Scientific publications

A vital issue for the manufacture of multifunctional thin films is to synthesize polymer/ceramic hybrid particles. Silicon dioxide (SiO2)/polymer composite particles were synthesized through dispersion copolymerization of methyl methacrylate (MMA) in the presence of SiO2 bullet-like particles, using a “grafting-through” approach. The SiO2 particles were previously modified with the silane-coupling agent 3-(trimethoxysilyl)propyl methacrylate (MPTS). Scanning electron microscopy and transmission electron microscopy analyses confirmed the formation of particles with a rough surface and flower-like morphology. Fourier transform infrared spectroscopy, thermogravimetric analysis, and energy-dispersive X-ray investigations indicated that a nucleation and aggregation process of the growing copolymer MPTS/poly(methyl methacrylate) (PMMA) occurred on the surface of the modified SiO2 particles. As a result, the SiO2 core became embedded in a PMMA shell. The influence of MPTS and the concentration of polyvinylpyrrolidone as a steric stabilizer on the flower-like morphology was demonstrated. Dispersion polymerizations have been proven to be simple and effective ways to synthesize composite particles with a high surface area. By using homogeneous systems (i.e., the monomer was soluble in the reaction solvent), no emulsification process was required, and copious amounts of well-dispersed particles were produced. These characteristics open many application possibilities for the use of the synthesized particles in functional coatings and optical devices, for mechanical reinforcement in polymeric materials, and as biomaterials.

Up to 25,000 people die each year from resistant infections in Europe alone, with increasing incidence. It is estimated that a continued rise in bacterial resistance by 2050 would lead up to 10 million annual deaths worldwide, exceeding the incidence of cancer deaths. Although the design of new antibiotics is still one way to tackle the problem, pharmaceutical companies investigate far less into new drugs than 30 years ago. Incorporation of antibiotics into nanoparticle drug carriers (“nanoantibiotics”) is currently investigated as a promising strategy to make existing antibiotics regain antimicrobial strength and overcome certain types of microbial drug resistance. Many of these synthetic systems enhance the antimicrobial effect of drugs by protecting antibiotics from degradation and reducing their side effects. Nevertheless, they often cannot selectively target pathogenic bacteria and – due to their synthetic origin – may induce side-effects themselves. In this work, we present the characterisation of naturally derived outer membrane vesicles (OMVs) as biocompatible and inherently antibiotic drug carriers. We isolated OMVs from two representative strains of myxobacteria, Cystobacter velatus Cbv34 and Sorangiineae species strain SBSr073, a bacterial order with the ability of lysing other bacterial strains and currently investigated as sources of new secondary metabolites. We investigated the myxobacterias' inherent antibacterial properties after isolation by differential centrifugation and purification by size-exclusion chromatography. OMVs have an average size range of 145–194 nm. We characterised their morphology by electron cryomicroscopy and found that OMVs are biocompatible with epithelial cells and differentiated macrophages. They showed a low endotoxin activity comparable to those of control samples, indicating a low acute inflammatory potential. In addition, OMVs showed inherent stability under different storage conditions, including 4 °C, −20 °C, −80 °C and freeze-drying. OMV uptake in Gram-negative model bacterium Escherichia coli (E. coli) showed similar to better incorporation than liposome controls, indicating the OMVs may interact with model bacteria via membrane fusion. Bacterial uptake correlated with antimicrobial activity of OMVs as measured by growth inhibition of E. coli. OMVs from Cbv34 inhibited growth of E. coli to a comparable extent as the clinically established antibiotic gentamicin. Liquid-chromatography coupled mass spectrometry analyses revealed the presence of cystobactamids in OMVs, inhibitors of bacterial topoisomerase currently studied to treat different Gram-negative and Gram-positive pathogens. This work, may serve as an important basis for further evaluation of OMVs derived from myxobacteria as novel therapeutic delivery systems against bacterial infections.

Granular metal thin films have a strain sensitivity much larger than continuous metal films. Experiments at high strain can help reveal their piezoresistive mechanisms. We deposit films of platinum nanoparticles in boron nitride (Pt:BN) as well as platinum particles in aluminum oxide (Pt:Al2O3) on polyimide foil as strain gauges. Under low strain of 0.1%, the films exhibit enhanced gauge factors, k=23 for Pt:BN and k=6 for Pt:Al2O3. Toward higher strain of 1.5%, Pt:BN shows reproducible and linear resistance-strain curves. In contrast, Pt:Al2O3 exhibits anomalies: The resistance-strain curves are highly nonlinear with an increasing slope before reaching saturation. The differential gauge factor versus strain increases from 9 to 9500, and the return curve shows large hysteresis. With scanning electron microscopy unstrained and in situ strained films are compared, Pt:BN shows no changes, whereas in Pt:Al2O3, large cracks develop. The relatively soft BN is less prone to cracks than the hard and brittle Al2O3. Hence, the gauge factor in Pt:BN can still be attributed to an electron tunneling mechanism, whereas Pt:Al2O3 becomes dominated by the influence of cracks. A model is presented, and we argue that the reproducible opening and closing of these cracks leads to the gigantic resistance increases at high strain.

Messenger RNA (mRNA) has gained remarkable attention as an alternative to DNA-based therapies in biomedical research. A variety of biodegradable nanoparticles (NPs) has been developed including lipid-based and polymer-based systems for mRNA delivery. However, both systems still lack in achieving an efficient transfection rate and a detailed understanding of the mRNA transgene expression kinetics. Therefore, quantitative analysis of the time-dependent translation behavior would provide a better understanding of mRNA’s transient nature and further aid the enhancement of appropriate carriers with the perspective to generate future precision nanomedicines with quick response to treat various diseases.

Low coefficient of thermal expansion (CTE) lattices occupy a unique area of property space. With such a system, it is possible to achieve relatively high stiffness, with opportunities to combine low thermal expansion and with a range of advantageous properties. Possibilities include combinations that are not rivaled by any bulk material, e.g., low CTE and high melting temperature, and low CTE with low conductivity. One design in particular, the UCSB Lattice, has biaxial stiffness very near theoretical upper bounds when the joints are pinned. Bonded lattices are found to inherit the near optimal performance of the parent pin-jointed design. Despite near optimal performance, however, stiffnesses and strengths are limited to a few percent of the relative property of the constituents. The local deformations necessary to accommodate low net CTE are similar to those of auxetic lattices, with similar behavior, having a low, zero, or negative tunable Poisson’s ratio. An investigative framework, including experiments, finite element, and analytical formulas, is used to construct these assessments.

The wear resistance of pure rubber materials is very limited in engineering applications, such as pneumatic or sealing elements. In order to improve their wear resistance, various fillers were incorporated into the rubber matrix. In this background, the present work deals with the investigations of the mechanical and tribological properties of SBR/NR rubber composites containing 1 part per hundred rubber (phr) graphene and cellulose nanocrystal (CNC), respectively. The sliding wear tests were performed on a block-on-ring tribometer against a 100Cr6 bearing steel ring under dry sliding conditions. The results revealed that the incorporation of graphene and CNC slightly increases the storage modulus and decreases the hysteresis loss. However, the glass transition temperature was not affected. In the studied range of load conditions, it was found that the friction and wear properties of the rubber composites strongly depend on the normal load and sliding velocity. The wear resistance was obviously improved, especially under low F·v-factors, when CNC were introduced into the rubber composite. Under F·v-condition of 12 N and 0.1 ms−1, the specific wear rate was reduced by approximate 70% after addition of CNC compared to that of the benchmark material. The optical analysis of the wear track on the steel counterface reveals that this low wear rate can be attribute to the formation of a thin tribofilm on the steel disc surface.

Polymeric materials filled with micro-sized short carbon fiber (SCF) and various internal lubricants, i.e. graphite and PTFE etc., have been proved as a beneficial tribomaterial formulation in contact with a steel counterbody. The SCFs carry the most load applied on the tribosystem, while the internal lubricants improve the friction behavior of the polymer matrix. In the present study, the roles of rigid particles on the friction and wear performance of SCF filled Polybutylenterephthalate (PBT) with and without graphite were investigated by using a pin-on-disc (PoD) tribometer under dry sliding condition. The experimental results show that the tribocomposite filled with nanoparticles without graphite particles presents outstanding friction and wear performance especially under moderate and severe load conditions in combination with superior mechanical properties compared with graphite-filled tribocomposite. The friction coefficient and wear rate under a pv-condition of 3 MPa and 2 m/s are 0.18 and 0.8*10−6 mm3/Nm, respectively. Based-on the optical analysis of the worn surfaces of the polymer samples and the transfer layers formed on the steel disc, the possible friction and wear mechanisms were discussed.

A fully coupled model for mass and heat transport, mechanics, and chemical reactions with trapping is proposed. It is rooted in non-equilibrium rational thermodynamics and assumes that displacements and strains are small. Balance laws for mass, linear and angular momentum, energy, and entropy are stated. Thermodynamic restrictions are identified, based on an additive strain decomposition and on the definition of the Helmholtz free energy. Constitutive theory and chemical kinetics are studied in order to finally write the governing equations for the multi-physics problem. The field equations are solved numerically with the finite element method, stemming from a three-fields variational formulation. Three case-studies on vacancies redistribution in metals, hydrogen embrittlement, and the charge–discharge of active particles in Li-ion batteries demonstrate the features and the potential of the proposed model.