Zirconium Alloys for Orthopaedic and Dental Applications

Zirconium alloys for biomedical applications are receiving increasing attention due to their two unique properties: 1) the formation of an intrinsic bone‐like apatite layer on their surfaces in body environments, and 2) better compatibility with magnetic resonance imaging (MRI) diagnostics due to their low magnetic susceptibility, as well as their overall excellent biocompatibility, mechanical properties, and bio‐corrosion resistance. In particular, since both of the MRI quality and speed depend on magnetic field strength, there is a compelling drive for use of high magnetic field strength (>3 Tesla) MRI systems. This paper provides a comprehensive review of the characteristics of commercially pure (CP) Zr and Zr‐based alloys as orthopaedic and dental implant materials. These include their 1) phase transformations; 2) unique properties including corrosion resistance, biocompatibility, magnetic susceptibility, shape memory effect, and super‐elasticity; 3) mechanical properties; 4) current orthopaedic and dental applications; and 5) the d‐electron theory for Zr alloy design and novel Zr‐alloys. The mechanical properties of Zr‐based bulk metallic glasses (BMGs) and their application as implant materials are also assessed. Future directions for extending the use of Zr‐alloys as orthopaedic and dental implants are discussed.

     

Spatial orientations and structural irregularities associated with the formation of microbands in a cold deformed Goss oriented Ni single crystal

The crystallographic nature of microband boundaries was investigated in a Goss oriented nickel single crystal following cold deformation in channel die plane strain compression. Standard electron backscatter diffraction (EBSD), three-dimensional (3-D)-EBSD and transmission electron microscopy (TEM) were used in the investigation. When viewed in the three orthogonal sections microband boundary traces were classically aligned in the transverse direction section at an acute angle from the rolling direction (RD), but appeared wavy in the normal direction (ND) section. The latter observation may lead to the conclusion that microband boundaries are non-crystallographic. 3-D EBSD was used to reconstruct actual microbands in a deformed volume that revealed significant new information about their structure. Here microband surfaces are largely planar over large distances, but frequently interrupted by local distortions and undulations due to interactions between intersecting non-coplanar microbands. The combined EBSD/TEM investigation has revealed that microband boundaries are aligned close to an active {1 1 1} slip plane (i.e. they are crystallographic), but the undulations and distortions they contain are non-crystallographic in the sense that they deviate from an active slip plane. The non-crystallographic features of microbands (as revealed by their wavy structure in the ND section) may be explained by the crystallographic oscillations of up to ±7.5° towards RD that occur during plastic deformation. Such oscillations result in varying fractions of slip on a given {1 1 1} plane, resulting in varying degrees of interaction between the two sets of non-coplanar microbands. These local and intense microband interactions result in their deviation from their active slip planes.     

Long‐Range Nanoparticle Surface‐Energy‐Transfer Ruler for Monitoring Photothermal Therapy Response

A recent gold nanotechnology‐driven approach opens up a new possibility for the destruction of cancer cells through photothermal therapy. Ultimately, photothermal therapy may enter into clinical therapy and, as a result, there is an urgent need for techniques to monitor the tumor response to therapy. Driven by this need, a nanoparticle surface‐energy‐transfer (NSET) approach to monitor the photothermal therapy process by measuring a simple fluorescence intensity change is reported. The fluorescence intensity change is due to the light‐controlled photothermal release of single‐stranded DNA/RNA via dehybridization during the therapy process. Time‐dependent results show that just by measuring the fluorescence intensity change, the photothermal therapy response during the therapy process can be monitored. The possible mechanism and operating principle of the NSET assay are discussed. Ultimately, this NSET assay could have enormous potential applications in rapid, on‐site monitoring of the photothermal therapy process, which is critical to providing effective treatment of cancer and multidrug‐resistant bacterial infections.     

Structural deformation and infrared sensor response of ultralong carbon nanotubes

We investigated the changes in the first- and second-order Raman spectra of suspended crossed ultralong carbon nanotube (CNT) junctions using different laser excitation energies. The CNT junctions were in situ fabricated by growing CNTs in two perpendicular directions using chemical vapor deposition (CVD) technique. Raman spectra substantiated the structural deformation by the compression between CNTs in the junction. I–V curves of crossed CNT junctions showed the linear behavior. These crossed CNT–CNT junctions have higher current values than individual CNTs. The coexisting suspended and unsuspended CNTs on the substrate showed higher sensitivity to infrared (IR) radiation but longer response time than those with only suspended ones or CNT junctions.     

Impact of high-κ dielectric and metal nanoparticles in simultaneous enhancement of programming speed and retention time of nano-flash memory

A methodology to simulate memory structures with metal nanocrystal islands embedded as floating gate in a high-κ dielectric material for simultaneous enhancement of programming speed and retention time is presented. The computational concept is based on a model for charge transport in nano-scaled structures presented earlier, where quantum mechanical tunneling is defined through the wave impedance that is analogous to the transmission line theory. The effects of substrate-tunnel dielectric conduction band offset and metal work function on the tunneling current that determines the programming speed and retention time is demonstrated. Simulation results confirm that a high-κ dielectric material can increase programming current due to its lower conduction band offset with the substrate and also can be effectively integrated with suitable embedded metal nanocrystals having high work function for efficient data retention. A nano-memory cell designed with silver (Ag) nanocrystals embedded in Al₂O₃ has been compared with similar structure consisting of Si nanocrystals in SiO₂ to validate the concept.     

Effects of Primary Mast Cell Disease on Hemostasis and Erythropoiesis

Mast cell disease is an epigenetically and genetically determined disease entity with very diverse clinical manifestations in potentially every system and tissue due to inap pro priate release of variable subsets of mast cell mediators together with accumulation of either morphologically normal or altered mast cells. Easy bruising, excessive bleeding, and aberrancies of erythropoiesis can frequently be observed in patients with mast cell disease. A thorough history, including a family history, will guide the appropriate work-up, and laboratory evaluations may provide clues to diagnosis. In recent years, our understanding of the involvement of coagulation and anticoagulant pathways, the fibrinolytic system, and erythropoiesis in the pathophysiology of mast cell disease has increased considerably. This review summarizes current knowledge of the impact of the disturbed hemostatic and erythropoietic balance in patients with mast cell disease and describes options of treatment.     

Numerical Simulation of Thermal Damage to Living Biological Tissues Induced by Laser Irradiation Based on a Generalized Dual Phase Lag Model

A generalized dual phase lag (DPL) bioheat model based on the nonequilibrium heat transfer in living biological tissues is applied to investigate thermal damage induced by laser irradiation. Comparisons of the temperature responses and thermal damages between the generalized and classical DPL bioheat model, derived from the constitutive DPL model and Pennes bioheat equation, are carried out in this study. It is shown that the generalized DPL model could predict significantly different temperature and thermal damage from the classical DPL model and Pennes bioheat conduction model. The generalized DPL equation can reduce to the classical Pennes heat conduction equation only when the phase lag times of temperature gradient (τ _T ) and heat flux vector (τ _q ) are both zero. The effects of laser parameters such as laser exposure time, laser irradiance, and coupling factor on the thermal damage are also studied.     

CMOS silicon avalanche photodiodes for NIR light detection: a survey

This paper surveys recent research on CMOS silicon avalanche photodiodes (SiAPD) and presents the design of a SiAPD based photoreceiver dedicated to near-infrared spectroscopy (NIRS) application. Near-infrared spectroscopy provides an inexpensive, non-invasive, and portable means to image brain function, and is one of the most efficient diagnostic techniques of different neurological diseases. In NIRS system, brain tissue is penetrated by near-infrared (NIR) radiation and the reflected signal is captured by a photodiode. Since the reflected NIR signal has very low amplitude, SiAPD is a better choice than regular photodiode for NIR signal detection due to SiAPD`s ability to amplify the photo generated signal by avalanche multiplication. Design requirements of using CMOS SiAPDs for NIR light detection are discussed, and the challenges of fabricating SiAPDs using standard CMOS process are addressed. Performances of state-of-the-art CMOS SiAPDs with different device structures are summarized and compared. The efficacy of the proposed SiAPD based photoreceiver is confirmed by post layout simulation. Finally, the SiAPD and its associated circuits has been implemented in one chip using 0.35 μm standard CMOS technology for an integrated NIRS system.     

Self-cleaning wool: effect of noble metals and silica on visible-light-induced functionalities of nano TiO2 colloid

This study intends to enhance the functionality of titanium dioxide (TiO₂) nanoparticles applied to wool fabrics under visible light. Herein, TiO₂, TiO₂/SiO₂, TiO₂/Metal, and TiO₂/Metal/SiO₂ nanocomposite sols were synthesized and applied to wool fabrics through a low-temperature sol–gel method. The impacts of three types of noble metals, namely gold (Au), platinum (Pt), and silver (Ag), on the photoefficiency of TiO₂ and TiO₂/SiO₂ under visible light were studied. Different molar ratios of Metal toTiO₂ (0.01, 0.1, 0.5, and 1%) were employed in synthesizing the sols. Photocatalytic efficiency of fabrics was analyzed through monitoring the removal of red wine stain and degradation of methylene blue under simulated sunlight and visible light, respectively. Also, the antimicrobial activity against Escherichia coli (E. coli) bacterium and the mechanical properties of fabrics were investigated. Through applying binary and ternary nanocomposite sols to fabrics, an enhanced visible-light-induced self-cleaning property was imparted to wool fabrics. It was concluded that the presence of silica and optimized amount of noble metals had a synergistic impact on boosting the photocatalytic and antimicrobial activities of coated samples. The fabrics were further characterized using attenuated total reflectance, energy-dispersive X-ray spectrometry, and scanning electron microscopy images.