Intelligent thermoresponsive polymeric micelles for targeted drug delivery

Biomimetic Gradient Hydrogel Actuators with Ultrafast Thermo-Responsiveness and High Strength

Most current hydrogel actuators suffer from either poor mechanical properties or limited responsiveness. Also, the widely used thermo-responsive poly-(N-isopropylacrylamide) (PNIPAM) homopolymer hydrogels have a slow response rate. Thus, it remains a challenge to fabricate thermo-responsive hydrogel actuators with both excellent mechanical and responsive properties. Herein, ultrafast thermo-responsive VSNPs-P(NIPAM-co-AA) hydrogels containing multivalent vinyl functionalized silica nanoparticles (VSNPs) are fabricated. The ultrafast thermo-responsiveness is due to the mobile polymer chains grafted from the surfaces of the VSNPs, which can facilitate hydrophobic aggregation, inducing the phase transition and generating water transport channels for quick water expulsion. In addition, the copolymerization of NIPAM with acrylic acid (AA) decreases the transition temperature of the thermo-responsive PNIPAM-based hydrogels, contributing to ultrafast thermo-responsive shrinking behavior with a large volume change of as high as 72.5%. Moreover, inspired by nature, intelligent hydrogel actuators with gradient structure can be facilely prepared through self-healing between the ultrafast thermo-responsive VSNPs-P(NIPAM-co-AA) hydrogel layers and high-strength VSNPs-PAA-Fe³⁺ multibond network (MBN) hydrogel layers. The obtained well-integrated gradient hydrogel actuators show ultrafast thermo-responsive performance within only 9 s in 60 °C water, as well as high strength, and can be used for more practical applications as intelligent soft actuators or artificial robots.

Constrained thermoresponsive polymers - new insights into fundamentals and applications

In the last decades, numerous stimuli-responsive polymers have been developed and investigated regarding their switching properties. In particular, thermoresponsive polymers, which form a miscibility gap with the ambient solvent with a lower or upper critical demixing point depending on the temperature, have been intensively studied in solution. For the application of such polymers in novel sensors, drug delivery systems or as multifunctional coatings, they typically have to be transferred into specific arrangements, such as micelles, polymer films or grafted nanoparticles. However, it turns out that the thermodynamic concept for the phase transition of free polymer chains fails, when thermoresponsive polymers are assembled into such sterically confined architectures. Whereas many published studies focus on synthetic aspects as well as individual applications of thermoresponsive polymers, the underlying structure-property relationships governing the thermoresponse of sterically constrained assemblies, are still poorly understood. Furthermore, the clear majority of publications deals with polymers that exhibit a lower critical solution temperature (LCST) behavior, with PNIPAAM as their main representative. In contrast, for polymer arrangements with an upper critical solution temperature (UCST), there is only limited knowledge about preparation, application and precise physical understanding of the phase transition. This review article provides an overview about the current knowledge of thermoresponsive polymers with limited mobility focusing on UCST behavior and the possibilities for influencing their thermoresponsive switching characteristics. It comprises star polymers, micelles as well as polymer chains grafted to flat substrates and particulate inorganic surfaces. The elaboration of the physicochemical interplay between the architecture of the polymer assembly and the resulting thermoresponsive switching behavior will be in the foreground of this consideration.

Palladium-Catalyzed Mizoroki-Heck and Copper-Free Sonogashira Coupling Reactions in Water Using Thermoresponsive Polymer Micelles

A few kinds of thermoresponsive diblock copolymers have been synthesized and utilized for palladium-catalyzed coupling reactions in water. Poly(N-isopropylacrylamide) (PNIPAAm) and poly(N,N-diethylacrylamide) (PDEAAm) are employed for thermoresponsive segments and poly(sodium 4-styrenesulfonate) (PSSNa) and poly(sodium 2-acrylamido-methylpropanesulfonate) (PAMPSNa) are employed for hydrophilic segments. Palladium-catalyzed Mizoroki-Heck reactions are performed in water and the efficiency of the extraction process is studied. More efficient extraction was observed for the PDEAAm copolymers when compared with the PNIPAAm copolymers and conventional surfactants. In the study of the Sonogashira coupling reactions in water, aggregative precipitation of the products was observed. Washing the precipitate with water gave the product with satisfactory purity with a good yield.

Internal Structure of Thermoresponsive Physically Crosslinked Nanogel of Poly[N-(2-hydroxypropyl)methacrylamide]-Block-Poly[N-(2,2-difluoroethyl)acrylamide], Prominent 19F MRI Tracer

Fluorine-19 MRI is a promising noninvasive diagnostic method. However, the absence of a nontoxic fluorine-19 MRI tracer that does not suffer from poor biodistribution as a result of its strong fluorophilicity is a constant hurdle in the widespread applicability of this otherwise versatile diagnostic technique. The poly[N-(2-hydroxypropyl)methacrylamide]-block-poly[N-(2,2-difluoroethyl)acrylamide] thermoresponsive copolymer was proposed as an alternative fluorine-19 MRI tracer capable of overcoming such shortcomings. In this paper, the internal structure of self-assembled particles of this copolymer was investigated by various methods including 1D and 2D NMR, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The elucidated structure appears to be that of a nanogel with greatly swollen hydrophilic chains and tightly packed thermoresponsive chains forming a network within the nanogel particles, which become more hydrophobic with increasing temperature. Its capacity to provide a measurable fluorine-19 NMR signal in its aggregated state at human body temperature was also investigated and confirmed. This capacity stems from the different fluorine-19 nuclei relaxation properties compared to those of hydrogen-1 nuclei.

Self-Cleaning Membranes from Comb-Shaped Copolymers with Photoresponsive Side Groups

In this study, we present a novel self-cleaning, photoresponsive membrane that is capable of removing predeposited foulant layers upon changes in surface morphology in response to UV or visible light irradiation while maintaining stable pore size and water permeance. These membranes were prepared by creating thin film composite (TFC) membranes by coating a porous support membrane with a thin layer of novel comb-shaped graft copolymers at two side-chain lengths featuring polyacrylonitrile (PAN) backbones and photoreactive side chains, synthesized by atom transfer radical polymerization (ATRP). Photoregulated control over membrane properties is attained through a light-induced transition, where the side chains switch between a hydrophobic spiropyran (SP) state and a zwitterionic, hydrophilic merocyanine (MC) state. The light-induced switch between the SP and MC forms changes surface hydrophilicity and causes morphological changes on the membrane surface as evidenced by atomic force microscopy (AFM). Before any phototreatment, the as-coated membrane surface comprises mostly hydrophobic SP groups that allow the adsorption of organic solutes such as proteins the membrane surface, reducing flow rate. Once exposed to UV light, conversion of the SP groups to hydrophilic MC groups leads to the release of adsorbed molecules and the full recovery of the initial water flux. A fouled membrane in the more hydrophilic MC form is also capable of self-cleaning upon conversion to the less hydrophilic SP form by visible light irradiation. The self-cleaning behavior observed for this system, where the surface became less hydrophilic but also experienced a morphological change, demonstrates a novel mechanism that has a mechanical component in addition to the changes in hydrophilicity. It is also the first report, to our knowledge, of self-cleaning performance accompanied by a decrease in hydrophilicity.

Polymeric materials for theranostic applications

Nanotechnology has continuously contributed to the fast development of diagnostic and therapeutic agents. Theranostic nanomedicine has encompassed the ongoing efforts on concurrent molecular imaging of biomarkers, delivery of therapeutic agents, and monitoring of therapy response. Among these formulations, polymer-based theranostic agents hold great promise for the construction of multifunctional agents for translational medicine. In this article, we reviewed the state-of-the-art polymeric nanoparticles, from preparation to application, as potential theranostic agents for diagnosis and therapy. We summarized several major polymer formulas, including polymeric conjugate complexes, nanospheres, micelles, and dendrimers for integrated molecular imaging and therapeutic applications.

A vision for better health: mass spectrometry imaging for clinical diagnostics

BACKGROUND

Mass spectrometry imaging (MSI) is a powerful tool that grants the ability to investigate a broad mass range of molecules from small molecules to large proteins by creating detailed distribution maps of selected compounds. Its usefulness in biomarker discovery towards clinical applications has obtained success by correlating the molecular expression of tissues acquired from MSI with well-established histology.

RESULTS

To date, MSI has demonstrated its versatility in clinical applications, such as biomarker diagnostics of different diseases, prognostics of disease severities and metabolic response to drug treatment, etc. These studies have provided significant insight in clinical studies over the years and current technical advances are further facilitating the improvement of this field. Although the underlying concept is simple, factors such as choice of ionization method, sample preparation, instrumentation and data analysis must be taken into account for successful applications of MSI. Herein, we briefly reviewed these key elements yet focused on the clinical applications of MSI that cannot be addressed by other means.

CONCLUSIONS

Challenges and future perspectives in this field are also discussed to conclude that the ever-growing applications with continuous development of this powerful analytical tool will lead to a better understanding of the biology of diseases and improvements in clinical diagnostics.

Polymer-functionalized gold nanoparticles as versatile sensing materials

In this brief review, gold nanoparticles conjugated with functional polymers are described from the viewpoint of application to sensing materials. The optical properties of gold nanoparticles, the synthesis of polymer-functionalized gold nanoparticles, and their analytical applications are discussed. Polymer-functionalized gold nanoparticles are categorized into two classes: biopolymer-conjugated gold nanoparticles and artificial-polymer conjugated gold nanoparticles. Fluorometric and colorimetric sensing using gold nanoparticles are focused; fluorometric detection enables us to exploit sensitive assays for practical use. Furthermore, chemical amplification using gold nanoparticles is also discussed for the sensitive probing.

Thermally controlled intracellular uptake system of polymeric micelles possessing poly(N-isopropylacrylamide)-based outer coronas

Temperature-induced intracellular uptake mechanism of thermoresponsive polymeric micelles comprising poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)-b-poly(d,l-lactide) (P(IPAAm-DMAAm)-b-PLA) inside cultured bovine carotid endothelial cells is investigated by flow cytometry and confocal laser scanning microscopy. Hydrodynamic sizes of P(IPAAm-DMAAm)-b-PLA micelles are approximately 20 nm below the lower critical solution temperature (LCST) of 39.4 degrees C, and their sizes increased to ca. 600 nm above the LCST due to the aggregation of micelles. Intracellular uptake of P(IPAAm-DMAAm)-b-PLA micelles is significantly limited at a temperature below the micellar LCST, 37 degrees C. Of great interest, the P(IPAAm-DMAAm)-b-PLA micelles are internalized into the cells above the micellar LCST (42 degrees C), being dependent on polymer concentration, time, and temperature. By contrast, no intracellular uptake of polyethylene glycol-b-PLA micelles is observed regardless of temperature changes. Enhanced intracellular micelle uptake is probably due to the enhanced interactions between the micelles and cell membranes through the dehydration of corona-forming thermoresponsive polymer chains. Internalization of submicrometer-scale micellar aggregates inside the cells is probably due to their various endocytosis mechanisms. P(IPAAm-DMAAm)-b-PLA micelles localize at the Golgi apparatus and endoplasmic reticulum, but not inside lysosomes. These results indicate that the thermoresponsive polymeric micelles are greatly promising as intracellular delivery tools of drugs, nucleic acids, and peptides/protein without lysosomal decomposition in conjunction with applied heating.

Self-assembly and dual-stimuli sensitivities of hydroxypropylcellulose-graft-poly(N,N-dimethyl aminoethyl methacrylate) copolymers in aqueous solution

The self-assembly and pH- and thermo-sensitivities properties of hydroxypropyl cellulose-graft-poly(N,N-dimethyl aminoethyl methacrylate) (HPC-g-PDMAEMA) copolymers in aqueous solutions were investigated by transmittance, dynamic light scattering (DLS), and (1)H NMR spectroscopy. Micelles with different structure can be formed by varying either pH value or temperature. At low pH, e.g., 3.0, the HPC backbone of the copolymer collapse to form the core of micelles stabilized with protonated PDMAEMA side chains on the surface of the micelles upon heating. At the medium pH, e.g., 8.1, both HPC backbone and PDMAEMA side chains collapse upon heating to form unstable aggregates. At high pH, e.g., 12.3, PDMAEMA side chains collapse first to form the core of micelles stabilized with HPC chains upon heating. Further heating the copolymer solution at this pH leads to the aggregation of the micelles due to the collapse of the shell HPC chains. The thermal sensitivity of the HPC-g-PDMAEMA copolymers is reversible.

Tri-Block Copolymers Obtained by RAFT Polymerization: A Promising Material for Drug-Delivery Systems

Tri-block copolymer with pH- and thermo-responsive consisting of poly(t-butylacrylate) and poly(vinylcaprolactam), (PtBA/PVCL) were prepared by RAFT polymerization and characterized by gel permeation chromatography (GPC) and 1H NMR. PtBA and PVCL were used as macro chain-transfer agents (MCTA) to synthesize PtBA-b-PVCL-b-PtBA and/or PVCL-b-PtBA-b-PVCL, which after partial hydrolysis led to amphiphilic tri-block copolymers P(tBA-co-AA)-b-PVCL-b-P(tBA-co-AA) and/or PVCL-b-P(tBA-co-AA)-b-PVCL.

Thermoresponsive degradable poly(ethylene glycol) analogues

Thermoresponsive polymers have many biomedical applications, but their nondegradability limits their in vivo applications. Herein, we report a new type of degradable thermoresponsive polymers-degradable poly (ethylene glycol) analogues (DPEGs) having lower critical solution temperatures (LCSTs) ranging 10-50 degrees C. DPEGs were synthesized by condensation polymerization of PEG-di(meth)acrylates (PEGDA or PEGDMA) with dithiols. Their LCSTs could be easily tuned by the PEG-chain length and the types of the double bond in the PEG monomers and dithiols. Long PEG chain and the presence of hydrophilic groups in the dithiol monomer increased the LCST of the resulting DPEG. Crosslinking DPEG chains produced thermoresponsive hydrogels. The hydrogels prepared by the end-capping method maintained the thermoresponsive properties of the linear DPEG. The degradable thermoresponsive DPEGs and their hydrogels have great potentials for in vivo biomedical applications.

Metabolic mimics: Thiol responsive drug release

A new approach to the design of selective release interfaces is assessed in which a hydrophobic component is functionalised with a receptor reactive toward reduced thiol peptides-principally glutathione. The assembly has been characterised using electrochemical techniques and its ability to form a coherent, water insoluble coating is demonstrated. The subsequent reaction with glutathione creates a supramolecular conjugate that exploits the hydrophilic nature of the amino acid chain as a route through which the protective coating can be eroded and hence the underlying substrate exposed. The efficacy of the release process has been critically assessed with a view to establishing the action and selectivity of the trigger mechanism.