Spatiotemporally Controlled Photoresponsive Hydrogels: Design and Predictive Modeling from Processing through Application

Abstract

Photoresponsive hydrogels (PRHs) are soft materials whose mechanical and chemical properties can be tuned spatially and temporally with relative ease. Both photo‐crosslinkable and photodegradable hydrogels find utility in a range of biomedical applications that require tissue‐like properties or programmable responses. Progress in engineering with PRHs is facilitated by the development of theoretical tools that enable optimization of their photochemistry, polymer matrices, nanofillers, and architecture. This review brings together models and design principles that enable key applications of PRHs in tissue engineering, drug delivery, and soft robotics, and highlights ongoing challenges in both modeling and application.

Orthogonal photochemistry-assisted printing of 3D tough and stretchable conductive hydrogels

“…2g and Supplementary Fig. 10 ) 34 – 36 . Moreover, real-time rheology and UV-vis spectroscopy were used to evaluate the controllability of this strategy for preparing 3D TCHs.…”

“…In typical 3D extrusion printing techniques, inks can be extruded on-demand and then processed to give pre-designed architectures via fast solidification 30 – 33 . Visible-light-induced photogelation is an ideal method for preparing such 3D hydrogels because it has excellent biocompatibility and enables easy spatial control 34 – 36 . Light at long wavelengths (>400 nm) is recognized as safer triggers and has lower potential harm to active materials of cells, proteins, and DNA when comparing to these high-energy light sources (UV light or γ rays).…”

Anomalous Loss of Stiffness with Increasing Reinforcement in a Photo‐Activated Nanocomposite

“…[20] The associated kinetics can be predicted by a set of ordinary differential equations (ODEs) describing detailed chemical reactions with kinetic constants that depend on both the composition of precursors and the experimental conditions of the reaction, including temperature, pH, and light intensity. [19,21,22] These kinetic processes determine the nanoscale network topology (e.g., crosslinks, loops, dangle chains) and then the mechanical properties of the hydrogels. [19,21,22] These well-known processes all change for the case of nanocomposite hydrogels.…”

“…[19,21,22] These kinetic processes determine the nanoscale network topology (e.g., crosslinks, loops, dangle chains) and then the mechanical properties of the hydrogels. [19,21,22] These well-known processes all change for the case of nanocomposite hydrogels. Nanofillers are believed to affect gelation kinetics by acting as proton donors for radical generation, [23,24] as radical scavengers, [25,26] or as diffusion barriers.…”

“…[30][31][32] Note that this latter factor is frequently violated by nanoscale particles with high surface energy. [19] Homogenization methods fall into two categories: bounds and estimates. [30,[32][33][34] Bounds such as the Voigt and Reuss bounds, [35,36] Hashin-Shtrikman bounds, [37,38] and three-point bounds [30,39] establish upper and lower limits on stiffening of elastic materials by filler; estimates such as the self-consistent method, [40,41] the Halpin-Tsai equations [42,43] and the Mori-Tanaka model, [44][45][46][47][48] provide estimates within these bounds, typically based on a combination of the Eshelby solution for an isolated ellipsoidal inclusion embedded in an infinite medium [49] with various of effective-medium approximations that model interactions between inclusions.…”