Noncovalent encapsulation stabilities in supramolecular nanoassemblies

Small molecule-based core and shell cross-linked nanoassemblies: from self-assembly and programmed disassembly to biological applications

Supramolecular assemblies of stimuli-responsive amphiphilic molecules have been of utmost interest in targeted drug delivery applications, owing to their capability of sequestering drug molecules in one set of conditions and releasing them in another. To minimize undesired disassembly and stabilize noncovalently encapsulated drug molecules, the strategy of core or shell cross-linking has become a fascinating approach to constructing cross-linked polymeric or small molecule-based nanoassemblies. In this article, we discuss the design and synthetic strategies for cross-linked nanoassemblies from small molecule-based amphiphiles, with robust stability and enhanced drug encapsulation capability. We highlight their potential biomedical applications, particularly in drug or gene delivery, and cell imaging. This feature article offers a comprehensive overview of the recent developments in the application of small molecule-based covalently cross-linked nanocarriers for materials and biomedical applications, which may inspire the use of these materials as a potential drug delivery system for future chemotherapeutic applications.

Enzyme-Triggered Degradation of Supramolecularly Cross-Linked Polymersomes of Azobenzene-Based Polyurethane: Cell-Selective Anticancer Drug Release

Enzyme-responsive self-assembled nanostructures for drug delivery applications have gained a lot of attention, as enzymes exhibit dysregulation in many disease-associated microenvironments. Azoreductase enzyme levels are strongly elevated in many tumor tissues; hence, here, we exploited the altered enzyme activity of the azoreductase enzyme and designed a main-chain azobenzene-based amphiphilic polyurethane, which self-assembles into a vesicular nanostructure and is programmed to disassemble in response to a specific enzyme, azoreductase, with the help of the nicotinamide adenine dinucleotide phosphate (NADPH) coenzyme in the hypoxic environment of solid tumors. The vesicular nanostructure sequesters, stabilizes the hydrophobic anticancer drug, and releases the drug in a controlled fashion in response to enzyme-triggered degradation of azo-bonds and disruption of vesicular assembly. The biological evaluation revealed tumor extracellular matrix pH-induced surface charge modulation, selective activated cellular uptake to azoreductase overexpressed lung cancer cells (A549), and the release of the anticancer drug followed by cell death. In contrast, the benign nature of the drug-loaded vesicular nanostructure toward normal cells (H9c2) suggested excellent cell specificity. We envision that the main-chain azobenzene-based polyurethane discussed in this manuscript could be considered as a possible selective chemotherapeutic cargo against the azoreductase overexpressed cancer cells while shielding the normal cells from off-target toxicity.

Carrier-Free Self-Assembled Nanomedicines for Promoting Apoptosis and Inhibiting Proliferation in Hepatocellular Carcinoma

In order to improve the effectiveness of tumor treatment and reduce the toxic side effects of drugs, we formed carrier-free multifunctional nanoparticles (BI NPs) by noncovalent interaction of berberine hydrochloride and IR780. BI NPs possessed the synergistic effects of promoting apoptosis, inhibiting proliferation and metastasis of tumors, and phototherapeutic treatment. Dispersive and passive targeting ability retention (EPR) effects of BI NPs on tumor sites in vivo could be monitored by fluorescence imaging. In addition, BI NPs exhibited effective reactive oxygen species (ROS) generation and photothermal conversion capabilities, photodynamic therapy (PDT), and photothermal therapy (PTT). Importantly, BI NPs inhibit tumor suppression through the AMPK/PI3K/AKT signaling pathway to inhibit tumor proliferation and metastasis. BI NPs not only have efficient in vivo multimodal therapeutic effects but also have good biosafety and potential clinical applications.

Förster resonance energy transfer within single chain nanoparticles

Single chain nanoparticles (SCNPs) are a highly versatile polymer architecture consisting of single polymer chains that are intramolecularly crosslinked. Currently, SCNPs are discussed as powerful macromolecular architectures for catalysis, delivery and sensors. Herein, we introduce a methodology based on Förster Resonance Energy Transfer (FRET) to evidence the folding of single polymer chains into SCNPs via fluorescence readout. We initially introduce a molecular FRET pair based on a bimane and nitrobenzoxadiazole (NBD) moiety and study its fluorescence properties in different solvents. We subsequently construct a low dispersity polymer chain carrying NBD units, while exploiting the bimane units for intramolecular chain collapse. Upon chain collapse and SCNP formation - thus bringing bimane and NBD units into close proximity - the SCNPs report their folded state by a strong and unambiguous FRET fluorescence signal. The herein introduced reporting of the folding state of SCNPs solely relies on an optical readout, opening avenues to monitoring SCNP folding without recourse to complex analytical methodologies.

Degradable Polymer-Based Nanoassemblies for Precise Targeting and Drug Delivery to Breast Cancer Cells without Affecting Normal Healthy Cells

Stimuli-responsive amphiphilic polymers are known to be precursors to forming promising nanoarchitectonics with tunable properties for application in biomedical sciences. Currently, self-immolative polymers are widely recognized as an emerging class of responsive materials with excellent degradability, which is one of the crucial criteria for designing a robust drug delivery vehicle. Here, we design an amphiphilic polyurethane endowed with a redox-responsive self-immolative linker and a pH-responsive tertiary amine on the backbone, which forms entropy-driven nanoscale supramolecular assemblies (average hydrodynamic diameter ∼110 nm) and is programmed to disassemble in a redox environment (GSH) due to the degradation of the polymer in a self-immolative fashion. The nanoassembly shows efficient drug sequestration and release in a controlled manner in response to glutathione (10 mM). The tertiary amine residing on the surface of the nanoassembly becomes protonated in the tumor microenvironment (pH ∼ 6.4-6.8) and generates positively charged nanoassembly (ζ-potential = +36 mV), which enhances the cancer cell-selective cellular uptake. The biological evaluation of the drug-loaded nanoassembly revealed triple-negative breast cancer (MDAMB-231) selective internalization and cell death while shielding normal cells (RBCs or PBMCs) from off-targeting toxicity. We envision that polyurethane with a redox-responsive self-immolative linker might open up new opportunities for a completely degradable polyurethane-based nanocarrier for drug delivery and diagnosis applications.

Harnessing biomaterial architecture to drive anticancer innate immunity

Immunomodulation is a powerful therapeutic approach that harnesses the body's own immune system and reprograms it to treat diseases, such as cancer. Innate immunity is key in mobilizing the rest of the immune system to respond to disease and is thus an attractive target for immunomodulation. Biomaterials have widely been employed as vehicles to deliver immunomodulatory therapeutic cargo to immune cells and raise robust antitumor immunity. However, it is key to consider the design of biomaterial chemical and physical structure, as it has direct impacts on innate immune activation and antigen presentation to stimulate downstream adaptive immunity. Herein, we highlight the widespread importance of structure-driven biomaterial design for the delivery of immunomodulatory cargo to innate immune cells. The incorporation of precise structural elements can be harnessed to improve delivery kinetics, uptake, and the targeting of biomaterials into innate immune cells, and enhance immune activation against cancer through temporal and spatial processing of cargo to overcome the immunosuppressive tumor microenvironment. Structural design of immunomodulatory biomaterials will profoundly improve the efficacy of current cancer immunotherapies by maximizing the impact of the innate immune system and thus has far-reaching translational potential against other diseases.

Intra-Lysosomal Peptide Assembly for the High Selectivity Index against Cancer

Lysosomes remain powerful organelles and important targets for cancer therapy because cancer cell proliferation is greatly dependent on effective lysosomal function. Recent studies have shown that lysosomal membrane permeabilization induces cell death and is an effective way to treat cancer by bypassing the classical caspase-dependent apoptotic pathway. However, most lysosome-targeted anticancer drugs have very low selectivity for cancer cells. Here, we show intra-lysosomal self-assembly of a peptide amphiphile as a powerful technique to overcome this problem. We designed a peptide amphiphile that localizes in the cancer lysosome and undergoes cathepsin B enzyme-instructed supramolecular assembly. This localized assembly induces lysosomal swelling, membrane permeabilization, and damage to the lysosome, which eventually causes caspase-independent apoptotic death of cancer cells without conventional chemotherapeutic drugs. It has specific anticancer effects and is effective against drug-resistant cancers. Moreover, this peptide amphiphile exhibits high tumor targeting when attached to a tumor-targeting ligand and causes significant inhibition of tumor growth both in cancer and drug-resistant cancer xenograft models.

Tumor acidity-induced surface charge modulation in covalent nanonetworks for activated cellular uptake: targeted delivery of anticancer drugs and selective cancer cell death

A β-thioester and tertiary amine based covalently cross-linked nanoassembly coined as a nanonetwork (NN) endowed with dual pH responsive features (tumor acidity induced surface charge modulation and endosomal pH triggered controlled degradation) has been designed and synthesized for stable sequestration and sustained release of drug molecules in response to endosomal pH. An amphiphile integrated with tertiary amine and acrylate (ATA) functionalities was synthesized to fabricate the nanonetwork. This amphiphile showed entropically driven self-assembly and micellar nanostructures (nanoassemblies), which can sequester hydrophobic drug molecules at neutral pH. To further stabilize the nanoassemblies and the sequestered drug molecules even below its critical aggregation concentration (CAC), the micellar core was cross-linked via the thiol-acrylate Michael addition click reaction to generate multiple copies of acid labile β-thioester functionalities in the core, which undergo slow hydrolysis at endosomal pH (∼5.0), thus enabling sustained release of the anti-cancer drug doxorubicin at endosomal pH. The nanonetworks showed a significant decrease in drug leakage compared to the nanoassemblies (NAs), which was also justified by a low leakage coefficient calculated from the fluorescence resonance energy transfer experiment. The NN also exhibited dilution insensitivity and high serum stability, whereas the NA disassembled upon dilution and during serum treatment. The biological evaluation revealed tumor extracellular matrix pH (∼6.4-6.8) induced surface charge modulation and cancer cell (HeLa) selective activated cellular uptake of the doxorubicin loaded nanonetwork (NN-DOX). In contrast, the benign nature of NN-DOX towards normal cells (H9c2) suggests excellent cell specificity. Thus, we believe that the ease of synthesis, nanonetwork fabrication reproducibility, robust stability, smart nature of tumor microenvironment sensitive surface charge modulation, boosted tumoral-cell uptake, and triggered drug release will make this system a potential nanomedicine for chemotherapeutic treatments.

Bioderived Lipoic Acid-Based Dynamic Covalent Nanonetworks of Poly(disulfide)s: Enhanced Encapsulation Stability and Cancer Cell-Selective Delivery of Drugs

Dynamic covalent poly(disulfide)-based cross-linked nanoaggregates, termed nanonetworks (NNs), endowed with pH- and redox-responsive degradation features have been fabricated for stable noncovalent encapsulation and triggered cargo release in a controlled fashion. A bioderived lipoic acid-based Gemini surfactant-like amphiphilic molecule was synthesized for the preparation of nanoaggregates. It self-assembles by a entropy-driven self-assembly process in aqueous milieu. To further stabilize the self-assembled nanostructure, the core was cross-linked by ring-opening disulfide exchange polymerization (RODEP) of 1,2-dithiolane rings situated inside the core of the nanoaggregates. The cross-linked nanoaggregates, i.e., nanonetwork, are found to be stable in the presence of blood serum, and also, they maintain the self-assembled structure even below the critical aggregation concentration (CAC) as probed by dynamic light scattering (DLS) experiments. The nanonetwork showed almost 50% reduction in guest leakage compared to that of the nanoaggregates as shown by the release profile in the absence of stimuli, suggesting high encapsulation stability as evidenced by the fluorescence resonance energy transfer (FRET) experiment. The decross-linking of the nanonetwork occurs in response to redox and pH stimuli due to disulfide reduction and β-thioester hydrolysis, respectively, thus empowering disassembly-mediated controlled cargo release up to ∼87% for 55 h of incubation. The biological evaluation of the doxorubicin (DOX)-loaded nanonetwork revealed environment-specific surface charge modulation-mediated cancer cell-selective cellular uptake and cytotoxicity. The benign nature of the nanonetwork toward normal cells makes the system very promising in targeted drug delivery applications. Thus, the ease of synthesis, nanonetwork fabrication reproducibility, robust stability, triggered drug release in a controlled fashion, and cell-selective cytotoxicity behavior, we believe, will make the system a potential candidate in the development of robust materials for chemotherapeutic applications.

Biomedicine Innovations and Its Nanohydrogel Classifications

As one of the most cutting-edge and promising polymer crosslinked network nanoparticle systems. Polymer nano-sized hydrogels (nanogels) have been a hot topic in the biomedical field over the last few decades. Due to their unique characteristics, which include their relatively high drug encapsulation efficiency, ease of preparation, high tunability, low toxicity, high stability in serum and responsive behavior to a range of stimuli to facilitate drug release. Nanogels are thought to be the next generation of drug delivery systems that can completely change the way that drug delivery systems have an impact on patients' lives. Nanogels have demonstrated significant potential in a variety of fields, including chemotherapy, diagnosis, organ targeting, and delivery of bioactive molecules of different dimensions. However, the lack of substantial clinical data from nanogels becomes one of the major barriers to translating the nanogel concept into a practical therapeutic application for many disease conditions. In addition, nanogel safety profiles have been the major concern that hinders it advancement to the clinical trial phase. This review aims to emphasize the unique properties of nanogels as delivery systems for a variety of bioactive molecules over other nano-delivery systems. Also, this review attempts to give insight into the recent progress in nanogels as a carrier in the field of nanomedicine to overcome complex biological barriers. Relevant scientific data and clinical rationale for the development and the potential use of nanogel as a carrier for targeted therapeutic interventions are discussed. Finally, the concluding points of this review highlight the importance of understanding the long-term toxicity profile of nanogel within the biological system to fully understand their biocompatibility.

Controlling Trapping, Release, and Exchange Dynamics of Micellar Core Components

Whereas the formation and overall stability of hierarchically organized self-assembled supramolecular structures have been extensively investigated, the mechanistic aspects of subcomponent dynamics are often poorly understood or controlled. Here we show that the dynamics of polyamidoamine (PAMAM) dendrimer based micelles can be manipulated by changes in dendrimer generation, pH, and stoichiometry, as proven by NMR and FRET. For this, dendrimers were functionalized with either fluorescein (donor) or rhodamine (acceptor) and encapsulated into separate micelles. Upon mixing, exchange of dendrimers is revealed by an increase in FRET. While dendrimicelles based on dendrimer generations 4 and 5 show a clear increase in FRET in time, revealing the dynamic exchange of dendrimers between micellar cores, generation 6 based micelles appear to be kinetically trapped systems. Interestingly, generation 6 based dendrimicelles prepared at a pH of 7.8 rather than 7.0 do show exchange dynamics, which can be attributed to about 25% less charge of the dendrimer, corresponding to the charge of a virtual generation 5.5 dendrimer at neutral pH. Changing the pH of dendrimicelle solutions prepared at a pH of 7.8 to 7.0 shows the activated release of dendrimers. High-resolution NMR spectra of the micellar core are obtained from a 1.2 GHz spectrometer with sub-micromolar sensitivity, with DOSY discriminating released dendrimers from dendrimers still present in the micellar core. This study shows that dendrimer generation, charge density, and stoichiometry are important mechanistic factors for controlling the dynamics of complex coacervate core micelles. This knowledge can be used to tune micelles between kinetically trapped and dynamic systems, with tuning of exchange and/or release speeds, to be tailored for applications in, e.g., material science, sensors, or drug delivery.

Fluorescence Resonance Energy Transfer Measurements in Polymer Science: A Review

Fluorescence resonance energy transfer (FRET) is a non-invasive characterization method for studying molecular structures and dynamics, providing high spatial resolution at nanometer scale. Over the past decades, FRET-based measurements are developed and widely implemented in synthetic polymer systems for understanding and detecting a variety of nanoscale phenomena, enabling significant advances in polymer science. In this review, the basic principles of fluorescence and FRET are briefly discussed. Several representative research areas are highlighted, where FRET spectroscopy and imaging can be employed to reveal polymer morphology and kinetics. These examples include understanding polymer micelle formation and stability, detecting guest molecule release from polymer host, characterizing supramolecular assembly, imaging composite interfaces, and determining polymer chain conformations and their diffusion kinetics. Finally, a perspective on the opportunities of FRET-based measurements is provided for further allowing their greater contributions in this exciting area.

Evolving era of "sponges": Nanosponges as a versatile nanocarrier for the effective skin delivery of drugs

BACKGROUND

Nanosponge, as a carrier for skin delivery system for drugs, plays a vital role. It not only serves to administer the drug to the targeted layer of skin but also increases the drug retention and deposition on the skin.

OBJECTIVE

In this review, we aim to highlight the effects of several process and formulation variables prompting the characteristics of various nanosponges for the delivery of drugs into/ across the skin.

METHOD

In the present review article, over-all introduction of nanosponges, its preparation, characterstics features, advanatges, disadvantages, factors affecting their preparation are covered. Furthermore, an elaborative description of nanosponges for skin delivery and its toxicological perspective with some referential examples of nanosponge drugs have also been deliberated here.

RESULTS

Factors associated with the formation of nanosponges can directly or indirectly affect its efficacy in skin delivery of drugs. These nanoforms are efficient in delivering the drugs which possess lower aqueous solubility, therefore, the aqueous solubility of drugs possessing a narrow therapeutic window can easily be enhanced. It also helps in achieving targeted drug delivery, controlled release of drugs, increases bioavailability, reduces drug toxicity, decreases drug degradation, and many more.

CONCLUSION

Nanosponges have been identified as a potential drug delivery carriers into as well as across skin. Delivery of biologics such as vaccines, enzymes, peptides, proteins, and antibodies, is also gaining attention in the recent past.

Carrier-Free Small Molecular Self-Assembly Based on Berberine and Curcumin Incorporated in Submicron Particles for Improving Antimicrobial Activity

Nanocarrier-based pesticide formulations have been severely restricted in agriculture practices due to their high-cost preparation process, poor loading capacity, and toxicity issues. To overcome these issues, carrier-free small molecular self-assembled submicron particles (SMPs) with an improved photoactivated antimicrobial activity based on two natural microbicides berberine hydrochloride (BBR) and curcumin (CM) are constructed by noncovalent interactions through a simple and fast preparation process (solvent exchange method) without using any adjuvant. The results show that the optimized molar ratio of BBR to CM is 2:1 at pH 5 and 25 °C in an aqueous solution for the formation of B-C SMPs. The obtained B-C SMPs exhibit excellent physicochemical properties, such as uniform morphology (407 nm), low polydispersity index (0.283), and strong ζ-potential (+24.4 mV). The antibacterial activities of B-C SMPs against Pseudomonas syringae pv. lachrymans, Clavibater michiganensis subsp. Michiganensis, and Sclerotinia sclerotiorum are 4, 2, and 1.5 times that of B + C MIX, respectively, suggesting a synergistic antimicrobial activity based on BBR and CM incorporation in the submicron particles. The genotoxicity evaluation results show that the self-assembled B-C SMPs are harmless to plant cells. Therefore, due to rational utilization of natural resources (natural microbicides, sunlight, and oxygen), carrier-free small molecular self-assembled B-C SMPs with synergistic photoactivated antimicrobial activity developed by a simple and fast preparation process would have great potential for sustainable plant disease management.

Programmed Macromolecular Assembly by Dipole-Dipole Interactions with Aggregation-Induced Enhanced Emission in Aqueous Medium

Self-assembling polymers by bioinspired directional supramolecular interactions currently hold great scientific and technological interests. Herein, we report an unorthodox strategy based on a dipole-dipole interaction-mediated extended antiparallel dipolar assembly of a model merocyanine (MC) dye for maneuvering the self-assembly of a highly water-soluble MC-functionalized block copolymer (P2). Unlike traditional amphiphilic block copolymers featuring distinct hydrophobic segments (flexible aliphatic hydrocarbon chains or rigid nonpolar aromatic scaffolds), P2 comprises polyethylene glycol monomethyl ether (PEG) as a hydrophilic block and an unconventional structure-directing acrylate block functionalized with polar MC-dyes in the side chains of every repeat unit. In the absence of any additional hydrophobic assistance, P2 spontaneously self-assembles in water through the continuous opposite alignment of its pendant MCs by multiple dipole-dipole interactions to cancel out their ground state dipole moments, which initially generates an H-aggregated species with ill-defined morphology (Aggregate 1). Upon thermal annealing, Aggregate 1 reorganizes into higher-order core-shell nanodisc-like structures (Aggregate 2) driven by the orthogonal π-stacking interactions of the rigid aromatic framework derived from the extended cofacial MC-stacks. The aromatic interiors of the nanodiscs gain colloidal stability from the externally decorated hydrophilic PEG chains. While the initially formed Aggregate 1, predominantly by dipole-dipole interactions, showed remarkable thermal stability due to the cooperative effect of the polymer chain, the hierarchical assembly guided by relatively weaker dispersion forces of the MC-stacked π-surfaces could be tailored by dilution or thermal treatment. Such organized packing of pendant MCs by the dual effect of dipole-dipole interactions and π-stacking conferred several exciting properties to the P2 assembly in water. Long-range ordered antiparallel stacking of the pendant MCs rendered outstanding aggregation-induced enhanced emission (AIEE) properties to the resultant nanostructures in water with increased fluorescence lifetime, quantum yield, and Stokes shift compared to nonaggregating P2 in CHCl₃. The remarkable thermal and kinetic stability of the nanodiscs, their guest loading ability, and very low critical aggregation concentration (CAC) were demonstrated by Förster resonance energy transfer (FRET) studies with an encapsulated donor-acceptor dye pair.

Solvent-Modulated Chiral Self-Assembly: Selective Formation of Helical Nanotubes, Nanotwists, and Energy Transfer

As the medium for self-assembly processes, solvents strongly influence the supramolecular assemblies via specific solute-solvent interactions, which may result in effective modulation of properties, self-assembled nanostructures, and functions through varying the solvent. Here, two kinds of pyridine-cyanostilbene functionalized chiral amphiphiles (l/d-PyPhG and l-PyG) were designed, and their self-assembly behaviors in different solvents were investigated. It was found that both amphiphiles formed gels in dimethyl sulfoxide (DMSO) and self-assembled into right-handed nanotwists, while they formed suspensions in ethanol consisting of left-handed nanotubes. Although the molecular chirality in the compounds remained unchanged in the two solvents, the nanoassemblies showed opposite handedness at the nanoscale together with opposite circular dichroism (CD) and circularly polarized luminescence (CPL) signals. Furthermore, when the amphiphiles were co-assembled with an achiral dye, it was found that efficient energy transfer took place in the systems composed of nanotubes rather than those composed of nanotwists. Therefore, by assembling molecules with the same molecular chirality in different solvents, a selective formation of helical nanotubes or nanotwists and the regulation of handedness as well as energy transfer efficiency were achieved.

Molecular bases for temperature sensitivity in supramolecular assemblies and their applications as thermoresponsive soft materials

Thermoresponsive supramolecular assemblies have been extensively explored in diverse formats, from injectable hydrogels to nanoscale carriers, for a variety of applications including drug delivery, tissue engineering and thermo-controlled catalysis. Understanding the molecular bases behind thermal sensitivity of materials is fundamentally important for the rational design of assemblies with optimal combination of properties and predictable tunability for specific applications. In this review, we summarize the recent advances in this area with a specific focus on the parameters and factors that influence thermoresponsive properties of soft materials. We summarize and analyze the effects of structures and architectures of molecules, hydrophilic and lipophilic balance, concentration, components and external additives upon the thermoresponsiveness of the corresponding molecular assemblies.

Supramolecularly cross-linked nanoassemblies of self-immolative polyurethane from recycled plastic waste: high encapsulation stability and triggered release of guest molecules

Stabilizing noncovalently encapsulated guest molecules inside a nanoassembly constructed from amphiphilic polymers has become a very challenging effort in the area of targeted drug delivery of biomedical applications. The unwanted...

Eu(III)-Chelated Polymeric Hybrid Nanoplatform for Luminescence Resonance Energy Transfer (LRET)-Based Real-Time Monitoring of Organic Cargo Release

The real-time monitoring of specific guest release from nanoscale assemblies has been of great interest for the potential application in nanomedicine. Herein, we present a facile one-pot strategy to achieve a metal-chelated nanoscale platform that enables a highly efficient luminescence resonance energy transfer (LRET) for the monitoring of hydrophobic cargo release. To this end, Eu(III) as a lanthanide luminophore was employed to induce the metal-mediated self-assembly of chelating block copolymers in the presence of fluorescent Nile Blue (NB) as an organic cargo, which can then produce a nanoscale assembly containing a hybrid polyionic complex (HPIC) of Eu(III) and NB as LRET pairs. Exploiting this Eu(III)-chelated, NB-incorporated polymeric assembly as a luminescent platform that allows for the intermolecular distance-sensitive LRET, we further demonstrate that the facile monitoring of NB release from the carriers was made possible upon the addition of serum albumin as a protein reservoir for the released hydrophobic guest molecules.

Encapsulation of Rhodamine 6G Dye Molecules for Affecting Symmetry of Supramolecular Crystals of Melamine-Barbiturate

Supramolecular organic systems can be used as a host for the encapsulation of small organic molecules. Here, we chose melamine barbiturate as a robust system capable of supramolecular assembly and the Rhodamine 6G dye entrapment as a guest molecule. The encapsulation of the dye was investigated by UV-visible spectroscopy, SEM and optical fluorescent microscopy while the insight into the crystal structure of the system was obtained by single crystal and powder XRD. For investigation of the system’s properties on a molecular level, the DFT and Classical Molecular Dynamics methods were utilized. Surprisingly, both theoretical and experimental data show not only the successful encapsulation of Rhodamine 6G molecules inside the supramolecular assembly, but also that inclusion of such molecules leads to the drastic improvement in the organic crystal shape. The melamine barbiturate in presence of the Rhodamine 6G molecules tend to form crystals with lesser degree of twinning and higher symmetry in shape than the ones without dye molecules.

Evaluating Endosomal Escape of Caspase-3-Containing Nanomaterials Using Split GFP

The ability for biologics to access intracellular targets hinges on the translocation of active, unmodified proteins. This is often achieved using nanoscale formulations, which enter cells through endocytosis. This uptake mechanism often limits the therapeutic potential of the biologics, as the propensity of the nanocarrier to escape the endosome becomes the key determinant. To appropriately evaluate and compare competing delivery systems of disparate compositions, it is therefore critical to assess endosomal escape efficiencies. Unfortunately, quantitative tools to assess endosomal escape are lacking, and standard approaches often lead to an erroneous interpretation of cytosolic localization. In this study we use a split-complementation endosomal escape (SEE) assay to evaluate levels of cytosolic caspase-3 following delivery by polymer nanogels and mesoporous silica nanoparticles. In particular, we use SEE as a means to enable the systematic investigation of the effect of polymer composition, polymer architecture (random vs block), hydrophobicity, and surface functionality. Although polymer structure had little influence on endosomal escape, nanogel functionalization with cationic and pH-sensitive peptides significantly enhanced endosomal escape levels and, further, significantly increased the amount of nanogel per endosome. This work serves as a guide for developing an optimal caspase-3 delivery system, as this caspase-3 variant can be easily substituted for a therapeutic caspase-3 cargo in any system that results in cytosolic accumulation and cargo release. In addition, these data provide a framework that can be readily applied to a wide variety of protein cargos to assess the independent contributions of both uptake and endosomal escape of a wide range of protein delivery vehicles.

Polymeric micelles in drug delivery: An insight of the techniques for their characterization and assessment in biorelevant conditions

Polymeric micelles, i.e. aggregation colloids formed in solution by self-assembling of amphiphilic polymers, represent an innovative tool to overcome several issues related to drug administration, from the low water-solubility to the poor drug permeability across biological barriers. With respect to other nanocarriers, polymeric micelles generally display smaller size, easier preparation and sterilization processes, and good solubilization properties, unfortunately associated with a lower stability in biological fluids and a more complicated characterization. Particularly challenging is the study of their interaction with the biological environment, essential to predict the real in vivo behavior after administration. In this review, after a general presentation on micelles features and properties, different characterization techniques are discussed, from the ones used for the determination of micelles basic characteristics (critical micellar concentration, size, surface charge, morphology) to the more complex approaches used to figure out micelles kinetic stability, drug release and behavior in the presence of biological substrates (fluids, cells and tissues). The techniques presented (such as dynamic light scattering, AFM, cryo-TEM, X-ray scattering, FRET, symmetrical flow field-flow fractionation (AF4) and density ultracentrifugation), each one with their own advantages and limitations, can be combined to achieve a deeper comprehension of polymeric micelles in vivo behavior. The set-up and validation of adequate methods for micelles description represent the essential starting point for their development and clinical success.

Optimal synthesis of polyelectrolyte nanogels by electrostatic assembly directed polymerization for dye loading and release

Polyelectrolyte (PE) nanogels which combine features of nanogels and polyelectrolytes have attracted significant attention as outstanding nano-carriers. However, and crucially, any large-scale application of PE nanogels can only materialize when an efficient production method is available. We recently developed such a robust approach, namely Electrostatic Assembly Directed Polymerization (EADP), in which ionic monomers are polymerized together with cross-linker in the presence of a polyion-neutral diblock copolymer as template. Although EADP achieves efficient and scalable preparation of diverse PE nanogels, the essential factors for the optimal and controlled synthesis of nanogels have remained elusive. In this article, we investigate systematically the effects of pH, salt concentration, and cross-linker fractions on the formation and properties of a PDMAEMA nanogel prepared with PAA-b-PEO as the template. We find that the electrostatic interaction between the building blocks is crucial to obtain assembly-controlled polymerization, and we establish preferred pH, salt concentration and cross-linker fractions. The obtained PDMAEMA nanogel exhibits dual-responses to pH and salt, which allow manipulation of the positive charges of the nanogels for selective loading and controlled release of anionic substances; we demonstrate this with an anionic dye. The study presented here fully addresses the process parameters of EADP regarding optimal and controlled preparation of PE nanogels, which should allow exploration of their potential vis-a-vis a variety of applications.

Energy transduction through FRET in self-assembled soft nanostructures based on surfactants/polymers: current scenario and prospects

The self-assembled systems of surfactants/polymers, which are capable of supporting energy funneling between fluorophores, have recently gained significant attraction. Surfactant and polymeric micelles form nanoscale structures spanning a radius of 2-10 nm are generally suitable for the transduction of energy among fluorophores. These systems have shown great potential in Förster resonance energy transfer (FRET) due to their unique characteristics of being aqueous based, tendency to remain self-assembled, spontaneous formation, tunable nature, and responsiveness to different external stimuli. This review presents current developments in the field of energy transfer, particularly the multi-step FRET processes in the self-assembled nanostructures of surfactants/polymers. The part one of this review presents a background and brief overview of soft systems and discusses certain aspects of the self-assemblies of surfactants/polymers and their co-solubilization property to bring fluorophores to close proximity to transduce energy. The second part of this review deals with single-step and multi-step FRET in the self-assemblies of surfactants/polymers and links FRET systems with advanced smart technologies including multicolor formation, data encryption, and artificial antenna systems. This review also discusses the diverse examples in the literature to present the emerging applications of FRET. Finally, the prospects regarding further improvement of FRET in self-assembled soft systems are outlined.

Understanding the Polymer Rearrangement of pH-Responsive Nanoparticles

The use of self-assembled nanoparticles for drug delivery has received significant attention in recent years. However, the dynamic nature of self-assembled polymeric systems means there is a need to develop greater understanding of the inherent stability of these systems. In particular, understanding if these materials remain as discrete nanoparticles, or if there is dynamic exchange of material between particles is critical. Herein, we labelled pH-responsive nanoparticles with fluorescent dyes and then investigated the change in fluorescence when the particles were mixed with unlabelled nanoparticles in order to investigate their potential for polymer rearrangement. Nanoparticles were formed by the nanoprecipitation of pH-responsive poly(ethylene glycol)-block-poly(2-(diethylamino)ethyl methacrylate) (PEG-b-PDEAEMA) as the shell and poly(2-(diethylamino)ethyl methacrylate)-random-poly(2-(diisopropylamino)ethyl methacrylate) (PDEAEMA-r-PDPAEMA) as the core. The core and shell were labelled by incorporating pentafluorophenyl methacrylate (PFPMA) in core or shell respectively and then coupling with either Sulfo-cyanine5 amine or Cyanine3 amine. Exchange of material between nanoparticles was probed by tracking changes in the self-quenching of fluorescently labelled polymers in the core of the nanoparticles. The fluorescence intensity of the labelled nanoparticles was stable when mixed with unlabelled nanoparticles at physiological pH (pH 7.4), suggesting there is limited migration of polymers between particles in this system. This study provides important insights into the use of non-crosslinked nanoparticles under biologically relevant conditions.

A bio-inspired injectable hydrogel as a cell platform for real-time glycaemic regulation

Frequent subcutaneous insulin injection and islet transplantation are promising therapeutic options for type 1 diabetes mellitus. However, poor patient compliance, insufficient appropriate islet β cell donors and body immune rejection limit their clinical applications. The design of a platform capable of encapsulating insulin-secreting cells and achieving real-time blood glucose regulation, is a so far unmet need. Herein, inspired by the natural processes of regulating blood glucose in pancreatic islet β cells, we developed a poly(N-isopropylacrylamide-co-dextran-maleic acid-co-3-acrylamidophenylboronic acid) (P(AAPBA-Dex-NIPAM)) hydrogel as a cell platform with glucose responsiveness and thermo-responsiveness for the therapy of diabetes. This platform showed good biocompatibility against insulin-secreting cells and presented glucose-dependent insulin release behaviour. The bioinspired P(AAPBA₆-Dex-NIPAM₆₄) hydrogel had a positive effect on real-time glycaemic regulation, as observed by intraperitoneal glucose tolerance tests. The non-fasting blood glucose of diabetic rats was restored to a normal level during the period of treatment. Additionally, the inflammatory response did not occur after administration of the platform. Collectively, we expected that the bio-mimetic platform combined with an insulin-secreting capability could be a new diabetic treatment strategy.

pH-responsive high stability polymeric nanoparticles for targeted delivery of anticancer therapeutics

The practical application of nanoparticles (NPs) as chemotherapeutic drug delivery systems is often hampered by issues such as poor circulation stability and targeting inefficiency. Here, we have utilized a simple approach to prepare biocompatible and biodegradable pH-responsive hybrid NPs that overcome these issues. The NPs consist of a drug-loaded polylactic-co-glycolic acid (PLGA) core covalently 'wrapped' with a crosslinked bovine serum albumin (BSA) shell designed to minimize interactions with serum proteins and macrophages that inhibit target recognition. The shell is functionalized with the acidity-triggered rational membrane (ATRAM) peptide to facilitate internalization specifically into cancer cells within the acidic tumor microenvironment. Following uptake, the unique intracellular conditions of cancer cells degrade the NPs, thereby releasing the chemotherapeutic cargo. The drug-loaded NPs showed potent anticancer activity in vitro and in vivo while exhibiting no toxicity to healthy tissue. Our results demonstrate that the ATRAM-BSA-PLGA NPs are a promising targeted cancer drug delivery platform.

Disulfide-containing Macromolecules for Therapeutic Delivery

Development of macromolecules provides applicable platforms for the delivery of therapeutics. In this general overview, we focus on the design principles of synthetic polymers, with disulfide bonds located in either the polymer backbone or side chains. We also discuss the role of disulfide bonds, as well as the remaining questions to better understand their applications in therapeutic delivery systems.

Supramolecularly cross-linked amphiphilic block copolymer assembly by the dipolar interaction of a merocyanine dye

Dipolar interaction driven dimerization of a merocyanine (MC) dye has been exploited to achieve non-covalently crosslinked stable micelles in water and reverse micelles in toluene with emissive properties from a MC-pendant amphiphilic block copolymer.

X-ray-Controlled Bilayer Permeability of Bionic Nanocapsules Stabilized by Nucleobase Pairing Interactions for Pulsatile Drug Delivery

The targeted and sustained drug release from stimuli-responsive nanodelivery systems is limited by the irreversible and uncontrolled disruption of the currently used nanostructures. Bionic nanocapsules are designed by cross-linking polythymine and photoisomerized polyazobenzene (PETAzo) with adenine-modified ZnS (ZnS-A) nanoparticles (NPs) via nucleobase pairing. The ZnS-A NPs convert X-rays into UV radiation that isomerizes the azobenzene groups, which allows controlled diffusion of the active payloads across the bilayer membranes. In addition, the nucleobase pairing interactions between PETAzo and ZnS-A prevent drug leakage during their in vivo circulation, which not only enhances tumor accumulation but also maintains stability. These nanocapsules with tunable permeability show prolonged retention, remotely controlled drug release, enhanced targeted accumulation, and effective antitumor effects, indicating their potential as an anticancer drug delivery system.

Role of Oligoethylene Glycol Side Chain Length in Responsive Polymeric Nanoassemblies

An oft-desired feature of a responsive nanomaterial is that it should undergo disassembly or morphological change upon application of a specific stimulus. The extent of response has been found to depend on factors such as the nature and the number of responsive functionalities incorporated into these particles. In this work, the length of oligoethylene glycol (OEG) side chains associated with the polymers has been shown to greatly influence the responsive behavior of polymeric nanoparticles. The integrity of these OEG-based polymeric assemblies was found to depend not only on the chemical cross-links but also on the physical cross-links in these aggregates in cases where the polymer chains bear long OEG side chains. The physical cross-linking in longer OEG side chain containing polymeric nanogels is present in the form of crystalline domains. Our results here highlight that these ethylene glycol-based hydrophilic units are not to be ignored as spectator units with water-solubilization characteristics but must be analyzed in the context of assembly stabilization and triggerability with the targeted stimulus.

Programmed supramolecular nanoassemblies: enhanced serum stability and cell specific triggered release of anti-cancer drugs

A bolaamphiphilic cross-linked nanoassembly endowed with pH responsive degradation features has been designed and fabricated for stable noncovalent guest encapsulation and controlled release. The self-assembled bolaamphiphile is utilized to prepare cross-linked nanoassemblies to further stabilize the noncovalent guest encapsulation at a concentration below its critical aggregation concentration (CAC) in a large volume of water or serum for drug delivery applications. Thus, this system can simultaneously address premature drug release and safety issues. The nanoassemblies integrated with a β-thioester linker, which can be hydrolyzed selectively under mildly acidic conditions (pH ∼ 5.3) at a slow rate, thus enable controlled release of guest molecules. Biological evaluation revealed that doxorubicin loaded cross-linked nanoassemblies (CNs-DOX) are nontoxic to normal cells such as HEK-293 or PBMC, but in contrast, showed a robust apoptotic effect on colon cancer cells, HCT-116, indicating excellent specificity. Thus, the fabrication reproducibility, robust stability, triggered drug release and cell selective toxicity behavior make this small molecular system very promising in the field of chemotherapeutic applications.

Redox-responsive degradable prodrug nanogels for intracellular drug delivery by crosslinking of amine-functionalized poly(N-vinylpyrrolidone) copolymers

HYPOTHESIS

Facile approaches for the development of new tailored drug carriers are of high importance for the controlled administration of drugs. Herein we report a method for the synthesis of water-soluble reactive copolymers with well-defined architectures for fabrication of redox-sensitive degradable prodrug nanogels for intracellular drug release.

EXPERIMENTS

Primary amine-functionalized statistical copolymers were obtained by hydrolysis of poly(N-vinylpyrrolidone-co-N-vinylformamide) copolymers which were synthesized via Reversible Addition-Fragmentation chain-Transfer (RAFT) polymerization. Redox-sensitive degradable nanogels with varying crosslinking densities were synthesized with a redox-sensitive cross-linker. Doxorubicin (DOX) was loaded to form prodrug nanogels (DNG) with hydrodynamic radius from 142 nm to 240 nm.

FINDINGS

The nanogels demonstrated slower degradation and retarded drug release rate with increased crosslinking density in the presence of 10 mM reduced glutathione (GSH) at 37 °C. The in vitro release studies revealed that maximum 85% DOX was released in 24 h under a reductive environment. Intracellular drug release profiles in HeLa cells indicated that the DOX delivery rate was tunable via varying crosslinking density of the nanogels. Cell viability assay demonstrated that the blank nanogels were biocompatible in wide concentrations up to 0.5 mg/mL while the DOX-loaded nanogels displayed medium antitumor activity with IC50 (half-maximal inhibitory concentration) of 1.80 μg/mL, 2.57 μg/mL, 3.01 μg/mL for DNG5, DNG10 and DNG15 respectively.

pH-Sensitive morphological transitions in polymeric tadpole assemblies for programmed tumor therapy

Ultrafine single-chain tadpole polymers (SCTPs), containing an intrachain crosslinked globule and a pH-sensitive linear polymer chain, have been synthesized. Self-assembly of these polymers depends on the linear block length and the pH, at which the polymer is assembled. Although the SCTPs themselves exhibit a size that is consistent with a single-chain species, the self-assembled SCTPs were found to be substantially larger. Since the transition between these two structures is reversibly dependent on pH, we explored the possibility of utilizing these assemblies to achieve deep tissue penetration in tumors. Our results indicate that there is indeed a pH-dependent deep tissue penetration in ex vivo tumor multicellular spheroids. Moreover, the multi-tadpole assemblies (MTAs) can stably encapsulate hydrophobic molecules, which have been used to encapsulate paclitaxel (PTX). These PTX/MTAs show excellent therapeutic efficacy and biosafety in 4 T1 xenograft mouse models. The innovative multi-compartment aggregates are able to fulfill structure-related function transitions with the variation of microenvironment, which has potential to extremely enrich the design of sophisticated biological agents.

Polymeric nanogels as drug delivery systems

The present review focuses on the description of the design, synthesis and physico-chemical and biological evaluation of polymer nanogels. Nanogels are robust swollen cross-linked polymer nanoparticles that can be used as highly efficient and biodegradable carriers for the transport of drugs in controlled drug delivery. In this article, various types of nanogels are described and methods for their preparation discussed. The possibility of using synthesized nanosystems for targeting are reviewed to show the potential of tailored structures to reach either solid tumor tissue or direct tumor cells. Finally, the methods for encapsulation or attachment of biologically active molecules, e.g. drugs, proteins, are described and compared.

The synthesis of poly(arylthiols) and their utilization in the preparation of cross-linked dynamic covalent polymer nanoparticles and hydrogels

Poly(arylthiols) can reversibly cross-link to form nanoparticles and hydrogels.

Tailorable degradation of pH-responsive all polyether micelles via copolymerisation with varying acetal groups

A facile approach with random copolymers composed of two epoxide monomers bearing different acetal groups realizes the tunable kinetics of micelle degradation.

Fluorescence Resonance Energy Transfer (FRET): A Powerful Tool for Probing Amphiphilic Polymer Aggregates and Supramolecular Polymers

This Review Article highlights the utility of the fluorescence resonance energy transfer (FRET) to probe the dynamics and related issues in amphiphilic polymeric aggregates and supramolecular polymers. Amphiphilic polymers are more attractive compared to their small molecule analogues because they exhibit significantly lower critical aggregation concentration, relatively larger particle size (suitable for the enhanced permeation and retention effect), and a much slower dynamics of exchange between the unimer and the aggregate. Representative examples of exchange dynamics in amphiphilic polymer aggregates and their noncovalent encapsulation stability as a function of the structure of the macromolecule, cross-linking, environmental parameters, and biological conditions, as probed by FRET studies, have been included in this article. Further, related observations on the utility of FRET in studying the exchange dynamics in supramolecular polymers, particularly in aqueous medium, have been discussed at length, revealing a strong impact of chirality, side chain polarity, and other parameters. Overall, this Review Article brings out the strength of this technique to probe dynamics of aggregates and assembled systems, mostly in water medium, which has a paramount importance in designing future biomaterials.

Understanding complex supramolecular landscapes: non-covalent macrocyclization equilibria examined by fluorescence resonance energy transfer

As molecular self-assembled systems increase in complexity, due to a large number of participating entities and/or the establishment of multiple competing equilibria, their full understanding becomes likewise more complicated, and the use of diverse analytical techniques that can afford complementary information is required. We demonstrate in this work that resonance excitation energy transfer phenomena, measured by fluorescence spectroscopy in combination with other optical spectroscopies, can be a valuable tool to obtain supplementary thermodynamic data about complex supramolecular landscapes that other methods fail to provide. In particular, noncovalent macrocyclization processes of lipophilic dinucleosides are studied here by setting up a competition between intra- and intermolecular association processes of Watson-Crick H-bonding pairs. Multiwavelength analysis of the monomer emission changes allowed us to determine cyclotetramerization constants and to quantify chelate cooperativity, which was confirmed to be substantially larger for the G-C than for the A-U pair. Furthermore, when bithiophene-BODIPY donor-acceptor energy transfer probes are employed in these competition experiments, fluorescence and circular dichroism spectroscopy measurements in different regions of the visible spectrum additionally reveal intermolecular interactions occurring simultaneously at both sides of the macrocyclization reaction: the cyclic product, acting as a host for the competitor, and the monomer reactant, ultimately leading to macrocycle denaturation.

Investigating supramolecular systems using Förster resonance energy transfer

Supramolecular systems have applications in areas as diverse as materials science, biochemistry, analytical chemistry, and nanomedicine. However, analyzing such systems can be challenging due to the wide range of time scales, binding strengths, distances, and concentrations at which non-covalent phenomena take place. Due to their versatility and sensitivity, Förster resonance energy transfer (FRET)-based techniques are excellently suited to meet such challenges. Here, we detail the ways in which FRET has been used to study non-covalent interactions in both synthetic and biological supramolecular systems. Among other topics, we examine methods to measure molecular forces, determine protein conformations, monitor assembly kinetics, and visualize in vivo drug release from nanoparticles. Furthermore, we highlight multiplex FRET techniques, discuss the field's limitations, and provide a perspective on new developments.