Surface Pre-treatment for Thermally Sprayed ZnAl15 Coatings

Pre-treatment of substrates is an important step in thermal spraying. It is widely accepted that mechanical interlocking is the dominant adhesion mechanism for most substrate-coating combinations. To prevent premature failure, minimum coating adhesion strength, surface preparation grades, and roughness parameters are often specified. For corrosion-protection coatings for offshore wind turbines, an adhesion strength ≥ 5 MPa is commonly assumed to ensure adhesion over service lifetime. In order to fulfill this requirement, Rz > 80 µm and a preparation grade of Sa3 are common specifications. In this study, the necessity of these requirements is investigated using the widely used combination of twin-wire arc-sprayed ZnAl15 on S355J2 + N as a test case. By using different blasting media and parameters, the correlation between coating adhesion and roughness parameters is analyzed. The adhesion strength of these systems is measured using a test method allowing measurements on real parts. The results are compared to DIN EN 582:1993, the European equivalent of ASTM-C633. In another series of experiments, the influence of surface pre-treatment grades Sa2.5 and Sa3 is considered. By combining the results of these three sets of experiments, a guideline for surface pre-treatment and adhesion testing on real parts is proposed for the considered system.     

Design and implementation of multiaxial force sensing gripper fingers

This paper focuses on the integration of elementary force sensors into the fingers of parallel grippers. The theory of the approach of integrating three sensor elements into a gripper finger is described and the results of the practical evaluations are given. Strain gauges are used as elementary sensor elements. Two different design approaches are evaluated. The first one uses H-shaped cut-outs to weaken the structure at designated areas. The measurement accuracy of this system is compared with a second approach without cut-outs, which is easier to manufacture. Finite element analysis is used in both approaches to simulate the behaviour and to determine the best locations for strain gauge application. The performances of both design concepts are experimentally evaluated. It can be seen that the results of the finite-element analysis are correct and that a satisfactory decoupling of the basic sensors can be achieved using a physical or mathematical approach. Both prototypes are able to measure the gripping force with sufficient accuracy.     

Controlling soil water content in fertiliser dissolution experiments

Phosphorus lost in runoff from agricultural land leads to the enrichment of surface waters and contributes to algal blooms. Fertilisers are one source of this P. To compare the water available P of different fertiliser formulations in the laboratory it is necessary to control environmental conditions, temperature, relative humidity and soil water content, prior to simulating rainfall. Two chambers were designed in which relative humidity and soil water content were controlled using salt solutions. An initial design comprising a sealed chamber with three layers of soil samples over a salt bath was found to be inferior to a single layer design. The changes in water content of soil samples were used to test the single layer chamber in a constant temperature environment (15 °C) using a saturated KCl solution (90% relative humidity). Based on the final soil water content of the samples, the spatial variation within the chamber was within tolerable limits. The single layer chamber was used for a simulation experiment comparing the water available P of two commercial fertilisers. Using a saturated resorcinol solution (95% relative humidity) soil samples were equilibrated at 15 °C for 21 days, fertiliser added, and the water available P measured up to 600 h after fertiliser application. The results indicate that the amount of water available P was related to the fertiliser compound and exponentially related to the time since fertiliser application. It was concluded that the single layer chamber is suitable for controlling relative humidity and soil water content in trials such as these where the water available P of fertilisers are being compared.     

3D printing of bone substitute implants using calcium phosphate and bioactive glasses

Customized implants for bone replacement are a great help for a surgeon to remodel maxillofacial or craniofacial defects in an esthetical way, and to significantly reduce operation times. The hypothesis of this study was that a composite of β-tricalcium phosphate (β-TCP) and a bioactive glass similar to the 45S5 Henchglass^® is suitable to manufacture customized implants via 3D-printing process. The composite was chosen because of the bioresorption properties of the β-TCP, its capability to react as bone cement, and because of the adjustability of the bioactive glass from inert to bioresorbable. Customized implants were manufactured using the 3D-printing technique. The four point bending strength of the printed specimens was 14.9 MPa after sintering. XRD analysis revealed the occurrence of two other phases, CaNaPO₄ and CaSiO₃, both biocompatible and with the potential of biodegradation. We conclude that it is possible to print tailored bone substitute implants using a bioactive TCP/glass composite. The glass is not involved as reactive substance in the printing process. This offers the opportunity to alter the glass composition and therefore to vary the composition of the implant.     

Synthesis and electrospun fiber mats of low Tg poly(propylene fumerate‐co‐propylene maleate)

Many publications have examined the biodegradable polymer poly(propylene fumate) (PPF) for use in tissue engineering applications. We have examined a similar crosslinkable polymer system, poly(propylene fumerate)‐co‐(propylene maleate) (PPFcPM), derived from maleic anhydride (MA) and 1,2‐propylene diol (PD). This copolymer system uses a less expensive monomer as well as leads to varied ratios of fumerate to maleate groups, allowing tuning of the crosslinked polymer properties such as degradation rate. Two different reaction conditions were used to synthesize the copolymer from MA and PD. In the first case (Method A), toluene was used as a solvent to azeotropically (85°C) remove water to drive the acid catalyzed esterification reaction. In the second case (Method B), the initial ring opening reaction was conducted, followed by addition of catalyst and removal of water to produce polymer of higher molecular weight. Both polymer systems had glass transition temperatures (T_g) below room temperature. The low T_g PPFcPM was dissolved in chloroform along with the photoinitiator phenylbis(2,4,6‐trimethylbenzoyl)‐phosphine oxide (BAPO) and electrospun. The polymer fibers were crosslinked soon after they formed to produce noncalendaring 3D porous scaffolds. Control experiments without the BAPO photoinitiator did not produce fiber mats. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Particle In-Flight and Coating Properties of Fe-Based Feedstock Materials Sprayed with Modern Thermal Spray Systems

New developments in the field of thermal spraying systems (increased particle velocities, enhanced process stability) are leading to improved coatings. Innovations in the field of feedstock materials are supporting this trend. The combination of both has led to a renaissance of Fe-based feedstocks. Using modern APS or HVOF systems, it is now possible to compete with classical materials for wear and corrosion applications like Ni-basis or metal-matrix composites. This study intends to give an analysis of the in-flight particle and spray jet properties achievable with two different modern thermal spraying systems using Fe-based powders. The velocity fields are measured with the Laser Doppler Anemometry. Resulting coatings are analyzed and a correlation with the particle in-flight properties is given. The experiments are accompanied by computational fluid dynamics simulations of spray jet and particle velocities, leading to a comprehensive analysis of the achievable particle properties with state-of-the-art HVOF and APS systems.     

Bioenergetic Alterations of Metabolic Redox Coenzymes as NADH,FAD and FMN by Means of Fluorescence Lifetime Imaging Techniques

Metabolic FLIM (fluorescence lifetime imaging) is used to image bioenergetic status in cells and tissue. Whereas an attribution of the fluorescence lifetime of coenzymes as an indicator for cell metabolism is mainly accepted, it is debated whether this is valid for the redox state of cells. In this regard, an innovative algorithm using the lifetime characteristics of nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD) to calculate the fluorescence lifetime induced redox ratio (FLIRR) has been reported so far. We extended the FLIRR approach and present new results, which includes FLIM data of the various enzymes, such as NAD(P)H, FAD, as well as flavin mononucleotide (FMN). Our algorithm uses a two-exponential fitting procedure for the NAD(P)H autofluorescence and a three-exponential fit of the flavin signal. By extending the FLIRR approach, we introduced FLIRR1 as protein-bound NAD(P)H related to protein-bound FAD, FLIRR2 as protein-bound NAD(P)H related to free (unbound) FAD and FLIRR3 as protein-bound NAD(P)H related to protein-bound FMN. We compared the significance of extended FLIRR to the metabolic index, defined as the ratio of protein-bound NAD(P)H to free NAD(P)H. The statistically significant difference for tumor and normal cells was found to be highest for FLIRR1.     

Expression Profiles of ASIC1/2 and TRPV1/4 in Common Skin Tumors

The acid-sensing ion channels ASIC1 and ASIC2, as well as the transient receptor potential vanilloid channels TRPV1 and TRPV4, are proton-gated cation channels that can be activated by low extracellular pH (pH_e), which is a hallmark of the tumor microenvironment in solid tumors. However, the role of these channels in the development of skin tumors is still unclear. In this study, we investigated the expression profiles of ASIC1, ASIC2, TRPV1 and TRPV4 in malignant melanoma (MM), squamous cell carcinoma (SCC), basal cell carcinoma (BCC) and in nevus cell nevi (NCN). We conducted immunohistochemistry using paraffin-embedded tissue samples from patients and found that most skin tumors express ASIC1/2 and TRPV1/4. Striking results were that BCCs are often negative for ASIC2, while nearly all SCCs express this marker. Epidermal MM sometimes seem to lack ASIC1 in contrast to NCN. Dermal portions of MM show strong expression of TRPV1 more frequently than dermal NCN portions. Some NCN show a decreasing ASIC1/2 expression in deeper dermal tumor tissue, while MM seem to not lose ASIC1/2 in deeper dermal portions. ASIC1, ASIC2, TRPV1 and TRPV4 in skin tumors might be involved in tumor progression, thus being potential diagnostic and therapeutic targets.