Delayed or severed tissue regeneration is often caused by dysfunctional immune system. One solution to tackle this issue is to design immunomodulatory materials that support tissue regeneration by priming immune system to a pro-regenerative state. For example, it is known that high molecular weight (>1000 kDa) hyaluronic acid (HA) can polarize macrophages to an M2 pro-regenerative phenotype, whereas low molecular weight HA drives pro-inflammatory M1 polarization. Understanding the rules for designing functional materials that incorporate immunomodulatory effects, biocompatibility and allow stable long-term polarization of macrophages is therefore of high interest in multiple tissue engineering (TE) scenarios, notably for 3D printing TE.
Here, to answer the new demands, we designed a selection of two-component hydrogels built from self-assembling β-sheet forming peptides and immunomodulatory tyramine-modified HA (THA), that can be processed by 3D micro-extrusion printing. A selection of peptide sequences was based on the alternation of hydrophobic and hydrophilic amino acids: XYXZXYXZ (X: hydrophobic residue: phenylalanine or tyrosine, Y/Z: hydrophilic residue e.g.: lysine or glutamic acid), stemming from the known parental FEFKFEFK sequence and it subsequent modifications. All parental peptides self-assemble into semi-flexible networks and hydrogels, as derived from oscillatory rheology measurements and contain high β-sheet content, as measured by FTIR. 280 kDa and 1640 kDa THA were synthesized as previously described. The successful THA synthesis was confirmed using 1H-NMR and degree of modification was calculated from UV absorption.
A parametric study was carried out to verify the effect of rational peptide sequence modification on final physico-chemical and biological properties of composite hydrogels. Self-assembly, and rheological properties can be controlled by the choice of primary peptide sequence, fabrication technique and final crosslinking mechanisms including enzymatic (HRP, H2O2) and visible green light crosslinking using Eosin. These hydrogels are characterised by shear-thinning behaviour and rapid recovery allowing extrusion-based fabrication of both simple (lines, grids) and more complex shapes retaining post-printing fidelity.
The versatile crosslinking mechanisms allow post-crosslinking structure stabilization with longer-term degradation, deeming them a modular and versatile inks platform to endow with multiple biological cues for TE and immunomodulation.
ACKNOWLEDGEMENTS: This work was supported by the European Union’s Horizon 2020 (H2020-MSCA-IF-2019) research and innovation programme under the Marie Skłodowska-Curie grant agreement 893099 — ImmunoBioInks.
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