This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400042527

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

Modern computer microprocessor chips are marvels of engineering complexity. For the current 45 nm technology node, there may be nearly a billion transistors on a chip barely 1 cm2 and more than 10 000 m of wiring connecting and powering these devices distributed over 9-10 wiring levels. This represents quite an advance from the first INTEL 4004B microprocessor chip introduced in 1971 with 10 μm minimum dimensions and 2 300 transistors on the chip! It has been disclosed that advanced microprocessor chips at the 32 nm node will have more than 2 billion transistors.1 For instance, Figure 1 shows a sectional 3D image of a 90 nm IBM microprocessor, containing several hundred million integrated devices and 10 levels of interconnect wiring, designated as the back-end-of-the-line (BEOL). Since the invention of microprocessors, the number of active devices on a chip has been exponentially increasing, approximately doubling every two years. This trend was first described in 1965 by Gordon Moore,2 although the original discussion suggested doubling the number of devices every year, and the phenomenon became popularly known as Moore’s Law. This progress has proven remarkably resilient and has persisted for more than 50 years. The enabler that has permitted these advances is known as scaling, that is, the reduction of minimum device dimensions by lithographic advances (photoresists, tooling, and process integration optimization) by ∼30% for each device generation.3 It allowed more active devices to be incorporated in a given area and improved the operating characteristics of the individual transistors. It should be emphasized that the earlier improvements in chip performance were achieved with very few changes in the materials used in the construction of the chips themselves. The increase of performance with scaling * Corresponding author. E-mail: gdubois@us.ibm.com. † IBM Almaden Research Center. ‡ Stanford University. Willi Volksen received his B.S. in Chemistry (magna cum laude) from New Mexico Institute of Mining and Technology in 1972 and his Ph.D. in Chemistry/Polymer Science from the University of Massachusetts, Lowell, in 1975. He then joined the research group of Prof. Harry Gray/Dr. Alan Rembaum at the California Institute of Technology as a postdoctoral fellow and upon completion of the one-year appointment joined Dr. Rembaum at the Jet Propulsion Laboratory as a Senior Chemist in 1976. In 1977 Dr. Volksen joined the IBM Research Division at the IBM Almaden Research Center in San Jose, CA, where he is an active research staff member in the Advanced Materials Group of the Science and Technology function.

Low dielectric constant materials.

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications.

Sol-gel based materials for biomedical applications

Water-based sol–gel synthesis of hydroxyapatite: process development

Enhanced adhesion of copper to dielectrics via titanium and chromium additions and sacrificial reactions

Chemical and structural evolution of hydroxyapatite thin films produced by sol-gel synthesis is characterized by ion beam analysis, X-ray diffraction, and Fourier transform infrared spectroscopy. Formation of the hydroxyapatite structure began at 500°C ; no other phases were observed at higher temperatures. Elimination of residual organics was observed in the form of the disappearance of excess oxygen, hydrogen and carbon. Crystal size increases with increasing anneal temperature ; spectroscopy indicates the formation of highly crystalline films. The analytical methods chosen provide insight into subtle chemical and structural changes which occur in films produced by this synthetic route.

Chemical and Structural Evolution of Sol-Gel-Derived Hydroxyapatite Thin Films under Rapid Thermal Processing

We observe that the crystallization of amorphous Si thin films in contact with a copper silicide layer occurs at a temperature of around 485 °C in the form of dendrites with a fractal dimension of 1.7. The in situ observation of both the silicidation reaction, forming Cu3Si, and the subsequent crystallization of the remaining amorphous silicon in the silicide matrix, were observed during annealing in a transmission electron microscope. We estimate the radial growth rate of these crystallites at 5 nm/s at this temperature. The fractal dimension of the dendrites indicates a growth process similar to one known as diffusion‐limited aggregation.

In situ observation of fractal growth during a‐Si crystallization in a Cu3Si matrix

First phase formation has been determined in Cu binary thin film systems with Ti, Zr, Mg, Sb, Pd, and Pt using transmission electron microscopy and Rutherford backscattering spectrometry. CuTi, CuZr, CuMg2, Cu2Sb, Cu3Pd, and Cu3Pt are the first phases to form upon annealing the Cu/metal bilayers. The effective heat of formation model is used to predict first phase formation in 14 Cu/metal systems.

Observation and prediction of first phase formation in binary Cu‐metal thin films

The reaction kinetics of Ti films on SiO2 were investigated using Rutherford backscattering spectrometry, x‐ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. Consistent with earlier studies, the reaction results in the formation of a TiOw/Ti5Si3/SiO2 stack at temperatures in the range 700–820 °C. As the silicide layer grows, the concentration of O in TiOw increases, with the reaction ceasing at w∼1.2. In addition, the reaction rate depends on the initial Ti thickness, as thicker Ti films possess faster reaction rates. Applying current diffusion‐controlled kinetic growth models, we find nominal agreement with our data at each thickness and predict activation energies in the range 3.0–3.4 eV. However, such a model is unable to account for either the Ti thickness dependence or the slowing and eventual cessation of silicide formation as the oxide composition approaches its limiting value. We implement a model which takes into account the reduction in the thermodynamic driving...

S. W. Russell

Papers

Enhanced adhesion of copper to dielectrics via titanium and chromium additions and sacrificial reactions

Chemical and Structural Evolution of Sol-Gel-Derived Hydroxyapatite Thin Films under Rapid Thermal Processing

In situ observation of fractal growth during a‐Si crystallization in a Cu3Si matrix

Observation and prediction of first phase formation in binary Cu‐metal thin films

Reaction kinetics in the Ti/SiO2 system and Ti thickness dependence on reaction rate