Macroporous methacrylated hyaluronic acid cryogels of high mechanical strength and flow-dependent viscoelasticity.

We present here a new approach for the fabrication of macroporous hyaluronic acid (HA) cryogels with a tunable porous structure, flow-dependent viscoelasticity, and a high mechanical strength. They were synthesized from methacrylated HA in aqueous solutions at -18 °C by free-radical mechanism using in situ prepared poly(N, N-dimethylacrylamide) (PDMAA) as a spacer. Both the porosity and the average diameter of the pores decrease from 99 to 90% and from 150 to 90 µm, respectively, with increasing PDMAA content of the cryogels due to the simultaneous decrease in the amount of ice template during cryogelation. The cryogels also exhibit reversible strain-dependent apparent gel-to-sol transition due to the flowing-out and flowing-in water through the pores. This flow-dependent viscoelasticity is of great interest as it protects HA network from damage under large strain and hence acts as a self-defense mechanism.

Mechanically robust and stretchable silk/hyaluronic acid hydrogels.

Combining the material and biological properties of hyaluronic acid (HA) and silk fibroin (SF) in a single hydrogel would expand the range of applications available to HA and SF individually. Here, we present a novel strategy to prepare mechanically robust and stretchable SF/HA hydrogels. The hydrogels were prepared from methacrylated HA (MeHA) and SF in aqueous solutions in the presence of a radical initiator. N, N-dimethylacrylamide (DMAA) monomer was also included into the reaction solution as a spacer to connect MeHA's through their pendant vinyl groups. The presence of SF significantly enhances the mechanical strength of HA hydrogels due to its ß-sheet domains acting as physical cross-links. The damage in SF network under large strain leads to a significant energy dissipation, which is responsible for the improved mechanical properties of SF/HA hydrogels.

Mechanically strong triple network hydrogels based on hyaluronan and poly(N,N-dimethylacrylamide).

Hyaluronan (HA) is a natural polyelectrolyte with distinctive biological functions. Cross-linking of HA to generate less degradable hydrogels for use in biomedical applications has attracted interest over many years. One limitation of HA hydrogels is that they are very brittle and/or easily dissolve in physiological environments, which limit their use in load-bearing applications. Herein, we describe the preparation of triple-network (TN) hydrogels based on HA and poly(N,N-dimethylacrylamide) (PDMA) of high mechanical strength by sequential gelation reactions. TN hydrogels containing 81-91% water sustain compressive stresses above 20 MPa and exhibit Young's moduli of up to 1 MPa. HA of various degrees of methacrylation was used as a multifunctional macromer for the synthesis of the brittle first-network component, while loosely cross-linked PDMA was used as the ductile, second and third network components of TN hydrogels. By tuning the methacrylation degree of HA, double-network hydrogels with a fracture stress above 10 MPa and a fracture strain of 96% were obtained. Increasing the ratio of ductile-to-brittle components via the TN approach further increases the fracture stress above 20 MPa. Cyclic mechanical tests show that, although TN hydrogels internally fracture even under small strain, the ductile components hinder macroscopic crack propagation by keeping the macroscopic gel samples together.