Controlled Release from Polyurethane Nanocapsules via pH-, UV-Light- or Temperature-Induced Stimuli

Green synthesis of sacrificial UV-sensitive core and biobased shell for obtaining optically hollow nanoparticles

Hollow nanoparticles have been extensively studied in recent years. Obtaining such structures with biobased materials, following greener synthetic routes, is still challenging, especially if accurate particle dimensions are required. This work reports the use of an innovative hybrid silica core (Si@azo) containing UV-sensitive molecule, wrapped in biobased multilayer shell composed of polysaccharides. It is a promising strategy for obtaining optically hollow nanoparticles. Indeed, Si@azo cores have the ability to be partially degraded when irradiated with UV light. Combined with a well-controlled and monodisperse diameter, they provide a good basis for layer-by-layer assembly, leading to a multilayer shell with controlled composition and thickness. Finally, UV irradiation of such a core-shell structure is harmless to the polysaccharide shell, but does impact the hybrid silica core, as revealed by turbidity measurements, among other. Each step, i.e. core synthesis, shell addition, and core-shell irradiation, has been carefully characterized at the macro (Fourier-transform infrared spectroscopy - FTIR, Dynamic Light Scattering - DLS, Zeta-potential measurement, Surface Plasmon Resonance - SPR, turbidity) and microscale (Transmission and Scanning Electron Microscopies). Emphasis is put on how turbidity measurements can be related to the core refractive index (ncore), giving information on the state of core degradation and whether the core-shell particle is optically hollow.

A Sacrificial Linker in Biodegradable Polyesters for Accelerated Photoinduced Degradation, Monitored by Continuous Atline SEC Analysis

Polymeric materials that undergo photoinduced degradation have wide application in fields such as controlled release. Most methods for photoinduced degradation rely on the UV or near-UV region of the electromagnetic spectrum; however, use of the deeply penetrating and benign wavelengths of visible light offers a multitude of advantages. Here we report a lactone monomer for ring-opening copolymerizations to introduce a sacrificial linker into a polymer backbone which can be cleaved by reactive oxygen species which are produced by a photocatalyst under visible light irradiation. We find that copolymers of this material readily degrade under visible light. We followed polymer degradation using a continuous flow size exclusion chromatography system, the components of which are described herein.

Novel Tumor-Targeted Self-Nanostructured and Compartmentalized Water-in-Oil-in-Water Polyurethane-Polyurea Nanocapsules for Cancer Theragnosis

Encapsulation of water-soluble bioactive compounds for enabling specific accumulation in tumor locations, while avoiding premature clearance and/or degradation in the bloodstream, is one of the main hallmarks in nanomedicine, especially that of NIR fluorescent probes for cancer theragnosis. The herein reported technology furnishes water-dispersible double-walled polyurethane-polyurea hybrid nanocapsules (NCs) loaded with indocyanine green (ICG-NCs), using a versatile and highly efficient one-pot and industrially scalable synthetic process based on the use of two different prepolymers to set up the NCs walls. Flow cytometry and confocal microscopy confirmed that both ICG-loaded NCs internalized in monocyte-derived dendritic cells (moDCs). The in vivo analysis of xenograft A375 mouse melanoma model revealed that amphoteric functionalization of NCs' surface promotes the selective accumulation of ICG-NCs in tumor tissues, making them promising agents for a less-invasive theragnosis of cancer.

Improving Photodynamic Therapy Anticancer Activity of a Mitochondria-Targeted Coumarin Photosensitizer Using a Polyurethane-Polyurea Hybrid Nanocarrier

Integration of photosensitizers (PSs) within nanoscale delivery systems offers great potential for overcoming some of the "Achiles' heels" of photodynamic therapy (PDT). Herein, we have encapsulated a mitochondria-targeted coumarin PS into amphoteric polyurethane-polyurea hybrid nanocapsules (NCs) with the aim of developing novel nanoPDT agents. The synthesis of coumarin-loaded NCs involved the nanoemulsification of a suitable prepolymer in the presence of a PS without needing external surfactants, and the resulting small nanoparticles showed improved photostability compared with the free compound. Nanoencapsulation reduced dark cytotoxicity of the coumarin PS and significantly improved in vitro photoactivity with red light toward cancer cells, which resulted in higher phototherapeutic indexes compared to free PS. Importantly, this nanoformulation impaired tumoral growth of clinically relevant three-dimensional multicellular tumor spheroids. Mitochondrial photodamage along with reactive oxygen species (ROS) photogeneration was found to trigger autophagy and apoptotic cell death of cancer cells.

Preparation and performance of chlorfenapyr microcapsules with a degradable polylactide-based polyurethane wall material

To improve the utilization rate of chlorfenapyr and make the wall material of chlorfenapyr microcapsules easily degradable, polylactide diol, toluene diisocyanate and 1,4-butanediol were used to prepare a chlorfenapyr microcapsule suspension by interfacial polymerization. The product was characterized by the methods of optical microscopy, scanning electron microscopy and Fourier-transform infrared spectroscopy. The results indicated that the microcapsule particles were spherical, with an encapsulation efficiency of 84.20%. The diluted product had good wetting and spreading abilities on cabbage leaves. Compared with other commercial formulations, the slow-release effect of the microcapsule suspension was more obvious and the release mechanisms conform to Fickian diffusion, with the release rate controllable by adjusting the external pH conditions. Furthermore, the wall material of the microcapsules showed good degradation performance in a phosphate-buffered solution. Microencapsulation by this method significantly increased the validity period of chlorfenapyr and the wall material was also degraded easily.

Backbone vs. side-chain: two light-degradable polyurethanes based on 6-nitropiperonal

Two novel polyurethanes, which are based on 6-nitropiperonal and differ in the implementation of the light-cleavable unit, were synthesized to develop a drug delivery system that only releases cargo upon application of a certain trigger.

Solid Polymeric Nanoparticles of Albendazole: Synthesis, Physico-Chemical Characterization and Biological Activity

Albendazole is a benzimidazole derivative with documented antitumor activity and low toxicity to healthy cells. The major disadvantage in terms of clinical use is its low aqueous solubility which limits its bioavailability. Albendazole was incorporated into stable and homogeneous polyurethane structures with the aim of obtaining an improved drug delivery system model. Spectral and thermal analysis was used to investigate the encapsulation process and confirmed the presence of albendazole inside the nanoparticles. The in vitro anticancer properties of albendazole encapsulated in polyurethane structures versus the un-encapsulated compound were tested on two breast cancer cell lines, MCF-7 and MDA-MB-231, in terms of cellular viability and apoptosis induction. The study showed that the encapsulation process enhanced the antitumor activity of albendazole on the MCF-7 and MDA-MB-23 breast cancer lines. The cytotoxic activity manifested in a concentration-dependent manner and was accompanied by changes in cell morphology and nuclear fragmentation.

Light-Responsive Serinol-Based Polyurethane Nanocarrier for Controlled Drug Release

In the present work, a new and facile strategy for the synthesis of light-responsive polyurethanes (LrPUs) based on serinol with o-nitrobenzyl pendent groups is developed. Stable monodisperse nanoparticles from these LrPUs can be formulated reproducibly in a simple manner, which is shown by dynamic light scattering (DLS) measurements. Upon irradiation with UV light, both polymers and nanoparticles undergo rapid degradation, which is investigated by DLS, scanning electron microscopy, size exclusion chromatography, and UV-vis spectroscopy. The nanoparticles are also employed for the encapsulation of the model drug Nile Red, and by exposure to UV light, a burst release of the payload is detected via fluorescence spectroscopy. This strategy can be easily applied to the straightforward synthesis of various new serinol-based monomers with different stimuli-responsive properties and therefore expand the family of biodegradable polymers.

Effect of a Surfactant in Microcapsule Synthesis on Self-Healing Behavior of Capsule Embedded Polymeric Films

Recently, there has been increased interest in self-healing membranes containing functional microcapsules in relation to challenges involving water treatment membranes. In this study, a self-healing membrane has been prepared by incorporating microcapsules with a polyurethane (PU) shell and a diisocyanate core in a poly(ether sulfone) (PES) membrane. Depending on the characteristics of the microcapsule, to precisely quantify the self-healing behavior and performance of the produced microcapsule embedded membranes, it is important to understand the effect of a used surfactant on microcapsule synthesis. It is noteworthy that mixed surfactants have been employed to control and tailor the size and morphology of microcapsules during the synthetic process, and the surfactant system employed was one of the most dominant parameters for affecting the healing capability of microcapsule embedded membranes. Various techniques including microscopy (optical and electron), thermal analyses (DSC and TGA), and water flux measurements have been employed. This article provides essential and important information for future research into the subtle relation between microcapsule properties with varied synthetic parameters and the self-healing behavior of membrane.

Porous epoxy phenolic novolac resin polymer microcapsules: Tunable release and bioactivity controlled by epoxy value

Microcapsules (MCs) prepared with diverse wall material structures may exhibit different properties. In this study, MCs were fabricated with three kinds of epoxy phenolic novolac resins (EPNs), which possessed unique epoxy values as wall-forming materials by interfacial polymerization. The effects of the EPN types on the surface morphology, particle size distribution, encapsulation efficiency, thermal stability as well as release behavior and bioactivity of the MCs were investigated. In all three samples, the MCs had nearly spherical shapes with fine monodispersities and sizes in the range of 7-30 μm. Scanning electron microscopy (SEM) images showed that some small pores (ranging from 50 nm to 400 nm) appeared on the microcapsule surfaces and that the porosity decreased with an increasing of epoxy value. The X-ray diffractometer (XRD) analysis indicated that the cured EPN shells had larger degrees of crosslinking with higher epoxy values, leading to better thermal stabilities. Moreover, the release rate of the core material (pendimethalin) decreased with an increasing of epoxy value and thus resulted in a lower herbicidal control efficacy. The results of our research will enhance the potential application of EPNs as smart wall-forming materials to prepare porous MCs for controlled release.

Controlling the Release from Enzyme-Responsive Microcapsules with a Smart Natural Shell

We design a natural and simple core-shell-structured microcapsule, which releases its cargo only when exposed to lipase. The cargo is entrapped inside a gel matrix, which is surrounded by a double-layer shell containing an inner solid lipid layer and an outer polymer layer. This outer polymer layer can be designed according to the intended biological system and is responsible for protecting the microcapsule architecture and transporting the cargo to the desired site of action. The lipid layer contains natural ester bonds, which are digested by lipase, controlling the release of cargo from the microcapsule core. To demonstrate the feasibility of this approach, our model system includes a colorant bixin entrapped inside a κ-carrageenan gel matrix. This core is surrounded by an inner beeswax-palmitic acid layer and an outer casein-poloxamer 338 layer. These fabricated microcapsules are then applied into Cheddar cheese, where they selectively color the cheese matrix.

Causation Analysis and Improvement Strategy for Reduced Pendimethalin Herbicidal Activity in the Field after Encapsulation in Polyurea

To reduce the amount of organic solvents in pendimethalin emulsifiable concentrate (EC), small-size microcapsules (S-MCs) and large-size microcapsules (L-MCs) were prepared with polyurea as a wall material. Petri-dish bioassays were carried out to investigate the bioactivity of formulations and the influence of both organic matter and moisture. The relationships between degradation and the biological activity of three pendimethalin formulations in the soil were investigated, and field experiments were executed to verify the laboratory results. The laboratory tests showed the following: (1) the bioactivity of EC and S-MCs was similar and greater than that of L-MCs; (2) organic matter could reduce the bioactivity of MCs and EC, and the impact of organic matter on L-MCs was greater; (3) increased soil moisture content had no significant effect on the bioactivity of EC but slightly reduced that of the MCs; and (4) the L-MCs showed significantly more prolonged residual and effective persistence in the soil than did EC and S-MCs. However, the field experiments indicated that the herbicidal efficacies of L-MCs at the early and late stages were both lower than those of EC. Comprehensive analysis of the results indicated that the main reason that the herbicidal efficacy of L-MCs was lower than that of EC in the field was that L-MCs missed the optimal herbicidal periods due to the slow-release characteristics of L-MCs. The S-MCs had both similar release rates and herbicidal efficacy in the field as EC. Therefore, to develop a good pesticide formulation, the occurrence and damage characteristic of pests must be considered.

Morphology-dependent pH-responsive release of hydrophilic payloads using biodegradable nanocarriers

The development of functional nanocarriers with stimuli-responsive properties has advanced tremendously to serve biomedical applications such as drug delivery and regenerative medicine. However, the development of biodegradable nanocarriers that can be loaded with hydrophilic compounds and ensure its controlled release in response to changes in the surrounding environment still remains very challenging. Herein, we achieved such demands via the preparation of aqueous core nanocapsules using a base-catalyzed interfacial reaction employing a diisocyanate monomer and functional monomers/polymers containing thiol and hydroxyl functionalities at the droplet interface. pH-responsive poly(thiourethane–urethane) nanocarriers with ester linkages were synthesized by incorporating polycaprolactone diol, which is susceptible to hydrolytic degradation via ester linkages, as a functional monomer in the reaction formulation. We could demonstrate that by systematically varying the number of biodegradable segments, the morphology of the nanocarriers can be tuned without imparting the efficient encapsulation of hydrophilic payload (>85% encapsulation efficiency) and its transfer from organic to aqueous phase. The developed nanocarriers allow for a fast release of hydrophilic payload that depends on pH, the number of biodegradable segments and nanocarrier morphology. Succinctly put, this study provides important information to develop pH-responsive nanocarriers with tunable morphology, using interfacial reactions in the inverse miniemulsion process, by controlling the number of degradable segments to adjust the release profile depending on the type of application envisaged.

The morphology and release properties of aqueous core nanocapsules for the pH-responsive release of hydrophilic payload was investigated by systematically varying the number of biodegradable segments.

Synthesis and Characterization of Microencapsulated Phase Change Materials with Poly(urea-urethane) Shells Containing Cellulose Nanocrystals

The main objective of this study is to develop microencapsulation technology for thermal energy storage incorporating a phase change material (PCM) in a composite wall shell, which can be used to create a stable environment and allow the PCM to undergo phase change without any outside influence. Surface modification of cellulose nanocrystals (CNCs) was conducted by grafting poly(lactic acid) oligomers and oleic acid to improve the dispersion of nanoparticles in a polymeric shell. A microencapsulated phase change material (methyl laurate) with poly(urea-urethane) (PU) composite shells containing the hydrophobized cellulose nanocrystals (hCNCs) was fabricated using an in situ emulsion interfacial polymerization process. The encapsulation process of the PCMs with subsequent interfacial hCNC-PU to form composite microcapsules as well as their morphology, composition, thermal properties, and release rates was examined in this study. Oil soluble Sudan II dye solution in methyl laurate was used as a model hydrophobic fill, representing other latent fills with low partition coefficients, and their encapsulation efficiency as well as dye release rates were measured spectroscopically in a water medium. The influence of polyol content in the PU polymer matrix of microcapsules was investigated. An increase in polyol contents leads to an increase in the mean size of microcapsules but a decrease in the gel content (degree of cross-linking density) and permeability of their shell structure. The encapsulated PCMs for thermal energy storage demonstrated here exhibited promising performance for possible use in building or paving materials in terms of released heat, desired phase transformation temperature, chemical and physical stability, and concrete durability during placement.

Silver Alginate Hydrogel Micro- and Nanocontainers for Theranostics: Synthesis, Encapsulation, Remote Release, and Detection

We have designed multifunctional silver alginate hydrogel microcontainers referred to as loaded microcapsules with different sizes by assembling them via a template assisted approach using natural, highly porous calcium carbonate cores. Sodium alginate was immobilized into the pores of calcium carbonate particles of different sizes followed by cross-linking via addition of silver ions, which had a dual purpose: on one hand, the were used as a cross-linking agent, albeit in the monovalent form, while on the other hand they have led to formation of silver nanoparticles. Monovalent silver ions, an unusual cross-linking agent, improve the sensitivity to ultrasound, lead to homogeneous distribution of silver nanoparticles. Silver nanoparticles appeared on the shell of the alginate microcapsules in the twin-structure as determined by transmission electron microscopy. Remote release of a payload from alginate containers by ultrasound was found to strongly depend on the particle size. The possibility to use such particles as a platform for label-free molecule detection based on the surface enhanced Raman scattering was demonstrated. Cytotoxicity and cell uptake studies conducted in this work have revealed that microcontainers exhibit nonessential level of toxicity with an efficient uptake of cells. The above-described functionalities constitute building blocks of a theranostic system, where detection and remote release can be achieved with the same carrier.

Sustained Dye Release Using Poly(urea-urethane)/Cellulose Nanocrystal Composite Microcapsules

The aim of this study is to develop methods to reinforce polymeric microspheres with cellulose nanocrystals (CNCs) to make eco-friendly microcapsules for a variety of applications such as medicines, perfumes, nutrients, pesticides, and phase change materials. Surface hydrophobization treatments for CNCs were performed by grafting poly(lactic acid) oligomers and fatty acids (FAs) to enhance the dispersion of nanoparticles in the polymeric shell. Then, a straightforward process is demonstrated to design sustained release microcapsules by the incorporation of the modified CNCs (mCNCs) in the shell structure. The combination of the mCNC dispersion with subsequent interfacial polyurea (PU) to form composite capsules as well as their morphology, composition, mechanical properties, and release rates were examined in this study. The PU microcapsules embedded with the mCNC were characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The morphologies of the microcapsules were characterized by optical microscopy (OM) and scanning electron microscope (SEM). The rupture stress and failure behavior of the microcapsules were determined through single-capsule compression tests. Oil-soluble Sudan II dye solution in mineral oil was utilized as a model hydrophobic fill, representing other latent fills with low partition coefficients, and their encapsulation efficiency was measured spectroscopically. The release rates of the encapsulated dye from the microcapsules were examined spectroscopically by both ethanol and 2-ethyl-1-hexanol medium at room temperature. The concentration of released dye was determined by using UV-vis absorption spectrometry (UV-vis). The mCNC embedded poly(urea-urethane) capsules have strong and dense walls, which function as excellent barriers against leakage due to their extended diffusion path length and ensure enough mechanical strength from rupture for handling or postprocessing.

Recent progress and advances in redox-responsive polymers as controlled delivery nanoplatforms

Recent advances and progress in redox-responsive polymeric nanosystems for biomedical applications are discussed in this review article.

Photodegradable polymer nanocapsules fabricated from dimethyldiethoxysilane emulsion templates for controlled release

A photodegradable polymer nanocapsule was prepared from dimethyldiethoxysilane emulsion templates and applied for light- and pH-controlled cargo release.

Facile Synthesis of Reductively Degradable Biopolymers Using Cystamine Diisocyanate as a Coupling Agent

Reductively degradable biopolymers have emerged as a unique class of smart biomedical materials. Here, a functional coupling agent, cystamine diisocyanate (CDI), was designed to offer a facile access to reductively degradable biopolymers via polycondensation with various diols. CDI was readily obtained with a decent yield of 46% by reacting cystamine dihydrochloride with triphosgene. The polycondensation of oligo(ethylene glycol) diol (Mn = 0.4 or 1.5 kg/mol) or oligo(ε-caprolactone) diol (Mn = 0.53 kg/mol) with CDI in N,N-dimethylformamide at 60 °C using dibutyltin dilaurate as a catalyst afforded reductively degradable poly(ethylene glycol) (SSPEG, Mn = 6.2-76.8 kg/mol) or poly(ε-caprolactone) (SSPCL, Mn = 6.8-16.3 kg/mol), in which molecular weights were well controlled by diol/CDI molar ratios. Moreover, PEG-SSPCL-PEG triblock copolymers could be readily prepared by reacting dihydroxyl-terminated SSPCL with PEG-isocyanate derivative. PEG-SSPCL-PEG with an Mn of 5.0-16.3-5.0 kg/mol formed small-sized micelles with an average diameter of about 85 nm in PB buffer. The in vitro release studies using doxorubicin (DOX) as a model drug showed that, in sharp contrast to reduction-insensitive PEG-PCL(HDI)-PEG controls, drug release from PEG-SSPCL-PEG micelles was fast and nearly complete in 24 h under a reductive condition containing 10 mM glutathione. The confocal microscopy experiments in drug-resistant MCF-7 cells (MCF-7/ADR) displayed efficient cytoplasmic DOX release from PEG-SSPCL-PEG micelles. MTT assays revealed that DOX-loaded PEG-SSPCL-PEG micelles were much more potent against MCF-7/ADR cells than reduction-insensitive PEG-PCL(HDI)-PEG controls (IC50: 6.3 vs 55.4 μg/mL). It should further be noted that blank PEG-SSPCL-PEG micelles were noncytotoxic up to a tested concentration of 1 mg/mL. Hence, cystamine diisocyanate appears to be an innovative coupling agent that facilitates versatile synthesis of biocompatible and reductively degradable biopolymers.

Polyurethane Microstructures-a Good or Bad in vitro Partner for the Isoflavone Genistein?

In recent years polyurethane microstructures (PM) have gained increasing attention in the pharmaceutical field due to the importance of their practical application. Since finding that such a formulation with genistein could improve its applications, we have conducted a preliminary study regarding the in vitro antiproliferative (MCF7, MDA-MB-231 and T47D) and antimicrobial ( Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella enteritidis (D), Bacillus subtilis, B. cereus, and Candida albicans) activity in order to test whether polyurethane micro structuresre present a good option for further modulation of genistein's bioavailability. It was concluded that the polyurethane micro structures are a bad in vitro partner for the isoflavone genistein.

The effect of polysaccharide types on adsorption properties of LbL assembled multilayer films

Three types of biocompatible films were fabricated via electrostatic layer-by-layer (LbL) adsorption of oppositely charged cationic polyurethane and anionic polysaccharides with different primary structures, including sodium hyaluronate, sodium carboxymethyl cellulose and sodium alginate. The adsorption behaviors of films were investigated by using the cationic dye methylene blue (MB) as a model drug at various pH values and salt concentrations. The relationship between the type of polysaccharide and the adsorption behavior of LbL films was comparatively studied. It was found that the adsorption capacity increased with an increase of the initial concentration of MB in the concentration range of the experiment to all of the films, and the pH of environment ranged from 3.0 to 9.0. The Langmuir equation fit perfectly to the experiment data. In addition, a pseudo second-order adsorption model can well describe the adsorption behaviors of MB for three films. The results showed that the type of side chains and the charge density of the polysaccharides played key roles in the adsorption properties of the PU/polysaccharide multilayer films.

Controlled release of encapsulated bioactive volatiles by rupture of the capsule wall through the light-induced generation of a gas

The encapsulation of photolabile 2-oxoacetates in core-shell microcapsules allows the light-induced, controlled release of bioactive compounds. On irradiation with UVA light these compounds degrade to generate an overpressure of gas inside the capsules, which expands or breaks the capsule wall. Headspace measurements confirmed the light-induced formation of CO and CO2 and the successful release of the bioactive compound, while optical microscopy demonstrated the formation of gas bubbles, the cleavage of the capsule wall, and the leakage of the oil phase out of the capsule. The efficiency of the delivery system depends on the structure of the 2-oxoacetate, the quantity used with respect to the thickness of the capsule wall, and the intensity of the irradiating UVA light.

Interfacial thiol–isocyanate reactions for functional nanocarriers: a facile route towards tunable morphologies and hydrophilic payload encapsulation

Design of nanocarriers with tunable morphology using the in situ thiol–isocyanate interfacial reactions.

In situ functionalization of hollow mesoporous hydroxyapatite with thermal-responsive on–off gates in supercritical CO2

Aliphatic PUA-grafted mesoporous hollow hydroxyapatite microparticles with thermal-responsive on–off gates for controllable drug delivery were prepared via in situ polymerization in supercritical CO₂.

Advanced stimuli-responsive polymer nanocapsules with enhanced capabilities for payloads delivery

Recent progress in the design, preparation, and application of stimuli-responsive polymer nanocapsules with enhanced capabilities for payloads delivery are reviewed.

Stimuli-responsive polymeric nanoparticles for nanomedicine

Nature continues to be the ultimate in nanotechnology, where polymeric nanometer-scale architectures play a central role in biological systems. Inspired by the way nature forms functional supramolecular assemblies, researchers are trying to make nanostructures and to incorporate these into macrostructures as nature does. Recent advances and progress in nanoscience have demonstrated the great potential that nanomaterials have for applications in healthcare. In the realm of drug delivery, nanomaterials have been used in vivo to protect the drug entity in the systemic circulation, ensuring reproducible absorption of bioactive molecules that do not naturally penetrate biological barriers, restricting drug access to specific target sites. Several building blocks have been used in the formulation of nanoparticles. Thus, stability, drug release, and targeting can be tailored by surface modification. Herein the state of the art of stimuli-responsive polymeric nanoparticles are reviewed. Such systems are able to control drug release by reacting to naturally occurring or external applied stimuli. Special attention is paid to the design and nanoparticle formulation of these so-called smart drug-delivery systems. Future strategies for further developments of a promising controlled drug delivery responsive system are also outlined.

Tailor-made nanocontainers for combined magnetic-field-induced release and MRI

The synthesis of a novel nanocapsule-based carrier system is described, possessing a triggered release in remote-controlled fashion upon application of an external magnetic field in combination with the possibility to use the capsules as contrast agents for magnetic resonance imaging (MRI). Therefore, polymeric nanocontainers containing a high amount of superparamagnetic MnFe2 O4 nanoparticles and a thermo-degradable shell are fabricated via a miniemulsion route. The process allows the facile encapsulation of hydrophilic compounds, as demonstrated for a model dye. Release of the encapsulated dye is achieved upon application of an external alternating magnetic field. While the magnetic nanoparticles here act as heat generators to stimulate the decomposition of the shell and subsequently a release of the payload, they additionally enable the use of the nanocapsules as imaging agents for MRI. Due to the encapsulated magnetic nanoparticles, the nanocapsules possess high r2 relaxivity values of 96-120 Hz mmol(-1) , which makes them suitable for MRI. In toxicity experiments, the nanocapsules show no cell toxicity up to fairly high concentrations (600 µg mL(-1) ). Due to their dual-functionality, the nanocapsules possess high potential as nanocarriers with combined magnetic-field-induced release capability and as contrast agents for MRI.

Biodegradable lignin nanocontainers

“Trees in miniemulsion” – the biopolymer lignin was used to generate biodegradable nanocontainers via an interfacial polyaddition reaction.

Synthesis of nanostructured materials in inverse miniemulsions and their applications

Polymeric nanogels, inorganic nanoparticles, and organic-inorganic hybrid nanoparticles can be prepared via the inverse miniemulsion technique. Hydrophilic functional cargos, such as proteins, DNA, and macromolecular fluoresceins, may be conveniently encapsulated in these nanostructured materials. In this review, the progress of inverse miniemulsions since 2000 is summarized on the basis of the types of reactions carried out in inverse miniemulsions, including conventional free radical polymerization, controlled/living radical polymerization, polycondensation, polyaddition, anionic polymerization, catalytic oxidation reaction, sol-gel process, and precipitation reaction of inorganic precursors. In addition, the applications of the nanostructured materials synthesized in inverse miniemulsions are also reviewed.