Challenges in nanoelectrochemical and nanomechanical studies of individual anisotropic gold nanoparticles.

The characterization of nanoparticles and the correlation of physical properties such as size and shape to their (electro)chemical properties is an emerging field, which may facilitate future optimization and tuning of devices involving nanoparticles. This requires the investigation of individual particles rather than obtaining averaged information on large ensembles. Here, we present atomic force - scanning electrochemical microscopy (AFM-SECM) measurements of soft conductive PDMS substrates modified with gold nanostars (i.e., multibranched Au nanoparticles) in peak force tapping mode, which next to the electrochemical characterization provides information on the adhesion, deformation properties, and Young's modulus of the sample. AFM-SECM probes with integrated nanodisc electrodes (radii < 50 nm) have been used for these measurements. Most studies attempting to map individual nanoparticles have to date been performed at spherical nanoparticles, rather than highly active asymmetric gold nanoparticles. Consequently, this study discusses challenges during the nanocharacterization of individual anisotropic gold nanostars.

Combining atomic force-fluorescence microscopy with a stretching device for analyzing mechanotransduction processes in living cells.

Mechanical forces affect biological systems in their natural environment in a widespread manner. Mechanical stress may either stimulate cells or even induce pathological processes. Cells sensing mechanical stress usually respond to such stressors with proliferation or differentiation. Hence, for in vitro studies, the ability to impose a controlled mechanical stress on cells combined with appropriate analytical tools providing an immediate answer is essential to understand such fundamental processes. Here, we present a novel uniaxial motorized cell stretching device that has been integrated into a combined fluorescence microscope (FM)-atomic force microscope (AFM) system, thereby enabling high-resolution topographic and fluorescent live cell imaging. This unique tool allows the investigation of mechanotransduction processes, as the cells may be exposed to deliberately controlled mechanical stress while simultaneously facilitating fluorescence imaging and AFM studies. The developed stretching device allows applying reproducible uniaxial strain from physiologically relevant to hyperphysiological levels to cultured cells grown on elastic polydimethylsiloxane (PDMS) membranes. Exemplarily, stretching experiments are shown for transfected squamous cell carcinoma cells (SCC-25) expressing fluorescent labeled cytokeratin, whereby fluorescence imaging and simultaneously performed AFM measurements reveal the cytokeratin (CSK) network. Topographical changes and mechanical characteristics such as elasticity changes were determined via AFM while the cells were exposed to mechanical stress. By applying a cell deformation of approx. 20%, changes in the Young's modulus of the cytoskeletal network due to stretching of the cells were observed. Consequently, integrating a stretching device into the combined atomic force-fluorescence microscope provides a unique tool for dynamically analyzing structural remodeling and mechanical properties in mechanically stressed cells.

[Impact and limitations of ultrasound examination immediately before delivery--a prospective evaluation with 1127 pregnant women]. / Möglichkeiten und Grenzen der Ultraschalluntersuchung zur Gewichtsermittlung des Kindes unmittelbar vor der Geburt - Eine prospektive Untersuchung an 1127 Schwangeren.

OBJECTIVE: Birth weight is an important confounder to foetal morbidity and mortality. There is controversy about the necessity of ultrasound examinations immediately before delivery. As only few studies on unselected populations have been published, some recommendations exist in the context with shoulder dystocia, water delivery and breech delivery. PATIENTS AND METHODS: Within 1 year we examined 1,127 consecutive pregnant women with 1,151 foetuses on the basis of a routine ultrasound examination. RESULTS: A total of 92% of all women were examined by ultrasound. Nearly 80% of these examinations took place within 72 h prior to delivery. The accuracy of foetal weight estimate (±10% variance) was 72% and did not gain due to the grade of the examiner's experience. There was no difference between routine and complicated conditions such as oligohydramnios, obesity, contractions. Also week of gestation had no influence. Macrosomic foetuses were underestimated in more than 50%. In 85% of pregnancies there was at least one risk factor and rate of Cesarean sections was due to this fact. Overall there were 8.5% macrosomic foetuses and 15.1% were SGA. 16.5% of the women were obese with BMI >30. CONCLUSION: Foetal weight estimation by means of ultrasound is easy and fast and does not need a high level of experience. There is no negative influence on accuracy of weight estimate by examination conditions and week of gestation. Ultrasound examinations also give information about foetal position, placental localisation and amount of amniotic fluid. Together with maternal risk factors, the prospective planning and leading of birth requires ultrasound biometry prior to delivery.

A mutation in the human MPDU1 gene causes congenital disorder of glycosylation type If (CDG-If).

We describe a new congenital disorder of glycosylation, CDG-If. The patient has severe psychomotor retardation, seizures, failure to thrive, dry skin and scaling with erythroderma, and impaired vision. CDG-If is caused by a defect in the gene MPDU1, the human homologue of hamster Lec35, and is the first disorder to affect the use, rather than the biosynthesis, of donor substrates for lipid-linked oligosaccharides. This leads to the synthesis of incomplete and poorly transferred precursor oligosaccharides lacking both mannose and glucose residues. The patient has a homozygous point mutation (221T-->C, L74S) in a semiconserved amino acid of MPDU1. Chinese hamster ovary Lec35 cells lack a functional Lec35 gene and synthesize truncated lipid-linked oligosaccharides similar to the patient's. They lack glucose and mannose residues donated by Glc-P-Dol and Man-P-Dol. Transfection with the normal human MPDU1 allele nearly completely restores normal glycosylation, whereas transfection with the patient's MPDU1 allele only weakly restores normal glycosylation. This work provides a new clinical picture for another CDG that may involve synthesis of multiple types of glycoconjugates.

FIB and MIP: understanding nanoscale porosity in molecularly imprinted polymers via 3D FIB/SEM tomography.

We present combined focused ion beam/scanning electron beam (FIB/SEM) tomography as innovative method for differentiating and visualizing the distribution and connectivity of pores within molecularly imprinted polymers (MIPs) and non-imprinted control polymers (NIPs). FIB/SEM tomography is used in cell biology for elucidating three-dimensional structures such as organelles, but has not yet been extensively applied for visualizing the heterogeneity of nanoscopic pore networks, interconnectivity, and tortuosity in polymers. To our best knowledge, the present study is the first application of this strategy for analyzing the nanoscale porosity of MIPs. MIPs imprinted for propranolol - and the corresponding NIPs - were investigated establishing FIB/SEM tomography as a viable future strategy complementing conventional isotherm studies. For visualizing and understanding the properties of pore networks in detail, polymer particles were stained with osmium tetroxide (OsO4) vapor, and embedded in epoxy resin. Staining with OsO4 provides excellent contrast during high-resolution SEM imaging. After optimizing the threshold to discriminate between the stained polymer matrix, and pores filled with epoxy resin, a 3D model of the sampled volume may be established for deriving not only the pore volume and pore surface area, but also to visualize the interconnectivity and tortuosity of the pores within the sampled polymer volume. Detailed studies using different types of cross-linkers and the effect of hydrolysis on the resulting polymer properties have been investigated. In comparison of MIP and NIP, it could be unambiguously shown that the interconnectivity of the visualized pores in MIPs is significantly higher vs. the non-imprinted polymer, and that the pore volume and pore area is 34% and approx. 35% higher within the MIP matrix. This confirms that the templating process not only induces selective binding sites, but indeed also affects the physical properties of such polymers down to the nanoscale, and that additional chemical modification, e.g., via hydrolysis clearly affects that nature of the polymer.

Inhibiting P. fluorescens biofilms with fluoropolymer-embedded silver nanoparticles: an in-situ spectroscopic study.

Surface colonization by microorganisms leads to the formation of biofilms, i.e. aggregates of bacteria embedded within a matrix of extracellular polymeric substance. This promotes adhesion to the surface and protects bacterial community, providing an antimicrobial-resistant environment. The inhibition of biofilm growth is a crucial issue for preventing bacterial infections. Inorganic nanoparticle/Teflon-like (CFx) composites deposited via ion beam sputtering demonstrated very efficient antimicrobial activity. In this study, we developed Ag-CFx thin films with tuneable metal loadings and exceptional in-plane morphological and chemical homogeneity. Ag-CFx antimicrobial activity was studied via mid-infrared attenuated total reflection spectroscopy utilizing specifically adapted multi-reflection waveguides. Biofilm was sampled by carefully depositing the Ag-CFx film on IR inactive regions of the waveguide. Real-time infrared spectroscopy was used to monitor Pseudomonas fluorescens biofilm growth inhibition induced by the bioactive silver ions released from the nanoantimicrobial coating. Few hours of Ag-CFx action were sufficient to affect significantly biofilm growth. These findings were corroborated by atomic force microscopy (AFM) studies on living bacteria exposed to the same nanoantimicrobial. Morphological analyses showed a severe bacterial stress, leading to membrane leakage/collapse or to extended cell lysis as a function of incubation time.

Probing the PEDOT:PSS/cell interface with conductive colloidal probe AFM-SECM.

Conductive colloidal probe Atomic Force-Scanning Electrochemical Microscopy (AFM-SECM) is a new approach, which employs electrically insulated AFM probes except for a gold-coated colloid located at the end of the cantilever. Hence, force measurements can be performed while biasing the conductive colloid under physiological conditions. Moreover, such colloids can be modified by electrochemical polymerization resulting, e.g. in conductive polymer-coated spheres, which in addition may be loaded with specific dopants. In contrast to other AFM-based single cell force spectroscopy measurements, these probes allow adhesion measurements at the cell-biomaterial interface on multiple cells in a rapid manner while the properties of the polymer can be changed by applying a bias. In addition, spatially resolved electrochemical information e.g., oxygen reduction can be obtained simultaneously. Conductive colloid AFM-SECM probes modified with poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate ( PEDOT: PSS) are used for single cell force measurements in mouse fibroblasts and single cell interactions are investigated as a function of the applied potential.

Pulse technique for the electrochemical deposition of polymer films on electrode surfaces.

Often, electrochemically-induced deposition of conducting polymer films on electrode surfaces fails using potentiostatic, galvanostatic or multisweep deposition procedures if bulky substituents at the monomer, nucleophilic attack at intermediate radical cations, hindered diffusional mass transport of the monomer to the electrode surface or the copolymerization of monomers with different oxidation potentials prevent fast chain propagation. A pulse profile for the electrochemical deposition of conducting polymer films has been developed based on the rationalization of the limiting steps and the concentration profiles in front of the electrode surface. The pulse deposition method could be advantageously applied for the localized deposition of conducting polymers using scanning electrochemical microscopy, for the copolymerization of pyrrole/[Os(2,2'-bipyridine)2(3-¿pyrrole-1-ylmethyl¿pyridine)C1]+ and for the entrapment of enzymes within the growing ramified network of the polymer.

Mapping of enzyme activity by detection of enzymatic products during AFM imaging with integrated SECM-AFM probes.

With the integration of submicro- and nanoelectrodes into atomic force microscopy (AFM) probes using microfabrication techniques, an elegant approach combining scanning electrochemical microscopy (SECM) with AFM has recently been introduced. Simultaneous contact mode imaging of a micropatterned sample with immobilized enzyme spots and imaging of enzyme activity is shown. In contrast to force spectroscopy the conversion of an enzymatic byproduct is directly detected during AFM imaging and correlated to the activity of the enzyme.

Clinical and finite element analysis of a modular femoral prosthesis consisting of a head and stem component in the treatment of pertrochanteric fractures.

OBJECTIVE: To determine the biomechanical characteristics and potential clinical efficacy of a cementless modular femoral prosthesis consisting of a variable head (50 to 80 millimeters) and stem (length 120 to 280 millimeters, diameter 10 to 20 millimeters) component in patients with pertrochanteric femoral fracture. DESIGN: Finite element analysis (FEA) of different lengths and diameters of prosthesis components and first clinical prospective study in pertrochanteric femoral fracture. METHOD: Using a 3D-CAD program, a model of femoral cortical bone with a pertrochanteric fracture was created and combined with a model of the prosthesis. This model was transferred into an FEA program. After applying a torsion-bending load of 2,000 N (25 degrees, 45 degrees) on the prosthesis, stress distribution in the cortical bone was determined for different lengths (160 to 240 millimeters) and diameters (10 and 12 millimeters) of stem. PATIENTS: Twenty-eight patients with pertrochanteric fractures (very unstable or osteoarthritis) were treated with a modular hip arthroplasty. Complications, fracture healing, and results at first follow-up (average 13 months) were determined. RESULTS: FEA analysis indicated that reduction in stress was less when a prosthesis with a short stem was used. Shear stress in the interface bone/prosthesis was not affected by stem length. Prostheses with thin stems produced higher sheer stresses than those with thick stems. Results of FEA were used as the basis for clinical application of the device. None of the patients died, and all patients were able to walk, although some needed a cane or walker after surgery. There was no increase in thigh pain compared with reported pretrauma levels. Radiographs showed subsidence of up to 5 millimeters in 20 percent of patients. However, all but one prosthesis was stable at follow-up. Fracture healing was achieved in all patients. CONCLUSIONS: If proximal fixation of a femoral uncemented stem cannot be achieved, stem diameter should provide maximum cortical contact to reduce sheer stress. Longer stems do not necessarily provide additional stability. By using this prosthesis and selection method, a good outcome at first follow-up was observed.

[Effects of inadequate cementing techniques on mechanical loading of bone cement]. / Einfluss von Zementierungsfehlern auf die mechanische Beanspruchung des Knochenzementes.

Good, painfree and durable function of an endoprosthesis is highly dependent on its anchorage in the bony bed. Apart from the problem of mechanical loading of the prosthesis and the change in the strains in the cortical bone, stresses on the bone cement as a force-transmitting element, are of considerable importance. Inadequate cementing technique and resulting faulty cementing is a common cause of loosening of the endoprosthesis. The present article investigates the influence of inadequate cementing technique on the stress and strain conditions of bone cement, in particular at the distal end of the prosthesis.

[Effects of hollow shaft endoprosthesis on stress distribution in cortical bone]. / Die Auswirkungen der Hohlschaftendoprothese auf die Spannungsverteilung in der Kortikalis.

Generally, conduction of the forces from the distal end of the prosthesis stem into the surrounding cortical bone effects a local load increase in the bone. Where bone and stem are in close contact "stress protection" is hardly avoidable, and this, together with the load increase, results in the formation of a "plug of bone" beneath the tip of the prosthesis. Since the prosthesis stem rests on this bone "plug", additional "stress protection" of the femur results, which may possibly lead to total failure of the femur and/or the prosthesis. A 3-dimensional FEM-analysis shows that the hollow-stem prosthesis helps to decrease the stress peak beneath the tip of the prosthesis, while at the same time the stress in the proximal cortical bone increases. The increase in the loading of the bone inevitably causes a reduction in bone breakdown through "stress shielding" in this region.

Nanoscopic polypyrrole AFM-SECM probes enabling force measurements under potential control.

Conductive polymers, and in particular polypyrrole, are frequently used as biomimetic interfaces facilitating growth and/or differentiation of cells and tissues. Hence, studying forces and local interactions between such polymer interfaces and cells at the nanoscale is of particular interest. Frequently, such force interactions are not directly accessible with high spatial resolution. Consequently, we have developed nanoscopic polypyrrole electrodes, which are integrated in AFM-SECM probes. Bifunctional AFM-SECM probes were modified via ion beam-induced deposition resulting in pyramidal conductive Pt-C composite electrodes. These nanoscopic electrodes then enabled localized polypyrrole deposition, thus resulting in polymer-modified AFM probes with a well-defined geometry. Furthermore, such probes may be reversibly switched from an insulating to a conductive state. In addition, the hydrophilicity of such polymer tips is dependent on the dopant, and hence, on the oxidation state. Force studies applying different tip potentials were performed at plasma-treated glass surfaces providing localized information on the associated force interactions, which are dependent on the applied potential and the dopant.

Characterization of stainless steel assisted bare gold nanoparticles and their analytical potential.

A simple, environmentally friendly, one-pot method to synthesize highly stable bare gold nanoparticles (AuNPs) has been developed. AuNPs have been synthesized from tetrachloroauric acid solution using steel or stainless steel as solid reducing agent, which can be reused. The proposed method yields bare gold nanoparticles at atmospheric pressure and room temperature for potentially producing large quantities. The obtained AuNPs have been characterized by SEM, TEM and AFM finding an average diameter of around 20 nm, polygonal yet nearly spherical shape and a narrow size distribution. The mechanism of reaction has been investigated by UV-vis spectroscopy, ICP-OES and EDX analysis. The obtained dispersed gold nanoparticles proved to be stable if stored a 4 °C for over four months without the addition of a stabilizing agent. Their analytical potential as SERS substrate has been demonstrated and their performance compared with that showed by citrate-coated gold nanoparticles. Thanks to their unique properties, their use as analytical tools provides analytical processes with enhanced selectivity and precision.

Multiple intrinsically identical single-photon emitters in the solid state.

Emitters of indistinguishable single photons are crucial for the growing field of quantum technologies. To realize scalability and increase the complexity of quantum optics technologies, multiple independent yet identical single-photon emitters are required. However, typical solid-state single-photon sources are inherently dissimilar, necessitating the use of electrical feedback or optical cavities to improve spectral overlap between distinct emitters. Here we demonstrate bright silicon vacancy (SiV(-)) centres in low-strain bulk diamond, which show spectral overlap of up to 91% and nearly transform-limited excitation linewidths. This is the first time that distinct single-photon emitters in the solid state have shown intrinsically identical spectral properties. Our results have impact on the application of single-photon sources for quantum optics and cryptography.