A Novel Design Strategy for Temperature-Responsive IPN Hydrogels Based on a Copolymer of Acrylamide and N-(1,1-Dimethyl-3-Oxobutyl)-Acrylamide

A methology is described for the synthesis of novel temperature-responsive interpenetrating polymer network (IPN) hydrogels with poly(2-acrylamido- 2-methylpropane sulfonic acid) (PAMPS) as a tightly crosslinked 1st network, temperature-responsive poly(acrylamide-co-N-(1,1-dimethyl-3-oxobutyl)- acrylamide) (P(AM-co-DAAM)) with low cost as a lossely crosslinked 2nd network. The structure and morphology of the IPN hydrogels were characterized by FTIR, TGA and SEM, and the results indicated that PAMPS network introduced P(AM-co-DAAM) hydrogels have large, thermally stable and interconnected porous network. The properties of the IPN hydrogels, which include: swelling capacity, equilibrium swelling/deswelling ratio, temperature- responsive behavior, and the dwelling kinetics as specific temperature, were investigated carefully. Results showed that the obtained IPN hydrogels displayed a controllable equilibrium swelling/deswelling behavior and possessed remarkable thermosensitivity. In addition, the results also indicate that the incorporation of the hydrophobic groups DAAM has a big effect on the LCST of the IPN hydrogels. Consequently, these novel temperature-responsive IPN hydrogels with low cost and slow-releasing performance would be promising for potential applications, such as environmental catalysis, water treatment, and agriculture.

Analysis of variation in temperature-responsive leaf color mutant lines induced from Gamma irradiation in rice(Oryza sativa L.)

Eight lines of temperature-responsive leaf colormutants induced by applying 300 Gy Gamma-ray irradiation to Thermo-sensitive genic malesterile line 2177s,were obtained through con-tinuous selection in seven generations..Theleaves of these lines started to become greenafter the fourth leaf extension,and except

4D printing of PLA/PCL shape memory composites with controllable sequential deformation

Shape memory polymers(SMPs)are a promising class of materials for biomedical applications due to their favorable mechanical properties,fast response,and good biocompatibility.However,it is difficult to achieve controllable sequential shape change for most SMPs due to their high deformation temperature and the simplex deformation process.Herein,shape memory composites based on polylactic acid(PLA)matrix and semi-crystalline linear polymer polycaprolactone(PCL)are fabricated using 4D printing technology.Compared with pure PLA,with the rise of PCL content,the 4D-printed PLA/PCL composites show decreased glass transition temperature(Tg)from 67.2 to 55.2°C.Through the precise control of the deformation condition,controllable sequential deformation with an outstanding shape memory effect can be achieved for the PLA/PCL shape memory composites.The response time of shape recovery is less than 1.2 s,and the shape fixation/recov-ery rates are above 92%.In order to simulate sequential petal opening and sequential drug releasing effects,a double-layer bionic flower and a drug release device,respectively,are presented by assembling PLA/PCL samples with different PLA/PCL ratios.The results indicate the potential applications of 4D-printed PLA/PCL composites in the field of bio-inspired robotics and biomedical devices.

Synthesis of P(NIPAM-co-Am)/Mesoporous Silica Composites and Their Temperature- Responsive Anion Exchange

The purpose of this study is to examine the structure and the temperature-responsive anion exchange property of amino-functionalized mesoporous silica coated with temperature-responsive copolymer, poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)). For this purpose, the composites which contained 0, 10, or 20 wt% of Am were synthesized. From the TG results, it was found that the amounts of copolymer immobilized on the mesoporous silica were 1.6 - 2.6 wt%. XRD patterns revealed that the structures of composites were hexagonal and almost the same as that of original mesoporous silica without polymer. At low temperature the methyl orange (MO) anions adsorbed and desorbed reversibly with changing pH of the solution, while at high temperature the MO anions did not. This temperature, at which the amount of adsorbed MO anions changed considerably, shifted to the higher temperature side with increasing the amount of added Am.

Preparation and chromatographic evaluation of thermoresponsive N-isopropylacrylamide copolymers stationary phases containing amino groups

Two cationic thermoresponsive stationary phases were designed and prepared containing poly [ N-isopropylacrylamide-co-（ 2-dimethylamino ） ethylmethacrylate ] and poly [ N-isopropylacryl- amide-co-（2-diethylamino） ethylmethacrylate] via a simple method, the direct copolymerization of monomers with double bonds on silica surfaces. The two copolymers were synthesized by radical polymerization and then characterized using Fourier transform infrared and gel permeation chroma- tography. The thermoresponsive property and amounts of copolymers grafted on silica were deter- mined through transmittance measurements and thermogravimetric analysis, respectively. The copol- ymers grafted silica particles were then applied as high-performance liquid phase （HPLC） stationary phases for chromatographic separation. Chromatographic properties of mobile phases at different pH values were evaluated by changing temperatures and using benzene and hydrocortisone as the test an- alytes. Retention time of the analytes was prolonged with increasing temperature on both thermore- sponsive columns due to enhanced hydrophobic interaction between analytes and stationary phases. The resolution increased with increasing pH of mobile phase. The optimal separation was obtained at phosphate buffer solution （ 10 raM, pH 8. 0） and at 50 ℃. The pH of mobile phase had a crucial effect on separation efficiency. The results illustrated that poly（ N-isopropylacrylamide-co-（2-diethyl- amino） ethylmethacrylate ] copolymer modified silica was more advantageous for the temperature-re- sponsive chromatographic separation because its lower critical solution temperature was relatively lower compared to the poly [ N-isopropylacrylamide-co-（2-dimethylamino） ethylmethacrylate ] sta- tionary phase.

The Aggregation of Bentonite Using Poly(N-isopropylacrylamide) as a Flocculant

Sedimentation tests of bentonite suspension were carried out by adding various concentrations of poly(N-isopropylacrylamide) (PNIPAM) with different molecular weights as flocculant below and above lower critical solution temperature (LCST). Also, the effect of PNIPAM on aggregation of bentonite was investigated by sedimentation rate, turbidity of supernatant. Additionally, XRD patterns and SEM photographs were measured in order to consider aggregation mechanism of PNIPAM. The sedimentation rate and turbidity for the PNIPAM with large molecular weight or PNIPAM solution of high concentration above LCST were faster and clearer than those with small molecular weight or low concentration. From XRD patterns, the peak of bentonite sediment with PNIPAM shifted to the low-angle side, suggesting that a part of PNIPAM chain entered between bentonite layers. Furthermore, it was confirmed by SEM photographs that PNIPAM covered bentonite surface after sedimentation test. It was indicated that PNIPAM adsorbs on the bentonite surface and aggregates each bentonite particle above LCST. From these results, PNIPAM works as a flocculant and the PNIPAM with large molecular weight has a good ability.

Temperature-responsive polymers： Synthesis, properties, and biomedical applications

Interest in temperature-responsive polymers has steadily grown over the past several decades, and numerous studies have been dedicated to developing temperature sensitive polymers that can be constructed into new smart materials for biomedical applications. Phase behavior of a temperature-responsive polymer plays a pivotal role in determining its biological performance in certain conditions. In addition to the additives （such as salts and proteins） in aqueous solutions, molecular weight, molecular weight distribution, and structural or compositional factors can also significantly affect the transition temperatures of the polymers. This review comprehensively describes well-established and newly developed synthetic strategies for preparing temperature-responsive polymers. The structural and compositional parameters that affect the transition temperatures and self-assembly behavior are discussed. Finally, the biomedical applications of the temperature-responsive polymers in drug delivery, immunotherapy, tissue engineering, and diagnosis are summarized.

Recent development of temperature-responsive surfaces and their application for cell sheet engineering

Cell sheet engineering,which fabricates sheet-like tissues without biodegradable scaffolds,has been proposed as a novel approach for tissue engineering.Cells have been cultured and proliferate to confluence on a temperature-responsive cell culture surface at 37℃.By decreasing temperature to 20℃,an intact cell sheet can be harvested from the culture surface without enzymatic treatment.This new approach enables cells to keep their cell–cell junction,cell surface proteins and extracellular matrix.Therefore,recovered cell sheet can be easily not only transplanted to host tissue,but also constructed a three-dimensional(3D)tissue by layering cell sheets.Moreover,cell sheet manipulation technology and bioreactor have been combined with the cell sheet technology to fabricate a complex and functional 3D tissue in vitro.So far,cell sheet technology has been applied in regenerative medicine for several tissues,and a number of clinical studies have been performed.In this review,recent advances in the preparation of temperature-responsive cell culture surface,the fabrication of organ-like tissue and the clinical application of cell sheet engineering are summarized and discussed.

Effect of Temperature-responsive Solution Behavior of PNIPAM-bPPEOMA-b-PNIPAM on Its Inclusion Complexation with α-Cyclodextrin

The effect of temperature-responsive solution behavior of PNIPAM-b-PPEOMA-b-PNIPAM on its inclusion complexation with α-cyclodextrin was studied. The triblock polymer was prepared by reversible addition-fragmentation chain transfer （RAFT） polymerization and formed inclusion complexes （ICs） after selective threading of the PEO segment of the triblock polymer through the cavities of α-CD units. For comparison, PPEOMA homopolymer was prepared and the inclusion complexation with α-CD was also studied. The ICs were prepared with a-CD when the polymer was in different conformations by changing the temperature, and the formed ICs were characterized by XRD, ^1H-NMR, TGA and DSC. The solutions of the ICs show temperature-responsive clear/turbid transition or fluidic emulsion/gel transition depending on the concentration of the α-CD added, and the stoichiometry determined by ^1H-NMR and TGA indicates that the stoichiometry of EO to α-CD of the resulted ICs increases with increasing of temperature.

Temperature-responsive Behavior of Polymer Fluorescent System via Electrostatic Interaction Mediated Aggregation/Deaggregation

A simple and effective polymer fluorescent thermosensitive system was successfully developed based on the synergistic effect of excimer/monomer interconversion of pyrene derivatives and electrostatic interaction between polyelectrolyte and charged fluorophore. As for the system, the excimer-monomer conversion, thermosensitive behavior and thermo-responsive reversibility were investigated experimentally. Temperature variation and temperature-distribution induced fluorescence changes can be observed directly by naked eyes. Thus, this polymer system holds promise for serving as a fluorescent thermometer.

A sustained-release microcarrier effectively prolongs and enhances the antibacterial activity of lysozyme

Bacterial infections have become a great threat to public health in recent years.A primary lysozyme is a natural antimicrobial protein;however,its widespread application is limited by its instability.Here,we present a poly(N-isopropylacrylamide)hydrogel inverse opal particle(PHIOP)as a microcarrier of lysozyme to prolong and enhance the efficiency against bacteria.This PHIOP-based lysozyme(PHIOP-Lys)formulation is temperature-responsive and exhibits long-term sustained release of lysozyme for up to 16 days.It shows a potent antibacterial effect toward both Escherichia coli and Staphylococcus aureus,which is even higher than that of free lysozyme in solution at the same concentration.PHIOPs-Lys were demonstrated to effectively inhibit bacterial infections and enhance wound healing in a full-thickness skin wound rat model.This study provides a novel pathway for prolonging the enzymatic activity and antibacterial effects of lysozyme.

Fabricated temperature sensitive photocatalyst of PNIPAM@ZnO/C for controllable photocatalytic activity

PNIPAM@ZnO/C composite photocatalyst was prepared by cross-linking polymerization technology with N-isopropylacrylamide used as functional monomer, N,N＇-methylenebis （acrylamide） used as cross- linking agent, ammonium persulfate used as initiator, and 3-（trimethoxysilyl） propyl methacrylate used as surface modification reagent. The morphology, structure, electrochemical and photocatalytic properties of as-prepared samples were characterized via the serial tests. The temperature-response performances of PNIPAM@ZnO/C were evaluated by the photocatalytic degradation of tetracycline （TC） under different temperatures. The results show that the synthesized composite photocatalysts possess the excellent and switchable photocatalytic activity. The photocatalytic degradation activity of PNIPAM@ZnO/C is suppressed above the lower critical solution temperature （LCST）, and it is enhanced below the LCST.

Temperature-induced resistance transition behaviors of melamine sponge composites wrapped with different graphene oxide derivatives

Temperature-re s ponsive resistance transition behaviors of the melamine sponges wrapped with different graphene oxide derivatives(i.e.nanoribbon,wide-ribbon and sheet)were investigated.Melamine sponge composites coated by three types of GO derivatives were prepared by a simple dip-coating approach.All these composites show good mechanical flexibility and reliability(almost unchanged compressive stress at 70%strain after 100 cycles),high hydrophobicity(water contact angle>120°),excellent flame resistance(self-extinguishing)and structural stability even after burning,which was used to construct the resistance-based fire alarm/warning sensor.Notably,the different resistance response behaviors of such sensors are strongly dependent on the GO size and network formed on the MF skeleton surface.Typically,at a fixed high temperature of~350℃,the three fire alarm sensors show different response time(to trigger the alarm light)of 6.3,8.4 and 11.1 s for nanoribbon,wide-ribbon and sheet at the same concentration,respectively.The structural observation and chemical analysis demonstrated that the discrepancy of temperature-responsive resistance transition behaviors of various GO derivatives was strongly determined by their different thermal reduction degrees during the high-tempe rature or flame treating process.This work offers a design and development for construction of smart fire alarm device for potential fire prevention and safety applications.

Preparation of poly（N-isopropylacrylamide） brush grafted silica particles via surface-initiated atom transfer radical polymerization used for aqueous chromatography

Thermoresponsive poly（N-isopropylacrylamide） （PNIPAAm） brushes were densely grafted onto silica surface via surface-initiated atom transfer radical polymeriza- tion （SI-ATRP）. The grafting reaction started from the surfaces of 2-bromoisobutyrate- functionalized silica particles in 2-propanol aqueous solution at ambient temperature using CuCIICuCI21N, N,N＇,N＇,N”.pentamethyldiethylenetriamine （PMDETA） as the catalytic system. Based on thermogravimetric analysis （TGA） results, the grafting amount and grafting density of PNIPAM chains on the surface of silica were calculated to be 1.29 mg/ m^2 and 0.0215 chains/nm^2, respectively. The gel permeation chromatography （GPC） result showed the relatively narrow molecular weight distribution （MwlMn= 1.21） of the grafted PNIPAAm. The modified silica particles were applied as high-performance liquid chromatography （HPLC） packing materials to successfully separate three aromatic compounds using water as mobile phase by changing column temperature. Temperature- dependent hydrophilic/hydrophobic property alteration of PNIPAAm brushes grafted on silica particles was determined with chromatographic interaction between stationary phase and analytes. Retention time was prolonged and resolution was improved with increasing temperature. Baseline separation with high resolution at relatively low temperatures was observed, demonstrating dense PNIPAAm brushes were grafted on silica surfaces.

Micromechanical properties of poly(N-isopropylacrylamide)hydrogel microspheres determined using a simple method

Temperature-responsive poly（N-isopropylacrylamide） （PNIPAM） hydrogel microspheres have attracted extensive attention because of their promising diverse biomedical applications. A quantitative understanding of the micromechanical properties of these microspheres is essential for their practical application. Here, we report a simple method for the characterization of the elastic properties of PNIPAM hydrogel microspheres. The results show that PNIPAM hydrogel microspheres exhibit elastic deformation and the obtained force-deformation experimental data fits the Hertz theory well. The moduli of elasticity of the PNIPAM hydrogel microspheres prepared under different conditions were systematically investigated in this work for the first time. The PN1PAM hydrogel microsphere composition significantly affects their micromechanical properties and their temperature sensitivity behavior. PNIPAM hydrogel microspheres with a larger equilibrium volume change have a lower modulus of elasticity. The modulus of elasticity of the PNIPAM hydrogel microspheres at body temperature （37 ℃, above the lower critical solution temperature （LCST） of PNIPAM） is much higher than that at room temperature （25 ℃, below the LCST of PNIPAM） because ofthermo-induced volume shrinkage and an increase in stiffness. These results provide valuable guidance for the design of smart materials for practical biomedical applications. Moreover, the simple microcompression method presented here also provides a versatile way to investigate the micromechanical properties of microscopic biomedical materials.

Synthesis of poly(amidoamine)-poly(ethyleneglycol)-poly(amidoamine) and preparation of its hydrogel solution containing doxorubicin

Many pH-and temperature-responsive polymers have been designed for preparing hydrogel.In the present study,in order to decrease the pH sensitivity of reported poly(amidoamine)-poly(ethyleneglycol)-poly(amidoamine)(PAA1580-PEG4600-PAA1580),we designed and synthesized poly(amidoamine)-poly(ethyleneglycol)-poly(amidoamine)(PAA-PEG-PAA)with shorter length of PAA chain by decreasing reaction temperature for preparing PAA-PEG-PAA hydrogel solution containing doxorubicin(DOX).The PAA-PEG-PAA was synthesized via the Michael-addition polymerization.The characteristic of PAA-PEG-PAA was evaluated.The PAA-PEG-PAA hydrogel solution was prepared and investigated.DOX-loaded PAA-PEG-PAA hydrogel solution was prepared,and its in vitro DOX release and in vitro anti-tumor activity were evaluated.Our results indicated that the viscosity of PAA-PEG-PAA hydrogel solution was concentration-and temperature-dependent.The sol-gel transition temperature of PAA-PEG-PAA hydrogel solution(12%,w/w)ranged from 35 to 29℃,and its pH ranged from 6.0 to 7.4.The released DOX from DOX-loaded PAA-PEG-PAA hydrogel showed sustained release characteristics.The in vitro anti-tumor activity of DOX-loaded PAA-PEG-PAA hydrogel was confirmed in B16 F10 cell line.Considering the acidic tumor microenvironment,this DOX-loaded PAA-PEG-PAA hydrogel solution would be easy in situ administration for intra-tumor injection or para-tumor injection forming hydrogel at body temperature.We suggested that this DOX-loaded PAA-PEG-PAAhydrogel solution,if containing photothermal conversion agents,would have a potential further use for photothermal therapy.