Vascularization remains a critical challenge in tissue engineering. glycol-co-lactide) acrylate (SPELA) poly (ethylene glycol) dimethacrylate (PEGDMA) and poly (ethylene glycol) diacrylate (PEGDA) hydrogels at different concentrations. In particular GelMA hydrogels were used as a model to demonstrate the functionality of the fabricated vascular networks in improving mass transport cellular viability and differentiation within the cell-laden tissue constructs. In addition successful formation of endothelial monolayers within the fabricated channels was confirmed. Overall our proposed strategy represents an effective technique for vascularization of hydrogel constructs with useful applications in tissue engineering and organs on a chip. models of drug discovery and organ on a chip platforms.7-10 The process of engineering vascularized engineered tissue constructs generally relies either on cell based strategies or fabrication of a network of microchannels.7 Cell-based approaches primarily involve endothelial cells often assisted by other cell types such as pericytes and stem cells to form self-organized and stable capillaries embedded within constructs.11-17 These processes however are usually Iopromide slow heavily depending on biological mechanisms such as cellular morphogenesis recruitment of mural cells18 and the fusion of intracellular vacuoles.16 Furthermore this strategy mostly remains restricted to relatively thin constructs.12 19 Alternatively the development of artificial microchannels depends on utilization of microfabrication techniques to form highly organized vascular networks. To date a number of reports have used perfusable constructs fabricated via layer-by-layer assembly of hydrogels with microfabricated grooves or microchannels.10 20 These methods however are generally restricted Iopromide to planar footprints and depend on multiple polymerization steps which result in undesirable interfaces within the engineered tissues. A recent strategy for fabrication of well defined microchannels within engineered tissues has been based on bioprinting techniques to position sacrificial template materials such as carbohydrate glass23 and Iopromide ‘fugitive inks’ of Pluronic CCND1 F12724-27 enclosed inside a hydrogel matrix. Upon bioprinting these templates are dissolved via external stimuli thus resulting in immediate formation of organized microchannels. Although bioprinting strategy exhibits several advantages in fabricating well defined microchannels compared to layer-by-layer assembly the proposed bioprinted sacrificial template materials have been usually associated with cytotoxic reaction byproducts originating from template dissolution.28 29 For instance bioprinted sacrificial glass carbohydrate templates have been reported to require coating with poly (D-lactide-co-glycolide) to prevent osmotic damage to cells enclosed inside the hydrogel.23 Similarly highly concentrated Pluronic F127 has shown significant cytotoxic effects.30 Therefore there exists a need to develop novel bioprinting-based techniques to engineer functional vascular networks within hydrogel constructs for tissue engineering and organs on a chip applications.19 In this paper we report a bioprinting-based strategy in which agarose a naturally derived polysaccharide is used as a permissive template material for vascularization of engineered hydrogel constructs. In the proposed strategy agarose fibers are bioprinted with a well-defined and controlled three dimensional (3D) architecture. Then a hydrogel precursor is usually casted over the bioprinted templates and subsequently photo polymerized. After gelation the bioprinted agarose fibers do not stick to the surrounding photo cross linked hydrogels. Hence the bioprinted templates can be easily removed to form Iopromide fully perfusable networks without any requirement for template dissolution (Physique 1). Herein we demonstrate the effectiveness of the proposed strategy in fabricating microchannel networks and microfluidics constructs in a wide variety of photo cross linkable hydrogels commonly used for tissue engineering applications. Furthermore we utilize cell-laden methacrylated gelatin (GelMA) Iopromide hydrogels as a model platform to demonstrate the effectiveness of the proposed technique in the development of vascularized.