Thermal Responsive Polymer Research Articles

NIR-Triggered "OFF/ON" Photodynamic Therapy through a Upper Critical Solution Temperature Block Copolymer.

Activatable photodynamic therapy (A-PDT) has attracted great attention in precision medicine, which can be activated by endogenous or exogenous stimuli to selectively produce reactive oxygen species (ROS) at the disease site. Thermal responsive polymers with a lower critical solution temperature (LCST) have normally been utilized for constructing A-PDT system. Herein, we fabricated a photothermal activatable photosensitizer (A-PS) by the combination of thermal responsive porphyrin-containing P(AAm-co-AN-co-TPP)-b-POEGMA amphiphilic block copolymer with an upper critical solution temperature (UCST) of 42 °C and a cyanine dye of IR780. The photoactivity of porphyrin units could be severely inhibited by IR780 due to the fluorescence resonance energy transfer (FRET) from TPP to IR780 during blood circulation process ("OFF" state). After an uptake by A549 cells and then irradiated with 808 nm laser, A-PS nanoparticles were subsequently dissociated owing to the increased local temperature above the UCST of the polymer chains by excellent photothermal conversion of IR780, resulting in the enhanced photoactivity of TPP ("ON" state) and the remarkable antitumor effect. Therefore, the UCST-based A-PS extended the biological application of thermal responsive polymers, which may provide a new insight into the design of smart cancer therapeutic systems.

Surface enhanced Raman scattering (SERS) effect using flexible and self-closing ZnO nanowire-Au nanoparticle heterostructures

Herein, we demonstrate a novel and flexible Surface enhanced Raman scattering (SERS) substrate comprised of thermally-responsive polymer film coated with ZnO nanowire-Au nanoparticle heterostructures. The heterostructure fabrication involved vapor-solid growth of ZnO nanowires and their subsequent decoration with Au nanoparticles via a wet-chemical and surfactant-free route. These heterostructures were further loaded with an analyte, methylene blue (MB). The mechanism of SERS relied on the Raman laser-based local heating of the thermally-responsive polymer substrate coated with MB-loaded heterostructures. This in-situ heating process caused the substrate to shrink and resulted in suitable hot spots between the heterostructures (“self-closing” mechanism) leading to MB Raman signal enhancement. The SERS effect was studied as a function of the substrate heating duration (0–10 s) and MB concentration (10−5–10−7 M). In addition, SERS substrate reusability was demonstrated by performing multi-spot analysis and photo-decomposition of loaded MB allowed for regeneration of the analyzed spot. The temperature distribution for the polymeric substrate under the incident Raman laser was calculated using finite element method (FEM). The plasmonic characteristics or hot spot formation for the self-closing heterostructures with varying distances between the two heterostructured targets was simulated using discrete dipole approximation (DDA) method.

Thermal-controlled releasing and assembling of functional nanomembranes through polymer pyrolysis

Pyrolysis, which involves thermal decomposition of materials at elevated temperatures, has been commonly applied in the chemical industry. Here we explored the pyrolysis process for 3D nanofabrication. By strain engineering of nanomembranes on a thermal responsive polymer as the sacrificial layer, we demonstrated that diverse 3D rolled-up microstructures with different functions could be achieved without any additional solution and drying process. We carefully studied the effect of molecular weight of the polymer in the pyrolysis process and identified that the rapid breakdown of molecular backbone to a monomer is the key for nanomembrane releasing and rolling. Preferential rolling direction and corresponding dynamics were studied by analyzing the real-time video of the rolling process. We further demonstrated the versatile functions of the fabricated 3D structures as catalytic microengines and optical resonators. The simple fabrication methodology developed here may have great potential in producing functional 3D tubular micro-/nanostructures.

Polymer Having Dicationic Structure in Dumbbell Shape for Forward Osmosis Process.

The thermal-responsive polymers, poly(alkane-1,#-diylbis(tri-n-butylphosphonium) 4-vinylbenzenesulfonate) (PSSBP#, # = 8, 6, and 4), where # is the number of carbon atoms in the central bridge structure of the dicationic phosphonium moiety, were synthesized to examine their potential application as draw solutes in forward osmosis (FO). The polymers exhibited low critical solution temperature (LCST) characteristics in aqueous solutions, which is essential for recovering a draw solute from pure water. The LCSTs of the 20 wt% aqueous solutions of PSSBP8, PSSBP6, and PSSBP4 were confirmed to be approximately 30, 38, and 26 °C, respectively, which is advantageous in terms of energy requirements for the recovering draw solute. When the concentration of the PSSBP4 draw solution was 20 wt%, water flux and reverse solute flux were approximately 1.61 LMH and 0.91 gMH, respectively, in the active layer facing the draw solution (AL-DS) system when the feed solution was distilled water. The PSSBP# thermal-responsive draw solute has considerable potential for use as a next-generation draw solute because of its excellent osmotic performance and efficient recovery. Therefore, this study provides inspiration for novel ideas regarding structural transformations of polymers and their applicability as draw solutes.

Immobilization of functional polymers on poly(4-benzoyl-pxylylene-co-p-xylylene) films via photochemical conjugation for modulation of cell adhesion.

Surface modification with functional materials, such as anti-fouling or thermal responsive polymers, on biomedical devices benefits their clinical performance. Simple and versatile technologies, which could be applied to a wide variety of substrates, are still highly desirable. Chemical vapor deposition (CVD) of 4-benzoyl-[2,2]paracyclophane (Benzoyl-PPX) layers attracts much attention because the photoreactive platform could be deposited onto almost every substrate for the conjugation of functional molecules. In this study, poly(ethylene glycol) (PEG) was conjugated onto Benzoyl-PPX via UV illumination. The deposited PEG films could effectively reduce protein adsorption and cell attachment. The low-fouling properties of the PEG films were positively correlated with the molecular weight and concentration of PEG. We found that a PEG film, thicker than 16 nm and with a water contact angle of 30°, is a prerequisite for effective inhibition of cell attachment. We also demonstrated that the PEG coating was stable under acidic and basic environments. Furthermore, poly(N-isopropyl acrylamide), PNIPAAm, could be also tethered on the Benzoyl-PPX via UV illumination, and possessed thermal-responsive properties. Intact cell sheets could be released from the PNIPAAm film by decreasing culture temperature. The results indicate that Benzoyl-PPX is an excellent photoreactive platform for the conjugation of functional polymers for modulation of cell attachment.

Photocaged PNIPAM: A Light Tunable Thermal Responsive Polymer

AbstractPhotocaged poly(N‐isopropyl acrylamide) (PNIPAM)s, copolymers consisting of N‐isopropyl acrylamide (NIPAM) and N‐isopropyl‐N‐(2‐nitrobenzyl) acrylamide, are prepared by free radical polymerization. Upon UV irradiation, the hydrophobic o‐nitrobenzyl group is cleaved, which subsequently releases the caged NH group and generates more hydrogen bonds with water. As a result, the lower critical solution temperature of caged PNIPAM can be obtained as a function of the photolysis degree of o‐nitrobenenzyl caged amides.

Mesoporous silica-coated gold nanorods with a thermally responsive polymeric cap for near-infrared-activated drug delivery

In this work, gold nanorods (AuNRs)/mesoporous silica (SiO2) nanoparticles capped with thermal-responsive polymer were fabricated to couple the photothermal property of AuNRs and the thermal-/pH-responsive properties of polymer in a single nanovehicle. Aliphatic poly(urethane-amine) (PUA) was employed as the smart polymer to cap the mesopores of AuNRs/SiO2 nanoparticles via in situ polymerization in supercritical CO2. Thermal-/pH-responsive PUA acted as the on–off switch to control the DOX release due to the stretch and shrinkage of the PUA polymer chains at different temperatures, whereas a remote near-infrared (NIR) light was used to activate the phase change and subsequent drug release. The in vitro drug release studies indicated that Au/SiO2/PUA nanoparticles exhibited distinguished pH-, thermal-, and NIR-dependent release properties. A short time exposure to NIR irradiation could distinctly increase the local temperature of nanoparticles, and the thermal-responsive polymeric cap enabled the DOX release in a significant reversible way by simply adjusting the NIR laser intensity. The present paper provides an ideal way to fabricate NIR-responsive drug carriers by combining stimuli-responsive polymer with inorganic matrix, which is highly attractive for remote controllable drug delivery.

Thermal-Responsive Polymers for Enhancing Safety of Electrochemical Storage Devices.

Thermal runway constitutes the most pressing safety issue in lithium-ion batteries and supercapacitors of large-scale and high-power density due to risks of fire or explosion. However, traditional strategies for averting thermal runaway do not enable the charging-discharging rate to change according to temperature or the original performance to resume when the device is cooled to room temperature. To efficiently control thermal runaway, thermal-responsive polymers provide a feasible and reversible strategy due to their ability to sense and subsequently act according to a predetermined sequence when triggered by heat. Herein, recent research progress on the use of thermal-responsive polymers to enhance the thermal safety of electrochemical storage devices is reviewed. First, a brief discussion is provided on the methods of preventing thermal runaway in electrochemical storage devices. Subsequently, a short review is provided on the different types of thermal-responsive polymers that can efficiently avoid thermal runaway, such as phase change polymers, polymers with sol-gel transitions, and polymers with positive temperature coefficients. The results represent the important development of thermal-responsive polymers toward the prevention of thermal runaway in next-generation smart electrochemical storage devices.

Self-Collapsing of Single Molecular Poly-Propylene Oxide (PPO) in a 3D DNA Network.

On the basis of DNA self-assembly, a thermal responsive polymer polypropylene oxide (PPO) is evenly inserted into a rigid 3D DNA network for the study of single molecular self-collapsing process. At low temperature, PPO is hydrophilic and dispersed uniformly in the network; when elevating temperature, PPO becomes hydrophobic but can only collapse on itself because of the fixation and separation of DNA rigid network. The process has been characterized by rheological test and Small Angle X-Ray Scattering test. It is also demonstrated that this self-collapsing process is reversible and it is believed that this strategy could provide a new tool to study the nucleation-growing process of block copolymers.

Mechanical properties and shape memory effect of thermal-responsive polymer based on PVA

In this study, the effect of content of glutaraldehyde (GA) on the shape memory behavior of a shape memory polymer based on polyvinyl alcohol chemically cross-linked with GA was investigated. Thermal-responsive shape memory composites with three different GA levels, GA-PVA (3 wt%, 5 wt%, 7 wt%), were prepared by particle melting, mold forming and freeze–drying technique. The mechanical properties, thermal properties and shape memory behavior were measured by differential scanning calorimeter, physical bending test and cyclic thermo-mechanical test. The addition of GA to PVA led to a steady shape memory transition temperature and an improved mechanical compressive strength. The composite with 5 wt% of GA exhibited the best shape recoverability. Further increase in the crosslinking agent content of GA would reduce the recovery force and prolong the recovery time due to restriction in the movement of the soft PVA chain segments. These results provide important information for the study on materials in 4D printing.

Dynamic furan/maleimide bond-incorporated cyclic polymer for topology transformation

The transformation of polymer topological structures by using an external stimulus has gained increasing attention because it is a versatile method to modify the properties of polymeric materials. Herein, cyclic poly(methyl methacrylate) linked by a dynamic covalent furan/maleimide bond was rationally designed and prepared. SEC, FTIR, NMR, and MALDI-TOF characterizations all confirmed the successful preparation of the polymer. By using the (retro)Diels-Alder reaction at a high temperature (110°C), the cyclic polymer was transformed to a linear monopolymer or linear multiblock polymer. In addition, the cyclic topology can also be fixed by eliminating the vinyl double group of furan/maleimide adduct by the photoinduced radical thiol-ene reaction. This work provides a novel and facile approach for cyclic-to-linear topological transformation, and many potentials based on this thermal-responsive polymer are envisioned.

Redox Responsive Fluorescent Probe Development for Super Resolution and Fluorescence Lifetime Microscopy

Redox-sensing in aqueous solutions using super resolution fluorescence or lifetime microscopy has been applied extensively to image metabolic events in biological systems. Typically, such probes are designed to fluoresce following reaction with (or capture of) a particular analyte, for example, reactive oxygen species or a redox-active metal ion. Using such probes as a guide, we have designed and characterized new redox-responsive fluorescent probes intended for fluorescence-based imaging of aqueous electrochemical systems. We present solution spectroelectrochemical characterization of the parent dye molecules as well as initial optical microscopy characterization of these redox-sensitive fluorophores attached to a thermally-responsive polymer gel. Using thermal-control of polymer matrix thickness, the surface density of dye on the electrode can be modulated and imaged using fluorescence lifetime with super resolution microscopy.

Facile Synthesis of Poly (N‐isopropylacrylamide) Coated SiO2 Core‐shell Microspheres via Surface‐initiated Atom Transfer Radical Polymerization for H2O2 Biosensor Applications

AbstractIn this study, inorganic/organic composites containing poly (N‐isopropylacrylamide) coated core‐shell SiO2 microspheres were prepared via surface‐initiated atom transfer radical polymerization (ATRP). The thermal responsive polymer, N‐isopropylacrylamide was treated with methanol, water and CuBr/CuBr2/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) at room temperature to form PNIPAM@SiO2 microspheres. The as‐prepared PNIPAM@SiO2 microspheres were characterized by FT‐IR, TGA, XPS, SEM, TEM analyses. Hemoglobin (Hb) was immobilized onto the surfaces of PNIPAM@SiO2 microspheres via hydrophobic and π‐π stacking interactions. The as‐prepared Hb/PNIPAM@SiO2 electrode exhibits well‐defined redox peak at a formal potential of −0.38 V, validating the direct electrochemistry of Hb. The Hb immobilized composite film retained its bioelectroactivity without any significant loss of catalytic activity. The modified electrode detects H2O2 over a wide linear concentration range (0.1 μM to 333 μM) with a detection limit of 0.07 μM. This modified electrode also successfully detects H2O2 from food and disinfectant samples with appreciable recovery values, validating its practicality. We believe that PNIPAM@SiO2 composite has great potential to be used in the detection of H2O2 and development of other enzyme based biosensors.

Near-infrared (NIR) controlled reversible cell adhesion on a responsive nano-biointerface

Light-activated dynamic variations have promoted the development of smart interfaces, especially nano-biointerfaces. In this article, the near-infrared (NIR)-responsive surface for controlling cell adhesion was designed by grafting a thermal responsive polymer (poly(N-isopropylacrylamide), PNIPAM) onto silicon nanowires (SiNWs) instead of the traditional photosensitive moieties. NIR induced the photothermal effect of the SiNWs, and the local heat induced thermodynamic phase transformation of PNIPAM. With the application of NIR radiation, the surface turned to a hydrophobic state, and restored to the hydrophilic state when NIR was switched off, leading to reversible cell adhesion and release. The switchable wettability of the surface and cell adhesion/release occurred efficiently even after 20 cycles. Proteins were anchored on the surface via hydrophobic interactions using NIR; further connection of a cell-capture agent helped in achieving specific cell capture. This dynamic control of cell adhesion via NIR may provide new clues for designing functional nano-biointerfaces.

Unidirectional Wetting of Liquids on “Janus” Nanostructure Arrays under Various Media

We report the unidirectional wetting behavior of liquids (water and oil) on Janus silicon cylinder arrays (Si-CAs) under various media (air, water, and oil). The Janus cylinders were prepared by chemical modification of nanocylinders with different molecules on two sides. Through adjusting surface energies of the modified molecules, the as-prepared surfaces could control the wetting behavior of different types of liquids under various media. We discuss the regularity systematically and propose a strategy for preparing anisotropic wetting surfaces under arbitrary media. That is, to find two surface modification molecules with different surface energies, one of the molecules is easy to be wetted by the liquid under the corresponding media, while the other one is difficult. Additionally, by introducing thermal-responsive polymer brushes onto one part of Janus Si-CAs, the surfaces show thermal-responsive anisotropic wetting property under various media. We believe that due to the excellent unidirectional wettability under various media, the Janus surfaces could be applied in water/oil transportation, oil-repellent and self-cleaning coatings, water/oil separation, microfluidics, and so on.

Thermal-Responsive Anisotropic Wetting Microstructures for Manipulation of Fluids in Microfluidics.

We show morphology-patterned stripes modified by thermal-responsive polymer for smartly guiding flow motion of fluid in chips. With a two-step modification process, we fabricated PNIPAAm-modified Si stripes on silicon slides, which were employed as substrates for fluid manipulation in microchannels. When the system temperature switches between above and below the lower critical solution temperature (LCST) of PNIPAAm, the wettability of the substrates also switches between strong anisotropy and weak anisotropy, which resulted in anisotropic (even unidirectional) flow and isotropic flow behavior of liquid in microchannels. The thermal-responsive flow motion of fluid in the chip is influenced by the applied pressure, the thickness of PNIPAAm, and dimension of the microchannels. Moreover, we measured the feasible applied pressure scopes under different structure factors. Because of the excellent reversibility and quick switching speed, the chip could be used as a thermal-responsive microvalve. Through tuning the system temperature and adding the assistant gas, we realized successive "valve" function. We believe that the practical and simple chip could be widely utilized in medical detection, immunodetection, protein analysis, and cell cultures.

Enabling the sunlight driven response of thermally induced shape memory polymers by rewritable CH3NH3PbI3 perovskite coating

(CH3NH3)PbI3 perovskite coating not only makes normal widely used thermal responsive shape memory polymers (SMPs) responsive to direct sunlight due to the strong photo-thermal effect of the coating, but also allows the material to be able to flexibly switch between photo-sensitive and photo-inert states by erasing and re-applying the coating.

The synthesis and self-assembly of bioconjugates composed of thermally-responsive polymer chains and pendant lysozyme molecules

Thermal-responsive polymer chains with pendant lysozyme molecules were prepared via a “grafting to” approach. The bioconjugates were able to self-assemble into mesoglobules at a temperature above their cloud point.

A copolymer capsule with a magnetic core for hydrophilic or hydrophobic drug delivery via thermo-responsive stimuli or carrier biodegradation

The glutathione-triggered and thermal-responsive polymer microcapsule carrier with magnetic core, Fe3O4@capsule is prepared for controlled release of hydrophilic or hydrophobic drug molecules.

Enzyme and Thermal Dual Responsive Amphiphilic Polymer Core-Shell Nanoparticle for Doxorubicin Delivery to Cancer Cells.

Dual responsive polymer nanoscaffolds for administering anticancer drugs both at the tumor site and intracellular compartments are made for improving treatment in cancers. The present work reports the design and development of new thermo- and enzyme-responsive amphiphilic copolymer core-shell nanoparticles for doxorubicin delivery at extracellular and intracellular compartments, respectively. A hydrophobic acrylate monomer was tailor-made from 3-pentadecylphenol (PDP, a natural resource) and copolymerized with oligoethylene glycol acrylate (as a hydrophilic monomer) to make new classes of thermo and enzyme dual responsive polymeric amphiphiles. Both radical and reversible addition-fragmentation chain transfer (RAFT) methodologies were adapted for making the amphiphilic copolymers. These amphiphilic copolymers were self-assembled to produce spherical core-shell nanoparticles in water. Upon heating, the core-shell nanoparticles underwent segregation to produce larger sized aggregates above the lower critical solution temperature (LCST). The dual responsive polymer scaffold was found to be capable of loading water insoluble drug, such as doxorubicin (DOX), and fluorescent probe-like Nile Red. The drug release kinetics revealed that DOX was preserved in the core-shell assemblies at normal body temperature (below LCST, ≤ 37 °C). At closer to cancer tissue temperature (above LCST, ∼43 °C), the polymeric scaffold underwent burst release to deliver 90% of loaded drugs within 2 h. At the intracellular environment (pH 7.4, 37 °C) in the presence of esterase enzyme, the amphiphilic copolymer ruptured in a slow and controlled manner to release >95% of the drugs in 12 h. Thus, both burst release of cargo at the tumor microenvironment and control delivery at intracellular compartments were accomplished in a single polymer scaffold. Cytotoxicity assays of the nascent and DOX-loaded polymer were carried out in breast cancer (MCF-7) and cervical cancer (HeLa) cells. Among the two cell lines, the DOX-loaded polymers showed enhanced killing in breast cancer cells. Furthermore, the cellular uptake of the DOX was studied by confocal and fluorescence microscopes. The present investigation opens a new enzyme and thermal-responsive polymer scaffold approach for DOX delivery in cancer cells.