Friction reducing ability of a poly-l-lysine and dopamine modified hyaluronan coating for polycaprolactone cartilage resurfacing implants

Frictional properties of cartilage resurfacing implants should be sufficiently low to limit damaging of the opposing cartilage during articulation. The present study determines if native lubricious molecule proteoglycan 4 (PRG4) can adsorb onto a layer-by-layer bioinspired coating composed of poly-l-lysine (PLL) and dopamine modified hyaluronic acid (HADN) and thereby can reduce the friction between implant and articular cartilage. An ELISA was developed to quantify the amount of immobilized human recombinant (rh)PRG4 after exposure to the PLL-HADN coating. The effect on lubrication was evaluated by comparing the coefficient of friction (CoF) of bare polycaprolactone (PCL) disks to that of PLL-HADN coated PCL disks while articulated against cartilage using a ring-on-disk geometry and a lubricant solution consisting of native synovial fluid components including rhPRG4. The PLL-HADN coating effectively immobilized rhPRG4. The surface roughness of PCL disks significantly increased while the water contact angle significantly decreased after application of the coating. The average CoF measured during the first minute of bare PCL against cartilage exceeded twice the CoF of the PLL-HADN coated PCL against cartilage. After 60 min, the CoF reached equilibrium values which were still significantly higher for bare PCL compared to coated PCL. The present study demonstrated that PCL can effectively be coated with PLL-HADN. Additionally, this coating reduces the friction between PCL and cartilage when a PRG4-rich lubricant is used, similar to the lubricating surface of native cartilage. This makes PLL-HADN coating a promising application to improve the clinical success of PCL-based cartilage resurfacing implants.</p

Long-term cortisol levels in hair of children and adolescents with Prader-Willi Syndrome

Context: Prader-Willi syndrome (PWS) is characterized by hypothalamic dysfunction. In children with PWS, stress-induced central adrenal insufficiency (CAI) has been described, however, daily life cortisol production may be normal. Hair cortisol concentration (HCC) is a marker of long-term systemic cortisol production. Cortisol awakening response (CAR) is the increase in cortisol level after awakening. A negative CAR might suggest hypothalamic-pituitary-adrenal (HPA)-axis reactivity problems. Little is known about HCC and CAR in children with PWS. Objective: To investigate long-term cortisol levels in hair and CAR in children with PWS. Design: Cross-sectional study. Patients: 41 children with PWS. Setting: Dutch PWS Reference Center. Main outcome measures: HCC and salivary cortisol measured by LCMS. Results: Median (IQR) HCC was 1.90 (1.02–3.30) pg/mg at a median (IQR) age of 14.5 (8.20–19.0) years, with median HCC in age-matched references being 2.63 pg/mg. Five patients (13.2%) had HCC &lt; 2.5th percentile for age and these patients had a repeatedly negative CAR. Median HCC was significantly lower in patients with negative CAR than in patients with normal CAR (1.00 (0.22–1.59) vs. 2.25 (1.47–3.26) pg/mg, p = 0.007). One patient had both HCC &lt; 2.5th percentile and repeatedly low morning salivary cortisol levels and negative CAR, and was diagnosed with adrenal insufficiency by overnight metyrapone test. Conclusions: HCC were normal in the majority of children with PWS. Our data suggest that children with HCC &lt; 2.5th percentile and (repeatedly) negative CAR might possibly have adrenal insufficiency or delayed HPA-axis responsiveness.</p

Development of the Surgical Patient safety Observation Tool (SPOT)

Background: A Surgical Patient safety Observation Tool (SPOT) was developed and tested in a multicentre observational pilot study. The tool enables monitoring and benchmarking perioperative safety performance across departments and hospitals, covering international patient safety goals. Methods: Nineteen perioperative patient safety observation topics were selected from Dutch perioperative patient safety guidelines, which also cover international patient safety goals. All items that measured these selected topics were then extracted from available local observation checklists of the participating hospitals. Experts individually prioritized the best measurement items per topic in an initial written Delphi round. The second (face to face) Delphi round resulted in consensus on the content of SPOT, after which the measurable elements (MEs) per topic were defined. Finally, the tool was piloted in eight hospitals for measurability, applicability, improvement potential, discriminatory capacity and feasibility. Results: The pilot test showed good measurability for all 19 patient safety topics (range of 8-291 MEs among topics), with good applicability (median 97 (range 11.8-100) per cent). The overall improvement potential appeared to be good (median 89 (range 72.5-100) per cent), and at topic level the tool showed good discriminatory capacity (variation 27.5 per cent, range in compliance 72.5-100 per cent). Overall scores showed relatively little variation between the participating hospitals (variation 13 per cent, range in compliance 83-96 per cent). All eight auditors considered SPOT a straightforward and easy-to-use tracer tool. Conclusion: A comprehensive tool to measure safety of care was developed and validated using a systematic, stepwise method, enabling hospitals to monitor, benchmark and improve perioperative safety performance

Topology of six degrees of freedom magnetic bearing

A novel magnetic topology has been designed for a six degrees of freedom, magnetically levitated and driven mirror, to be used in a three dimensional (3D) measurement system based on laser interferometry. The translations of the mirror are to be kept small, whereas the rotations are to be controlled over a large range with a high bandwidth and high accuracy. Finite element modelling (FEM) is used to analyze the proposed topology. For computational load reduction, a 2D FEM model has been derived from the actual 3D topology, which incorporates most of the magnetic subsystems. Simulations show that cross-influence between the actuators is small, that the forces and torques are proportional to the applied currents and that the angle of the rotor is of little influence. This allows the multiple in multiple out system to be regarded as multiple linear single in single out systems. ©2000 American Institute of Physics

Moving targets in space: Movement distance as a predictor for experiences of movement agency

Previous research indicates that the experience of agency over one's actions and movements is influenced by movement predictability as well as movement distance (Hon, Seow, & Pereira, 2018). Addressing previous limitations, we present a compelling test of the relation between movement distance and movement agency. Participants in two studies moved targets predictably or unpredictably, and for short, medium, or long distances. Following prior research, distractor cues moved in the opposite direction of the targets. Results showed that movement agency scores were higher for predictable compared to unpredictable movements. Results also consistently showed that when movements were predictable, longer distances by either the target or the distractor cues increased agency relative to shorter distances. Our findings replicate and extend previous findings showing that stimulus movement distances influence judgments of movement agency

NonPharmacologic Management of Atrial Fibrillation Using the Dynamic Atrial Overdrive Algorithm

A concomitant condition found in many patients with atrial fibrillation (AF) commonly requires bradycardia pacing. Comparing AAI to VVI pacing, atrial pacing appears to have an apparent protective effect on the subsequent development of AF. By addressing the proposed mechanisms responsible for AF (long-short cycles, increased temporal dispersion of refractoriness, frequent atrial ectopic beats), overdrive appears to be a promising technique to postpone or even prevent entirely the development of chronic AF while reducing the incidence of paroxysmal AF. These observations led to the development of a pacing algorithm (Dynamic Atrial Overdrive-DAO) designed to provide a high percentage of atrial pacing just above the patient's own intrinsic atrial rate. The algorithm is a dynamic stimulation technique to suppress AF effectively, overdrives the atrium just enough to prevent the intrinsic rhythm from emerging while maintaining both normal diurnal variation and rate response. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Dynamic Atrial Overdrive is a unique pacemaker algorithm designed specifically for suppression of paroxysmal AF arising from either an absolute or relative bradycardia. By maintaining an atrial stimulation rate just above the intrinsic rate, the goal is to control both the atrial rate and rhythm, reducing the incidence of ectopic beats which might be a trigger, long-short cycles, or the dispersion of refractoriness from initiating AF. In addition, because the algorithm routinely searches for intrinsic atrial activity and adjusts the stimulation rate accordingly, it avoids sustained periods of rapid stimulation that may not be required. At the same time, it preserves the normal circadian rate variation in association with normal sinus function or in the presence of sinus node dysfunction if the sleep rate feature is also enabled

Ultrafast pump-probe dynamics in ZnSe-based semiconductor quantum-wells

Pump-probe experiments are used as a controllable way to investigate the properties of photoexcited semiconductors, in particular, the absorption saturation. We present an experiment-theory comparison for ZnSe quantum wells, investigating the energy renormalization and bleaching of the excitonic resonances. Experiments were performed with spin-selective excitation and above-bandgap pumping. The model, based on the semiconductor Bloch equations in the screened Hartree-Fock approximation, takes various scattering processes into account phenomenologically. Comparing numerical results with available experimental data, we explain the experimental results and find that the electron spin-flip occurs on a time scale of 30 ps.Comment: 10 pages, 9 figures. Key words: nonlinear and ultrafast optics, modeling of femtosecond pump-probe experiments, electron spin-flip tim

Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process

Manufacturing superconducting circuits out of ultrathin films is a challenging task when it comes to patterning complex compounds, which are likely to be deteriorated by the patterning process. With the purpose of developing high-T$_c$ superconducting photon detectors, we designed a novel route to pattern ultrathin YBCO films down to the nanometric scale. We believe that our method, based on a specific use of a focused-ion beam, consists in locally implanting Ga^{3+} ions and/or defects instead of etching the film. This protocol could be of interest to engineer high-T$_c$ superconducting devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to treat other sensitive compounds.Comment: 13 pages, 7 figure

Eddington-limited X-ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34

We investigate the limitations of thermonuclear X-ray bursts as a distance indicator for the weakly-magnetized accreting neutron star 4U 1728-34. We measured the unabsorbed peak flux of 81 bursts in public data from the Rossi X-Ray Timing Explorer (RXTE). The distribution of peak fluxes was bimodal: 66 bursts exhibited photospheric radius expansion and were distributed about a mean bolometric flux of 9.2e-8 erg/cm^2/s, while the remaining (non-radius expansion) bursts reached 4.5e-8 erg/cm^2/s, on average. The peak fluxes of the radius-expansion bursts were not constant, exhibiting a standard deviation of 9.4% and a total variation of 46%. These bursts showed significant correlations between their peak flux and the X-ray colors of the persistent emission immediately prior to the burst. We also found evidence for quasi-periodic variation of the peak fluxes of radius-expansion bursts, with a time scale of approximately 40 d. The persistent flux observed with RXTE/ASM over 5.8 yr exhibited quasi-periodic variability on a similar time scale. We suggest that these variations may have a common origin in reflection from a warped accretion disk. Once the systematic variation of the peak burst fluxes is subtracted, the residual scatter is only approximately 3%, roughly consistent with the measurement uncertainties. The narrowness of this distribution strongly suggests that i) the radiation from the neutron star atmosphere during radius-expansion episodes is nearly spherically symmetric, and ii) the radius-expansion bursts reach a common peak flux which may be interpreted as a standard candle intensity.Adopting the minimum peak flux for the radius-expansion bursts as the Eddington flux limit, we derive a distance for the source of 4.4-4.8 kpc.Comment: 9 pages, 7 figures, accepted by ApJ. Minor referee's revisions, also includes 9 newly public X-ray burst