although recent studies have demonstrated the formation of vessel-like structures in a tissue model, long-term culture is still challenging due to the lack of active perfusion in vascular networks. Here, we present a method to create a three-dimensional cellular spheroid with a perfusable vascular network in a microfluidic device. By the definition of the cellular interaction between human lung fibroblasts (hLFs) in a spheroid and human umbilical vein endothelial cells (HUVECs) in microchannels, angiogenic sprouts were induced from microchannels toward the spheroid; the sprouts reached the vessel-like structures in a spheroid to form a continuous lumen. We demonstrated that the vascular network could administer biological substances to the interior of the spheroid. As cell density in the spheroid is similar to that of a tissue, the perfusable vasculature model opens up new possibilities for a long-term tissue culture in vitro.

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Conformational changes in cystine disulfide bridges of bovine serum albumin during acid-induced isomerization (N -»F and F -> E transitions) have been studied with Raman spectroscopy. In an X-ray crystallographic study of human serum albumin, Carter and Ho reported that all disulfide bridges of the albumin molecule are in the gauche-gauche-gauche conformation [1]. On the other hand, the solution structure of bovine serum albumin examined by Raman spectroscopy differs from its crystal structure in the conformation of some of the disulfide bridges. Two Raman bands were detected at 520 and 505 cm * in the disulfide stretching mode region, suggesting that the 17 disulfide bridges in the N-form of bovine serum albumin solution take both the gauche-gauche-gauche and gauche-gauche-trans conformations. The ratio of the peak intensities at 520 and 505 cm _1 (I505/I520) is increased from 1.6 to 2.1 and from 2.1 to 6.3 on going from the N-to the F-form and from the F-to the Eform, respectively, indicating that the gauche-gauche-trans conformation of the disulfide bridges is converted to a gauchegauche-gauche one which is the most energetically stable form during the acid-induced isomerization. However, small amounts of gauche-gauche-trans conformation still remain even in the E-form.

Serum albumin is the most abundant protein in extracellular fluids such as blood plasma and interstitial fluid. One of the most important features of the molecular structure of albumin is the presence of a highly reactive free sulfhydryl group in position 34

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