Dongyan Tang

Stimuli-responsive electrospun nanofibers from poly(N-isopropylacrylamide)-co-poly(acrylic acid) copolymer and polyurethane

A thermo- and pH-sensitive copolymer of poly(N-isopropylacrylamide)-co-poly(acrylic acid) (P(NIPAAm-co-AAc)) with an adjusted lower critical solution temperature (LCST)(at 37 °C) in an aqueous medium and pH of 7.4 was synthesized by a radical copolymerization, and was characterized by Fourier-transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H-NMR) spectroscopy. Then, nanofibers composed of P(NIPAAm-co-AAc) and polyurethane (PU) were fabricated by the single-spinneret electrospinning technique and used as drug carriers by co-spinning with the water insoluble drug nifedipine (NIF). The thermo-responsive behavior of the nanofibers was detected by contact angle (CA) measurements. The release behavior of the NIF from nanofibers was observed by scanning electron microscopy (SEM) and demonstrated by UV-vis spectroscopy. It was found that the wettability of the P(NIPAAm-co-AAc) nanofibers could be switched, due to the incorporation of PU. The release amount of NIF from the nanofibers could be controlled effectively by adjusting the temperature or pH value of the aqueous medium and incorporating the hydrophobic PU.

Electrospun poly(N-isopropylacrylamide)/poly(caprolactone)-based polyurethane nanofibers as drug carriers and temperature-controlled release

Electrospun micro- and nanofibers are being increasingly investigated for drug delivery. The components and stimuli-responsive properties of the fibers are important factors influencing the drug release behavior. The aim of this study was to fabricate thermo-responsive poly(N-isopropylacrylamide) (PNIPAAm)/polyurethane (PU) nanofibers using a single-spinneret electrospinning technique. The electrospun nanofibers were used as drug carriers by co-spinning with nifedipine (NIF) and the release behavior of NIF can be controlled by the response of the nanofibers to temperature. The morphologies of the nanofibers and the composites with NIF were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The interactions between PNIPAAm and PU and the existence of the water-insoluble drug NIF were introduced and confirmed by Fourier-transform infrared spectroscopy (FTIR). The thermo-responsive behavior of the nanofibers was detected by contact angle (CA) measurements. Mechanical properties were analyzed by tensile test and the release behavior of NIF from the PNIPAAm/PU nanofibers was observed by SEM and demonstrated by UV-vis spectroscopy. It was found that uniform fibers of NIF and PNIPAAm/PU could be fabricated without the appearance of particles on the surface. The release of NIF from the nanofibers could be controlled effectively by adjusting the temperature of the environment surrounding the thermo-responsive nanofibers.

Self-assembly and controlled release behaviour of the water-insoluble drug nifedipine from electrospun PCL-based polyurethane nanofibres

Electrospun micro‐ and nanofibres are increasingly being investigated for drug delivery. The components of nanofibres are important influences on the drug release behaviour. The aim of this study was to investigate the self‐assembly and release behaviour of drug from nanofibres.

Temperature-responsive zinc oxide nanorods arrays grafted with poly(N-isopropylacrylamide) via SI-ATRP

Well fabricated ZnO nanorods (ZnO NRs) arrays with preferred-orientation that grown on pre-deposited ZnO seed layers substrate were selected to graft thermo-responsive polymers of poly(N-isopropylacrylamide) (PNIPAM) by surface-initiated atom transfer radical polymerization (SI-ATRP). As a controlled/“living” radical polymerization, SI-ATRP could endow the systems with the characteristics of the grafted PNIPAM, meanwhile, with the maintaining of the properties of the ZnO NRs. The structures of ZnO and the grafted polymer with the relatively high molecular weights (Mn, 24 300) and narrow molecular weight distributions (Mw/Mn, 1.19) that determined by GPC detection, were characterized by XRD and FT-IR. The graft amount of PNIPAM on ZnO NRs and the interactions between the two components were determined by TG and XPS, respectively. The relatively thin layers of PNIPAM (∼15 nm) formed around NRs via SI-ATRP method were observed by SEM. And the temperature-sensitivity of the grafted nanorods were proved by contact angles measurements. Furthermore, photodegradation of Rhodamine B (Rh-B) by the grafted nanorods revealed that ZnO NRs–PNIPAM exhibited photocatalysis and temperature responsibility characteristics, indicating the significant potential applications with tunable responsiveness by changing the environmental conditions.

Controlled synthesis of amphiphilic graft copolymer for superhydrophobic electrospun fibres with effective surface fluorine enrichment: the role of electric field and solvent

Effective surface fluorine enrichment has great potential application value for superhydrophobic electrospun films, which has presented a challenge to researchers. The aim is expected to be achieved by electrospinning functional polymers with controlled structure based on the polarization characteristics of functional groups in polymer chains and their directional ordering induced by an electric field. Herein, an amphiphilic graft copolymer of poly(methyl methacrylate-ran-hydroxypropyl acrylate)-graft-poly(dodecafluoroheptyl methacrylate) (PMMA-r-PHPA-g-PDFMA) was synthesized by the combination of free radical polymerization and atom transfer radical polymerization (ATRP). Superhydrophobic fibrous films with high surface fluorine atomic content of 29.1% and even up to 34.8% were fabricated by eletrospinning the resultant fluoropolymer. It is concluded that the electric field can drive the surface segregation of positively charged fluorinated groups and bulk segregation of negatively charged -OH groups, thus contributing to the effective surface fluorine enrichment, which was confirmed by XPS results. Additionally, we also found that the superhydrophobicity of electrospun films has no apparent dependence on fibre morphologies. The variation in the surface wettability can be attributed to the difference in surface compositions obtained by changing the applied electric field strength and solvents. This research would present potential application prospects in fabricating high surface fluorinated superhydrophobic electrospun fibres or novel surface functionalized electrospun fibres.

Fabrication of PVCL-co-PMMA nanofibers with tunable volume phase transition temperatures and maintainable shape for anti-cancer drug release

This work is to fabricate thermo responsive nanofibers of which the thermo response temperatures could be easily tuned, and of which the fibrous shapes could be maintained after heating–cooling cycles in aqueous solution. The nanofibers were further fabricated into a nonwoven mat with size-variable pores for temperature controlled release of a model drug, Erlotinib. The thermo responsive nanofibers were electrospun from the copolymers of PMMA-co-PVCL (synthesized from MMA and PVCL, and had different LCSTs) by changing the solvents and the ratio of initiator/monomer. FT-IR and 1H NMR were used for molecular structural characterization; UV-vis spectra were used for LCST measurement; SEM and metalloscope were used to determine the optimal electrospinning parameters and to observe the shape maintaining abilities of the nanofibers after the heating–cooling recycles. Then, anti-cancer drug, Erlotinib, was incorporated into PMMA/PVCL nanofibers (represent as ‘model I’), or put in a drug reservoir and covered with the PMMA/PVCL electrospinning mat (presented as ‘model II’). UV-vis spectra were used to study the drug release behavior of each model. Results indicate that in model I, drug release was “switch on” below LCST, and “switch off” above LCST; in model II, drug release was faster above LCST than below LCST.

FABRICATION OF UNIFORM AND COMPACT ZnO THIN FILMS BY LANGMUIR–BLODGETT METHOD

In this paper, stearic acid/Zn2+ monolayer were formed at air–water interface and then multilayers were deposited onto a glass slide by Langmuir–Blodgett method. After annealing at 300°C for 0.25 h and 550°C for 2 h, ZnO thin films were fabricated. The optimized parameters for monolayer formation and multilayers deposition were determined by the surface pressure-surface area (Π-A) isotherm and transfer ratio (t.r.), respectively. The results of X-ray diffraction showed that multilayers changed into ZnO thin films with hexagonal structure and of high crystallization after annealing at high temperature. The observation of SEM images indicated that ZnO thin films had a uniform and flat surface with compact arrangement.

PEGMa modified molybdenum oxide as a NIR photothermal agent for composite thermal/pH-responsive p(NIPAM-co-MAA) microgels

Molybdenum oxide nanomaterials have received increasing attention in recent years for their strong localized surface plasmon resonance (LSPR) absorption in the near-infrared (NIR) region and pH-dependent degradability. However, the rapid degradation of MoOx at physiological pH values would decrease the NIR photothermal effect. Here, we designed and prepared PEGMa–MoOx/p(NIPAM-co-MAA) microgels (NCs) exhibiting adjustable degradation. For that purpose, PEGMa (Mn = 400) modified MoOx was synthesized through a simple hydrothermal process. Then, PEGMa–MoOx with existing CC groups was continually polymerized with NIPAM and MAA through emulsion polymerization. MAA was introduced to provide an acidic microenvironment (pH at 3–5) to control the degradation rate of PEGMa–MoOx. The photothermal efficiency of the NCs could be maintained at 54% even after 14 days. Meanwhile, the NCs also displayed a pH-dependent thermal response. Moreover, PEGMa was added again in the emulsion polymerization process to elevate the photothermal efficiency, and the irradiation result indicated that the NCs could increase the temperature by 27 °C. The complex microgel integrates pH/temperature/photothermal triple response characteristics and exhibits huge potential for chemo-photothermal combination cancer therapy.

Effects Of Substrate And Experimental Conditions On The Fabrication Of Well-Ordered Silica Particulate Langmuir–Blodgett Films

The dependence of particulate Langmuir–Blodgett (LB) monolayer quality on the surface nature of the substrate was investigated by pretreating the substrates with different methods, and the optimal withdrawal speed was determined by detecting the quality of particulate monolayers deposited at different withdrawal speeds. Furthermore, the effects of stearic acid (SA) concentration on the quality of particulate monolayers were discussed. Results indicated that surface amination would favor the transfer of the floating particulate monolayer from the interface to the substrate, which would be attributed to the formation of chemical bonds between the –NH2 groups on the substrate surface and the functional groups of –COOH and Si–OH groups on surfaces of particles floating at the interface. And the withdrawal speed of 1 mm ⋅ min-1 was appropriate for the fabrication of high-quality particulate LB monolayer because low withdrawal speed can offer sufficient time to form chemical bonds and expel the subphase from the substrate. Additionally, SEM images illustrated that the SA concentration of 0.40 mg ⋅ mL-1 was suitable for the fabrication of well-ordered particulate LB monolayers composed by the particles of 380 nm.

FABRICATION AND OPTOELECTRONIC PROPERTIES OF MgxZn1-xO ULTRATHIN FILMS BY LANGMUIR–BLODGETT TECHNOLOGY

By transferring MgxZn1-xO sol and stearic acid onto a hydrophilic silicon wafer or glass plate, the Langmuir–Blodgett (LB) multilayers of MgxZn1-xO (x:0, 0.2, 0.4) were deposited. After calcinations at 350°C for 0.5 h and at 500°C for 3 h, MgxZn1-xO ultrathin films were fabricated. The optimized parameters for monolayer formation and multilayer deposition were determined by the surface pressure-surface (Π-A) area and the transfer coefficient, respectively. The expended areas of stearic acid with MgxZn1-xO sols under Π-A isotherms inferred the interaction of stearic acid with MgxZn1-xO sols during the formation of monolayer at air–water interface. X-ray diffraction (XRD) was used to determine the crystal structures of MgxZn1-xO nanoparticles and ultrathin films. The surface morphologies of MgxZn1-xO ultrathin films were observed by scanning probe microscopy (AFM). And the optoelectronic properties of MgxZn1-xO were detected and discussed based on photoluminescence (PL) spectra.