Evaluation of Osseointegration of Titanium Alloyed Implants Modified by Plasma Polymerization

By means of plasma polymerization, positively charged, nanometre-thin coatings can be applied to implant surfaces. The aim of the present study was to quantify the adhesion of human bone cells in vitro and to evaluate the bone ongrowth in vivo, on titanium surfaces modified by plasma polymer coatings. Different implant surface configurations were examined: titanium alloy (Ti6Al4V) coated with plasma-polymerized allylamine (PPAAm) and plasma-polymerized ethylenediamine (PPEDA) versus uncoated. Shear stress on human osteoblast-like MG-63 cells was investigated in vitro using a spinning disc device. Furthermore, bone-to-implant contact (BIC) was evaluated in vivo. Custom-made conical titanium implants were inserted at the medial tibia of female Sprague-Dawley rats. After a follow-up of six weeks, the BIC was determined by means of histomorphometry. The quantification of cell adhesion showed a significantly higher shear stress for MG-63 cells on PPAAm and PPEDA compared to uncoated Ti6Al4V. Uncoated titanium alloyed implants showed the lowest BIC (40.4%). Implants with PPAAm coating revealed a clear but not significant increase of the BIC (58.5%) and implants with PPEDA a significantly increased BIC (63.7%). In conclusion, plasma polymer coatings demonstrate enhanced cell adhesion and bone ongrowth compared to uncoated titanium surfaces.     

Effect of curing conditions on strength development in an epoxy resin for structural strengthening

Civil structures such as bridges and buildings can be strengthened with prestressed fibre reinforced polymer (FRP) strips to enhance both their stiffness and load-bearing capacity. End anchorage is a crucial issue for prestressed FRP strips. An innovative anchorage procedure, called the “gradient anchorage method” and based on the possible accelerated curing of the epoxy-resin in the end region of the FRP strip, has recently been conceived with the aim of avoiding more invasive mechanical fastening systems. An in-depth knowledge of the actual development of the key mechanical properties of resins under different curing conditions (i.e., in terms of curing temperature) is of paramount importance for employing the above mentioned gradient method in practical applications. This paper presents experimental results and analytical investigations aimed at developing a better understanding of the strength development of a commercial adhesive under different curing times and temperatures. Firstly, direct tensile tests on epoxy specimens were performed at different curing temperatures. It was shown that the necessary curing time to reach the maximum tensile strength can be significantly reduced from several hours at room temperature to approximately 30 min at 90 °C. Furthermore, higher curing temperatures reduced the activation time after which strength starts to increase. The experimental observations are shown graphically with both the activation time and reaction duration at different curing temperatures. Secondly, pull-off bond tests were conducted on 100 mm wide and 1.2 mm thick FRP strips bonded to concrete using epoxy adhesives cured either at 90 °C for different durations or at room temperature. An optical image correlation system (ICS) allowed the load transfer behaviour of the inhomogeneous cured adhesive between the FRP strip(s) and concrete to be studied. Finally, using the experimental measurements, the bond shear stress–slip interface relationships for the different test specimens were identified in order to present the effect of elevated curing temperatures and curing durations.     

Two Base Pair Duplexes Suffice to Build a Novel Material

Tetrahedral DNA hybrids with tetrakis(p‐hydroxyphenyl)methane cores hybridize in a sequence‐specific fashion at much higher temperatures than isolated linear duplexes. Dinucleotide DNA arms suffice to induce the formation of a solid at room temperature; this demonstrates the strength of multivalent binding. The graphic shows a view of a modeled assembly.

     

Symmetric matrix-valued frequency to time transformation for unbounded domains applied to infinite beams

In structural dynamics coupled systems with unbounded deformable members are characterized by radiation damping. Typically, the unbounded subsystem is described in the frequency domain; either numerically or analytically by means of dynamical stiffness matrices. Recent papers describe a matrix-valued rational interpolation of the dynamical stiffness and straightforward transformation into the time-domain. In addition, the asymptotic behaviour has been considered, too, by adding fractional derivatives. However, the matrices involved in this process are unsymmetric even if the original dynamical stiffnesses are symmetric. The approach presented in this paper maintains the symmetry a priori without any numerical operations by simply using a rational approximation with a matrix-valued numerator but a scalar-valued denominator and contains some further numerical advantages. The method is demonstrated by treating an infinite beam on an elastic foundation.     

Multi-sided platform and data-driven care research

Electronic Markets - Multi-sided platforms in healthcare often focus their business model on standardizing care for wide-spread, chronic diseases. However, there is a lack of knowledge surrounding...     

Low-cost fiber-optic waveguide sensor for the colorimetric detection of ammonia

We present the development and characterization of a low-cost fiber-optic colorimetric gas sensor for ammonia combined with the electronic circuitry for measurement control and RFID communication. The gas sensor detects ammonia using a 300?μm polyolefin fiber coated with a gas-sensitive polymer film. The spectral and time-dependent sensitivity of various polymer films was tested in transmission measurements at λ?=?590?nm. A prototype of the gas sensor was tested under realistic measurement conditions, i.e. battery-driven and in a completely autonomous mode. The sensor system showed good sensitivity to the ammonia concentrations and response times in the order of minutes. The achievable power consumption was below 100?μW. Bromophenol blue-based films showed a strong reaction to ammonia, with saturation concentrations around 1,000?ppm and response times of about 15?s to 100?ppm. The colorimetric reaction was simulated using a simple kinetic model which was in good agreement with the experimental results.     

Metallo-porphyrin zinc as gas sensitive material for colorimetric gas sensors on planar optical waveguides

The presented work focuses on the investigations of a metallo-porphyrin and its gasochromic behavior to different gases. Gasochromic materials change their color while they are exposed to a certain gas. So they offer the possibility to develop highly selective chemical gas sensors and gas sensing systems. The focus of this work is the characterization of the metallo-porphyrin 5, 10, 15, 20-tetraphenylporphyrin-zinc (ZnTPP). Nonetheless, there is a wide range of other possible metallo-porphyrins. When embedded into a polymeric matrix (PVC) a color change to the toxic gas NO₂ can be detected. To develop a stand-alone gas sensor, the porphyrin/PVC matrix is deposited onto a planar optical waveguide. The color change of the porphyrin dye can be detected in the evanescent field of the optical waveguide. Therefore, the light of a high power LED is coupled into the waveguide. The color change of the porphyrin is detectable with photodiodes as a variation of the out-coupled light intensity. The sensor shows no unwished sensitivities to CO₂ and CO and only low to NH₃. NO₂ is detectable with a resolution of 1?ppm.     

Experimental Study of Strengthening for Increased Shear Bearing Capacity

The need for structural rehabilitation of concrete structures all over the world is well known, and a great amount of research is going on in this field. The use of carbon fiber-reinforced polymer (CFRP) plate bonding has been shown to be a competitive method with regard to both structural performance and economic factors. This method consists of bonding a thin carbon-fiber laminate or sheet to the surface of the structure to act as an outer reinforcement layer. However, most research in this area has been undertaken to study flexural behavior. This paper deals with shear strengthening of reinforced concrete members by use of CFRP. Tests on rectangular beams 3.5 to 4.5 m long have been undertaken to study different parameters, such as fatigue, anchorage, and others. The strain field in shear spans of beams simultaneously subjected to shear and bending is also studied. The tests presented also contribute to the existing literature on tests of concrete members strengthened for increased shear capacity.     

Effect of hydrogen addition on the route preference in natural gas flow in regular,horizontal T-junctions

During the transport of natural gas through pipelines small amounts of condensate can be formed due to temperature and pressure changes. If this natural gas/condensate flow arrives at a regular, sharp-edged T-junction in the pipeline system an interesting phenomenon may be observed i.e. unequal phase splitting of gas and condensate. In this paper its has been shown that the addition of hydrogen into a natural gas stream results in a different splitting behaviour in comparison with the natural gas flow without hydrogen addition.