Toward self-assembly of nanoparticles on polymeric microshells: near-IR release and permeability

Polypeptide-based multilayer nanoarchitectures: Controlled assembly on planar and colloidal substrates for biomedical applications

Polypeptides have shown an excellent potential in nanomedicine thanks to their biocompatibility, biodegradability, high functionality, and responsiveness to several stimuli. Polypeptides exhibit high propensity to organize at the supramolecular level; hence, they have been extensively considered as building blocks in the layer-by-layer (LbL) assembly. The LbL technique is a highly versatile methodology, which involves the sequential assembly of building blocks, mainly driven by electrostatic interactions, onto planar or colloidal templates to fabricate sophisticated multilayer nanoarchitectures. The simplicity and the mild conditions required in the LbL approach have led to the inclusion of biopolymers and bioactive molecules for the fabrication of a wide spectrum of biodegradable, biocompatible, and precisely engineered multilayer films for biomedical applications. This review focuses on those examples in which polypeptides have been used as building blocks of multilayer nanoarchitectures for tissue engineering and drug delivery applications, highlighting the characteristics of the polypeptides and the strategies adopted to increase the stability of the multilayer film. Cross-linking is presented as a powerful strategy to enhance the stability and stiffness of the multilayer network, which is a fundamental requirement for biomedical applications. For example, in tissue engineering, a stiff multilayer coating, the presence of adhesion promoters, and/or bioactive molecules boost the adhesion, growth, and differentiation of cells. On the contrary, antimicrobial coatings should repel and inhibit the growth of bacteria. In drug delivery applications, mainly focused on particles and capsules at the micro- and nano-meter scale, the stability of the multilayer film is crucial in terms of retention and controlled release of the payload. Recent advances have shown the key role of the polypeptides in the adsorption of genetic material with high loading efficiency, and in addressing different pathways of the particles/capsules during the intracellular uptake, paving the way for applications in personalized medicine. Although there are a few studies, the responsiveness of the polypeptides to the pH changes, together with the inclusion of stimuli-responsive entities into the multilayer network, represents a further key factor for the development of smart drug delivery systems to promote a sustained release of therapeutics. The degradability of polypeptides may be an obstacle in certain scenarios for the controlled intracellular release of a drug once an external stimulus is applied. Nowadays, the highly engineered design of biodegradable LbL particles/capsules is oriented on the development of theranostics that, limited to use of polypeptides, are still in their infancy.

Nanoparticle-Empowered Core-Shell Microcapsules: From Architecture Design to Fabrication and Functions

Compartmentalization is a powerful concept to integrate multiscale components with diverse functionalities into miniature architectures. Inspired by evolution-optimized cell compartments, synthetic core-shell capsules enable storage of actives and on-demand delivery of programmed functions, driving scientific progress across various fields including adaptive materials, sustainable electronics, soft robotics, and precision medicine. To simultaneously maximize structural stability and environmental sensitivity, which are the two most critical characteristics dictating performance, diverse nanoparticles are incorporated into microcapsules with a dense shell and a liquid core. Recent studies have revealed that these nano-additives not only enhance the intrinsic properties of capsules including mechanical robustness, optical behaviors, and thermal conductivity, but also empower dynamic features such as triggered release, deformable structures, and fueled mobility. In this review, the physicochemical principles that govern nanoparticle assembly during microencapsulation are examined in detail and the architecture-controlled functionalities are outlined. Through the analysis of how each primary method implants nanoparticles into microcapsules, their distinct spatial organizations within the core-shell structures are highlighted. Following a detailed discussion of the specialized functions enabled by specific nanoparticles, the vision of the required fundamental insights and experimental studies for this class of microcarriers to fulfill its potential are sketched.

A decade of developing applications exploiting the properties of polyelectrolyte multilayer capsules

Transferring the layer-by-layer (LbL) coating approach from planar surfaces to spherical templates and subsequently dissolving these templates leads to the fabrication of polyelectrolyte multilayer capsules. The versatility of the coatings of capsules and their flexibility upon bringing in virtually any material into the coatings has quickly drawn substantial attention. Here, we provide an overview of the main developments in this field, highlighting the trends in the last decade. In the beginning, various methods of encapsulation and release are discussed followed by a broad range of applications, which were developed and explored. We also outline the current trends, where the range of applications is continuing to grow, including addition of whole new and different application areas.

A dual-responsive "Yin-Yang" photothermal delivery system to accelerate Parthenolide anti-tumor efficacy

Parthenolide (PTL), a germacrane sesquiterpene lactone extracted from the "Yin" Chinese traditional herb feverfew, has gained interest due to its lethal effects on tumor cells and its pharmacological effects within traditional Chinese medicine theory. To overcome low, non-targeted accumulation and uncontrolled release of PTL administration, a dual-responsive PTL-liposomes@chitosan@gold nanoshells (PTL-Lips@CS@GNS) system was fabricated. Hyperthermia generated under light irradiation in the near-infrared region via local surface plasmon resonance of gold nanoshells induced photothermal therapy, which also stimulated PTL release due to the liposomes gel-to-liquid crystalline phase transition. Additionally, PTL-Lips@CS@GNS exhibited a pH-responsive release in the acidic tumor microenvironment. Collectively, this study provides a realistic strategy for an effective combination of traditional Chinese medicine and current nanotechnology for tumor therapy.

Real-Time Temperature Monitoring of Photoinduced Cargo Release inside Living Cells Using Hybrid Capsules Decorated with Gold Nanoparticles and Fluorescent Nanodiamonds

Real-time temperature monitoring within biological objects is a key fundamental issue for understanding the heating process and performing remote-controlled release of bioactive compounds upon laser irradiation. The lack of accurate thermal control significantly limits the translation of optical laser techniques into nanomedicine. Here, we design and develop hybrid (complex) carriers based on multilayered capsules combined with nanodiamonds (NV centers) as nanothermometers and gold nanoparticles (Au NPs) as nanoheaters to estimate an effective laser-induced temperature rise required for capsule rupture and further release of cargo molecules outside and inside cancerous (B16-F10) cells. We integrate both elements (NV centers and Au NPs) in the capsule structure using two strategies: (i) loading inside the capsule's cavity (CORE) and incorporating them inside the capsule's wall (WALL). Theoretically and experimentally, we show the highest and lowest heat release from capsule samples (CORE or WALL) under laser irradiation depending on the Au NP arrangement within the capsule. Applying NV centers, we measure the local temperature of capsule rupture inside and outside the cells, which is determined to be 128 ± 1.12 °C. Finally, the developed hybrid containers can be used to perform the photoinduced release of cargo molecules with simultaneous real-time temperature monitoring inside the cells.

Mimicking natural strategies to create multi-environment enzymatic reactors: From natural cell compartments to artificial polyelectrolyte reactors

Engineering microenvironments for sequential enzymatic reactions has attracted specific interest within different fields of research as an effective strategy to improve the catalytic performance of enzymes. While in industry most enzymatic reactions occur in a single compartment carrier, living cells are however able to conduct multiple reactions simultaneously within confined sub-compartments, or organelles. Engineering multi-compartments with regulated environments and transformation properties enhances enzyme activity and stability and thus increases the overall yield of final products. In this review, we discuss current and potential methods to fabricate artificial cells for sequential enzymatic reactions, which are inspired by mechanisms and metabolic pathways developed by living cells. We aim to advance the understanding of living cell complexity and its compartmentalization and present solutions to mimic these processes in vitro. Particular attention has been given to layer-by-layer assembly of polyelectrolytes for developing multi-compartments. We hope this review paves the way for the next steps toward engineering of smart artificial multi-compartments with adoptive stimuli-responsive properties, mimicking living cells to improve catalytic properties and efficiency of the enzymes and enhance their stability.

Antibacterial Activity of Porous Gold Nanocomposites via NIR Light-Triggered Photothermal and Photodynamic Effects

Phototherapeutic approaches, including photothermal therapy (PTT) and photodynamic therapy (PDT), have become a promising strategy to combat microbial pathogens and tackle the crisis brought about by antibiotic-resistant strains. Herein, porous gold nanoparticles (AuPNs) were synthesized as photothermal agents and loaded with indocyanine green (ICG), a common photosensitizer for PDT, to fabricate a nanosystem presenting near-infrared (NIR) light-triggered synchronous PTT and PDT effects. The AuPNs can not only convert NIR light into heat with a high photothermal conversion efficiency (50.6-68.5%), but also provide a porous structure to facilely load ICG molecules. The adsorption of ICG onto AuPNs was mainly driven by electrostatic and hydrophobic interactions with the surfactant layer of AuPNs, and the aggregate state of ICG significantly enhanced its generation of reactive oxygen species. Moreover, taking advantage of its synergistic PTT and PDT effect, the hybrid nanocomposites displayed a remarkable antibacterial effect to the gram-positive pathogen Staphylococcus aureus (S. aureus) upon 808 nm laser irradiation.

Durable Polyelectrolyte Microcapsules with Near-Infrared-Triggered Loading and Nondestructive Release of Cargo

Microcapsules formed using a "layer-by-layer" alternating deposition of oppositely charged polyelectrolytes on sacrificial templates have reached high interest because of their facile fabrication procedure using a broad range of materials and tailored properties. However, their practical applications as microcarriers are limited as the capsules commonly suffer from low mechanical stability that can be enhanced by chemical or physical crosslinking but at the expense of decreasing permeability of the capsules' walls. It is demonstrated here that the incorporation of multiwalled carbon nanotubes in a relatively small amount (3.5%) arranged in the direction perpendicular to the capsules' walls led to an almost 20-fold increase of the apparent elastic modulus of the microcapsules as shown using the osmotic pressure method. Importantly, the introduced carbon nanotubes due to their absorption in the near-infrared region and specific arrangement enabled also a light-triggered increase of permeability of the capsules in a reversible, nondestructive manner as shown using fluorescently labeled dextrans of various molar masses. Such results imply durability and facile loading/unloading of the microcapsules that are both crucial for their practical applications as microcontainers and microreactors.

Methods to Scale Down Graphene Oxide Size and Size Implication in Anti-cancer Applications

Despite considerable progress in the comprehension of the mechanisms involved in the origin and development of cancer, with improved diagnosis and treatment, this disease remains a major public health challenge with a considerable impact on the social and economic system, as well as on the individual. One way to improve effectiveness and reduce side effects is to consider responsive stimuli delivery systems that provide tailor-made release profiles with excellent spatial and temporal control. 2D nanomaterials possess special physicochemical properties (e.g., light, ultrasonic and magnetic responses) and biological behaviors such as endocytosis, biodistribution, biodegradation, and excretory pathways, which lead to their use in various biomedical applications. In particular, among 2D nanomaterials, graphene and its derivatives, namely graphene oxide (GO) nanomaterials, have attracted enormous attention in cancer diagnosis and therapy because they combine, in a unique material, extremely small size, NIR absorption, delocalized electrons, extremely high surface area, and versatile surface functionality. Taking into account the fundamental role played by GO size, in this review, we summarize the main methods employed to reduce and homogenize in nanometric scale the lateral dimensions of graphene oxide produced by chemical exfoliation of graphite, as well as post-synthesis separation techniques to uniform the size. We also discuss the implication of the small size in cancer treatment by exploiting GO nanocarriers as an effective theranostic tool.

Multilayer capsules made of weak polyelectrolytes: a review on the preparation, functionalization and applications in drug delivery

Multilayer capsules have been of great interest for scientists and medical communities in multidisciplinary fields of research, such as drug delivery, sensing, biomedicine, theranostics and gene therapy. The most essential attributes of a drug delivery system are considered to be multi-functionality and stimuli responsiveness against a range of external and internal stimuli. Apart from the highly explored strong polyelectrolytes, weak polyelectrolytes offer great versatility with a highly controllable architecture, unique stimuli responsiveness and easy tuning of the properties for intracellular delivery of cargo. This review describes the progress in the preparation, functionalization and applications of capsules made of weak polyelectrolytes or their combination with biopolymers. The selection of a sacrificial template for capsule formation, the driving forces involved, the encapsulation of a variety of cargo and release based on different internal and external stimuli have also been addressed. We describe recent perspectives and obstacles of weak polyelectrolyte/biopolymer systems in applications such as therapeutics, biosensing, bioimaging, bioreactors, vaccination, tissue engineering and gene delivery. This review gives an emerging outlook on the advantages and unique responsiveness of weak polyelectrolyte based systems that can enable their widespread use in potential applications.

Classification of analytics, sensorics, and bioanalytics with polyelectrolyte multilayer capsules

Polyelectrolyte multilayer (PEM) capsules, constructed by LbL (layer-by-layer)-adsorbing polymers on sacrificial templates, have become important carriers due to multifunctionality of materials adsorbed on their surface or encapsulated into their interior. They have been also been used broadly used as analytical tools. Chronologically and traditionally, chemical analytics has been developed first, which has long been synonymous with all analytics. But it is not the only development. To the best of our knowledge, a summary of all advances including their classification is not available to date. Here, we classify analytics, sensorics, and biosensorics functionalities implemented with polyelectrolyte multilayer capsules and coated particles according to the respective stimuli and application areas. In this classification, three distinct categories are identified: (I) chemical analytics (pH; K⁺, Na⁺, and Pb²⁺ ion; oxygen; and hydrogen peroxide sensors and chemical sensing with surface-enhanced Raman scattering (SERS)); (II) physical sensorics (temperature, mechanical properties and forces, and osmotic pressure); and (III) biosensorics and bioanalytics (fluorescence, glucose, urea, and protease biosensing and theranostics). In addition to this classification, we discuss also principles of detection using the above-mentioned stimuli. These application areas are expected to grow further, but the classification provided here should help (a) to realize the wealth of already available analytical and bioanalytical tools developed with capsules using inputs of chemical, physical, and biological stimuli and (b) to position future developments in their respective fields according to employed stimuli and application areas. Graphical abstract.

Enhanced Antifungal Activities of Eugenol-Entrapped Casein Nanoparticles against Anthracnose in Postharvest Fruits

This study aims to improve the antifungal effects of eugenol through low-energy self-assembly fabrication and optimization of eugenol-casein nanoparticles (EC-NPs). Optimized EC-NPs (eugenol/casein ratio of 1:5) were obtained with a mean size of 307.4 ± 2.5 nm and entrapment efficiency of 86.3% ± 0.2%, and showed high stability under incubated at 20 and 37 °C for 48 h. EC-NPs exhibited satisfactory sustained-release effect at 20 °C or 37 °C, with remaining eugenols amounts of 79.51% and 53.41% after 72 h incubation, respectively, which were significantly higher than that of native eugenol (only 26.40% and 19.82% after the first 12 h). EC-NPs exhibited a greater antifungal activity (>95.7%) against spore germination of fungus that was greater than that of native eugenol, showed 100% inhibition of the anthracnose incidence in postharvest pear after 7 d. EC-NPs is potential as an environmental-friendly preservatives in the food industry.

Mussel-Inspired pH-Switched Assembly of Capsules with an Ultrathin and Robust Nanoshell

Enclosed films, also called capsules, bearing an ultrathin and robust nanoshell have sparked much interest for use in many applications, for which facile preparation methods are urgently pursued. Inspired by the pH-programmed adhesion/cohesion of mussel-secreted foot proteins, polyphenol/polyamine capsules with an ultrathin and robust nanoshell are fabricated through a pH-switched assembly on sacrificial calcium carbonate (CaCO₃) templates. Polyphenols adhere to the templates at pH 6.0 and rapidly cohere with polyamines at pH 8.0. The pH-switched assembly process is accomplished in only a few minutes where multiple instances of electrostatic interactions and chemical conjugation between polyphenols and polyamines occur. As a result, the capsules exhibit a nanoshell thickness of ∼10 nm and a superior mechanical strength of ∼1.575 GPa (elasticity modulus). Cell mimics are prepared through encasing enzymes in the lumen and present an activity recovery of ∼70% along with little activity decline during reuse. Amine or phenolic groups on the nanoshell of capsules are then applied to induce the generation of titania or silver nanoparticles, which may expand the applications of the capsules to the photo- and biorelated realms. Our study not only deepens the understanding of the adhering process of mussels but also offers a generic method toward functional materials for diverse applications.

Hybrids of Polymeric Capsules, Lipids, and Nanoparticles: Thermodynamics and Temperature Rise at the Nanoscale and Emerging Applications

The importance of thermodynamics does not need to be emphasized. Indeed, elevated temperature processes govern not only industrial scale production but also self-assembly, chemical reaction, interaction between molecules, etc. Not surprisingly, biological processes typically take place at a specific temperature. Here, we look at possibilities to raise the localized temperature by a laser around noble-metal nanoparticles incorporated into shells of layer-by-layer polyelectrolyte microcapsules-freely suspended delivery vehicles in an aqueous solution, developed in the Department of Interfaces, Max Planck Institute of Colloids and Interfaces, headed by Helmuth Möhwald. Understanding the mechanisms of localized temperature rise is essential, that is why we analyze the influence of incident intensity, nanoparticle size, their distribution and aggregation state, as well as thermodynamics at the nanoscale. This leads us to scrutinize "global" (used for thermal encapsulation) versus "local" (used for release of encapsulated materials) temperature rise. Similar analysis is extended to planar polymeric coatings, the lipid membrane system of vesicles and cells, on which nanoparticles are adsorbed. Insights are provided into the mechanisms of physicochemical and biological effects, the nature of which has always been profoundly, interactively, and engagingly discussed in the Department of Interfaces. This analysis is combined with recent developments providing outlook and highlighting a broad range of emerging applications.

The practical self-targeted oncolytic adenoviral nanosphere based on immuno-obstruction method via polyprotein surface precipitation technique enhances transfection efficiency for virotherapy

Recent developments in tumour treatment had focused on virotherapies that were currently revolutionising new innovated treatment pathways. This study focused on the fabrication of oncolytic adenoviral vector (Ad) nanosphere that self-targeted at lung tumour cells (A549), utilising the immune response for upper respiratory tract infection, caused by the Ad infection. This system was dependent upon T-cell immune response, surface charge and blood metabolism. Oncolytic Ad attacked lung A549 tumour cells by incorporated its own DNA to replace A549's, the triggered immune response generated T-cells also further attack A549. Direct Ad injection was demonstrated to be lethal and prohibited in vivo. In this research a multifunctional principal using polyprotein surface precipitation technique (PSP) whist maintaining biological controls for self-assembly polyprotein Ad nanosphere both biocompatible and reproducible, was demonstrated as a result of the enhanced transfection efficiency and a successful multifunctional drug delivery system for virotherapy.

Laser-induced remote release in vivo in C. elegans from novel silver nanoparticles-alginate hydrogel shells

Non-destructive, controllable, remote light-induced release inside cells enables studying time- and space-specific processes in biology. In this work we demonstrate the remote release of tagged proteins in Caenorhabditis elegans (C. elegans) worms using a near-infrared laser light as a trigger from novel hydrogel shells functionalized with silver nanoparticles responsive to laser light. A new type of hydrogel shells was developed capable of withstanding prolonged storage in the lyophilized state to enable the uptake of the shell by worms, which takes place on an agar plate under standard culture conditions. Uptake of the shells by C. elegans was confirmed using confocal laser scanning microscopy, while release from alginate shells in C. elegans and the laser effect on the shells on a substrate in air was followed using fluorescence microscopy. In addition, Raman microscopy was used to track the localization of particles to avoid the influence of autofluorescence. Hierarchical cluster spectral analysis is used to extract information about the biochemical composition of an area of a nematode containing the hydrogel shells, whose Raman signal is enhanced by the SERS (Surface Enhanced Raman Scattering) effect due to hot spots formed by silver nanoparticles present in the shells. The in vivo release demonstrated here can be used to study intestinal microbiota and probiotic compounds as well as a possible future strategy for gene delivery in the worms, other insects and other organisms.

Polymeric and Lipid Membranes-From Spheres to Flat Membranes and vice versa

Membranes are important components in a number of systems, where separation and control of the flow of molecules is desirable. Controllable membranes represent an even more coveted and desirable entity and their development is considered to be the next step of development. Typically, membranes are considered on flat surfaces, but spherical capsules possess a perfect "infinite" or fully suspended membranes. Similarities and transitions between spherical and flat membranes are discussed, while applications of membranes are also emphasized.

Preparation of Ultrathin, Robust Nanohybrid Capsules through a "Beyond Biomineralization" Method

Herein, a facile and generic method is developed to prepare ultrathin, robust nanohybrid capsules by manipulating the dynamic structure of supramolecular nanocoatings on CaCO₃ sacrificial templates by incorporating a multivalent-anion substitution process into biomineralization. Above the biomineralization level, multivalent anions, for example, phosphate, sulfate, or citrate, are used to initiate the assembly of polyamine into continuous (nonsegregated) polyamine-anion supramolecular nanocoatings on CaCO₃ sacrificial templates. When contacting with the sodium silicate solution, the multivalent anions in the supramolecular nanocoatings are substituted by silicate because of the difference in dissociation behavior, facilitating the structure-reconstruction of supramolecular nanocoatings. At the biomineralization level, the substituted silicate can not only bind to the polyamine through electrostatic and hydrogen bonding interactions but also undergo silicification to generate an interpenetrating silica framework. After dissolution of CaCO₃, polyamine-silica nanohybrid capsules bearing an ultrathin wall of ∼10-17 nm in thickness are formed, which exhibit a super-high mechanical strength of ∼2337 MPa in elasticity modulus. The capsules are then utilized for bioreactor construction by encapsulating glucose oxidase. The ultrathin capsule wall facilitates the diffusion of substrates/products and elevates the conversion efficiency, whereas the high mechanical strength ensures the structural integrity of the capsules during multiple-cycle reactions. This method can also be applied for the preparation of ultrathin films on planar substrates, which would open a feasible way to prepare nanohybrid materials with different compositions and shapes.

Multifunctional polyelectrolyte microcapsules as a contrast agent for photoacoustic imaging in blood

The polyelectrolyte microcapsules that can be accurate either visualized in biological media or in tissue would enhance their further in vivo application both as a carrier of active payloads and as a specific sensor. The immobilization of active species, for instance fluorescent dyes, quantum dots, metal nanoparticles, in polymeric shell enables visualization of capsules by optical imaging techniques in aqueous solution. However, for visualization of capsules in complex media an instrument with high contrast modality requires. Herein, we show for the first time photoacoustic imaging (PAI) of multifunctional microcapsules in water and in blood. The microcapsules exhibit greater photoacoustic intensity compare to microparticles with the same composition of polymeric shell presumably their higher thermal expansion. Photoacoustic intensity form microcapsules dispersed in blood displays an enhancement (2-fold) of signal compare to blood. Photoacoustic imaging of microcapsules might contribute to non-invasive carrier visualization and further their in vivo distribution.

Sequential co-delivery of miR-21 inhibitor followed by burst release doxorubicin using NIR-responsive hollow gold nanoparticle to enhance anticancer efficacy

Previous literature and our study showed the delivery sequence of microRNA inhibitor and chemotherapeutic compounds achieve distinct therapeutic anticancer efficacy. Yet, it is challenging to use nanoparticle to achieve sequential drug delivery. In the current study, we designed sequential co-delivery system using a near-infrared-radiation (NIR) responsive hollow gold nanoparticle (HGNPs) to achieve sequential release of microRNA inhibitor (miR-21i)/doxirubicin(Dox) in order to achieve synergistic efficacy. PAMAM modified HGNPs was used to encapsulate miR-21i and Dox. Upon entering tumor cells, miRNA-21i was released first to sensitize the cancer cells, the subsequent burst release of Dox was achieved by NIR triggered collapse of HGNPs. This sequential delivery of miRNA-21i and Dox produced a synergistic apoptotic response, thereby enhancing anticancer efficacy by 8-fold and increasing anti-cancer stem cell activity by 50-fold. The sequential delivery of miR-21i and Dox using HGNPs under NIR after intravenous administration showed high tumor accumulation and significantly improved efficacy, which was 4-fold compared to free Dox group. These data suggested that the sequential co-delivery of miR-21i followed by burst release Dox using NIR-responsive HGNPs sensitized cancer cells to chemotherapeutic compound, which provided a novel concept for co-delivery miRNA inhibitors and chemotherapeutic compounds to enhance their efficacy.

Hollow silver alginate microspheres for drug delivery and surface enhanced Raman scattering detection

Multifunctional silver alginate hydrogel microspheres are assembled via a template assisted approach using calcium carbonate cores.

Catalysis by multifunctional polyelectrolyte capsules

Gold and iron oxide modified polyelectrolyte capsules have been used as multifunctional platforms for catalysis and magnetic separation. Gold nanoparticle size and shell composition had an influence on their catalytic activity.

Nanoplasmonically-induced defects in lipid membrane monitored by ion current: transient nanopores versus membrane rupture

We have developed a nanoplasmonic-based approach to induce nanometer-sized local defects in the phospholipid membranes. Here, gold nanorods and nanoparticles having plasmon resonances in the near-infrared (NIR) spectral range are used as optical absorption centers in the lipid membrane. Defects optically induced by NIR-laser irradiation of gold nanoparticles are continuously monitored by high-precision ion conductance measurement. Localized laser-mediated heating of nanorods and nanoparticle aggregates cause either (a) transient nanopores in lipid membranes or (b) irreversible rupture of the membrane. To monitor transient opening and closing, an electrophysiological setup is assembled wherein a giant liposome is spread over a micrometer hole in a glass slide forming a single bilayer of high Ohmic resistance (so-called gigaseal), while laser light is coupled in and focused on the membrane. The energy associated with the localized heating is discussed and compared with typical elastic parameters in the lipid membranes. The method presented here provides a novel methodology for better understanding of transport across artificial or natural biological membranes.

High-throughput synthesis of single-layer MoS2 nanosheets as a near-infrared photothermal-triggered drug delivery for effective cancer therapy

We report here a simple, high-yield yet low-cost approach to design single-layer MoS2 nanosheets with controllable size via an improved oleum treatment exfoliation process. By decorating MoS2 nanosheets with chitosan, these functionalized MoS2 nanosheets have been developed as a chemotherapeutic drug nanocarrier for near-infrared (NIR) photothermal-triggered drug delivery, facilitating the combination of chemotherapy and photothermal therapy into one system for cancer therapy. Loaded doxorubicin could be controllably released upon the photothermal effect induced by 808 nm NIR laser irradiation. In vitro and in vivo tumor ablation studies demonstrate a better synergistic therapeutic effect of the combined treatment, compared with either chemotherapy or photothermal therapy alone. Finally, MoS2 nanosheets can also be used as a promising contrast agent in X-ray computed tomography imaging due to the obvious X-ray absorption ability of Mo. As a result, the high-throughput oleum treatment exfoliation process could be extended for fabricating other 2D nanomaterials, and the NIR-triggered drug release strategy was encouraging for simultaneous imaging-guided cancer theranostic application.

Taking the temperature of the interiors of magnetically heated nanoparticles

The temperature increase inside mesoporous silica nanoparticles induced by encapsulated smaller superparamagnetic nanocrystals in an oscillating magnetic field is measured using a crystalline optical nanothermometer. The detection mechanism is based on the temperature-dependent intensity ratio of two luminescence bands in the upconversion emission spectrum of NaYF4:Yb(3+), Er(3+). A facile stepwise phase transfer method is developed to construct a dual-core mesoporous silica nanoparticle that contains both a nanoheater and a nanothermometer in its interior. The magnetically induced heating inside the nanoparticles varies with different experimental conditions, including the magnetic field induction power, the exposure time to the magnetic field, and the magnetic nanocrystal size. The temperature increase of the immediate nanoenvironment around the magnetic nanocrystals is monitored continuously during the magnetic oscillating field exposure. The interior of the nanoparticles becomes much hotter than the macroscopic solution and cools to the temperature of the ambient fluid on a time scale of seconds after the magnetic field is turned off. This continuous absolute temperature detection method offers quantitative insight into the nanoenvironment around magnetic materials and opens a path for optimizing local temperature controls for physical and biomedical applications.

Thermoresponsive layer-by-layer assemblies for nanoparticle-based drug delivery

Layer-by-layer (LbL) capsules, known for their versatility and smart response to environmental stimuli, have attracted great interest in drug delivery applications. However, achieving a desired drug delivery system with sustained and tunable drug release is still challenging. Here, a thermoresponsive drug delivery system of solid dexamethasone nanoparticles (DXM NPs, 200 ± 100 nm) encapsulated in a model LbL assembly of tunable thickness consisting of strong polyelectrolytes poly(diallyldimethylammonium chloride)/poly(styrenesulfonate) (PDAC/PSS) is constructed. The influence of various parameters on drug release, such as number of layers, ionic strength of the adsorption solution, temperature, and outermost layer, is investigated. Increasing the number of layers results in a thicker encapsulating nanoshell and decreases the rate of dexamethasone release. LbL assemblies created in the absence of salt are most responsive to temperature, yielding the greatest contrast in drug release. Relationships between drug release and LbL architecture are attributed to the size and concentration of free volume cavities within the assemblies. By tailoring the properties of those cavities, a thermoresponsive drug delivery system may be obtained. This work provides a promising example of how LbL assemblies may be implemented as temperature-gated materials for the controlled release of drug, thus providing an alternative approach to the delivery of therapeutics with reduced toxic effects.

UV light stimulated encapsulation and release by polyelectrolyte microcapsules

Layer-by-layer assembled polyelectrolyte capsules with well-controlled architectures and great versatility have been the subject of great interest, due to their unique advantages and tremendous potentials of being excellent candidates in multidisciplinary fields. UV light responsive microcapsules, as one class of the stimuli responsive capsules, possess the abilities to active their functionalities by responding to the UV stimulus remotely without requirement of direct contact or interaction. Therefore, any advances in this field will be of great value for the establishment of approaches to fabricate UV responsive polyelectrolyte capsules for desired uses. This review presents current development of UV responsive capsules, with emphasis on the underlying design strategies and their potential applications as delivery vesicles. In particular, UV-stimulated capsule functionalities, such as cargo encapsulation, release and combined multifunctionalities by the multilayers, have been addressed.

UV-induced disruption of microcapsules with azobenzene groups

UV responsive microcapsules containing azobenzene were fabricated by sequential deposition of oppositely charged poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) and poly(diallyldimethyl ammonium) chloride (PDADMAC). As found in this work, combination of PDADMAC and PAZO led to aggregation of PAZO segments in the progress of polymer deposition, which facilitated the large extent of J aggregates when the capsules were exposed to UV light. J aggregate assemblies destroyed the integrity of capsule shell formations, demonstrating capsule swelling and further breakage. This UV induced capsule breakage offered a new way to modulate the release of encapsulated cargos.

Hollow hierarchical hydroxyapatite/Au/polyelectrolyte hybrid microparticles for multi-responsive drug delivery

Hollow hierarchical hydroxyapatite/Au/polyelectrolyte hybrid microparticles with a hollow HAP core and polymer multilayer/Au nanoparticle shell for multi-responsive drug delivery have been prepared via an LbL technique.

25th anniversary article: Dynamic interfaces for responsive encapsulation systems

Encapsulation systems are urgently needed both as micrometer and sub-micrometer capsules for active chemicals' delivery, to encapsulate biological objects and capsules immobilized on surfaces for a wide variety of advanced applications. Methods for encapsulation, prolonged storage and controllable release are discussed in this review. Formation of stimuli responsive systems via layer-by-layer (LbL) assembly, as well as via mobile chemical bonding (hydrogen bonds, chemisorptions) and formation of special dynamic stoppers are presented. The most essential advances of the systems presented are multifunctionality and responsiveness to a multitude of stimuli - the possibility of formation of multi-modal systems. Specific examples of advanced applications - drug delivery, diagnostics, tissue engineering, lab-on-chip and organ-on-chip, bio-sensors, membranes, templates for synthesis, optical systems, and antifouling, self-healing materials and coatings - are provided. Finally, we try to outline emerging developments.

Multiple internalization pathways of polyelectrolyte multilayer capsules into mammalian cells

Polyelectrolyte multilayer (PEM) capsules are carrier vehicles with great potential for biomedical applications. With the future aim of designing biocompatible, effective therapeutic delivery systems (e.g., for cancer), the pathway of internalization (uptake and fate) of PEM capsules was investigated. In particular the following experiments were performed: (i) the study of capsule co-localization with established endocytic markers, (ii) switching-off endocytotic pathways with pharmaceutical/chemical inhibitors, and (iii) characterization and quantification of capsule uptake with confocal and electron microscopy. As result, capsules co-localized with lipid rafts and with phagolysosomes, but not with other endocytic vesicles. Chemical interference of endocytosis with chemical blockers indicated that PEM capsules enter the investigated cell lines through a mechanism slightly sensitive to electrostatic interactions, independent of clathrin and caveolae, and strongly dependent on cholesterol-rich domains and organelle acidification. Microscopic characterization of cells during capsule uptake showed the formation of phagocytic cups (vesicles) to engulf the capsules, an increased number of mitochondria, and a final localization in the perinuclear cytoplasma. Combining all these indicators we conclude that PEM capsule internalization in general occurs as a combination of different sequential mechanisms. Initially, an adsorptive mechanism due to strong electrostatic interactions governs the stabilization of the capsules at the cell surface. Membrane ruffling and filopodia extensions are responsible for capsule engulfing through the formation of a phagocytic cup. Co-localization with lipid raft domains activates the cell to initiate a lipid-raft-mediated macropinocytosis. Internalization vesicles are very acidic and co-localize only with phagolysosome markers, excluding caveolin-mediated pathways and indicating that upon phagocytosis the capsules are sorted to heterophagolysosomes.

Smart Layer-by-Layer Assemblies for Drug Delivery

Layer-by-layer (LbL) assembly is an effective tool for development of surface coatings and capsules for localized, controlled delivery of bioactive molecules. Because of the unprecedented versatility of the technique, a broad range of nanoobjects, including molecules, particles, micelles, vesicles and others with diverse chemistry and architecture can be used as building blocks for LbL assemblies, opening various routes for inclusion and delivery of functional molecules to/from LbL films. Moreover, the LbL technique continues to show its power in constructing three-dimensional (3D) delivery containers, in which LbL walls can additionally control delivery of functional molecules incorporated in the capsule interior. In this chapter, we discuss recent progress in the use of LbL assemblies to control release of therapeutic compounds via diffusion, hydrolytic degradation, pH, ionic strength or temperature variations, application of light, ultrasound, electric and magnetic field stimuli, redox activation or biological stimuli.

Cell-specific multifunctional processing of heterogeneous cell systems in a single laser pulse treatment

Current methods of cell processing for gene and cell therapies use several separate procedures for gene transfer and cell separation or elimination, because no current technology can offer simultaneous multifunctional processing of specific cell subsets in highly heterogeneous cell systems. Using the cell-specific generation of plasmonic nanobubbles of different sizes around cell-targeted gold nanoshells and nanospheres, we achieved simultaneous multifunctional cell-specific processing in a rapid single 70 ps laser pulse bulk treatment of heterogeneous cell suspension. This method supported the detection of cells, delivery of external molecular cargo to one type of cells and the concomitant destruction of another type of cells without damaging other cells in suspension, and real-time guidance of the above two cellular effects.

Laser-induced cell detachment, patterning, and regrowth on gold nanoparticle functionalized surfaces

We report on the selective cell detachment from nanoengineered gold nanoparticle (AuNP) surfaces triggered by laser irradiation, which occurs in a nonthermal manner. The gold nanoparticle-based surfaces reveal good adhesion of NIH3T3 fibroblast cells. Patterning is achieved by lithographic microcontact printing, selective gold nanoparticle deposition, and by laser beam profiling. It is shown that the effectiveness of fibroblast cell detachment depends on the cell age, laser power, and AuNP patterning profile. Heat distribution and temperature rise around gold nanoparticle functionalized surfaces is modeled, revealing low heating of nanoparticles by laser illumination. The nonthermal photochemical mechanism of cell detachment due to production of reactive oxygen species under illumination of gold nanoparticles by green laser light is studied. We also demonstrate that cells migrate from unirradiated areas leading to their reattachment and surface recovery which is important for controlled spatial organization of cells in wound healing and tissue engineering. Research presented in this work is targeted at designing biointerfaces for cell cultures.

Red blood cells and polyelectrolyte multilayer capsules: natural carriers versus polymer-based drug delivery vehicles

INTRODUCTION

Red blood cells (RBCs) and lipid-based carriers on the one hand and polymeric capsules on the other hand represent two of the most widely used carriers in drug delivery. Each class of these carriers has its own set of properties, specificity and advantages. Thorough comparative studies of such systems are reported here for the first time.

AREAS COVERED

In this review, RBCs are described in comparison with synthetic polymeric drug delivery vehicles using polyelectrolyte multilayer capsules as an example. Lipid-based composition of the shell in the former case is particularly attractive due to their inherent biocompatibility and flexibility of the carriers. On the other hand, synthetic approaches to fabrication of polyelectrolyte multilayer capsules permit manipulation of the permeability of their shell as well as tuning their composition, mechanical properties, release methods and targeting.

EXPERT OPINION

In conclusion, properties of RBCs and polyelectrolyte multilayer capsules are reported here highlighting similarities and differences in their preparation and applications. In addition, their advantages and disadvantages are discussed.

Controlled enzyme-catalyzed degradation of polymeric capsules templated on CaCO₃: influence of the number of LbL layers, conditions of degradation, and disassembly of multicompartments

Enzyme-catalyzed degradation of CaCO₃-templated capsules is presented. We investigate a) biodegradable, b) mixed biodegradable/synthetic, and c) multicompartment polyelectrolyte multilayer capsules with different numbers of polymer layers. Using confocal laser scanning microscopy we observed the kinetics of the non-specific protease Pronase-induced degradation of capsules is slowed down on the order of hours by either increasing the number of layers in the wall of biodegradable capsules, or by inserting synthetic polyelectrolyte multilayers into the shell comprised of biodegradable polymers. The degradation rate increases with the concentration of Pronase. Controlled detachment of subcompartments of multicompartment capsules, with potential for intracellular delivery or in-vivo applications, is also shown.

UV-cross-linkable multilayer microcapsules made of weak polyelectrolytes

Microcapsules composed of weak polyelectrolytes modified with UV-responsive benzophenone (BP) groups were fabricated by the layer-by-layer (LbL) technique. Being exposed to UV lights, capsules shrunk in the time course of minutes at irradiation intensity of 5 mW/cm(2). The shrinkage adjusted the capsule permeability, providing a novel way to encapsulate fluorescence-labeled dextran molecules without heating. Cross-linking within the capsule shells based on hydrogen abstraction via excited benzophenone units by UV showed a reliable and swift approach to tighten and stabilize the capsule shell without losing the pH-responsive properties of the weak polyelectrolyte multilayers.

Nanoplasmonics for dual-molecule release through nanopores in the membrane of red blood cells

A nanoplasmonics-based opto-nanoporation method of creating nanopores upon laser illumination is applied for inducing diffusion and triggered release of small and large molecules from red blood cells (RBCs). The method is implemented using absorbing gold nanoparticle (Au-NP) aggregates on the membrane of loaded RBCs, which, upon near-IR laser light absorption, induce release of encapsulated molecules from selected cells. The binding of Au-NPs to RBCs is characterized by Raman spectroscopy. The process of release is driven by heating localized at nanoparticles, which impacts the permeability of the membrane by affecting the lipid bilayer and/or trans-membrane proteins. Localized heating and temperature rise around Au-NP aggregates is simulated and discussed. Research reported in this work is relevant for generating nanopores for biomolecule trafficking through polymeric and lipid membranes as well as cell membranes, while dual- and multi-molecule release is relevant for theragnostics and a wide range of therapies.