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Biomedical subjects

L C Lucas

Publications and source records attributed to L C Lucas.

At least 37 records · Page 2Linked to original sources
PubMed1995

Characterization of high velocity oxy-fuel combustion sprayed hydroxyapatite.

Bioceramic coatings, created by the high velocity oxy-fuel combustion spraying of hydroxyapatite (HA) powders onto commercially pure titanium, were characterized in order to determine whether this relatively new coating process can be successfully applied to bioceramic coatings of orthopaedic and dental implants. Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy were used to characterize both the HA starting powders and coatings. A 12 wk immersion test was conducted and the resulting changes in the coatings were also characterized. Calcium ion release during dissolution was measured with flame atomic absorption during the first 6 weeks of the immersion study. A comparison of powder and coating X-ray diffraction patterns and lattice parameters revealed an HA-type coating with some loss in crystallinity. Fourier transform infrared results showed a partial loss of the OH- group during spraying, however the phosphate groups were still present. Scanning electron microscopy analysis showed a lamellar structure with very close coating-to-substrate apposition. The coatings experienced a loss of calcium during the immersion study, with the greatest release in calcium occurring during the first 6 days of the study. No significant structural or chemical changes were observed during the 12 wk immersion study. These results indicate that the high velocity oxy-fuel process can produce an HA-type coating; however, the process needs further optimization, specifically in the areas of coating-to-substrate bond strength and minimization of phases present other than HA, before it would be recommended for commercial use.

Aerosols↗
PubMed1995

Cellular response to metallic ions released from nickel-chromium dental alloys.

Concerns exist over the potential release of elevated levels of metal ions such as Ni and Be from Ni-Cr dental casting alloys, due to their susceptibility to accelerated corrosion. In this investigation, we evaluated the release of metal ions from four commercial Ni-Cr alloys, representing a range of compositions, in three-day cell culture tests. Metal ion release, as measured by atomic absorption spectroscopy, was correlated to changes in cellular morphology, viability, and proliferation. The results showed that the test alloys and their corrosion products did not affect cellular morphology or viabilities, but did decrease cellular proliferation. The types and amounts of metal ions released, which corresponded to the alloys' reported surface and corrosion properties, also correlated to observed decreases in cellular proliferation after 72 h. Neptune, which caused the smallest decrease in cellular proliferation as compared with control cells, released the lowest amount of corrosion products, due to its corrosion-resistant, high-Cr-Mo-containing, homogeneous surface oxide. The other test alloys, which were susceptible to accelerated corrosion processes, released higher levels of metal ions that correlated to larger decreases in thymidine incorporation. Metal ion levels increased with test time for all alloys but were not proportional to bulk alloy compositions. Ni ions were released at slightly higher than bulk alloy compositions, while Be was released at from four to six times that of bulk alloy compositions. The elevated release of Be ions was associated with reduced cellular proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Beryllium↗
PubMed1994

Corrosion and cell culture evaluations of nickel-chromium dental casting alloys.

In this study, the corrosion and surface properties of four commercially available nickel-chromium dental casting alloys, were evaluated using electrochemical corrision testing and Auger electron microscopy. The corrosion tests were conducted under cell culture conditions of 5% CO 2 humidified atmosphere at 37 degrees C in minimum essential medium (MEM) balanced salt solution, 95% MEM-5% FBS (fetal bovine serum) cell culture media, and in 95% MEM-5% FBS media after cold solution sterilization of test samples. The results of the surface and corrision analyses were correlated to cytotoxicity and metal ion release from the alloys using agarose overlay and direct contact cell culture tests. The surface and electrochemical corrision analyses demonstrated that the non-beryllium containing alloys were more resistant to accelerated corrosion processes as compared to the beryllium-containing alloys. All alloys demonstrated decreased corrision rates in cell culture solutions after cold solution sterilization treatment. The corrision products released from the nickel-based alloys failed to alter the cellular morphology and viability of human gingival fibroblasts, however they did cause reductions in cellular proliferation. The potential for accelerated corrision and the exposure of local and systemic tissues to elevated levels of corrision products raises concerns over the biocompatibility of these alloys.

Cells, Cultured↗
PubMed1994

Dissolution/reprecipitation and protein adsorption studies of calcium phosphate coatings by FT-IR/ATR techniques.

The surfaces of bioactive Ca-P ceramics immediately change when exposed to proteinaceous solutions. The dissolution behavior and protein interactions of these bioactive materials at the bone/implant interface need to be investigated to understand their material-cellular interactions fully. In this study, FT-IR/ATR techniques were used to study the in situ phosphate release kinetics of Ca-P coatings. The net loss of phosphate molecules from coatings was slower in saline solutions compared with alpha-MEM solutions. Coatings exposed to alpha-MEM solutions containing fibronectin released phosphate molecules slower than coatings exposed to alpha-MEM solutions containing albumin. Conformational changes in fibronectin and albumin adsorbed onto Ca-P and uncoated germanium surfaces were also investigated using FT-IR/ATR spectroscopy. Analysis of changes in the amide I bands indicated that there was a greater loss of beta-sheet structure in adsorbed fibronectin on Ca-P coatings when compared with bare germanium surfaces. Although albumin did change its structure upon adsorption on both Ca-P and germanium, unlike fibronectin, adsorbed albumin structure was similar on Ca-P coatings and germanium. Furthermore, with time the conformation of adsorbed fibronectin and albumin appeared to be very stable on Ca-P coatings, whereas albumin adsorbed to germanium exhibited an increase in ratio of alpha-helix to beta-turn.

Adsorption↗
PubMed1994

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.

Calcium Phosphates↗
PubMed1993

Structure and integrity of a plasma sprayed hydroxylapatite coating on titanium.

Plasma sprayed hydroxylapatite (HA) coatings on titanium substrates were analyzed for process-induced compositional and structural changes. The HA starting powder and the resulting HA coatings were characterized using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The integrity of the ceramic-to-substrate bond strength was also determined, by subjecting plasma sprayed HA coatings to shear/cantilever bond testing. The ceramic coatings retained the basic apatitic crystal structure of the starting powder; however, a considerable amount of amorphous material was created during the plasma spray process. FTIR and Raman spectroscopy revealed that the resulting coatings were partially dehydroxylated. Both XRD and FTIR spectroscopy results also suggested that amorphous material, as well as additional calcium phosphate phases such as alpha-tricalcium phosphate (TCP) not in the starting powder, were present in the HA coating. Average bond strengths of the HA coatings to Ti were determined to be 14.8 MPa +/- 3.5, with fracture occurring at the interface and within the coating itself.

Argon↗
PubMed1993

Surface analysis of nickel-chromium dental alloys.

In this study, the surface compositions of four commercially available nickel-chromium alloys, Neptune, Rexalloy, Regalloy T, and Vera Bond, were compared and correlated to the alloys' corrosion behavior. The alloys were chosen to be representative of alloys with acceptable and unacceptable Cr levels, with and without Be additions. The results showed that the non-Be-containing alloys exhibited a homogeneous Cr-Mo oxide surface which resulted in more corrosion resistant alloys. The Be-containing alloys were shown to have non-uniform oxide surfaces. Areas on the surfaces of these alloys were low in Cr and O and enriched in Be. The oxide surfaces of these alloys were more easily disrupted and provided little resistance to accelerated corrosion processes. Thus, it was found that not only were the Cr and Mo content of the alloys important for corrosion resistance, but the composition of the surface oxide as well.

Aluminum↗
PubMed1993

Effects of copper-based dental casting alloys on two lymphocyte cell lines and the secretion of interleukin 2 and IgG.

In the oral environment, gingival lymphocytes are involved in maintaining the local immune defense of periodontal tissues. The corrosion rates of copper-based dental casting alloys and the accumulation of corrosion products in host gingiva raise concerns about the effects of these corrosion products on immune responses in the oral cavity. The aim of this study ws to investigate the hypothesis that immune function may be altered by copper dental alloy corrosion products. In vitro cell culture studies were used to analyze the effects of three copper-based dental alloys on a T-cell and B-cell line and their secretion of soluble immune mediators (IL-2) and effectors (IgG), respectively. Results of this study revealed that corrosion products released from copper alloys in 24 h have the ability to reduce cellular viability, alter proliferation, and modulate the production of soluble immune mediators. These results support the hypothesis that copper dental ally corrosion products may alter immune responses and thereby contribute to a variety of dental pathological conditions.

B-Lymphocytes↗
PubMed1993

The effect of dissolution on plasma sprayed hydroxylapatite coatings on titanium.

Plasma sprayed hydroxylapatite (HA) coated titanium specimens were immersed into Ca-free Hank's balanced salt solution for periods of 1, 2, 4, and 6 weeks. At each of the respective time intervals the HA coatings were analyzed with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy to determine the effect of dissolution on the structure and composition of the coatings. At the 2- and 6-week intervals, additional samples were removed from solution and shear tested to evaluate the effect of dissolution on the coating-to-substrate interfacial bond strength. XRD results revealed that the plasma sprayed coatings retained their basic apatitic structure throughout the 6-week period in solution. There was, however, a trend towards a more definitive baseline, suggesting a loss of amorphous material by dissolution. FTIR and Raman analyses of the as-sprayed and dissolution specimens showed that the phosphate groups were not lost during the time in solution; however, there was a decrease in hydroxyl content as a result of dissolution mechanisms. FTIR also revealed an increase in carbonate content within the coating during immersion in the simulated physiological balanced salt solution. The average shear bond strengths for the as-sprayed, 2-, and 6-week dissolution specimens were 14.82+/-3.52 MPa, 12.51+/-3.41 MPa, and 12.54+/-2.02 MPa, respectively. Duncan's multiple range test confirmed that the shear bond strength was not significantly reduced after 6 weeks in solution, but there was evidence that suggested a decrease in interfacial bond strength as a result of dissolution mechanisms.

Humans↗
PubMed1992

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.

Bone and Bones↗
PubMed1992

Intraoral corrosion resulting from coupling dental implants and restorative metallic systems.

Materials used for the construction of dental restorations and implants include a wide range of metals and alloys, ceramics and carbons, and polymers. When metals and alloys are placed in direct contact in the oral cavity, a galvanic cell can be formed that may compromise the longevity of one or more of the materials in the couple. In vitro electrochemical corrosion analyses have proven to be a valuable tool for providing guidance on the selection of metallic materials. These analyses can provide basic data on electrochemical potentials, current rates, and the evaluation of galvanic corrosion conditions. This article seeks to provide the clinician with information that can be valuable in the selection of metallic materials that may be placed in direct contact with one another in the oral cavity.

Copper↗
PubMed1992

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.

Biodegradation, Environmental↗
PubMed1991

In vitro vs in vivo corrosion analyses of two alloys.

The in vitro and in vivo corrosion characteristics of two alloys, cast Co-Cr-Mo (ASTM F75) and wrought Ni-Cr-Mo, were evaluated using electro-chemical corrosion analysis. Two in vitro electrolytic solutions were utilized, an isotonic saline solution consisting of 0.9 w/o NaCl in distilled water and an isotonic saline solution with 10 v/o sterile calf serum. The in vivo environment was created by implanting cylindrically shaped specimens of each alloy into the back muscles of New Zealand white rabbits. Cyclic anodic and cathodic polarization curves were generated for the three test conditions and subsequently were compared. Anodic curves conducted using the isotonic saline and isotonic saline plus serum electrolyte solutions were very similar to the anodic curves generated for the implanted alloy specimens for both alloys. The corrosion rates predicted from the in vitro and in vivo cathodic polarization curves were not statistically different for the three test conditions. Overall, the corrosion data generated using the in vitro environmental conditions adequately predicted the in vivo corrosion behavior of the cast Co-Cr-Mo and wrought Ni-Cr-Mo alloys.

Animals↗
PubMed1989

Toxicity of copper-based dental alloys in cell culture.

The biocompatibility of three commercial copper-based dental casting alloys--Duracast MS, Goldent, and Trindium--three experimental copper alloys, and a control gold alloy, Modulay, were investigated. Trindium, Duracast MS, experimental alloys 1 and 2 are aluminum bronzes; Goldent is a hybrid aluminum-brass alloy; and experimental alloy #3 is a high zinc brass alloy. ASTM F813-83 Standard Practice for Direct Contact Cell Culture Evaluation of Materials for Medical Devices, a 3-day direct-contact cell culture regimen and atomic absorption spectroscopy were utilized for evaluating the biocompatibility of these alloys in both Waymouth's and RPMI 1640 complete media. Cellular proliferation assays, using 3H-thymidine uptake, were also conducted in Waymouth's media. In this investigation, only the experimental alloy #3 elicited alterations in morphology and viability of the fibroblast monolayer during the ASTM and 3-day culture tests in either media. Cell cultures exposed to experimental alloy #3 experienced copper concentrations greater than 16.0 ppm in Waymouth's and 10 ppm copper in RPMI 1640 media. Differences in the size of the cytotoxic zone around experimental alloy #3 were also observed, with the larger zone occurring in Waymouth's media. In contrast to the direct cell contact studies, all alloys caused decreases in 3H-thymidine uptake in Waymouth's media at much reduced metal ion concentrations as compared to the controls. Thus, adverse changes in DNA synthesis occurred at much lower copper and zinc concentrations than changes in morphology and viability. Consequently, the assessment of biocompatibility is dependent on the parameters evaluated, and several parameters must be analyzed before a material may be considered biocompatible.

Cell Division↗
PubMed1989

Corrosion of copper, nickel, and gold dental casting alloys: an in vitro and in vivo study.

The corrosion behavior of commercially available copper, nickel, and gold alloys for dental castings was investigated. The alloys investigated included: three copper alloys (76-87Cu, 6-11A1, 0-12Zn, 1-5Ni, 0-4Fe, 0.5-1.2Mn), two nickel alloys (68-78Ni, 12-16Cr, 4-14Mo, 0-1.7Be), and one gold alloy (77Au, 14Ag, 8Cu, 1Pd). Anodic and cathodic polarization curves, long-term immersion tests in saline and artificial saliva solutions, and dog crown studies were conducted to evaluate both the in vitro and in vivo corrosion characteristics of the alloys. All evaluations conducted demonstrated that the copper alloys were highly susceptible to corrosion attack. High corrosion currents were observed in the in vitro tests, and SEM of the alloys specimens showed significantly altered surfaces. The anodic polarization curves predicted that the beryllium-containing nickel alloy should be susceptible to localized corrosion and SEM revealed an etched surface with corrosion of certain microstructural features. No significant corrosion was predicted or observed for the non-beryllium nickel alloy and the gold alloy. The in vitro corrosion evaluations predicted the in vivo corrosion behavior for the alloys. Since the three copper alloys and the beryllium-containing nickel alloy demonstrated significant corrosion under the tested conditions, the use of these alloys for restorative procedures is questionable due to the release of significant levels of selected ions to the oral cavity.

Animals↗
PubMed1986

Properties of biomaterials.

Metallic biomaterials, including iron-, cobalt-, and titanium-based systems, have a long history of applications for surgical implant devices. The mechanical properties of these alloys (modulus, strength, and ductility) have been used to make devices to replace skeletal structures with long-term in vivo stabilities. In addition, the passive surface oxide layers have provided chemical inertness within biologic environments. Recent trends to provide porous metallic conditions for biologic ingrowth and fixation have introduced questions with regard to the relative strength and biodegradation properties. Some biomaterial strengths have been reduced to magnitudes less than 50% of the nonporous alloys, which emphasizes the criticality of design. Surface area increases of 3-10 times has emphasized biocorrosion magnitudes, the elements released to the tissues, and the biologic consequences of these products. This article provides a brief review of these issues with emphasis on mechanical-biomechanical and chemical-biochemical properties of metallic alloys.

Alloys↗
PubMed1986

Corrosion and ion transfer from porous metallic alloys to tissues.

Investigations on porous and nonporous alloys currently available for surgical implant device stabilization through tissue ingrowth have shown microstructures that are characteristic of the thermal processing history of the device and alloy with differences between the nonporous and porous devices of the same nominal chemical analysis, in vitro corrosion potentials that are similar for porous and nonporous alloys and corrosion rates that are approximately proportional to the increases in relative surface areas (X 2 to X 10); local tissue interactions at the cellular level that are specific to the type and amount of elemental constituents present at the interface; and no direct correlations between the local cellular responses (fibroblasts) and the potential for hypersensitivity and other systemically mediated responses. Evaluations of the available published literature and available information on device retrievals and analyses support the opinion that no quantitative, statistically based epidemiologic studies have yet established significant correlations between selected metallic ions and major types of tissue lesions. However, with the changes in surface area and basic surface chemistry for existing alloy systems, research on the long-term tissue responses should be emphasized. In our opinion, biomaterial surface modifications are possible, whereby the relative quantities of released ions available to the environment could be significantly reduced.

Alloys↗