Synthesis, Characterization, and Long-Term Stability of Hollow Polymer Nanocapsules with Nanometer-Thin Walls

A Potentially Versatile Enzyme Sensor Platform: Enzyme-Loaded, Tagged, Porous Polymeric Nanocapsules

Enzymes are essential to life and indispensable in a wide range of industries (food, pharmaceutical, medical, biosensing, etc.); however, a significant shortcoming of these fragile biological catalysts is their poor stability. To address this challenge, a variety of immobilization methods have been described to enhance the enzyme's stability. These immobilization methods generally are specific to an individual enzyme or optimal for a particular application. The aim of this study is to explore the utility of porous, indicator moiety-tagged, polymeric nanocapsules (NCs) for the encapsulation of enzymes and measurement of the enzyme's substrate. As a model enzyme, glucose oxidase (GOx) is used. The GOx enzyme-loaded, fluorophore-tagged NCs were synthesized by using self-assembled surfactant vesicle templates. To show that the biological activity of GOx is preserved during entrapment, the rate of the GOx enzyme catalyzed reaction was measured. To evaluate the protective features of the porous NCs, the encapsulated GOx enzyme activity was followed in the presence of hydrolytic enzymes. During the encapsulation of GOx and the purification of the GOx-loaded NCs, the GOx activity decayed less than 10%, and up to 30% of the encapsulated GOx activity could be retained for 3-5 days in the presence of hydrolytic enzymes. In support of the potentially unique advantages of the enzyme-loaded NCs, as a proof-of-concept example, the fluorophore-tagged, GOx-loaded NCs were used for the determination of glucose in the concentration range between 18 and 162 mg/dL and for imaging the distribution of glucose concentration in imaging experiments.

QbD Assisted Development of Lipidic Nanocapsules for Antiestrogenic Activity of Exemestane in Breast Cancer

Some breast cancers are caused by hormonal imbalances, such as estrogen and progesterone.These hormones play a function in directing the growth of cancer cells. The hormone receptors in hormone receptor-positive breast cancer lead breast cells to proliferate out of control. Cancer therapy such as hormonal, targeted, radiation is still unsatisfactory because of these challenges viz. MDR (Multiple drug resistance), off-targeting, severe adverse effects. A novel aromatase inhibitor exemestane (Exe) exhibits promising therapy in breast cancer. This study aims to develop and optimize Exe-loaded lipid nanocapsules (LNCs) by using DSPC, PF68 and olive oil as lipid, surfactant and oil phase, respectively and to characterize the same. The prepared nanocapsules were investigated via in-vitro cell culture and in-vivo animal models. The LNCs exhibited cytotoxicity in MCF-7 cell lines and enhanced anti-cancer activity and reduced cardiotoxicity in DMBA-induced animal model when compared to the drug. Additionally, in-vivo pharmacokinetics revealed a 4.2-fold increased oral bioavailability when compared with Exe suspension. This study demonstrated that oral administration of Exe-loaded LNCs holds promise for the antiestrogenic activity of exemestane in breast cancer.

Bilayer-Templated Two-Dimensional RAFT Polymerization for Directed Assembly of Polymer Nanostructures

Co-localization of monomers, crosslinkers, and chain-transfer agents (CTA) within self-assembled bilayers in an aqueous suspension enabled the successful directed assembly of nanocapsules using a reversible addition-fragmentation chain transfer (RAFT) process without compromising the polymerization kinetics. This study uncovered substantial influence of the organized medium on the course of the reaction, including differential reactivity based on placement and mobility of monomers, crosslinkers, and CTAs within the bilayer.

Morphology Control of Liposome - RAFT Oligomer Precursors to Complex Polymer Nanostructures

Different types of butyl acrylate (BA)-co-acrylic acid (AA) oligomers were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and mixed with extruded 200 nm dimethyldioctadecylammonium bromide vesicles. The resulting precursor structures form the basis for subsequent vesicle-templated polymerizations. Systematic variations in temperature, pH, oligomer length, and oligomer composition and their effects on precursor morphology were studied. Surprisingly, different morphologies were obtained, including capsules, protruded capsules, solid spheres, and multicompartment structures. For example, capsules and multicompartment structures were found to result from higher AA contents, and protruded capsules and solid particles resulted from lower AA contents. Subsequent chain extension of the RAFT oligomers resulted in polymer nanostructures resembling the precursor morphologies.

Deciphering and Controlling Structural and Functional Parameters of the Shells in Vesicle-Templated Polymer Nanocapsules

Vesicle-templated nanocapsules are prepared by polymerization of hydrophobic acrylic monomers and cross-linkers in the hydrophobic interior of self-assembled bilayers. Understanding the mechanism of capsule formation and the influence of synthetic parameters on the structural features and functional performance of nanocapsules is critical for the rational design of functional nanodevices, an emerging trend of application of the nanocapsule platform. This study investigated the relationship between basic parameters of the formulation and synthesis of nanocapsules and structural and functional characteristics of the resulting structures. Variations in the monomer/surfactant ratio, temperature of polymerization, and the molar fraction of the free-radical initiators were investigated with a multipronged approach, including shell thickness measurements using small-angle neutron scattering, evaluation of the structural integrity of nanocapsules with scanning electron microscopy, and determination of the retention of entrapped molecules using absorbance and fluorescence spectroscopy. Surprisingly, the thickness of the shells did not correlate with the monomer/surfactant ratio, supporting the hypothesis of substantial stabilization of the surfactant bilayer with loaded monomers. Decreasing the temperature of polymerization had no effect on the spherical structure of nanocapsules but resulted in progressively lower retention of entrapped molecules, suggesting that a spherical skeleton of nanocapsule forms rapidly, followed by filling the gaps to create the structure without pinholes. Lower content of initiators resulted in slower reactions, outlining the baseline conditions for practical synthetic protocols. Taken together, these findings provide insights into the formation of nanocapsules and offer methods for controlling the properties of nanocapsules in viable synthetic methods.

Building Functional Nanodevices with Vesicle-Templated Porous Polymer Nanocapsules

Vesicle-templated nanocapsules offer a unique combination of properties enabled by robust shells with single-nanometer thickness containing programmed uniform pores capable of fast and selective mass transfer. These capsules emerged as a versatile platform for creating functional devices, such as nanoreactors, nanosensors, and containers for the delivery of drugs and imaging agents. Nanocapsules are synthesized by a directed assembly method using self-assembled bilayers of vesicles as temporary scaffolds. In this approach, hydrophobic building blocks are loaded into the hydrophobic interior of vesicles formed from lipids or surfactants. Pore-forming templates are codissolved with the monomers and cross-linkers in the interior of the bilayer. The polymerization forms a cross-linked shell with embedded pore-forming templates. Removal of the surfactant scaffold and pore-forming templates leads to free-standing nanocapsules with shells containing uniform imprinted nanopores. Development of reliable and scalable synthetic methods for the modular construction of capsules with tunable properties has opened the opportunity to pursue practical applications of nanocapsules. In this Account, we discuss how unique properties of vesicle-templated nanocapsules translate into the creation of functional nanodevices. Specifically, we focus the conversation on applications aiming at the delivery of drugs and imaging agents, creation of fast-acting and selective nanoreactors, and fabrication of nanoprobes for sensing and imaging. We present a brief overview of the synthesis of nanocapsules with an emphasis on recent developments leading to robust synthetic methods including the synthesis under physiological conditions and creation of biodegradable nanocapsules. We then highlight unique properties of nanocapsules essential for practical applications, such as precise control of pore size and chemical environment, selective permeability, and ultrafast transport through the pores. We discuss new motifs for catch and release of small molecules with porous nanocapsules based on controlling the microenvironment inside the nanocapsules, regulating the charge on the orifice of nanopores in the shells, and reversible synergistic action of host and guest forming a supramolecular complex in nanocapsules. We demonstrate successful creation of fast-acting and selective nanoreactors by encapsulation of diverse homogeneous and nanoparticle catalysts. Due to unhindered flow of substrates and products through the nanopores, encapsulation did not compromise catalytic efficiency and, in fact, improved the stability of entrapped catalysts. We present robust nanoprobes based on nanocapsules with entrapped sensing agents and show how the encapsulation resulted in selective measurements with fast response times in challenging conditions, such as small volumes and complex mixtures. Throughout this Account, we highlight the advantages of encapsulation and discuss the opportunities for future design of nanodevices.

Chiral helical substituted polyacetylene grafted on hollow polymer particles: preparation and enantioselective adsorption towards cinchona alkaloids

Hollow polymer particles tethering chiral helical polymer chains and functional carboxyl groups were prepared and applied in enantioselective adsorption.

Evidence for diffusing atomic oxygen uncovered by separating reactants with a semi-permeable nanocapsule barrier

Ground-state atomic oxygen [O(³P)] is an oxidant whose formation in solution was proposed but never proven.

Facile Synthesis of Chiral Polymers with Defined Architecture via Cooperative Assembly of Confined Templates

Herein is presented the synergistically self-assembled system as biomimetic polymerization media. This approach allows the facile synthesis of chiral amino acid-based polymers with high molecular weight and low dispersity inside of the bilayer of catanionic vesicles by using a conventional radical polymerization under moderate conditions.

Nanoreactors for green catalysis

Sustainable and environmentally benign production are key drivers for developments in the chemical industrial sector, as protecting our planet has become a significant element that should be considered for every industrial breakthrough or technological advancement. As a result, the concept of green chemistry has been recently defined to guide chemists towards minimizing any harmful outcome of chemical processes in either industry or research. Towards greener reactions, scientists have developed various approaches in order to decrease environmental risks while attaining chemical sustainability and elegancy. Utilizing catalytic nanoreactors for greener reactions, for facilitating multistep synthetic pathways in one-pot procedures, is imperative with far-reaching implications in the field. This review is focused on the applications of some of the most used nanoreactors in catalysis, namely: (polymer) vesicles, micelles, dendrimers and nanogels. The ability and efficiency of catalytic nanoreactors to carry out organic reactions in water, to perform cascade reaction and their ability to be recycled will be discussed.

Controlling the Encapsulation of Charged Molecules in Vesicle-Templated Nanocontainers through Electrostatic Interactions with the Bilayer Scaffold

This work addresses the challenge of creating hollow nanocapsules with a controlled quantity of encapsulated molecules. Such nanocontainers or nanorattle-like structures represent an attractive platform for building functional devices, including nanoreactors and nanosensors. By taking advantage of the electrostatic attraction between oppositely charged cargo molecules and the surface of the templating bilayer of catanionic vesicles, formed by mixing single-tailed cationic and anionic surfactants, we were able to achieve a substantial increase in the local concentration of molecules inside the vesicle-templated nanocapsules. Control of electrostatic interactions through changes in the formulation of catanionic vesicles or the pH of the solution enabled fine tuning of the encapsulation efficiency in capturing ionic solutes. The ability to control the quantity of entrapped molecules greatly expands the application of nanocontainers in the creation of functional nanodevices.

Unraveling the Single-Nanometer Thickness of Shells of Vesicle-Templated Polymer Nanocapsules

Vesicle-templated nanocapsules have emerged as a viable platform for diverse applications. Shell thickness is a critical structural parameter of nanocapsules, where the shell plays a crucial role providing mechanical stability and control of permeability. Here we used small-angle neutron scattering (SANS) to determine the thickness of freestanding and surfactant-stabilized nanocapsules. Despite being at the edge of detectability, we were able to show the polymer shell thickness to be typically 1.0 ± 0.1 nm, which places vesicle-templated nanocapsules among the thinnest materials ever created. The extreme thinness of the shells has implications for several areas: mass-transport through nanopores is relatively unimpeded; pore-forming molecules are not limited to those spanning the entire bilayer; the internal volume of the capsules is maximized; and insight has been gained on how polymerization occurs in the confined geometry of a bilayer scaffold, being predominantly located at the phase-separated layer of monomers and cross-linkers between the surfactant leaflets.

Encapsulation of Homogeneous Catalysts in Porous Polymer Nanocapsules Produces Fast-Acting Selective Nanoreactors

Nanoreactors were created by entrapping homogeneous catalysts in hollow nanocapsules with 200 nm diameter and semipermeable nanometer-thin shells. The capsules were produced by the polymerization of hydrophobic monomers in the hydrophobic interior of the bilayers of self-assembled surfactant vesicles. Controlled nanopores in the shells of nanocapsules ensured long-term retention of the catalysts coupled with the rapid flow of substrates and products in and out of nanocapsules. The study evaluated the effect of encapsulation on the catalytic activity and stability of five different catalysts. Comparison of kinetics of five diverse reactions performed in five different solvents revealed the same reaction rates for free and encapsulated catalysts. Identical reaction kinetics confirmed that placement of catalysts in the homogeneous interior of polymer nanocapsules did not compromise catalytic efficiency. Encapsulated organometallic catalysts showed no loss of metal ions from nanocapsules suggesting stabilization of the complexes was provided by nanocapsules. Controlled permeability of the shells of nanocapsules enabled size-selective catalytic reactions.

Controlled Permeability in Porous Polymer Nanocapsules Enabling Size- and Charge-Selective SERS Nanoprobes

Nanoprobes for surface-enhanced Raman scattering (SERS) were prepared by creating nanorattles, or yolk-shell structures, containing gold or silver nanoparticles entrapped in porous hollow polymer nanocapsules. Controlled permeability of the shells of nanocapsules, achieved by controlling the pore size and/or shell surface functionalization, resulted in size- and charge-selective SERS analyses. For example, a trace amount of phenanthroline, a model analyte, was detected in human blood plasma without preprocessing of plasma samples. Comparison with commercially available nanoparticles showed superior performance of the newly prepared nanorattle structures.

Temperature-dependent shape-responsive fluorescent nanospheres for image-guided drug delivery

Temperature-responsive nanoparticles used in conjunction with hyperthermia promise to provide synergistic effects for increasing drug efficacy. We propose a near-infared (NIR) fluorescent system based on a upper critical solution temperature (UCST) polymer, ISP2, integrated with a NIR fluorescent dye HITC for in vivo tracking. The system forms a nanoparticle that increases its volume as temperature increases, similar to the expansion of a Hoberman sphere. The nanospheres nearly doubled in size, from 80 nm to 140 nm, during a temperature increase from 40°C to 60°C.

Biomimetic and Bioinspired Synthesis of Nanomaterials/Nanostructures

In recent years, due to its unparalleled advantages, the biomimetic and bioinspired synthesis of nanomaterials/nanostructures has drawn increasing interest and attention. Generally, biomimetic synthesis can be conducted either by mimicking the functions of natural materials/structures or by mimicking the biological processes that organisms employ to produce substances or materials. Biomimetic synthesis is therefore divided here into "functional biomimetic synthesis" and "process biomimetic synthesis". Process biomimetic synthesis is the focus of this review. First, the above two terms are defined and their relationship is discussed. Next different levels of biological processes that can be used for process biomimetic synthesis are compiled. Then the current progress of process biomimetic synthesis is systematically summarized and reviewed from the following five perspectives: i) elementary biomimetic system via biomass templates, ii) high-level biomimetic system via soft/hard-combined films, iii) intelligent biomimetic systems via liquid membranes, iv) living-organism biomimetic systems, and v) macromolecular bioinspired systems. Moreover, for these five biomimetic systems, the synthesis procedures, basic principles, and relationships are discussed, and the challenges that are encountered and directions for further development are considered.

Optically active hollow nanoparticles constructed by chirally helical substituted polyacetylene

Hollow nanoparticles were constructed by chirally helical substituted polyacetylene and they demonstrated intriguing optical activity and high stability.

Synthesis of crosslinked polymeric nanocapsules using catanionic vesicle templates stabilized by compressed CO2

The synthesis of polymeric nanocapsules in the approximate diameter range 40-100 nm (TEM/SEM) using catanionic surfactant vesicle templates stabilized by subcritical CO2 is demonstrated. Near equimolar aqueous solutions of the surfactants sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) experienced immediate vesicle destabilization and precipitation in the absence of CO2. However, pressurization with CO2 (5 MPa) dramatically enhanced the stability of the initial vesicles, and enabled swelling of the bilayers with hydrophobic monomers via diffusion loading (loading of monomers into preformed bilayers). Subsequent radical crosslinking polymerization of the monomers n-butyl methacrylate/tert-butyl methacrylate/ethylene glycol dimethacrylate contained within the bilayers was conducted at room temperature using UV-initiation under CO2 pressure. The hollow structure of the resultant nano-objects was confirmed by successful encapsulation and retention of the dye Nile Blue. It is demonstrated that using this method, polymeric nanocapsules can be successfully prepared using diffusion loading of up to 94 wt% monomer (rel. to surfactant) stabilized by CO2.

Nitroarene reduction: a trusted model reaction to test nanoparticle catalysts

Nitrophenol reduction to aminophenol with a reducing agent is conveniently carried out in aqueous medium mainly with a metal or metal oxide catalyst. This reduction is presently considered as a benchmark reaction to test a catalyst nanoparticle. Thousands of original reports have enriched this field of nanoparticle catalyzed reaction. Synthesis of different metal and metal oxide nanoparticles and their composites along with their role as catalysts for nitrophenol reduction with varying reducing agents have been elucidated here. The progress of the reaction is conveniently monitored by UV-visible spectrophotometry and hence it becomes a universally accepted model reaction. In this review we have discussed the reaction kinetics considering its elegance and importance enlightening the long known Langmuir-Hinshelwood mechanism and Eley-Rideal mechanism at length, along with a few other mechanisms recently reported. A brief description of the synthetic procedures of various nanoparticles and their respective catalytic behaviour towards nitroarene reduction has also been accounted here.

Directed assembly of vesicle-templated polymer nanocapsules under near-physiological conditions

This work addresses the challenge of creating hollow polymer capsules with wall thickness in the single-nanometer range under mild conditions. We present a simple and scalable method for the synthesis of hollow polymer nanocapsules in the bilayers of spontaneously assembled surfactant vesicles. Polymerization is initiated thermally with the help of a peroxide initiator and an amine activator codissolved with monomers and cross-linkers in the hydrophobic interior of the surfactant bilayer. To avoid premature polymerization, the initiator and the activator were added separately to the mixtures of cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS) containing monomers and cross-linkers. Upon hydration and mixing of the aqueous solutions, equilibrium monomer-loaded vesicles formed spontaneously after a brief incubation. The removal of oxygen and further incubation at slightly elevated temperatures (35-40 °C) for 1 to 2 h has led to the formation of hollow polymer nanocapsules. Structural and permeability characterization supported the high yield of nanocapsules with no pinhole defects.

Recent progress in designing shell cross-linked polymer capsules for drug delivery

This tutorial review highlights the progress made during recent years in the development of the shell cross-linked (SCL) polymer nanocapsules and the impact of the most important scientific ideas on this field of knowledge.

Nanocapsules for 5-fluorouracil delivery decorated with a poly(2-ethylhexyl methacrylate-co-7-(4-trifluoromethyl)coumarin acrylamide) cross-linked wall

Nanocapsules with reverse cross-linked polymer walls containing coumarin moieties are capable of encapsulating 5-fluorouracil and accomplishing a comprehensive strategy in a drug delivery system.

Design of fluorescent nanocapsules as ratiometric nanothermometers

We have developed a novel design of optical nanothermometers that can measure the surrounding temperature in the range of 20-85 °C. The nanothermometers comprise two organic fluorophores encapsulated in a crosslinked polymethacrylate nanoshell. The role of the nanocapsule shell around the fluorophores is to form a well-defined and stable microenvironment to prevent other factors besides temperature from affecting the dyes' fluorescence. The two fluorophores feature different temperature-dependent emission profiles; a fluorophore with relatively insensitive fluorescence (rhodamine 640) serves as a reference whereas a sensitive fluorophore (indocyanine green) serves as a sensor. The sensitivity of the nanothermometers depends on the type of nanocapsule-forming lipid and is affected by the phase transition temperature. Both the fluorescence intensity and the fluorescence lifetime can be utilized to measure the temperature.

Facile directed assembly of hollow polymer nanocapsules within spontaneously formed catanionic surfactant vesicles

Surfactant vesicles containing monomers in the interior of the bilayer were used to template hollow polymer nanocapsules. This study investigated the formation of surfactant/monomer assemblies by two loading methods, concurrent loading and diffusion loading. The assembly process and the resulting aggregates were investigated with dynamic light scattering, small angle neutron scattering, and small-angle X-ray scattering. Acrylic monomers formed vesicles with a mixture of cationic and anionic surfactants in a broad range of surfactant ratios. Regions with predominant formation of vesicles were broader for compositions containing acrylic monomers compared with blank surfactants. This observation supports the stabilization of the vesicular structure by acrylic monomers. Diffusion loading produced monomer-loaded vesicles unless vesicles were composed from surfactants at the ratios close to the boundary of a vesicular phase region on a phase diagram. Both concurrent-loaded and diffusion-loaded surfactant/monomer vesicles produced hollow polymer nanocapsules upon the polymerization of monomers in the bilayer followed by removal of surfactant scaffolds.

Physicochemical characteristics of polymer-coated metal-oxide nanoparticles and their toxicological effects on zebrafish (Danio rerio) development

Coated nanoparticles (NPs) will end up in the environment due to their proposed use in agricultural applications and may potentially cause toxic effects due to their unique properties. To determine the effects of coated NPs on zebrafish (Danio rerio) development, we tested aqueous poly(acrylic acid) (PAA)-coated metal-oxide NPs including TiO2, ZnO, Fe2O3, and CeO2, as well as the polymer coating alone (nanocapsule). Zebrafish embryos were exposed to NPs over a 72 h period at 1, 10, 50, 100, 200, 400, 800, 1200, 1600, and 2000 mg/L to measure various end points. We also ran free metal controls. Time-dependent changes in physicochemical properties of NPs were characterized using dynamic light scattering. Dissolution experiments over 72 h showed minimal free metals were present in stock suspensions and released from the NPs. Interestingly, nanocapsules (≥ 800 mg/L) cause inhibition of hatch, and we suggest that a low pH environment may explain this effect. This study has also demonstrated that CeO2 NPs and nanocapsules containing Nile red are able to traverse the chorion. Overall, our findings indicate that each NP type is stable and neither the NP or encapsulating PAA coating causes apparent toxicity to developing zebrafish.

Fabrication of polymer nanocapsules with controllable oligo(ethylene glycol) densities, permeation properties and robustly crosslinked walls

P(TMSPMA-co-OEGMA) nanocapsules with controllable oligo(ethylene glycol) (OEG) densities and robustly cross-linked structures were successfully fabricated from the cross-linkable copolymer, poly[3-(trimethoxysilyl)propyl methacrylate-co-oligo(ethylene glycol) methacrylate] (P(TMSPMA-co-OEGMA)). The densities of OEG segments of the resultant P(TMSPMA-co-OEGMA) nanocapsules could be easily controlled by tuning the OEGMA contents of copolymer P(TMSPMA-co-OEGMA). The microenvironments of the P(TMSPMA-co-OEGMA) nanocapsules were determined to be hydrophobic. It was demonstrated that hydrophobic pyrene could be in situ loaded into the P(TMSPMA-co-OEGMA) nanocapsules during the fabrication procedure. The release rates of pyrene from the P(TMSPMA-co-OEGMA) nanocapsules were dependent on the contents of OEGMA, indicating that the permeation properties of P(TMSPMA-co-OEGMA) nanocapsules could be tuned by varying the cross-linked densities of the nanocapsule walls. It was further demonstrated that other functional groups could be easily incorporated into the resultant polymer nanocapsules by using the similar procedure. The preparation of polymer nanocapsules with various functionalities and robustly cross-linked walls without any further post modification process, any sacrificial core and surfactant would be beneficial from scientific and technical point of views.

Hollow block copolymer nanoparticles through a spontaneous one-step structural reorganization

The spontaneous one-step synthesis of hollow nanocages and nanotubes from spherical and cylindrical micelles based on poly(acrylic acid)-b-polylactide (P(AA)-b-P(LA)) block copolymers (BCPs) has been achieved. This structural reorganization, which occurs simply upon drying of the samples, was elucidated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). We show that it was necessary to use stain-free imaging to examine these nanoscale assemblies, as the hollow nature of the particles was obscured by application of a heavy metal stain. Additionally, the internal topology of the P(AA)-b-P(LA) particles could be tuned by manipulating the drying conditions to give solid or compartmentalized structures. Upon resuspension, these reorganized nanoparticles retain their hollow structure and display significantly enhanced loading of a hydrophobic dye compared to the original solid cylinders.

BLOOD TRIGGERED RAPID RELEASE POROUS NANOCAPSULES

Rapid-release drug delivery systems present a new paradigm in emergency care treatments. Such systems combine a long shelf life with the ability to provide a significant dose of the drug to the bloodstream in the shortest period of time. Until now, development of delivery formulations has concentrated on slow release systems to ensure a steady concentration of the drug. To address the need for quick release system, we created hollow polyacrylate nanocapsules with nanometer-thin porous walls. Burst release occurs upon interaction with blood components that leads to escape of the cargo. The likely mechanism of release involves a conformational change of the polymer shell caused by binding albumin. To demonstrate this concept, a near-infrared fluorescent dye indocyanine green (ICG) was incorporated inside the nanocapsules. ICG-loaded nanocapsules demonstrated remarkable shelf life in aqueous buffers with no release of ICG for twelve months. Rapid release of the dye was demonstrated first in vitro using albumin solution and serum. SEM and light scattering analysis demonstrated the retention of the nanocapsule architecture after the release of the dye upon contact with albumin. In vivo studies using fluorescence lifetime imaging confirmed quick discharge of ICG from the nanocapsules following intravenous injection.

Facile fabrication of polymer nanocapsules with cross-linked organic-inorganic hybrid walls

A facile method was developed for the fabrication of polymer nanocapsules with organic-inorganic hybrid walls and controllable morphologies from a cross-linkable polymer, poly[3-(trimethoxysilyl)propyl methacrylate] (PTMSPMA). With the combination of emulsion, hydrolysis, and condensation reaction as well as the internal phase separation, cross-linked PTMSPMA nanocapsules with classic hollow structures, collapsed hollow structures with Kippah, and multi-fold morphologies could be successfully obtained by simply mixing the toluene solution of PTMSPMA with water under vigorous stirring for 48 h at different temperatures. The hydrolysis and condensation of methoxysilyl groups resulted in the phase separation of PTMSPMA inside the toluene droplets and the migration of PTMSPMA to the interface of toluene and water. The cross-linking reaction of methoxysilyl groups further fixed the interfacial phase of PTMSPMA, leading the formation of PTMSPMA nanocapsules with robust cross-linked organic-inorganic hybrid walls. Such nanocapsules with robust cross-linking structures may find potential applications for the encapsulations of many functional species.

Soft vesicles in the synthesis of hard materials

Vesicles of surfactants in aqueous solution have received considerable attention because of their use as simple model systems for biological membranes and their applications in various fields including colloids, pharmaceuticals, and materials. Because of their architecture, vesicles could prove useful as "soft" templates for the synthesis of "hard materials". The vesicle phase, however, has been challenging and difficult to work with in the construction of hard materials. In the solution-phase synthesis of various inorganic or macromolecular materials, templating methods provide a powerful strategy to control the size, morphology, and composition of the resulting micro- and nanostructures. In comparison with hard templates, soft templates are generally constructed using amphiphilic molecules, especially surfactants and amphiphilic polymers. These types of compounds offer advantages including the wide variety of available templates, simple fabrication processes under mild conditions, and easy removal of the templates with less damage to the final structures. Researchers have used many ordered molecular aggregates such as vesicles, micelles, liquid crystals, emulsion droplets, and lipid nanotubes as templates or structure-directing agents to control the synthesis or assembly hard micro- and nanomaterials composed from inorganic compounds or polymers. In addition to their range of sizes and morphologies, vesicles present unique structures that can simultaneously supply different microenvironments for the growth and assembly of hard materials: the inner chamber of vesicles, the outer surface of the vesicles, and the space between bilayers. Two main approaches for applying vesicles in the field of hard materials have been explored: (i) in situ synthesis of micro- or nanomaterials within a specific microenvironment by vesicle templating and (ii) the assembly or incorporation of guest materials during the formation of vesicles. This Account provides an in-depth look at the research concerning the association of soft vesicles with hard materials by our laboratory and others. We summarize three main principles of soft vesicle usage in the synthesis of hard materials and detailed procedures for vesicle templating and the characterization of the synthetic mechanisms. By use of these guiding principles, a variety of inorganic materials have been prepared, such as quantum dots, noble metal nanoparticles, mesoporous structures, and hollow capsules. Polymerization within the vesicle bilayers enhances vesicle stability, and this strategy has been developed to synthesize hollow polymer materials. Since 2004, our group has pursued a completely different strategy in the synthesis of micro- and nanomaterials using vesicles as reactive templates. In this method, the vesicles act not only as templates but also as reactive precursors. Because of the location of metal ions on the bilayer membranes, such reactions are restricted to the interface of the vesicle membrane and solution. Finally, using the perspective of soft matter chemistry, we stress some basic criteria for vesicle templating.

Stimuli-responsive LbL capsules and nanoshells for drug delivery

Review of basic principles and recent developments in the area of stimuli responsive polymeric capsules and nanoshells formed via layer-by-layer (LbL) is presented. The most essential attributes of the LbL approach are multifunctionality and responsiveness to a multitude of stimuli. The stimuli can be logically divided into three categories: physical (light, electric, magnetic, ultrasound, mechanical, and temperature), chemical (pH, ionic strength, solvent, and electrochemical) and biological (enzymes and receptors). Using these stimuli, numerous functionalities of nanoshells have been demonstrated: encapsulation, release including that inside living cells or in tissue, sensors, enzymatic reactions, enhancement of mechanical properties, and fusion. This review describes mechanisms and basic principles of stimuli effects, describes progress in the area, and gives an outlook on emerging trends such as theranostics and nanomedicine.

Safety profile and cellular uptake of biotemplated nanocapsules with nanometre-thin walls

Polymeric nanocapsules with nanometre-thin walls offer a promising platform for controlled cellular delivery of therapeutic or diagnostic agents. Therefore, their biocompatibility is crucial for future applications in the human body. However, there is little knowledge about their interaction with biological systems. In this study, polymeric nanocapsules containing different amounts of lipids and representing different scenarios for handling and storing nanocapsules are investigated. We find that all nanocapsules in our study can enter human cells and the presence of an outer lipid shell facilitates the process. These nanocapsules do not inhibit cell proliferation at concentrations up to 200 μg mL(-1) of nanocapsules. No cellular ROS, apoptosis or cell cycle perturbation is detected at this dose. These comprehensive examinations demonstrate that polymeric nanocapsules are promising nano-carriers for cellular delivery.

Scattering studies of hydrophobic monomers in liposomal bilayers: an expanding shell model of monomer distribution

Hydrophobic monomers partially phase separate from saturated lipids when loaded into lipid bilayers in amounts exceeding a 1:1 monomer/lipid molar ratio. This conclusion is based on the agreement between two independent methods of examining the structure of monomer-loaded bilayers. Complete phase separation of monomers from lipids would result in an increase in bilayer thickness and a slight increase in the diameter of liposomes. A homogeneous distribution of monomers within the bilayer would not change the bilayer thickness and would lead to an increase in the liposome diameter. The increase in bilayer thickness, measured by the combination of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS), was approximately half of what was predicted for complete phase separation. The increase in liposome diameter, measured by dynamic light scattering (DLS), was intermediate between values predicted for a homogeneous distribution and complete phase separation. Combined SANS, SAXS, and DLS data suggest that at a 1.2 monomer/lipid ratio approximately half of the monomers are located in an interstitial layer sandwiched between lipid sheets. These results expand our understanding of using self-assembled bilayers as scaffolds for the directed covalent assembly of organic nanomaterials. In particular, the partial phase separation of monomers from lipids corroborates the successful creation of nanothin polymer materials with uniform imprinted nanopores. Pore-forming templates do not need to span the lipid bilayer to create a pore in the bilayer-templated films.