A Universal and Simple Method to Obtain Hydrogels with Combined Extreme Mechanical Properties and Their Application as Tendon Substitutes

Smart hydrogel-based trends in future tendon injury repair: A review

Despite advances in tissue engineering for tendon repair, rapid functional repair is still challenging due to its specificity and is prone to complications such as postoperative infections and tendon adhesions. Smart responsive hydrogels provide new ideas for tendon therapy with their flexibly designed three-dimensional cross-linked polymer networks that respond to specific stimuli. In recent years, a variety of smart-responsive hydrogels have been developed for the treatment of tendon disorders, showing great research promise and ability to address complex challenges. This article provides a comprehensive review of recent advances in the field of smart-responsive hydrogels for the treatment of tendon disorders, with a special focus on their response properties to different physical, chemical and biological stimuli. The multiple functional properties of these innovative materials are discussed in depth, including excellent biocompatibility and biodegradability, excellent mechanical properties, biomimetic structural design, convenient injectability, and unique self-healing capabilities. These properties enable the smart-responsive hydrogels to demonstrate significant advantages in solving difficult problems in the treatment of tendon disorders, such as precise drug delivery, tendon adhesion prevention and postoperative infection control. In addition, the article looks at the future prospects of smart-responsive hydrogels and analyses the challenges they may face in achieving widespread application.

Digital light processing printed hydrogel scaffolds with adjustable modulus

Hydrogels are extensively explored as biomaterials for tissue scaffolds, and their controlled fabrication has been the subject of wide investigation. However, the tedious mechanical property adjusting process through formula control hindered their application for diverse tissue scaffolds. To overcome this limitation, we proposed a two-step process to realize simple adjustment of mechanical modulus over a broad range, by combining digital light processing (DLP) and post-processing steps. UV-curable hydrogels (polyacrylamide-alginate) are 3D printed via DLP, with the ability to create complex 3D patterns. Subsequent post-processing with Fe3+ ions bath induces secondary crosslinking of hydrogel scaffolds, tuning the modulus as required through soaking in solutions with different Fe3+ concentrations. This innovative two-step process offers high-precision (10 μm) and broad modulus adjusting capability (15.8-345 kPa), covering a broad range of tissues in the human body. As a practical demonstration, hydrogel scaffolds with tissue-mimicking patterns were printed for cultivating cardiac tissue and vascular scaffolds, which can effectively support tissue growth and induce tissue morphologies.

Tough Hydrogels for Load-Bearing Applications

Tough hydrogels have emerged as a promising class of materials to target load-bearing applications, where the material has to resist multiple cycles of extreme mechanical impact. A variety of chemical interactions and network architectures are used to enhance the mechanical properties and fracture mechanics of hydrogels making them stiffer and tougher. In recent years, the mechanical properties of tough, high-performance hydrogels have been benchmarked, however, this is often incomplete as important variables like water content are largely ignored. In this review, the aim is to clarify the reported mechanical properties of state-of-the-art tough hydrogels by providing a comprehensive library of fracture and mechanical property data. First, common methods for mechanical characterization of such high-performance hydrogels are introduced. Then, various modes of energy dissipation to obtain tough hydrogels are discussed and used to categorize the individual datasets helping to asses the material's (fracture) mechanical properties. Finally, current applications are considered, tough high-performance hydrogels are compared with existing materials, and promising future opportunities are discussed.

Sustained-Drug-Release, Strong, and Anti-Swelling Water-Lipid Biphasic Hydrogels Prepared via Digital Light Processing 3D Printing for Protection against Osteoarthritis: Demonstration in a Porcine Model

Osteoarthritis is a serious disease affecting joint cartilage. Owing to poor blood supply, the meniscus and acetabular labrum of joints heal poorly after injury. However, the development of artificial alternatives to these components that have similar mechanical properties and cartilage-protection ability is challenging. In this study, a strong hydrogel with a biomimetic microstructure is prepared with an emulsion-type photosensitive resin, where both hydrophilic and hydrophobic monomers, photo-initiator, and drugs can be adopted. In this system, the hydrophobic monomer forms uniformly dispersed aggregates after curing, improving the mechanical properties of the hydrogel significantly. Furthermore, the coordination bonds between nontoxic Zr4+ cations and sulfonic acid groups prevent hydrogel swelling. In addition, the water-oil biphasic hydrogel ink enables the loading of water- and lipid-soluble drugs, yielding hydrogel scaffolds with sustained dual-drug release ability. Crucially, hydrogel scaffolds having excellent mechanical properties, low swelling, and sustained biphasic drug release ability can be prepared using digital light processing 3D printing technology, owing to the high curing rate of the hydrophobic photo-initiator. These hydrogel scaffolds are applied as meniscal and labral replacements in a porcine model and show great promise for the prevention of secondary osteoarthritis, demonstrating the broad potential clinical applications of this material.