Functional 3D tissue models are a potentially valuable tool to provide more transferable test results regarding basic research, drug development or other applications than classic 2D cell culture. The biggest bottleneck in the generation of functional 3D tissue models is the incorporation of a reproducible and perfusable vascularization, which on the one side mimics the in vivo hierarchy accurately, and on the other side keeps the tissue alive. Furthermore, perfusable vascularization provides the possibility to enhance the height of the tissue model above a threshold (usually 1-2 mm), where cells normally die due to lack of nutrients and oxygen.
An interesting approach to generate microchannel networks in 3D tissue models is the utilization of sacrificial scaffolds. These scaffolds are prefabricated and can be introduced into cytocompatible hydrogels and, after gelation of the hydrogel, dissolved to generate channels. However, current methods are based on using sacrificial carbohydrates, which directly dissolve upon contact with aqueous environment. Thus, to create stable channels within a hydrogel system, these scaffolds require laborious postfabrication processing (e.g., coatings) to prevent their early dissolution during the hydrogel gelation process.
In this work, we introduce biocompatible poly(2-oxazoline)s as material for sacrificial scaffolds. These polymers are thermoresponsive in aqueous solutions, meaning that they dissolve on demand by temperature reduction, a very cytocompatible stimulus. This further leads to an increased dissolution timeframe without the need of any postfabrication processing and enables the utilization of many currently used hydrogels for biofabrication (e.g., methacrylated gelatin or collagen).
Interestingly, poly(2-oxazoline)s can be fabricated via modern additive manufacturing technologies like Melt Electrowriting and Freeform Printing to generate microfiber networks in 2D and 3D. This enables the generation of interconnected channel networks with bifurcations, resembling the natural vascularization. Furthermore, the characteristics of the polymer allow the prefixation of the scaffolds in specialized perfusion chambers. By simple addition of a cell-laden hydrogel, these perfusion chambers mediate the generation of microchannel-networks and their leakage-free connection to media-reservoirs. Furthermore, this allows the direct cultivation and endothelialization of the perfusable tissue construct in the perfusion chamber and its connection to perfusion devices.
Taken together, the utilization of poly(2-oxazoline)s as sacrificial scaffolds is a reliable technology, which enables the simple generation and cultivation of perfusable vascularized tissue constructs.