Hematopoietic stem cells (HSCs) are rare cells residing in the bone marrow and give rise to millions of new blood cells daily throughout life. Because of their multipotent, self-renewing nature, they have also been used for several decades to treat hematological disorders. However, HSCs are scarce and difficult to maintain ex vivo, demonstrating the need for developing novel in vitro methods to expand HSCs that mimic the complex in vivo microenvironment in suitable culture tissue plates, in extracellular matrix scaffolds, or on a biochip. One component to include in such an artificial microenvironment is HSC-related growth factors (GFs) immobilized on surfaces that mimic membrane-bound GFs in vivo. In this paper, we have initiated the development of an ex vivo system to study the immobilization of growth factors that sustain HSC maintenance and possibly expansion. However, since HSC-related GFs are expensive we have developed a proof-of-concept model using bovine serum albumin (BSA) as an alternative. Polypyrrole (PPy) was electrochemically synthesized in the presence of dicarboxylic acids with different hydrocarbon chain lengths and polycarboxylic acids with different molecular weights as dopants. BSA was immobilized on the PPy surface using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) to couple BSA to the carboxylic acid dopant of PPy. These PPy films with different dopants showed different abilities to immobilize BSA using EDC/NHS coupling and also different surface properties. In addition, owing to the interesting switchable properties of PPy upon alteration of the oxidation/reduction potential, the immobilized BSA could change its presentation on the PPy surface depending on the redox state. To characterize the PPy surfaces and to study the different immobilization results of BSA on these PPy variants with different dopants and different presentation behavior upon redox switching, the electrochemical properties, hydrophobicity, thickness, roughness, surface COOH density and fluorescence labeling were investigated. The results indicate that the polycarboxylic acid dopants could immobilize more BSA on the PPy surface. Moreover, the BSA in the as-fabricated state shows a "collapsed" presentation on the PPy surface, a "less collapsed" presentation in the oxidized state and an "erected" presentation in the reduced state. Cell viability studies using hematopoietic cells showed that the developed PPy-BSA surfaces did not negatively alter cell viability or cell proliferation compared to the control.

In the domain of organic mixed ionic-electronic conductors (OMIECs), simultaneous transport and coupling of ionic and electronic charges are crucial for the function of electrochemical devices in organic electronics. Understanding conduction mechanisms and chemical reactions in operational devices is pivotal for performance enhancement and is necessary for the informed and systematic development of more promising materials. Surface-enhanced Raman spectroscopy (SERS) is a potent tool for monitoring electrochemical evolution and dynamic doping in operational devices, offering enhanced sensitivity to subtle spectral changes. We demonstrate the utility of SERS for in situ tracking of doping in OMIECs in an organic light-emitting electrochemical cell (LEC) containing a conjugated polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]; MEH-PPV), a molecular anion (lithium triflate), and an electrolyte network (poly(ethylene oxide); PEO). SERS enhancement is achieved via an interleaved layer of gold particles formed by spontaneous breakup of a deposited thin gold film. The results successfully highlight the ability of SERS to unveil time-resolved MEH-PPV doping and polaron formation, elucidating the effects of triflate ion transfer in the operating device and validating the electrochemical doping model in LECs.

The two-electron oxygen reduction reaction (ORR), powered by affordable renewable energy, presents a more promising and sustainable approach to hydrogen peroxide production than traditional methods. In this study, we introduce a membrane electrolyzer for ORR-to-H2O2 generation. The conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) acts as the cathode that aids the oxygen reduction reaction through a two-electron pathway to produce H2O2. At the anode, we employed the oxidation of a model organic molecule, 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate (tiron). This catalyst-free anode process, as an alternative to the sluggish water oxidation reaction commonly used in classical electrolyzers, reduces voltage loss to release protons, cross the membrane, and feed the ORR at the cathode. Our study investigated the often-neglected issue of organic crossover during electrolyzer operation and its significant impact on transport behavior. This research paves the way for the development of crossover-free flow cells, extending the realm of electrochemical devices based on the electrolyte fed and the membrane. We introduce a membrane electrolyzer for the generation of hydrogen peroxide via oxygen reduction and catalyst-free oxidation of quinones. The study reports the effect of the applied coulombic forces on ions, which is the origin of crossover.

Silk fibers have unique mechanical properties, and many studies of silk aim at understanding how these properties are related to secondary structure content, which often is determined by infrared spectroscopy. We report significant method-induced irreversible structural changes to both natural and synthetic spider silk fibers, derived from the widely used attenuated total reflection Fourier-transform infrared (ATR-FTIR) technique. By varying the force used to bring fibers into contact with the internal reflection elements of ATR-FTIR accessories, we observed correlated and largely irreversible changes in the secondary structure, with shape relaxation under pressure occurring within minutes. Fitting of spectral components shows that these changes agree with transformations from the alpha-helix to the beta-sheet secondary structure with possible contributions from other secondary structure elements. We further confirm the findings with IR microspectroscopy, where similar differences were seen between the pressed and unaffected regions of spider silk fibers. Our findings show that ATR-FTIR spectroscopy requires care in its use and in the interpretation of the results.

Neutron reflectivity at the solid/liquid interface offers unique opportunities for resolving the structure–function relationships of interfacial layers in soft matter science. It is a non-destructive technique for detailed analysis of layered structures on molecular length scales, providing thickness, density, roughness, and composition of individual layers or components of adsorbed films. However, there are also some well-known limitations of this method, such as the lack of chemical information, the difficulties in determining large layer thicknesses, and the limited time resolution. We have addressed these shortcomings by designing and implementing a portable sample environment for in situ characterization at neutron reflectometry beamlines, integrating infrared spectroscopy under attenuated total reflection for determination of molecular entities and their conformation, and spectroscopic ellipsometry for rapid and independent measurement of layer thicknesses and refractive indices. The utility of this combined setup is demonstrated by two projects investigating (a) pH-dependent swelling of polyelectrolyte layers and (b) the impact of nanoparticles on lipid membranes to identify potential mechanisms of nanotoxicity. 

Producing thick films of conducting polymers by a low-cost manufacturing technique would enable new applications. However, removing huge solvent volume from diluted suspension or dispersion (1-3 wt%) in which conducting polymers are typically obtained is a true manufacturing challenge. In this work, a procedure is proposed to quickly remove water from the conducting polymer poly(3,4-ethylenedioxythiophene:poly(4-styrene sulfonate) (PEDOT:PSS) suspension. The PEDOT:PSS suspension is first flocculated with 1 m H2SO4 transforming PEDOT nanoparticles (approximate to 50-500 nm) into soft microparticles. A filtration process inspired by pulp dewatering in a paper machine on a wire mesh with apertures dimension between 60 mu m and 0.5 mm leads to thick free-standing films (approximate to 0.5 mm). Wire mesh clogging that hinders dewatering (known as dead-end filtration) is overcome by adding to the flocculated PEDOT: PSS dispersion carbon fibers that aggregate and form efficient water channels. Moreover, this enables fast formation of thick layers under simple atmospheric pressure filtration, thus making the process truly scalable. Thick freestanding PEDOT films thus obtained are used as electrocatalysts for efficient reduction of oxygen to hydrogen peroxide, a promising green chemical and fuel. The inhomogeneity of the films does not affect their electrochemical function.

A common way of determining the majority charge carriers of pristine and doped semiconducting polymers is to measure the sign of the Seebeck coefficient. However, a polarity change of the Seebeck coefficient has recently been observed to occur in highly doped polymers. Here, it is shown that the Seebeck coefficient inversion is the result of the density of states filling and opening of a hard Coulomb gap around the Fermi energy at high doping levels. Electrochemical n-doping is used to induce high carrier density (>1 charge/monomer) in the model system poly(benzimidazobenzophenanthroline) (BBL). By combining conductivity and Seebeck coefficient measurements with in situ electron paramagnetic resonance, UV-vis-NIR, Raman spectroelectrochemistry, density functional theory calculations, and kinetic Monte Carlo simulations, the formation of multiply charged species and the opening of a hard Coulomb gap in the density of states, which is responsible for the Seebeck coefficient inversion and drop in electrical conductivity, are uncovered. The findings provide a simple picture that clarifies the roles of energetic disorder and Coulomb interactions in highly doped polymers and have implications for the molecular design of next-generation conjugated polymers.

Cells adhering onto surfaces sense and respond to chemical and physical surface features. The control over cell adhesion behavior influences cell migration, proliferation, and differentiation, which are important considerations in biomaterial design for cell culture, tissue engineering, and regenerative medicine. Here, we report on a supramolecular-based approach to prepare reversible self-assembled monolayers (rSAMs) with tunable lateral mobility and dynamic control over surface composition to regulate cell adhesion behavior. These layers were prepared by incubating oxoacid-terminated thiol SAMs on gold in a pH 8 HEPES buffer solution containing different mole fractions of omega-(ethylene glycol),(2-)(4)- and omega-(GRGDS)-, alpha-benzamidino bolaamphiphiles. Cell shape and morphology were influenced by the strength of the interactions between the amidine-functionalized amphiphiles and the oxoacid of the underlying SAMs. Dynamic control over surface composition, achieved by the addition of inert filler amphiphiles to the RGD-functionalized rSAMs, reversed the cell adhesion process. In summary, rSAMs featuring mobile bioactive ligands offer unique capabilities to influence and control cell adhesion behavior, suggesting a broad use in biomaterial design, tissue engineering, and regenerative medicine.

Self-initiated photografting and photopolymerization (SI-PGP) uses UV illumination to graft polymers to surfaces without additional photoinitiators using the monomers as initiators, “inimers”. A wider use of this method is obstructed by a lack of understanding of the resulting, presumably heterogeneous, polymer structure and of the parallel degradation under continuous UV illumination. We have used neutron reflectometry to investigate the structure of hydrated SI-PGP-prepared poly(HEMA-co-PEG₁₀MA) (poly(2-hydroxyethyl methacrylate-co-(ethylene glycol)₁₀ methacrylate)) films and compared parabolic, sigmoidal, and Gaussian models for the polymer volume fraction distributions. Results from fitting these models to the data suggest that either model can be used to approximate the volume fraction profile to similar accuracy. In addition, a second layer of deuterated poly(methacrylic acid) (poly(dMAA)) was grafted over the existing poly(HEMA-co-PEG₁₀MA) layer, and the resulting double-grafted films were also studied by neutron reflectometry to shed light on the UV-polymerization process and the inevitable UV-induced degradation which competes with the grafting.

Green hydrogen is identified as one of the prime clean energy carriers due to its high energy density and a zero emission of CO2. A possible solution for the transport of H2 in a safe and low-cost way is in the form of liquid organic hydrogen carriers (LOHCs). As an alternative to loading LOHC with H2 via a two-step procedure involving preliminary electrolytic production of H2 and subsequent chemical hydrogenation of the LOHC, we explore here the possibility of electrochemical hydrogen storage (EHS) via conversion of proton of a proton donor into a hydrogen atom involved in covalent bonds with the LOHC (R) via a protoncoupled electron transfer (PCET) reaction: . We chose 9-fluorenone/ fluorenol (Fnone/Fnol) conversion as such a model PCET reaction. The electrochemical activation of Fnone via two sequential electron transfers was monitored with in-situ and operando spectroscopies in absence and in presence of different alcohols as proton donors of different reactivity, which enabled us to both quantify and get the mechanistic insight on PCET. The possibility of hydrogen extraction from the loaded carrier molecule was illustrated by chemical activation.