Visible light is an easily achievable and mild trigger for self‐healing materials. By incorporating dynamic diselenide bonds into polyurethane, visible‐light‐induced self‐healing materials can be ...fabricated. Besides mild visible light, the healing process can also be realized using directional laser irradiation, which makes the system a remotely controllable self‐healing system.
Although researchers have made great progress in the development of responsive polymeric materials for controlled drug release or diagnostics over the last 10 years, therapeutic results still lag ...behind expectations. The development of special materials that respond to physiological relevant concentrations, typically within the micromolar or nanomolar concentration regime, remains challenging. Therefore, researchers continue to pursue new biomaterials with unique properties and that respond to mild biochemical signals or biomarkers. Selenium is an essential element in human body with potential antioxidant properties. Because of selenium’s electronegativity and atomic radius, selenium-containing compounds exhibit unique bond energy (C–Se bond 244 kJ mol–1; Se–Se bond 172 kJ mol–1). These values give the C–Se or Se–Se covalent bonds dynamic character and make them responsive to mild stimuli. Therefore, selenium-containing polymers can disassemble in response to changes under physiological relevant conditions. This property makes them a promising biomaterial for controlled release of drugs or synthetic enzyme mimics. Until recently, few researchers have looked at selenium-containing polymers as novel biomaterials. In this Account, we summarize our recent research on selenium-containing polymers and show their potential application as mild-responsive drug delivery vehicles and artificial enzymes. We begin by reviewing the current state of the art in the synthesis of selenium-containing main chain block copolymers. We highlight the dual redox and gamma-irradiation behaviors of diselenide-containing block copolymers assemblies, discussing the possibility of their use in a combination of chemotherapy and actinotherapy. We also describe the coordination of platinum with monoselenide containing block copolymers. Such structures offer the possibility of fabricating multidrug systems for cooperative chemotherapy. In addition, we summarize the methods for the covalent and noncovalent preparation of selenium-containing polymers with side chains, which highlight the opportunity to reversibly tune the amphiphilicity of selenium-containing polymers. Finally, we present strategies for the design of highly efficient selenium-containing dendritic polymers that can mimic enzymes. This field is still in its infancy period, and further research can only be limited by our imagination.
Selenium is a semimetallic element lying in group XVI of the periodic table with its chemical properties resembling sulfur. But owing to its relatively low electronegativity and large atomic radius ...compared with sulfur, selenium also shows unique properties. This feature endows selenium-containing compounds with high reactivity and sensitivity. Although organic selenium chemistry has been developing very fast, the successful introduction of selenium into polymer science is rather scarce. Fortunately, we have seen a drastic rising trend in the area of selenium-containing polymers over the past decade. In this Perspective, the synthetic routes of selenium-containing polymers are summarized, and their unique stimuli-responsive properties are elaborated on, together with their diverse applications in the field of adaptive and biomedical materials.
Dynamic covalent bonds are extensively employed in dynamic combinatorial chemistry. The metathesis reaction of disulfide bonds is widely used, but requires catalysis or irradiation with ultraviolet ...(UV) light. It was found that diselenide bonds are dynamic covalent bonds and undergo dynamic exchange reactions under mild conditions for diselenide metathesis. This reaction is induced by irradiation with visible light and stops in the dark. The exchange is assumed to proceed through a radical mechanism, and experiments with 2,2,6,6‐tetramethylpiperidin‐1‐yloxyl (TEMPO) support this assumption. Furthermore, the reaction can be conducted in different solvents, including protic solvents. Diselenide metathesis can also be used to synthesize diselenide‐containing asymmetric block copolymers. This work thus entails the use of diselenide bonds as dynamic covalent bonds, the development of a dynamic exchange reaction under mild conditions, and an extension of selenium‐related dynamic chemistry.
Diselenide bonds are dynamic covalent bonds. Their metathesis can be induced by irradiation with visible light and likely proceeds through a radical mechanism, as the exchange reaction between two different diselenides was suppressed by the addition of the radical scavenger 2,2,6,6‐tetramethylpiperidine N‐oxide (TEMPO).
Heteroatom doping is an effective way to adjust the fluorescent properties of carbon quantum dots. However, selenium‐doped carbon dots have rarely been reported, even though selenium has unique ...chemical properties such as redox‐responsive properties owing to its special electronegativity. Herein, a facile and high‐output strategy to fabricate selenium‐doped carbon quantum dots (Se‐CQDs) with green fluorescence (quantum yield 7.6 %) is developed through the hydrothermal treatment of selenocystine under mild conditions. Selenium heteroatoms endow the Se‐CQDs with redox‐dependent reversible fluorescence. Furthermore, free radicals such as .OH can be effectively scavenged by the Se‐CQDs. Once Se‐CQDs are internalized into cells, harmful high levels of reactive oxygen species (ROS) in the cells are decreased. This property makes the Se‐CQDs capable of protecting biosystems from oxidative stress.
Hydrothermal treatment of selenocystine enabled selenium‐doped carbon quantum dots (Se‐CQDs) with redox‐dependent reversible fluorescence and free radical‐scavenging capability to be fabricated. Once Se‐CQDs are internalized into cells, harmful high levels of reactive oxygen species (ROS) in the cells are decreased. This property makes the Se‐CQDs capable of protecting biosystems from oxidative stress.
Amphiphilicity is one of the molecular bases for self‐assembly. By tuning the amphiphilicity of building blocks, controllable self‐assembly can be realized. This article reviews different routes for ...tuning amphiphilicity and discusses different possibilities for self‐assembly and disassembly in a controlled manner. In general, this includes irreversible and reversible routes. The irreversible routes concern irreversible reactions taking place on the building blocks and changing their molecular amphiphilicity. The building blocks are then able to self‐assemble to form different supramolecular structures, but cannot remain stable upon loss of amphiphilicity. Compared to the irreversible routes, the reversible routes are more attractive due to the good control over the assembly and disassembly of the supramolecular structure formed via tuning of the amphiphilicity. These routes involve reversible chemical reactions and supramolecular approaches, and different external stimuli can be used to trigger reversible changes of amphiphilicity, including light, redox, pH, and enzymes. It is anticipated that this line of research can lead to the fabrication of new functional supramolecular assemblies and materials.
Amphiphilicity is one of the molecular bases for self‐assembly. This review gives an overview on progress in controlled self‐assembly and disassembly through tuning the amphiphilicity of building blocks for the fabrication of functional supramolecular materials.
Wavelength‐controlled dynamic processes are mostly based on light‐triggered isomerization or the cleavage/formation of molecular connections. Control over dynamic metathesis reactions by different ...light wavelengths, which would be useful in controllable dynamic chemistry, has rarely been studied. Taking advantage of the different bond energies of disulfide and diselenide bonds, we have developed a wavelength‐driven exchange reaction between disulfides and diselenides, which underwent metathesis under UV light to produce Se−S bonds. When irradiated with visible light, the Se−S bonds were reversed back to those of the original reactants. The conversion of the exchange depends on the wavelength of the incident light. This light‐driven metathesis chemistry was also applied to tune the mechanical properties of polymer materials. The visible‐light‐induced reverse reaction was compatible with reductant‐catalyzed disulfide/diselenide metathesis, and could be utilized to develop a dissipative system with light as the energy input.
Controlled metathesis: Metathesis between disulfide and diselenide bonds was realized under irradiation, and the conversion of the exchange reaction could be controlled by modulating the wavelength of the light. This chemistry was applied to polymer materials to control the cleavage of polymers from a distance.
Plasticity of thermoset polymers has been realized by introducing exchangeable bonds, and the plasticity is mostly triggered via heat or UV light. Visible light is a relatively mild trigger that has ...not been used to induce plasticity in polymer materials. Herein, thermoset polyurethanes (PUs) containing diselenide bonds are fabricated that possess visible light-induced plasticity along with shape memory behavior. A series of PUs with different diselenide bond contents were tested and their shape memory properties and plasticity varied. With a higher diselenide bond content, both shape memory and light-induced plasticity are achieved. By combining these two properties, reshaping the permanent shapes of the PUs is easier. Compared with heat or UV light, visible light has the advantage of spatial control. For instance, a pattern of visible light was introduced by a commercial projector to demonstrate facile reshaping of the materials. Because visible light can be introduced via various methods, PUs with visible light-induced plasticity have great potential applications.
Cancer remains a major global health problem, causing significant economic burden worldwide. Current clinical cancer treatments are unsatisfactory in terms of both antitumor efficacy and ...biocompatibility. Meanwhile, nanomaterials attract much attention as potential treatment strategies with improved antitumor efficacy and reduced side effects. Selenium-containing nanomaterials are considered to be a promising biomaterial candidate among many different approaches during the last decade. Selenium-containing nanomaterials exhibit good biocompatibility since selenium is an essential trace element in human body. With rational design, selenium-containing nanomaterials show high sensitivity to redox stimuli and anticancer activity. Here, we discuss the development of selenium-containing nanomaterials as drug delivery carriers and anticancer drugs for cancer treatment. The nanomaterials with promising performance both in vitro and in vivo could advance to clinical therapies.
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Selenium-containing nanomaterial has been realized as a promising biomaterial during the last decade. Li and Xu discuss the development of selenium-containing nanomaterials as drug delivery carriers and anticancer drugs for cancer treatment. The nanomaterials with promising in vitro and in vivo performances are expected for clinical cancer therapies.
The development of efficient multiresponsive drug delivery systems (DDSs) to control drug release has been widely explored. Herein, a facile strategy is reported that enables the micelles of the ...selenium‐containing polymer with the drug to be encapsulated in metal‐organic frameworks (MOFs), which serves as multiresponsive drug release by employing the selenium‐containing polymers with redox‐triggered property and the MOFs with pH‐triggered property in DDS. In this case, the micelles of selenium‐containing polymers, as core easily disassembles in the presence of redox agents, can then release the drug in MOFs matrixes. The ZIF‐8 (one type of MOFs) crystal frameworks serving as shell can collapse only under low pH conditions, and the drug can be further released. In the presence of external redox agents as well as the pH stimuli, the prepared nanocomposite (P@ZIF‐8) drug system exhibits the capability of multiresponsive release of the doxorubicin (DOX) and possesses good selectivity in releasing the DOX under low pH conditions instead of normal pH conditions. In addition, the merits of P@ZIF‐8 such as good biocompatibility, multiresponsive release properties, and especially the selective release properties under different pH conditions make the materials highly promising candidates for the realization of controlled drug delivery in tumor tissue systems.
The multiresponsive P@ZIF‐8 as an advanced biocompatible drug delivery system (DDS) has been successfully prepared. The as‐prepared P@ZIF‐8 has excellent biocompatibility, good loading capacity, and controllable drug release and is suitable for doxorubicin storage/release as a smart DDS. These results suggest that hybrid nanocomposites may provide new possibilities for controllable drug release in biomaterials.
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