Modern Strategies To Achieve Tissue-Mimetic, Mechanically Robust Hydrogels

Abstract

Hydrogels are frequently used biomaterials due to their similarity in hydration and structure to biological tissues. However, their utility is limited by poor mechanical properties, namely, a lack of strength and stiffness that mimic that of tissues, particularly load-bearing tissues. Thus, numerous recent strategies have sought to enhance and tune these properties in hydrogels, including interpenetrating networks (IPNs), macromolecular cross-linking, composites, thermal conditioning, polyampholytes, and dual cross-linking. Individually, these approaches have achieved hydrogels with either high strength (σ f > 10 MPa), high stiffness (E > 1 MPa), or, less commonly, both high strength and stiffness (σ f > 10 MPa and E > 1 MPa). However, only certain unique combinations of these approaches have been able to synergistically achieve retention of a high, tissuelike water content as well as high strength and stiffness. Applying such methods to stimuliresponsive hydrogels has also produced robust, smart biomaterials. Overall, methods to achieve hydrogels that simultaneously mimic the hydration, strength, and stiffness of soft and load-bearing tissues have the potential to be used in a much broader range of biomedical applications.

High strength and low swelling composite hydrogels from gelatin and delignified wood

“…The water content was lower than those for neat gelatin hydrogel due to the interaction between gelatin and delignified wood and the structural confinement provided by the wood cell wall structure as evidenced by FTIR analysis and swelling behaviour discussed in latter sections. Nonetheless, a highly hydrated network (water content > 80 wt%) was maintained in the composite hydrogels, which is of great interests for ultra-stiff/strong hydrogel preparation 34 . Both gelatin hydrogel and the delignified wood/gelatin hydrogels showed a dark blue colour (Fig.…”

Multiply Interpenetrating Polymer Networks: Preparation, Mechanical Properties, and Applications

“…The modularity in the procedure for the preparation of multiple network hydrogels makes their synthesis very easy, and the addition of extra functionalities very simple. This would be particularly useful for the incorporation of new functions from the rapidly growing polymer hydrogel literature, including, but not limited to, elements that further improve network mechanical properties [32,33,34,35,36,37]. Thus, we predict a bright future for this field, where a variety of carefully chosen properties are introduced, so that these materials perfectly match an intended application.…”

Bio-based composite hydrogels for biomedical applications

“…70 This section focuses on recent examples of bio-based hydrogels containing mainly noncellulose fibers; the emerging field of nanocellulose-containing bio-based hydrogels will be covered separately in the last section of this review. The reader is referred to a number of excellent reviews concerning hydrogels with incorporated electrospun fibers that focus on specific application areas such as tissue engineering, [70][71][72] osteochondral regeneration 73 and wound dressings. 74 Since the mechanical performance of hydrogel scaffolds is often inferior to that of native tissues, the development of mechanically robust hydrogels is especially important to provide optimal performance in tissue engineering applications.…”