Structure-Function Insights into Thermoresponsive Copolymers as Lanthanide Precipitants

The synthetic toolbox for stimuli-responsive polymers has broadened to include many tunable variables, making these materials applicable in diverse technologies. However, unraveling the key composition-structure-function relationships to facilitate ground-up design remains a challenge due to the inherent dispersity in sequence and conformations for synthetic polymers. We here present a systematic study of these relationships using a model system of copolymers with a thermoresponsive (N-isopropylacrylamide) backbone in addition to metal-chelating (acrylic acid) and hydrophobic structural comonomers and evaluate their efficiency at isolating technologically critical lanthanide ions. The efficiency of lanthanide ion extraction by precipitation was quantitated with a metallochromic dye to reveal trends relating copolymer hydrophobicity to improved separations. Further, we examined the role of different hydrophobic comonomers in dictating the solution-phase conformation of the polymer in the presence and absence of lanthanide ions, and we correlated key features of the hydrophobic comonomer to extraction efficiency. Finally, we identified how the local proximity of thermoresponsive, chelating, and hydrophobic subunits facilitates metal extraction by manipulating the copolymer sequence with multiblock polymerization. Through mechanistic analysis, we propose a binding-then-assembly process through which metal ions are coprecipitated with macromolecular chelators.

Biophysical investigation of liposome systems decorated with bioconjugated copolymers in the presence of amantadine

Liposome-based technologies derived from lipids and polymers (e.g., PEGylated liposomes) have been recognized because of their applications in nanomedicine. However, since such systems represent myriad challenges and may promote immune responses, investigation of new biomaterials is mandatory. Here, we report on a biophysical investigation of liposomes decorated with bioconjugated copolymers in the presence (or absence) of amantadine (an antiviral medication). First, copolymers of poly(N,N-dimethylacrylamide-co-fluoresceinacrylate-co-acrylic acid-N-succinimide ester)-block-poly(N-isopropylacrylamide) (PDMA-b-PNIPAM) containing a fluorescence label were biofunctionalized with short peptides that resemble the sequence of the loops 220 and 130 of the binding receptor of the hemagglutinin (HA) protein of the influenza A virus. Then, the bioconjugated copolymers were self-assembled along with liposomes composed of 1,2 dimyristoyl-sn-glycero-3-phosphocholine, sphingomyelin, and cholesterol (MSC). These biohybrid systems, with and without amantadine, were systematically characterized using differential scanning calorimetry (DSC), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryoTEM). Finally, the systems were tested in an in vitro study to evaluate cytotoxicity and direct immunofluorescence in Madin Darbin Canine Kidney (MDCK) cells. The biohybrid systems displayed long-term stability, thermo-responsiveness, hydrophilic-hydrophobic features, and fluorescence properties and were presumable endowed with cell targeting properties intrinsically integrated into the amino acid sequences of the utilized peptides, which indeed turn them into promising nanodevices for biomedical applications.

Morphology and thermal transitions of self-assembled NIPAM-DMA copolymers in aqueous media depend on copolymer composition profile

HYPOTHESIS

There is a lack of understanding of the interplay between the copolymer composition profile and thermal transition observed in aqueous solutions of N-isopropyl acrylamide (NIPAM) copolymers, as well as the correlation between this transition and the formation and structure of copolymer self-assemblies.

EXPERIMENTS

For this purpose, we investigated the response of five copolymers with the same molar mass and chemical composition, but with different composition profile in aqueous solution against temperature. Using complementary analytical techniques, we probed structural properties at different length scales, from the molecular scale with Nuclear Magnetic Resonance (NMR) to the colloidal scale with Dynamic Light Scattering (DLS) and Small Angle Neutron Scattering (SANS).

FINDINGS

NMR and SANS investigations strengthen each other and allow a clear picture of the change of copolymer solubility and related copolymer self-assembly as a function of temperature. At the molecular scale, dehydrating NIPAM units drag N,N-dimethyl acrylamide (DMA) moieties with them in a gradual collapse of the copolymer chain; this induces a morphological transition of the self-assemblies from star-like nanostructures to crew-cut micelles. Interestingly, the transition spans a temperature range which depends on the monomer distribution profile in the copolymer chain, with the asymmetric triblock copolymer specimen revealing the broadest one. We show that the broad morphological transitions associated with gradient copolymers can be mimicked and even surpassed by the use of stepwise gradient (asymmetric) copolymers, which can be more easily and reproducibly synthesized than linear gradient copolymers.

Drug-Polymer Nanodroplet Formation and Morphology Drive Solubility Enhancement of GDC-0810

Nanodroplet formation is important to achieve supersaturation of active pharmaceutical ingredients (APIs) in an amorphous solid dispersion. The aim of the current study was to explore how polymer composition, architecture, molar mass, and surfactant concentration affect polymer-drug nanodroplet morphology with the breast cancer API, GDC-0810. The impact of nanodroplet size and morphology on dissolution efficacy and drug loading capacity was explored using polarized light microscopy, dynamic light scattering, and cryogenic transmission electron microscopy. Poly(N-isopropylacrylamide-stat-N,N-dimethylacrylamide) (PND) was synthesized as two linear derivatives and two bottlebrush derivatives with carboxylated or PEGylated end-groups. Hydroxypropyl methylcellulose acetate succinate grade MF (HPMCAS-MF) and poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA) were included as commercial polymer controls. We report the first copolymerization synthesis of a PVPVA bottlebrush copolymer, which was the highest performing excipient in this study, maintaining 688 μg/mL GDC-0810 concentration at 60 wt % drug loading. This is likely due to strong polymer-drug noncovalent interactions and the compaction of GDC-0810 along the PVPVA bottlebrush backbone. Overall, it was observed that the most effective formulations had a hydrodynamic radius less than 25 nm with tightly compacted nanodroplet morphologies.

Regulating Electrostatic Interactions toward Thermoresponsive Hydrogels with Low Critical Solution Temperature

Low critical solution temperature (LCST) of commonly used thermoresponsive polymers in water is basically dominated by hydrophobic interactions. Herein, a novel thermoresponsive system based on electrostatic interactions is reported. By simply loading aluminum chloride (AlCl3 ) into non-responsive poly(2-hydroxyethyl acrylate) (PHEA) hydrogels, PHEA-Al gels turn to have reversible thermoresponsive behavior between transparent and opaque without any volume change. Further investigations by changing metal ion-polymer compositions unravel the necessity of specific electrostatic interactions, namely, cation-dipole bonding interactions between hydroxy groups and trivalent metal ions. The thermoresponsive hydrogel demonstrates high transparency (≈95%), excellent luminous modulation capability (>98%), and cyclic reliability, suggesting great potential as an energy-saving material. Although LCST control by salt addition is widely known, salt-induced expression of thermoresponsiveness has barely been discussed before. This design provides a new approach of easy fabrication, low cost, and scalability to develop stimuli-responsive materials.

Vancomycin-loaded hydrogels with thermal-responsive, self-peeling, and sustainable antibacterial properties for wound dressing

Wound dressings play an important role in wound healing. However, many wound dressings lack antibacterial properties and are difficult to remove from newly grown tissues, causing secondary wound injuries and repeated medical treatment. This study reports a new type of thermal-responsive hydrogel dressing consisting of vancomycin-loaded gelatin nanospheres (GNs) and poly((N-isopropylacrylamide)-co-N-(methylol acrylamide)) functional components that could impart self-peeling and sustainable antibacterial properties. SEM images showed that the prepared hydrogel possessed a porous microstructure and the homogeneous distribution of GNs in its network. Excellent swelling ratios and thermal-induced self-peeling characteristics were confirmed by qualitative analysis. The GNs not only enhanced the strain at break of the hydrogel, but also acted as drug carriers to slow down the drug release from the hydrogel, achieving sustainable antibacterial properties and balanced biocompatibility. Therefore, this vancomycin-loaded hydrogel with self-peeling characteristics provides an effective way of preventing wound infection and can be used as a novel platform for wide-ranging applications of wound dressings.

Integrated FRET Polymers Spatially Reveal Micro- to Nanostructure and Irregularities in Electrospun Microfibers

A spatial view of macroscopic polymer material properties, in terms of nanostructure and irregularities, can help to better understand engineering processes such as when materials may fail. However, bridging the gap between the molecular-scale arrangement of polymer chains and the spatially resolved macroscopic properties of a material poses numerous difficulties. Herein, an integrated messenger material that can report on the material micro- to nanostructure and its processes is introduced. It is based on polymer chains labeled with fluorescent dyes that feature Förster resonance energy transfer (FRET) dependent on chain conformation and concentration within a host polymer material. These FRET materials are integrated within electrospun polystyrene microfibers, and the FRET is analyzed by confocal laser scanning microscopy (CLSM). Importantly, the use of CLSM allows a spatial view of material nanostructure and irregularities within the microfibers, where changes in FRET are significant when differences in fiber geometries and regularities exist. Furthermore, changes in FRET observed in damaged regions of the fibers indicate changes in polymer conformation and/or concentration as the material changes during compression. The system promises high utility for applications where nano-to-macro communication is needed for a better understanding of material processes.

Discovery of Kinetic Trapping of Poloxamers inside Liposomes via Thermal Treatment

Poloxamers, a class of biocompatible, commercially available amphiphilic block polymers (ABPs) comprising poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) blocks, interact with phospholipid bilayers, resulting in altered mechanical and surface properties. These block copolymers are useful in a variety of applications including therapeutics for Duchenne muscular dystrophy, as cell membrane stabilizers, and for drug delivery, as liposome surface modifying agents. Hydrogen bonding between water and oxygen atoms in PEO and PPO units results in thermoresponsive behavior because the bound water shell around both blocks dehydrates as the temperature increases. This motivated an investigation of poloxamer-lipid bilayer interactions as a function of temperature and thermal history. In this study, we applied pulsed-field-gradient NMR spectroscopy to measure the fraction of chains bound to 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) liposomes between 10 and 50 °C. We measured an (11 ± 3)-fold increase in binding affinity at 37 °C relative to 27 °C. Moreover, following incubation at 37 °C, it takes weeks for the system to re-equilibrate at 25 °C. Such slow desorption kinetics suggests that at elevated temperatures polymer chains can pass through the bilayer and access the interior of the liposomes, a mechanism that is inaccessible at lower temperatures. We propose a molecular mechanism to explain this effect, which could have important ramifications on the cellular distribution of ABPs and could be exploited to modulate the mechanical and surface properties of liposomes and cell membranes.

Four-Dimensional Printed Construct from Temperature-Responsive Self-Folding Feedstock for Pharmaceutical Applications with Machine Learning Modeling

Four-dimensional (4D) printing, as a newly evolving technology to formulate drug delivery devices, displays distinctive advantages that can autonomously monitor drug release according to the actual physiological circumstances. In this work, we reported our earlier synthesized novel thermo-responsive self-folding feedstock for possible SSE-mediated 3D printing to form a 4D printed construct deploying machine learning (ML) modeling to determine its shape recovery behavior followed by its potential drug delivery applications. Therefore, in the present study, we converted our earlier synthesized temperature-responsive self-folding (both placebo and drug-loaded) feedstock into 4D printed constructs using SSE-mediated 3D printing technology. Further, the shape memory programming of the printed 4D construct was achieved at 50 °C followed by shape fixation at 4 °C. The shape recovery was achieved at 37 °C, and the obtained data were used to train and ML algorithms for batch optimization. The optimized batch showed a shape recovery ratio of 97.41. Further, the optimized batch was used for the drug delivery application using paracetamol (PCM) as a model drug. The % entrapment efficiency of the PCM-loaded 4D construct was found to be 98.11 ± 1.5%. In addition, the in vitro release of PCM from this programmed 4D printed construct confirms temperature-responsive shrinkage/swelling properties via releasing almost 100% ± 4.19 of PCM within 4.0 h. at gastric pH medium. In summary, the proposed 4D printing strategy pioneers the paradigm that can independently control drug release with respect to the actual physiological environment.

Fibrillar biocompatible colloidal gels based on cellulose nanocrystals and poly(N-isopropylacrylamide) for direct ink writing

HYPOTHESIS

Hydrogels based on cellulose nanocrystals (CNC) have attracted great interest because of their sustainability, biocompatibility, mechanical strength and fibrillar structure. Gelation of colloidal particles can be induced by the introduction of polymers. Existing examples include gels based on CNC and derivatives of cellulose or poly(vinyl alcohol), however, gel structure and their application for extrusion printing were not shown. Hence, we rationalize formation of colloidal gels based on mixture of poly(N-isopropylacrylamide) (PNIPAM) and CNC and control their structure and mechanical properties by variation of components ratio.

EXPERIMENTS

State diagram for colloidal system based on mixture of PNIPAM and CNC were established at 25 and 37 °C. Biocompatibility, fiber diameter and rheological properties of the gels were studied for different PNIPAM/CNC ratio.

FINDINGS

We show that depending on the ratio between PNIPAM and CNC, colloidal system could be in sol or gel state at 25 °C and at gel state or phase separated at 37 °C. Physically crosslinked hydrogels were thermosensitive and could reversibly change it transparency from translucent to opaque in biologically relevant temperature range. These colloidal hydrogels were biocompatible, had fibrillar structure and demonstrate shear-thinning behavior, which makes them a promising material for bioapplications related to extrusion printing.

Stimulus-Responsive Transport Properties of Nanocolloidal Hydrogels

Applications of polymer hydrogels in separation technologies, environmental remediation, and drug delivery require control of hydrogel transport properties that are largely governed by the pore dimensions. Stimulus-responsive change in pore size offers the capability to change gel's transport properties "on demand". Here, we report a nanocolloidal hydrogel that exhibits temperature-controlled increase in pore size and, as a result, enhanced transport of encapsulated species from the gel. The hydrogel was formed by the covalent cross-linking of aldehyde-modified cellulose nanocrystals and chitosan carrying end-grafted poly(N-isopropylacrylamide) (pNIPAm) molecules. Owing to the temperature-mediated coil-to-globule transition of pNIPAm grafts, they acted as a temperature-responsive "gate" in the hydrogel. At elevated temperature, the size of the pores showed up to a 4-fold increase, with no significant changes in volume, in contrast with conventional pNIPAm-derived gels exhibiting a reduction in both pore size and volume in similar conditions. Temperature-mediated transport properties of the gel were explored by studying diffusion of nanoparticles with different dimensions from the gel, leading to the established correlation between the kinetics of diffusion-governed nanoparticle release and the ratio nanoparticle dimensions-to-pore size. The proposed approach to stimulus-responsive control of hydrogel transport properties has many applications, including their use in nanomedicine and tissue engineering.

Controlling the LCST-Phase Transition in Azobenzene-Functionalized Poly (N-Isopropylacrlyamide) Hydrogels by Light

Poly(N-isopropylacrylamide) PNIPAAm hydrogels were modified with a new azobenzene-containing co-monomer. In this work, light responsiveness as an additional functionality, is conceptualized to induce two phase transitions in the same material, which can be controlled by light. For a hydrogel with merely 2.5 mol% of this co-monomer, the lower critical solution transition temperature (LCST) was lowered by 12 °C (to 20 °C) compared to PNIPAAm (LCST at 32 °C), as analyzed by differential scanning calorimetry (DSC). The untreated unimodal endotherm split into a bimodal peak upon irradiation with UV-light, giving a second onset due to the switched (Z) isomer-rich regions, LCST*_H2.5%-(Z) = 26 °C. On irradiation with 450 nm, leading to the reverse (Z) to (E) isomerization, the endotherm was also reversible. Thus, a photo-switchable hydrogel whose LCST and structure are tunable with the hydrophobicity-hydrophilicity of the (E) and (Z) isomeric state of azobenzene was obtained. The influence of the increase in the mol% of azoacrylate on the LCST was evaluated via DSC, in combination with NMR studies, UV-vis spectroscopy and control experiments with linear polymers. The large light-driven modulation of the LCST adds bistability in thermoresponsive hydrogels, which may open diverse applications in the field of soft robotics actuators.

Double Stimuli-Responsive di- and Triblock Copolymers of Poly(N-isopropylacrylamide) and Poly(1-vinylimidazole): Synthesis and Self-Assembly

For the first time, double stimuli-responsive properties of poly(N-isopropylacrylamide) (PNIPA) and poly(1-vinylimidazole) (PVIM) block copolymers in aqueous solutions were studied. The synthesis of PNIPA60-b-PVIM90 and PNIPA28-b-PVIM62-b-PNIPA29 was performed using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymers were characterized by size exclusion chromatography and 1H NMR spectroscopy. The conformational behavior of the polymers was studied using dynamic light scattering (DLS) and fluorescence spectroscopy (FS). It was found that PNIPA and block copolymers conformation and ability for self-assembly in aqueous medium below and above cloud point temperature depend on the locus of hydrophobic groups derived from the RAFT agent within the chain. Additionally, the length of PVIM block, its locus in the chain and charge perform an important role in the stabilization of macromolecular micelles and aggregates below and above cloud point temperature. At 25 °C the average hydrodynamic radius (Rh) of the block copolymer particles at pH 3 is lower than at pH 9 implying the self-assembling of macromolecules in the latter case. Cloud points of PNIPA60-b-PVIM90 are ~43 °C and ~37 °C at a pH of 3 and 9 and of PNIPA28-b-PVIM62-b-PNIPA29 they are ~35 °C and 31 °C at a pH of 3 and 9. Around cloud point independently of pH, the Rh value for triblock copolymer rises sharply, achieves the maximum value, then falls and reaches the constant value, while for diblock copolymer, it steadily grows after reaching cloud point. The information about polarity of microenvironment around polymer obtained by FS accords with DLS data.

Synthesis and Characterization of a Novel Dual-Responsive Nanogel for Anticancer Drug Delivery

In this study, to reduce the side effects of anticancer drugs and also to increase the efficiency of current drug delivery systems, a pH and temperature-responsive polymeric nanogel was synthesized by copolymerization of N-vinylcaprolactam (VCL) and acrylic acid (AA) monomers (P(VCL-co-AA)) with a novel cross-linker, triethylene glycol dimethacrylate (TEGDMA), as a biocompatible and nontoxic component. The structural and physicochemical features of the P(VCL-co-AA) nanogel were characterized by FT-IR, DLS/Zeta potential, FE-SEM, and 1HNMR techniques. The results indicated that spherical polymeric nanogel was successfully synthesized with a 182 nm diameter. The results showed that the polymerization process continues with the opening of the carbon-carbon double bond of monomers, which was approved by C-C band removing located at 1600 cm-1. Doxorubicin (Dox) as a chemotherapeutic agent was loaded into the P(VCL-co-AA), whit a significant loading of Dox (83%), and the drug release profile was investigated in the physiological and cancerous site simulated conditions. P(VCL-co-AA) exhibited a pH and temperature-responsive behavior, with an enhanced release rate in the cancerous site condition. The biocompatibility and nontoxicity of P(VCL-co-AA) were approved by MTT assay on the normal human foreskin fibroblasts-2 (HFF-2) cell line. Also, Dox-loaded P(VCL-co-AA) had excellent toxic behavior on the Michigan Cancer Foundation-7 (MCF-7) cell line as model cancerous cells. Moreover, Dox-loaded P(VCL-co-AA) had higher toxicity in comparison with free Dox, which would be a vast advantage in reducing Dox side effects in the clinical cancer treatment applications.

Poly(N-isopropylacrylamide)-Based Hydrogels for Biomedical Applications: A Review of the State-of-the-Art

A prominent research topic in contemporary advanced functional materials science is the production of smart materials based on polymers that may independently adjust their physical and/or chemical characteristics when subjected to external stimuli. Smart hydrogels based on poly(N-isopropylacrylamide) (PNIPAM) demonstrate distinct thermoresponsive features close to a lower critical solution temperature (LCST) that enhance their capability in various biomedical applications such as drug delivery, tissue engineering, and wound dressings. Nevertheless, they have intrinsic shortcomings such as poor mechanical properties, limited loading capacity of actives, and poor biodegradability. Formulation of PNIPAM with diverse functional constituents to develop hydrogel composites is an efficient scheme to overcome these defects, which can significantly help for practicable application. This review reports on the latest developments in functional PNIPAM-based smart hydrogels for various biomedical applications. The first section describes the properties of PNIPAM-based hydrogels, followed by potential applications in diverse fields. Ultimately, this review summarizes the challenges and opportunities in this emerging area of research and development concerning this fascinating polymer-based system deep-rooted in chemistry and material science.

Effects of oppositely charged moieties on the self-assembly and biophysicochemical properties of polyurethane micelles

Gemini quaternary ammonium (GQA), a type of cationic surfactant, exhibits excellent micellization ability and acts as a cell internalization promoter to increase the permeability of the cell membrane. GQA is sensitive to ionic solutions, which disturb its stabilization and leads to the rapid degradation of its polymer micelles due to its unique hydrophilic N⁺ structure. However, the effect of negatively charged moieties in the polymer chains of GQA on its action in polymer micelles, typically with regard to its micellization and biological performance, remains unclear. In this work, a series of polyurethane micelles containing various ratios of oppositely charged moieties was prepared. We found that the interchain electrostatic interaction severely undermines the function of the GQA surfactant and hinders the self-assembly and stabilization of polyurethane micelles. Specifically, a hydrophilic corona with a longer length cannot completely overcome this effect. By regulating the ratio of oppositely charged moieties, micelles exhibited tunable biological properties, such as biocompatibility, cytotoxicity, cell internalization, and phagocytosis by macrophages. Based on our results, a moderate molecular weight of mPEG (Mn = 1900) and a slight positive surface potential (∼10 mV) are the best surface parameters for the comprehensive performance of the studied nanoplatforms. This study provides a further understanding of the electrostatic interaction effect on the properties of the cationic GQA, offering rational guidance for the design and fabrication of GQA polymer micelles.

Photo- and thermo-responsive microgels with supramolecular crosslinks for wavelength tunability of the volume phase transition temperature

Functional microgels have powerful applications, especially due to their quick responsiveness to different external stimuli such as temperature, pH, ionic strength, solvent composition and light. Here, we describe the synthesis of novel dual-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels and demonstrate that, in addition to temperature, light changes their properties. The crosslinks inside the microgels were achieved by the host-guest interactions between the trans azobenzene (transAzo) and β-cyclodextrin (βCD) units. transAzo can be photoisomerized to cisAzo which exhibits significant lower binding affinity to βCD. As a consequence, the crosslink density, and thus several microgel properties, can be controlled by light irradiation. Surprisingly, this irradiation with light can significantly change the volume phase transition temperature (VPTT) by several degrees centigrade, presumably due to the fact that the polar βCD shields the transAzo bound to it, whereas the unbound cisAzo is rather apolar. As a result, continuous irradiation with specific wavelengths until reaching the respective photostationary state allows for a full control over the VPTT within the physiologically relevant range between 32 °C and 38 °C.

Reducing thermal damage to adjacent normal tissue with dual thermo-responsive polymer via thermo-induced phase transition for precise photothermal theranosis

Photothermal therapy has been extensively studied to improve the light-to-heat efficiency for tumor ablation, but could cause severe damage to adjacent healthy tissue due to the thermal transfer, the random distribution of photothermal agents (PTAs), or combination hereof. Herein, we solve this dilemma with a material design strategy to develop a P(AAm-co-AN)-b-P(NIPAM-co-DMAa)-b-P(AAm-co-AN) ABA triblock copolymer by RAFT polymerization, which exhibits both UCST and LCST dual thermo-responsive behaviors in aqueous solution. The P(AAm-co-AN) block with appropriate AN content allows to finely tune its UCST to ∼ 43°C, which can effectively co-assemble with camptothecin (CPT) and Cy7-TCF, a near-infrared (NIR) PTA, realizing the photo-activated "on-demand" release of CPT and Cy7-TCF. The LCST of P(NIPAM-co-DMAa) segment is adjusted to ∼ 53°C by varying DMAa content, enabling an irreversible sol-to-gel transition. The heat transfer in hydrogel and heat dissipation at the interface of hydrogel-adjacent tissue are limited, resulting in selectively cell killing in tumor, with little hyperthermia in adjacent tissues. Moreover, the hydrogel continues to release CPT to enhance the synergistic efficacy of PTT with chemotherapy. These results suggest that dual thermo-responsive polymer can contribute PTT with high selectivity and negligible side effects for precise medicine. STATEMENT OF SIGNIFICANCE: Photothermal therapy exploits the susceptibility of tumor cells toward external light-induced hyperthermia, but can cause severe damage to adjacent healthy tissue due to thermal transfer, random distribution of photothermal agents (PTAs), or combination hereof. Here, we solve this dilemma by developing a P(AAm-co-AN)-b-P(NIPAM-co-DMAa)-b-P(AAm-co-AN) triblock copolymer with UCST and LCST dual thermo-responsive behaviors, realizing the sequential micelle-unimer-hydrogel phase transitions. The polymer can effectively encapsulate PTA/drug, achieve long systemic circulation, accumulate in tumor through EPR effect, regulate drug release by controlling tumor temperature above UCST via irradiation, and finally exhibit a sol-gel transition, eradicating the heat transfer to adjacent tissue. This represents a practicable strategy to guide the design of next-generation polymeric vector that can contribute PTT with negligible side effects.

Thermoresponsive Self-Assembly of Twofold Fluorescently Labeled Block Copolymers in Aqueous Solution and Microemulsions

A nonionic double hydrophilic block copolymer with a long permanently hydrophilic and a small thermoresponsive block is synthesized by reversible addition-fragmentation chain-transfer polymerization (RAFT). By employing a specifically designed chain-transfer agent, the polymer is functionalized with complementary end groups which are suited for Förster resonance energy transfer (FRET). The end group attached to the permanently hydrophilic block of poly(N,N-dimethylacrylamide) pDMAm is designed as a permanently hydrophobic segment ("sticker") comprising a long alkyl chain and the 4-aminonaphthalimide fluorophore. The other end attached to the thermoresponsive block of poly(N-isopropylacrylamide) pNiPAm incorporates a coumarin fluorophore. The temperature-dependent self-assembly of the twofold fluorescently labeled copolymer is studied in pure aqueous solution as well as in an o/w microemulsion by several techniques including turbidimetry, dynamic light scattering (DLS), and fluorescence spectroscopy. It is compared to the behaviors of the analogous twofold-labeled pDMAm and pNiPAm homopolymer references. The findings indicate that the block copolymer behaves as a polymeric surfactant at low temperatures, with one relatively small hydrophobic end block and an extended hydrophilic chain forming "hairy micelles". At elevated temperatures above the LCST phase transition of the pNiPAm block, however, the copolymer behaves as an associative telechelic polymer with two nonsymmetrical hydrophobic end blocks, which do not mix. Thus, instead of a network of bridged "flower micelles", large dynamic aggregates are formed. These are connected alternatingly by the original micellar cores as well as by clusters of the collapsed pNiPAm blocks. This type of structure is even more favored in the o/w microemulsion than in pure aqueous solution, as the microemulsion droplets constitute an attractive anchoring point for the hydrophobic dodecyl sticker but not for the collapsed pNiPAm chains.

Double thermoresponsive graft copolymers with different chain ends: feasible precursors for covalently crosslinked hydrogels

The tailored synthesis of graft copolymers from acrylic and methacrylic monomers can be accomplished solely through photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization. Samples with poly[oligo(ethylene glycol) methacrylate] (POEGMA) backbones synthesized under green light irradiation and poly(N-isopropylacrylamide) (PNIPAM) side chains growing under blue light irradiation are presented. As monitored by temperature-dependent dynamic light scattering (DLS) measurements and temperature-variable nuclear magnetic resonance (NMR) spectroscopy, the architecture of the graft copolymers allows unique two-step lower critical solution temperature (LCST) transitions in aqueous solutions. Meanwhile, different end-groups introduced by the corresponding RAFT agents affect the detailed thermoresponsive behavior remarkably. This RAFT strategy shows more advantages when the multiple trithiocarbonate groups are converted into thiol reactive pyridyl disulfide (PDS) groups via a facile post-polymerization modification. The PDS-terminated graft copolymer can then be regarded as a usable precursor for various applications, such as thermoresponsive hydrogels.

End-functionalized polymers by controlled/living radical polymerizations: synthesis and applications

This review focuses on end-functionalized polymers synthesized by controlled/living radical polymerizations and the applications in fields including bioconjugate formation, surface modification, topology construction, and self-assembly.

Thermal Response and Thermochromism of Methyl Red-Based Copolymer Systems - Coupled Responsiveness in Critical Solution Behaviour and Optical Absorption Properties

Until now, only limited experimental knowledge and sparse theoretical treatment about the mechanisms of thermochromism of azo dyes in solution has been available. Especially the coupling of thermoresponsiveness of polymers...

Precision synthesis for well-defined linear and/or architecturally controlled thermoresponsive poly(N-substituted acrylamide)s

We describe the progress in precision polymerizations of specific kinds of N-alkylacrylamides and N,N-dialkylacrylamides to produce polymers showing thermoresponsive properties in aqueous media, which representatively include the reversible-deactivation radical polymerizations...

Gated Photoreactivity of Pyrene Copolymers in Multiresponsive Cross-Linked starPEG-Hydrogels

The synthesis and manufacturing of multiresponsive polymer hydrogels using simple components is a notable challenge. Pyrene is an excimer-forming fluorophore mostly used as microenvironmental probe and for the localization of molecules in close proximity in artificial and biomaterials. Here we make use of the solvophobic preaggregation and photolysis properties of pyrene to construct multiresponsive hydrogels. We synthesize poly(ethylene glycol) (PEG) hydrogels from well-defined pyrene-substituted macro-cross-linkers and elucidate their intricate intra- and intermolecular excimer formation pathways. We find that controlling the water content of the hydrogels through the degree of swelling acts as a gating stimulus governing the photoinduced solvolysis of pyrenylmethyl esters from their poly(methacrylate) backbone. This allows the implementation of a simple transient photolithography process. We thus demonstrate that multiresponsive soft materials with complex optical and mechanical responses can be obtained with comparatively little synthetic effort.

Stimuli-Responsive, Hydrolyzable Poly(Vinyl Laurate-co-vinyl Acetate) Nanoparticle Platform for In Situ Release of Surfactants

A stimuli-responsive, sub-100 nm nanoparticle (NP) platform with a hydrolyzable ester side chain for in situ generation of surfactants is demonstrated. The NPs were synthesized via copolymerization of vinyl-laurate and vinyl-acetate [p-(VL-co-VA), 3:1 molar ratio] and stabilized with a protective poly(ethylene-glycol) shell. The NPs are ∼55 nm in diameter with a zeta potential of -54 mV. Hydrolysis kinetics in an accelerated, base-catalyzed reaction show release of about 11 and 30% of the available surfactant at 25 and 80 °C, respectively. The corresponding values in seawater are 22 and 76%. The efficiency of the released surfactant in reducing the interfacial tension, altering wettability, and stabilizing oil-water emulsion was investigated through contact angle measurements and laser confocal scanning microscopy and benchmarked to sodium laurate, a commercially available surfactant. All these measurements demonstrate both the efficacy of the NP system for surfactant delivery and the ability of the released surfactant to alter wettability and stabilize an oil-water emulsion.

A novel 'smart' PNIPAM-based copolymer for breast cancer targeted therapy: Synthesis, and characterization of dual pH/temperature-responsive lactoferrin-targeted PNIPAM-co-AA

Despite the active research towards introducing novel anticancer agents, the long-term sequelae and side effects of chemotherapy remain the major obstacle to achieving clinical success. Recent cancer research is now utilizing the medicinal chemistry toolbox to tailor novel 'smart' carrier systems that can reduce the major limitations of chemotherapy ranging from non-specificity and ubiquitous biodistribution to systemic toxicity. In this aspect, various stimuli-responsive polymers have gained considerable interest due to their intrinsic tumor targeting properties. Among these polymers, poly(N-isopropylacrylamide (PNIPAM) has been chemically modified to tune its thermoresponsivity or even copolymerized to endow new stimulus responsiveness for enhancing tumor targeting. Herein, we set our design rationale to impart additional active targeting entity to pH/temperature-responsive PNIPAM-based polymer for more efficient controlled payloads accumulation at the tumor through cellular internalization via synthesizing novel "super intelligent" lactoferrin conjugated PNIPAM-acrylic acid (LF-PNIPAM-co-AA) copolymer. The synthesized copolymer was physicochemically characterized and evaluated as a smart nanocarrier for targeting breast cancer. In this regard, Honokiol (HK) was utilized as a model anticancer drug and encapsulated in the nanoparticles to overcome its lipophilic nature and allow its parenteral administration, for achieving sustainable drug release with targeting action. Results showed that the developed HK-loaded LF-PNIPAM-co-AA nanohydrogels displayed high drug loading capacity reaching to 18.65 wt.% with excellent physical and serum stability. Moreover, the prepared HK-loaded nanohydrogels exhibited efficient in vitro and in vivo antitumor activities. In vivo, HK-loaded nanohydrogels demonstrated suppression of VEGF-1 and Ki-67 expression levels, besides inducing apoptosis through upregulating the expression level of active caspase-3 in breast cancer-bearing mice. Overall, the developed nanohydrogels (NGs) with pH and temperature responsivity provide a promising nanocarrier for anticancer treatment.

Near-Infrared-Triggered Photothermal Aggregation of Polymer-Grafted Gold Nanorods in a Simulated Blood Fluid

Gold nanorods were decorated with thermoresponsive copolymers of tailored architecture and constructed from N-isopropyl acrylamide and acrylamide. The copolymers were prepared via reversible addition-fragmentation chain transfer polymerization (RAFT) and immobilized on the gold nanorod surface taking advantage of the aurophilicity of its inherently formed trithiocarbonate groups. The topology as well as the average molecular weight of the copolymers was altered using either a monofunctional or 3-arm star RAFT agent. Two-dimensional arrays of the self-assembled core-shell nanostructures were fabricated by drop-casting showing tunable interparticle spacings. In a simulated blood fluid, the lower critical solution temperature of the nanohybrids could be modified over a significant temperature range around body temperature by adjusting the copolymer composition, the architecture, and/or the size of the polymer. The intrinsic photothermal properties of the gold nanorods were utilized to trigger particle aggregation by irradiation at 808 nm in the optical window of human tissues. In effect, a new nanohybrid system with remotely controllable aggregation via an external NIR-light stimulus for nanomedical applications was developed.

Effect of heterogeneous and homogeneous polymerisation on the structure of pNIPAm nanogels

The choice of the polymerisation temperature and initiator in the synthesis of poly(N-isopropylacrylamide)-based nanogels can significantly influence their structure, morphology and thermoresponsive properties.

Thermal Behaviour of Common Thermoresponsive Polymers in Phosphate Buffer and in Its Salt Solutions

Thermoresponsive polymers are a promising material for drug nanocarrier preparation, which makes the study of their aggregation in physiological conditions very important. In this paper, the thermal behaviour of the thermoresponsive polymers poly(N-isopropylacrylamide), poly(2-isopropyl-2-oxazoline-co-2-n-propyl-2-oxazoline) and poly[(2-hydroxyethyl methacrylate)-co-oligo(ethylene glycol) methyl ether methacrylate] were studied in phosphate buffer (PBS) and solutions of its salts in concentration as in PBS. The thermal response of the polymers was measured using UV-Vis and dynamic light scattering (DLS). The salts shifted the cloud point temperature (TCP) of the (co)polymers to higher values compared to the TCP of aqueous polymer solutions. In PBS and NaCl solutions, all polymers exhibited an unexpected and previously unreported transmittance profile. During heating, an additional aggregation of polymers appeared above the TCP accompanied by the formation of a precipitate. In monosodium phosphate solutions and pure water, the studied polymers showed lower critical solution temperature (LCST-type) behaviour. DLS measurements showed that a salt influenced the size of the resulting polymer particles. The sizes and stability of particles depended on the heating rate. In PBS and NaCl solutions, the size of particles in the dispersion decreased above 60 °C, and the precipitate appeared on the bottom of the cuvette. The additional aggregation of polymer and its falling out of solution may hinder the removal of carriers from the body and has to be taken into account when preparing nanocarriers.

Determining population densities in bimodal micellar solutions using contrast-variation small angle neutron scattering

Self-assembly of amphiphilic polymers in water is of fundamental and practical importance. Significant amounts of free unimers and associated micellar aggregates often coexist over a wide range of phase regions. The thermodynamic and kinetic properties of the microphase separation are closely related to the relative population density of unimers and micelles. Although the scattering technique has been employed to identify the structure of micellar aggregates as well as their time-evolution, the determination of the population ratio of micelles to unimers remains a challenging problem due to their difference in scattering power. Here, using small-angle neutron scattering (SANS), we present a comprehensive structural study of amphiphilic n-dodecyl-PNIPAm polymers, which shows a bimodal size distribution in water. By adjusting the deuterium/hydrogen ratio of water, the intra-micellar polymer and water distributions are obtained from the SANS spectra. The micellar size and number density are further determined, and the population densities of micelles and unimers are calculated to quantitatively address the degree of micellization at different temperatures. Our method can be used to provide an in-depth insight into the solution properties of microphase separation, which are present in many amphiphilic systems.

Influence of Buffers, Ionic Strength, and pH on the Volume Phase Transition Behavior of Acrylamide-Based Nanogels

The use of covalently crosslinked nanogels for applications in biology and medicine is dependent on their properties and characteristics, which often change because of the biological media involved. Understanding the role of salts, ionic strength and pH in altering specific properties is key to progress in this area. We studied the effect of both chemical structure and media environment on the thermoresponsive behavior of nanogels. A small library of methylenebisacrylamide (MBA) crosslinked nanogels were prepared using N-isopropylacrylamide (NIPAM) or N-n-propylacrylamide (NPAM), in combination with functional monomers N-hydroxyethylacrylamide (HEAM) and N-acryloyl-l-proline (APrOH). The thermoresponsive properties of nanogels were evaluated in phosphate buffer, tris-acetate buffer and Ringer HEPES, with varying concentrations and ionic strengths. The presence of ions facilitates the phase separation of nanogels, and this “salting-out” effect strongly depends on the electrolyte concentration as well as the specificity of individual anions, e.g., their positions in the Hofmeister series. A subtle change in the chemical structure of the side chain of the monomer from NIPAM to NPAM leads to a reduction of the volume phase transition temperature (VPTT) value by ~10 °C. The addition of hydrophilic comonomers such as HEAM, on the other hand, causes a ~20 °C shift in VPTT to higher values. The data highlight the significant role played by the chemical structure of the monomers used, with hydrophobicity and rigidity closely interlinked in determining thermoresponsive behavior. Furthermore, the volume phase transition temperature (VPTT) of nanogels copolymerized with ionizable APrOH comonomer can be tailored by changes in the pH of buffer solutions. This temperature-controlled phase transition is driven by intricate interplay involving the entropy of mixing, electrostatic interactions, conformational transitions, and structural rigidity. These results highlight the importance of understanding the physiochemical properties and behavior of covalently crosslinked nanogels in a biological environment prior to their applications in life-science, such as temperature/pH-triggered drug delivery systems.

Poly(N,N-bis(2-methoxyethyl)acrylamide), a thermoresponsive non-ionic polymer combining the amide and the ethyleneglycolether motifs

Poly(N,N-bis(2-methoxyethyl)acrylamide) (PbMOEAm) featuring two classical chemical motifs from non-ionic water-soluble polymers, namely, the amide and ethyleneglycolether moieties, was synthesized by reversible addition fragmentation transfer (RAFT) polymerization. This tertiary polyacrylamide is thermoresponsive exhibiting a lower critical solution temperature (LCST)–type phase transition. A series of homo- and block copolymers with varying molar masses but low dispersities and different end groups were prepared. Their thermoresponsive behavior in aqueous solution was analyzed via turbidimetry and dynamic light scattering (DLS). The cloud points (CP) increased with increasing molar masses, converging to 46 °C for 1 wt% solutions. This rise is attributed to the polymers’ hydrophobic end groups incorporated via the RAFT agents. When a surfactant-like strongly hydrophobic end group was attached using a functional RAFT agent, CP was lowered to 42 °C, i.e., closer to human body temperature. Also, the effect of added salts, in particular, the role of the Hofmeister series, on the phase transition of PbMOEAm was investigated, exemplified for the kosmotropic fluoride, intermediate chloride, and chaotropic thiocyanate anions. A pronounced shift of the cloud point of about 10 °C to lower or higher temperatures was observed for 0.2 M fluoride and thiocyanate, respectively. When PbMOEAm was attached to a long hydrophilic block of poly(N,N-dimethylacrylamide) (PDMAm), the cloud points of these block copolymers were strongly shifted towards higher temperatures. While no phase transition was observed for PDMAm-b-pbMOEAm with short thermoresponsive blocks, block copolymers with about equally sized PbMOEAm and PDMAm blocks underwent the coil-to-globule transition around 60 °C.

Amides and Heparin-Like Polymer Co-Functionalized Graphene Oxide Based Core @ Polyethersulfone Based Shell Beads for Bilirubin Adsorption

Excessive bilirubin in the body of patient with liver dysfunction or metabolic obstruction may cause jaundice with irreversible brain damage, and new type of adsorbent for bilirubin is under frequent investigation. Herein, graphene oxide based core @ polyethersulfone-based shell beads are fabricated by phase inversion method, amides and heparin-like polymer are introduced to functionalize the core-shell beads. The beads are successfully prepared with obvious core-shell structure, adequate thermostability and porous shell. Clotting times and protein adsorption are investigated to inspect the hemocompatibility property of the beads. The adsorption of bilirubin is systematically investigated by evaluating the effects of contacting time, initial concentration and temperature on the adsorption, which exhibits improved bilirubin adsorption amount for the beads with amides contained cores or/and shells. It is worth believing that the amides and heparin-like polymer co-functionalized core-shell beads may be utilized in the field of hemoperfusion for bilirubin adsorption.

The Two Phase Transitions of Hydrophobically End-Capped Poly(N-isopropylacrylamide)s in Water

High-sensitivity differential scanning calorimetry (HS-DSC) thermograms of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions present a sharp unimodal endotherm that signals the heat-induced dehydration/collapse of the PNIPAM chain. Similarly, α,ω-di-n-octadecyl-PNIPAM (C18-PN-C18) aqueous solutions exhibit a unimodal endotherm. In contrast, aqueous solutions of α,ω-hydrophobically modified PNIPAMs with polycyclic terminal groups, such as pyrenylbutyl (Py-PN-Py), adamantylethyl (Ad-PN-Ad), and azopyridine- (C12-PN-AzPy) moieties, exhibit bimodal thermograms. The origin of the two transitions was probed using microcalorimetry measurements, turbidity tests, variable temperature ¹H NMR (VT-NMR) spectroscopy, and 2-dimensional NOESY experiments with solutions of polymers of molar mass (M_n) from 5 to 20 kDa and polymer concentrations of 0.1 to 3.0 mg/mL. The analysis outcome led us to conclude that the difference of the thermograms reflects the distinct self-assembly structures of the polymers. C18-PN-C18 assembles in water in the form of flower micelles held together by a core of tightly packed n-C18 chains. In contrast, polymers end-tagged with azopyridine, pyrenylbutyl, or adamantylethyl form a loose core that allows chain ends to escape from the micelles, to reinsert in them, or to dangle in surrounding water. The predominant low temperature (T₁) endotherm, which is insensitive to polymer concentration, corresponds to the dehydration/collapse of PNIPAM chains within the micelles, while the higher temperature (T₂) endotherm is attributed to the dehydration of dangling chains and intermicellar bridges. This study of the two phase transitions of telechelic PNIPAM homopolymer highlights the rich variety of morphologies attainable via responsive hydrophobically modified aqueous polymers and may open the way to a variety of practical applications.

Solvent effects leading to a variety of different 2D structures in the self-assembly of a crystalline-coil block copolymer with an amphiphilic corona-forming block

We describe a polyferrocenyldimethylsilane (PFS) block copolymer (BCP), PFS27-b-P(TDMA65-ran-OEGMA69) (the subscripts refer to the mean degrees of polymerization), in which the corona-forming block is a random brush copolymer of hydrophobic tetradecyl methacrylate (TDMA) and hydrophilic oligo(ethylene glycol) methyl ether methacrylate (OEGMA). Thus, the corona is amphiphilic. This BCP generates a remarkable series of different structures when subjected to crystallization-driven self-assembly (CDSA) in solvents of different polarity. Long ribbon-like micelles formed in isopropanol, and their lengths could be controlled using both self-seeding and seeded growth protocols. In hexanol, the BCP formed more complex structures. These objects consisted of oval platelets connected to long fiber-like micelles that were uniform in width but polydisperse in length. In octane, relatively uniform rectangular platelets formed. Finally, a distinct morphology formed in a mixture of octane/hexanol, namely uniform oval structures, whose height corresponded to the fully extended PFS block. Both long and short axes of these ovals increased with the initial annealing temperature and with the BCP concentration. The self-seeding protocol also afforded uniform two-dimensional structures. Seeded growth experiments, in which a solution of the BCP in THF was added to a colloidal solution of the oval micelles led to a linear increase in area while maintaining the aspect ratio of the ovals. These experiments demonstrate the powerful effect of the amphiphilic corona chains on the CDSA of a core crystalline BCP in solvents of different hydrophilicity.

Recent Advances in Understanding the Micro- and Nanoscale Phenomena of Amorphous Solid Dispersions

Many pharmaceutical drugs in the marketplace and discovery pipeline suffer from poor aqueous solubility, thereby limiting their effectiveness for oral delivery. The use of an amorphous solid dispersion (ASD), a mixture of an active pharmaceutical ingredient and a polymer excipient, greatly enhances the aqueous dissolution performance of a drug without the need for chemical modification. Although this method is versatile and scalable, deficient understanding of the interactions between drugs and polymers inhibits ASD rational design. This current Review details recent progress in understanding the mechanisms that control ASD performance. In the solid-state, the use of high-resolution theoretical, computational, and experimental tools resolved the influence of drug/polymer phase behavior and dynamics on stability during storage. During dissolution in aqueous media, novel characterization methods revealed that ASDs can form complex nanostructures, which maintain and improve supersaturation of the drug. The studies discussed here illustrate that nanoscale phenomena, which have been directly observed and quantified, strongly affect the stability and bioavailability of ASD systems, and provide a promising direction for optimizing drug/polymer formulations.

A new visible light and temperature responsive diblock copolymer

A visible light and temperature responsive diblock copolymer of poly[6-(2,6,2′,6′-tetramethoxy-4′-oxyazobenzene) hexyl methacrylate]-block-poly(N-isopropylacrylamide) (PmAzo-b-PNIPAM) was synthesized via RAFT polymerization by carefully tuning the polymerization conditions.