Sol-gel chemistry of transition metal oxides

This review focuses on calcium phosphate-based bone substitute materials that are used (or can be used) for teeth or bone replacement, bone repair, augmentation, or regeneration. This review will also include some properties of bone (e.g., interconnected porosity, biodegradability, bioactivity, osteoconductivity) that are being mimicked in the manufacture of calcium phosphate-based biomaterials and some of the reported factors and strategies that can make the calcium phosphate-based biomaterials acquire osteoinductive properties. Archaeological findings showed that attempts to replace missing teeth date back to the prehistoric period. The materials used then included shells, corals, ivory (from elephant tusks), metals, and human (from corpses) and animal bones. Because of the practice of cremation in many societies, not much is known about prehistoric materials used to replace bones lost to accident or disease. Presently, autografts (bones obtained from another anatomic site in the same subject) remain the gold standard for bone repair, substitution, and augmentation followed by allografts (bones from another subject, such as processed cadaver bones). Autografts and allografts while having the important advantage of being osteogenic or osteoinductive (i.e., inducing bone formation), suffer from several disadvantages. With autografts the drawbacks include additional expense and trauma to the patient, possibility of donor site morbidity, and limited availability. In the case of allografts, in addition to limited supply and high cost, potential viral transmission and immunogenicity are of serious concern. Because of the high cost and limited availability of autografts and allografts, there is a great need to develop synthetic alternative biomaterials for bone replacement, repair, and augmentation. Current commercial substitute materials to replace or repair teeth and bones include metals, polymers (natural or synthetic), corals, human bones (processed cadaver bones), animal bones (processed cow bones), corals and coral derived, synthetic ceramics (calcium phosphates, calcium sulfates, calcium carbonate, bioactive glasses), and composites. It is interesting to note that several of the materials used in prehistoric times are similar to the materials used presently (e.g., coral and coral derived, animal bone derived, metals). Generally, depending on the ability to stimulate bone tissue, materials for tooth or bone repair or replacement are classified as bioinert or bioactive. Bioinert materials do not stimulate bone formation but instead stimulate formation of fibrous tissue and therefore do not directly bond to bone and thus form a weak biomaterial-bone interface. Bioactive materials stimulate bone tissue formation and therefore directly bond with bone and thus form a uniquely strong biomaterial-bone interface. Bioinert materials include metals (e.g., titanium or titanium alloys, stainless steel, cobalt-chromium, Co-Cr, alloys), some synthetic polymers (e.g., PEEK, Teflon-type), and some ceramics (e.g., alumina, * To whom correspondence should be addressed. Phone: (212) 998-9580. Fax: (212) 995-4244. E-mail: rzl1@nyu.edu. Racquel Zapanta LeGeros received her Ph.D. degree from New York University. She is currently a Professor and Associate Chair of the Department of Biomaterials and Biomimetics at New York University College of Dentistry. Her pioneering work was on substitution in the apatite structure and effect on properties. Her research interests includes biologic and synthetic apatites and related calcium phosphates, calcium phosphatebased biomaterials in the form of granules, scaffolds, cements, and coatings, and implant surface modifications. Her current research is on the development of calcium phosphate-based biomaterial for prevention of bone loss induced by diseases (e.g., osteoporosis), therapy (e.g., radiation), condition (e.g., mineral deficiency, immobility), and recovery of bone loss. She is married to Dr. John P. LeGeros and mother of Bernard, David, Katherine, and Alessandra. Chem. Rev. 2008, 108, 4742–4753 4742

Calcium phosphate-based osteoinductive materials.

Synthesis methods for nanosized hydroxyapatite with diverse structures.

The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating.

Material fundamentals and clinical performance of plasma-sprayed hydroxyapatite coatings: A review

Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

Infrared and Raman spectra were measured for a series of glass compositions in the binary B2O3-GeO2 system at room and elevated temperatures. No coordination changes were detected from spectral analysis for either boron or germanium with concentration or temperature changes. Interpretation of the vibrational spectra indicated that both boroxol rings and BO3-triangular units were present as the basic units in glasses with higher B2O3 concentrations. Only BO3-triangular units were detected as the basic units in glasses with lower B2O3 concentrations. Raman spectra of glasses measured at higher temperatures (>Tg) indicated that their boroxol ring concentrations decreased as a function of temperature. The enthalpy for ring rupture in 35GeO2–65B2O3 glass was 7.7 kcal/mol. Also, spectral analysis indicated that the boroxol ring concentrations of these glasses at room temperature were dependent upon their previous heat treatments.

The vibrational spectra of B2O3−GeO2 glasses

Lead Titanate (FT) materials were prepared by a sol-gel process in an air atmosphere using lead acetate and titanium propoxide in methoxyethanol as the precursor materials. FTIR and Raman spectroscopy were used to characterize the various structural changes that occurred during various stages of the preparation. A new crystalline lead titanate phase was detected by both Raman spectral and X-ray diffraction techniques when heating the gelled material at 430°C. In-situ Raman spectra were measured at high temperatures for the resulting sol-gel prepared PT material to investigate its phase-transition and soft-mode behavior.

A Ftir and Raman Spectral Study of the Preparation of Lead Titanate (PbTiO3) by a Sol-Gel Method

FTIR spectral/structural investigation of the ion exchange/thermal treatment of silver ions into a silicate glass

Vibrational spectra were measured and analyzed for HfO2–ZrO2 solid solutions. Some Raman bands in the high–wave–number region shift almost linearly with changes in ZrO2 concentration between the pure end–members; their band locations can be used to determine ZrO2 concentrations in annealed solid solutions. The Raman bands of pure ZrO2 and HfO2 can be correlated using the band shifts of the solid solutions. Induced stress causes band shifts for the solid solutions.

Vibrational Spectra of HfO2–ZrO2 Solid Solutions

Transparent, conductive indium-tin oxide (ITO) and tin oxide thin films were deposited on soda-lime-silicate (SLS) float glass and silica glass substrates by an RF aerosol plasma technique in an atmospheric environment. The ITO films were deposited from solutions with various In: Sn ratios. The dependence of the film properties on the substrate temperature, deposition time, and tin concentration has been studied. The films were characterized by several techniques including XRD, EDS, electrical resistivity, SEM, optical (IR-UV-Vis transmission), Mossbauer, and infrared spectroscopy. The results showed that film phase, morphology, thickness, crystallite size, and conductivity depend on the solution composition and deposition parameters. XRD revealed that In2O3 was present in the film when a In: Sn ratio of 5: 5 or higher was used; otherwise only SnO2 shown. SEM analysis showed that dense and uniform films were formed with particle sizes ranging from approximately 50 nm to 150 nm. The resistivity of the ITO films ranged from 0.12 to 5.0 ohm-cm at room temperature. Optical transmission of the ITO-coated glasses was not different from the uncoated samples. Infrared results indicated that the structure of the near surface of the glasses was significantly modified with a higher indium concentration. The advantages of the atmospheric, RF aerosol plasma deposition process over other techniques are discussed.

Robert A. Condrate

Papers

The vibrational spectra of B2O3−GeO2 glasses

A Ftir and Raman Spectral Study of the Preparation of Lead Titanate (PbTiO3) by a Sol-Gel Method

FTIR spectral/structural investigation of the ion exchange/thermal treatment of silver ions into a silicate glass

Vibrational Spectra of HfO2–ZrO2 Solid Solutions

RF aerosol plasma fabrication of indium tin oxide and tin oxide thin films