Schematic illustration of 3D Col-Tgel tumor model.

<p>A, Enzymatic crosslinking of collagen base gel by transglutaminase. B, Tumor cells suspended in soluble gel at desired densities. C, Gel was pipetted into a single well as a droplet, or multi droplets in single dish after addition of crosslinker, Tgase. D&E, Comparison of transparency of three different 3D matrices, Type I collagen, Matrigel, and Col-Tgel. F, The stiffness of Col-Tgel was manipulated by changing the gel concentrations.