**6.3 Vascularization**

Small and simpler organ printing has been successful, without much difficulty. However, it is not simple when comes to bigger and complex organ, due to difficulty in vascularization. Small tissues are avascular, and most of the time, aneural, alymphatic, and thin or hollow. They can receive nutrition from host vasculature. But when the transplanted tissue is thicker than 150–200 μm, oxygen cannot be diffused from host tissue to it. As such, to create a functional bigger and complex tissue or organ, an integrated vascular system is to be created, which is still not in place [105].
