Antibacterial properties of novel poly(methyl methacrylate) nanofiber containing silver nanoparticles

Poly(methyl methacrylate) (PMMA) nanofiber containing silver nanoparticles was synthesized by radical-mediated dispersion polymerization and applied to an antibacterial agent. UV-vis spectroscopic analysis indicated that the silver nanoparticles were continually released from the polymer nanofiber in aqueous solution. The antibacterial properties of silver/PMMA nanofiber against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria were evaluated using minimum inhibitory concentration (MIC), the modified Kirby-Bauer method, and a kinetic test. The MIC test demonstrated that the silver/PMMA nanofiber had enhanced antimicrobial efficacy compared to that of silver sulfadiazine and silver nitrate at the same silver concentration.     

Interaction of cetyl-trimethylammonium bromide with swollen and collapsed poly(N-isopropylacrylamide) nanogel particles

The interaction of cetyl-trimethylammonium bromide (CTAB) with swollen and collapsed poly(N-isopropylacrylamide) (pNIPAM) monodisperse nanogel particles was investigated by electrophoretic mobility, dynamic light scattering, and potentiometric surfactant activity measurements. The surfactant binds to the nanogel particles as monomers in the whole CTAB concentration range and binds in the form of surfactant aggregates as well above a critical concentration (cac) in both the swollen and collapsed state of the pNIPAM. The swollen particle system is a thermodynamically stable solution. The collapsed nanogel particle system is an electrically stabilized colloid dispersion, which coagulates when the particles are near the electrically neutral state. An analytically undetectably small amount of surfactant binding (5 × 10(-7) mol/g of pNIPAM) leads to a dramatic effect on the stability of the pNIPAM nanogel system. The electrokinetic potential versus surfactant concentration functions unexpectedly strongly depend upon the temperature around the lower critical solution temperature (LCST) of the polymer, which was interpreted by the change of the polymer segment density in the surface layer of the collapsing nanogel particles.     

Fluorocarbon- containing hydrophobically modified poly(N-isopropylacrylamide)

A fluorocarbon-modified poly(N-isopropylacrylamide) has been synthesized by copolymerization of N-isopropyl acrylamide with a small amount of acrylate or methacrylate containing a perfluoroalkyl group. It was found that the hydrophilicity of macromolecular backbone is an important factor to the solution properties of the copolymers and that hydrophobic association between fluorocarbon groups is stronger than that between the corresponding hydrocarbon analogies. The viscosity of some of the copolymer solutions was very sensitive to temperature. It was dilatant at higher fluorocarbon comonomer content ( > 0.20-1.0 mol%) and was Newtonian at very low fluorocarbon comonomer content (0.03-0.2 mol% ) . Evidence for hydrophobic association of the fluorocarbon groups was obtained from the effects of adding Nad and surfactants on the solution viscosity. The LC-ST properties of these copolymers were studied by DSC method and this was also found to be consistent with hydrophobic association between the fluorocarbo     

Synthesis and optical properties of silver nanoparticles and arrays.

This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

Thermodynamics of aqueous solutions containing poly (N-isopropylacrylamide)

Hydrogels undergo reversible and discontinuous volume changes in response to variation of solution conditions such as solvent composition, temperature, salt concentration, and pH. In this contribution we focus our attention on the experimental and theoretical investigation of these swelling equilibria of aqueous cross-linked poly (N-isopropylacrylamide) solutions as well as on the connected demixing behavior of the linear polymer dissolved in water. For the experimental study of the (liquid + liquid) equilibrium an alternative method based on refractive index measurements is suggested. In order to calculate the swelling behavior a model combining an expression for the Gibbs free energy of mixing with an expression for the elastic network is applied. As a model for the Gibbs free energy of mixing the UNIQUAC-approach and the Koningsveld–Kleintjens model are used. For the elastic network contribution again two different theories, namely the phantom network theory and the affine network theory, were applied. Whereas the type of network theory has only a small influence on the calculation results, the Gibbs free energy of mixing has a large impact. Using the UNIQUAC-approach the swelling equilibria can be correlated close to the experimental data, however, this model predicts a homogeneous mixture for linear polymer chains in water. In contrast to this situation the Koningsveld–Kleintjens model does a good job in calculating the swelling equilibria as well as the demixing curve, however, the adjustable parameter must be changed slightly.     

Epidermal cellular response to poly(vinyl alcohol) nanofibers containing silver nanoparticles

A heat-treated PVA nanofibrous matrix containing silver (Ag) was prepared by electrospinning an aqueous 10 wt% PVA solution and followed by heat treatment at 150 °C for 10 min. The average diameter of the as-spun and heat-treated PVA nanofibers was 330 nm. The heat-treated PVA nanofibrous matrix containing Ag was irradiated with UV light to transform the Ag ions in the nanofibrous matrix into Ag nanoparticles. The in vitro cytotoxicity of the Ag ions and/or nanoparticles on normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) cultures was examined. The PVA nanofibrous matrix containing Ag showed slightly higher level of attachment and spreading in the early stage culture (1 h) than the PVA nanofibers without Ag (control). However, compared with the PVA nanofibers without Ag, the heat-treated and UV-irradiated PVA nanofibers, containing mainly Ag ions and nanoparticles, respectively, showed reduced cell attachment and spreading. This shows that both Ag ions and Ag nanoparticles are cytotoxic to NHEK and NHEF. There was no significant difference in cytotoxicity to NHEK and NHEF between Ag ions and Ag nanoparticles. NHEF appeared to be more sensitive to Ag ions or particles than NHEK. In addition, the residual nitrate ions (NO₃⁻) in the PVA nanofibers had an adverse effect on the culture of both cells.     

Tailoring thermoresponsive nanostructured poly(N-isopropylacrylamide) hydrogels made with poly(acrylamide) nanoparticles

The thermoresponsive behavior and mechanical properties of nanostructured hydrogels, which consist of poly(acrylamide) nanoparticles embedded in a cross-linked poly(N-isopropylacrylamide) hydrogel matrix, are reported here. Nanostructured hydrogels exhibit a tuned volume phase transition temperature (T _VPT), which varies with nanoparticle content in the range from 32 up to 39–40 °C. Moreover, larger equilibrium water uptake, faster swelling and de-swelling rates, and larger equilibrium swelling at 25 °C were obtained with nanostructured hydrogels compared with those of conventional ones. Elastic and Young’s moduli were larger than those of conventional hydrogels at similar swelling ratios. The tuned T _VPT and the de-swelling rate were predicted with a modified Flory–Rehner equation coupled with a mixing rule that considers the contribution of both polymers. These behaviors are explained by a combination of hydrophilic/hydrophobic interactions and by the controlled inhomogeneities (nanoparticles) introduced by the method of synthesis.     

Synthesis and characterization of surface-cyanofunctionalized poly (N-isopropylacrylamide) latexes

 A series of P[N-isopropylacrylamide (NIPAM)] latexes with different contents of cyano groups were successfully prepared by either seeded or shot-growth polymerizations of an aqueous solution containing acrylonitrile (AN) onto a seed P[NIPAM] latex, respectively, and further characterized by FT-IR, ¹H-NMR, elemental analysis, as well as by quasielastic light scattering (QELS) and scanning electron microscopy (SEM). All prepared surface-cyanofunctionalized P[NIPAM] latexes exhibited the same range of lower critical solution temperature (LCST) as a pure P[NIPAM] latex. The shot polymerization process proved more efficient at yielding cyano derivatized latexes than the seeded polymerization technique. The amount of incorporated cyano groups onto the particles was determined with a good correlation both by ¹H-NMR and elemental analysis. The higher the amount of initially introduced AN monomer in the reaction mixture, the more cyano groups were incorporated onto the particles. The surface of the particles with high content of cyano groups appeared quite rough by SEM in comparison with that of the pure P[NIPAM] particles. Received: 25 February 1998 Accepted: 23 June 1998     

Dynamic surface properties of poly(N-isopropylacrylamide) solutions

The dynamic surface elasticity of aqueous solutions of poly(N-isopropylacrylamide) (pNIPAM) has been measured by the oscillating barrier and capillary wave methods as a function of time and concentration. While the real and imaginary parts of the surface elasticity almost did not change with the concentration, their kinetic dependencies proved to be nonmonotonic. Simultaneous measurements of the film thickness and adsorbed amount by null-ellipsometry showed that the pNIPAM adsorption can be divided into two steps corresponding to the formation of a concentrated narrow region close to the air phase and a region of tails and loops protruding into the bulk liquid. The local maximum of the elasticity can be observed in the course of the first step when the adsorbed macromolecules do not form long loops and tails. The results are in agreement with recent data on the nonequilibrium surface properties of solutions of other nonionic homopolymers and the theory of dilational surface viscoelasticity.     

Release property of temperature-sensitive alginate beads containing poly(N-isopropylacrylamide)

The graft copolymer (APN) of alginate and poly(N-isopropylacrylamide) (PNIPAM) were synthesized and APN beads were prepared by dropping the aqueous solution of the copolymer into an aqueous solution of Ca(2+) solution. Alginate chains were employed to play a role in forming beads by electrostatic interactions with a multivalent ion, Ca(2+). Grafted PNIPAM segments were adopted to act as a valve for the pores of the beads, since they exhibit the properties of thermal contraction and expansion. The percent of release of blue dextran from APN beads was higher at 40 degrees C than at 25 degrees C. The difference in the release between two temperatures became more distinguishable when the content of PNIPAM in APN beads is higher. Below lower critical solution temperature (LCST), the expanded PNIPAM would close the pores of the beads, resulting in a lower release rate. Above LCST, the thermally contracted polymer would open the pores, resulting in a higher release rate. The percent of release from APN beads were investigated when the temperature of the release medium is altered. The release rate was relatively low at 25 degrees C. The temperature, however, changed up to 40 degrees C, a marked increase in the release rate was observed. These trends were found to be reproducible when the temperature was repeatedly altered between 25 and 40 degrees C. As a result, a stepwise response to the temperature alteration was obtained.     

Synthesis of thermoresponsive polystyrene-based comb-type grafted poly(N-isopropylacrylamide)

Narrowly distributed polystyrene-g-p(N-isopropylacrylamide) (PSt-g-PNIPAM) was prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using the brominated polystyrene as macroinitiator and CuCl combined with hexamethyltriethylenetetramine as catalyst. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of PSt-g-PNIPAM. The gel permeation chromatography (GPC) showed that the graft copoly- mer had a single distribution peak with molecular weight, Mn (g/mol) of 19815 g/mol (using polystyrene as the standard). Differential scanning calorimetry (DSC) revealed that due to both effects of hydro- phobic isopropyl groups and hydrogen bonds in the amide group, the glass transition temperature (Tg) of PSt-g-PNIPAM enhanced 16.0 ℃ compared to the Tg of the polystyrene.     

Structural characterization of nanoparticles from thermoresponsive poly(N-isopropylacrylamide)-DNA conjugate

Poly(N-isopropylacrylamide) (PNIPAAm) grafted with single-stranded (ss) DNA conjugate (PNIPAAm-g-DNA) self-assembles above its lower critical solution temperature to form colloidal particles. When the ssDNA within the particle hybridizes with its complementary DNA, the particles aggregate above a certain threshold of salt concentration with drastically increased turbidity in solution. Detailed structural information of the particle was obtained mainly by small-angle X-ray scattering. The influence of copolymer composition on the morphology of particle and non-crosslinking aggregation was examined. The particle consists of hydrophobic PNIPAAm core surrounded by hydrophilic DNA strands. The increase in DNA fraction brought about a significant decrease in core size, whereas the shell thickness little changed and corresponded to the length of DNA. A structural model with a sticky potential was applied to the analysis of particle aggregate. This analysis provided that the particles aggregate while the coronal layers interpenetrate each other. The interaction between the particles was quantified in terms of the sticky potential and showed a trend to be influenced by the particle size rather than the graft density of DNA strands on the particle.     

Rapid and precise release from nano-tracted poly(N-isopropylacrylamide) hydrogels containing linear poly(acrylic acid)

We investigated the rapid and precise molecular release from hydrogels in response to dual stimuli. To achieve precise on/off drug release using thermoresponsive poly(N-isopropylacrylamide) hydrogels, we prepared nano-structured semi-IPNs, which consisted of thermosensitive PNIPAAm networks penetrated by pH-responsive poly(acrylic acid) (PAAc) linear chains and perforated to create nano-tracts as a molecular pathway. The present nano-tracted semi-IPNs show a rapid deswelling response to both temperature and pH. Model drug releases were investigated when simultaneous changes in temperature and pH were applied. We observed that the cationic drug was rapidly released and then abruptly discontinued from the nano-tracted semi-IPNs in response to the dual stimuli, and clear release and stopping cycles were repeatedly observed on successive steps. Moreover, the release rates and amount of drug released were controllable by the deswelling speed of the gels and the PAAc content inside the gels. This novel release system using the nano-tracted semi-IPNs may be useful for the high performance, pulsed release of molecules.     

Synthesis and properties of a poly(diphenylacetylene) containing carbazolyl groups

1-(p-N-Carbazolylphenyl)-2-phenylacetylene (p-CzDPA) was polymerized by TaCl₅–co-catalyst systems (cocatalysts: n-Bu₁Sn, Et₃SiH, and 9BBN) to produce acetone-insoluble polymers in about 60-70% yields. Poly(p-CzDPA) was a yellowish-orange solid, most part of which was soluble in toluene, chloroform, etc., and its weight-average molecular weights were around 4×10⁵. This polymer formed a tough film by solution casting, and was thermally very stable (the onset temperature of weight loss in TGA in air 470°C). The oxygen per-meability coefficient of the polymer at 25°C was lower than two barrers. The present polymer showed photoconductivity and redox activity. © 1995 John Wiley & Sons, Inc.     

Preparation and antibacterial activity of electrospun chitosan/poly(ethylene oxide) membranes containing silver nanoparticles

Fairly uniform chitosan (CS)/poly(ethylene oxide) (PEO) ultrafine fibers containing silver nanoparticles (AgNPs) were successfully prepared by electrospinning of CS/PEO solutions containing Ag/CS colloids by means of in situ chemical reduction of Ag ions. The presence of AgNPs in the electrospun ultrafine fibers was confirmed by X-ray diffraction patterns. The AgNPs were evenly distributed in CS/PEO ultrafine fibers with the size less than 5 nm observed under a transmission electron microscope. X-ray photoelectron spectroscopy suggested that the existence of Ag―O bond in the composite ultrafine fibers led to the tight combination between Ag and CS. Evaluation of antimicrobial activities of the electrospun Ag/CS/PEO fibrous membranes against Escherichia coli showed that the AgNPs in the ultrafine fibers significantly enhanced the inactivation of bacteria.     

Structural properties of thermoresponsive poly(N-isopropylacrylamide)-poly(ethyleneglycol) microgels

We present investigations of the structural properties of thermoresponsive poly(N-isopropylacrylamide) (PNiPAM) microgels dispersed in an aqueous solvent. In this particular work poly(ethyleneglycol) (PEG) units flanked with acrylate groups are employed as cross-linkers, providing an architecture designed to resist protein fouling. Dynamic light scattering (DLS), static light scattering (SLS), and small angle neutron scattering (SANS) are employed to study the microgels as a function of temperature over the range 10 °C ≤ T ≤ 40 °C. DLS and SLS measurements are simultaneously performed and, respectively, allow determination of the particle hydrodynamic radius, R(h), and radius of gyration, R(g), at each temperature. The thermal variation of these magnitudes reveals the microgel deswelling at the PNiPAM lower critical solution temperature (LCST). However, the hydrodynamic radius displays a second transition to larger radii at temperatures T ≤ 20 °C. This feature is atypical in standard PNiPAM microgels and suggests a structural reconfiguration within the polymer network at those temperatures. To better understand this behavior we perform neutron scattering measurements at different temperatures. In striking contrast to the scattering profile of soft sphere microgels, the SANS profiles for T ≤ LCST of our PNiPAM-PEG suspensions indicate that the particles exhibit structural properties characteristic of star polymer configurations. The star polymer radius of gyration and correlation length gradually decrease with increasing temperature despite maintenance of the star polymer configuration. At temperatures above the LCST, the scattered SANS intensity is typical of soft sphere systems.     

Synthesis and characterization of thermally reversible macroporous poly(N-isopropylacrylamide) hydrogels

Macroporous hydrogels are characterized by large pore sizes, high pore volumes, and high specific surface area. Besides these characteristics, macroporous hydrogels based on thermally reversible polymers respond to temperature changes much faster than hydrogels prepared by a conventional method. Crosslinked poly(N-isopropylacrylamide) (polyNIPAAm) forms a thermally reversible hydrogel which shows a lower critical solution temperature (LCST) ca. 33°C in aqueous solutions. We have synthesized thermally reversible polyNIPAAm hydrogels having macroporous structures by a new method. These macroporous hydrogels have large pore volumes, large average pore sizes, and faster macromolecule permeation rates in comparison to conventional polyNIPAAm hydrogels synthesized by a conventional method. Compared with conventional polyNIPAAm hydrogels, the macroporous polyNIPAAm hydrogels have higher swelling ratios at temperatures below the LCST and exhibit faster deswelling and reswelling rates. The deswelling rates are especially rapid. These thermally reversible macroporous hydrogels may be very useful in controlled active agent delivery and toxin removal, as well as dewatering of solutions. Peptides or proteins may behave as if they were in bulk solution within the large aqueous pores, and this may reduce their inactivation when such gels are used for their storage and later release. The gels may also be useful in microrobotic devices due to their fast response to temperature. © 1992 John Wiley & Sons, Inc.     

Functional group distributions in carboxylic acid containing poly(N-isopropylacrylamide) microgels

Control of the functional group distribution is of fundamental importance in the design of functional polymer particles, particularly in biological applications. Surface-functionalized particles are useful for bioconjugation and medical diagnostics, while internally functionalized particles may have applications in drug delivery. We have prepared a series oftemperature-sensitive poly(N-isopropylacrylamide) (PNIPAM)-based microgels containing carboxylic acid functional groups via copolymerization with methacrylic acid and acrylamide, which was selectively hydrolyzed under optimized conditions to generate the carboxylic acid functionality. The resulting microgels were analyzed using conductometric and potentiometric titration, dynamic light scattering, and electrophoresis. Acrylamide-containing microgels hydrolyzed below the volume phase transition temperature (VPTT) show broad particle size versus temperature profiles, relatively low electrophoretic mobilities at basic pH, and time-dependent base titration profiles, suggesting the presence of internal functional groups whose titration is diffusion-controlled. Methacrylic acid containing microgels show sharper particle size versus temperature profiles, higher electrophoretic mobilities at basic pH, and time-independent base titration profiles, suggesting the presence of a "core-shell" structure with primarily surface functionalization. Similar results were obtained when acrylamide-containing microgels were hydrolyzed at temperatures above the VPTT. Thus, through selection of comonomer and hydrolysis conditions, we have developed strategies to control and characterize the number and distribution ofcarboxylic acid functional groups in PNIPAM-based microgels.