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.

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.

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.

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.

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.

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.

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.

Integrating an ultramicroelectrode in an AFM cantilever: combined technology for enhanced information

We present a novel approach to develop and process a microelectrode integrated in a standard AFM tip. The presented fabrication process allows the integration of an electroactive area at an exactly defined distance above of the end of a scanning probe tip and the subsequent remodeling and sharpening of the original AFM tip using a focused ion beam (FIB) technique (See ref 1 for patent information). Thus, the functionality of scanning electrochemical microscopy (SECM) can be integrated into any standard atomic force microscope (AFM). With the demonstrated approach, a precisely defined and constant distance between the microelectrode and the sample surface can be obtained, alternatively to the indirect determination of this distance usually applied in SECM experiments. Hence, a complete separation of the topographical information and the electrochemical signal is possible. The presented technique is a significant step toward electrochemical imaging with submicrometer electrodes as demonstrated by the development of the first integrated frame submicroelectrode.

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.

Facilitated tip-positioning and applications of non-electrode tips in scanning electrochemical microscopy using a shear force based constant-distance mode

In scanning electrochemical microscopy (SECM) a microelectrode is usually scanned over a sample without following topographic changes (constant-height mode). Therefore, deconvolution of effects from distance variations arising from non-flat sample surface and electrochemical surface properties is in general not possible. Using a shear force-based constant distance mode, information about the morphology of a sample and its localized electrochemical activity can be obtained simultaneously. The setup of the SECM with integrated constant-distance mode and its application to non-flat or tilted surfaces, as well as samples with three-dimensional surface structures are presented and discussed. The facilitated use of non-amperometric tips in SECM like enzyme-filled glass capillaries is demonstrated.

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.

[Effects of inadequate cementing techniques on mechanical loading of bone cement]

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]

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.

[Optimization of the dynamic compression in angle-plated osteosynthesis by static interfragmentary compression--experimental results]

Osteosynthesis with an angled plate after intertrochanteric osteotomy is mainly a tension-band-osteosynthesis. Because of the lack of interfragmentary compression at the medial corticalis this technique may lead to pseudarthrosis or delayed bone union. On the basis of theoretical considerations and extensive experiments, we found a distinct improvement in interfragmentary compression when the osteotomy-planes are set at an angle of 6 degrees open to the lateral side before external compression with 1000 N. In this way "functional plate-prebending" is achieved. Thus tension-band-osteosynthesis is completed by compression osteosynthesis.

[Effect of natural isotope contents of nutrients on the background in 13C breath tests]

The long-term variation of the mean delta 13C-value of breath-CO2 of Europeans (base value -26%) was +/- 1% over a period of several months. However, the ingestion of products from corn, a C4-plant, caused remarkably higher shifts. In a fasted state and during rest a stability of the base value of +/- 0.3% could be attained for several hours. Longer fasting periods imply a shift of the CO2-delta-value due to the metabolism of body products. - By a change of the main energy source to corn products the delta 13C-base line could be shifted to -18% within one day. After this shift even the metabolism of products from C3-plants could be investigated. The degradation curve and the integral degradation of fats were largely dependent on the method of application, and the base value largely interfered with the results. The period of maximum disintegration for a naturally and uniformly labelled fat was different from that of an artificially labelled trilinoleate. The results shall be used for the adjustment and the correction of the base line in 13C-breath tests, especially with patients under parenteral nutrition.