Coaxial bioprinting of cellulose nanocrystal-reinforced core-sheath strands for alginate hydrogel construct fabrication

Alginate is among the most popular bioinks for 3D bioprinting because it is biocompatible, biodegradable, and is easily crosslinked using divalent cations. Here, we investigate the addition of cellulose nanocrystals (CNCs) to an alginate-based bioink to strengthen bioprinted structures. Using coaxial 3D bioprinting, alginate strands were constructed with a core-sheath structure reinforced by CNCs within the core. The addition of CNCs resulted in an increase in the storage modulus. Formulations containing CNCs resulted in more stable strands with uniformity factors and printability numbers close to 1. Based on the uniformity factor, the formulations containing 1.5 wt% CNCs deviated the least from a theoretically flawless strand. The alginate strands displayed microporous internal structures that were evident by scanning electron microscopy of the strand cross-sections. The addition of CNCs to the core compartment doubled both the modulus and the tensile strength, and the material was able to resist a strain above 50% before failure, thus demonstrating that the addition of the CNCs to the core of the strand leads to resilient printed structures.