L. C. Lucas

Structure, solubility and bond strength of thin calcium phosphate coatings produced by ion beam sputter deposition

Ion beam sputter deposition was used to produce thin calcium phosphate coatings on titanium substrates. Structure, solubility and bond strength of the as-sputtered and heat treated coatings were evaluated. X-ray diffraction (XRD) analysis of the heat treated coatings revealed a hydroxyapatite-type structure. The heat treated coatings were found to have significantly lower solubility as compared to the amorphous as-sputtered coatings. Although the crystalline coatings exhibited the lowest solubility, in general, the bond strengths were lower for the heat treated coatings.

Post-deposition heat treatments for ion beam sputter deposited calcium phosphate coatings

Calcium phosphate coatings produced using the ion beam sputter deposition process are amorphous. To produce crystalline coatings, a series of different post-deposition heat treatments were conducted. Heat treatments conducted at temperatures less than 500 degrees C did not produce crystalline phases in the coatings. A 500 degrees C post-deposition heat treatment provided the energy required to produce a hydroxyapatite (HA)-type coating as determined using X-ray diffraction and Fourier transform IR spectroscopy (FTIR). Although post-deposition heat treatments can reduce the adhesion of a coating to its substrate, the 500 degrees C heat treatment did not decrease the coating bond strength. Heat treatments conducted at 600 degrees C were found to produce crystalline HA-type coatings but these heat treatments significantly reduced the coating bond strength. Cracks were observed on the surface of the 600 degrees C heat treated coatings. FTIR analysis revealed a new absorption band at 820 cm-1 for the 600 degrees C heat treated coatings, suggesting the formation of a new phase.

Spectroscopic characterization of passivated titanium in a physiologic solution

Titanium (Ti) has been used for many biomedical applications. Surface characteristics of titanium devices are critical to their success. In this study, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to analyse Ti surfaces prior to immersion in alpha-modification of Eagles medium (α-MEM). The ionic constituents deposited onto Ti surfaces after in vitro exposure to α-MEM were investigated using XPS and Fourier transform infrared spectroscopy (FTIR). Surface studies revealed an amorphous oxide layer on the Ti surface, with a chemistry similar to TiO2. However, after exposure to the physiologic solution for 12 days, dynamic changes in surface chemistry were observed. Ions such as phosphorus (P) and calcium (Ca) were increasingly deposited as amorphous fine crystalline calcium-phosphate (Ca−P) compounds, having a Ca/P ratio of 1.2 and a chemistry similar to brushite.

Biodegradation of Restorative Metallic Systems

Metallic materials utilized for the construction of intra-oral and implant dental restorations include a wide range of relatively pure metals and multicomponent alloys. Basic corrosion and biodegradation properties of these alloys have been studied by both in vitro and in vivo techniques. These property characteristics have been shown to be dependent on composition and metallurgical state, combinations within a construct, surface conditions, mechanical aspects of function, and the local and systemic host environment. The susceptibility of these metallic materials to various forms of biodegradation will be presented, with emphasis on corrosion.

Proteoglycans at the bone-implant interface.

The widespread success of clinical implantology stems from bones ability to form rigid, load-bearing connections to titanium and certain bioactive coatings. Adhesive biomolecules in the extracellular matrix are presumably responsible for much of the strength and stability of these junctures. Histochemical and spectroscopic analyses of retrievals have been supplemented by studies of osteoblastic cells cultured on implant materials and of the adsorption of biomolecules to titanium powder. These data have often been interpreted to suggest that proteoglycans permeate a thin, collagen-free zone at the most intimate contact points with implant surfaces. This conclusion has important implications for the development of surface modifications to enhance osseointegration. The evidence for proteoglycans at the interface, however, is somewhat less than compelling due to the lack of specificity of certain histochemical techniques and to possible sectioning artifacts. With this caveat in mind, we have devised a working model to explain certain observations of implant interfaces in light of the known physical and biological properties of bone proteoglycans. This model proposes that titanium surfaces accelerate osseointegration by causing the rapid degradation of a hyaluronan meshwork formed as part of the wound-healing response. It further suggests that the adhesive strength of the thin, collagen-free zone is provided by a bilayer of decorin proteoglycans held in tight association by their overlapping glycosaminoglycan chains.

Electrochemical corrosion analyses and characterization of surface-modified titanium

Titanium (ASTM F76) samples received three different surface treatments after which the resulting oxides were characterized and the corrosion behavior was evaluated. No differences in the corrosion potential (Ecorr) were observed for the non-passivated and passivated Ti samples. However, the anodized Ti samples exhibited a significantly more noble Ecorr. At potentials higher than Ecorr, significant differences in current densities were observed for all three different Ti surfaces, with lower current densities observed for anodized Ti samples as compared to the non-passivated and passivated Ti samples. X-ray photoelectron spectroscopy indicated predominantly TiO2 on all Ti surfaces, with a higher concentration of carboxyl species for the anodized Ti surfaces as compared to the non-passivated Ti surfaces. Auger electron spectroscopy revealed a 10-fold thicker oxide layer for anodized Ti surfaces as compared to non-passivated and passivated Ti surfaces.

Evaluations of metabolic activities as biocompatibility tools: a study of individual ions’ effects on fibroblasts

OBJECTIVES Nickel-based dental alloys have been in use since 1930. However, there are concerns regarding the release of metal ions from these alloys to surrounding tissues. Cell culture evaluations can be used to address these concerns and to develop a biocompatibility model by providing a more basic understanding of the metabolic response to individual ions released from dental alloys. This study evaluates the metabolic as well as the morphological response of cultured human gingival fibroblasts to salt solutions of ions which may be released from these alloys; beryllium (Be2+), chromium (Cr6+ and Cr3+), nickel (Ni2+), molybdenum (Mo6+). METHODS These evaluations include viability, lysosomal activity, oxygen consumption, membrane integrity, DNA synthesis, RNA synthesis, protein synthesis, intracellular ATP levels, and glucose-6-phosphate dehydrogenase activity. The results of all cell culture evaluations are reported as the concentration (ppm) required to cause a significant change from the controls, as determined by Duncans multiple comparison test at 0.05 significance level. RESULTS While Ni2+ ion solutions altered metabolic functions at 3-30 ppm and Cr3+ and Mo6+ both at 10 and 100 ppm, Cr6+ and Be2+ were the most toxic causing cellular alterations at 0.04-12 ppm. SIGNIFICANCE These studies indicated that monitoring metabolic activities may be better than the normally used morphology and viability assays for evaluating biocompatibility.

Calcium phosphate coatings for medical and dental implants

Abstract Long-term fixation of metallic dental and medical implants in bony tissues continues to be a problem. One possible solution involves the application of calcium phosphate (Ca-P) ceramic coatings such as hydroxyapatite (HA) onto the metallic devices. Two methods being investigated for producing the coatings include plasma spraying, a commercially available process, and ion-beam sputter deposition, a technique being experimentally investigated. The plasma spraying process produces coatings on the order of 40–60 μm thick. The chemistry and structure of the coatings are similar to those of HA; however, the plasma spraying process will result in the formation of amorphous and other Ca-P phases in the resulting coatings. One concern with respect to these coatings is their relatively low bond strength. The ion-beam sputtering process produces thin (0.6–1 μm) Ca-P coatings that have a significantly higher bond strength than the plasma-sprayed coatings. One concern with the sputtered coatings relates to the amorphous structure obtained after sputtering. These amorphous coatings have high dissolution rates, and a post-deposition heat treatment is required to form more stable crystalline phases in the coatings. The chemistry and structure of the heat-treated coatings are again similar to those of HA; however, other phases can result from this process as well. Both deposition processes result in the formation of HA-type coatings; however, optimization of various coating properties such as stability and bond strength remain a challenge which must be addressed before an optimal tissue response can be attained.

Cytotoxicity of nickel-chromium alloys: Bulk alloys compared to multiple ion salt solutions

OBJECTIVE Nickel-based alloys have been in use since the 1930s; however, there are concerns regarding the biocompatibility of the metallic ions released from these alloys to surrounding tissues. The objective of this study was to better understand nickel-based alloy cytotoxicity as well as determine if multiple ion salt solutions can be used to model the cytotoxic effects of bulk implant alloys. METHODS This study evaluated cellular morphology, viability, membrane integrity, and alterations in metabolic activity, including DNA synthesis, RNA synthesis, protein synthesis, oxygen consumption, intracellular ATP levels, and glucose-6-phosphate dehydrogenase in response to bulk alloys and multiple ion salt solutions. RESULTS Over a 24- or 72-h exposure time, the nickel-based alloys released a total ion concentration in the parts per billion range and caused alterations in DNA, RNA, and protein synthesis, intracellular ATP levels, and glucose-6-phosphate dehydrogenase activity. Interestingly, cellular responses to the salt solutions representing the ions released from the alloys were not consistently significantly similar to those elicited from the alloys. SIGNIFICANCE From these studies, it was shown that a number of cellular functions are altered in response to ions released from these implant alloys. However, cellular functions were not similarly altered in response to salt solutions representing the ions released from the alloys. These results demonstrated salt solutions cannot be easily used to represent alloy cytotoxicity, and ionic release from alloys is a complex process dependent on variables including ion chemistry, ion valence, and dose-time dependence. This study provides a better understanding of the metabolic response of fibroblasts to ions released from dental alloys; and is a good first step towards developing a more reliable cell culture model of cytotoxicity.

Effects of metallic ion toxicity on human gingival fibroblasts morphology

Alloys used as implant materials release metal ions to surrounding tissues. Cytotoxic substances attack at the molecular level, and these effects are reflected in the structure of the cells and organelles. The objective of this study was to evaluate the cellular morphology and ultrastructural changes of cultured human gingival fibroblasts to salt solutions of ions (beryllium (Be+2), chromium (Cr+6 and Cr+3), nickel (Ni+2), molybdenum (Mo+6)) which may be released from nickel-chromium dental alloys. The concentrations chosen were based on previously conducted cell culture studies. Fibroblasts were exposed to the different ion concentrations for 24 or 72 h. Cellular morphology and ultrastructural features were examined using scanning electron microscopy and transmission electron microscopy. Ultrastructural alterations observed included irregular shaped nuclei for cells exposed to hexavalent chromium and nickel, pseudopodia for cells exposed to beryllium and molybdenum, and lipid droplet formation in cells exposed to nickel.