Enzyme-Responsive Molecular Assemblies Based on Host-Guest Chemistry

An enzyme/pH dual-responsive supramolecular fluorescent vesicle with tunable size fabricated by europium complex and polypseudorotaxanes

The fluorescent vesicles based on lanthanide ions are considered as an ideal biomimetic optical nanoplatform for simulating biological processes of cell membrane. However, the accurately and controllably adjusting the size of vesicles based on lanthanides while ensuring their fluorescence performance and stability still remains a challenge. Herein, a dual-stimuli-responsive fluorescent supramolecular vesicle with tunable size has been designed based on host-guest interaction and coordinating aggregation. Europium complexes can be encapsulated within supramolecular assemblies by assembling with polypseudorotaxanes (PPRs), which are formed by F127 and carboxymethyl-β-cyclodextrin (CMCD) through host-guest interaction. The fluorescence properties of the europium complexes have been significantly enhanced by confining and shielding them within vesicles. Upon the addition of α-amylase and HCl, the fluorescence intensity of the vesicles will gradually and significantly quench as a result of CMCD degradation and dissociation of the europium complexes. This research presents a convenient method for regulating the size of lanthanide fluorescent vesicles, and the supramolecular vesicles obtained with multi-stimuli response are anticipated to be utilized in the diagnosis of relevant diseases and targeted drug delivery.

Enzyme-Responsive Supramolecular Self-Assembly in Small Amphiphiles

Enzyme-responsive molecular assemblies have recently made remarkable progress, owing to their widespread applications. As a class of catalysts with high specificity and efficiency, enzymes play a critical role in producing new molecules and maintaining metabolic stability in living organisms. Therefore, the study of enzyme-responsive assembly aids in understanding the origin of life and the physiological processes occurring within living bodies, contributing to further advancements across various disciplines. In this Review, we summarize three kinds of enzyme-responsive assembly systems in amphiphiles: enzyme-triggered assembly, disassembly, and structural transformation. Furthermore, motivated by the fact that biological macromolecules and complex structures all originated with small molecules, our focus lies on the small amphiphiles (e.g., peptides, surfactants, fluorescent molecules, and drug molecules). We also provide an outlook on the potential of enzyme-responsive assembly systems for biomimetic development and hope this Review will attract more attention to this emerging research branch at the intersection of assembly chemistry and biological science.

Propulsion mechanisms of micro/nanorobots: a review

Micro/nanomotors (MNMs) are intelligent, efficient and promising micro/nanorobots (MNR) that can respond to external stimuli (e.g., chemical energy, temperature, light, pH, ultrasound, magnetic, biosignals, ions) and perform specific tasks. The MNR can adapt to different external stimuli and transform into various functional forms to match different application scenarios. So far, MNR have found extensive application in targeted therapy, drug delivery, tissue engineering, environmental remediation, and other fields. Despite the promise of MNR, there are few reviews that focus on them. To shed new light on the further development of the field, it is necessary to provide an overview of the current state of development of these MNR. Therefore, this paper reviews the research progress of MNR in terms of propulsion mechanisms, and points out the pros and cons of different stimulus types. Finally, this paper highlights the current challenges faced by MNR and proposes possible solutions to facilitate the practical application of MNR.

Expanding the scope of self-assembled supramolecular biosensors: a highly selective and sensitive enzyme-responsive AIE-based fluorescent biosensor for trypsin detection and inhibitor screening

Trypsin, a pancreatic enzyme associated with diseases like pancreatic cancer and cystic fibrosis, requires effective diagnostic tools. Current detection systems seldom utilize macrocyclic molecules and tetraphenyl ethylene (TPE) derivative-based supramolecular assemblies, known for their biocompatibility and aggregation-induced emission (AIE) properties, for trypsin detection. This study presents an enzyme-responsive, AIE-based fluorescence 'Turn-On' sensing platform for trypsin detection, employing sulfated-β-cyclodextrin (S-βCD), an imidazolium derivative of TPE (TPE-IM), and protamine sulfate (PrS). The anionic S-βCD and cationic TPE-IM formed a strongly fluorescent supramolecular aggregation complex in an aqueous buffer. However, PrS suppresses fluorescence because of its strong binding affinity with S-βCD. The non-fluorescent TPE-IM/S-βCD/PrS supramolecular assembly system exhibits trypsin-responsive properties, as PrS is a known trypsin substrate. Trypsin restores fluorescence in the TPE-IM/S-βCD system through the enzymatic cleavage of PrS, correlating linearly with trypsin catalytic activity in the 0-10 nM concentration range. The limit of detection is 10 pM. This work contributes to the development of self-assembled supramolecular biosensors using charged TPE derivatives and β-cyclodextrin-based host-guest chemistry, offering an innovative fluorescence 'Turn-On' trypsin sensing platform. The sensing system is highly stable under various conditions, selective for trypsin, and demonstrates potential for biological analysis and disease diagnosis in human serum. Additionally, it shows promise for the screening of trypsin inhibitors.

Enzyme-Instructed Host-Guest Assembly/Disassembly for Biomedical Applications

Compared with the normal assembly/disassembly approaches, enzyme-instructed host-guest assembly/disassembly strategies due to their superior biocompatibility and specificity for specific substrates, can more effectively and precisely release molecules at lesions for reflecting in vivo biological events. Specifically, due to the over-expression of enzymes in specific tissues, the assembly/disassembly processes can directly occur on the pathological sites (or regions of interest), thus these enzyme-instructed processes are widely and effectively used for disease treatment or precise bioimaging. Based on it, we introduce the concept and major strategies of enzyme-instructed host-guest assembly/disassembly, illustrate their importance in the diagnosis and treatment of diseases, and review their advances in biomedical applications. Further, the challenges of these strategies in the clinic and future tendencies are also prospected.

Preparation, Stimulus-Response Mechanisms and Applications of Micro/Nanorobots

Micro- and nanorobots are highly intelligent and efficient. They can perform various complex tasks as per the external stimuli. These robots can adapt to the required functional form, depending on the different stimuli, thus being able to meet the requirements of various application scenarios. So far, microrobots have been widely used in the fields of targeted therapy, drug delivery, tissue engineering, environmental remediation and so on. Although microbots are promising in some fields, few reviews have yet focused on them. It is therefore necessary to outline the current status of these microbots' development to provide some new insights into the further evolution of this field. This paper critically assesses the research progress of microbots with respect to their preparation methods, stimulus-response mechanisms and applications. It highlights the suitability of different preparation methods and stimulus types, while outlining the challenges experienced by microbots. Viable solutions are also proposed for the promotion of their practical use.

Stimuli-Responsive Functional Micro-/Nanorobots: A Review

Stimuli-responsive functional micro-/nanorobots (srFM/Ns) are a class of intelligent, efficient, and promising microrobots that can react to external stimuli (such as temperature, light, ultrasound, pH, ion, and magnetic field) and perform designated tasks. Through adaptive transformation into the corresponding functional forms, they can perfectly match the demands depending on different applications, which manifest extremely important roles in targeted therapy, biological detection, tissue engineering, and other fields. Promising as srFM/Ns can be, few reviews have focused on them. It is therefore necessary to provide an overview of the current development of these intelligent srFM/Ns to provide clear inspiration for further development of this field. Hence, this review summarizes the current advances of stimuli-responsive functional microrobots regarding their response mechanism, the achieved functions, and their applications to highlight the pros and cons of different stimuli. Finally, we emphasize the existing challenges of srFM/Ns and propose possible strategies to help accelerate the study of this field and promote srFM/Ns toward actual applications.

Crosslinked and Multi-Responsive Polymeric Vesicles as a Platform to Study Enzyme-Mediated Undocking Behavior: Toward Future Artificial Organelle Communication

Various cellular functions are successfully mimicked, opening the door to the next generation of therapeutic approaches and systems biology. Herein, the first steps are taken toward the construction of artificial organelles for mimicking cell communication by docking and undocking of cargo in the membrane of swollen artificial organelles. Stimuli-responsive and crosslinked polymeric vesicles are used to allow docking processes at acidic pH at which ferrocene units in the swollen membrane state can undergo desired specific host-guest interaction using β-cyclodextrin as model cargo. The release of the cargo mediated by two different enzymes, glucose oxidase and α-amylase, is investigated, triggered by distinct enzymatic undocking mechanisms. Different release times for a useful transport are shown that can be adapted to different communication pathways. In addition, Förster resonance energy transfer (FRET) experiments further support the hypotheses of host-guest inclusion complexation formation and their time-dependent breakdown. This work paves a way to a platform based on polymeric vesicles for synthetic biology, cell functions mimicking, and the construction of multifunctional cargo delivery system.

Hyaluronidase-trigger nanocarriers for targeted delivery of anti-liver cancer compound

Chemotherapy is recognized as one of the significant treatment methods for liver cancer. The compound celastrol (CSL) could effectively inhibit the proliferation, migration, and invasion of liver cancer cells, which is regarded as a promising candidate to become a mainstream anti-liver cancer drug. However, the application of CSL in liver cancer chemotherapy is limited due to its systemic toxicity, poor water solubility, multidrug resistance, premature degradation, and lack of tumor targeting. Meanwhile, in order to comply with the current concept of precision medicine, precisely targeted delivery of the anti-liver compound CSL was desired. This paper takes into account that liver cancer cells were equipped with hyaluronic acid (HA) receptors (CD44) on their surface and overexpressed. Hyaluronidase (HAase) capable of degrading HA, HAase-responsive nanocarriers (NCs), named HA/(MI)₇-β-CD NCs, were prepared based on the electrostatic interaction between HA and imidazole moieties modified β-cyclodextrin (MI)₇-β-CD. HA/(MI)₇-β-CD NCs showed disassembly properties under HAase stimuli, which was utilized to trap, deliver, and the controllable release of the anti-liver cancer compound CSL. Furthermore, cytotoxicity assay experiments revealed that CSL-trapped HA/(MI)₇-β-CD NCs not only reduced cytotoxicity for normal cells but also effectively inhibited the survival for five tumor cells, and even the apoptotic effect of CSL-trapped NCs with a concentration of 5 μg mL^-1 on tumor cells (SMMC-7721) was consistent with free CSL. Cell uptake experiments demonstrated HA/(MI)₇-β-CD NCs possessed the capability of targeted drug delivery to cancerous cells. HA/(MI)₇-β-CD NCs exhibited site-specific and controllable release performance, which is anticipated to proceed further in precision-targeted drug delivery systems.

Controlled Cascade-Release and High Selective Sterilization by Core-Shell Nanogels for Microenvironment Regulation of Aerobic Vaginitis

Aerobic vaginitis (AV) is a gynecological disease associated with vaginal flora imbalance. The nonselective bactericidal nature of antibiotics and low customization rate of probiotic supplementation in existing treatments lead to AV recurrence. Here, a drug delivery strategy is proposed that works with the changing dynamics of the bacterial flora. In particular, a core-shell nanogel (CSNG) is designed to encapsulate prebiotic inulin and antimicrobial peptide Cath 30. The proposed strategy allows for the sequential release of both drugs using gelatinase produced by AV pathogenic bacteria, initially selectively killing pathogenic bacteria and subsequently promoting the proliferation of beneficial bacteria in the vagina. In a simulated infection environment in vitro, the outer layer of CSNGs, Cath 30 is rapidly degraded and potently killed the pathogenic bacterium Staphylococcus aureus at 2-6 h. CSNGs enhances proliferation of the beneficial bacterium Lactobacillus crispatus by more than 50% at 24 h. In a rat AV model, the drug delivery strategy precisely regulated the bacterial microenvironment while controlling the inflammatory response of the vaginal microenvironment. This new treatment approach, configured on demand and precisely controlled, offers a new strategy for the treatment of vaginal diseases.

Multiple Effects of an Anionic Cyclodextrin Macrocycle on the Reversible Isomerization of a Photoactive Guest Dye

Understanding and controlling the reversible isomerization of photoactive molecules in order to obtain a tunable optical response is desirable for many photofunctional applications. This study describes the interesting effects of an anionic cyclodextrin host (sulfated-βCD, SCD) on the photoisomerization and protonation equilibrium of an important hemicyanine dye (trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide, DSP). The SCD host assists in unlocking the photoisomerization potential of DSP by promoting protonation of the dye. It also assists in stabilizing the cis isomer of the protonated dye, thereby significantly delaying the reverse cis to trans isomerization of DSPH⁺. Furthermore, the interplay of both hydrophobic and electrostatic interactions in the complex formation of SCD with DSPH⁺ makes the reverse cis to trans isomerization of DSPH⁺ amenable to influence by the added salt. The stimuli-responsive reversible isomerization of SCD-DSPH⁺ is an interesting case from the perspective of chemical sensing or light operated functional materials with host-guest systems.

Stretchable and fatigue resistant hydrogels constructed by natural galactomannan for flexible sensing application

Exploration of sustainable and functional materials from biomolecules has received much interest, while the limited mechanical property and possible bacterial contamination were proved to be their major shortages. Here, we proposed novel double network (DN) hydrogels based on galactomannan (GM) polysaccharide as backbone. Folic acid (FA) and polyacrylamide (PAM) were introduced to form hydrogen bond linkages and covalent bond networks respectively. The three-dimensional hydrogel networks showed greatly improved mechanical strength. Impressive compressive fatigue resistance was present for 100 cycles' compression forming only 0.7 % shape deformation. The phenomenon was mainly attributed to promoted stress-bearing and energy dissipation from the DN cross-linking. The GM hydrogels also exhibited good electronic conductivity and excellent anti-bacterial capabilities with inhibition against more than 80 % of E. coli., attributing to the tunable attachments of FA. Thus, we provided multi-functional hydrogels of high potential serving as anti-fatigue/bacterial and conductive strain sensors on the fields of wearable devices.

Exploring the membrane fluidity of phenyl boronic acid functionalized polymersomes using the FRAP technique and their application in the pH-sensitive release of curcumin

FRAP study to examine alterations in the membrane fluidity of functionalized polymersomes and pH responsive targeted delivery of curcumin.