Viscoelastic Chondroitin Sulfate and Hyaluronic Acid Double-Network Hydrogels with Reversible Cross-Links

Abstract

Viscoelastic hydrogels are gaining interest as they possess necessary requirements for bioprinting and injectability. By means of reversible, dynamic covalent bonds, it is possible to achieve features that recapitulate the dynamic character of the extracellular matrix. Dually cross-linked and double-network (DN) hydrogels seem to be ideal for the design of novel biomaterials and bioinks, as a wide range of properties required for mimicking advanced and complex tissues can be achieved. In this study, we investigated the fabrication of chondroitin sulfate/hyaluronic acid (CS/HA)-based DN hydrogels, in which two networks are interpenetrated and cross-linked with the dynamic covalent bonds of very different lifetimes. Namely, Diels–Alder adducts (between methylfuran and maleimide) and hydrazone bonds (between aldehyde and hydrazide) were chosen as cross-links, leading to viscoelastic hydrogels. Furthermore, we show that viscoelasticity and the dynamic character of the resulting hydrogels could be tuned by changing the composition, that is, the ratio between the two types of cross-links. Also, due to a very dynamic nature and short lifetime of hydrazone cross-links (∼800 s), the DN hydrogel is easily processable (e.g., injectable) in the first stages of gelation, allowing the material to be used in extrusion-based 3D printing. The more long-lasting and robust Diels–Alder cross-links are responsible for giving the network enhanced mechanical strength and structural stability. Being highly charged and hydrophilic, the cross-linked CS and HA enable a high swelling capacity (maximum swelling ratio ranging from 6 to 12), which upon confinement results in osmotically stiffened constructs, able to mimic the mechanical properties of cartilage tissue, with the equilibrium moduli ranging from 0.3 to 0.5 MPa. Moreover, the mesenchymal stromal cells were viable in the presence of the hydrogels, and the effect of the degradation products on the macrophages suggests their safe use for further translational applications. The DN hydrogels with dynamic covalent cross-links hold great potential for the development of novel smart and tunable viscoelastic materials to be used as biomaterial inks or bioinks in bioprinting and regenerative medicine.

Creating a Functional Biomimetic Cartilage Implant Using Hydrogels Based on Methacrylated Chondroitin Sulfate and Hyaluronic Acid

“…Nevertheless, the cell viability was sufficient to further investigate the CSMA/HAMA HydroSpacer as a potential strategy and as a regenerative application in cartilage tissue engineering. Moreover, the aim of this research was to demonstrate the initial cell viability, and an optimized cell culture system might lead to a higher cell viability which is more in line with previous research using chondroitin sulfate and hyaluronic acid-based hydrogels [ 78 , 79 ].…”

Bioinspired Hydrogels as Platforms for Life-Science Applications: Challenges and Opportunities

“…By means of reversible, dynamic covalent bonds, it is possible to achieve features that resembles to the dynamics ECM. From chondroitin sulfate and HA, new bio-inks were designed as DN viscoelastic hydrogels reproducing the mechanical properties of cartilage tissue [245].…”

Dynamic Covalent Hydrogels: Strong yet Dynamic

“…In addition, a dual-network hydrogel containing different-lifetime crosslinkers was designed to tune the viscoelasticity and the dynamic character of hydrogel. Mihajlovic and coworkers have investigated the fabrication of chondroitin sulfate/hyaluronic acid (CS/HA)-based DN hydrogels containing Diels–Alder adducts and hydrazone bonds, whereas the viscoelasticity could be directly tuned by changing the ratio between the two types of crosslinkers ( Figure 4 E) [ 125 ]. Viscoelastic hydrogels can be used to study the influence of matrix relaxation on cell morphology ( Figure 5 B), migration and proliferation, as well as to understand the cell–cell and cell–ECM interactions ( Figure 5 A).…”

“…Copyright © 2021 Wiley-VCH GmbH ( D ) The alginate hydrogels exhibited highly tunable stress relaxation and mechanical properties, which can be achieved by systematically varying the composition (concentration, polymer mixing ratios, degree of oxidation of NaAlg-Ald) to change crosslink density [ 124 ]. Copyright © 2019, American Chemical Society; ( E ) double network (DN) hydrogels, containing Diels-Alder adducts and hydrazone bonds, whose viscoelasticity could be highly tuned by changing the ratio between the two types of crosslinks [ 125 ].…”