Leonid Gurevich

Long-range charge transport in single G-quadruplex DNA molecules

DNA and DNA-based polymers are of interest in molecular electronics because of their versatile and programmable structures. However, transport measurements have produced a range of seemingly contradictory results due to differences in the measured molecules and experimental set-ups, and transporting significant current through individual DNA-based molecules remains a considerable challenge. Here, we report reproducible charge transport in guanine-quadruplex (G4) DNA molecules adsorbed on a mica substrate. Currents ranging from tens of picoamperes to more than 100 pA were measured in the G4-DNA over distances ranging from tens of nanometres to more than 100 nm. Our experimental results, combined with theoretical modelling, suggest that transport occurs via a thermally activated long-range hopping between multi-tetrad segments of DNA. These results could re-ignite interest in DNA-based wires and devices, and in the use of such systems in the development of programmable circuits.

Patterned poly(lactic acid) films support growth and spontaneous multilineage gene expression of adipose-derived stem cells

Conventional culture surfaces do not provide optimal environmental cues for expansion or differentiation of adult stem cells. Aiming to increase the efficiency of the in vitro culture conditions, biocompatible and biodegradable biomaterials such as poly(lactic acid) (PLA) have been proposed to engineer the stem cell microenvironment. In this study, we explored the feasibility of using PLA substrates to control the responses of adipose-derived stem cells (ASCs). The substrates consisted of flat and patterned PLA films fabricated by casting a chloroform-PLA solution on a glass surface. Patterning was achieved through the condensation of nano-sized water droplets during chloroform evaporation, which resulted in films displaying irregularly distributed circular indentations with a mean diameter of 248±65 nm. Both types of PLA substrates were assessed for protein adsorption using fibronectin and in vitro cell culturing. Tissue-culture polystyrene (TCPS) plates were used as control surfaces. The experiments demonstrated that the patterned PLA substrates had a significantly higher fibronectin adsorption capacity when compared with the flat counterparts. For the entire duration of the culture period, there was no significant difference in cell growth rate on the PLA surfaces with respect to TCPS despite signs of reduced adhesion. In addition, the semi-quantitative real-time RT-PCR analysis of a set of 14 lineage-specific genes revealed that the PLA-related transcriptional activity significantly surpassed that of TCPS. Remarkably, when assessing the effect of patterning, the patterned films proved superior regarding the activation of genes involved in the skeletal myogenic, cardiomyogenic, chondrogenic, and adipogenic pathways. Taken together, our data provide evidence that the surface patterning can exert such an influence on the stem cell microenvironment that the differentiation process can be effectively modulated. Consequently, the patterned PLA surfaces could potentially be used as a platform for localized delivery and engraftment of stem cells.

Pore size dependence of diffuse light scattering from anodized aluminum solar cell backside reflectors

The development of backside reflectors (BSRs) is crucial for the efficiency of future low cost thin-film silicon solar cells. In this work, the scattering efficiency of bare aluminum BSRs with different pore sizes and ordering of surface microstructures are investigated. The BSRs were fabricated by utilizing the process of self-ordering anodic oxidation on aluminum foils resulting in regions with an approximately hexagonally periodic surface microstructure. It was found that the total and diffuse light scattering reflectance spectra showed opposite tendencies when increasing the pore size of the microstructures. When the pore size was increased to 700 nm, more than 68% of the incident light with wavelengths from 250 nm to 800 nm was reflected by scattering. For a similar geometry, except that it had less ordering, this number was increased to around 80%. This large fraction of reflected light observed in the form of scattering is promising for the use of the considered geometries as BSRs in thin-film silicon solar cells.

Increased connective tissue attachment to silicone implants by a water vapor plasma treatment

Polydimethylsiloxane (PDMS) is the most common type of silicone polymer for the fabrication of implantable medical devices. Because of its inherent hydrophobic nature, the PDMS surface does not readily promote cellular adhesion, which leads to diverse clinical issues. Previously, we reported a simple water vapor plasma treatment of PDMS surfaces that resulted in stable long-term wettability and excellent in vitro cell compatibility. In this work, we report investigation of the in vivo local responses to PDMS implants treated by water vapor plasma using a subcutaneous rat model. The local tissue responses were assessed after 2 and 4 weeks of implantation by means of macroscopic and histomorphometric analysis. After 2 weeks of implantation, the plasma-treated implants elicited the formation of fibrous tissue capsules that were significantly thinner, more adherent, and vascularized than the control counterparts. The improved cell adhesion was correlated with an increased amount of cells attached to the implant surface after retrieval. There was no difference in the inflammatory response between untreated and treated samples. This study provides a rational approach to optimize the long-term performance of silicone implants, which is likely to have a significant impact in clinical applications demanding enhanced tissue integration of the implants.

Evaluation of electroporation-induced adverse effects on adipose-derived stem cell exosomes

In the recent years, the possibility of utilizing extracellular vesicles for drug delivery purposes has been investigated in various models, suggesting that these vesicles may have such potential. In addition to the choice of donor cell type for vesicle production, a major obstacle still exists with respect of loading the extracellular vesicles efficiently with the drug of choice. One of the proposed solutions to this problem has been drug loading by electroporation, where small pores are created in the membrane of the extracellular vesicles, hereby allowing for free diffusion of the drug compound into the interior of the vesicle. We investigated the utility of adipose-derived stem cells (ASCs) as an efficient exosome donor cell type with a particular focus on the treatment of glioblastoma multiforme (GBM). In addition, we evaluated electroporation-induced effects on the ASC exosomes with respect to their endogenous potential of stimulating GBM proliferation, and morphological changes to single and multiple ASC exosomes. We found that electroporation does not change the endogenous stimulatory capacity of ASC exosomes on GBM cell proliferation, but mediates adverse morphological changes including aggregation of the exosomes. In order to address this issue, we have successfully optimized the use of a trehalose-containing buffer system as a way of maintaining the structural integrity of the exosomes.

Patterned polymeric surfaces to study the influence of nanotopography on the growth and differentiation of mesenchymal stem cells.

The implementation of micro- and nanotechnologies to biomaterials constitutes a unique platform to improve our understanding on microenvironmental regulation of stem cell functions. In the recent years, various methods have been developed for the fabrication of micro- and nanopatterned polymeric culture substrates, and many of these novel surfaces are opening possibilities for new applications. Here, we provide procedures for creating nanoscale topographic features on films of poly(lactic acid), a biodegradable polymer frequently used for the fabrication of tissue engineering scaffolds. In addition, we provide methods to assess the growth and differentiation of mesenchymal stem cells cultured on the substrates.

Resistance to protein adsorption and adhesion of fibroblasts on nanocrystalline diamond films: the role of topography and boron doping

Boron-doped nanocrystalline diamond (BNCD) films exhibit outstanding electrochemical properties that make them very attractive for the fabrication of electrodes for novel neural interfaces and prosthetics. In these devices, the physicochemical properties of the electrode materials are critical to ensure an efficient long-term performance. The aim of this study was to investigate the relative contribution of topography and doping to the biological performance of BNCD films. For this purpose, undoped and boron-doped NCD films were deposited on low roughness (LR) and high roughness (HR) substrates, which were studied in vitro by means of protein adsorption and fibroblast growth assays. Our results show that BNCD films significantly reduce the adsorption of serum proteins, mostly on the LR substrates. As compared to fibroblasts cultured on LR BNCD films, cells grown on the HR BNCD films showed significantly reduced adhesion and lower growth rates. The mean length of fibronectin fibrils deposited by the cells was significantly increased in the BNCD coated substrates, mainly in the LR surfaces. Overall, the largest influence on protein adsorption, cell adhesion, proliferation, and fibronectin deposition was due to the underlying sub-micron topography, with little or no influence of boron doping. In perspective, BNCD films displaying surface roughness in the submicron range may be used as a strategy to reduce the fibroblast growth on the surface of neural electrodes.Graphical Abstract

Controlled deposition and combing of DNA across lithographically defined patterns on silicon

Summary We have developed a new procedure for efficient combing of DNA on a silicon substrate, which allows reproducible deposition and alignment of DNA molecules across lithographically defined patterns. The technique involves surface modification of Si/SiO2 substrates with a hydrophobic silane by using gas-phase deposition. Thereafter, DNA molecules are aligned by dragging the droplet on the hydrophobic substrate with a pipette tip. Using this procedure, DNA molecules were stretched to an average value of 122% of their contour length. Furthermore, we demonstrated combing of ca. 900 nm long stretches of genomic DNA across nanofabricated electrodes, which was not possible by using other available combing methods. Similar results were also obtained for DNA–peptide conjugates. We suggest this method as a simple yet reliable technique for depositing and aligning DNA and DNA derivatives across nanofabricated patterns.

The Many Faces of Diphenylalanine

Diphenylalanine is well known to form complex self-assembled structures, including peptide nanowires, with morphologies depending on N- and Cterminal modifications. Here we report that significant morphological variations of self-assembled structures are attainable through pH variation of unmodified diphenylalanine in trifluoroethanol. The obtained self-assembled diphenylalanine nanostructures are found to vary drastically with pH, incubation time, and diphenylalanine concentration in solution. The observed structures ranged from structured films at neutral and alkaline conditions to vertically aligned nanowires and sponge-like structures at acidic conditions. These observations are corroborated by the results of electrostatic modelling, indicating the disappearance of the dipole moment at high pH values. This also emphasizes the importance of the dipole moment for the resulting selfassembledstructures.Ourresultssuggestthat,incomparisontothecommonly described procedure of diphenylaniline nanowire growth through aniline vapor treatment, strictly anhydrous conditions are not necessarily required.

Roll coated large area ITO- and vacuum-free all organic solar cells from diketopyrrolopyrrole based non-fullerene acceptors with molecular geometry effects

In this paper, we investigate three diketopyrrolopyrrole (DPP) based small molecular non-fullerene acceptors, namely Ph(DPP)3, Ph(DPP)2, and PhDMe(DPP)2, focusing on molecular geometry effects on the frontier orbital level, light absorption, molecular configuration, electron mobility, thin film morphology, and photovoltaic performance of both spin-coated ITO based and roll coated large area, ITO- and vacuum-free organic solar cells (OSCs). For spin-coated devices based on P3HT as the donor polymer the solar cells gave power conversion efficiencies (PCEs) in the following order for (P3HT:PhDMe(DPP)2, 0.65%) > (P3HT:Ph(DPP)2, 0.48%) > (P3HT:Ph(DPP)3, 0.31%). All devices present an open circuit voltage (Voc) higher than 1.0 V. For the roll-coated devices, the PCEs were found to fall in another order and with lower values (P3HT:Ph(DPP)3, 0.54%) > (P3HT:Ph(DPP)2, 0.43%) > (P3HT:PhDMe(DPP)2, 0.04%) and the highest Voc was 0.82 V. Our preliminary results highlight the influence of geometry, structure and processing on the performance of non-fullerene acceptors.