Hydrogels are increasingly employed as multidimensional cell culture platforms often with a necessity that they respond to or control the cellular environment. Specifically, synthetic hydrogels, such ...as poly(ethylene glycol) (PEG)‐based gels, are frequently utilized for probing the microenvironment's influence on cell function, as the gel properties can be precisely controlled in space and time. Synthetically tunable parameters, such as monomer structure and concentration, facilitate initial gel property control, while incorporation of responsive degradable units enables cell‐ and/or user‐directed degradation. Such responsive gel systems are complex with dynamic changes occurring over multiple time‐scales, and cells encapsulated in these synthetic hydrogels often experience and dictate local property changes profoundly different from those in the bulk material. Consequently, advances in bulk and local measurement techniques are needed to monitor property evolution quantatively and understand its effect on cell function. Here, recent progress in cell‐responsive PEG hydrogel synthesis and mechanical property characterization is reviewed.
Hydrogels are increasingly employed as cell culture platforms, often with a necessity that they respond to or control the cellular environment. Gel properties, such as crosslinking density (ρx) and modulus (E), can be precisely controlled in space and time and can dictate cell morphology, cytoskeletal organization, and function; quantifying the evolving mechanical properties of these gel systems is important.
Covalently crosslinked materials, classically referred to as thermosets, represent a broad class of elastic materials that readily retain their shape and molecular architecture through covalent bonds ...that are ubiquitous throughout the network structure. These materials, in particular in their swollen gel state, have been widely used as stimuli responsive materials with their ability to change volume in response to changes in temperature, pH, or other solvent conditions and have also been used in shape memory applications. However, the existence of a permanent, unalterable shape and structure dictated by the covalently crosslinked structure has dramatically limited their abilities in this and many other areas. These materials are not generally reconfigurable, recyclable, reprocessable, and have limited ability to alter permanently their stress state, topography, topology, or structure. Recently, a new paradigm has been explored in crosslinked polymers - that of covalent adaptable networks (CANs) in which covalently crosslinked networks are formed such that triggerable, reversible chemical structures persist throughout the network. These reversible covalent bonds can be triggered through molecular triggers, light or other incident radiation, or temperature changes. Upon application of this stimulus, rather than causing a temporary shape change, the CAN structure responds by permanently adjusting its structure through either reversible addition/condensation or through reversible bond exchange mechanisms, either of which allow the material to essentially reequilibrate to its new state and condition. Here, we provide a tutorial review on these materials and their responsiveness to applied stimuli. In particular, we review the broad classification of these materials, the nature of the chemical bonds that enable the adaptable structure, how the properties of these materials depend on the reversible structure, and how the application of a stimulus causes these materials to alter their shape, topography, and properties.
Classification of covalent adaptable networks is reviewed, providing insight into their unique properties achieved
via
reversible chemistries and molecular architectures.
Click Chemistry in Materials Science Xi, Weixian; Scott, Timothy F.; Kloxin, Christopher J. ...
Advanced functional materials,
05/2014, Letnik:
24, Številka:
18
Journal Article
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Despite originating only a little more than a decade ago, click chemistry has become one of the most powerful paradigms in materials science, synthesis, and modification. By developing and ...implementing simple, robust chemistries that do not require difficult separations or harsh conditions, the ability to form, modify, and control the structure of materials on various length scales has become more broadly available to those in the materials science community. As such, click chemistry has seen broad implementation in polymer functionalization, surface modification, block copolymer and dendrimer synthesis, biomaterials fabrication, biofunctionalization, and in many other areas of materials science. Here, the basic reactions, approaches, and applications of click chemistry in materials science are highlighted, and a brief look is taken into the future enabling developments in this field.
Click chemistry has become one of the most powerful paradigms in materials science, synthesis and modification. This feature article delivers highlights of the basic reactions, approaches, and applications of click chemistry in materials science as well as briefly looking to the future, enabling developments in this field.
Photolabile moieties have been utilized in applications ranging from peptide synthesis and controlled protein activation to tunable and dynamic materials. The photochromic properties of nitrobenzyl ...(NB) based linkers are readily tuned to respond to cytocompatible light doses and are widely utilized in cell culture and other biological applications. While widely utilized, little is known about how the microenvironment, particularly confined aqueous environments (e.g., hydrogels), affects both the mode and rate of cleavage of NB moieties, leading to unpredictable limitations in control over system properties (e.g., rapid hydrolysis or slow photolysis). To address these challenges, we synthesized and characterized the photolysis and hydrolysis of NB moieties containing different labile bonds (i.e., ester, amide, carbonate, or carbamate) that served as labile crosslinks within step-growth hydrogels. We observed that NB ester bond exhibited significant rates of both photolysis and hydrolysis, whereas, importantly, the NB carbamate bond had superior light responsiveness and resistance to hydrolysis within the hydrogel microenvironment. Exploiting this synergy and orthogonality of photolytic and hydrolytic degradation, we designed concentric cylinder hydrogels loaded with different cargoes (e.g., model protein with different fluorophores) for either combinatorial or sequential release, respectively. Overall, this work provides new facile chemical approaches for tuning the degradability of NB linkers and an innovative strategy for the construction of multimodal degradable hydrogels, which can be utilized to guide the design of not only tunable materials platforms but also controlled synthetic protocols or surface modification strategies.
As the demand for polymeric materials transitions towards the need for customizable, high value, specialty polymeric materials, the ability to use light to initiate various physicochemical changes in ...polymers represents one of the most powerful and rapidly evolving approaches. Whether for polymer formation, polymer modification, shape change, or inducing smart material responses, light has the unique capacity for enabling 4D manipulation of each of those processes. Given the simple, 3D ability to focus light on a targeted voxel and the even simpler ability to turn a light on and off to facilitate temporal control, light has been used widely in various polymer modifications. Further, in addition to the ability to enhance the control of various reactive processes, due to the much greater energy available in a photon as compared to the thermal energy available, light enables chemical processes to occur at ambient conditions that are otherwise inaccessible without heating. In particular, within the polymer chemistry field, light has been used to cause bond formation, bond degradation, and isomerization, with subsequent reactions including polymerization, polymer degradation, polymer functionalization, and responsive changes in properties of smart materials. Here, this article attempts to provide a fundamental basis for the various photochemical processes implemented in polymer systems, followed by selected examples of that implementation in various polymerization, functionalization, degradation, and other reactions.
The use of light to manipulate polymer formation, structure and properties represents one of the most powerful paradigms in polymer science.
Smart and responsive: Reversible transesterification reactions were recently used within a polymer network to create a covalently crosslinked material that is capable of being processed as well as ...mended and recycled. This work is highlighted in the context of the covalent adaptable network approach and illustrates the bond cleavage and reformation mechanism that enable the adaptability of these materials (see picture).
Peptides have been extensively utilized to construct nanomaterials that display targeted structure through hierarchical assembly. The self-assembly of both rationally designed peptides derived from ...naturally occurring domains in proteins as well as intuitively or computationally designed peptides that form β-sheets and helical secondary structures have been widely successful in constructing nanoscale morphologies with well-defined 1-d, 2-d, and 3-d architectures. In this review, we discuss these successes of peptide self-assembly, especially in the context of designing hierarchical materials. In particular, we emphasize the differences in the level of peptide design as an indicator of complexity within the targeted self-assembled materials and highlight future avenues for scientific and technological advances in this field.
Photochemical processes enable spatial and temporal control of reactions, which can be implemented as an accurate external control approach in both polymer synthesis and materials applications. ...“Click” reactions have also been employed as efficient tools in the same field. Herein, we combined photochemical processes and thiol-Michael “click” reactions to achieve a “photo-click” reaction that can be used in surface patterning and controlled polymer network formation, owing to the ease of spatial and temporal control through use of photolabile amines as appropriate catalysts.
A thermally reversible polymeric network with imbedded ferromagnetic particles was synthesized via the Diels‐Alder reaction. When placed in an alternating magnetic field (see figure) the material is ...heated in situ by the self‐limiting heating behavior of ferromagnetic particles and subsequently reverts to a liquid. As a consequence, the material properties are unchanged even after ten cycles of fracture and repair.
The click reaction paradigm is focused on the development and implementation of reactions that are simple to perform while being robust and providing exquisite control of the reaction and its ...products. Arguably the most prolific and powerful of these reactions, the copper-catalysed alkyne-azide reaction (CuAAC) is highly efficient and ubiquitous in an ever increasing number of synthetic methodologies and applications, including bioconjugation, labelling, surface functionalization, dendrimer synthesis, polymer synthesis and polymer modification. Unfortunately, as the Cu(I) catalyst is typically generated by the chemical reduction of Cu(II) to Cu(I), or added as a Cu(I) salt, temporal and spatial control of the CuAAC reaction is not readily achieved. Here, we demonstrate catalysis of the CuAAC reaction via the photochemical reduction of Cu(II) to Cu(I), affording comprehensive spatial and temporal control of the CuAAC reaction using standard photolithographic techniques. Results reveal the diverse capability of this technique in small molecule synthesis, patterned material fabrication and patterned chemical modification.
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