I. Introduction A FUNCTIONAL relationship between cell growth and the initiation and progression of events associated with differentiation has been a fundamental question challenging developmental biologists for more than a century. In the case of bone, as observed with other cells and tissue, the relationship of growth and differentiation must be maintained and stringently regulated, both during development and throughout the life of the organism, to support tissue remodeling. For many years, bone was defined anatomically and examined largely in a descriptive manner by ultrastructural analysis and by biochemical and histochemical methods. These studies provided the basis for our understanding of bone tissue organization and orchestration of the progressive recruitment, proliferation, and differentiation of the various cellular components of bone tissue. Now, complemented by an increased knowledge of molecular mechanisms that are associated with and regulate expression of genes encoding phenotypic compone...

Molecular mechanism mediating proliferation, defferentiation interralationships during progressie development of the osteoblast phenotype

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Th antibacterial activity of metal oxide nanoparticles has received marked global attention as they can be specifically synthesized to exhibit significant toxicity to bacteria. The importance of their application as antibacterial agents is evident keeping in mind the limited range and effectiveness of antibiotics, on one hand, and the plethora of metal oxides, on the other, along with the propensity of nanoparticles to induce resistance being much lower than that of antibiotics. Effective inhibition against a wide range of bacteria is well known for several nano oxides consisting of one metal (Fe3O4, TiO2, CuO, ZnO), whereas, research in the field of multi-metal oxides still demands extensive exploration. This is understandable given that the relationship between physicochemical properties and biological activity seems to be complex and difficult to generalize even for metal oxide nanoparticles consisting of only one metal component. Also, despite the broad scope that metal oxide nanoparticles have as antibacterial agents, there arise problems in practical applications taking into account the cytotoxic effects. In this respect, the consideration of polymetallic oxides for biological applications becomes even greater since these can provide synergetic effects and unify the best physicochemical properties of their components. For instance, strong antibacterial efficiency specific of one metal oxide can be complemented by non-cytotoxicity of another. This review presents the main methods and technological advances in fabrication of nanostructured metal oxides with a particular emphasis to multi-metal oxide nanoparticles, their antibacterial effects and cytotoxicity.

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Pure and multi metal oxide nanoparticles: synthesis, antibacterial and cytotoxic properties

Processing parameters in laser powder bed fusion metal additive manufacturing

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Laser welding of Ti6Al4V titanium alloys

Alumina ceramics have found wide range of applications from semiconductors, communication technologies, medical devices, automotive to aerospace industries. Processing of alumina ceramics is rather difficult due to its high degree of brittleness, hardness, low thermal diffusivity and conductivity. Rapid improvements in laser technologies in recent years make the laser among the most convenient processing tools for difficult-to-machine materials such as hardened metals, ceramics and composites. This is particularly evident as lasers have become an inexpensive and controllable alternative to conventional hole drilling methods. This paper reports theoretical and experimental results of drilling the alumina ceramic with thicknesses of 5 mm and 10.5 mm using milisecond pulsed Nd:YAG laser. Effects of the laser peak power, pulse duration, repetition rate and focal plane position have been determined using optical and Scanning Electron Microscopy (SEM) images taken from cross-sections of the drilled alumina ceramic samples. In addition to dimensional analysis of the samples, microstructural investigations have also been examined. It has been observed that, the depth of the crater can be controlled as a function of the peak power and the pulse duration for a single laser pulse application without any defect. Crater depth can be increased by increasing the number of laser pulses with some defects. In addition to experimental work, conditions have been simulated using ANYS FLUENT package providing results, which are in good agreement with the experimental results.

Experimental and theoretical investigation of the drilling of alumina ceramic using Nd:YAG pulsed laser

Characterization of the drilling alumina ceramic using Nd:YAG pulsed laser

This paper reports an experimental study of welding of dissimilar materials between transparent Polymethylmethacrylate (PMMA) and stainless steel 304 sheets using a pulsed mode Nd:YAG laser The process was carried out for two cases; laser transmission joining (LTJ) and conduction joining (CJ) The former is achieved when the joint is irradiated from the polymer side and the latter when the joint is irradiated from the opposite side (metal side) The light and process parameters represented by the peak power (Pp), pulse duration (τ), pulse repetition rate (PRR), scanning speed (ν) and pulse shape have a significant effect on the joint strength (Fb), joint bead width (b), joint quality and appearance The optimum parameters were determined according to joint quality, joint strength and bead width The optimum results for the joint strength and bead width for both LTJ and CJ are 925 N, 725 mm and 495 N, 8 mm respectively using a rectangular pulse shape (RC) Further modeling studies were carried out based on two methods; one factor at a time method (OFM) and surface response methodology (RSM) method RSM was used to determine optimum parameters for the experimental data building mathematical models for correlating parameters and responses (Fb and b) as well as to investigate how different parameters interact with each other and their effect on the weld quality

Evaluation of PMMA joining to stainless steel 304 using pulsed Nd:YAG laser

Production of the nanoparticles (NPs) by laser ablation from a solid target emerges as an alternative physical method. When a solid target is irradiated by a femtosecond laser, radiation energy is absorbed by the material, followed by, ejection of atoms/small atomic clusters. In this study, the plasmonic behaviour and size variation of silver nanoparticles produced in an aqueous solution of sodium dodecyl sulfate (SDS) has been investigated using an ultrafast Ti:Sapphire laser. After the production of silver nanoparticles in 30 min of laser irradiation, the fundamental and the second harmonics of the Ti:Sapphire laser wavelengths are re-applied for different times (10, 50, 90 min) to diluted SDS solution which contains silver colloids in order to investigate the effect of laser wavelength on agglomerated particles, particle size and shift of the absorption wavelength towards UV. We report that particle size and particle size distribution range can be decreased for both Ti:Sapphire laser wavelengths. Due to the absorption spectrum of the silver nanoparticles, at the end of the 90 min re-irradiation process, sizes of the nanoparticles decreased to 11 nm and 22 nm for 400 nm and the 800 nm laser irradiations, respectively. Depending on the variation of the nanoparticle sizes, in the case of the 400 nm laser irradiation, the shift towards UV is more than the shift produced by 800 nm laser irradiation. The experimental results show that the aggloremation and nanoparticle sizes can be reduced by the second application of the laser beam. # 2011 Elsevier B.V. All rights reserved.

E. Akman

Papers

Laser welding of Ti6Al4V titanium alloys

Experimental and theoretical investigation of the drilling of alumina ceramic using Nd:YAG pulsed laser

Characterization of the drilling alumina ceramic using Nd:YAG pulsed laser

Evaluation of PMMA joining to stainless steel 304 using pulsed Nd:YAG laser

Effect of femtosecond Ti:Sapphire laser wavelengths on plasmonic behaviour and size evolution of silver nanoparticles