INTRODUCTION: Embedded 3D bioprinting is a promising approach to engineer complex tissues such as patterned or pre-vascularized tissue constructs1,2. However, the resulting tissue constructs are often mechanically weak, unable to form mechanical or chemical gradients, and lack on-demand tunability. Here, we report on dual crosslinkable dextran-based hydrogel as a hydrogel bath for embedded bioprinting, which uniquely allows for local on-demand functionalization as well as formation of spatially controlled chemical and mechanical gradients within printed tissues.
METHODS: Dextran was functionalized with tyramine and biotin moieties to create a dual crosslinkable polymer3. Physically crosslinked embedding baths were created via biotin/avidin protein/ligand interaction. A gelatin or PEG based sacrificial bioink was extruded into the hydrogel using an Inkredible+ 3D printer. Covalent enzymatic or photo-initiated crosslinking of the printing bath was used to create mechanically robust tissues. The tissue’s biotin moieties were subsequently used for on-demand biochemical functionalization of the bulk and/or the channel surfaces.
RESULTS & DISCUSSION: Rheological characterization of the physically crosslinked bath revealed shear-thinning and self-healing properties that were highly suitable for embedded bioprinting. Covalent crosslinking resulted in a three-fold increase of the storage modulus of the hydrogels, which enabled the stabilization of printed channel networks, while diffusion of crosslinking agents from the ink resulted in controllable stiffness gradients in the bulk. Without photocrosslinking the bulk, tubular structures were created via enzymatic inside-out crosslinking. Here, tube diameter and channel wall thickness could be independently controlled through variation of the printing speed and crosslinker concentration, respectively. Furthermore, the ink/bath interface allowed for one-step functionalization by loading the ink with biotin-coupled cell bioinstructive moieties.
CONCLUSION: We report on a novel and dual crosslinkable hydrogel suitable for embedded bioprinting, which offers mechanical stability, mechanical tunability, with on-demand biochemical functionalization of tubular and pre-vascularized engineered tissues.
ACKNOWEDGEMENTS: Financial support was received from the European Research Council (ERC, Starting Grant, #759425) and the Dutch Research Council (NWO, Vidi Grant, #17522).
1 Lee, A. et al., Science 365, (2019).
2 Highley, C. B. et al., Adv Mater 27, (2015).
3 Kamperman, T. et al., Nat Commun 10, (2019).