Search

International audience; Hydrogels are deployed widely in all areas of regenerative medicine, including bioprinting. The transport and mechanical properties exhibited by hydrogel assemblies are controlled by their organization and hierarchical assembly. This paper points out the role of the nanoscale size and ordering of hydrophobic cross-linked domains on the mechanical and degradation properties of three-dimensional (3D) printed amphiphilic hydrogels. A series of six poly(propylene fumarate)-block-poly(ethylene glycol)-block-poly(propylene fumarate) (PPF-b-PEG-b-PPF) ABA triblock copolymers were synthesized by varying both the water-soluble PEG block and the cross-linkable hydrophobic terminal PPF block lengths. Self-assembled hydrogels were formed by dissolving these amphiphilic PPF-b-PEG-b-PPF copolymers in water and covalently cross-linking the PPF units via digital light processing (DLP) additive manufacturing. Differential scanning calorimetry (DSC), in situ diffuse reflectance infrared spectroscopy (DRIFTS-IR) measurements, small-angle neutron scattering (SANS), and compressive measurements highlight how structural properties correlate with mechanical properties within this hydrogel system. Finally, swelling and in vitro degradation tests showed the influence of the nanoscale ordering on the degradation timescale.

International audience; We report on how the local structure and the diffusional motion change upon increasing the alkyl chain length in 1-alkyl-3-methylimidazolium cation ionic liquids. This study has been performed by combining pulse field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and small angle X-ray scattering (SAXS) experiments. The cationic side chain length varies from ethyl (n = 2) to hexadodecyl (n = 16), while the anion is always bis(trifluoromethanesulfonyl)imide (TFSI). We find that the self-diffusivity of the individual ionic species is correlated to the local structure in the corresponding ionic liquid, namely the nano-segregation into polar and non-polar domains. In agreement with previous results, we observe that for relatively short alkyl chains the cations diffuse faster than the anions; however we also note that this difference becomes less evident for longer alkyl chains and a cross-over is identified at n ≈ 8 with the anions diffusing faster than the cations. Our results indicate that this controversial behavior can be rationalized in terms of different types of cation–cation and anion–anion orderings, as revealed by a detailed analysis of the correlation lengths and their dispersion curves obtained from SAXS data. We also discuss the validity of the Stokes–Einstein relation for these ionic liquids and the evolution of the extrapolated cationic radius that was found to depend non-strictly linearly on n, in agreement with the cation–cation correlation lengths.