Patrycja Bober

Biocomposites of Nanofibrillated Cellulose, Polypyrrole, and Silver Nanoparticles with Electroconductive and Antimicrobial Properties

In this work, flexible and free-standing composite films of nanofibrillated cellulose/polypyrrole (NFC/PPy) and NFC/PPy-silver nanoparticles (NFC/PPy-Ag) have been synthesized for the first time via in situ one-step chemical polymerization and applied in potential biomedical applications. Incorporation of NFC into PPy significantly improved its film formation ability resulting in composite materials with good mechanical and electrical properties. It is shown that the NFC/PPy-Ag composite films have strong inhibition effect against the growth of Gram-positive bacteria, e.g., Staphylococcus aureus. The electrical conductivity and strong antimicrobial activity makes it possible to use the silver composites in various applications aimed at biomedical treatments and diagnostics. Additionally, we report here the structural and morphological characterization of the composite materials with Fourier-transform infrared spectroscopy, atomic force microscopy, and scanning and transmission electron microscopy techniques.

Polypyrrole nanotubes: mechanism of formation

This article presents a contribution to better understanding of the processes which take place during the synthesis of polypyrrole nanotubes using a structure-guiding agent, methyl orange. Polypyrrole was prepared by oxidation of pyrrole monomer with iron(III) chloride. In the presence of methyl orange, the formation of nanotubes was observed instead of the globular morphology. Two reaction schemes with reversed additions of oxidant and monomer have been tested and they show remarkable influence on the produced morphology. Nanotubes with circular or rectangular profiles and diameters from tens to hundreds of nanometres have been obtained. FTIR and Raman spectra were used to assess the molecular structure of polypyrrole and detect residual methyl orange in the samples. The conductivity of nanotubes compressed into pellets was as high as 68 S cm−1. The mechanism of nanotubular formation starting at the nucleus produced with the participation of organic dye is proposed. The growth of a nanotube, however, proceeds in the absence of a template. An alternative mechanism for the formation of nanotubes, the coating of solid templates with a polypyrrole overlayer, is also discussed.

Polypyrrole–silver composites prepared by the reduction of silver ions with polypyrrole nanotubes

Polypyrrole nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the presence of methyl orange. They were subsequently used for the reduction of silver ions to silver nanoparticles. The nanotubular form of polypyrrole is compared with the classical globular morphology in its ability to reduce silver ions. Both polypyrrole salts and bases were used in the experiments. The content of metallic silver in the resulting composite, determined by thermogravimetric analysis, was 21–31 wt%. Elemental composition is also discussed on the basis of energy-dispersive X-ray spectroscopy. Contrary to the expectation, the conductivity of polypyrrole nanotubes in salt form, 35.7 S cm−1, was reduced to 20.9 S cm−1 after the incorporation of silver. The presence of silver had generally little effect on the conductivity. The temperature dependence of conductivity reveals that the composites maintain the semiconducting character of polypyrrole and their conductivity increased with increasing temperature. The conductivity of the composites surprisingly increased when the samples were placed in vacuo.

Polypyrrole salts and bases: superior conductivity of nanotubes and their stability towards the loss of conductivity by deprotonation

Polypyrrole nanotubes exhibit conductivity of tens S cm−1 which is one of the highest among the current conducting polymers. They are thus superior to the common globular form with the conductivity of units of S cm−1 or lower. The conductivity of both forms is reduced after treatment with alkalis but still remains high, units of S cm−1 and 10−2 S cm−1, respectively. The deprotonation, which is responsible for conductivity reduction, is discussed on the basis of salt–base transition in polypyrrole. It is not fully reversible, and the reprotonation with acids recovers the conductivity only in part. The role of methyl orange, which was used to support the formation of nanotubes, is proposed to be similar to that of surfactants. FTIR and Raman spectroscopies prove that methyl orange is strongly bound to polypyrrole in its acid form, and an “insertion” mechanism is proposed to explain the resistance towards the deprotonation of nanotubes. The spectra also illustrate that the molecular structure of nanotubular polypyrrole is preserved even under highly alkaline conditions at a pH close to 14, where the globular form becomes damaged. Polypyrrole, especially in its nanotubular form, is of promise in applications requiring electrical conduction even under neutral or alkaline conditions, where other conducting polymers, such as polyaniline, lose their exploitable conductivity.

Cotton fabric coated with conducting polymers and its application in monitoring of carnivorous plant response

The paper describes the electrical plant response to mechanical stimulation monitored with the help of conducting polymers deposited on cotton fabric. Cotton fabric was coated with conducting polymers, polyaniline or polypyrrole, in situ during the oxidation of respective monomers in aqueous medium. Thus, modified fabrics were again coated with polypyrrole or polyaniline, respectively, in order to investigate any synergetic effect between both polymers with respect to conductivity and its stability during repeated dry cleaning. The coating was confirmed by infrared spectroscopy. The resulting fabrics have been used as electrodes to collect the electrical response to the stimulation of a Venus flytrap plant. This is a paradigm of the use of conducting polymers in monitoring of plant neurobiology.

Conducting polyaniline based cell culture substrate for embryonic stem cells and embryoid bodies

In this work, thin films consisting of electrically conducting polyaniline (PANI) and poly(2-acrylamido-2-methyl-1-propanesulfonate) (PAMPSA) have been used as cell culture substrates for embryonic stem cells (ESC) and embryoid bodies (EMB). The PANI–PAMPSA films having fibrillar morphology were electrochemically polymerized in a single-step by cyclic voltammetry from an aqueous solution containing aniline and PAMPSA. UV-visible spectroscopy showed that the PANI films were electrically conducting still at pH 10. This makes them suitable for tissue engineering applications operating at physiological pH, in contrast to the commonly used PANI hydrochloride films which loose their electrical conductivity at pH ≥ 4. Our results reveal that the PANI–PAMPSA films allow only for limited ESC adhesion and growth. The inhibition of the EMB growth and adhesion on the PANI–PAMPSA surface in serum-free medium indicates that it can be used as a cell-selective substrate for the growth of only some specific differentiated EMB cell types.

Blood coagulation and platelet adhesion on polyaniline films

Polyaniline is a promising conducting polymer with still increasing application potential in biomedicine. Its surface modification can be an efficient way how to introduce desired functional groups and to control its properties while keeping the bulk characteristics of the material unchanged. The purpose of the study was to synthetize thin films of pristine conducting polyaniline hydrochloride, non-conducting polyaniline base and polyaniline modified with poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) and investigate chosen parameters of their hemocompatibility. The modification was performed either by introduction of PAMPSA during the synthesis or by reprotonation of polyaniline base. The polyaniline hydrochloride and polyaniline base had no impact on blood coagulation and platelet adhesion. By contrast, the polyaniline reprotonated with PAMPSA completely hindered coagulation thanks to its interaction with coagulation factors Xa, Va and IIa. The significantly lower platelets adhesion was also found on this surface. Moreover, this film maintains its conductivity at pH of 6, which is an improvement in comparison with standard polyaniline hydrochloride losing most of its conductivity at pH of 4. Polyaniline film with PAMPSA introduced during synthesis had an impact on platelet adhesion but not on coagulation. The combined conductivity, anticoagulation activity, low platelet adhesion and improved conductivity at pH closer to physiological, open up new possibilities for application of polyaniline reprotonated by PAMPSA in blood-contacting devices, such as catheters or blood vessel grafts.

Polypyrrole prepared in the presence of methyl orange and ethyl orange: nanotubes versus globules in conductivity enhancement

The preparation of highly conducting polymer nanostructures with defined and uniform nanoscale morphologies presents a research challenge. Polypyrrole nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the presence of methyl orange. The reactant concentrations and the oxidant-to-pyrrole mole ratio were varied in order to obtain the product with the highest conductivity in good yield. The conductivity increased from 1.55 S cm−1 for the standard globular morphology to 119 S cm−1 for nanotubes prepared under optimized conditions. The replacement of methyl orange with the closely related ethyl orange has led exclusively to the globular morphology of polypyrrole but the conductivity still improved to 27.3 S cm−1. The marked difference in morphology is explained by the ability of methyl orange salt to produce a solid template for the nanotubular growth of polypyrrole under acidic conditions, in contrast to ethyl orange. The latter dye, however, acts similarly to surfactants and it also enhances the conductivity of polypyrrole. The results are discussed in detail on the basis of FTIR and Raman spectra.

Polypyrrole Nanotubes and Their Carbonized Analogs: Synthesis, Characterization, Gas Sensing Properties.

Polypyrrole (PPy) in globular form and as nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the absence and presence of methyl orange, respectively. They were subsequently converted to nitrogen-containing carbons at 650 °C in an inert atmosphere. The course of carbonization was followed by thermogravimetric analysis and the accompanying changes in molecular structure by Fourier Transform Infrared and Raman spectroscopies. Both the original and carbonized materials have been tested in sensing of polar and non-polar organic vapors. The resistivity of sensing element using globular PPy was too high and only nanotubular PPy could be used. The sensitivity of the PPy nanotubes to ethanol vapors was nearly on the same level as that of their carbonized analogs (i.e., ~18% and 24%, respectively). Surprisingly, there was a high sensitivity of PPy nanotubes to the n-heptane vapors (~110%), while that of their carbonized analog remained at ~20%. The recovery process was significantly faster for carbonized PPy nanotubes (in order of seconds) compared with 10 s of seconds for original nanotubes, respectively, due to higher specific surface area after carbonization.

Electrical transport properties of poly(aniline-co-p-phenylenediamine) and its composites with incorporated silver particles

Statistical copolymers of aniline and p-phenylenediamine, poly(aniline-co-p-phenylenediamine)s, were synthesised by oxidative polymerisation using various oxidants, ammonium peroxydisulphate or silver nitrate. Depending on the choice of oxidant, copolymers or composites with silver particles were obtained. Different molar concentrations of p-phenylenediamine in the reaction mixture provided materials of different conductivities. The influence of both the copolymer composition and the presence of discrete silver particles on the electric and dielectric properties of the system was studied. The results showed a decrease in the conductivity of copolymers and their composites with the silver content compared with the content of standard polyaniline salt. The reduction in conductivity was described in terms of the decreased density of hopping centres due to defects in the copolymer structure. The dielectric relaxations observed were described in terms of their activation energies and were linked to the corresponding conduction mechanism.