Peter Filip

Single walled carbon nanotube composites for bone tissue engineering

The purpose of this study was to develop single walled carbon nanotubes (SWCNT) and poly lactic‐co‐glycolic acid (PLAGA) composites for orthopedic applications and to evaluate the interaction of human stem cells (hBMSCs) and osteoblasts (MC3T3‐E1 cells) via cell growth, proliferation, gene expression, extracellular matrix production and mineralization. PLAGA and SWCNT/PLAGA composites were fabricated with various amounts of SWCNT (5, 10, 20, 40, and 100 mg), characterized and degradation studies were performed. Cells were seeded and cell adhesion/morphology, growth/survival, proliferation and gene expression analysis were performed to evaluate biocompatibility. Imaging studies demonstrated uniform incorporation of SWCNT into the PLAGA matrix and addition of SWCNT did not affect the degradation rate. Imaging studies revealed that MC3T3‐E1 and hBMSCs cells exhibited normal, non‐stressed morphology on the composites and all were biocompatible. Composites with 10 mg SWCNT resulted in highest rate of cell proliferation (p < 0.05) among all composites. Gene expression of alkaline phosphatase, collagen I, osteocalcin, osteopontin, Runx‐2, and Bone Sialoprotein was observed on all composites. In conclusion, SWCNT/PLAGA composites imparted beneficial cellular growth capabilities and gene expression, and mineralization abilities were well established. These results demonstrate the potential of SWCNT/PLAGA composites for musculoskeletal regeneration and bone tissue engineering (BTE) and are promising for orthopedic applications.

Titanium-Nickel Shape Memory Alloys in Medical Applications

Shape memory alloys (SMAs) are special metallic materials, which spontaneously recover shape after being subjected to macroscopic deformation higher than their elastic limit. Recovery of shape may occur after heating or after release of loads. Applied deformation can be quite complex. Combinations of different deformation sequences are as readily recoverable as simple tension or compression. Numerous alloy systems, polymers, and ceramics have been found to exhibit shape memory behavior [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].

Investigation of High-Frequency Squeal in a Disc Brake System Using a Friction Layer-Based Coupling Stiffness:

Abstract This paper presents a two degree of freedom model for disk brake systems that makes use of the concept of a friction layer-based coupling stiffness. This model is then used to investigate noise and vibration, especially high-frequency squeal. It is shown that for automotive brake systems, the friction layer plays a significant role in the performance characteristics. Hence, the coupling stiffness between the brake pad and the rotor is modelled as a combination of the elastic stiffness of the friction layer superimposed on the coupling modal stiffness of the brake-pad combination. The elastic properties of the friction layer are obtained from nano-indentor tests and the contact area is approximated using light microscopy and scanning electron microscopy analysis. The coupling modal stiffnesses are obtained from impact tests and finite element studies. Preliminary results from the model are consistent with the actual high squeal data collected from the field. The main objective of this work is to introduce a new way of modelling the coupling stiffness based on the properties of the friction layer, which has not been extensively studied till now.

C/C composite brake disk nondestructive evaluation by IR thermography

This paper discusses the non-destructive evaluation of thick Carbon/Carbon (C/C) composite aircraft brake disks by using transient infrared thermography (IRT) approach. Thermal diffusivity measurement technique was applied to identify the subsurface anomalies in thick C/C brake disks. In addition, finite element analysis (FEA) modeling tool was used to determine the transient thermal response of the C/C disks that were subjected to flash heating. For this, series of finite element models were built and thermal responses with various thermal diffusivities subjected to different heating conditions were investigated. Experiments were conducted to verify the models by using custom built in-house IRT system and commercial turnkey system. The analysis and experimental results showed good correlation between thermal diffusivity value and anomalies within the disk. It was demonstrated that the step-heating transient thermal approach could be effectively applied to obtain the whole field thermal diffusivity value of C/C composites.

Dissolution of copper and iron from automotive brake pad wear debris enhances growth and accumulation by the invasive macrophyte Salvinia molesta Mitchell

Automotive vehicles release particulate matter into the environment when their brakes are applied. The environmental effects of this automotive brake pad wear debris (BPWD) on the environment is a matter of growing debate yet the effects on plants have been largely untested. In this study, the effect of BPWD on the growth of the aquatic invasive Salvinia molesta Mitchell was examined. Salvinia molesta, plants were grown hydroponically in distilled water or in a distilled water extract containing BPWD. Growth of floating leaves, submerged leaves, and leaf nodes were measured over 20 d at 4-d intervals. At the conclusion of the study the amount of BPWD present in solutions and plant tissues was quantified using atomic absorption spectrometry (AAS). Cultivation of S. molesta in the water containing BPWD resulted in greater dissolution of Cu and Fe than occurred in the absence of plants. The tissue Cu and Fe concentrations of plants cultivated in the BPWD were significantly higher than plants grown in the absence of BPWD. Growth of S. molesta significantly increased when cultivated in the BPWD solutions in comparison to the distilled water. The results suggest that S. molesta and similar aquatic plants may be capable of increasing the dissolution of metal micronutrients from BPWD and utilizing those micronutrients to increase growth. Such growth responses could indicate that BPWD may interact with invasive floating macrophytes to more rapidly degrade the quality and stability of aquatic communities.

The Effect of Wear Groove on Vibration and Noise of Aircraft Brakes: Theoretical and Experimental Evidence

The goal of this paper is to delineate recent experimental evidence that the presence of conforming surface wear groove tends to stabilize the vibration and noise response of aircraft brakes. This finding is consistent with an earlier theoretical study in which the contact between Carbon-Carbon (C/C) composite brake disks were assumed to be visco-elastic and through this assumption it was found that the existence of conforming grooves results in increasing dynamic stability of brake disk interaction. Therefore, the presumption of visco-elastic contact for C/C brakes seems to agree with the experimental observation in a subscale dynamometer. The present paper summarizes both theoretical analysis and the test results. In the tests C/C composites were heat treated for one hour at temperatures 1800°C and 2400°C, respectively. They were then subjected to frictional tests in a subscale aircraft brake dynamometer at 50 % relative humidity (RH) level. Coefficient of friction (μ), vibration and noise were recorded during simulated braking. The surface topography was determined after each sequence of friction tests. The nanohardness of fiber and matrix in bulk composite were measured using a nanoindenter. The hardness of fiber was found to be two times of that of the matrix for the samples heat treated at 2400°C as compared to the samples heat treated at 1800°C. The surface roughness (sRa) was measured as 1.96 μm for the sample heat treated at 2400°C after the 100% simulated normal landing energy conditions. The sample heat treated at 1800°C exhibited smoother friction surface (sRa=0.86μm). During braking, μ varied by a factor of 2 or more which led to undesirable vibration. Both the theoretical model and the tests results point to the same conclusion; existence of conforming grooves enhances dynamic stability of a disk pair, resulting in significant reduction in vibration and noise in braking.

Automotive airborne brake wear debris nanoparticles and cytokinesis-block micronucleus assay in peripheral blood lymphocytes: A pilot study

Motor vehicle exhaust and non-exhaust processes play a significant role in environmental pollution, as they are a source of the finest particulate matter. Emissions from non-exhaust processes include wear-products of brakes, tires, automotive hardware, road surface, and traffic signs, but still are paid little attention to. Automotive friction composites for brake pads are composite materials which may consist of potentially hazardous materials and there is a lack of information regarding the potential influence of the brake wear debris (BWD) on the environment, especially on human health. Thus, we focused our study on the genotoxicity of the airborne fraction of BWD using a brake pad model representing an average low-metallic formulation available in the EU market. BWD was generated in the laboratory by a full-scale brake dynamometer and characterized by Raman microspectroscopy, scanning electron microscopy, and transmission electron microscopy showing that it contains nano-sized crystalline metal-based particles. Genotoxicity tested in human lymphocytes in different testing conditions showed an increase in frequencies of micronucleated binucleated cells (MNBNCs) exposed for 48h to BWD nanoparticles (NPs) (with 10% of foetal calf serum in culture medium) compared with lymphocytes exposed to medium alone, statistically significant only at the concentration 3µg/cm(2) (p=0.032).

Detection of nano- and micro-sized particles in routine biopsy material - pilot study

BACKGROUND Nanotechnology is receiving enormous funding. Very little however is known about the health dangers of this technology so far. Chronic tonsillitis is one of a number of diseases called idiopathic. Among other factors, the tonsils are exposed to suspended particles in inhaled air including nano particles. The objective of this study was to detect and evaluate metallic particles in human tonsil tissue diagnosed with chronic tonsillitis and in amniotic fluid as a comparison. METHODS . Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) was used for identification of solid particles in a total of 64 samples of routinely analyzed biopsy and cytologic material. RESULTS Almost all samples were found to contain solid particles of various metals. The most frequent, regardless of diagnosis, were iron, chromium, nickel and aluminium. The size, determined using SEM, varied from around 500 nm to 25 µm. The majority formed aggregates of several micrometers in size but there were a significant number of smaller (sub-micrometer or nano-sized) particles present. The incidence of metallic particles was similar in child and adult tissues. The difference was in composition: the presence of several metals in adults was due to occupational exposure. CONCLUSIONS The presence of metallic particles in pathologically altered tissues may signal an alternative causation of some diseases. The ethiopathogenic explanation of these diseases associated with the presence of nano-sized particles in the organism has emerged into a new field of pathology, nanopathology.

Cementless modular total hip arthroplasty: a retrieval analysis

This paper reports the analysis of a modular S-ROM hip implant, which was retrieved at revision, secondary to aseptic loosening approximately after 24-months of implantation. Microscopic analysis confirmed the presence of pitting, fretting corrosion, plastic deformation, and stress induced corrosion cracking. Energy-dispersive x-ray microanalysis of the stem surface revealed the release of metal ions. High resolution inductively coupled plasma mass spectroscopy confirmed elevated titanium ion levels (4.66 ppb) in blood serum. Finite element analysis of the implant showed that the micromotion and stress levels were the maximum at the proximal-lateral region of the taper junction, in congruence with the observation.

Analysis of High Frequency Squeal in a Disc-Brake System Using a Stick-Slip Friction Model

This paper presents a two degree of freedom (2-DOF) stick-slip friction model for studying the effect of contact stiffness on the stability of the system. It is shown that the stability is not only a function of non-linear variation in the friction force provide by stick-slip but also depends on the variation in stiffness of contact due to the formation of friction layers on the surface of the rotor and the brake pad. Parametric studies have been presented to show the effect of variation in coefficient of friction and contact stiffness on the system stability.Copyright