Essi Sarlin

Engineering and Characterization of Bacterial Nanocellulose Films as Low Cost and Flexible Sensor Material

Some bacterial strains such as Komagataeibacter xylinus are able to produce cellulose as an extracellular matrix. In comparison to wood-based cellulose, bacterial cellulose (BC) holds interesting properties such as biodegradability, high purity, water-holding capacity, and superior mechanical and structural properties. Aiming toward improvement in BC production titer and tailored alterations to the BC film, we engineered K. xylinus to overexpress partial and complete bacterial cellulose synthase operon that encodes activities for BC production. The changes in cell growth, end metabolite, and BC production titers from the engineered strains were compared with the wild-type K. xylinus. Although there were no significant differences between the growth of wild-type and engineered strains, the engineered K. xylinus strains demonstrated faster BC production, generating 2-4-fold higher production titer (the highest observed titer was obtained with K. xylinus-bcsABCD strain producing 4.3 ± 0.46 g/L BC in 4 days). The mechanical and structural characteristics of cellulose produced from the wild-type and engineered K. xylinus strains were analyzed with a stylus profilometer, in-house built tensile strength measurement system, a scanning electron microscope, and an X-ray diffractometer. Results from the profilometer indicated that the engineered K. xylinus strains produced thicker BC films (wild type, 5.1 μm, and engineered K. xylinus strains, 6.2-10.2 μm). Scanning electron microscope revealed no principal differences in the structure of the different type BC films. The crystallinity index of all films was high (from 88.6 to 97.5%). All BC films showed significant piezoelectric response (5.0-20 pC/N), indicating BC as a promising sensor material.

Insight to Nanoparticle Size Analysis—Novel and Convenient Image Analysis Method Versus Conventional Techniques

The aim of this paper is to introduce a new image analysis program “Nanoannotator” particularly developed for analyzing individual nanoparticles in transmission electron microscopy images. This paper describes the usefulness and efficiency of the program when analyzing nanoparticles, and at the same time, we compare it to more conventional nanoparticle analysis techniques. The techniques which we are concentrating here are transmission electron microscopy (TEM) linked with different image analysis methods and X-ray diffraction techniques. The developed program appeared as a good supplement to the field of particle analysis techniques, since the traditional image analysis programs suffer from the inability to separate the individual particles from agglomerates in the TEM images. The program is more efficient, and it offers more detailed morphological information of the particles than the manual technique. However, particle shapes that are very different from spherical proved to be problematic also for the novel program. When compared to X-ray techniques, the main advantage of the small-angle X-ray scattering (SAXS) method is the average data it provides from a very large amount of particles. However, the SAXS method does not provide any data about the shape or appearance of the sample.

Optimized dispersion quality of aqueous carbon nanotube colloids as a function of sonochemical yield and surfactant/CNT ratio

In this paper, we propose and verify a theoretical model of the development of dispersion quality of aqueous carbon nanotube (CNT) colloid as a function of sonochemical yield of the sonication process. Four different surfactants; Triton X-100, Pluronic F-127, CTAB and SDS were studied. From these four SDS had the lowest dispersion performance which was surprising. Optical dispersion quality results fits well with proposed theoretical model.

Tailored Fabrication of Transferable and Hollow Weblike Titanium Dioxide Structures

The preparation of weblike titanium dioxide thin films by atomic layer deposition on cellulose biotemplates is reported. The method produces a TiO2 web, which is flexible and transferable from the deposition substrate to that of the end application. Removal of the cellulose template by calcination converts the amorphous titania to crystalline anatase and gives the structure a hollow morphology. The TiO2 webs are thoroughly characterized using electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy to give new insight into manufacturing of porous titanium dioxide structures by means of template-based methods. Functionality and integrity of the TiO2 hollow weblike thin films were successfully confirmed by applying them as electrodes in dye-sensitized solar cells.

In vitro platelet activation, aggregation and platelet–granulocyte complex formation induced by surface modified single-walled carbon nanotubes

Surface modification of single-walled carbon nanotubes (SWCNTs) such as carboxylation, amidation, hydroxylation and pegylation is used to reduce the nanotube toxicity and render them more suitable for biomedical applications than their pristine counterparts. Toxicity can be manifested in platelet activation as it has been shown for SWCNTs. However, the effect of various surface modifications on the platelet activating potential of SWCNTs has not been tested yet. In vitro platelet activation (CD62P) as well as the platelet-granulocyte complex formation (CD15/CD41 double positivity) in human whole blood were measured by flow cytometry in the presence of 0.1mg/ml of pristine or various surface modified SWCNTs. The effect of various SWCNTs was tested by whole blood impedance aggregometry, too. All tested SWCNTs but the hydroxylated ones activate platelets and promote platelet-granulocyte complex formation in vitro. Carboxylated, pegylated and pristine SWCNTs induce whole blood aggregation as well. Although pegylation is preferred from biomedical point of view, among the samples tested by us pegylated SWCNTs induced far the most prominent activation and a well detectable aggregation of platelets in whole blood.

Apparent Fracture Toughness Versus Micro-Scale Fracture Toughness of Interfaces—The Challenge of Critical Values

This study aims to shed light on the conflict between macroscopic fracture toughness and small-scale measures of interface strength when the interface is simulated with an increasing resolution. In the design of practical structures, crack initiation is the critical, limiting phase of material behavior and needs to be defined by lucid means. In this study, we model an example structure, namely a fracture test specimen, including a bi-material interface having micro-roughness and thermal residual stresses. The initiation of secondary cracks, which is one of the microscopic mechanisms leading to crack coalescence, is studied. The work focuses on the effects of the bi-materials Youngs modulus, residual stresses, and flaws. The simulation of crack propagation shows that the overall crack tip loading mode mixity distribution is not essentially affected when the Youngs modulus of the bi-materials coating is doubled. The analysis of the secondary crack initiation due to interfacial flaws in turn showed that increasing the Youngs modulus of either the bi-materials substrate or coating resulted in immediate interface collapse via an elongated ‘damage region’ along the interface.

Temperature Scanning Stress Relaxation of an Autonomous Self-Healing Elastomer Containing Non-Covalent Reversible Network Junctions

In this work, we report about the mechanical relaxation characteristics of an intrinsically self-healable imidazole modified commercial rubber. This kind of self-healing rubber was prepared by melt mixing of 1-butyl imidazole with bromo-butyl rubber (bromine modified isoprene-isobutylene copolymer, BIIR). By this melt mixing process, the reactive allylic bromine of bromo-butyl rubber was converted into imidazole bromide salt. The resulting development of an ionic character to the polymer backbone leads to an ionic association of the groups which ultimately results to the formation of a network structure of the rubber chains. The modified BIIR thus behaves like a robust crosslinked rubber and shows unusual self-healing properties. The non-covalent reversible network has been studied in detail with respect to stress relaxation experiments, scanning electron microscopic and X-ray scattering.

Layered structure graphene oxide/methylcellulose composites with enhanced mechanical and gas barrier properties

Layered structure graphene oxide (GO)/methylcellulose (MC) composite films with excellent mechanical and gas barrier properties were achieved for the first time by a simple solvent evaporation assisted assembly of GO/MC composite solutions. 1, 3 and 5 wt% of GO composites with respect to MC were fabricated and denoted as GO1, GO3 and GO5, respectively. The interactions of the hydrophobic associated domains of MC (formed during solvent evaporation) with the π cloud of GO (hydrophobic interaction) and the oxygen-containing groups of MC with the oxygen-containing functional groups of GO (H-bonding interaction) govern the formation of self-assembled thick MC coated layered structure GO/MC composites. The obtained composite films were highly flexible and characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), wide angle X-ray scattering (WAXS), Simultaneous Thermal Analysis (STA), and mechanical and oxygen gas permeation studies. The FESEM analysis shows the formation of a layered structure as well as good dispersion of thick MC coated GO sheets in the MC matrix. WAXS studies also illustrate that the GO sheets remain in a highly exfoliated state in the MC matrix. The FTIR results indicate the presence of interfacial interaction between the GO and MC molecules. The GO/MC composite films exhibit a significant enhancement of mechanical properties compared to pure MC films. The stress at break and Youngs modulus of GO5 were determined to be 104 ± 3 MPa and 3.8 ± 0.2, respectively. In addition to the mechanical properties, the oxygen gas barrier properties of the composites were also enhanced significantly. The GO1 film shows a 98% decrease of oxygen permeation with respect to pure MC films.

Improved Stability of Atomic Layer Deposited Amorphous TiO2 Photoelectrode Coatings by Thermally Induced Oxygen Defects

Amorphous titanium dioxide (a-TiO2) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO2 without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO2 induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO2 is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO2. The surface analysis allows us to interpret the improved stability to the thermally induced formation of O– species within a-TiO2 that are essentially electronic defects in the anionic framework.

Nanocellulose and chitosan based films as low cost, green piezoelectric materials

Nanocellulose and chitosan have recently started to get attention as environmentally friendly piezoelectric materials for sensor and energy harvesting applications. Conversely, current commercially available flexible piezoelectric films made of for example polyvinylidene difluoride (PVDF) are relatively expensive and made from non-renewable materials. We measured the piezoelectric responses (2-8 pC/N) for solvent casted films based on nanocellulose, microcrystalline chitosan and their blends. In addition, the tensile properties of the piezoelectric films were characterized to find out if chitosan could be used to enhance the flexibility of the brittle nanocellulose films. Based on the results, plain chitosan is an interesting piezoelectric material itself. In addition, blending nanocellulose and chitosan could be a potential method for tailoring the properties of solvent casted low cost, green piezoelectric films.