Pre-Crosslinking with Hydrogel Microparticles Enhances the Printability of Alginate-Based Inks

Abstract

The main challenge in extrusion-based bioprinting is to develop inks which must comprise a manifold of characteristics before, during, and after printing. To tackle the challenge of good shape fidelity and printability of low concentration inks, in this study hydrogel microparticles (HMPs) are proposed to produce internally pre-crosslinked inks. Alginate (Alg) and oxidized alginate (OA)-based HMPs are fabricated and used as Ca2+-releasing reservoirs. OA HMPs are used to demonstrate the versatility of this approach and to show its suitability also for chemically modified alginate. Embedded in either fresh Alg or OA solution, HMPs are used to pre-crosslink the inks. Rheological measurements revealed that HMP pre-crosslinking increases the yield stress and viscosity while reducing the loss angle of bioinks. Moreover, printing experiments reveal that being able to tailor rheological properties is an effective tool to improve printability. Furthermore, pre-crosslinking significantly alters the hydogel internal microstructure. In vitro studies show that NIH/3T3 cells proliferate in HMP pre-crosslinked bioinks modified with gelatin. Altogether, a low-cost and easy to use setup to prepare HMPs is presented and for the first time, the possibility of using such HMPs as pre-crosslinking agent to tailor the printability of alginate-based bioinks is demonstrated.