Smart Nanoscale Drug Delivery Platforms from Stimuli-Responsive Polymers and Liposomes

Hydrogel-based technologies in liquid biopsy for the detection of circulating clinical markers: challenges and prospects

Liquid biopsy, which promises noninvasive detection of tumor-derived material, has recently been highlighted because of its potential to lead us to an era of precision medicine. However, its development has encountered challenges owing to the extremely low frequency and low purity of circulating tumor markers, such as circulating tumor cells (CTCs), circulating exosomes, and circulating tumor nucleic acids (ctNAs). Much effort has been made to overcome this limitation over the last decade, and an increasing number of studies have shown interest in the special characteristics of hydrogels. This hydrophilic and biocompatible polymeric network, which absorbs a large amount of water, can aid in the isolation, protection, and analysis of these low-abundance and short-lived circulating biomarkers. The role of hydrogels in liquid biopsy is extensive and ranges from enrichment to encapsulation. This review provides an overview of hydrogel-based technologies to pave the way in liquid biopsy.

Lipid-Polymer Hybrid Nanosystems: A Rational Fusion for Advanced Therapeutic Delivery

Lipid nanoparticles (LNPs) are spherical vesicles composed of ionizable lipids that are neutral at physiological pH. Despite their benefits, unmodified LNP drug delivery systems have substantial drawbacks, including a lack of targeted selectivity, a short blood circulation period, and in vivo instability. lipid-polymer hybrid nanoparticles (LPHNPs) are the next generation of nanoparticles, having the combined benefits of polymeric nanoparticles and liposomes. LPHNPs are being prepared from both natural and synthetic polymers with various techniques, including one- or two-step methods, emulsification solvent evaporation (ESE) method, and the nanoprecipitation method. Varieties of LPHNPs, including monolithic hybrid nanoparticles, core-shell nanoparticles, hollow core-shell nanoparticles, biomimetic lipid-polymer hybrid nanoparticles, and polymer-caged liposomes, have been investigated for various drug delivery applications. However, core-shell nanoparticles having a polymeric core surrounded by a highly biocompatible lipid shell are the most commonly explored LPHNPs for the treatment of various diseases. In this review, we will shed light on the composition, methods of preparation, classification, surface functionalization, release mechanism, advantages and disadvantages, patents, and clinical trials of LPHNPs, with an emphasis on core-shell-structured LPHNPs.

Multi-responsive on-demand drug delivery PMMA-co-PDEAEMA platform based on CO2, electric potential, and pH switchable nanofibrous membranes

This study investigated the release characteristics of curcumin (CUR)-loaded switchable poly(methyl methacrylate)-co-poly(N,N-diethylaminoethyl methacrylate) (PMMA-co-PDEAEMA) membranes following the application of various stimuli, as well as the platform's applicability in wound dressing and tissue engineering applications. The free-radical polymerization method was used to synthesize the PMMA-co-PDEAEMA copolymer. The drug-loaded nanofibrous membrane with electric potential (EP)-, CO₂-, and pH-responsive properties was developed by the electrospinning of PMMA-co-PDEAEMA and CUR. The resulted structure was characterized by a scanning electron microscope (SEM) coupled with X-ray energy dispersive spectroscopy and wide-angle X-ray scattering measurements. The release characteristics of the CUR-loaded wound covering were analyzed in various simulated environments at varying voltages, alternated CO₂/N₂ gas bubbling, and at two different pH values; the results demonstrated high drug release controllability. Loaded CUR displayed high stability and better solubility compared with free CUR. The CUR-loaded tissue also exhibited high antibacterial activity against Escherichia coli and staphylococcus aureus bacteria. In addition, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay depicted high biocompatibility of up to 95% in the CUR-loaded membrane. This platform could be a promising candidate for usage in tissue engineering and medical applications such as targeted drug delivery, biodetection, reversible cell capture-and-release systems, and biosensors.

Targeted chitosan nanoparticles embedded into graphene oxide functionalized with caffeic acid as a potential drug delivery system: New insight into cancer therapy

As a novel drug delivery technology, chitosan (CHI) nanoparticles are encapsulated in graphene oxide (GO) with caffeic acid (CA). The nanocarrier technique combines targeted drug delivery with molecular imaging to provide new cancer insights. Attachment of CA, an anticancer agent for controlled drug release, to functionalized graphene oxide (GON) utilizing 3-aminopropyltriethoxysilane (APTES) was followed by encapsulation of GO with folic acid (FA) attached CHI to produce this novel system. FT-IR was used to characterize and confirm the chemical production process. Brunau-Emmet-Teller (BET) analysis was used to validate multi-holes and nanometric dimensions (1-100 nm) and assess their drug administration use. Release and loading tests showed a pH dependence and implied CA hydrogen-bonding in GON. CA encapsulation and loading percentages are 86 % and 67 %, respectively. The acidic environment (pH 5.3) of tumor cells may produce a larger release of CA, and the release rate of CA maintains a constant trend, indicating the drug is released for more than a week (because the release rate has not reached zero). The proposed method provides a potential candidate for a novel drug delivery system in cancer therapy. The resulting nanohybrid system is a new way to combine biodegradable materials, that can be used in biomedical applications.

Struct2Graph: a graph attention network for structure based predictions of protein–protein interactions

Background

Development of new methods for analysis of protein–protein interactions (PPIs) at molecular and nanometer scales gives insights into intracellular signaling pathways and will improve understanding of protein functions, as well as other nanoscale structures of biological and abiological origins. Recent advances in computational tools, particularly the ones involving modern deep learning algorithms, have been shown to complement experimental approaches for describing and rationalizing PPIs. However, most of the existing works on PPI predictions use protein-sequence information, and thus have difficulties in accounting for the three-dimensional organization of the protein chains.

Results

In this study, we address this problem and describe a PPI analysis based on a graph attention network, named Struct2Graph, for identifying PPIs directly from the structural data of folded protein globules. Our method is capable of predicting the PPI with an accuracy of 98.89% on the balanced set consisting of an equal number of positive and negative pairs. On the unbalanced set with the ratio of 1:10 between positive and negative pairs, Struct2Graph achieves a fivefold cross validation average accuracy of 99.42%. Moreover, Struct2Graph can potentially identify residues that likely contribute to the formation of the protein–protein complex. The identification of important residues is tested for two different interaction types: (a) Proteins with multiple ligands competing for the same binding area, (b) Dynamic protein–protein adhesion interaction. Struct2Graph identifies interacting residues with 30% sensitivity, 89% specificity, and 87% accuracy.

Conclusions

In this manuscript, we address the problem of prediction of PPIs using a first of its kind, 3D-structure-based graph attention network (code available at https://github.com/baranwa2/Struct2Graph). Furthermore, the novel mutual attention mechanism provides insights into likely interaction sites through its unsupervised knowledge selection process. This study demonstrates that a relatively low-dimensional feature embedding learned from graph structures of individual proteins outperforms other modern machine learning classifiers based on global protein features. In addition, through the analysis of single amino acid variations, the attention mechanism shows preference for disease-causing residue variations over benign polymorphisms, demonstrating that it is not limited to interface residues.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04910-9.

Thermoresponsive chimeric nanocarriers as drug delivery systems

Chimeric or mixed nanosystems belong to the class of advanced therapeutics. Their distinctive characteristic compared with other types of nanoparticles is that they combine two or more different classes of biomaterials. These platforms have created a promising and versatile field of nanomedicine, incorporating materials that are biocompatible, such as lipids, but also functional, such as stimuli-responsive polymers. In the present work, thermoresponsive chimeric nanocarriers composed of l-α-phosphatidylcholine (Egg, Chicken) (EPC) phospholipids and poly(N-isopropylacrylamide)-b-poly(lauryl acrylate) (PNIPAM-b-PLA) block copolymers were designed and developed. Initially, model lipid bilayers with incorporated polymers and drug molecule TRAM-34 were built and studied for their thermodynamics, in order to assess the stability and functionality of the systems. Chimeric nanoparticles of EPC and PNIPAM-b-PLA were then developed and evaluated for their physicochemical properties in different medium conditions, as well as for their morphology. Polymer incorporation led to alterations in the properties and morphology of the nanoparticles, while interactions with serum proteins were absent. TRAM-34 was also incorporated inside the developed nanocarriers, followed by incorporation and release studies, which revealed the functionality of the system in elevated temperature conditions. Finally, in vitro studies on normal cells suggest the biocompatibility of these nanosystems. The proposed platforms are promising for further studies and applications in vitro and in vivo.

Engineering of hybrid anticancer drug-loaded polymeric nanoparticles delivery system for the treatment and care of lung cancer therapy

Chemotherapy with combination drugs has become one of the most commonly used cancer prevention treatments, with positive clinical results. The goal of this study was to develop compostable polymeric nanomaterials (NMs) for the delivery of puerarin (PRN) and 5-fluorouracil (5FU), as well as to investigate the anticancer activity of the drug delivery system (PRN-5FU NMs) against in vitro and in vivo lung cancer cells. Since double antitumor drugs PRN and 5FU are insufficiently compressed in polymer-based bio-degradable nanoparticles, encapsulation of PRN and 5FU antitumor drugs were co-encapsulated with polyethylene glycol and polylactidecoglycolide nanoparticles (NMs) is efficient. The arrangement of PRN NMs, 5FU NMs, and PRN-5FU NMs, as well as the nanoparticles shape and scale, were studied using transmission electron microscopy (TEM). 5FU-PRN NMs triggered apoptosis in lung carcinoma cell lines such as HEL-299 and A549 in vitro. Acridine orange/ethidium bromide (AO/EB) and nuclear damaging staining techniques were used to observe morphologies and cell death. The mechanistic analysis of apoptosis was also confirmed by flow cytometry analysis using dual staining. When compared to free anticancer products, the hemolysis analysis findings of the 5FU-PRN NMs showed excellent biocompatibility. Taken together the advantages, this combination drug conveyance strategy exposed that 5FU-PRN NMs could have a significant promising to improve the effectiveness of lung cancer cells.

Association of the Thermodynamics with the Functionality of Thermoresponsive Chimeric Nanosystems

Stimuli-responsive nanosystems are an emerging technology in the field of therapy and are very promising for various applications, including targeted drug delivery. In this chapter, our scope is to integrate two different methodologies, namely differential scanning calorimetry (DSC) and dynamic light scattering (DLS), in order to rationally approach the functional behavior of thermoresponsive chimeric/mixed liposomes and interpret their thermoresponsiveness on a thermodynamic basis. In particular, chimeric bilayers comprised of the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and two different-in-composition thermoresponsive amphiphilic block copolymers poly(N-isopropylacrylamide)-b-poly(lauryl acrylate) (PNIPAM-b-PLA) 1 or 2 were built by a conventional evaporation technique, followed by DSC, and chimeric liposomes of DPPC and PNIPAM-b-PLA 1 were developed and studied by DLS, after preparation and after a simple heating protocol. The results from both methodologies indicate the composition- and concentration-dependent lyotropic effect of the foreign copolymer molecule on the properties and functionality of the lipidic membrane.

Coarse-grained simulation of the self-assembly of lipid vesicles concomitantly with novel block copolymers with multiple tails

We carried out a series of coarse-grained molecular dynamics liposome-copolymer simulations with varying extent of copolymer concentration in an attempt to understand the effect of copolymer structure and concentration on vesicle self-assembly and stability. For one particular case molecular dynamics simulation data was successfully verified against experimental NMR results enhancing the credulity in the simulation methodology. The study focused on a new class of promising copolymers based on ethylene oxide (EO) chains and short blocks of aliphatic double chains that mimic lipid tails. The lipid mimetic units are based on 1,3-didodecyloxy-2-glycidylglycerol (DDGG) and 1,3-didodecyloxy-propane-2-ol (DDP). The conducted simulations indicate that multiple lipid anchor-bearing copolymers lead to stable hybrid liposome formations. Single lipid bearing might incur liposome-stabilizing potential for relatively small ethylene oxide chains but fails dramatically in combination with a longer EO-based moiety. The consistency of the theoretical evidence with experimental NMR observation for certain cases provides confidence for the relevance of the methodology in eliciting the factors governing liposome-polymer stability which is of fundamental and practical significance.

Lipid-polymer hybrid nanoparticles in cancer therapy: current overview and future directions

Cancer remains one of the leading cause of death worldwide. Current therapies are still ineffective in completely eradicating the disease. In the last two decades, the use of nanodelivery systems has emerged as an effective way to potentiate the therapeutic properties of anti-cancer drugs by improving their solubility and stability, prolong drug half-lives in plasma, minimize drug’s toxicity by reducing its off-target distribution, and promote drugs’ accumulation at the desired target site. Liposomes and polymer nanoparticles are the most studied and have demonstrated to be the most effective delivery systems for anti-cancer drugs. However, both liposomes and polymeric nanoparticles suffer from limitations, including high instability, rapid drug release, limited drug loading capacity, low biocompatibility and lack of suitability for large-scale production. To overcome these limitations, lipid-polymer hybrid nanoparticles (LPHNPs) have been developed to merge the advantages of both lipid- and polymer-based nanocarriers, such as high biocompatibility and stability, improved drug loading and controlled release, as well as increased drug half-lives and therapeutic efficacy. This review provides an overview on the synthesis, properties and application of LPHNPs for cancer therapy.

Chimeric liposomes incorporating functional copolymers: preparation and pH/thermo-responsive behaviour in aqueous solutions

The purpose of this study is to prepare stimuli-responsive chimeric liposomes (i.e. hybrid polymer-lipid liposomes) containing functional copolymers and conduct aqueous solution studies in order to determine their properties and potential as drug-delivery nanocarriers. Two random copolymers, composed of the hydrophilic, pH and thermo-responsive 2-(dimethyl amino) ethyl methacrylate (DMAEMA) monomer and the hydrophobic stearyl methacrylate (SMA) monomer, were synthesized via free-radical polymerization and molecularly characterized using SEC, FTIR, and 1H-NMR. The synthesis was followed by aqueous solution studies, utilising dynamic light scattering (DLS) in order to determine their stimuli responsive self-assembly properties. The preparation of chimeric liposomes was mediated by thin film deposition and hydration, followed by aqueous solution studies via DLS, ζ-potential and fluorescence spectroscopy. The drug-loading studies include curcumin loading via a thin film deposition and hydration technique, while aqueous solution properties of the drug-loaded chimeric liposomes were determined utilizing DLS, and UV-Vis spectroscopy.

Photo- and pH-Responsive Polycarbonate Block Copolymer Prodrug Nanomicelles for Controlled Release of Doxorubicin

Photo/pH dual-responsive amphiphilic diblock copolymers with alkyne functionalized pendant o-nitrobenzyl ester group are synthesized using poly(ethylene glycol) as a macroinitiator. The pendant alkynes are functionalized as aldehyde groups by the azide-alkyne Huisgen cycloaddition. The anticancer drug doxorubicin (DOX) molecules are then covalently conjugated through acid-sensitive Schiff-base linkage. The resultant prodrug copolymers self-assemble into nanomicelles in aqueous solution. The prodrug nanomicelles have a well-defined morphology with an average size of 20-40 nm. The dual-stimuli are applied individually or simultaneously to study the release behavior of DOX. Under UV light irradiation, nanomicelles are disassembled due to the ONB ester photocleavage. The light-controlled DOX release behavior is demonstrated using fluorescence spectroscopy. Due to the pH-sensitive imine linkage the DOX molecules are released rapidly from the nanomicelles at the acidic pH of 5.0, whereas only minimal amount of DOX molecules is released at the pH of 7.4. The DOX release rate is tunable by applying the dual-stimuli simultaneously. In vitro studies against colon cancer cells demonstrate that the nanomicelles show the efficient cellular uptake and the intracellular DOX release, indicating that the newly designed copolymers with dual-stimuli-response have significant potential applications as a smart nanomedicine against cancer.

Nanoparticle-Loaded Hydrogel for the Light-Activated Release and Photothermal Enhancement of Antimicrobial Peptides

Rising concerns over multidrug-resistant bacteria have necessitated an expansion to the current antimicrobial arsenal and forced the development of novel delivery strategies that enhance the efficacy of existing treatments. Antimicrobial peptides (AMPs) are a promising antibiotic alternative that physically disrupts the membrane of bacteria, resulting in rapid bactericidal activity; however, clinical translation of AMPs has been hindered by their susceptibility to protease degradation. Through the co-loading of liposomes encapsulating model AMP, IRIKIRIK-CONH₂ (IK8), and gold nanorods (AuNRs) into a poly(ethylene glycol) (PEG) hydrogel, we have demonstrated the ability to protect encapsulated materials from proteolysis and provide the first instance of the triggered AMP release. Laser irradiation at 860 nm, at 2.1 W cm^-2, for 10 min led to the photothermal triggered release of IK8, resulting in bactericidal activity against Gram-negative Pseudonomas aeruginosa and Gram-positive Staphylococcus aureus. Furthermore, by increasing the laser intensity to 2.4 W cm^-2, we have shown the thermal enhancement of AMP activity. The photothermal triggered release, and enhancement of AMP efficacy, was demonstrated to treat two rounds of fresh S. aureus, indicating that the therapeutic gel has the potential for multiple rounds of treatment. Taken together, this novel therapeutic hydrogel system demonstrates the stimuli-responsive release of AMPs with photothermal enhanced antimicrobial efficacy to treat pathogenic bacteria.

Stimuli-Responsive Polysaccharide Enveloped Liposome for Targeting and Penetrating Delivery of survivin-shRNA into Breast Tumor

Silencing the inhibitor of apoptosis (IAP) by RNAi is a promising method for tumor therapy. One of the major challenges lies in how to sequentially overcome the system barriers in the course of the tumor targeting delivery, especially in the tumor accumulation and penetration. Herein we developed a novel stimuli-responsive polysaccharide enveloped liposome carrier, which was constructed by layer-by-layer depositing redox-sensitive amphiphilic chitosan (CS) and hyaluronic acid (HA) onto the liposome and then loading IAP inhibitor survivin-shRNA gene and permeation promoter hyaluronidase (HAase) sequentially. The as-prepared HA/HAase/CS/liposome/shRNA (HCLR) nanocarrier was verified to be stable in blood circulation due to the negative charged HA shield. The tumor targeting recognition and the enhanced tumor accumulation of HCLR were visualized by fluorescence resonance energy transfer (FRET) and in vivo fluorescence biodistribution. The deshielding of HA and the protonizing of CS in slightly acidic tumor extracellular pH environment (pH_e, 6.8-6.5) were demonstrated by ζ potential change from -23.1 to 29.9 mV. The pH_e-responsive HAase release was confirmed in the tumor extracellular mimicking environments, and the intratumoral biodistribution showed that the tumor penetration of HCLR was improved. The cell uptake of HCLR in pH_e environment was significantly enhanced compared with that in physiological pH environment. The increased shRNA release of HCLR was approved in 10 mM glutathione (GSH) and tumor cells. Surprisingly, HCLR suppressed the tumor growth markedly through survivin silencing and meanwhile maintained low toxicity to mice. This study indicates that the novel polysaccharide enveloped HCLR is promising in clinical translation, thanks to the stimuli-triggered tumor accumulation, tumor penetration, cell uptake, and intracellular gene release.

Temperature-Directed Micellar Morphological Transformation Using CABC-Block Copolymers and Its Applications in Encapsulation and Hidden Segment

A temperature-directed micellar morphological transformation was developed using CABC multi-block copolymers with a hydrophobic block A, a hydrophilic block B, and a thermally responsive block C with a lower critical solution temperature (LCST). The micellar structure was switched from a star (below LCST) to a flower (above LCST). The transition temperature was tunable in a wide range (11-90 °C) by varying the C monomer composition. The large difference in the loading capacity between the star and flower enabled efficient encapsulation and controlled release of external molecules. Unlike conventional systems, the present star-to-flower transformation keeps micellar structures and hence does not liberate polymers but only external molecules selectively. Another application is a hidden functional segment. A functional segment is hidden (shielded) below the LCST and exposed to interact with external molecules or surfaces above the LCST.

Polymeric Core-Shell Combinatorial Nanomedicine for Synergistic Anticancer Therapy

Core-shell nanostructures are promising platforms for combination drug delivery. However, their complicated synthesis process, poor stability, surface engineering, and low biocompatibility are major hurdles. Herein, a carboxymethyl chitosan-coated poly(lactide-co-glycolide) (cmcPLGA) core-shell nanostructure is prepared via a simple one-step nanoprecipitation self-assembly process. Engineered core-shell nanostructures are tested for combination delivery of loaded docetaxel and doxorubicin in a cancer-mimicked environment. The drugs are compartmentalized in a shell (doxorubicin, Dox) and a core (docetaxel, Dtxl) with loading contents of ∼1.2 and ∼2.06%, respectively. Carboxymethyl chitosan with both amine and carboxyl groups act as a polyampholyte in diminishing ζ-potential of nanoparticles from fairly negative (-13 mV) to near neutral (-2 mV) while moving from a physiological pH (7.4) to an acidic tumor pH (6) that can help the nanoparticles to accumulate and release the drug on-site. The dual-drug formulation was found to carry a clinically comparable 1.7:1 weight ratio of Dtxl/Dox, nanoengineered for the sequential release of Dox followed by Dtxl. Single and engineered combinatorial nanoformulations show better growth inhibition toward three different cancer cells compared to free drug treatment. Importantly, Dox-Dtxl cmcPLGA nanoparticles scored synergism with combination index values between 0.2 and 0.3 in BT549 (breast ductal carcinoma), PC3 (prostate cancer), and A549 (lung adenocarcinoma) cell lines, demonstrating significant cell growth inhibition at lower drug concentrations as compared to single-drug control groups. The observed promising performance of dual-drug formulation is due to the G2/M phase arrest and apoptosis.

Theoretical Study of the Optimal Design of a UV-Controllable Smart Surface Decorated by a Hybrid Azobenzene-Containing Polymer Layer

Although grafting polymers onto surfaces is widely suggested for designing smart systems, optimizing the performance of such systems is not simple. In this article, we investigate an azo-polymer-based smart surface using the single-chain-in-mean-field theory. Through the numerical simulations, we study the adhesion/erasion transition of the system and show that the performance of the smart surface can be characterized by the difference between the effective nanoparticle-surface interactions in the UV-on and UV-off states. Further exploring the optimization of the smart surface, we find that the distribution function of the receptor can have typical bimodal characteristics, which is crucial for optimizing the position of the azo-bond along the azo-polymer, f. Moreover, the presence of the homopolymer is also essential for the optimal performance of the smart surface, and we build a reference map for the good combinations of f and the homopolymer design f_homo.

Phenylboronic Acid-Dopamine Dynamic Covalent Bond Involved Dual-Responsive Polymeric Complex: Construction and Anticancer Investigation

In cancer treatment, prolonging the retention time of therapeutic agents in tumor tissues is a key point in enhancing the therapeutic efficacy. However, drug delivery by intravenous injection is always subjected to a "CAPIR" cascade, including circulation, accumulation, penetration, internalization, and release. Intratumoral administration has gradually emerged as an ideal alternative approach for nanomedicine because of its independence of blood constituents and minimal systemic toxicities. In this contribution, based on the dynamically reversible interaction between boronic acid (BA) and dopamine (DA), a thermo- and pH-responsive polymeric complex is rationally obtained by facile mixing of phenylboronic acid (PBA)- and tetraphenylethene (TPE)-modified poly(N-isopropylacrylamide)-b-poly(phenyl isocyanide)s block copolymers, PNIPAM-b-P(PBAPI-co-TPEPI), and tetra(ethylene glycol) methyl ether acrylate (OEGA)- and DA-containing hydrophilic P(DA-co-OEGA) copolymers. The resultant complex exhibited temperature- and pH-dependent size change as well as sustained nile red (NR) release profiles in a mimic tumor environment. Moreover, thanks to the opposite optical behavior of TPE and NR molecules, the complex could be served as a fluorescence ratiometric cell imaging agent, avoiding the interference of background fluorescence and improving correlated resolution. After encapsulation of camptothecin (anticancer drug), the efficient killing on HeLa cells was achieved in vitro, and the structural integrity of the complex endowed its extended retention time in tumor tissues. Considering these advantages, the reversible covalent interaction between PBA and diols can be used as an efficient driving force to form dynamic drug-delivery vectors, which are promising to be an effective nanoplatform for injectable medical treatments.

Surfactant-Induced Self-Assembly of CdTe Quantum Dots into Multicolor Luminescent Hybrid Vesicles

Here, we report the interaction of mercaptosuccinic acid (MSA)-capped CdTe quantum dots (QDs) with hexadecyltrimethylammonium bromide (CTAB) surfactant and subsequent formation of self-assembled multicolor luminescent vesicles in aqueous medium. A continuous phase sequence from clear (C1) to turbid (T1), precipitate (P), turbid (T2), and clear (C2) has been observed for QD solution upon increasing the concentration of positively charged CTAB, indicating dynamic equilibrium between various self-assembled supramolecular structures. In contrast, no such changes have been observed in the presence of negatively charged sodium dodecyl sulfate and neutral Triton X-100 surfactants, indicating specific electrostatic interactions behind the observed phase separation behavior. Epi-fluorescence imaging in the C1 and C2 regions reveals the presence of surfactant-induced aggregates of QD. The morphologies and photoluminescence properties of self-assembled supramolecular structures in the T1 and T2 region have been explored by using scanning electron microscopy (SEM), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM). SEM and AFM images reveal distinct spherical vesicles in the T1 and T2 regions of the binary mixture. Moreover, CLSM results show that these spherical vesicles are inherently luminescent due to the presence of self-assembled QDs. Fabrication of multicolor luminescent vesicles has been demonstrated by tuning the size of CdTe QD. Using CLSM, we have further demonstrated efficient encapsulation of Rhodamine 6G dye into these self-assembled vesicles without any structural disruption. While these luminescent vesicles are quite stable in neutral and basic pH (pH = 6.5-11), they are unstable in acidic pH (pH = 4.5-5.5). Moreover, it has been observed that this pH-responsive structural change is totally reversible. The present findings of self-assembled luminescent vesicles from QD-CTAB binary mixture may open up new opportunities in various applications such as bioimaging, drug delivery, and sensing.

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.

Ferrocene-containing amphiphilic polynorbornenes as biocompatible drug carriers

Ferrocene-containing diblock and random polynorbornene-based copolymers were synthesized by ROMP and used as biocompatible drug carrier micelles.

Highly Stable, Ultrasmall Polymer-Grafted Nanobins (usPGNs) with Stimuli-Responsive Capability

Highly stable and stimuli/pH-responsive ultrasmall polymer-grafted nanobins (usPGNs) have been developed by grafting a small amount (10 mol %) of short (4.3 kDa) cholesterol-terminated poly(acrylic acid) (Chol-PAA) into an ultrasmall unilamellar vesicle (uSUV). The usPGNs are stable against fusion and aggregation over several weeks, exhibiting over 10-fold enhanced cargo retention in biologically relevant media at pH 7.4 in comparison with the parent uSUV template. Coarse-grained molecular dynamics (CGMD) simulations confirm that the presence of the cholesterol moiety can greatly stabilize the lipid bilayer. They also show extended PAA chain conformations that can be interpreted as causing repulsion between colloidal particles, thus stabilizing them against fusion. Notably, CGMD predicted a clustering of the Chol-PAA chains on the lipid bilayer under acidic conditions due to intra- and interchain hydrogen bonding, leading to the destabilization of local membrane areas. This explains the experimental observation that usPGNs can be triggered to release a significant amount of cargo upon acidification to pH 5. These developments put the lipid-bilayer-embedded Chol-PAA in stark contrast with traditional poly(acrylic acid) systems where the molar mass (Mn) of the polymer chains must exceed 16.5 kDa to achieve stimuli-responsive changes in conformation. They also distinguish the small usPGNs from the much-larger polymer-caged nanobin platform where the Chol-PAA chains must be covalently cross-linked to engender stimuli-responsive behaviors.

Photoactivation of Ligands for Extrinsically and Intrinsically Triggered Disassembly of Amphiphilic Nanoassemblies

Specific response to the concurrent presence of two different inputs is one of the hallmarks of incorporating specificities in nature. Artificial nanoassemblies that concurrently respond to two very different inputs are of great interest in a variety of applications, especially in biomedicine. Here, we present a design strategy for amphiphilic nanoassemblies with such capabilities, enabled by photocaging a ligand moiety that is capable of binding to a specific protein. New molecular designs that offer nanoassemblies that respond to either of two inputs or only to the concurrent presence of two inputs are outlined. Such biomimetic nanoassemblies could find use in many applications, including drug delivery and diagnostics.

Stimulus-responsive liposomes as smart nanoplatforms for drug delivery applications

Liposomes are known to be promising nanoparticles (NPs) for drug delivery applications. Among different types of self-assembled NPs, liposomes stand out for their non-toxic nature, and their possession of dual hydrophilic-hydrophobic domains. Advantages of liposomes include the ability to solubilize hydrophobic drugs, the ability to incorporate different hydrophilic and lipophilic drugs at the same time, lessening the exposure of host organs to potentially toxic drugs and allowing modification of the surface by a variety of different chemical groups. This modification of the surface, or of the individual constituents, may be used to achieve two important goals. Firstly, ligands for active targeting can be attached that are recognized by cognate receptors over-expressed on the target cells of tissues. Secondly, modification can be used to impart a stimulus-responsive or "smart" character to the liposomes, whereby the cargo is released on demand only when certain internal stimuli (pH, reducing agents, specific enzymes) or external stimuli (light, magnetic field or ultrasound) are present. Here, we review the field of smart liposomes for drug delivery applications.

Temperature-Responsive Polymer Microgel-Gold Nanorods Composite Particles: Physicochemical Characterization and Cytocompatibility

In this paper, we report an easy route for preparing new metal nanorod-polymer composites consisting of gold nanorods, Au NRs, and temperature responsive copolymer "microgel" particles. The microgel particles of ~200 nm in size, which contain carboxylic acid groups, were prepared by surfactant-free emulsion polymerization of a selected mixture made of N-isopropylacylamide and acrylic acid in the presence of a cross-linker N,N'-methylenebisacrylamide. The electrostatic interactions between the cationic cetyltrimethylammonium bromide (CTAB) stabilized Au NRs and anionic microgel particles were expected to occur in order to prepare stable Au NRs-microgel composite particles. The optical and structural characterization of the composite was achieved using UV-Vis spectroscopy, Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and dynamic light scattering (DLS). TEM image shows that Au NRs are attached on the surface of the microgel particles. Dynamic light scattering measurements prove that the composite particles are temperature responsive, which means the particles undergo a decrease in size as the temperature increases above its phase transition temperature. In vitro cytotoxicity of the composite materials were tested by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Lactate dehydrogenase (LDH), and hemolysis assay, which showed non-toxicity (biocompatibility).

Phospholipase A2-Responsive Phosphate Micelle-Loaded UCNPs for Bioimaging of Prostate Cancer Cells

We report the effective synthesis of biocompatible upconversion nanoparticles (UCNP)-loaded phosphate micelles and successful delivery of UCNPs to prostate cancer cells via secreted phospholipase A2 (sPLA-2) enzyme cleavage of the loaded micelles for the first time. The activity of the (sPLA-2) enzyme toward the synthesized micelles was investigated and confirmed by LC-MS. TEM results showed that the micelles have a size distribution of 80 to 150 nm, whereas UCNP-loaded micelles range from 200 to 350 nm, indicating the successful loading of UCNPs. The selective release of UCNPs to prostate cancer cells rather than other cells, specifically cervical cancer cells, was observed and confirmed by a range of bioimaging studies. Moreover, cytotoxicity assays confirmed the biocompatibility of the UCNP-loaded micelles.

A Comparative Study of Natural Antimicrobial Delivery Systems for Microbial Safety and Quality of Fresh-Cut Lettuce

Nanoencapsulation can provide a means to effectively deliver antimicrobial compounds and enhance the safety of fresh produce. However, to date there are no studies which directly compares how different nanoencapsulation systems affect fresh produce safety and quality. This study compared the effects on quality and safety of fresh-cut lettuce treated with free and nanoencapsulated natural antimicrobial, cinnamon bark extract (CBE). A challenge study compared antimicrobial efficacy of 3 different nanoencapsulated CBE systems. The most effective antimicrobial treatment against Listeria monocytogenes was chitosan-co-poly-N-isopropylacrylamide (chitosan-PNIPAAM) encapsulated CBE, with a reduction on bacterial load up to 2 log10 CFU/g (P < 0.05) compared to the other encapsulation systems when fresh-cut lettuce was stored at 5 °C and 10 °C for 15 d. Subsequently, chitosan-PNIPAAM-CBE nanoparticles (20, 40, and 80 mg/mL) were compared to a control and free CBE (400, 800, and 1600 μg/mL) for its effects on fresh-cut lettuce quality over 15 d at 5 °C. By the 10th day, the most effective antimicrobial concentration was 80 mg/mL for chitosan-PNIPAAM-CBE, up to 2 log10 CFU/g reduction (P < 0.05), compared with the other treatments. There was no significant difference between control and treated samples up to day 10 for the quality attributes evaluated. Chitosan-PNIPAAM-CBE nanoparticles effectively inhibited spoilage microorganisms' growth and extended fresh-cut lettuce shelf-life. Overall, nanoencapsulation provided a method to effectively deliver essential oil and enhanced produce safety, while creating little to no detrimental quality changes on the fresh-cut lettuce.

Delivery of growth factor-based therapeutics in vascular diseases: Challenges and strategies

Either cardiovascular or peripheral vascular diseases have become the major cause of morbidity and mortality worldwide. Recently, growth factors therapeutics, whatever administrated in form of exogenous growth factors or their relevant genes have been discovered to be an effective strategy for the prevention and therapy of vascular diseases, because of their promoting angiogenesis. Besides, as an alternative, stem cell-based therapy has been also developed in view of their paracrine-mediated effect or ability of differentiation toward angiogenesis-related cells under assistance of growth factors. Despite of being specific and potent, no matter growth factors or stem cells-based therapy, their full clinical transformation is limited from bench to bedside. In this review, the potential choices of therapeutic modes based on types of different growth factors or stem cells were firstly summarized for vascular diseases. The confronted various challenges such as lack of non-invasive delivery method, the physiochemical challenge, the short half-life time, and poor cell survival, were carefully analyzed for these therapeutic modes. Various strategies to overcome these limitations are put forward from the perspective of drug delivery. The expertised design of a suitable delivery form will undoubtedly provide valuable insight into their clinical application in the regenerative medicine.

Smart Release Nano-formulation of Cytochrome C and Hyaluronic Acid Induces Apoptosis in Cancer Cells

Herein we tested a nanosized cancer-cell targeted delivery system based on cytochrome c (Cyt c) and hyaluronic acid. Cyt c was chosen since it is a per se non-toxic protein but causes apoptosis when delivered to the cytoplasm of target cells. Hyaluronic acid was employed to create the nanosized delivery system with passive targeting capability in order to exploit the enhanced permeation and retention (EPR) effect and active targeting capability of hyaluronic acid. In addition, our goal was to incorporate a smart release strategy to only promote protein release upon reaching its target.

Nanoparticles were formed by a simple yet precise nanoprecipitation process based on desolvation. They were physically characterized to select precipitation conditions leading to adequate size, shape, protein bioactivity, and protein loading to produce a feasible targeted cancer treatment. We synthesized nanoparticles of around 500 nm diameter with a 60% protein loading and more than 80% of protein bioactivity. In vitro, cumulative release of 92% of Cyt c was observed after 8 h under conditions mimicking the reductive intracellular environment, while under non-denaturing conditions only 20% was released. The nanoparticles displayed a selective cytotoxic effect on cancer cells. After 6 h of incubation with the nanoparticles, hyaluronic acid receptor over expressing A549 human lung adenocarcinoma cells showed a viability of ca. 20% at 0.16 mg/ml of Cyt c concentration. Only a negligible effect was observed on viability of COS-7 African green monkey kidney fibroblast, a normal cell line notoverexpressing the hyaluronic acid receptor. Confocal microscopy confirmed that the drug delivery system indeed delivered Cyt c to the cytoplasm of the target cells. We conclude that we were able to create a smart stimuli-responsive targeted drug delivery system with significant potential in cancer therapy.

pH-Responsive ZnO Nanocluster for Lung Cancer Chemotherapy

Here, we demonstrated a pH-responsive nanocluster based on ZnO quantum dots (QDs) and investigated its potential in drug delivery with tumor-specific accumulation. The nanoclusters were composed of small single ZnO QDs by cross-linking dicarboxyl-terminated poly(ethylene glycol) (PEG), showing high stability and biocompatibility in physiological fluids. The clustered ZnO QDs were capable of loading a large quantity of doxorubicin (DOX) via complexation and covalent interactions. After cellular uptake, the drug was efficiently released because the carrier was completely dissolved; the metal-drug complex was disassembled in response to decreasing pH in the endosomes within tumor cells. Moreover, the viability of cancer cells was significantly decreased because the ZnO QDs exhibited cytotoxicity postdissolution and preferentially killed cancerous cells compared to normal cells. Furthermore, this pH-responsive PEG-cZnO QDs cluster system may be capable of tumor homing while circulating in the blood via the enhanced permeability and retention (EPR) effect.

Reduction-responsive dithiomaleimide-based polymeric micelles for controlled anti-cancer drug delivery and bioimaging

The biocompatible amphiphilic block copolymers and the CPT model drug were self-assembled into micelles with bright fluorescence and taken up by tumor cells. Then, the disulfide bonds in the micelles were cleaved to release CPT at a high GSH concentration.