Speaker
Description
Introduction
3D printing of hydrogels usually relies on a combination of fine-tuned material chemistry and polymer chain architecture to produce inks with adequate viscoelastic properties such as yield-stress flow, shear-thinning and self-healing behavior. [1] Complex coacervates are versatile materials obtained through an associative liquid-liquid phase separation phenomenon driven by electrostatic attraction between oppositely charged macro-ions (e.g. polysaccharides, proteins etc.) that show a great potential for the use as biomaterial inks. Indeed, for a given polyelectrolyte couple, depending on the salt concentration of the medium, a complex coacervate either behaves as a free-flowing viscoelastic fluid or a rigid polyelectrolyte complex or anything in between [2]. In our work, we leveraged complex coacervation between biological polyelectrolytes either as linear chains or as jammed hybrid microgels, so-called granular hydrogels [3], to develop 3D printable scaffolds with responsive biocompatible and contractible properties without need of post-printing crosslinking (Figure 1).
Methods
In this presentation, we first focus on the use of complex coacervates made of hyaluronic acid – chitosan linear chains (HA-CHI) as a biomaterial ink for 3D printing. By carefully optimizing, the physico-chemical parameters of the system, meaning pH, salinity and molecular weight of the polymers, we were able to produce a set of biomaterial inks that can be used in different environmental conditions. In parallel, we also synthesized hybrid microgels composed of methacrylated HA (HAMA) and chitosan (CHIMA) that were co-crosslinked by UV-irradiation in a batch emulsion process. Once jammed by centrifugation, the salt-reponsiveness of the resulting complex coacervate granular hydrogels was investigated in a range of physiologically relevant salt concentrations.
Results
The developed inks based on HA-CHI can not only be dried and re-hydrated without loss of shape fidelity, but also be printed into a liquid medium (fresh-printing) without the need of any chemical modification or post-printing curing process. We also show that an additional responsive dimension can be obtained by using the HAMA-CHIMA granular hydrogels. By decreasing the salt concentration of the medium below the critical concentration for electrostatic association between the polyelectrolytes, microgels with decreasing size leading to hydrogels with tunable stiffness, packing density and size were obtained. The 3D printed scaffolds exhibit long-term stability without need of chemical crosslinking and post-printing modulation of the resolution is also rendered possible.
Discussion
By combining oppositely charged biopolymers in aqueous conditions, either as linear chains or as hybrid microgels, we could highlight the potential of complex coacervates to be used as 2D and 3D scaffolds in cell culture studies.This approach also opens up the way to the design of more functional 3D hydrogel constructs with biocompatible and dynamic mechanical properties.
References
1. C. E. Sing, S. L. Perry, Soft Matter, 2020, 16, 2885-2914
2. Q. Wang, J. B. Schlenoff, Macromolecules 2014, 47, 3108-3116
3. Daly, A. C.; Riley, L.; Segura, T.; Burdick, Nature Reviews Materials 2019, 5 (1), 20-43.
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