Moving from static to dynamic complexity in hydrogel design

Abstract

Hydrogels are water-swollen polymer networks that have found a range of applications from biological scaffolds to contact lenses. Historically, their design has consisted primarily of static systems and those that exhibit simple degradation. However, advances in polymer synthesis and processing have led to a new generation of dynamic systems that are capable of responding to artificial triggers and biological signals with spatial precision. These systems will open up new possibilities for the use of hydrogels as model biological structures and in tissue regeneration.H ydrogels are water-swollen polymer networks that have been used for many decades, with applications as varied as contact lenses and super-absorbant materials. As the field of biomedical engineering has developed, hydrogels have become a prime candidate for application as molecule delivery vehicles and as carriers for cells in tissue engineering, owing to their ability to mimic many aspects of the native cellular environment (for example, high water content, mechanical properties that match soft tissues). Traditional hydrogels, formed through the covalent and non-covalent crosslinking of polymer chains, were regarded as relatively inert materials, providing a simple biomimetic three-dimensional (3D) environment, either for tissue production by local resident cells or for positioning of cells delivered in vivo. However, the simplicity of these materials may have in fact hindered their application, restricting cellular interactions with the environment and preventing uniform extracellular matrix (ECM) production and proper tissue development. In addition, these materials were limited to modelling static environments and lacked the spatiotemporal dynamic properties relevant for complex tissue processes. Fortunately, during the last decade the concepts of hydrogel design and cellular interaction have evolved, shedding light on how they may control cell behaviour, particularly for tissue engineering applications.Hydrogels with a range of mechanical properties, and capable of incorporating a wide range of biologically relevant molecules, from individual functional groups to multidomain proteins, are currently in development 1 . In addition, hydrogels are being designed with spatial heterogeneity, to either replicate properties in native tissue structures or to produce constructs with distinct regionally specific cell behavior 2 . As a result, studies to date have clearly demonstrated the possibility of creating well-defined microenvironments with control over the 3D presentation of signals to cells 3 . However, recently there has been a focus on the concept of hydrogels that exhibit dynamic complexity. These materials should evolve with time and in response to

An instant multi-responsive porous polymer actuator driven by solvent molecule sorption

“…On the other hand, the hygroscopic movements of pine cones 24 and ice plant seed capsules 22 , although slower, can function even when the host organisms are dead. Recently, enormous efforts have been paid to these bio-prototypes, with progress being made on responsive nanocomposites and surfaces 3 , energy generators and transducers 25,26 , programmable origami 27 , soft robotics [28][29][30] , smart gels [31][32][33] and artificial muscles [34][35][36] . Yet, most of the polymer actuators suffer from the relatively slow and small scale movements; furthermore, they are susceptible to severe circumstances and involve complex preparation such as multistep lithographic processes 21,37 .…”

Evidence‐based topical management of chronic wounds according to the T.I.M.E. principle

“…Further meta-analyses confirmed this result for diabetic ulcers [18]. The choice of hydrogels must still be made critically due to the increased irritation and sensitization potential -particularly in patients with leg ulcers [19,20]. In chronic wounds with extensive necrotic areas, autolytic debridement is often less efficient and must therefore be supported by other varieties of tissue management.…”

Mechanotransduction and Growth Factor Signalling to Engineer Cellular Microenvironments

“…[88] In the last years, dynamic biomaterial properties such time-dependent matrix stiffening, degradability, viscoelasticity and surface mobility are beginning to attract attention in the field of regenerative medicine. [89][90][91][92] …”