Light-Pipe FRESH 3D Bioprinting for Engineering Spatial Heterogeneity in Tissue Constructs

Native tissues are complex: they incorporate spatial heterogeneity, multicellular composition and hierarchical architecture. Hence, rebuilding human tissue requires the ability to recreate complex structural and functional relationships that span from molecular to organ length scales. Embedded bioprinting methods, such as Freeform Reversible Embedding of Suspended Hydrogels (FRESH), have enabled the biofabrication of architecturally-complex constructs with shape fidelity by extruding bioinks within a support bath. However, beyond their hierarchical architectures, native tissues are often characterized with gradual transition of niche cues in a gradient manner, which cannot be mimicked easily by using discrete hydrogel compositions. In that regard, photochemical reactions are widely regarded for their spatiotemporal control, where the desired reaction occurs when and where the light is delivered to the system; and such chemistry has been used to introduce continuous gradients of biochemical and physical cues into hydrogels. My doctoral work aims to combine spatiotemporal control of photochemistry with the existing advantages of the FRESH technique in order to advance the complexity of engineered tissues. To do this, I developed a novel light-based bioprinting technique called light-pipe FRESH 3D bioprinting, where the light delivered from the tip of a fiber optic cannula enables photoactivation of the support bath or an extruded bioink in a layer by-layer fashion. The result of this work demonstrated that light-pipe FRESH 3D bioprinting enhances the spatiotemporal heterogeneity of tissue constructs in multiple ways such as generation of mechanical gradients, multi-material bioprinting, photoconjugation of biomolecules and multi-wavelength photoactivation.