Reversible Polymer Research Articles

Effect of cylindrical heat pipes on electrochemical hydrogen adsorption within a carbon electrode employed in a modified reversible PEM fuel cell

The presented work is a maiden experimental attempt on thermal management of a modified reversible polymer electrolyte membrane fuel cell (MRPEMFC) using a passive cooling approach to enhance the hydrogen (H)-adsorption capacity of an integrated activated carbon (aC) electrode. In the current study, cylindrical heat pipes (CHPs) are installed on the hydrogen side (H-side) and oxygen side (O-side) bi-polar end plates (BEPs) of the developed cell to maintain a temperature within tolerable limits during the charging operation. The noteworthy achievement with the integration of a CHP on the H-side of the MRPEMFC is a 12 °C reduction in the operating temperature. While, the highest obtained gravimetric H-storage density is recorded 1.52 wt percent (wt%) with the integration of CHPs on H- and O-side BEPs, which is 40% higher than without CHPs. Furthermore, CHPs assisted-MPEMFC is able to supply 0.4 mA constant current for the first 3 min during the discharging operation.

Self‐Closing and Self‐Healing Multi‐Material Suction Cups for Energy‐Efficient Vacuum Grippers

While vacuum grippers offer an economical solution, the environmental impact of energy waste through their suction cups (SCs) cannot be overlooked. This waste stems from three key factors: i) air losses from idle SCs arranged in arrays, ii) inadequate sealing on target surfaces leading to air leaks, and iii) damage from sharp objects resulting in leaking perforations. To overcome these challenges, in this article, a comprehensive approach is presented that involves the development of a i) self‐closing, ii) multi‐material, and iii) self‐healing system based on reversible elastomers cross‐linked via the Diels–Alder (DA) reaction. The system incorporates a fully autonomous self‐closing mechanism to prevent energy waste in SC arrays during periods of non‐contact. Fluid–structure interaction simulations are utilized to analyze the design. Versatility and stability are achieved by incorporating hyper‐flexible and stiff elastomers in a multi‐material design, supported by covalent DA cross‐links that ensure robustness through high‐strength multi‐material interfaces. These DA cross‐links also enable self‐healing capabilities, allowing the SCs to recover from macroscopic damages within 1 day at ambient conditions or in a single hour with mild heating (80–90 °C), restoring full performance. Additionally, in the article, a recycling method is introduced for multi‐material SCs based on the mechanical separation of reversible polymers.

Electrically and thermally healable nanocomposites via one-step Diels-Alder reaction on carbon nanotubes

Carbon nanotubes (CNTs) were directly employed as reactive fillers in furan-pendant polyketones via the Diels-Alder (DA) reaction. CNTs and furan groups function as dienophile and diene, respectively, forming a reversible crosslinking network. Here, pristine CNTs not only serve as crosslinking agents, but also improve the thermal and electrical conductivity. The DA covalent linkage was confirmed by IR, TGA, DSC, elemental analysis and dispersion tests. This one-step approach offers a facile route to synthesize reversibly crosslinked thermoset polymer nanocomposites. The rigidity of the nanocomposites could be controlled through the number of furan groups in order to achieve distinct properties. The nanocomposites demonstrated dynamic temperature-dependent behavior due to the retro Diels-Alder reaction. Cyclic tests via rheology showed good reversibility below 120 °C. However, an irreversible increase of modulus was observed at higher temperatures, which is possibly attributed to a side reaction. At filler loadings above 5%, both electrical and thermal self-healing tests showed good results. The Diels-Alder reaction between CNTs and furan-pendant polymers opens up a new possibility of directly employing fillers in the polymer matrix without any prior modifications. It is also possible to use other fillers with diene/dienophile properties in future reversible polymer nanocomposites.

Diels‐Alder Macromolecular Networks in Recyclable, Repairable and Reprocessable Polymer Composites for the Circular Economy – A Review

AbstractIn the expanding field of high‐performance materials, polymer‐based thermoset composites play an important role due to their favorably‐high strength/weight ratio and their mechanical performance, thermal stability, and chemical resistance. However, their chemically‐crosslinked nature hampers their re‐processability and efficient recyclability, thus making them not compliant with the principles of the circular economy and of end‐of‐life valorization. Dynamic covalent polymers able to modify their network topology upon thermal stimulus can be considered valid alternatives to commonly used thermosets as they offer advantages in terms of recyclability and reusability, normally not achievable with conventional cross‐linked systems. Within the broad field of dynamic polymers, thermally‐triggered Diels‐Alder based materials represent reliable platforms with enormous technological and industrial potential as repairable, reusable and recyclable matrices in composites given their chemical versatility, suitable mechanical performance and ease of production and processing. In this review, a comprehensive discussion of the most recent demonstrations of the reversibility, reprocessability and recyclablability of such systems is provided, in the context of their use as polymer matrices in composites. It is hoped that this work will stimulate further discussion and research in the area of reversible polymer composites with increased functionality and extended lifetime, in view of their application in future circular economy scenarios.

Controlled Degradation of Polycaprolactone Polymers through Ultrasound Stimulation.

This study describes the development of an ultrasound-responsive polymer system that provides on-demand degradation when exposed to high-intensity focused ultrasound (HIFU). Diels-Alder cycloadducts were used to crosslink polycaprolactone (PCL) polymers and underwent a retro Diels-Alder reaction when stimulated with HIFU. Two Diels-Alder polymer compositions were explored to evaluate the link between reverse reaction energy barriers and polymer degradation rates. PCL crosslinked with isosorbide was also used as a non-Diels-Alder-based control polymer. An increase of HIFU exposure time and amplitude correlated with an increase of PCL degradation for Diels-Alder-based polymers. Ultrasound imaging during HIFU allowed for real-time visualization of the on-demand degradation through cavitation-based mechanisms. The temperature surrounding the sample was monitored with a thermocouple during HIFU stimulation; a minimal increase in temperature was observed. PCL polymers were characterized using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), optical profilometry, and mechanical testing. PCL degradation byproducts were identified by mass spectrometry, and their cytocompatibility was evaluated in vitro. Overall, this study demonstrated that HIFU is an effective image-guided, external stimulus to control the degradation of Diels-Alder-based PCL polymers on-demand.

Ultra-tough and stress-free two-way shape memory polyurethane induced by polymer segment “spring”

Two-way shape memory polymers (2WSMP) are highly desired for artificial muscles, soft actuators and sensors, while the stress-free 2WSMP greatly expands the practical potential of shape memory polymers. However, traditional 2WSMP cannot show high strength or good mechanical properties, which limited its practical application. It is important to create a new reversible polymer system in order to obtain more intricate movements, precise control and great mechanical properties. Herein, a two-way shape memory polyurethane was created using a new molecular strategy, which shows great properties, i.e., 2342% super stretch strain, 591 MPa true tensile strength, 708.04 J/kg of energy density, and 667.96 W/kg of power density. In addition, the 2WSMP could achieve a maximum 24.53% reversible transformation under 1 MPa stress, and 13.7% two-way shape change without external stress, respectively. In this polyurethane, the great mechanical properties and stress-free two-way shape memory effect are caused by the elastic polybutadiene (PB) segments, which acts as a “molecular spring.” Furthermore, this 2WSMP could simulate reversible muscle-like motion, and be employed in ligaments. Consequently, this polyurethane offers a fresh design concept for stress-free two-way performance memory polymers and has a wide range of potential applications in the field of artificial muscles, soft actuators and ligaments.

Insights into Uniaxial Tension and Relaxation of Nanorod-Filled Polymer Vitrimer Nanocomposites: A Molecular Dynamics Simulation

The mechanical properties of polymer nanocomposites (PNCs) depend sensitively on the structure (e.g., orientation, dispersion, and so on) of the incorporated nanofillers. Many studies have shown that the alignment of anisotropic nanofillers can improve the mechanical properties of PNCs. However, achieving this alignment typically requires complex preparation processes. To address this challenge, researchers have introduced dynamic covalent bonds to form reversible cross-linked polymer systems, which would lead to unique properties, such as self-healing, recyclability, and reprocessibility. In addition, inspired by the above ideas, we introduce nanorods as fillers into a linear vitrimer system to form nanorod vitrimer composites (NVCs). In NVCs, we can easily manipulate the alignment of the nanorods due to bond exchange reactions (BERs) in the vitrimer matrices. By using coarse-grained molecular dynamics (CGMD) simulations, we systematically investigate the factors affecting the nanorod orientation in NVCs. We find that the main factor affecting the nanorod orientation is the network rearrangement caused by BERs. Specifically, the BER potential barrier (ΔEsw) directly determines the probability of BERs’ occurrence. At the same time, the increase of the interfacial interaction between polymer chains and nanorods (εnp) confines the motion of the active beads, which slows down the rate of BERs. Additionally, the impact of temperature (T) and aspect ratio (ld) on the orientation of nanorods during uniaxial stretching or stress relaxation are also discussed. Finally, by combining uniaxial stretching and stress relaxation processes, we elucidate the orientation retention mechanism of NVCs and demonstrate the mechanical property enhancement phenomenon of the pre-oriented NVC systems. This work provides a simple strategy for manipulating the nanorod alignment in vitrimer matrices and uncovers guidelines for designing new functional polymer vitrimer nanocomposites at the molecular level.

Toughening and Stiffening in Thermoreversible Diels–Alder Polymer Network Blends

The thermophysical properties, mechanical behavior, and healing performance of Diels–Alder-based polymer networks can be tuned widely by changing the molar mass, functionality, and stoichiometric ratio of the multifunctional diene (e.g., furan) and dienophile (e.g., maleimide) monomers. Blending furan-functionalized monomers with a high and low molar mass opens a new dimension in tuning the properties of the resulting reversible polymer network blends (RPNBs), containing different ratios of elastomeric and thermoset phases, with low and high crosslink densities and glass transitions below and above room temperature, respectively. Increasing the thermoset content up to 20 wt % raises the gel transition temperature (Tgel), relaxation time (τ), rubbery plateau modulus, ultimate stress, and Young’s modulus of the stiffened elastomers, while the strain at fracture and self-healing efficiency remained mostly unchanged. Conversely, the addition of up to 20 wt % of the elastomer phase drastically toughens the thermosets because of stress dissipation, which can suppress the stress concentration in the phase-separated network blends. The blends showed higher stress and strain at break while retaining similar Young’s moduli. The toughness increases up to an order of magnitude at 50 wt %, compared to the pure thermoset. The phase-separated morphologies were evidenced by the presence of the Tg’s of the pure networks in DSC and DMA.

Two-Way Reversible Shape Memory Behavior of Chitosan/Glycerol Film Triggered by Water.

Reversible shape memory polymers (SRMPs) have been identified as having great potential for biomedical applications due to their ability to switch between different shapes responding to stimuli. In this paper, a chitosan/glycerol (CS/GL) film with a reversible shape memory behavior was prepared, and the reversible shape memory effect (SME) and its mechanism were systematically investigated. The film with 40% glycerin/chitosan mass ratio demonstrated the best performance, with 95.7% shape recovery ratio to temporary shape one and 89.4% shape recovery ratio to temporary shape two. Moreover, it shows the capability to undergo four consecutive shape memory cycles. In addition, a new curvature measurement method was used to accurately calculate the shape recovery ratio. The suction and discharge of free water change the binding form of the hydrogen bonds inside the material, which makes a great reversible shape memory impact on the composite film. The incorporation of glycerol can enhance the precision and repeatability of the reversible shape memory effect and shortens the time used during this process. This paper gives a hypothetical premise to the preparation of two-way reversible shape memory polymers.

Flexible reversible polymer nano-composite thin film patch for wearable temperature sensor

A flexible polymer nano-composite thin film patch for wearable temperature sensors was fabricated, which presents excellent energy storage and temperature indication properties. In this composite patch, conductive silver (Ag) nanoparticles (NPs) were used as functional fillers while polyvinyl alcohol (PVA) used as polymer material. The effects of Ag NPs concentration on morphology and temperature indication were experimentally investigated using a field-emission scanning electron microscope (FE-SEM), thermogravimetric analyser (TGA) and differential thermal analysis (DTA). The findings showed that Ag was uniformly distributed across matrix membranes. Also, the prepared PVA-Ag nanocomposite thin film patch showed improved mechanical properties and conductivity. The consequence of X-Ray Diffraction (XRD) displayed a semi-crystalline nature. The results show the potential for incorporating subordinate AgNP concentrations as a substitute to enhance performance in terms of mechanical, thermal, and antibacterial qualities without treatment. The electrical properties were studied through the current-voltage(I–V) characteristics showing the linear I–V ohmic contact and low contact resistance. With heat storage and temperature regulation capabilities, a flexible polymer nano-composite patch for a wearable temperature sensor was created and has significant promise for use in the future in energy storage, thermal management, and wearable temperature sensors.

Strong, Supertough and Self‐Healing Biomimetic Layered Nanocomposites Enabled by Reversible Interfacial Polymer Chain Sliding

AbstractDespite the remarkable progress in ultrastrong mechanical laminate materials, the simultaneous achievement of toughness, stretchability and self‐healing properties in biomimetic layered nanocomposites remains a great challenge due to the intrinsic limitations of their hard essences and lack of effective stress transfer at the organic‐inorganic fragile boundary. Here, an ultratough nanocomposite laminate is prepared by constructing chain‐sliding cross‐linking at the interface between sulfonated graphene nanosheets and polyurethane layers based on the ring molecules sliding on the linear polymer chains to release stresses. Unlike traditional supramolecular bonding toughening with limited sliding spacing, our strategy enables interfacial molecular chains reversible slippage when the inorganic nanosheets bear stretching force, providing sufficient interlayer spatial distance for relative sliding to dissipate more energy. The resulting laminates exhibit strong strength (22.33 MPa), supertoughness (219.08 MJ m−3), ultrahigh stretchability (>1900 %) and self‐healing ability (99.7 %), which far surpass most of reported synthetic and natural laminate materials. Moreover, the fabricated proof‐of‐concept electronic skin shows excellent flexibility, sensitivity and healability for human physiological signals monitoring. This strategy breaks through the challenge that traditional layered nanocomposites are intrinsically stiff and opens up the functional application of layered nanocomposites in flexible devices.

Strong, Supertough and Self-Healing Biomimetic Layered Nanocomposites Enabled by Reversible Interfacial Polymer Chain Sliding.

Despite the remarkable progress in ultrastrong mechanical laminate materials, the simultaneous achievement of toughness, stretchability and self-healing properties in biomimetic layered nanocomposites remains a great challenge due to the intrinsic limitations of their hard essences and lack of effective stress transfer at the organic-inorganic fragile boundary. Here, an ultratough nanocomposite laminate is prepared by constructing chain-sliding cross-linking at the interface between sulfonated graphene nanosheets and polyurethane layers based on the ring molecules sliding on the linear polymer chains to release stresses. Unlike traditional supramolecular bonding toughening with limited sliding spacing, our strategy enables interfacial molecular chains reversible slippage when the inorganic nanosheets bear stretching force, providing sufficient interlayer spatial distance for relative sliding to dissipate more energy. The resulting laminates exhibit strong strength (22.33 MPa), supertoughness (219.08 MJ m-3 ), ultrahigh stretchability (>1900 %) and self-healing ability (99.7 %), which far surpass most of reported synthetic and natural laminate materials. Moreover, the fabricated proof-of-concept electronic skin shows excellent flexibility, sensitivity and healability for human physiological signals monitoring. This strategy breaks through the challenge that traditional layered nanocomposites are intrinsically stiff and opens up the functional application of layered nanocomposites in flexible devices.

Reconfigurable, Multi-Material, Voxel-Based Soft Robots

Voxel-based robots are aggregations of soft and simple building blocks that have been extensively evolved and simulated to perform various tasks, like walking, jumping or swimming. However, real-life voxel-based robots are rather scarce because of their challenging design and assembly. With the current materials and assembling methods, the interfaces between the soft multi-material voxels are prone to failure. This work proposes to make voxels out of reversible Diels-Alder polymers, which are available in a broad range of mechanical properties. By doing so, the covalent bonds at the multi-material interface ensure strong chemical connections, while allowing for reconfiguration. A first voxel-based gripper is thus robustly assembled, then disassembled, using its pieces (voxels) for reassembling another robot, i.e. a voxel-based walking robot. This reconfigurable property allows iterative validation of the simulated voxel-based robots and fine-tuning of the simulations parameters in a sustainable and economical way. Both physical voxel-based robots show similar behaviors as their simulations with root-mean-square errors down to 10.4%.

Preparation of reverse mode polymer dispersion liquid crystals with vertically oriented layers and the electro-optical properties

ABSTRACT The reverse-mode polymer dispersed liquid crystals (re-mode PDLC) are feasible to be prepared by polyimide vertically oriented layers. The indium tin oxide (ITO) glass coated with polyimide-oriented layer was prepared by centrifugal spin coating and high temperature curing, and the re-mode PDLC film was prepared by polymerisation-induced phase separation method. After that the effects of diluent, negative liquid crystal and gadolinium oxide (Gd2O3) nanoparticle content on the morphology and electro-optical properties of re-mode PDLC were comprehensively investigated. The results show that the re-mode PDLC with appropriate diluent and negative liquid crystal content has stable contrast ratio and driving voltage, and the re-mode PDLC samples doped with Gd2O3 nanoparticles can further increase the contrast ratio to improve the problem of low contrast of ordinary re-mode PDLC samples. In the thermal ageing life test, the driving voltage ageing degree of the nanoparticle-doped re-mode PDLC samples can be stabilised, which has some significance for use of re-mode PDLC.

Composition-Property Relationships of pH-Responsive Poly[(2-vinylpyridine)-co-(butyl methacrylate)] Copolymers for Reverse Enteric Coatings.

The taste-masking of bitter-tasting active pharmaceutical ingredients is key to ensuring patient compliance when producing oral pharmaceutical formulations. This is generally achieved via the incorporation of pH-responsive, reverse enteric polymers, that prevent the dissolution of the formulation in the oral environment, but rapidly mediate it within the gastric environment. Reverse enteric polymers are commonly applied as coatings on oral dosage forms via spray atomisation (e.g., fluidised-bed spray coating), and generally exhibit the most efficient taste-masking. However, currently used reverse enteric coatings require high mass gains (% w/w) during coating to mediate taste-masking, and thereby exhibit delayed release within the gastric environment. Therefore, there remains a need for the development of new reverse enteric coatings, that can efficiently taste-mask at low mass gains and maintain rapid release characteristics within the gastric environment. Herein we report the synthesis and evaluation of a series of addition copolymers of 2-vinylpyridine and butyl methacrylate, methyl methacrylate and isobornyl methacrylate. The thermal, solubility, and water absorption properties of the copolymers were effectively tuned by altering the mol% fraction of the constitutive monomers. Based on their physical properties, selected copolymers were preliminarily evaluated for their compatibility with fluidised-bed spray coating, and effectiveness as taste-masking reverse enteric coatings. The copolymers poly[(2-vinylpyridine)-co-(butyl methacrylate)] (mol% ratio 40:60) and poly[(2-vinylpyridine)-co-(butyl methacrylate)-co-(methyl methacrylate)] (mol% ratio 40:50:10) were found to exhibit excellent taste-masking properties following fluidised-bed spray coating onto Suglets® sugar spheres. Suglets® bearing a film coating of either copolymer (5.2-6.5% w/w mass gain) were found to effectively impede the release of a model drug formulation for up to 72 h in a simulated salivary environment, and rapidly release it (<10 min) within a simulated gastric environment. The results demonstrated the potential of poly[(2-vinylpyridine)-co-(butyl methacrylate)] copolymers to form effectively taste-masked, reverse enteric dosage forms, and suggested that these copolymers may provide improved performance compared to currently available polymers.

Reversible Polymer-Protein Functionalization by Stepwise Introduction of Amine-Reactive, Reductive-Responsive Self-Immolative End Groups onto RAFT-Derived Polymers.

Many promising therapeutic protein or peptide drug candidates are rapidly excreted from an organism due to their small size or their inherent immunogenicity. One way to counteract these effects is PEGylation, in which the biopolymer is shielded by synthetic polymers exploiting their stealth properties. However, these modifications are often accompanied by a reduction in the biological function of the protein. By using responsive moieties that bridge the polymer to the protein, a reversible character is provided to this type of conjugation. In this regard, the reductive-responsive nature of disulfides can be exploited via self-immolative structures for reversible linkage to aminic lysine residues and the N-terminus on the protein surface. They enable a traceless release of the intact protein without any further modification and thus preserve the protein's bioactivity. In this study, we demonstrate how this chemistry can be made broadly accessible to RAFT-derived water-soluble polymers like poly(N,N-dimethylacrylamide) (pDMA) as a relevant PEG alternative. A terminal reactive imidazole carbamate with an adjacent self-immolative motif was generated in a gradual manner onto the trithiocarbonate chain transfer moiety of the polymer by first substituting it with a disulfide-bridged alcohol and subsequently converting it into an amine reactive imidazole carbamate. Successful synthesis and complete characterization were demonstrated by NMR, size exclusion chromatography, and mass spectrometry. Finally, two model proteins, lysozyme and a therapeutically relevant nanobody, were functionalized with the generated polymer, which was found to be fully reversible under reductive conditions in the presence of free thiols. This strategy has the potential to extend the generation of reversible reductive-responsive polymer-protein hybrids to the broad field of available functional RAFT-derived polymers.

Efficacy and Safety of Mitomycin Gel (UGN-101) as an Adjuvant Therapy After Complete Endoscopic Management of Upper Tract Urothelial Carcinoma.

We describe a novel application of the reverse thermal polymer gel of mitomycin C (UGN-101) as adjuvant therapy after complete endoscopic ablation of upper tract urothelial carcinoma. We retrospectively reviewed patients treated with UGN-101 from 15 high-volume centers. Adjuvant therapy was defined as treatment administered following visually complete endoscopic ablation. Response at primary endoscopic evaluation was defined as no visual tumor or negative biopsy. Ipsilateral disease-free and progression-free survival were estimated by the Kaplan-Meier method. Ureteral stenosis and other adverse events were abstracted from the medical records. Ureteral stenosis was defined as a condition requiring ureteral stent or nephrostomy, or that would typically warrant stent or nephrostomy. Adjuvant UGN-101 after complete endoscopic ablation was used in 52 of 115 (45%) renal units in the oncologic analysis. At first endoscopic evaluation, 36/52 (69%) were without visible disease. At 6.8 months' median follow-up, the ipsilateral disease-free rate was 63%. Recurrence after adjuvant UGN-101 therapy was more likely in multifocal tumors compared to unifocal (HR 3.3, 95% CI 1.07-9.91). Compared with UGN-101 treatment for chemoablation of measurable disease, there were significantly fewer disease detections with adjuvant therapy (P < .001). Ureteral stenosis after UGN-101 was diagnosed in 10 patients (19%) undergoing adjuvant therapy compared to 17 (29%) undergoing chemoablative therapy (P = .28). In patients being considered for UGN-101, maximal endoscopic ablation prior to UGN-101 treatment may result in fewer patients with disease at first endoscopy and possibly fewer adverse events than primary chemoablative therapy. Longer follow-up is needed to determine if UGN-101 after complete endoscopic ablation will lead to durable disease-free interval.

High-contrast reversible multiple color-tunable solid luminescent ionic polymers for dynamic multilevel anti-counterfeiting.

Dynamic color-tunable luminescent materials, which possess huge potential applications in advanced multilevel luminescence anti-counterfeiting, are of considerable interest. However, it remains challenging to develop simple high-contrast reversible multiple (triple or more than triple) color-tunable high-efficiency solid luminescent materials with low cost, facile synthesis, and good processability. Herein, by simply grafting charged multi-color AIEgen-based chromophores into polymers, a series of high-efficiency multiple color-tunable luminescent single ionic polymers are constructed through tuning feed ratios, counter anions and reaction solvents. Remarkably, some ionic polymers can not only achieve rare high-contrast reversible multiple color-tunable emission in solid states in response to different solvent stimuli, but also could realize excitation-dependent color-tunable emission. To the best of our knowledge, such charming multiple (triple or more than triple) color-tunable solid polymers responding to multiple external stimuli are still rare. Based on comparative studies of emission spectra, excitation spectra and fluorescence lifetimes before and after swelling, it could be inferred that solvent stimuli could induce microstructure changes of these ionic polymers and then change the aggregated-states of their corresponding AIE-active emission centers. Moreover, the different solvent stimuli could induce to produce different degrees of microstructure changes, resulting in their unique multiple color-tunable emission. More significantly, these smart color-tunable ionic polymers show great promise for applications in dynamic multilevel (three-level or even more than three-level) anti-counterfeiting.

Molecular in situ monitoring of the pH-triggered response in adaptive polymers by two-dimensional Raman micro-correlation-spectroscopy.

Stimuli-responsive polymers can switch specific physical properties in response to a change of the environmental conditions. This behavior offers unique advantages in applications where adaptive materials are needed. To tune the properties of stimuli-responsive polymers, a detailed understanding of the relationship between the applied stimulus and changes in molecular structure as well as the relationship between the latter and macroscopic properties is required, which until now has required laborious methods. Here, we present a straightforward way to investigate the progressing trigger, the change of the chemical composition of the polymer and the macroscopic properties simultaneously. Thereby, the response behavior of the reversible polymer is studied in situ with molecular sensitivity and spatial as well as temporal resolution utilizing Raman micro-spectroscopy. Combined with two-dimensional correlation analysis (2DCOS), this method reveals the stimuli-response on a molecular level and determines the sequence of changes and the diffusion rate inside the polymer. Due to the label-free and non-invasive approach, it is furthermore possible to combine this method with the investigation of macroscopic properties revealing the response of the polymer to the external stimulus on both the molecular and the macroscopic level.

Infection Microenvironment-Sensitive Photothermal Nanotherapeutic Platform to Inhibit Methicillin-Resistant Staphylococcus aureus Infection.

Methicillin-resistant Staphylococcus aureus (MRSA) can induce multiple inflammations. The biofilm formed by MRSA is resistant to a variety of antibiotics and is extremely difficult to cure, which seriously threatens human health. Herein, a nanoparticle encapsulating berberine with polypyrrole core and pH-sensitive shell to provide chemo-photothermal dual therapy for MRSA infection is reported. By integrating photothermal agent polypyrrole, berberine, acid-degradable crosslinker, and acid-induced charge reversal polymer, the nanoparticle exhibited highly efficient MRSA infection treatment. In normal uninfected areas and bloodstream, nanoparticles showed negatively charged, demonstrating high biocompatibility and excellent hemocompatibility. However, once arriving at the MRSA infection site, the nanoparticle can penetrate and accumulate in the biofilm within 2h. Simultaneously, berberine can be released into biofilm rapidly. Under the combined effect of photothermal response and berberine inhibition, 88.7% of the biofilm is removed at 1000µgmL-1 . Moreover, the nanoparticles have an excellent inhibitory effect on biofilm formation, the biofilm inhibition capacity can reach up to 90.3%. Taken together, this pH-tunable nanoparticle can be employed as a new generation treatment strategy to fight against the fast-growing MRSA infection.