Rheological and tribological behavior of polyacrylamide-base solutions for artificial synovial fluid.

PURPOSE: This paper presents tribological and rheological analysis results of artificial synovial fluid base solutions. Special attention was paid to polyacrylamide preparations with different molecular weights and concentrations. METHODS: Tribological tests were conducted using the Al2O3-CoCrMo friction pair in the presence of investigated lubricants. Confocal microscopy was used to analyze and assess of volume, depth, and width of wear traces. Moreover, the viscosity and viscoelasticity tests of analyzed solutions were carried out. The rheological measurements were focused on the oscillatory tests, which allowed us to determine the elasticity modulus (G') and viscosity (G″). RESULTS: Viscoelastic nature of the tested preparations depends on the strain rate. It has been shown that elastic properties dominate at higher frequencies. The molecular weight of the polymer has a particular influence on these properties. The most promising results were obtained for 6% and 8 % high molecular weight polyacrylamide compositions. CONCLUSIONS: However, all tested polyacrylamide solutions show better rheological and tribological characteristics than commercial preparation based on hyaluronic acid.

Fretting and Fretting Corrosion Processes of Ti6Al4V Implant Alloy in Simulated Oral Cavity Environment.

The paper presents the results of in vitro studies of fretting and fretting corrosion processes of Ti6Al4V implant alloy in the environment of natural saliva and self-made mucin-based artificial saliva solutions. The study was performed on a specially designed fretting pin-on-disc tester, which was combined with a set used for electrochemical research. The open circuit potential measurements and potentiodynamic method were used for corrosion tests. The worn surfaces were subjected to microscopic observations and an evaluation of wear. Results were interpreted using the dissipated energy and third-body approaches. The X-ray diffraction analysis showed that titanium oxides constitute over 80% of the friction products. Special attention was paid to the role of saliva and its substitutes, which in certain cases can lead to the intensification of fretting wear. On the basis of the received results, a new phenomenological model of fretting corrosion processes was proposed. This model involves the formation of an abrasive paste that is a combination of metal oxides and the organic components of saliva.

Glutathione Metabolism, Mitochondria Activity, and Nitrosative Stress in Patients Treated for Mandible Fractures.

The aim of the study was to evaluate the effect of titanium bone fixations on mitochondrial activity, reactive oxygen species (ROS) production, glutathione metabolism, and selected markers of oxidative/nitrosative stress in the periosteum-like tissue of patients treated with mandible fractures. The study group consisted of 30 patients with bilateral fractures of the mandible body eligible for surgical treatment. Our study is the first one that indicates disturbances of mitochondrial activity as well as a higher production of ROS in the periosteum-like tissue covering titanium fixations of the mandible. We also found significantly higher levels of reduced glutathione and enhanced activity of glutathione reductase in the periosteum homogenates of patients in the study group compared to the control group. Levels of nitrosative (S-nitrosothiols, peroxynitrite, nitrotyrosine) and oxidative stress biomarkers (malondialdehyde, protein carbonyls, dityrosine, kynurenine, and N-formylkynurenine) were statistically elevated in periosteum-like tissue covering titanium fixations. Although exposure to titanium fixations induces local antioxidant mechanisms, patients suffer oxidative damage, and in the periosteum-like tissue the phenomenon of metallosis was observed. Titanium implants cause oxidative/nitrosative stress as well as disturbances in mitochondrial activity.

Artificial Mucin-based Saliva Preparations - Physicochemical and Tribological Properties.

PURPOSE: To create and investigate artificial mucin-based saliva substitutes with properties similar to natural saliva. MATERIALS AND METHODS: Natural saliva and six saliva preparations were tested. Saliva substitutes were made using phosphate buffered saline (PBS) prepared in deionised water or plasma-treated water (PBSPT) with addition of porcine gastric mucin and guar gum or poloxamer 407. A wide range of properties were characterised: physicochemical (changes of pH, conductivity and surface tension over time: 1, 24, 96, 168 h after mixing ingredients), rheological (viscosity and viscoelasticity), tribological (coefficient of friction for titanium alloy Ti-6Al-7Nb kinematic couple) and corrosive (open circuit potential, corrosion potential, polarisation resistance). RESULTS: Saliva preparations based only on mucin had pH, viscosity, coefficient of friction and corrosion parameters similar to those of natural saliva. Guar gum increased the values of viscosity, viscoelasticity and the coefficient of friction. Similar results were obtained for poloxamer 407, whereas it decreased the surface tension of tested preparations. Plasma-treated PBS enhanced the corrosion resistance of saliva substitutes with guar gum and poloxamer 407. CONCLUSION: Among the tested compositions, saliva substitutes based only on mucin were found to have parameters similar to human whole saliva. Mucin saliva preparations may have wide applicability for patients with e.g. xerostomia or patients using a metal prosthesis.

Biocorrosion of 316LV steel used in oral cavity due to Desulfotomaculum nigrificans bacteria.

Corrosion processes of metallic biomaterials in the oral cavity pose a significant limitation to the life and reliable functioning of dental materials. In this article, the influence of environment bacteria Desulfotomaculum nigrificans sulfate reducing bacteria on the corrosion processes of 316LV steel was assessed. After 14 and 28 days of contact of the material with the bacterial environment, the surfaces of the tested biomaterial were observed by means of confocal scanning laser microscopy, and their chemical composition was studied using X-Ray Photoelectron Spectrometry and a scanning transmission electron microscopy. Corrosive changes, the presence of sulfur (with atomic concentration of 0.5%) on the surface of the biomaterial and the presence of a thin oxide layer (thickness of ∼20 nm) under the surface of the steel were observed. This corrosion layer with significant size reduction of grains was characterized by an increased amount of oxygen (18% mas., p < 0.001) in comparison to untreated 316LV steel (where oxygen concentration - 10% mas.). Image analysis conducted using APHELION software indicated that corrosion pits took up ∼2.8% of the total tested surface. The greatest number of corrosion pits had a surface area within the range of 100-200 µm2 . © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 222-229, 2017.

Influence of self-made saliva substitutes on tribological characteristics of human enamel.

This paper describes the results of tests on the influence of human saliva and its substitutes on tribological characteristics of friction pairs. Each pair consists of enamel and one of the following materials: ceramics, the Meridian B2 dental composite, the GK dental amalgam, and Ti-6Al-4V titanium alloy. The saliva substitutes used were prepared using pyrophosphates, xanthan gum, and mucins dissolved in a saline buffer. The results of the tribological tests show that the values of the parameters under investigation (coefficient of friction and linear wear) were different from each other. Some similarity was observed between the evaluated level of wear characteristics after the friction process in the environment of human saliva and that in the environment of one of the mucins tested. Microscopic observations of the surfaces of the enamel samples after friction revealed varied forms of tribological wear.

Fluoride release and antibacterial activity of selected dental materials.

The aim of the study was to assess the fluoride ion release and antibacterial activities of the glassionomer cement Fuji IX and the compomer (composite modified polyacid) Dyract AP. Fluoride ion release was measured using direct potentiometry with an Orion fluoride ion selective electrode. The measurement was carried out after 1, 4, 7, 14, 30, and 60 days of storage in phosphate buffer at pH 6.8. The antibacterial activity of the materials was evaluated against the bacteria Streptococcus mutans ATCC 35668, Streptococcus salivarius ATCC 13419, Streptococcus sanguis ATCC 10556, and Lactobacillus casei subsp. casei ATCC 393. The agar diffusion test was applied. The material specimens were assessed twice: after setting and seven days later. Zones of bacterial growth inhibition were measured in millimeters after 24 hours. The results of the study showed that both materials released ion fluoride, with a higher emission of Fuji IX than Dyract AP. The highest level of emission was observed on the seventh day of the study in both materials. After 24 hours of bonding there was inhibition of bacterial growth by Fuji IX, whereas Dyract AP did not show similar activity. On the eighth day after polymerization, Dyract AP was significantly more active towards Streptococcus sanguis and salivarius.