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5-fluorouracil (5-FU) forms the basis of many chemotherapy regimens and is one of the most common preferred chemotherapeutic drugs. In this study, the synthesis of temperature and pH responsive hydrogels in the release of 5-fluorouracil (5-FU) was studied to prevent drug release during blood circulation and uncontrolled overdose drug concentration at the tumor site. In this regard, the synthesis of temperature sensitive polymer Poly(N-vinylcaprolactam) PNVCL, temperature and pH sensitive polymers P(NVCL-co-VIm) and P(NVCL-co-VIm)/PVP hydrogels was carried out by the free radical polymerization method. DSC analysis revealed that as a result of copolymerization of PNVCL with hydrophilic 1-vinylimidazole (VIm) and polyvinylpyrrolidone (PVP), the lower critical solution temperature (LCST) increased and was close to the human body temperature. In addition, it was concluded from pH sensitivity analysis that the swelling ratios of the hydrogels changed with the medium pH. Additionally, hydrogels swelled in the acidic medium but shrunk in the alkaline medium. Accordingly, 5-FU release was investigated in different temperatures (25 °C and 37 °C) and pH (pH 5.5 and 7.4) medium and approximately 96% drug release was reached at 37 °C and pH 7.4. Consequently, P(NVCL-co-VIm)/PVP hydrogels at different pH and temperature mediums could be beneficially utilized as a material with the potential to be used in targeted drug delivery systems. [ABSTRACT FROM AUTHOR]

This article reports the synthesis of poly(N-vinylcaprolactam-co-N-methylolacrylamide) (P(NVCL-co-NMA)) nanogels and investigates their thermo-/pH-responsive behavior. The formation of nanogels was synthesized using free radical emulsion polymerization by varying the monomer composition of NVCL:NMA, and their molecular structure was characterized by 1H-NMR and FTIR. It was found that the nanogels were successfully prepared, and the nanogels exhibited LCST-type phase transition behavior. Cloud point transition temperature (Tc) was studied as a function of copolymer composition, MBA concentration, and pH of the solution by exploring their changes in turbidity using UV–vis spectrophotometer. Our studies reveal that Tc nanogels increased with increasing concentration of NMA, which is due to the hydrophilicity of NMA. Our research also demonstrated that the increase in MBA percentage could decrease the Tc of the synthesized nanogels. Interestingly, P(NVCL-co-NMA) nanogels showed not only a thermoresponsive behavior but also a pH response with increasing Tc in a strong acidic environment owing to the H-bonds within the polymer chains. The results show that nanogels with initial monomer composition of NVCL and NMA of 75% and 25%, respectively, and using 4% of MBA showed Tc around 35°C at pH 7.4. In addition, DLS studies also confirmed this result since the particle sizes became much larger after surpassing the temperature of 35°C. Due to this founding, such nanogels might have potential application in controlled release. Nevertheless, further studies regarding the adjustment of Tc are still needed.

This work focuses on the pH‐triggered disassembly of supramacromolecular microgels, which are composed of the temperature‐responsive poly(N‐vinylcaprolactam) (PVCL) and the natural polyphenol tannic acid (TA). A systematic investigation of the microgel formation demonstrates that a retarded addition of tannic acid during semi‐batch precipitation polymerization influences the yield, chemical composition, and properties of the microgels to a great extent. Microgel properties, such as size, deformability, and chemical stability, can be easily tuned by varying the ratio between both building blocks PVCL and TA. Finally, the pH‐triggered disassembly of supramacromolecular microgels at different pH and temperatures demonstrates that their chemical structure can precisely control the degradation profile. Temperatures lower than the volume phase transition temperature (VPTT) of PVCL (T < 32 °C) and a pH > 10 result in a complete disassembly of the microgels into PVCL chains and TA due to the destruction of the hydrogen bonds responsible for the formation of a colloidal microgel. Interestingly, at temperatures above VPTT, the microgels keep their integrity due to enhanced hydrophobic interactions between the polymer chains of the microgel and are no longer affected by pH changes. [ABSTRACT FROM AUTHOR]

This article reports the synthesis of poly(N-vinylcaprolactam-co-N-methylolacrylamide) (P(NVCL-co-NMA)) nanogels and investigates their thermo-/pH-responsive behavior. The formation of nanogels was synthesized using free radical emulsion polymerization by varying the monomer composition of NVCL:NMA, and their molecular structure was characterized by 1H-NMR and FTIR. It was found that the nanogels were successfully prepared, and the nanogels exhibited LCST-type phase transition behavior. Cloud point transition temperature (Tc) was studied as a function of copolymer composition, MBA concentration, and pH of the solution by exploring their changes in turbidity using UV–vis spectrophotometer. Our studies reveal that Tc nanogels increased with increasing concentration of NMA, which is due to the hydrophilicity of NMA. Our research also demonstrated that the increase in MBA percentage could decrease the Tc of the synthesized nanogels. Interestingly, P(NVCL-co-NMA) nanogels showed not only a thermoresponsive behavior but also a pH response with increasing Tc in a strong acidic environment owing to the H-bonds within the polymer chains. The results show that nanogels with initial monomer composition of NVCL and NMA of 75% and 25%, respectively, and using 4% of MBA showed Tc around 35°C at pH 7.4. In addition, DLS studies also confirmed this result since the particle sizes became much larger after surpassing the temperature of 35°C. Due to this founding, such nanogels might have potential application in controlled release. Nevertheless, further studies regarding the adjustment of Tc are still needed. [ABSTRACT FROM AUTHOR]

Ibuprofen sodium (IBP) is a commonly used NSAID for multiple pain conditions. However, despite its extensive use, it is associated with multiple GIT adverse effects after oral administration. In the present study, we have fabricated thermoresponsive gel depot using Poly (N-vinylcaprolactam) and sodium alginate as polymers. The designed formulations are intended to be used as IBP depot after being administered subcutaneously. The sol-gel phase transition temperature and gelation time of gel samples were optimized by tube inversion, rheological exploration and optical transmittances. Temperature sweep experiments confirmed that optimized gel samples have sol-gel transition between 32°C and 37°C. Swelling and in vitro drug release displayed that optimized gels have maximum swelling and IBP release at pH 7.4 and at 35°C confirming their pH/thermo sensitivity. The degradation profile of hydrogels displayed controlled degradation for 6 days that with increasing contents. MTT assay showed L929 cells displayed more than 90% cell viability against blank and IBP-loaded PNVCL/NaAlg hydrogels at optimized concentrations. Fourier transform infrared spectroscopy confirmed the polymer blend hydrogels structure formation. Thermogravimetric analysis confirmed the presence of thermoresponsive moieties and thermal stability of polymer blend hydrogel sample. While scanning electron microscopy showed that hydrogel has channels in structure that might facilitate the diffusion of solvent. Results concluded that PNVCL/NaAlg hydrogels can be utilized as IBP sustained depot following subcutaneous application invivo and GIT adverse effects could be avoided associated with its oral administration., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2024 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Smart cotton fibers with temperature-driven sensitivity were developed by simple finishing with poly(N-vinylcaprolactam-co-tricyanofuranhydrazone);PVCH.Vinyl-bearing tricyanofuranhydrazone was prepared by an azo-coupling of 2-allyloxy-4-nitroaniline diazonium salt with tricyanofuran. Poly(N-vinylcaprolactam) labeled with tricyanofuranhydrazone probe was then prepared in situ by free radical polymerization. The chemical formulae of the hydrazone chromophore and PVCH were examined by FTIR, NMR and CHN elemental analysis. The PVCH-finished cotton functioned as a thermochromic assay producing an instantaneous colorimetric change from yellow to purple when the temperature increases from 34 to 49 °C. Changes in color were studied by the CIE Lab color parameters. The absorbance spectra showed a temperature-driven red shift from 429 to 564 nm. This can be attributed to the formation of push-π-pull hydrazone type chromophore due to temperature-driven proton abstraction leading to intramolecular charge transfer. The surface morphology of cotton immobilized with poly(VC–co–H) nanofibers was examined by scanning electron microscope (SEM) and infrared spectroscopy (FT-IR). The PVCH nanofibers were also inspected by transmission electron microscopy (TEM), showing fibers with diameter of 2–10 nm and length of 148–152 nm. No considerable defects were detected in bending length and permeability to air of the PVCH-finished fibers. In addition, high colorfastness properties were observed for the treated cotton substrates. Upon exposure to gaseous ammonia, the vapochromic cotton was able to rapidly change color from yellow to purple, and then recover back to yellow instantly when removing the vapochromic fabric away from the ammonia source. The current cotton assay showed a detection limit (LOD) of 10 to 250 ppm for aqueous ammonia. The cytotoxic properties of the thermochromic cotton fibers were also examined. Mechanistic study accounting for the thermochromic activity of poly(N-vinylcaprolactam-co-tricyanofuranhydrazone) is proposed. [ABSTRACT FROM AUTHOR]

Thermosensitive nanocomposites of poly(N-vinylcaprolactam) and hydroxyapatite nanoparticles synthesized by hydrothermal processing were prepared by in situ polymerization in dimethyl sulfoxide, using azobisisobutyronitrile as a radical initiator. Polymerization was performed in the presence of nanoparticles (1% w/w) at 70 °C during 4 h to obtain a new stimuli-responsive biomaterial for medical/dental applications. The biocompatibility of the injectable nanocomposites was verified through the survival ratio and eclosion ratio of zebrafish embryos, which revealed a polymer of low toxicity, showing an average survival ratio of 93% after 96 h of exposition up to 25% of nanocomposites in water. In this sense, this work introduces an injectable hydrogel biomaterial with potential osseointegration properties for bone tissue engineering. [ABSTRACT FROM AUTHOR]

A new MoS2/Fe3O4 dendrimer grafted polystyrene (PST)/poly(N-vinylcaprolactam) (PNVCL) was prepared as a temperature-sensitive nanocomposite for adsorption and controlled release of sertraline. The maximum adsorption capacity of nanocomposite for sertraline was about 5.24 mgg−1 under optimum pH of 8, equilibrium time of 30 min and adsorbent dosage of 5 gL−1. The kinetic of sertraline sorption follow the pseudo-second-order kinetic model, and the corresponding isotherm was well fitted with the Redlich–Peterson isotherm model. The highest release of sertraline was obtained at 50 °C during 24 h. The non-Fickian diffusion of the sertraline release from nanocomposite was achieved at 37 and 50 °C. [ABSTRACT FROM AUTHOR]

Chemical pretreatment followed by enzymatic hydrolysis has been regarded as a viable way to produce fermentable sugars. Phenylsulfonic acid (PSA) pretreatment could efficiently fractionate the non-cellulosic components (hemicelluloses and lignin) from bamboo and result in increased cellulose accessibility that was 10 times that of untreated bamboo. However, deposited lignin could trigger non-productive adsorption to enzymes, which therefore significantly decreased the enzymatic hydrolysis efficiency of PSA-pretreated bamboo substrates. Herein, poly(N-vinylcaprolactam) (PNVCL), a non-ionic surfactant, was developed as a novel additive for overcoming the non-productive adsorption of lignin during enzymatic hydrolysis. PNVCL was found to be not only more effective than those of commonly used lignosulfonate and polyvinyl alcohol for overcoming the negative effect of lignin, but also comparable to the robust Tween 20 and bovine serum albumin additives. A PNVCL loading at 1.2 g/L during enzymatic hydrolysis of PSA pretreated bamboo substrate could achieve an 80% cellulosic enzymatic conversion and meanwhile reduce the cellulase loading by three times as compared to that without additive. Mechanistic investigations indicated that PNVCL could block lignin residues through hydrophobic interactions and the resultant PNVCL coating resisted the adsorption of cellulase via electrostatic repulsion and/or hydration. This practical method can improve the lignocellulosic enzymatic hydrolysis efficiency and thereby increase the productivity and profitability of biorefinery.

We report on a simple approach for synthesis of temperature-responsive giant unilamellar vesicles (GUVs) from poly(N-vinylcaprolactam)15-block-poly(dimethylsiloxane)65-block-poly(N-vinylcaprolactam)15 (PVCL15-PDMS65-PVCL15) triblock copolymer and non-temperature responsive small and giant vesicles from novel poly(N-vinylpyrrolidone)-block-poly(dimethylsiloxane)-block-poly(N-vinylpyrrolidone) (PVPON15-PDMS65-PVPON15 and PVPON6-PDMS30-PVPON6) triblock copolymers using microfluidic mixing at 25 °C. We show that temperature-responsive PVCL15-PDMS65-PVCL15 GUVs with the average diameter of 1.4 ± 0.2 µm while being stable at room temperature for at least 14 days, transformed irreversibly into small vesicles of 168 ± 40 nm after incubation of their aqueous solution at 42 °C for 24 h. We hypothesized that this transformation is induced by local compressive stresses of the vesicle membrane due to the collapse of PVCL blocks above the copolymer lower critical solution temperature (LCST) leading to the decrease of the vesicle membrane thickness. Consequently, we found that the temperature-induced size transformation of the PVCL-based GUVs at 42°C can be suppressed by substituting PVCL with its hydrophilic homologue PVPON, or by suppressing the PVCL's LCST behavior through hydrogen-bonding with tannic acid molecules. In the former case, novel PVPONn-PDMSm-PVPONn triblock copolymers (n = 15, m = 65 and n = 6, m = 30) assemble into vesicles stable from 25 °C to 55 °C as confirmed by optical and electron microscopy, dynamic light scattering (DLS) and small-angle neutron scattering (SANS). In the latter, hydrogen bonding interactions of PVCL with the polyphenol tannic acid (TA) at room temperature resulted in stable PVCL-based GUVs at 42°C as confirmed by optical, electron, and atomic force microscopies. We also found that physical crosslinking of the PVCL corona through hydrogen bonding with TA in PVCL15-PDMS65-PVCL15 GUVs will delay their low pH-induced degradation at 37°C by 48 h compared to non-modified GUVs. Our findings open opportunities for the development of temperature-regulated stable micro-vehicles that would change their structural characteristics in the physiologically relevant temperature range from 25 to 42°C and can be utilized for cell mimicking studies. The developed GUVs also have potential in theranostic drug delivery as substitutes for polymer microcapsules and lipid microbubbles as well as for stimuli-triggered sensing, protection, and rapid response in an aqueous environment.

Limited tissue selectivity and targeting of anticancer therapeutics in systemic administration can produce harmful side effects in the body. Various polymer nano-vehicles have been developed to encapsulate therapeutics and prevent premature drug release. Dually responsive polymeric vesicles (polymersomes) assembled from temperature-/pH-sensitive block copolymers are particularly interesting for the delivery of encapsulated therapeutics to targeted tumors and inflamed tissues. We have previously demonstrated that temperature-responsive poly(N-vinylcaprolactam) (PVCL)-b-poly(dimethylsiloxane) (PDMS)-b-PVCL polymersomes exhibit high loading efficiency of anticancer therapeutics in physiological conditions. However, the in-vivo toxicity of these polymersomes as biocompatible materials has not yet been explored. Nevertheless, developing an advanced therapeutic nanocarrier must provide the knowledge of possible risks from the material’s toxicity to support its future clinical research in humans. Herein, we studied pH-induced degradation of PVCL10-b-PDMS65-b-PVCL10 vesicles in-situ and their dually (pH- and temperature-) responsive release of the anticancer drug, doxorubicin, using NMR, DLS, TEM, and absorbance spectroscopy. The toxic potential of the polymersomes was evaluated in-vivo by intravenous injection (40 mg kg−1 single dose) of PVCL10-PDMS65-PVCL10 vesicles to mice. The sub-acute toxicity study (14 days) included gravimetric, histological, and hematological analyses and provided evidence for good biocompatibility and non-toxicity of the biomaterial. These results show the potential of these vesicles to be used in clinical research.

Aim: Smart mesoporous silica nanoparticles (MSNs) coated with carbon dots (CDs) and poly(N-vinylcaprolactam) (PNVCL) as a mixed shell (CDs/PNVCL polymer grafted MSNs) were prepared for pH-trigged anticancer drug release and real-time monitoring. Materials & methods: The amino-terminated PNVCL and amino-rich CDs were grafted onto the surface of aldehyde group functionalized MSNs through Schiff base reaction. Doxorubicin (DOX) was loaded into the prepared nanoparticles. Results: DOX could be quickly released in the tumor environment, leading to cell apoptosis. The linear fit between the percentage of released DOX and the fluorescence intensity of CDs indicated that the change in fluorescence intensity could be used to monitor drug release in real time. Conclusion: The as-prepared CDs/PNVCL polymer grafted MSNs are promising candidates for integrating controllable release and real-time monitoring in cancer treatment. [ABSTRACT FROM AUTHOR]

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• Small hydrophilic groups affected both KHI performance and biodegradability of PVCap. • Appropriate amphiphilic was essential for effective KHIs. • Groups can be expanded to lots of biodegradable chains for green and efficient KHIs. Traditional amide-based hydrate inhibitors, vital for preventing blockages, face limitations due to increasingly stringent environmental regulations. This study focuses on modifying poly(N-vinylcaprolactam) (PVCap) to improve its inhibition and biodegradation properties, by introducing –OH, –NH 2 , or –COOH groups into the molecular structure. The results revealed that the –OH group significantly improved both hydrate inhibition and biodegradability, while the –COOH and - NH 2 groups had moderate and counter-effects, respectively. Compared to end hydroxyl modification, multiple –OH groups in the vinylcaprolactam/vinylalcohol copolymer weaken the inhibition effect, despite enhancing biodegradability. Optimal hydrophilicity was found to enhance PVCap's KHI performance, emphasizing the delicate balance needed to optimize stability and effectiveness. PXRD, Raman spectroscopy and interfacial tension tests were used to elucidate the impact of the modified PVCaps on hydrate structure and gas–liquid interfacial properties. The results further highlighted the significance of appropriate amphiphilicity in augmenting the KHI effect of the modified PVCaps. [ABSTRACT FROM AUTHOR]

Poly (N -vinylcaprolactam) (PNVCL) is a thermoresponsive, biocompatible, non-toxic polymer with a phase transition temperature from hydrophilic to hydrophobic state (T pt) close to the physiological one. This temperature is influenced by PNVCL molar mass and its copolymerization. In this work, gamma radiation at doses of 5 and 20 kGy was used to graft PNVCL chains onto films of thermoplastic polyurethane (TPU). PNVCL homopolymers were also developed by gamma radiation at the same conditions. The materials were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), viscometry and thermogravimetric analaysis (TGA). PNVCL grafting enabled thermoresponsive character to TPU films, as observed by changes in water-surface contact angles above and below T pt. The T pt of the developed homopolymers determined by cloud point and rheological analysis was close to 30 °C. These results demonstrated the feasibility of developing a graft copolymer with thermoresponsive properties, with the innovation of grafting PNVCL onto TPU films using gamma radiation. • A graft of PNVCL onto TPU films and polymerization of NVCL were synthesized by gamma-radiation. • Different Mv of the PNVCL homopolymers were obtained with the radiation dose conditions. • The T pt of the developed homopolymers was close to 30 °C. • The TPU-g-PNVCL samples showed the presence of both polymers was even after multiple washes. • The thermoresponsive character of TPU-g-PNVCLs were observed by water contact angle. [ABSTRACT FROM AUTHOR]

Thermoresponsive poly (N -vinylcaprolactam) (PVCL) has received growing interest due to a temperature-induced phase transition, which switches its solubility in aqueous solutions. However, the lower critical solution temperature (LCST) of PVCL is greatly influenced by the molecular weight, morphology and the environment. Therefore, despite of numerous experimental studies of the thermal response of PVCL, a driving force and a molecular origin of conformation transitions in solution remain far less studied. To get a better understanding of the coil-to-globule conformation transition of PVCL in aqueous solution, we examined the structure and conformation dynamics of a single-chain PVCL 30 in a temperature range of 280–360 K by using atomistic molecular dynamics (MD) simulations. The united-atom GROMOS G53a6 force field was re-parameterized and fine-tuned by DFT calculations to reproduce the experimental LCST transition of PVCL. Our MD model reproduces the LCST transition of PVCL 30 to occur within a temperature range of 34.6–38.5°. MD simulation results suggest a significant difference between the hydration state of the carbonyl group of PVCL below and above the LCST threshold. The analysis of the number of hydrogen bonds of PVCL with water molecules demonstrates that dehydration of the polymer plays an important role and drives the temperature-induced polymer collapse. Finally, the developed MD model and FF parameters were successfully tested for large-scale systems, such as mixture PVCL 30 oligomer and single-chain PVCL 816 polymer, respectively. Image 1 • The new atomistic MD model for thermoresponsive poly (N -vinylcaprolactam) (PVCL) was developed. • The MD model reproduced the experimental conformation transition with the lower critical solution temperature (LCST) of 34.6–38.5 °C. • The structural analysis indicated that dehydration of the polymer and the weakening of polymer-water H-bonding play a crucial role in the temperature-induced polymer collapse. [ABSTRACT FROM AUTHOR]

The influence of different salts and pH on the stability of the aqueous dispersion of multiwalled carbon nanotubes (MWCNTs) non-covalently modified by thermosensitive poly(N-vinylcaprolactam) (PVCL) was studied. The PVCL/MWCNT dispersion was prepared by adding MWCNTs into aqueous PVCL solution with the subsequent ultrasonication and centrifugation. The morphology of MWCNTs and MWCNT/PVCL composites was characterized by TEM. The aggregation temperatures of the MWCNT/PVCL dispersion and the lower critical solution temperature (LCST) of PVCL aqueous solution were determined for different salt types and concentrations as well as pH in the temperature range between 20 and 60 °C. Specific ion effect on LCST of PVCL was analyzed in terms of the Hofmeister series. In the presence of kosmotropes, both the MWCNT/PVCL dispersion aggregation temperature and the LCST of PVCL are well consistent with the Hofmeister series of ions. However, opposite trends were observed for LCST of PVCL and the MWCNT/PVCL dispersion aggregation temperature when adding chaotropic anions. The dynamic light scattering (DLS) technique was used to study the PVCL aggregation kinetics at a temperature above the LCST at different pH values. These results demonstrate that specific thermoresponsive properties of the MWCNT/PVCL dispersion at pH < 3 correlate with the behavior of the individual PVCL macromolecules in acid media above the LCST. Graphical abstract [ABSTRACT FROM AUTHOR]

Polymer material used for hydrogel should have capability to swell and to keep water molecules in its structure without solubilised in water. Natural polymers has functional groups which can perform as active sites in modification to produce polymer with better characteristic. Chitosan is a natural polymer which has good swelling ability but lack of structural strength. Synthesis of chitosan hydrogel by interpenetrating polymer network (IPN) will increase its strength through crosslinking. In this research, the first step of modification was the synthesis of chitosan polymer network crosslinked by acetaldehyde. The next step was the synthesis of PNVCL polymer network crosslinked by N,N-methylbisacrylamide (MBA) through free radical polymerization of NVCL monomer with ammonium persulfat (APS) as the initiatior. Optimum reaction time, chitosan/PNVCL ratio (w/w %), concentration of crosslinker agent, and concentration of initiator had been observed. The optimum conditions were obtained as followed: 2 hours reaction, the ratio chitosan/PNVCL of 90:10 (w/w %), %-w MBA concentration of 0.5%, and APS concentration of 3%. The swelling ratio of the hydrogel was 380.66% while the crosslinking degree was 60.85%. Fourier transfor infrared spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), Scanning Electron Microscope (SEM), and X-Ray diffraction (XRD) were used for the characterization of the hydrogel.

Hydrocortisone, a commonly used anti-inflammatory drug, has limited aqueous solubility and several side effects. To address this challenge, as a proof-of-concept, this article demonstrates the development of a controlled-release drug delivery system (DDS) for hydrocortisone using chitosan-grafted poly( N -vinylcaprolactam) (CS- g -PNVCL)-coated core-shell Fe 3 O 4 @SiO 2 nanoformulations (NFs). Reported magnetic nanoparticles (NPs) were synthesized and modified with silica, PNVCL, and CS precursors to enhance the biocompatibility of DDS and drug-loading efficiency. The release rate of hydrocortisone from Fe 3 O 4 @SiO 2 @CS- g -PNVCL NFs was observed to be higher at lower pH values, and the smart polymer coating demonstrated temperature responsiveness, facilitating drug release at higher temperatures. Fe 3 O 4 @SiO 2 @CS- g -PNVCL NFs exhibited a cell viability of around 97.2 to 87.3% (5-100 μg/mL) after 24-48 h, while the hydrocortisone-NFs had a cell viability of around 93.2 to 82.3%. Our findings suggest that CS- g -PNVCL-coated Fe 3 O 4 @SiO 2 NPs effectively enhance the solubility, loading capacity, and targeted delivery of poorly soluble drugs, thereby improving their therapeutic efficacy and bioavailability.

Poly(N-vinylcaprolactam) (PNVCL) is attracting increasing interest as a polymer for biomedical application. However, it is not biodegradable, which is an important drawback for such applications. The present paper describes the synthesis and characterization of novel thermosensitive PNVCL copolymers able to hydrolytically degrade, which were prepared by the RAFT/MADIX copolymerization of NVCL and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO). The RAFT/MADIX polymerization process displayed a moderate degree of control under the experimental conditions employed as proven by GPC measurements. The formation of the NVCL-BMDO copolymers was demonstrated by 1H NMR analyses which showed the presence of the in-chain ester groups resulted from the ring-opening polymerization of BMDO. The BMDO content of the copolymers was much lower than in the feed, indicating a higher reactivity of NVCL, which was confirmed through the estimation of the monomer reactivity ratios by applying the non-linear least squares method to fit the experimental results to the Lowry-Meyer integrated form of the Mayo-Lewis copolymer composition equation. The glass transition temperature of the copolymers diminished with the BMDO unit concentration within the chain. The phase transition temperature of the copolymers in 0.5-wt% aqueous solution decreased with the BMDO content as proven by transmittance measurements, in agreement with the increasing hydrophobic character. The degradability of the copolymers was demonstrated by the hydrolysis of the in-chain ester groups in 1-N KOH solution. The degraded polymer displayed a higher phase transition temperature than the original polymer, as expected. The results described within this paper may find applications for the synthesis of new biomaterials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Thermosensitive PNVCL was synthesized by radical polymerization. • PNVCL/EC/Eudragit hybrid fibers were fabricated by twin-jet electrospinning. • The wettability of PNVCL-containing fibers changed as the temperature increased. • KET loaded-fibers showed dual-sensitive properties with sustained release. Abstract We report a dual-responsive drug delivery system prepared by electrospinning. Blend fibers of poly(N-vinylcaprolactam) (PNVCL) and ethyl cellulose (EC) were first prepared, with the aim of developing thermoresponsive sustained release formulations. Eudragit L100-based fibers were then generated to yield pH-sensitive materials. Attempts to produce three-polymer fibers of EC, PNVCL and Eudragit were unsuccessful, and therefore hybrid mats containing two fiber populations (one made of PNVCL/EC, one comprising Eudragit) were instead fabricated by twin-jet electrospinning. Analogous drug-loaded versions of all the formulations were also prepared containing ketoprofen (KET). The fibers were largely smooth and homogeneous, and the addition of KET did not affect their morphology. The PNVCL-containing fiber mats changed from being hydrophilic to hydrophobic when the temperature was increased through the lower critical solution temperature of 33 °C. In vitro drug release profiles showed that the hybrid fiber mats were able to combine the properties of the three polymers, exhibiting both pH-sensitive and thermosensitive properties with sustained release. In addition, they were found to be nontoxic and suitable for cell growth. This study therefore demonstrates that PNVCL/EC/KET-Eudragit/KET multicomponent fiber mats comprise effective and biocompatible materials for targeted drug delivery. [ABSTRACT FROM AUTHOR]

The aim of this research was to synthesize Poly(N-vinylcaprolactam) (PNVCL) with the incorporation of hydrophilic acetic acid with thermosensitive N-vinylcaprolactam for potential drug delivery applications. Preparation of the heterogeneous mixture involved photopolymerization of a combination of N-vinylcaprolactam and acetic acid at different ratios. By altering the feed ratio, hydrogels were synthesized to have lower critical solution temperature close to physiological temperature. This ability to shift the phase transition temperature of PNVCL provides excellent flexibility in tailoring transitions to suit physiological temperature, inheriting great potential in drug delivery. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present study is the design and development of thermoresponsive nanogels based on ulvan, a sulphated heteropolysaccharide of algal origins with unique biological and chemical properties. Hybrid nanogels are successfully synthesized by means of UV‐initiated radical copolymerization of N‐vinylcaprolactam with an ulvan derivate as a novel crosslinker. In nanogels, the ulvan‐grafted poly(N‐vinylcaprolactam) chains represent the thermoresponsive component. The most promising candidates, selected after a thorough physical–chemical characterization of nanogels in terms of size and responsivity to thermal variation at physiological conditions, are loaded with bovine serum albumin (BSA) as model bioactive compound. The developed nanogels display BAS loading efficiency values similar to those obtained by using synthetic crosslinkers, and thus indicating the suitability of the developed ulvan‐acrylate to act as novel macromolecular crosslinker for thermoresponsive nanogels preparation. [ABSTRACT FROM AUTHOR]

A series of reactive poly([2-(acryloyloxy)ethyl]trimethylammonium chloride) (P(AETAC)) cationic polymers with varying degrees of polymerization were synthesized by RAFT/MADIX polymerization and investigated as stabilizers for the emulsion polymerization of N-vinylcaprolactam (PVCL) in the presence of a cross-linker. It was demonstrated that the xanthate chain end of the cationic P(AETAC-X) polymers played a crucial role to produce stable cationic PVCL-based microgels at higher initial solids content (5-10 wt %) than usually reported for the synthesis of PVCL microgels. The thermoresponsive PVCL microgels with cationic shell undergo a reversible volume shrinkage upon heating in the absence of any hysteresis in accordance with the narrow particle size distribution. The values of the volume phase transition temperature ranged between 28 and 30 °C for the microgels synthesized using 4 and 8 wt % of P(AETAC-X) based on VCL. The presence of a cationic outer shell onto the microgels was evidenced by the positive values of the electrophoretic mobility. The swelling behavior of the thermoresponsive microgel particles can be tuned by playing on two synthesis variables which are the initial solids content and the content of P(AETAC-X) macro-RAFT stabilizer. Furthermore, the inner structure of the synthesized microgels was probed by transverse relaxation nuclear magnetic resonance (T2 NMR) and small-angle neutron scattering (SANS) measurements. The fit of T2 NMR data confirmed a core-shell morphology with different cross-linking density in PVCL microgels. Through the determination of the network mesh size, SANS was suitable to explain the increase of the values of the PVCL microgel swelling ratios by increasing the initial solids content of their synthesis. [ABSTRACT FROM AUTHOR]

In this study, the dissociation behavior of CH 4 hydrate in the absence and presence of poly(N-vinylcaprolactam) (PVCap) was closely investigated using a combination of experimental techniques, including in-situ Raman spectroscopy and high-pressure micro-differential scanning calorimetry (HP μ-DSC), and molecular dynamics (MD) simulations. The experimental results clearly demonstrated that CH 4 hydrate dissociated more slowly and in two steps in the presence of PVCap. The MD simulations revealed that this slow and two-step dissociation was mainly due to the adsorption of PVCap onto the hydrate surface, which hindered the mass transfer of CH 4 from the hydrate into the solution. The high viscosity and steric hindrance of PVCap also impeded the formation and growth of CH 4 bubbles during the hydrate dissociation, contributing to the slower dissociation of CH 4 hydrate in the PVCap solution. The broad and asymmetric shape of the last endothermic peak observed via HP μ-DSC was caused by the adsorption of PVCap during CH 4 hydrate dissociation. The findings of this study provide valuable insights into the precise mechanism of hydrate dissociation in the presence of kinetic hydrate inhibitors. [Display omitted] • The dissociation behaviors of CH 4 hydrate in the presence of PVCap were investigated. • Slow and multi-step dissociation of CH 4 hydrate occurred in the presence of PVCap. • PVCap adsorption on the hydrate surface hindered the mass transfer of CH 4 into the solution. • The high viscosity and steric hindrance of PVCap impeded the formation and growth of CH 4 bubbles. [ABSTRACT FROM AUTHOR]

Previous studies involving poly N-vinylcaprolactam (PNVCL) and itaconic acid (IA) have synthesised the hydrogels with the presence of a solvent and a crosslinker, producing chemically crosslinked hydrogel systems. In this study, however, temperature sensitive PNVCL was physically crosslinked with a pH-sensitive comonomer IA through ultraviolet (UV) free-radical polymerization, without the presence of a solvent, to produce hydrogels with dual sensitivity. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy indicated successful polymerisation of the hydrogels. The temperature and pH sensitivity of the hydrogels was investigated. The lower critical solution temperature (LCST) of the gels was determined using the UV spectrometry and it was found that the incorporation of IA decreased the LCST. Rheology was conducted to investigate the mechanical and viscoelastic properties of the hydrogels, with results indicating IA that enhances the mechanical properties of the gels. Swelling studies were carried out at ~20 °C and 37 °C in different buffer solutions simulating the gastrointestinal tract (pH 2.2 and pH 6.8). In acidic conditions, the gels showed gradual increase in swelling while remaining structurally intact. While in basic conditions, the gels had a burst in swelling and began to gradually degrade after 30 min. Results were similar for drug release studies. Acetaminophen was incorporated into the hydrogels. Drug dissolution studies were carried out at 37 °C in pH 2.2 and pH 6.8. It was found that

ABSTRACT Four generations of new amphiphilic thermoresponsive linear-dendritic block copolymers (LDBCs) with a linear poly( N-vinylcaprolactam) (PNVCL) block and a dendritic poly(benzyl ether) block are synthesized by atom transfer radical polymerization (ATRP) of N-vinylcaprolactam (NVCL) using dendritic poly(benzyl ether) chlorides as initiators. The copolymers have been characterized by 1H NMR, FTIR, and GPC showing controlled molecular weight and narrow molecular weight distribution (PDI ≤ 1.25). Their self-organization in aqueous media and thermoresponsive property are highly dependent on the generation of dendritic poly(benzyl ether) block. It is observed for the LDBCs that the self-assembled morphology changes from irregularly spherical micelles, vesicles, rod-like large compound vesicles (LCVs), to the coexistence of spherical micelles and rod-like LCVs, as the generation of the dendritic poly(benzyl ether) increases. The results of a cytotoxicity study using an MTT assay method with L929 cells show that the LDBCs are biocompatible. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 300-308 [ABSTRACT FROM AUTHOR]

A mini-library of star-shaped thermoresponsive polymers having six arms was prepared using a hexafunctional xanthate by reversible addition-fragmentation chain transfer (RAFT) polymerization. Star polymers with homopolymeric arms of poly(N-vinylcaprolactam) (PNVCL), copolymeric arms of poly(N-vinylcaprolactam-co-N-vinylpyrrolidone) (PNVCL-co-PNVP) and also arms of block copolymers of PNVCL-b-PVAc, (PNVCL-co-PNVP)-b-PVAc, and combinations of them changing the order of the block was achieved exploiting the R-RAFT synthetic methodology (or R-group approach), wherein the thiocarbonyl group is transferred to the polymeric chain end. Taking advantage of the RAFT benefits, the molecular weight of the star polymers was controlled (Mn = 11,880-153,400 g/mol) to yield star polymers of different sizes and lower critical solution temperature (LCST) values. Removing the xanthate group of the star polymers allowed for the introduction of specific functional groups at the ends of the star arms and resulted in an increase of the LCST values. Star PNVCL-b-PVAc diblock copolymers with PVAc contents of 5-26 mol % were prepared; the hydrophobic segment (PVAc) is located at the end of the star arms. Interestingly, when the PVAc content was 5-7 mol %, the hydrodynamic diameter (Dh) value of the aggregates formed in water was almost the same sa the Dh of the corresponding PNVCL star homopolymers. It is proposed that these star block copolymers self-assemble into single flowerlike micelles, showing great stability in aqueous solution. Star block copolymers with the PVAc hydrophobic block in the core of the star, such as PVAc-b-(PNVCL-co-PNVP), form micellar aggregates in aqueous solution with Dh values in the range from ~115 to 245 nm while maintaining a thermoresponsive behavior. Micellar aggregates of selected star polymers were used to encapsulate methotrexate (MTX) showing their potential in the temperature controlled release of this antineoplasic drug. The importance of the order in which each block constituent is introduced in the arms of the star polymers for their solution/aggregation behavior is demonstrated. [ABSTRACT FROM AUTHOR]

In this study, we synthesized poly(N-vinylcaprolactam)-g-collagen (PNVCL-g-Col) by grafting collagen with carboxyl group-terminated thermosensitive PNVCL-COOH. The resulting biopolymer was evaluated for its structural, thermal, and rheological properties. Aqueous solutions of PNVCL-g-Col exhibited a temperature-dependent phase transition around human physiological temperature (at ∼38.5 °C), and temperature-dependent tunability. PNVCL-g-Col exhibited temperature-dependent release of the model drugs, lidocaine hydrochloride and bovine serum albumin. Thus, PNVCL-g-Col biopolymer may have wide potential use in various biomedical applications, including controlled release and tissue engineering. [ABSTRACT FROM PUBLISHER]

We report nanothin temperature-responsive hydrogel films of poly(N-vinylcaprolactam) nanoparticles (νPVCL) with remarkably high loading capacity for topical drug delivery. Highly swollen (νPVCL) n multilayer hydrogels, where n denotes the number of nanoparticle layers, are produced by layer-by-layer hydrogen-bonded assembly of core-shell PVCL- co -acrylic acid nanoparticles with linear PVPON followed by cross-linking of the acrylic acid shell with either ethylene diamine (EDA) or adipic acid dihydrazide (AAD). We demonstrate that a (νPVCL) 5 film undergoes dramatic and reversible swelling up to 9 times its dry thickness at pH = 7.5, indicating 89 v/v % of water inside the network. These hydrogels exhibit highly reversible ∼3-fold thickness changes with temperature variations from 25 to 50 °C at pH = 5, the average pH of human skin. We also show that a (νPVCL) 30 hydrogel loaded with ∼120 µg cm −2 sodium diclofenac, a non-steroidal anti-inflammatory drug used for osteoarthritis pain management, provides sustained permeation of this drug through an artificial skin membrane for up to 24 h at 32 °C (the average human skin surface temperature). The cumulative amount of diclofenac transported at 32 °C from the (νPVCL) 30 hydrogel after 24 h is 12 times higher than that from the (νPVCL) 30 hydrogel at 22 °C. Finally, we demonstrate that the (νPVCL) hydrogels can be used for multiple drug delivery by inclusion of Nile red, fluorescein and DAPI dyes within the νPVCL nanoparticles prior to hydrogel assembly. Using confocal microscopy we observed the presence of separate dye-loaded νPVCL compartments within the hydrogel matrix with all three dyes confined to the nanogel particles without intermixing between the dyes. Our study provides opportunity for development of temperature-responsive multilayer hydrogel coatings made via the assembly of core-shell nanogel particles which can be used for skin-sensitive materials for topical drug delivery. [ABSTRACT FROM AUTHOR]

Poly(N-vinylcaprolactam) (PNVCL) and poly(N-vinylcaprolactam-co-acrylic acid) (poly(NVCL-co-AA)) were synthesized by solution-free radical polymerization and displayed thermo-responsive behavior, with lower critical solution temperatures (LCSTs) of 35 °C and 39 °C, respectively. The incorporation of AA unities made the poly(NVCL-co-AA) sensitive to both pH and temperature. They were exploited in this work in preparing microparticles loaded with ketoprofen via spray-drying to modulate the drug release rate by changing pH or temperature. The interaction between polymer and drug was studied using X-ray diffractometry, Raman spectrometry and scanning electron microscopy (SEM). The biocompatibility of pure polymers, free ketoprofen as well as the spray-dried particles was demonstratedin vitroby low cytotoxicity and a lack of nitric oxide production in macrophages at concentrations as high as 100 µg/ml. The release profile of ketoprofen was evaluated byin vitroassays at different temperatures and pH values. Drug diffusion out of PNVCL’s hydrated polymer network is increased at temperatures below the LCST. However, when poly(NVCL-co-AA) was used as the matrix, the release of ketoprofen was primarily controlled by the pH of the medium. These results indicated that PNVCL and the novel poly(NVCL-co-AA) could be promising candidates for pH and temperature-responsive drug delivery systems. [ABSTRACT FROM AUTHOR]

This work presents experimental results on the inhibition performance of kinetic hydrate inhibitors (KHIs) of structure-II hydrates. The studied KHIs, namely derivatives of copolymers of N -vinylcaprolactam (VCap) and alkylimidazolium salts, were synthesized at the Mexican Petroleum Institute with the objective of producing copolymers with higher cloud points than that exhibited by the poly( N -vinylcaprolactam) homopolymer. Three experimental methods were used to evaluate the hydrate inhibition performance of the synthesized copolymers: the capacity to inhibit the formation of tetrahydrofuran (THF) hydrates (under atmospheric pressure and at a temperature of −0.5 °C; i.e., a subcooling for THF hydrates of about 3.4 °C); the capacity to inhibit the formation of natural gas hydrates under high pressure (about 6 MPa) and low temperature conditions (about 1 °C; i.e. a subcooling of 16 °C for the studied natural gas sample); and the determination of the cloud point temperature of the studied copolymers in aqueous systems of varying salinity (under atmospheric pressure and temperatures ranging from 2 to 81 °C). The inhibition performance and the high solubility (in highly saline aqueous systems) of the synthesized copolymers seems to indicate that these compounds can be considered as promising low dosage inhibitors to prevent or delay the formation of hydrates during the production and transport of hydrocarbons. [ABSTRACT FROM AUTHOR]

A soluble poly (n-vinyl carbazole)–polypyrrole (PNVC–Ppy) copolymer was prepared through oxidative chemical polymerization wherein dodecyl benzene sulfonic acid (DBSA) was used as a dopant to facilitate polymer-organic solvent interaction and ammonium persulfate (APS) was used as an oxidant. Compared with undoped PNVC–Ppy, the DBSA-doped PNVC–Ppy copolymer showed higher solubility in some selected organic solvents. The composition and structural characteristics of the DBSA-doped PNVC–Ppy were determined by Fourier transform infrared, ultraviolet–visible, and X-ray diffraction spectroscopic methods. Field emission scanning electron microscopic method was employed to observe the morphology of the DBSA-doped PNVC–Ppy copolymer. The electrical conductivity of the DBSA-doped PNVC–Ppy copolymer was measured at room temperature. The conductivity increased with increasing concentration of APS oxidant, and the highest conductivity was recorded at 0.004 mol/dm3APS at a polymerization temperature of −5 °C. The increased conductivity can be explained by the extended half-life of pyrrole free radical at a lower temperature and a gradual increase in chain length over a prolonged time due to the slow addition of APS. Furthermore, the obtained soluble copolymer exhibits unique optical and thermal properties different from those of PNVC and Ppy. [ABSTRACT FROM PUBLISHER]

The thermo-sensitive copolymer poly( N -vinylcaprolactam- co -methacrylic acid) (PNVCL- co -MAA) was synthesized by free radical polymerization and the resulting nanofibers were fabricated using an electrospinning process. The molecular weight of the copolymer was adjusted by varying the content of methacrylic acid (MAA) while keeping that of N -vinylcaprolactam (NVCL) constant. Hydrophilic captopril and hydrophobic ketoprofen were used as model drugs, and PNVCL- co -MAA nanofibers were used as the drug carrier to investigate the effects of drug on its release properties from nanofibers at different temperatures. The results showed that slow release over several hours was observed at 40 °C (above the lower critical solution temperature (LCST) of PNVCL- co -MAA), while the drugs exhibited a burst release of several seconds at 20 °C (below the LCST). Drug release slowed with increasing content of the hydrophobic monomer NVCL. The hydrophilic captopril was released at a higher rate than the hydrophobic ketoprofen. The drug release characteristics were dependent on the temperature, the portion of hydrophilic groups and hydrophobic groups in the copolymer and hydrophilicity/hydrophobicity of drug. Study on the mechanism of release showed that Korsmeyer–Peppas model as a major drug release mechanism. Given these results, the PNVCL- co -MAA copolymers are proposed to have useful applications in intellectual drug delivery systems. [ABSTRACT FROM AUTHOR]

Two modifications of poly(N-vinylcaprolactam)-PVCL25 and PVCL40 (drying of a PVCL solution at 25 and 40°С, respectively)-as powdered films and their solutions were systematically investigated for the first time. Powders were studied by X-ray diffraction, IR spectroscopy, scanning electron microscopy, low-temperature krypton adsorption, and differential scanning calorimetry. Solutions were studied by smallangle X-ray scattering and dynamic light scattering. It was demonstrated that powders of PVCL25 and PVCL40 differ in the characteristics of the sub- and microstructure and in the water content and the solutions differ in the particle size. The relationships between the characteristics of the systems in the solid and liquid state and between the hydrodynamic diameter of PVCL particles in solution and their coagulation time were found. [ABSTRACT FROM AUTHOR]

A series of new fluorescent dye bearing monomers, including glycomonomers, based on maleamide and maleic esteramide was synthesized. The dye monomers were incorporated by radical copolymerization into thermo-responsive poly(N-vinyl-caprolactam) that displays a lower critical solution temperature (LCST) in aqueous solution. The effects of the local molecular environment on the polymers' luminescence, in particular on the fluorescence intensity and the extent of solvatochromism, were investigated below as well as above the phase transition. By attaching substituents of varying size and polarity in the close vicinity of the fluorophore, and by varying the spacer groups connecting the dyes to the polymer backbone, we explored the underlying structure-property relationships, in order to establish rules for successful sensor designs, e.g., for molecular thermometers. Most importantly, spacer groups of sufficient length separating the fluorophore from the polymer backbone proved to be crucial for obtaining pronounced temperature regulated fluorescence responses. [ABSTRACT FROM AUTHOR]

Water-insoluble poly(N-vinylcaprolactam) (PVCL) electrospun nanofibres have been prepared for the first time by direct electrospinning with Tannic acid (TA) in apolar protic solvents. The PVCL/TA nanofiber mats have been fabricated through a facile one-step procedure which will increase their potential applications in the biomedical field where material stability in an aqueous environment is crucial. Hydrogen bonding between TA and PVCL resulted in nanofibers that are non-water soluble after drying, and the TA/PVCL interactions were confirmed through rheological and infrared spectroscopy measurements. In addition, the optimal ratio of TA and PVCL essential for the production of uniform, insoluble fibres in the range of hundreds of nanometres was established. The contact angle measurements confirmed that the roughness induced by the fibrous morphology of the TA/PVCL mats resulted in hydrophobic surfaces (CA>120°) from materials that otherwise exhibited hydrophilic behaviour (CA<90°) on flat surfaces. This method of using TA as a crosslinker for direct electrospinning of PVCL fibres requires no chemical modification or complex post-synthesis steps, thus facilitating the potential use of these novel PVCL nanofibers for applications as biomedical scaffolds in aqueous environments. [ABSTRACT FROM AUTHOR]

Poly( N -vinylcaprolactam) (PNVCL) is a temperature-responsive polymer, only second to poly( N -isopropylacrylamide), the most popular temperature-responsive polymer. Its applications include its use in cosmetics, as an anticlogging agent in pipelines and increasingly, in biomedical applications. This review highlights the controlled synthesis of PNVCL in different architectures: random copolymers, block copolymers, graft copolymers, nanogels, and their applications in the biomedical field, e.g., drug delivery, cell detachment, entrapment of enzymes, tissue engineering, among others. Emerging applications in areas that are expected to grow are also presented where PNVCL will play a pivotal roll: nanotechnology and the environment. [ABSTRACT FROM AUTHOR]

ABSTRACT The synthesis and self-assembling of a thermoresponsive conjugate of hyaluronic acid (HA) and poly( N-vinylcaprolactam) (PVCL) is reported. Both polymers were end functionalized: HA via reductive amination, thereby introducing an azide endgroup to the chain end, and PVCL via thioetherification to introduce a propargyl group. The two were coupled with a copper assisted 'click' reaction into a bioconjugate composed of HA blocks with the molar mass 3,600 g mol−1 (1618 saccharide units) and PVCL blocks of 3,500 g mol−1 (∼25 repeating units). The cloud point temperature measured by transmittance was 50-51 °C in water. The calorimetrically observed phase transition temperature of PVCL in the conjugate increased by 2 °C to 47.7 °C, whereas the enthalpy of the phase transition was unaffected by the conjugation. HA-PVCL conjugate self-assembles in water upon heating into monodisperse, colloidally stable, hollow spherical particles whose size may be tuned with the heating rate of the solution. Slow and fast heating resulted in vesicles with the hydrodynamic radii of 443 or 275 nm, respectively. The heating rate did not, however, affect the cloud point. Salt did not noticeably affect the size of the polymer particles, presumably because of interactions between the HA and PVCL blocks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 425-436 [ABSTRACT FROM AUTHOR]

A series of thermoresponsive copolymers based on chitosan- g -poly( N -vinylcaprolactam) were synthesized by amidation reaction using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride as coupling reagent. The effect of molecular architecture on the thermoresponsive properties of the graft copolymers solutions was studied by varying the chain length of the grafted poly( N -vinylcaprolactam), PVCL, (in the range from 4 to 26 kDa) and the spacing between grafted chains onto the chitosan backbone. The most interesting characteristic of these copolymers is their solubility in water at temperatures below their lower critical solution temperature (LCST). These solutions presented a LCST between 36 and 44 °C, which decreases with the spacing and length of grafted PVCL chains onto the chitosan backbone, in contrast with the limited decrease of the LCST of PVCL above a critical M ¯ n value around 18 kDa. This behavior offers tangible possibilities for the preparation and application of sensitive bioactive formulations and “smart” drug delivery systems. [ABSTRACT FROM AUTHOR]

Stimuli-responsive microgels have great potential for biomedical applications owing to their well-defined structure and tunable swelling-collapse behavior in response to environmental conditions changes. Herein, thermo- and pH-responsive biocompatible microgels have been developed via surfactant-free precipitation polymerization of N -vinylcaprolactam (NVCL) in aqueous media using acrylic or itaconic acid (AA or IA) as acidic comonomers. A comparative study was performed regarding the incorporation of acidic comonomers and their effect on the stimuli-responsive behavior and nanoparticles stability in aqueous dispersion. The particles size, polydispersity as well as temperature- and pH-responsiveness were characterized by Dynamic Light Scattering experiments. The results indicated that the acidic segments in the microgel networks not only rendered pH-responsiveness behavior but were also capable to stabilize the nanoparticles due to the negative charges from carboxyl groups present in AA and IA. Smaller particles diameters were obtained when IA was used as the ionizable comonomer. Moreover, IA proved to be more efficient in the stability of the dispersions against time. The microgels morphology was accessed by Electron Transmission Microscopy, which revealed their spherical shape and low polydispersity, although a tendency for particles aggregation. All microgels were well tolerated by murine peritoneal macrophages, as revealed by cytotoxic tests. These results provide important information for further studies on the incorporation of active ingredients in such microgels for controlled drug release systems. [ABSTRACT FROM AUTHOR]