System for Living ROMP of a Paramagnetic FeCl4--Based Ionic Liquid Monomer: Direct Synthesis of Magnetically Responsive Block Copolymers

Direct, living ring-opening metathesis polymerization of a highly paramagnetic, norbornene-based imidazolium FeCl₄^- ionic liquid monomer was achieved using the Grubbs third-generation catalyst and starting the polymerization off with an uncharged, nonparamagnetic norbornene monomer in a sequential block copolymerization. Preparing the paramagnetic norbornene imidazolium FeCl₄^- monomer in high purity was found to be crucial for enabling living polymerization behavior and generating paramagnetic diblock copolymers with predictable block lengths and compositions.

Development of multi-layered and multi-sensitive polymeric nanocontainers for cancer therapy: in vitro evaluation

Nanoscale drug delivery systems represent a promising strategy to treat cancer and to overcome the side effects of chemotherapy. In particular, hollow polymeric nanocontainers have attracted great interest because of their structural and morphological advantages and the variety of polymers that can be used, allowing the synthesis of stimuli-responsive materials capable of responding to the biochemical alterations of the tumour microenvironment. Here are reported the synthesis, characterization and in vitro evaluation of a three-stimuli-sensitive hollow nanocontainer consisting of three different shells, each one sensitive to a specific tumoral stimulus: in order pH, temperature and reducing environment. To test its properties, daunorubicin was used as a model drug, for which the nanocontainers exhibited excellent encapsulation ability. The in vitro drug release behaviour was studied under different conditions, where the system proved capable of responding to the selected tumoral stimuli by releasing a larger amount of drug than in physiological environment. The hollow system itself showed negligible cytotoxicity but the loaded nanocontainers and free drug showed identical cytotoxicity and intracellular localization. Therefore, this formulation can be considered as a promising platform to develop an injectable delivery system capable of improving systematic toxicity without affecting or reducing the activity of the encapsulated drug.

Redox-Responsive Molecular Systems and Materials

Redox reactions can alter the electronic, optical, and magnetic properties of molecules and their ensembles by adding or removing electrons. Here, the developments made over the past 10 years using molecular events are discussed, such as assembly/disassembly, transformation of ensembles, geometric changes, and molecular motions that are designed to be redox-responsive. Considerable progress has occurred in the application of these events to the realization of electronic memory, color displays, actuators, adhesives, and drug delivery. In these cases, systems behave in either a highly or a poorly correlated manner depending on the number of redox-active units involved, based on the method of integration. One of the great advantages of redox-responsive devices and materials is that they have the potential to be readily integrated into existing electronic technologies.

Dynamic Nanoparticle Assemblies for Biomedical Applications

Designed synthesis and assembly of nanoparticles assisted by their surface ligands can create "smart" materials with programmed responses to external stimuli for biomedical applications. These assemblies can be designed to respond either exogenously (for example, to magnetic field, temperature, ultrasound, light, or electric pulses) or endogenously (to pH, enzymatic activity, or redox gradients) and play an increasingly important role in a diverse range of biomedical applications, such as biosensors, drug delivery, molecular imaging, and novel theranostic systems. In this review, the recent advances and challenges in the development of stimuli-responsive nanoparticle assemblies are summarized; in particular, the application-driven design of surface ligands for stimuli-responsive nanoparticle assemblies that are capable of sensing small changes in the disease microenvironment, which induce the related changes in their physico-chemical properties, is described. Finally, possible future research directions and problems that have to be addressed are briefly discussed.

“Click” functionalization of dual stimuli-responsive polymer nanocapsules for drug delivery systems

“Clickable” and dual stimuli-responsive nanocapsules were developed for facile surface functionalizationviathiol–yne click chemistry and employed as drug nano-carriers.

Hollow double-layered polymer nanoparticles with S-nitrosothiols for tumor targeted therapy

Tumor targeted hollow double-layered polymer nanoparticles (HDPNs) withS-nitrosothiols for nitric oxide (NO)-release as chemotherapy were described.

Smart micro/nanoparticles in stimulus-responsive drug/gene delivery systems

New achievements in the realm of nanoscience and innovative techniques of nanomedicine have moved micro/nanoparticles (MNPs) to the point of becoming actually useful for practical applications in the near future. Various differences between the extracellular and intracellular environments of cancerous and normal cells and the particular characteristics of tumors such as physicochemical properties, neovasculature, elasticity, surface electrical charge, and pH have motivated the design and fabrication of inventive "smart" MNPs for stimulus-responsive controlled drug release. These novel MNPs can be tailored to be responsive to pH variations, redox potential, enzymatic activation, thermal gradients, magnetic fields, light, and ultrasound (US), or can even be responsive to dual or multi-combinations of different stimuli. This unparalleled capability has increased their importance as site-specific controlled drug delivery systems (DDSs) and has encouraged their rapid development in recent years. An in-depth understanding of the underlying mechanisms of these DDS approaches is expected to further contribute to this groundbreaking field of nanomedicine. Smart nanocarriers in the form of MNPs that can be triggered by internal or external stimulus are summarized and discussed in the present review, including pH-sensitive peptides and polymers, redox-responsive micelles and nanogels, thermo- or magnetic-responsive nanoparticles (NPs), mechanical- or electrical-responsive MNPs, light or ultrasound-sensitive particles, and multi-responsive MNPs including dual stimuli-sensitive nanosheets of graphene. This review highlights the recent advances of smart MNPs categorized according to their activation stimulus (physical, chemical, or biological) and looks forward to future pharmaceutical applications.

Nanostructured magnetic nanocomposites as MRI contrast agents

Magnetic resonance imaging (MRI) has become an integral part of modern clinical imaging due to its non-invasiveness and versatility in providing tissue and organ images with high spatial resolution. With the current MRI advancement, MRI imaging probes with suitable biocompatibility, good colloidal stability, enhanced relaxometric properties and advanced functionalities are highly demanded. As such, MRI contrast agents (CAs) have been an extensive research and development area. In the recent years, different inorganic-based nanoprobes comprising inorganic magnetic nanoparticles (MNPs) with an organic functional coating have been engineered to obtain a suitable contrast enhancement effect. For biomedical applications, the organic functional coating is critical to improve colloidal stability and biocompatibility. Simultaneously, it also provides a building block for generating a higher dimensional secondary structure. In this review, the combinatorial design approach by a self-assembling pre-formed hydrophobic inorganic MNPs core (from non-polar thermolysis synthesis) into various functional organic coatings (e.g. ligands, amphiphilic polymers and graphene oxide) to form water soluble nanocomposites will be discussed. The resultant magnetic ensembles were classified based on their dimensionality, namely, 0-D, 1-D, 2-D and 3-D structures. This classification provides further insight into their subsequent potential use as MRI CAs. Special attention will be dedicated towards the correlation between the spatial distribution and the associated MRI applications, which include (i) coating optimization-induced MR relaxivity enhancement, (ii) aggregation-induced MR relaxivity enhancement, (iii) off-resonance saturation imaging (ORS), (iv) magnetically-induced off-resonance imaging (ORI), (v) dual-modalities MR imaging and (vi) multifunctional nanoprobes.

Polyvinylpyrrolidone-stabilized magnetic nickel nanochains for cancer hyperthermia and catalysis applications

Novel polyvinylpyrrolidone-stabilized magnetic nickel nanochain (Ni-NC@PVP) have been reported by simple solvothermal method for potential cancer hyperthermia and catalytic applications.

Synthesis of paramagnetic polymers based on polyethyleneimine (PEI)

Paramagnetic polymers with high spin FeCl₄ anion were prepared via the post-modification of PEI facilely. The resultant polymers showed a magnetic response under the attraction of a magnetic field.

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.

Polymersome magneto-valves for reversible capture and release of nanoparticles

Stomatocytes are polymersomes with an infolded bowl-shaped architecture. This internal cavity is connected to the outside environment via a small 'mouth' region. Stomatocytes are assembled from diamagnetic amphiphilic block-copolymers with a highly anisotropic magnetic susceptibility, which permits to magnetically align and deform the polymeric self-assemblies. Here we show the reversible opening and closing of the mouth region of stomatocytes in homogeneous magnetic fields. The control over the size of the opening yields magneto-responsive supramolecular valves that are able to reversibly capture and release cargo. Furthermore, the increase in the size of the opening is gradual and starts at fields below 10 T, which opens the possibility of using these structures for delivery and nanoreactor applications.

Folic acid-conjugated pH/temperature/redox multi-stimuli responsive polymer microspheres for delivery of anti-cancer drug

The folic acid (FA)-conjugated pH/temperature/redox multi-stimuli responsive poly(methacrylic acid-co-N,N-bis(acryloyl)cystamine/poly(N-isopropylacrylamide-co-glycidyl methacrylate-co-N,N-bis(acryloyl)cystamine) microspheres were prepared by a two-stage distillation-precipitation polymerization with subsequent surface modification with FA. The microspheres were characterized by transmission electron microscopy, dynamical light scattering, Fourier-transform infrared spectra, UV-vis spectra and elemental analysis. The degradation of the functional microspheres could be triggered by a reductive reagent, such as glutathione, due to presence of BAC crosslinker. The drug-loaded microspheres exhibited a pH/temperature/redox multi-stimuli responsive drug release character for doxorubicin hydrochloride as a model anti-cancer drug, which was efficiently loaded into the microspheres with a high loading capacity of 208.0% and an encapsulation efficiency of 85.4%. In vitro drug delivery study indicated that the FA-conjugated microspheres could deliver Dox into MCF-7 cells more efficiently than the microspheres without functionalization of FA. Furthermore, WST-1 assay showed that the microspheres had no obvious toxicity to MCF-7 cells even at a high concentration of 2000 μg mL(-1). The resultant microsphere may be a promising vector for delivery of anti-cancer drugs as it exhibits a low cytotoxicity and degradability, precise molecular targeting property and multi-stimuli responsively controlled drug release.

Magnetic norbornene polymer as multiresponsive nanocarrier for site specific cancer therapy

A site-specific, stimuli-responsive nanocarrier has been synthesized by conjugating folate, magnetic particles and doxorubicin to the backbone of norbornene polymer. Monomers, namely, cis-5-norbornene-6-(diethoxyphosphoryl)hexanote (mono 1), norbornene grafted poly(ethyleneglycol)-folate (mono 2), and norbornene derived doxorubicin (mono 3) are carefully designed to demonstrate the smart nanorcarrier capabilities. The synthesis and complete characterization of all three monomers are elaborately discussed. Their copolymerization is done by controlled/living ring-opening metathesis polymerization (ROMP) to get the triblock copolymer PHOS-FOL-DOX. NMR spectroscopy and gel permeation chromatography confirm the formation of the triblock copolymer, while FT-IR spectroscopy, thermogravimetric analysis, along with transmission electron microscope confirm the anchoring of iron particle (Fe3O4) to the PHOS-FOL-DOX. Drug release profile shows the importance of having the hydrazone linker that helps to release the drug exactly at the mild acidic conditions resembling the pH of the cancerous cells. The newly designed nanocarrier shows greater internalization (about 8 times) due to magnetic field. Also, increased intracellular DOX release is observed due to the folate receptor. From these results, it is clear that PHOS-FOL-DOX has the potential to act as a smart nanoreservoir with the magnetic field guidance, folate receptor targeting, and finally pH stimulation.

Thermo, pH and reduction responsive coaggregates comprising AB2C2 star terpolymers for multi-triggered release of doxorubicin

Novel disulfide-linked PEG(PCL)₂(PNIPAM)₂ and PEG(PCL)₂(PAA)₂ star terpolymers were synthesized and coassembled into mixed micelles or vesicles for multi-triggered drug release.

Dynamic in vivo imaging of dual-triggered microspheres for sustained release applications: synthesis, characterization and cytotoxicity study

This paper deals with the synthesis, characterization and property evaluation of drug-loaded magnetic microspheres with pH-responsive cross-linked polymer shell. The synthetic procedure consists of 3 steps, of which the first two comprise the synthesis of a poly methyl methacrylate (PMMA) template and the synthesis of a shell by using acrylic acid (AA) and methyl methacrylate (MMA) as monomers, and divinyl benzene (DVB) as cross-linker. The third step of the procedure refers to the formation of magnetic nanoparticles on the microsphere's surface. AA that attaches pH-sensitivity in the microspheres and magnetic nanoparticles in the inner and the outer surface of the microspheres, enhance the efficacy of this intelligent drug delivery system (DDS), which constitutes a promising approach toward cancer therapy. A number of experimental techniques were used to characterize the resulting microspheres. In order to investigate the in vitro controlled release behavior of the synthesized microspheres, we studied the Dox release percentage under different pH conditions and under external magnetic field. Hyperthermia caused by an alternating magnetic field (AFM) is used in order to study the doxorubicin (Dox) release behavior from microspheres with pH functionality. The in vivo fate of these hybrid-microspheres was tracked by labeling them with the γ-emitting radioisotope (99m)Tc after being intravenously injected in normal mice. According to our results, microsphere present a pH depending and a magnetic heating, release behavior. As expected, labeled microspheres were mainly found in the mononuclear phagocyte system (MPS). The highlights of the current research are: (i) to illustrate the advantages of controlled release by combining hyperthermia and pH-sensitivity and (ii) to provide noninvasive, in vivo information on the spatiotemporal biodistribution of these microsphere by dynamic γ-imaging.

Nanostructuring the surface of dual responsive hollow polymer microspheres for versatile utilization in nanomedicine-related applications

The design and fabrication of hollow polymer microspheres responsive to various stimuli comprises a promising approach for the development of multifunctional and efficient systems for various nanomedicine-related applications. In this paper, we present the preparation of poly(methacrylic acid-co-N,N'-methylenebis(acrylamide)-co-poly(ethylene glycol) methyl ether methacrylate-co-N,N'-bis(acryloyl)cystamine) (PMAA(S-S)) hollow microspheres following a two-stage distillation precipitation polymerization procedure. Magnetic and silver nanocrystals were chemically grown on the surface of the hollow polymer microspheres, resulting in a composite system with interesting properties. We evaluated the performance of the composite hollow microspheres as magnetic hyperthermia mediators and their surface-enhanced Raman spectroscopy activity. Assessment of Daunorubicin-loaded PMAA(S-S) hollow microspheres performance as effective drug carriers was carried out through drug release experiments upon application of different pH and reducing conditions. pH and redox responsiveness as well as basic mechanisms of release profiles are discussed. Furthermore, in vitro cytotoxicity of empty and drug-loaded PMAA(S-S) hollow microspheres against MCF-7 cancer cells was investigated in order to evaluate their performance as drug carriers.

Microspheres as therapeutic delivery agents: synthesis and biological evaluation of pH responsiveness

A soft template method was used for the synthesis of pH-responsive microcontainers with an inner cavity. Poly(glycidyl methacrylate) (PGMA) microspheres of narrow size distribution were synthesized by soap-free radical emulsion polymerization and the coating of the microspheres was carried out by the same procedure. The procedure consists of two steps. In the first step the sacrificial template is synthesized and in the second step the shell is formed. Acrylic acid was used as a coating monomer, with the aim of introducing pH sensitivity in the synthesized microcontainers. A loading and release study of the anthracycline drug doxorubicin (DOX) was also carried out. The toxicity evaluation of the drug was carried out using the MTT assay, and the necrotic effect was studied using trypan blue.