Transition-Metal-Based Nanozymes: Synthesis, Mechanisms of Therapeutic Action, and Applications in Cancer Treatment

Cancer, as one of the leading causes of death worldwide, drives the advancement of cutting-edge technologies for cancer treatment. Transition-metal-based nanozymes emerge as promising therapeutic nanodrugs that provide a reference for cancer therapy. In this review, we present recent breakthrough nanozymes for cancer treatment. First, we comprehensively outline the preparation strategies involved in creating transition-metal-based nanozymes, including hydrothermal method, solvothermal method, chemical reduction method, biomimetic mineralization method, and sol-gel method. Subsequently, we elucidate the catalytic mechanisms (catalase (CAT)-like activities), peroxidase (POD)-like activities), oxidase (OXD)-like activities) and superoxide dismutase (SOD)-like activities) of transition-metal-based nanozymes along with their activity regulation strategies such as morphology control, size manipulation, modulation, composition adjustment and surface modification under environmental stimulation. Furthermore, we elaborate on the diverse applications of transition-metal-based nanozymes in anticancer therapies encompassing radiotherapy (RT), chemodynamic therapy (CDT), photodynamic therapy (PDT), photothermal therapy (PTT), sonodynamic therapy (SDT), immunotherapy, and synergistic therapy. Finally, the challenges faced by transition-metal-based nanozymes are discussed alongside future research directions. The purpose of this review is to offer scientific guidance that will enhance the clinical applications of nanozymes based on transition metals.

DNA Hydrogels with Programmable Condensation, Expansion, and Degradation for Molecular Carriers

Molecular carriers are necessary for the controlled release of drugs and genes to achieve the desired therapeutic outcomes. DNA hydrogels can be a promising candidate in this application with their distinctive sequence-dependent programmability, which allows precise encapsulation of specific cargo molecules and stimuli-responsive release of them at the target. However, DNA hydrogels are inherently susceptible to the degradation of nucleases, making them vulnerable in a physiological environment. To be an effective molecular carrier, DNA hydrogels should be able to protect encapsulated cargo molecules until they reach the target and release them once they are reached. Here, we develop a simple way of controlling the enzyme resistance of DNA hydrogels for cargo protection and release by using cation-mediated condensation and expansion. We found that DNA hydrogels condensed by spermine are highly resistant to enzymatic degradation. They become degradable again if expanded back to their original, uncondensed state by sodium ions interfering with the interaction between spermine and DNA. These controllable condensation, expansion, and degradation of DNA hydrogels pave the way for the development of DNA hydrogels as an effective molecular carrier.

Custom-Design of Multi-Stimuli-Responsive Degradable Silica Nanoparticles for Advanced Cancer-Specific Chemotherapy

Chemotherapy is crucial in oncology for combating malignant tumors but often encounters obatacles such as severe adverse effects, drug resistance, and biocompatibility issues. The advantages of degradable silica nanoparticles in tumor diagnosis and treatment lie in their ability to target drug delivery, minimizing toxicity to normal tissues while enhancing therapeutic efficacy. Moreover, their responsiveness to both endogenous and exogenous stimuli opens up new possibilities for integrating multiple treatment modalities. This review scrutinizes the burgeoning utility of degradable silica nanoparticles in combination with chemotherapy and other treatment modalities. Commencing the elucidation of degradable silica synthesis and degradation mechanisms, emphasis is placed on the responsiveness of these materials to endogenous (e.g., pH, redox reactions, hypoxia, and enzymes) and exogenous stimuli (e.g., light and high-intensity focused ultrasound). Moreover, this exploration delves into strategies harnessing degradable silica nanoparticles in chemotherapy alone, coupled with radiotherapy, photothermal therapy, photodynamic therapy, gas therapy, immunotherapy, starvation therapy, and chemodynamic therapy, elucidating multimodal synergies. Concluding with an assessment of advances, challenges, and constraints in oncology, despite hurdles, future investigations are anticipated to augment the role of degradable silica in cancer therapy. These insights can serve as a compass for devising more efficacious combined tumor treatment strategies.

Responsive Supramolecular Polymers for Diagnosis and Treatment

Stimuli-responsive supramolecular polymers are ordered nanosized materials that are held together by non-covalent interactions (hydrogen-bonding, metal-ligand coordination, π-stacking and, host-guest interactions) and can reversibly undergo self-assembly. Their non-covalent nature endows supramolecular polymers with the ability to respond to external stimuli (temperature, light, ultrasound, electric/magnetic field) or environmental changes (temperature, pH, redox potential, enzyme activity), making them attractive candidates for a variety of biomedical applications. To date, supramolecular research has largely evolved in the development of smart water-soluble self-assemblies with the aim of mimicking the biological function of natural supramolecular systems. Indeed, there is a wide variety of synthetic biomaterials formulated with responsiveness to control and trigger, or not to trigger, aqueous self-assembly. The design of responsive supramolecular polymers ranges from the use of hydrophobic cores (i.e., benzene-1,3,5-tricarboxamide) to the introduction of macrocyclic hosts (i.e., cyclodextrins). In this review, we summarize the most relevant advances achieved in the design of stimuli-responsive supramolecular systems used to control transport and release of both diagnosis agents and therapeutic drugs in order to prevent, diagnose, and treat human diseases.

Molecularly Imprinted Nanomaterials with Stimuli Responsiveness for Applications in Biomedicine

The review aims to summarize recent reports of stimuli-responsive nanomaterials based on molecularly imprinted polymers (MIPs) and discuss their applications in biomedicine. In the past few decades, MIPs have been proven to show widespread applications as new molecular recognition materials. The development of stimuli-responsive nanomaterials has successfully endowed MIPs with not only affinity properties comparable to those of natural antibodies but also the ability to respond to external stimuli (stimuli-responsive MIPs). In this review, we will discuss the synthesis of MIPs, the classification of stimuli-responsive MIP nanomaterials (MIP-NMs), their dynamic mechanisms, and their applications in biomedicine, including bioanalysis and diagnosis, biological imaging, drug delivery, disease intervention, and others. This review mainly focuses on studies of smart MIP-NMs with biomedical perspectives after 2015. We believe that this review will be helpful for the further exploration of stimuli-responsive MIP-NMs and contribute to expanding their practical applications especially in biomedicine in the near future.

Stimuli-Responsive Sponge for Imaging and Measuring Weak Compression Stresses

Imaging and measuring compression stresses secure a safe and healthy life. Compression stresses in kPa range are not easily detected by conventional mechanoresponsive materials because microscopic molecular motion of the chromophores is not induced by such weak stresses. Moreover, imaging of the stress distribution is not achieved so far. The present study shows a sponge device combining two stimuli-responsive materials, a capsule releasing interior liquid and color-changing polymer in responses to compression stress and chemical stimulus, respectively. The stimuli-responsive capsule is dispersed on a melamine sponge comprised of the fibers with coating the layered polydiacetylene (PDA). The application of weak compression stresses induces collapse of the capsules, outflow of the interior liquid, and subsequent irreversible color change of PDA. The cascading response in the sponge device colorimetrically enables imaging of the distribution and measuring the strength of the compression stresses in kPa range. Furthermore, the device demonstrates imaging and measuring unknown weak compression stresses applied by the irregular-shaped objects. A couple of clinical issues in surgical operation of intestine are studied using the stress-imaging sponge device. The device and its design strategy can be applied to stress imaging in a variety of fields.

Dual-Responsive Glycopolymers for Intracellular Codelivery of Antigen and Lipophilic Adjuvants

Traditional approaches to vaccines use whole organisms to trigger an immune response, but they do not typically generate robust cellular-mediated immunity and have various safety risks. Subunit vaccines composed of proteins and/or peptides represent an attractive and safe alternative to whole organism vaccines, but they are poorly immunogenic. Though there are biological reasons for the poor immunogenicity of proteins and peptides, one other key to their relative lack of immunogenicity could be attributed to the poor pharmacokinetic properties of exogenously delivered proteins and peptides. For instance, peptides often aggregate at the site of injection and are not stable in biological fluids, proteins and peptides are rapidly cleared from circulation, and both have poor cellular internalization and endosomal escape. Herein, we developed a delivery system to address the lack of protein immunogenicity by overcoming delivery barriers as well as codelivering immune-stimulating adjuvants. The glycopolymeric nanoparticles (glycoNPs) are composed of a dual-stimuli-responsive block glycopolymer, poly[2-(diisopropylamino)ethyl methacrylate]-b-poly[(pyridyl disulfide ethyl methacrylate)-co-(methacrylamidoglucopyranose)] (p[DPA-b-(PDSMA-co-MAG)]). This polymer facilitates protein conjugation and cytosolic release, the pH-responsive release of lipophilic adjuvants, and pH-dependent membrane disruption to ensure cytosolic delivery of antigens. We synthesized p[DPA-b-(PDSMA-co-MAG)] by reversible addition-fragmentation chain transfer (RAFT) polymerization, followed by the formation and physicochemical characterization of glycoNPs using the p[DPA-b-(PDSMA-co-MAG)] building blocks. These glycoNPs conjugated the model antigen ovalbumin (OVA) and released OVA in response to elevated glutathione levels. Moreover, the glycoNPs displayed pH-dependent drug release of the model hydrophobic drug Nile Red while also exhibiting pH-responsive endosomolytic behavior as indicated by a red blood cell hemolysis assay. GlycoNPs coloaded with OVA and the toll-like receptor 7/8 (TLR-7/8) agonist Resiquimod (R848) activated DC 2.4 dendritic cells (DCs) significantly more than free OVA and R848 and led to robust antigen presentation of the OVA epitope SIINFEKL on major histocompatibility complex I (MHC-I). In sum, the dual-stimuli-responsive glycopolymer introduced here overcomes major protein and peptide delivery barriers and could vastly improve the immunogenicity of protein-based vaccines.

Stimuli-responsive crosslinked nanomedicine for cancer treatment

Nanomedicines are attractive paradigms to deliver drugs, contrast agents, immunomodulators, and gene editors for cancer therapy and diagnosis. However, the currently developed nanomedicine suffers from poor serum stability, premature drug release, and lack of responsiveness. Crosslinking strategy can be utilized to overcome these shortcomings by employing stimuli-responsive chemical bonds to tightly hold the nanostructure and releasing the payloads spatiotemporally in a highly controlled manner. In this Review, we summarize the recently ingenious design of the stimuli-responsive crosslinked nanomedicines (SCN) in the field of cancer treatment and their advances in circumventing the drawbacks of the conventional drug delivery system. We classify the SCNs into three categories based on the crosslinking strategies, including built-in, on-surface, and inter-particle crosslinking nanomedicines. Thanks to the stimuli-responsive crosslinkages, SCNs are capable of keeping robust stability during systemic circulation. They also respond to the particular tumoral conditions to experience a series of dynamic changes, such as the changes in size, surface charge, targeting moieties, integrity, and imaging signals. These characteristics allow them to efficiently overcome different biological barriers and substantially improve the drug delivery efficiency, tumor-targeting ability, and imaging sensitivities. With the examples discussed, we envision that our perspectives can inspire more attempts to engineer intelligent nanomedicine to achieve effective cancer therapy and diagnosis.

Fabrication Strategies Towards Hydrogels for Biomedical Application: Chemical and Mechanical Insights

This review aims at giving selected chemical and mechanical insights on design criteria that should be taken into account in hydrogel production for biomedical applications. Particular emphasis will be given to the chemical aspects involved in hydrogel design: macromer chemical composition, cross-linking strategies and chemistry towards "conventional" and smart/stimuli responsive hydrogels. Mechanical properties of hydrogels in view of regenerative medicine applications will also be considered.

Emerging Strategies in Stimuli-Responsive Prodrug Nanosystems for Cancer Therapy

Prodrugs are chemically modified drug molecules that are inactive before administration. After administration, they are converted in situ to parent drugs and induce the mechanism of action. The development of prodrugs has upgraded conventional drug treatments in terms of bioavailability, targeting, and reduced side effects. Especially in cancer therapy, the application of prodrugs has achieved substantial therapeutic effects. From serendipitous discovery in the early stage to functional design with pertinence nowadays, the importance of prodrugs in drug design is self-evident. At present, studying stimuli-responsive activation mechanisms, regulating the stimuli intensity in vivo, and designing nanoscale prodrug formulations are the major strategies to promote the development of prodrugs. In this review, we provide an outlook of recent cutting-edge studies on stimuli-responsive prodrug nanosystems from these three aspects. We also discuss prospects and challenges in the future development of such prodrugs.

Recent Advances in Stimuli-Responsive DNA-Based Hydrogels

Stimuli-responsive DNA-based hydrogels are attracting growing interest because of their smart responsiveness, excellent biocompatibility, regulated biodegradability, and programmable design properties. Integration of reconfigurable DNA architectures and switchable supramolecular moieties (as cross-linkers) in hydrogels by responding to external stimuli provides an ideal approach for the reversible tuning structural and mechanical properties of the hydrogels, which can be exploited in the development of intelligent DNA-based materials. This review highlights recent advances in the design of responsive pure DNA hydrogels, DNA-polymer hybrid hydrogels, and autonomous DNA-based hydrogels with transient behaviors. A variety of chemically and physically triggered DNA-based stimuli-responsive hydrogels and their versatile applications in biosensing, biocatalysis, cell culture and separation, drug delivery, shape memory, self-healing, and robotic actuators are summarized. Finally, we address the key challenges that the field will face in the coming years, and future prospects are identified.

Drug Delivery Based on Stimuli-Responsive Injectable Hydrogels for Breast Cancer Therapy: A Review

Breast cancer is the most common and biggest health threat for women. There is an urgent need to develop novel breast cancer therapies to overcome the shortcomings of conventional surgery and chemotherapy, which include poor drug efficiency, damage to normal tissues, and increased side effects. Drug delivery systems based on injectable hydrogels have recently gained remarkable attention, as they offer encouraging solutions for localized, targeted, and controlled drug release to the tumor site. Such systems have great potential for improving drug efficiency and reducing the side effects caused by long-term exposure to chemotherapy. The present review aims to provide a critical analysis of the latest developments in the application of drug delivery systems using stimuli-responsive injectable hydrogels for breast cancer treatment. The focus is on discussing how such hydrogel systems enhance treatment efficacy and incorporate multiple breast cancer therapies into one system, in response to multiple stimuli, including temperature, pH, photo-, magnetic field, and glutathione. The present work also features a brief outline of the recent progress in the use of tough hydrogels. As the breast undergoes significant physical stress and movement during sporting and daily activities, it is important for drug delivery hydrogels to have sufficient mechanical toughness to maintain structural integrity for a desired period of time.

Toward enzyme-responsive polymersome drug delivery

In drug delivery, enzyme-responsive drug carriers are becoming increasingly relevant because of the growing association of disease pathology with enzyme overexpression. Polymersomes are of interest to such applications because of their tunable properties. While polymersomes open up a wide range of chemical and physical properties to explore, they also present a challenge in developing generalized rules for the synthesis of novel systems. Motivated by this issue, in this perspective, we summarize the existing knowledge on enzyme-responsive polymersomes and outline the main design choices. Then, we propose heuristics to guide the design of novel systems. Finally, we discuss the potential of an integrated approach using computer simulations and experimental studies to streamline this design process and close the existing knowledge gaps.

Macrocycle Dynamics in a Branched [8]Catenane Controlled by Three Different Stimuli in Three Different Regions

A branched [8]catenane from an efficient one-pot synthesis (72 % HPLC yield, 59 % isolated yield) featuring the simultaneous use of three kinds of templates and cucurbit[6]uril-mediated azide-alkyne cycloaddition (CBAAC) for ring-closing is reported. Design and assembly of the [8]catenane precursors are unexpectedly complex that can involve cooperating, competing and non-influencing interactions. Due to the branched structure, dynamics of the [8]catenane can be modulated in different extent by rigidifying/loosening the mechanical bonds at different regions by using solvent polarity, acid-base and metal ions as the stimuli. This work not only highlights the importance of understanding the delicate interplay of the weak and non-obvious supramolecular interactions in the synthesis of high-order [n]catenane, but also demonstrates a complex control of dynamics and flexibility for exploiting [n]catenanes applications.

Photocrosslinked, Tunable Protein Vesicles for Drug Delivery Applications

Recombinant proteins have emerged as promising building blocks for vesicle self-assembly because of their versatility through genetic manipulation and biocompatibility. Vesicles composed of thermally responsive elastin-like polypeptide (ELP) fusion proteins encapsulate cargo during assembly. However, vesicle stability in physiological environments remains a significant challenge for biofunctional applications. Here, incorporation of an unnatural amino acid, para-azido phenylalanine, into the ELP domain is reported to enable photocrosslinking of protein vesicles and tuning of vesicle size and swelling. The size of the vesicles can be tuned by changing ELP hydrophobicity and ionic strength. Protein vesicles are assessed for their ability to encapsulate doxorubicin and dually deliver doxorubicin and fluorescent protein in vitro as a proof of concept. The resulting photocrosslinkable vesicles made from full-sized, functional proteins show high potential in drug delivery applications, especially for small molecule/protein combination therapies or targeted therapies.

Smart Cargo Delivery System based on Mesoporous Nanoparticles for Bone Disease Diagnosis and Treatment

Bone diseases constitute a major issue for modern societies as a consequence of progressive aging. Advantages such as open mesoporous channel, high specific surface area, ease of surface modification, and multifunctional integration are the driving forces for the application of mesoporous nanoparticles (MNs) in bone disease diagnosis and treatment. To achieve better therapeutic effects, it is necessary to understand the properties of MNs and cargo delivery mechanisms, which are the foundation and key in the design of MNs. The main types and characteristics of MNs for bone regeneration, such as mesoporous silica (mSiO2 ), mesoporous hydroxyapatite (mHAP), mesoporous calcium phosphates (mCaPs) are introduced. Additionally, the relationship between the cargo release mechanisms and bone regeneration of MNs-based nanocarriers is elucidated in detail. Particularly, MNs-based smart cargo transport strategies such as sustained cargo release, stimuli-responsive (e.g., pH, photo, ultrasound, and multi-stimuli) controllable delivery, and specific bone-targeted therapy for bone disease diagnosis and treatment are analyzed and discussed in depth. Lastly, the conclusions and outlook about the design and development of MNs-based cargo delivery systems in diagnosis and treatment for bone tissue engineering are provided to inspire new ideas and attract researchers' attention from multidisciplinary areas spanning chemistry, materials science, and biomedicine.

Targeted Delivery of Persulfides to the Gut: Effects on the Microbiome

Persulfides (R-SSH) have been hypothesized as potent redox modulators and signaling compounds. Reported herein is the synthesis, characterization, and in vivo evaluation of a persulfide donor that releases N-acetyl cysteine persulfide (NAC-SSH) in response to the prokaryote-specific enzyme nitroreductase. The donor, termed NDP-NAC, decomposed in response to E. coli nitroreductase, resulting in release of NAC-SSH. NDP-NAC elicited gastroprotective effects in mice that were not observed in animals treated with control compounds incapable of persulfide release or in animals treated with Na2 S. NDP-NAC induced these effects by the upregulation of beneficial small- and medium-chain fatty acids and through increasing growth of Turicibacter sanguinis, a beneficial gut bacterium. It also decreased the populations of Synergistales bacteria, opportunistic pathogens implicated in gastrointestinal infections. This study reveals the possibility of maintaining gut health or treating microbiome-related diseases by the targeted delivery of reactive sulfur species.

Responsive Photonic Liquid Marbles

Liquid marbles have potential to serve as mini-reactors for fabricating new materials, but this has been exploited little and mostly for conventional chemical reactions. Here, we uncover the unparalleled capability of liquid marbles to act as platforms for controlling the self-assembly of a bio-derived polymer, hydroxypropyl cellulose, into a cholesteric liquid crystalline phase showing structural coloration by Bragg reflection. By adjusting the cholesteric pitch via quantitative water extraction, we achieve liquid marbles that we can tailor for structural color anywhere in the visible range. Liquid marbles respond with color change that can be detected by eye, to changes in temperature, exposure to toxic chemicals and mechanical deformation. Our concept demonstrates the advantages of using liquid marbles as a miniature platform for controlling the liquid crystal self-assembly of bio-derived polymers, and their exploitation to fabricate sustainable, responsive soft photonic objects.

Toward Stimuli-Responsive Dynamic Thermosets through Continuous Development and Improvements in Covalent Adaptable Networks (CANs)

Covalent adaptable networks (CANs), unlike typical thermosets or other covalently crosslinked networks, possess a unique, often dormant ability to activate one or more forms of stimuli-responsive, dynamic covalent chemistries as a means to transition their behavior from that of a viscoelastic solid to a material with fluid-like plastic flow. Upon application of a stimulus, such as light or other irradiation, temperature, or even a distinct chemical signal, the CAN responds by transforming to a state of temporal plasticity through activation of either reversible addition or reversible bond exchange, either of which allows the material to essentially re-equilibrate to an altered set of conditions that are distinct from those in which the original covalently crosslinked network is formed, often simultaneously enabling a new and distinct shape, function, and characteristics. As such, CANs span the divide between thermosets and thermoplastics, thus offering unprecedented possibilities for innovation in polymer and materials science. Without attempting to comprehensively review the literature, recent developments in CANs are discussed here with an emphasis on the most effective dynamic chemistries that render these materials to be stimuli responsive, enabling features that make CANs more broadly applicable.

Self-Assembly of Supramolecular DNA Amphiphiles through Host-Guest Interaction and Their Stimuli-Responsiveness

Smart DNA nanostructures have found potential application in material science and biomedicine. Most building blocks are DNA amphiphiles covalently synthesized from DNA and hydrophobic molecules. Here, the noncovalent approach based on the host-guest interaction between cucurbit[7]uril (CB[7]) and two hydrophobic guests with different topologies is utilized to modularly construct supramolecular DNA amphiphiles including DNA-CB[7]/ferrocene derivative and DNA-CB[7]/adamantine derivative. Both of the supramolecular DNA amphiphiles assemble into uniform spherical micelles, which can encapsulate hydrophobic Nile Red molecules and anchor gold nanoparticles through DNA hybridization. In addition, 1-adamantanamine hydrochloride, a competitive guest with a strong binding constant with CB[7], induces the dissociation of DNA-CB[7]/ferrocene derivative micelles. More importantly, the redox properties of ferrocene induce reversible morphology changes between the spherical micelles and the dissociated state. These stimuli-responsive DNA supra-amphiphilic micelles, as novel vehicles, expand the family of smart DNA nanostructures.

pH-Induced Transition Between Single-Chain Macrocyclic Amphiphile and [c2]Daisy Chain-Based Bola-Type Amphiphile and the Related Self-Assembly Behavior in Water

Macrocyclic amphiphiles, a type of amphiphiles synthesized based on macrocyclic compounds, have attracted much attention over the past decades due to their unique superiority in the construction of various functional nanomaterials. The regulation of the state of macrocyclic amphiphiles by introducing stimuli-responsive motif to macrocyclic amphiphiles is an efficient way to extend their applications in diverse fields. Herein, pillararene-based macrocyclic amphiphile H1 was prepared. H1 can act as single-chain amphiphile to self-assemble into micelles in water when the pH was ≥5.0. H1 can be protonated to turn into H2 when pH changed to <5.0. Interestingly, H2 formed [c2]daisy chain-based bola-type supramolecular amphiphile. This bola-type supramolecular amphiphile self-assembled into nanosheets in water. Therefore, pH-induced transition between single-chain macrocyclic amphiphile and bola-type amphiphile and the corresponding self-assembly system based on pillararene in water were constructed.

Tunable Decoupling of Dual Drug Release of Oppositely Charged, Stimuli-Responsive Anisotropic Nanoparticles

Multicompartmentalized nanostructures are of interest because they can provide unique physicochemical properties and multifunctionalities in each compartment. Furthermore, stimuli-responsive anisotropic nanostructures (ANPs) with distinct opposite charges would be useful for drug delivery systems because different drug release kinetics could be achieved from each compartment in response to both charge and stimuli. In this study, stimuli-responsive ANPs were formed via electrohydrodynamic cojetting of poly(N-isopropylacrylamide)-based copolymers with opposite charges. The positively charged compartment consisted of poly(N-isopropylacylamide-co-stearyl acrylate-co-allylamine) (poly(NIPAM-co-SA-co-AAm)) (i.e., PNSAAm) and poly(N-isopropylacylamide-co-stearyl acrylate-co-acrylic acid) (poly(NIPAM-co-SA-co-AAc)) (i.e., PNSAAc). The two distinct compartments of ANPs were physically cross-linked through hydrophobic interactions within the copolymers. Oppositely charged, small-molecule model drugs (fluorescein sodium salt and rhodamine 6G) were separately encapsulated within each compartment and released based on changes in noncovalent interactions and temperature. Furthermore, two different biomacromolecule drugs with opposite charges, bovine serum albumin and lysozyme (which were complexed with polysaccharides by hydrophobic ion pairing), were loaded within the ANPs. Electrostatic interactions between the encapsulated drugs and each ANP compartment controlled the rate of drug release from the ANPs. In addition, these ANPs showed a thermally induced actuation, leading to drug release at different rates due to the collapse of poly(NIPAM)-based copolymers under aqueous conditions. This work may be useful for decoupled drug release kinetics.

Stimuli-Responsive Hydrogels with Antibacterial Activity Assembled from Guanosine, Aminoglycoside, and a Bifunctional Anchor

Multistimuli-responsive hydrogels with specific functions have attracted great interest for biomedical applications; however, these smart hydrogels usually require the presynthesis of macromolecular building blocks with multiple ligands and the integration of bioactive cargoes into the gels. Here, a multistimuli-responsive hydrogel with potent antibacterial activity by a combination of supramolecular assembly and iminoboronate chemistry is reported. The hydrogel consists of all-small-molecule building blocks including aminoglycoside, guanosine, potassium ion, and a bifunctional anchor bearing both boronic acid and aldehyde groups. Guanosines form quadruplexes in the presence of potassium ions via supramolecular assembly, and the bifunctional anchor connects aminoglycosides, a class of potent antibiotics to cis-diol groups on quadruplexes via dynamic iminoboronate chemistry, yielding a smart hydrogel containing abundant antibiotics. The hydrogel is sensitive to multistimuli such as heat, acids, oxidants, glucose and crown ether, which promote the release of antibiotics from the gels. Moreover, the prepared hydrogels show potent antibacterial activities both in vitro and in vivo. The results provide a new option to prepare antibacterial hydrogels with multistimuli responsiveness via facile chemistry using all-small-molecule building blocks.

Biotinylated Bilirubin Nanoparticles as a Tumor Microenvironment-Responsive Drug Delivery System for Targeted Cancer Therapy

The tumor microenvironment (TME) plays a crucial role in tumorigenesis and cancer cell metastasis. Accordingly, a drug-delivery system (DDS) that is capable of targeting tumor and releasing drugs in response to TME-associated stimuli should lead to potent antitumor efficacy. Here, a cancer targeting, reactive oxygen species (ROS)-responsive drug delivery vehicle as an example of a TME-targeting DDS is reported. Tumor targeting is achieved using biotin as a ligand for "biotin transporter"-overexpressing malignant tumors, and bilirubin-based nanoparticles (BRNPs) are used as a drug-delivery carrier that enables ROS-responsive drug release. Doxorubicin-loaded, biotinylated BRNPs (Dox@bt-BRNPs) with size of ≈100 nm are prepared by a one-step self-assembly process. Dox@bt-BRNPs exhibit accelerated Dox-release behavior in response to ROS and show specific binding as well as anticancer activity against biotin transporter-overexpressing HeLa cells in vitro. bt-BRNPs labeled with cypate, near-infrared dye, show much greater accumulation at tumor sites in HeLa tumor-bearing mice than BRNPs lacking the biotin ligand. Finally, intravenous injection of Dox@bt-BRNPs into HeLa tumor-bearing mice results in greater antitumor efficacy compared with free Dox, bt-BRNPs only, and Dox@BRNPs without causing any appreciable body weight loss. Collectively, these findings suggest that bt-BRNPs hold potential as a new TME-responsive DDS for effectively treating various tumors.

Hybrid Nanoparticles as Drug Carriers for Controlled Chemotherapy of Cancer

Rapid developments in materials science and biological mechanisms have greatly boosted the research discoveries of new drug delivery systems. In the past few decades, hundreds of nanoparticle-based drug carriers have been reported almost on a daily basis, in which new materials, structures, and mechanisms are proposed and evaluated. Standing out among the drug carriers, the hybrid nanoparticle systems offer a great opportunity for the optimization and improvement of conventional chemotherapy. By combining several features of functional components, these hybrid nanoparticles have shown excellent promises of improved biosafety, biocompatibility, multifunctionality, biodegradability, and so forth. In this Personal Account, we highlight the recent research advances of some representative hybrid nanoparticles as drug delivery systems and discuss their design strategies and responsive mechanisms for controlled drug delivery.

Supramolecular Assemblies Responsive to Biomolecules toward Biological Applications

Stimuli-responsive supramolecular assemblies consisting of small molecules are attractive functional materials for biological applications such as drug delivery, medical diagnosis, enzyme immobilization, and tissue engineering. By use of their dynamic and reversible properties, many supramolecular assemblies responsive to a variety of biomolecules have been designed and synthesized. This review focuses on promising strategies for the construction of such dynamic supramolecular assemblies and their functions. While studies of biomolecule-responsive supramolecular assemblies have mainly been performed in vitro, it has recently been demonstrated that some of them can work in live cells. Supramolecular assemblies now open up new avenues in chemical biology and biofunctional materials.

Fabrication and characterization of anisotropic nanofiber scaffolds for advanced drug delivery systems

Stimuli-responsive, polymer-based nanostructures with anisotropic compartments are of great interest as advanced materials because they are capable of switching their shape via environmentally-triggered conformational changes, while maintaining discrete compartments. In this study, a new class of stimuli-responsive, anisotropic nanofiber scaffolds with physically and chemically distinct compartments was prepared via electrohydrodynamic cojetting with side-by-side needle geometry. These nanofibers have a thermally responsive, physically-crosslinked compartment, and a chemically-crosslinked compartment at the nanoscale. The thermally responsive compartment is composed of physically crosslinkable poly(N-isopropylacrylamide) poly(NIPAM) copolymers, and poly(NIPAM-co-stearyl acrylate) poly(NIPAM-co-SA), while the thermally-unresponsive compartment is composed of polyethylene glycol dimethacrylates. The two distinct compartments were physically crosslinked by the hydrophobic interaction of the stearyl chains of poly(NIPAM-co-SA) or chemically stabilized via ultraviolet irradiation, and were swollen in physiologically relevant buffers due to their hydrophilic polymer networks. Bicompartmental nanofibers with the physically-crosslinked network of the poly(NIPAM-co-SA) compartment showed a thermally-triggered shape change due to thermally-induced aggregation of poly(NIPAM-co-SA). Furthermore, when bovine serum albumin and dexamethasone phosphate were separately loaded into each compartment, the bicompartmental nanofibers with anisotropic actuation exhibited decoupled, controlled release profiles of both drugs in response to a temperature. A new class of multicompartmental nanofibers could be useful for advanced nanofiber scaffolds with two or more drugs released with different kinetics in response to environmental stimuli.

Rapid and extensive collapse from electrically responsive macroporous hydrogels

Electrically responsive hydrogels are created with interconnected macropores, which greatly enhance their ability to rapidly undergo volumetric collapse when subjected to moderate electric fields. When optimized, these electrogels are easily integrated into arrays capable of rapid configurational and chromatic optical modulations, and when loaded with drugs, are able to coordinate the delivery profile of multiple drugs.