Biomedical subjects

L C Lucas

Publications and source records attributed to L C Lucas.

At least 19 recordsLinked to original sources

PubMed2002

Localization of metallic ions with gingival fibroblast subcellular fractions.

Nickel-based alloys have been in use since the 1930s; however, there are concerns regarding the release of metal ions (Be(+2), Cr(+6), Cr(+3), Ni(+2), Mo(+6)) from these alloys into surrounding tissues. Therefore, the objective of this study was to determine the cellular location and accumulation of ions using atomic absorption spectroscopy and correlate location with the cytotoxic, morphologic, and ultrastructural evaluations reported previously. Human gingival fibroblasts were exposed to the metal ions for 72 h. Controlled atomic absorption spectroscopy studies were used to determine the intracellular location of these ions reported as parts per million metal ions per milligram protein. Enzymatic markers were shown to correspond to the appropriate fraction indicating success in fractionation of the gingival fibroblasts. These results correspond with the cytotoxic, morphologic, and ultrastructural alterations reported previously for fibroblasts exposed to these ions. The highest concentration of beryllium ions occurred in the low-density molecule fraction, where lipofuscin granules were found, which has been shown to contain metal ions. The highest concentrations of hexavalent chromium ions occurred in the plasma membrane and nuclear fractions followed by the mitochondria fraction, which is supported by the ions' ability to oxidize to trivalent chromium accumulating at the membrane as well as the alterations in nuclear and mitochondrial function. For trivalent chromium, the highest concentrations occurred in the low-density molecule and the plasma membrane fractions, which correlates with the ions' inability to readily cross membranes. The highest concentration of molybdenum ions occurred in the plasma membrane fraction correlating with alterations in membrane morphology and increased numbers of myelin figures. The highest concentration of nickel ions was associated with the cytosol fraction where lipid droplets seen in the transmission electron micrographs were located. The current study demonstrates that a successful subcellular fractionation was obtained on gingival fibroblasts and that the location of metallic ions within the fractions correlated with cellular alterations reported previously.

Beryllium↗

PubMed2002

Production of thin calcium phosphate coatings from glass source materials.

Calcium phosphate (CaP) coatings, from 40,000 to 200,000 nm thick, on titanium and titanium alloy substrates, were produced using radio frequency (RF) sputtering. Such coatings on dental implants have the potential for improving initial bone ingrowth rates. The success of these coatings may allow the movement from two stage implant systems to single stage implant systems, significantly reducing the time required for healing and fixture placement. Glass source materials were developed for the RF sputtering facility and the resultant coatings were characterized and compared to coatings sputtered from a conventional plasma sprayed hydroxyapatite (HA) source material. The coatings were characterized according to their chemistry, crystalline orientation, and residual strain.

Journal Article↗

PubMed2001

Influence of coating strain on calcium phosphate thin-film dissolution.

The success of calcium phosphate (CaP) coatings used to accelerate initial bone growth onto dental implants can vary depending on the CaP phases present in the coating. In this study, the effect of CaP coating crystal structure and morphology on dissolution rates was investigated. RF magnetron-sputtered CaP coatings (NTC) were compared to a less strained coating (HTC) obtained from heat treatment of sputtered samples at 550 degrees C. Coating strain differences were apparent in XRD spectra where hydroxyapatite-like planes shifted by 0.5 degrees 2theta and 0.05 degrees 2theta for the NTC and HTC coatings, respectively. HTC XRD peak widths were broader than NTC peak widths, indicating smaller crystals or grain sizes. These differences in grain size were corroborated by imaging with scanning probe microscopy. NTC coatings dissolved at a 300% faster rate than HTC coatings. A major factor contributing to this kinetic effect was the level of strain in both coatings. These results suggest an alternate design for CaP coatings can be obtained through the manipulation of coating strain. Using this approach, delivery of different ionic gradients from CaP coatings to surrounding tissue environments can be obtained from surfaces having similar chemistries.

Calcium Phosphates↗

PubMed2000

An investigation of fibroblast mitochondria enzyme activity and respiration in response to metallic ions released from dental alloys.

Most cellular functions evaluated for biocompatibility are high-energy processes such as proliferation and therefore are not usually affected before a decrease in energy production is observed. Several studies have shown that metabolic functions are altered at much lower concentrations than several normally used biocompatibility tests such as viability. Therefore, the purpose of this study was to provide an in-depth evaluation of metallic ion effects on mitochondria function and thereby biocompatibility. These studies evaluated the mitochondrial function of human gingival fibroblasts exposed to the salt solutions of ions released from nickel-based dental alloys, particularly beryllium (Be(2+)), chromium (Cr(6+) and Cr(3+)), nickel (Ni(2+)), and molybdenum (Mo(6+)). Mitochondrial function was examined by NADH:CoQ reductase activity, succinate dehydrogenase activity, and oxygen consumption.

Adult↗

PubMed2000

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.

Adenosine Triphosphate↗

PubMed2000

The effect of nitrogen diffusion hardening on the surface chemistry and scratch resistance of Ti-6A1-4V alloy.

Modular, head-stem, mixed-metal connections are susceptible to mechanically mediated electrochemical interactions. Any attempt to improve the performance of these connections should center around increasing their resistance to mechanical damage, particularly the titanium alloy (Ti64). This study investigated the effect of a nitrogen-diffusion-hardening process on Ti64, with specific reference to changes in composition, chemistry, electrochemistry and its ability to resist and/or repassivate scratch damage. The nitrogen-diffusion-hardened Ti64 alloy had TiN and TiNO complexes at the immediate surface and sub-surface layers. The diffusion-hardened samples also had a deeper penetration of oxygen compared to regular Ti64 alloy samples. The electrochemical impedance spectroscopy data corroborated the increased thickness of the barrier oxide on the diffusion-hardened samples. The nitrogen-diffusion-hardened samples were more resistant to scratch damage and repaired/repassivated faster after such damage. The results suggest that the nitrogen-diffusion-hardened titanium alloy should exhibit increased resistance to mechanical-electrochemical interactions in mixed-metal modular interfaces in total hip prostheses.

Alloys↗

PubMed1999

Analytical and mechanical testing of high velocity oxy-fuel thermal sprayed and plasma sprayed calcium phosphate coatings.

Plasma spraying (PS) is the most frequently used coating technique for implants; however, in other industries a cheaper, more efficient process, high-velocity oxy-fuel thermal spraying (HVOF), is in use. This process provides higher purity, denser, more adherent coatings than plasma spraying. The primary objective of this work was to determine if the use of HVOF could improve the mechanical properties of calcium phosphate coatings. Previous studies have shown that HVOF calcium phosphate coatings are more crystalline than plasma sprayed coatings. In addition, because the coatings are exposed to more complex loading profiles in vivo than standard ASTM tensile tests provide, a secondary objective of this study was to determine the applicability of four-point bend testing for these coatings. Coatings produced by HVOF and PS were analyzed by profilometry, diffuse reflectance Fourier transform infrared spectroscopy, X-ray diffraction, four-point bend, and ASTM C633 tensile testing. HVOF coatings were found to have lower amorphous calcium phosphate content, higher roughness values, and lower ASTM C633 bond strengths than PS coatings; however, both coatings had similar crystal unit cell sizes, phases present (including hydroxyapatite, beta-tricalcium phosphate, and tetracalcium phosphate), and four-point bend bond strengths. Thus, the chemical, structural, and mechanical results of this study, in general, indicate that the use of HVOF to produce calcium phosphate coatings is equivalent to those produced by plasma spraying.

Calcium Phosphates↗

PubMed1999

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 Duncan's 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.

Beryllium↗

PubMed1999

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.

Alloys↗

PubMed1999

Surface topography, corrosion and microhardness of nitrogen-diffusion-hardened titanium alloy.

Mechanical-electrochemical interactions accelerate corrosion in mixed-metal modular hip prostheses. These interactions can be reduced by improving the modular component machining tolerances or by improving the resistance of the components to scratch or fretting damage. Wrought cobalt-alloy (CoCrMo) is known to have better tribological properties compared to the titanium alloy (Ti64). Thus, improving the tribological properties of this mixed-metal interface should center around improving the tribological properties of the Ti64 alloy. This study used scanning probe microscopy (contact, tapping and phase contrast mode), scanning electron microscopy, corrosion testing, and microhardness testing to determine the effect of a nitrogen-diffusion hardening process on the surface morphology, electrochemistry and surface hardness of the Ti64 alloy. The nitrogen-diffusion-hardened titanium alloy samples (N-Ti64) had a more pronounced grain structure, more nodular surface, and significantly (P<0.01) higher mean roughness values than the control-Ti64 samples. The N-Ti64 samples also exhibited at least equivalent corrosion behavior and a definite increase in surface hardness compared to the control Ti64 samples. The equivalent corrosion behavior and improved surface hardness indicate the potential for N-Ti64 samples to resist similar and mixed-metal scratch and fretting damage. The use of N-Ti64 as opposed to control-Ti64 may therefore reduce the occurrence of mechanical-electrochemical degradation in mixed-metal modular total hip prostheses.

Alloys↗

PubMed1998

Evaluation of restorative and implant alloys galvanically coupled to titanium.

OBJECTIVES: As the success of implants leads to their increasing use in restorative dentistry, attention should be devoted to the galvanic combination of restorative materials with titanium. This paper used continuous corrosion potential monitoring in conjunction with zero-resistance ammetry to obtain galvanic corrosion properties of restorative and implant materials coupled with titanium (ASTM F67-Grade II). METHODS: Direct coupling or galvanic experiments were conducted on eight restorative and implant materials coupled to titanium. Deaerated artificial saliva solution in a specifically designed corrosion cell simulated an oral crevice situation. Open circuit potentials (Eo.c.) of each material in the couple, coupled corrosion potentials (Ecouple corr), coupled corrosion current density (lcouple corr) and the resultant charge transfer were monitored. The results were analyzed using single factor ANOVA and Duncan's multiple range tests. RESULTS: Noble restorative (Au-, Ag-, and Pd-based) alloys coupled to titanium were found to be least susceptible to galvanic corrosion. Co-Cr-Mo, Ni-Cr and Fe-based alloys coupled to tatanium were found to be moderately susceptible to galvanic corrosion due to mechanical-electrochemical interaction. Ni-Cr-Be alloy coupled to titanium was found to be highly susceptible to galvanic corrosion. The in vitro test results for the titanium/Disperalloy combination does not concur with the published clinical performance of this combination, and thus warrants further investigation. SIGNIFICANCE: From the data obtained in this study and current literature profiles, acceptable restorative couples were developed for use as clinical guidelines in restorative dentistry.

Analysis of Variance↗

PubMed1998

The effect of water contamination on dimensional change and corrosion properties of a gallium alloy.

OBJECTIVE: This aim of this study was to determine the effect of water contamination on the dimensional change over time and the corrosion properties of a gallium-based alloy (Galloy, SDI), compared to an amalgam (Tytin, Kerr). METHODS: Normal and water-contaminated (10 microL of dH2O during condensation) Galloy and Tytin samples were fabricated using a split metal mold and mechanical condenser. The normal samples were tested for dimensional change under dry and wet (immersed in dH2O) conditions. The water-contaminated samples were tested for dimensional change under only dry conditions. Linear measurements were made over a 7 day period using a stage-equipped dial micrometer. The corrosion potential (Ecorr), the corrosion current density (lcorr), the passive current density (lp), the protective scale formation current density (lps) and potential (Eps), and the breakdown potential (Ebd) were obtained from the polarization curves generated in oxygenated saline solution. Single factor ANOVA and Duncan's multiple range tests were used to determine differences between the various samples. RESULTS: The water-contaminated Galloy samples contracted to a minimum of -3.42 +/- 1.73 microns cm-1 in 5 h followed by expansion to a maximum of 22.56 +/- 3.90 microns cm-1 at the end of 7 days. Normal Galloy and Tytin samples and water-contaminated Tytin samples exhibited rapid contraction during the first 24 h, followed by minimal change over the next 7 days. The Ecorr of normal and water-contaminated Galloy samples was more active than that of the normal and water-contaminated Tytin samples. The lcorr of the normal and water-contaminated Galloy samples was three orders of magnitude greater than the lcorr of normal and water-contaminated Tytin samples. The Eps for the water-contaminated Galloy and Tytin samples was more noble than for the normal Galloy and Tytin samples. The Ebd for the Tytin and water-contaminated Tytin samples was greater than the corresponding values for the Galloy and water-contaminated Galloy samples. SIGNIFICANCE: The gallium-based alloy exhibited expansion if contaminated with water during the condensing and setting process. Post-setting exposure to water did not result in expansion of the gallium-based alloy. The alloy also exhibited a greater susceptibility to corrosion than the amalgam. Due to the possibility of delayed expansion, this material should be used cautiously, particularly in applications involving weakened tooth structure.

Analysis of Variance↗

PubMed1998

Auger electron spectroscopy and its use for the characterization of titanium and hydroxyapatite surfaces.

This review paper provides the basic background and underlying theory behind Auger electron spectroscopy (AES). Among the many surface analytical tools, AES has been shown to be very effective for surface composition analysis. These analyses are critically needed to better understand the interactions between the host and implant. The use of AES for titanium (Ti) and hydroxyapatite (HA) biomaterials characterization is demonstrated in this paper. The relative peak heights of TiL(2,3)M(2,3)V can be used as 'fingerprints' for TiO2 surfaces which have undergone different degrees of reduction. Similarly, for HA coatings, a shift in the phosphorus Auger peaks to a higher kinetic energy indicates the presence of a phosphate group, with strong P-O bonds. Depth compositional profiling and thin-film analysis can be performed using AES. In our studies, oxide thicknesses on Ti surfaces range from 36.8 +/- 7.4 A to 436 +/- 49 A depending on the surface treatment. Depth profiling can also be used to determine the subsurface composition of biomaterials. For HA coatings, a phosphorus concentration at the oxide/metal interface has been observed to be higher than at the outermost oxide surface. The HA coatings have also been observed to coexist within the titanium oxide, suggesting the occurrence of chemical bonding between the coatings and the metallic substrates. However, like other analytical tools, AES has its limitations. The electron beam damage can severely limit useful analysis of organic and biological materials and occasionally ceramic materials. Carbide buildup during long beam exposure times has been shown to affect the relative peak-to-peak intensities of the oxygen and metal Auger signals. The determination of film thickness requires a standard of known thickness and depth profiling of overlapping peaks can be very problematic. Even with these limitation, AES can be a powerful analytical tool for the characterization of biomaterial surfaces.

Biocompatible Materials↗

PubMed1998

Dissolution kinetics of calcium phosphate coatings.

Plasma spray and high velocity oxy-fuel (HVOF) techniques produce coatings with varying composition and amounts of amorphous and crystalline phases. For coatings containing greater amorphous phases, a higher release of calcium ions is evident when samples are placed in Hank's calcium-free balanced salt solutions. Calcium is released from the amorphous phases in the coating, a conclusion that is supported by x-ray powder diffraction (XRD) results. Ion beam sputtering and RF magnetron sputtering under lower energy conditions produce amorphous coatings that will dissolve in a very short time period. When heat treated, crystalline phases are produced in the coatings. Heat-treated coatings are significantly more stable than the amorphous coatings. The dissolution rates of both amorphous and crystalline coatings produced by RF magnetron sputtering have been measured under constant solution conditions at pH 6.50. No reprecipitation is possible under these conditions. The amorphous coating dissolved at a significantly higher rate than the heat-treated coating. Reprecipitation of calcium phosphate onto amorphous coatings is possible in a physiological pH solution. Under these conditions, the dissolution rate of the amorphous coating is four times slower than at the pH 6.50 conditions.

Calcium↗

PubMed1998

Proteoglycans at the bone-implant interface.

The widespread success of clinical implantology stems from bone's 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.

Animals↗

PubMed1996

Effect of surface topography of titanium on surface chemistry and cellular response.

Surface topography plays a critical role in the interaction of dental implants with adjacent tissues. It has been hypothesized that an increase in surface roughness will result in an increase in calcium and phosphorus deposition after immersion in a simulated physiological solution and will increase protein production and calcium uptake by osteoblast-like cells. With the use of a profilometer, titanium samples ground with 600 grit silicon carbide paper were observed to have an average roughness (Ra) value of 0.28 +/- 0.03 micron, whereas titanium samples polished with 0.3 micron Al2O3 exhibited a Ra value of 0.11 +/- 0.01 micron. X-ray photoelectron spectroscopy analyses indicated the presence of calcium, phosphorus, sodium, and chlorine on both surface conditions after immersion in a protein-free physiologic solution. No significant difference in calcium and phosphorus concentrations were observed between the 600 grit or Al2O3 polished titanium samples after immersion in solution. The Ca/P ratio for both 600 grit and Al2O3 polished titanium was in the range of 0.8 to 1.1 after 12 days in solution. The percent protein retained by the rat bone marrow cell layer on both the Al2O3 polished and 600 grit titanium surfaces increased dramatically during the initial 3 days of the study. The 45Ca assays revealed no significant difference in cellular calcification on Al2O3 polished and 600 grit titanium surfaces. For both the Al2O3 polished and 600 grit surfaces, a sharp increase in 45Ca incorporation was observed after 9 days incubation.

Aluminum Oxide↗

PubMed1995

Cellular response to well-characterized calcium phosphate coatings and titanium surfaces in vitro.

The cellular response to well-characterized Ca-P and Ti surfaces was analyzed. This study indicated that the ion-beam sputtering process could produce a hydroxyapatite-type coating. However, structural alterations such as the incorporation of CO3 and the loss of the OH groups were observed. The Ti surfaces were shown to be predominantly amorphous TiO2. The in vitro cell culture study showed no significant differences in cell number for the Ti and Ca-P surfaces throughout the 12-day study. Furthermore, the initial percentage of protein within the cell layers was significantly lower for cells on Ca-P surfaces compared with the cell layer on Ti surfaces. However, after 3 h incubation, no significant difference in the percentage of protein was observed for the Ti and Ca-P surfaces.

Animals↗

PubMed1995

Effect of nickel-based dental casting alloys on fibroblast metabolism and ultrastructural organization.

Previous cell culture evaluations have shown that nickel-chromium dental alloys did not affect cellular viability or morphology. However, nickel-based alloys released corrosion products which decreased cellular proliferation. It was hypothesized that this decrease was due to an interference of cellular energy metabolism by released metal ions. To test this hypothesis, we evaluated the effects on cellular energy metabolism, adenosine triphosphate (ATP) levels, and cellular ultrastructure by four nickel-based alloys, including high and low chromium alloys with and without beryllium additions, in human gingival fibroblast cell cultures. Energy metabolism was evaluated by measuring glucose-6-phosphate dehydrogenase (G-6-PDH) activity. ATP levels were measured with the luciferin-luciferase method. Cellular membranes and ultrastructural organization were evaluated by scanning and transmission electron microscopy. The results of this study showed that metal ions released from all alloys completely inhibited G-6-PDH activity and reduced cellular ATP levels as compared to controls. The reduction in intracellular ATP was greater for the beryllium containing alloys than the non-beryllium-containing alloys. However, no morphologic changes in cellular membranes or organelles were observed. These results support the hypothesis that metal ions released from nickel-based dental casting alloys interfere with cellular energy metabolism.

Adenosine Triphosphate↗