Lower Critical Solubility Temperature Research Articles

Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by 2H NMR field-cycling relaxometry

We use 2H nuclear magnetic resonance to study the dynamics of deuterated water in a solution of linear poly (N-isopropyl acrylamide) (pNIPAM, 4 wt%) across its coil-to-globule transition at a lower critical solubility temperature (LCST) around 32°C. In agreement with previous studies, we find that the 2H spin-lattice (T1) and, in particular, spin-spin (T2) relaxation times abruptly decrease when heating through the LCST, indicating that the polymer collapse causes an emergence of a water fraction with strongly reduced mobility. To quantify the dynamics of this slow water fraction, we exploit the fact that 2H field-cycling relaxometry allows us to measure the spectral density of the water reorientation in a broad frequency range. We find that the slow water fraction is characterised by a broad logarithmic Gaussian distribution of correlation times (σLG = 2.3), which is centred about τLG ≈ 10–9 s near the LCST. Hence, the common assumption of a Debye spectral density does not apply. We argue that a minor water fraction, which is located inside the pNIPAM globules and shows dynamics governed by the disordered polymer matrix, accompanies a major water fraction with bulk-like dynamics above the LCST. The former fraction amounts to about 0.4 water molecules per NIPAM monomer. Several findings indicate fast exchange between these bound and free water fractions on the T1 and T2 time scales.

Multiresponsive Nanoscale Self-Assembly of Azurin-Elastin-like Polypeptide Fusion Protein for Enhanced Prostate Cancer Therapy.

A fusion protein composed of a bacterial protein, azurin, having antineoplastic properties and a thermally responsive structural cationic elastin-like protein (ELP), is designed, cloned, expressed, and purified. A simple method of inverse transition cycle (ITC) is employed to purify the fusion protein azurin-ELP diblock copolymer (d-bc). The molecular weight of the azurin-ELP fusion protein is ∼32 kDa. Further, its self-assembly properties are investigated. Interestingly, the engineered azurin-ELP d-bc in response to increasing temperature shows a dual-step phase separation into biofunctional nanostructures. Around the physiological temperature, azurin-ELP d-bc forms stable coacervates, which is dependent on the concentration and time of incubation. These coacervates are formed below the lower critical solubility temperature (LCST) of the ELP block at physiological temperature. Above LCST, i.e., 50-55°C, micelles of size ranging from 25 to 30 nm are formed. The cytotoxicity of azurin-ELP d-bc depends on the size of the coacervates formed and their cellular uptake at physiological temperature. Further, MTT assay of azurin-ELP d-bc in the cross-linked micelles prepared ex situ shows > six times higher killing of LNCaP cells than the unimeric form of azurin-ELP at 5 μM concentration. The flow cytometric results of these micelles at 20 μM concentration show ∼97% LNCaP cells in the apoptotic phase. Thus, azurin-ELP cross-linked micelles have enhanced potential for anticancer therapy due to their higher avidity.

Study of the Dynamic Viscoelasticity of Single Poly(N-isopropylacrylamide) Chains Using Atomic Force Microscopy

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) is of great interest in the fields of medicine and pharmacology because its lower critical solubility temperature (LCST) is close to the physiological temperature. The understanding of the phase transfer mechanism of PNIPAM near the LCST is of great significance for the design, development, and application of its derivatives. In this study, a dynamic single-molecule force spectroscopy (SMFS) approach was used to quantitatively assess the dynamic viscoelasticity of single PNIPAM chains at different temperatures. We found that the relationship between the viscoelasticity coefficient of a single polymer chain in the low elongation region and the number of chain segments below the LCST was in accordance with the prediction of the Kirkwood model. Above the LCST, the PNIPAM chains exhibited different viscoelastic behaviors that were determined by their conformations. Importantly, the characterization of dynamic viscoelasticity allowed us to observe the phase transition behavior of single polymer chains in the low elongation region where they are similar to random coils, which helped us to understand the microscopic mechanism of their temperature response. In particular, above the LCST, the PNIPAM chains no longer underwent purely entropic elastic behavior but instead displayed enthalpic viscoelastic behavior dominated by intramolecular hydrogen bonds.

Glycan-selective in-situ growth of thermoresponsive polymers for thermoprecipitation and enrichment of N-glycoprotein/glycopeptides

In view of the biological significance and micro-heterogeneity of protein glycosylation for human health, specific enrichment of N-glycosylated proteins/peptides from complex biological samples is a prerequisite for the discovery of disease biomarkers and clinical diagnosis. In this work, we propose a “grafting-from” N-glycoprotein enriching method based on the in-situ growth of thermoresponsive polymer brushes from the N-glycosylated site of proteins. The initiator was first attached to the pre-oxidized glycan moieties by hydrazide chemistry, from which the thermoresponsive polymers can be grown to form giant protein-polymer conjugates (PPC). The thermosensitive PPC can be precipitated and separated by raising the temperature to above its lower critical solubility temperature (LCST). Mass spectrometry verified 210 N-glycopeptides corresponding to 136 N-glycoproteins in the rabbit serum. These results demonstrate the capability of the tandem thermoprecipitation strategy to enrich and separate N-glycoprotein/glycopeptide. Due to its simplicity and efficiency specifically, this method holds the potential for identifying biomarkers from biological samples in N-glycoproteome analysis.

An Account on Functional Polymer Composite for Multivariant Application: A Mechanistic Approach

The presented article reports a detailed review of the polymer composite and its applications in multifaceted areas. The novelty of the report is in establishing the mechanistic overview on the functionalization of polymer for selective applications. The most important and established application of polymer is in sensing, polymer electrolyte, biomedical application, point of care application etc. The utilization of functional polymer in fluorescence thermometers is dependent on the maintenance of their lower critical solubility temperature. Polyelectrolytes like conducting polymers are widely applied for chemo sensing applications. The primary mechanism for the functionality of these conducting polymers is the presence of altering single and double bonds which enables the thorough flow of charge within the matrix system. Furthermore, the macromolecular synthetic polymer is subjected to functionalization through composite upon combing with specific salts and filler components. The addition of unreactive/reactive filler components in minute amounts is reported to significantly reduce the polarization loss and increase the cyclability of the matrix when applied to solid-state devices like sensors, fuel cells for stationary and mobile applications, etc. Fuels cells being an example of renewable energy is reported to attract the modern market with emphasis on polymer membrane-based system wherein sulphonic acid-based electrolyte membrane act as the ionic electrolyte conductor. The mechanism of ion conduction within the polymer matrix plays an important role in the application in solid-state devices like sensors, fuel cells, batteries, etc. The review briefly explains the role of ionic conduction as explained using two primary mechanisms like Arrhenius and Vogel Tammann Fulcher. Finally, the role of polymer bio composites is discussed in light of biomedical applications.

A Multiple-Stimuli-Responsive Amphiphilic Copolymer for Antifouling and Antibacterial Functionality via a "Resistance-Kill-Release" Mechanism.

In recent years, polymers with stimuli-responsive properties have been increasingly reported on due to their diverse applications. However, most of the studies have only focused on the performance of polymers under specific scenarios. The laws of changes in the properties in response to various external stimuli have been less systematically and quantitatively studied. In this paper, we prepared an amphiphilic polymer (PadaMX and PAdaM3QA−X) with temperature-, pH-, ion-, and β-cyclodextrin (β-CD)-responsive properties. According to the cloud point tested by the UV-Vis method, the lower critical soluble temperature (LCST) of PAdaM3QA−10% was more sensitive to a change in pH and less sensitive to a change in ions compared with PadaM3 due to quaternized side chains with a stronger intramolecular mutual repulsion. We then fabricated the coatings with responsive properties by immobilizing the adamantyl groups on β-CD-modified surfaces. The hydrophilicity of the coatings was improved after quaternization, as proven by the water contact angle (WCA) measurement. The antifouling and antibacterial performance was further evaluated via the fluorescence intensity of bovine serum albumin (BSA) adsorbed on the surfaces and the spread plate method. A 78.4% BSA desorption rate and a 96.8% sterilization rate were achieved by the PAdaM3QA−10% coating. In summary, this work prepared a multiple-stimuli-responsive amphiphilic copolymer for antifouling and antibacterial functionality via a “resistance–kill–release” mechanism.

Amphiphilic and segmented polyurethanes based on poly(ε-caprolactone)diol and poly(2-ethyl-2-oxazoline)diol: Synthesis, properties, and a preliminary performance study of the 3D printing

Polyurethanes (PU) have a wide variety of applications due to possessing tailored properties which can be imparted by composition. The combination of polyols in different ratios provide specific properties for the segmented PU, such as mechanical strength, elasticity, hydrophilicity and so on. In this work, amphiphilic and segmented polyurethanes, based on poly(ε-caprolactone)diol (PCL-diol) and poly(2-ethyl-2-oxazoline)diol (PEtOx-diol) at variable mass fractions, were synthesized by a two-step route and characterized according to composition, molar mass, thermal, dynamic mechanical, and rheological properties. Polyurethanes with molar masses ranging from 17.9 to 39.6 kDa, and a molar mass dispersity in the range of 2.0–4.0, are capable of swelling in water, with the swelling coefficient being modulated by the polyurethane composition and by the temperature because of the lower critical solubility temperature (LCST) behavior of PEtOx in an aqueous medium. PCL and PEtOx segments in the PU chains are partially miscible, therefore the polyurethanes are heterogeneous, presenting a PCL/PEtOx miscible phase dispersed in a PCL rich matrix in the solid state. PU with 50% mass fraction of PEtOx presented a gelation temperature of 69 °C, as determined by rheology, and was evaluated for Fused Deposition Modelling (FDM) 3D printing, showing promising features, although with a low resolution and fidelity to the computational project, mainly due to its high viscoelasticity which may be modulated by the molar mass of the polymer. Moreover, cell viability tests suggest that the polyurethanes are compatible with biomedical applications.

Formation of helices with controllable chirality in gel-fiber composites

While microscale helices with specified chirality are pervasive in biological systems, driving purely synthetic materials to self-organize into such useful structures remains a significant challenge. Through theory and simulations, we model the behavior of initially flat ribbons of gel-fiber composites and show that these materials self-organize into three-dimensional helices with the application of heat. We specifically focus on thermo-responsive gels, which shrink when heated to a point near the lower critical solubility temperature (LCST). Within the composite, regions of the LCST gel that lie far from the fibers can readily shrink in response to the increased temperature; however, near the fibers the network is inhibited from undergoing the heat-induced collapse. This competition between the constrained and the unconstrained regions of the heated sample plays a vital role in the structural evolution of the material. We find that this dynamic process can be controlled through the careful placement of the fibers on the outer surface of the gel. We specifically identify fiber arrangements that lead to the formation of helical structures with controlled chirality. Moreover, we isolate scenarios where constraining the movement of one or both the free ends of the sample promotes and stabilizes the formation of helical structures with specified handedness. Such structurally tailored composites are useful for creating mechanically robust actuators, and “appendages” for soft robots that can controllably curl and uncurl with variations in temperature.

Synthesis of PDMS-b-POEGMA Diblock Copolymers and Their Application for the Thermoresponsive Stabilization of Water-Supercritical Carbon Dioxide Emulsions.

In this study, PDMS13-b-POEGMAx diblock copolymers consisting of a CO2-philic poly(dimethylsiloxane) (PDMS) block connected to a thermosensitive hydrophilic poly(oligoethylene glycol methacrylate) (POEGMA) block were synthesized by reversible addition-fragmentation chain-transfer (RAFT) radical polymerization. Their ability to decrease the water-supercritical CO2 (scCO2) interfacial tension (γ) and to stabilize water-scCO2 emulsions was investigated using an original homemade device developed in the laboratory. This device is able to control the pressure from 1 to 250 bar and the temperature from 40 to 80 °C. It was implemented with 2 visualization windows, a drop tensiometer and a remote optical head for dynamic light scattering (DLS) measurements. These experiments revealed that PDMS-b-POEGMA decreased γ down to 1-2 mN/m and was the most efficient at high pressure (250 bar) and low temperature (40 °C) where PDMS and POEGMA blocks exhibited the highest affinity for their respective phase. The diblock copolymers were shown to stabilize water-scCO2 emulsions. Moreover, the thermosensitive behavior of the POEGMA block in water (with a lower critical solubility temperature around 65 °C) resulted in the formation of temperature-responsive emulsions that could reversibly switch at 100 bar from stable at 40 °C to unstable at 80 °C. These results were rationalized based on the solubility of each individual block of the copolymers in water and scCO2 as a function of temperature and pressure.

Temperature and Redox‐Responsive Hydrogels Based on Nitroxide Radicals and Oligoethyleneglycol Methacrylate

AbstractA temperature and redox‐responsive polymer hydrogel is constructed by randomly incorporating 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐methacrylate (TEMPO) stable nitroxide radicals and oligoethyleneglycol methacrylate (OEGMA) groups in a polymer network. TEMPO can be reversibly oxidized into an oxoammonium cation (TEMPO+) providing the redox‐responsive properties while the lower critical solubility temperature (LCST) of OEGMA results in temperature‐responsive properties. Since a rather low amount of di(ethylene glycol) dimethacrylate (OEGMA2) is used to chemically crosslink the polymer network, the accordingly formed hydrogels obtained after swelling with water consist of microgel particles with entangled polymer chains that are not chemically crosslinked. By varying the amount of TEMPO in the polymer network, it is demonstrated that the radical form of TEMPO aggregates into hydrophobic domains acting as physical crosslinking nodes in the hydrogels and further increasing the cohesion between microgel particles. Increasing the temperature results in two opposite effects on the solubility of TEMPO and OEGMA units. The oxidation of TEMPO into TEMPO+ also results in a deep change in the hydrogel properties since TEMPO+ units are essentially hydrophilic and do not aggregate into physical crosslinking nodes.

Mechanism of globule-to-coil transition of poly(N-isopropylacrylamide) in water: Relevance to cold denaturation of a protein

In water, poly(N-isopropylacrylamide) (PNIPAM) is in a soluble coil state below the lower critical soluble temperature (LCST) but in an insoluble globule state above LCST. Namely, as the temperature decreases, PNIPAM exhibits a globule-to-coil transition at LCST~305 K. We generate structural ensembles of coil and globule states by all-atom molecular dynamics simulations conducted at 273 and 323 K, respectively. We then calculate a variety of energetic and entropic components of thermodynamic quantities of the two states at the two temperatures using our recently developed, accurate statistical-mechanical method for solute hydration where molecular models are employed for water and the PNIPAM structure is taken into account at the atomic level. We identify the physical factors driving or opposing the transition and evaluate their relative magnitudes and temperature dependences. The presence of PNIPAM generates an excluded volume (EV) which is inaccessible to the centers of water molecules in the entire system. The presence of a water molecule also generates an EV for the other water molecules with the result that all of the water molecules are entropically correlated, causing water crowding. The globule state, where the EV is smaller and water crowding is less significant, is more favored in terms of the translational, configurational entropy of water. This effect always opposes the globule-to-coil transition. At low temperatures, however, this effect becomes significantly weaker, yielding to the factors driving it. The mechanism of the transition is physically the same as that of cold denaturation of a protein.

Structural transitions and encapsulation selectivity of thermoresponsive polyelectrolyte complex micelles.

Polyelectrolyte complex (PEC) micelles are formed by mixing a block copolymer composed of a neutral block and a charged block, with an oppositely charged polymer. The micelles formed have a PEC core, capable of encapsulating charged molecules like nucleic acids or proteins, while the neutral block(s) forms the corona that offers protection that can prevent cargo from being degraded under physiological conditions. This work explores using a thermosensitive polymer, poly(N-isopropyl acrylamide) (pNIPAM), as the primary corona-forming block and how that can be leveraged in the context of drug delivery. pNIPAM has a lower critical solubility temperature (LCST), above which a hydrophilic to hydrophobic transition occurs. We are characterizing micelles formed using a diblock copolymer of pNIPAM-b-poly(acrylic acid) with (1) poly(lysine) and (2) poly(ethylene glycol)-b-poly(lysine) using dynamic light scattering, small angle X-ray scattering, absorbance and fluorescence spectroscopy, and transmission electron microscopy. Our results indicate that mixing pNIPAM-b-poly(acrylic acid) and poly(lysine) creates worm-like micelles, while mixing the same diblock with poly(ethylene glycol)-b-poly(lysine) forms spherical micelles. At temperatures above 35 °C, the transition temperature of pNIPAM-b-poly(acrylic acid), the worm-like micelles lose their structure, while the spherical micelles retain their structure, but both aggregate into larger assemblies. Lastly, we evaluate the ability of these micelles to encapsulate and release model charged therapeutics, using a cationic monoion, methylene blue and a cationic polyion, polylysine conjugated rhodamine. We find that methylene blue is not encapsulated by the micelle, and instead exhibits counterion-like behaviour upon polyelectrolyte complex formation. Conversely, fluorescence measurements of rhodamine-labelled polylysine show fluorescence quenching indicating that the polyion is encapsulated. By mixing quenched and unlabelled micelles, we show that both systems are immune to molecular exchange with their environment and instead the cargo remains trapped in the quenched micellar cores. Measurement of the micelle fluorescence above the LCST, decreases indicating no substantial release for either system. However, the increase in micelle quenching above the LCST and its persistence after cooling may offer an additional protective environment for cargo that can be triggered by temperature.

Modeling Biofilm Formation on Dynamically Reconfigurable Composite Surfaces.

We augment the dissipative particle dynamics (DPD) simulation method to model the salient features of biofilm formation. We simulate a cell as a particle containing hundreds of DPD beads and specify p, the probability of breaking the bond between the particle and surface or between the particles. At the early stages of film growth, we set p = 1, allowing all bonding interactions to be reversible. Once the bound clusters reach a critical size, we investigate scenarios where p = 0, so that incoming species form irreversible bonds, as well as cases where p lies in the range of 0.1-0.5. Using this approach, we examine the nascent biofilm development on a coating composed of a thermoresponsive gel and the embedded rigid posts. We impose a shear flow and characterize the growth rate and the morphology of the clusters on the surface at temperatures above and below Tc, the volume phase transition temperature of a gel that displays lower critical solubility temperature (LCST). At temperatures above Tc, the posts effectively inhibit the development of the nascent biofilm. For temperatures below Tc, the swelling of the gel plays the dominant role and prevents the formation of large clusters of cells. Both these antifouling mechanisms rely on physical phenomena and, hence, are advantageous over chemical methods, which can lead to unwanted, deleterious effects on the environment.

Electrothermal silver nanowire thin films for In-Situ observation of thermally-driven chemical processes

We develop a novel device comprised of high optical transmittance thin films containing silver nanowires (AgNWs) in poly(methyl methacrylate) (PMMA) acting as heating elements. The electrothermal control of the AgNWs network allows us to externally trigger and tune the temperature conditions required to run chemical reactions and physicochemical processes. The device was successfully applied for the spectroscopic in-situ observation of three different model reactions: i) the thermal equilibrium of a CoCl2/HCl/H2O complex, ii) the reversible macromolecular phase transition of a pNIPAM solution, and iii) the nucleation and growth of gold nanoparticles (AuNPs). In the first case, the color of the Co2+ complex was reversibly switched from pink to blue when changing the thermal equilibrium condition. In the second one, the optical transmittance of an aqueous solution of carboxylic-terminated pNIPAM polymer was cycled from high to low as the temperature of the solution was below or above the lower critical solubility temperature (LCST) respectively. Finally, the electrothermal control on the device was applied to the study of the nucleation and growth of AuNPs in an organic solution of AuCl3 containing oleylamine acting as both the reducer and the stabilizing agent. The versatility of the electrothermal device provides an easy way to undertake thermally controlled processes and develop optical elements such as smart windows and lab-on-a-chip devices. The AgNWs-PMMA nanocomposite was also applied successfully as an electrothermal ink on the external side walls of a test tube.

A method for preparation of hydrogel microcapsules for stem cell bioprocessing and stem cell therapy

A method for the preparation of suspension culture microcapsules used in the bioprocessing of human mesenchymal stem cells (hMSCs) is reported. The microcapsules are prepared from a semi-synthetic hydrogel comprising Pluronic®F127 conjugated to denatured fibrinogen. The Pluronic-fibrinogen adducts display a lower critical solubility temperature (LCST) at ∼30°C, thus enabling mild, cell-compatible physical crosslinking of the microcapsules in a warm gelation bath. Cell-laden microgels were prepared from a solution of Pluronic-fibrinogen hydrogel precursor and hMSCs; these were cultivated for up to 15days in laboratory-scale suspension bioreactors and harvested by reducing the temperature of the microcapsules to disassemble the physical polymer network. The viability, proliferation and cell recovery yields of the hMSCs were shown to be better than photo-chemically crosslinked microcapsules made from a similar material. The cell culture yields, which exceeded 300% after 15days in suspension culture, were comparable to other microcarrier systems used for the mass production of hMSCs. The simplicity of this methodology, both in terms of the cell inoculation and mild recovery conditions, represent distinct advantages for stem cell bioprocessing with suspension culture bioreactors.

Scalable Fabrication of Low Elastic Modulus Polymeric Nanocarriers With Controlled Shapes for Diagnostics and Drug Delivery

A new process, decoupled functional imprint lithography (D-FIL), is presented for fabricating low elastic modulus polymeric nanocarriers possessing Young's modulus of bulk material as low as sub-1 MPa. This method is employed to fabricate sub-50 nm diameter cylinders with >3:1 aspect ratio and other challenging shapes from low elastic modulus polymers such as N-isopropylacrylamide (NIPAM) and poly(ethylene glycol) di-acrylate (PEGDA), possessing Young's modulus of bulk material <10 MPa which is cannot otherwise be imprinted in similar size and pitch using existing imprint techniques. Standard imprint lithography polymers have Young's modulus >1 GPa, and so these polymers used in nanocarrier fabrication in comparison have very low elastic modulus. Monodispersed, shape- and size-specific nanocarriers composed of NIPAM with material elastic modulus of <1 MPa have been fabricated and show thermal responsive behavior at the lower critical solubility temperature (LCST) of ∼32 °C. In addition, re-entrant shaped nanocarriers composed of PEGDA with elastic modulus <10 MPa are also fabricated. Nanocarriers fabricated from PEGDA are shown with model imaging agent and anticancer drug (Doxorubicin) encapsulated in as small as 50 nm cylindrical nanocarriers.

Thermally Responsive Amphiphilic Conetworks and Gels Based on Poly(N-isopropylacrylamide) and Polyisobutylene

Novel amphiphilic conetworks (APCN) consisting of thermoresponsive poly(N-isoproplyacrylamide) (PNiPAAm) cross-linked by hydrophobic methacrylate-telechelic polyisobutylene (MA-PIB-MA) were successfully synthesized in a broad composition range. The resulting PNiPAAm-l-PIB conetworks (“l” stands for “linked by”) were obtained by radical copolymerization of NiPAAm with MA-PIB-MA in tetrahydrofuran, a cosolvent for all the components. Low amounts of extractables substantiated efficient network formation. The composition dependent two glass transition temperatures (Tg) by DSC analysis indicate microphase separation of the cross-linked components without mixed phases. It was found that the PNiPAAm-l-PIB conetworks are uniformly swellable in both water and n-hexane; i.e., these new materials behave either as hydrogels or as hydrophobic gels in aqueous or nonpolar media, respectively. The uniform swelling in both polar and nonpolar solutes indicates cocontinuous (bicontinuous) phase morphology. The equilibrium swelling degrees (R) depend on composition, that is, the higher the PIB content, the lower the R in water and the higher in n-hexane. The PNiPAAm phase keeps its thermoresponsive behavior in the conetworks as shown by significant decrease of the swelling degree in water between 20 and 35 °C. The lower critical solubility temperature (LCST) values determined by DSC are found to decrease from 34.1 °C (for the pure PNiPAAm homopolymer) to the range of 25–28 °C in the conetworks, and the extent of the LCST decrease is proportional with the PIB content. Deswelling-swelling, i.e., heating–cooling, cycle indicates insignificant hysteresis in these new thermoresponsive materials. This indicates that PNiPAAm-l-PIB conetworks with predetermined and thermoresponsive swelling behavior can be designed and utilized in several advanced applications on the basis of results obtained in the course of this study.

Versatile thiolated thermosensitive polymers synthesized by ATRP of MEO2MA and AcSEMA, a new methacrylic monomer with a protected thiol group

Herein, the synthesis of a new monomer containing a protected thiol group, 2-(acetylthio)ethyl methacrylate (AcSEMA), is introduced. The monomer has been copolymerized via atom transfer radical polymerization (ATRP) with 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) to obtain a series of well-defined hidden-thiol functionalized thermosensitive polymers. The new system exhibits a sharp lower critical solubility temperature (LCST) and after hydrolysis of the acetyl group, the thiolated copolymers exhibit pH responsiveness. Moreover, to show the versatility of AcSEMA, P(MEO2MA-co-AcSEMA) copolymers were in situ hydrolyzed and modified by thiol-ene Michael addition with some acrylate compounds. The click reaction was successfully performed as revealed by NMR and the change in the LCST. We finally demonstrate that the addition of these polymer coatings onto gold nanoparticles (AuNPs) results in the formation of stable, colloidal thermosensitive polymer@AuNP complexes due to bridge formation between the thiol groups of AcSEMA and the metallic NP surfaces. The formation of temperature responsive polymer coated plasmonic nanoparticles shows the promise of P(MEO2MA-co-AcSEMA) copolymers for building multifunctional nanostructures for drug-delivery, diagnosis, tagging, catalysis and organic electronics systems.

Thermo-responsive peptide-based triblock copolymer hydrogels

A series of novel thermo-responsive peptide-based triblock copolymers, poly(L-glutamic acid)-b-poly(N-isopropylacrylamide)-b-poly(L-glutamic acid) (PLGA-b-PNIPAM-b-PLGA), were successfully synthesized via ring opening polymerization (ROP) of the γ-benzyl L-glutamate derivative (BLG-NCA) using a diamino-terminated PNIPAM as a macroinitiator, followed by de-protection of the benzyl groups. These triblock copolymers form physically crosslinked networks after complexation with a diamino-terminated poly(ethylene oxide) (PEO) in an organic solvent through acid–base proton transfer and successive ionic-bonding confirmed by Fourier transform infrared (FTIR) spectroscopy. The secondary structure of the peptide block, before and after complexation, was confirmed by circular dichroism (CD) experiments, showing an α-helix conformation of the PLGA segments. Swelling experiments on the ionic-bonded networks showed that the water uptake process strongly depends on the temperature and relative humidity conditions. Thus, higher humidity and temperatures below the lower critical solubility temperature (LCST) of the PNIPAM block increase the amount of water absorbed into the network. These swollen ionic complexes contract and reject water when these thermo-responsive peptide-based hydrogels are heated up above their LCST, making them promising for biomedical applications and drug delivery systems.

Ionic Transport Through Single Solid‐State Nanopores Controlled with Thermally Nanoactuated Macromolecular Gates

Single solid-state nanopores modified with poly-N-isopropylacrylamide (NIPAM) brushes display thermally controlled gating properties. Below the lower critical solubility temperature (LCST) NIPAM brushes are swollen and, consequently, dramatically reduce the effective cross section of the nanopores (see image). Conversely, above the LCST the brushes dehydrate and suffer a transition into a collapsed state, which promotes the widening of the nanopore and enables a substantial flow of ions.