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The use of waste or natural resources is an interesting approach to preparing adsorbent materials. Most adsorption materials are powder-based, making them impractical for a variety of applications. In this work, the natural kaolin clay and hydroxyapatite synthesized from biogenic waste were studied as defluoridation materials. The point of zero charge (pHPZC), the fluoride adsorption capability and the adsorption isotherm of calcined kaolin and mixed calcined kaolin/hydroxyapatite in both powdered and moulded forms were investigated. The hardness of the moulded (post-formed) samples was tested before and after in immersion in a fluoride solution. The maximum hardness was 15.8 kilo-pounds for the post-formed calcined kaolin sample. Sample hardness values slightly decreased after immersion in a fluoride solution due to the formation of micro-cracks. Most samples presented high pHPZC values, implying that these materials are suitable for the capture of fluoride anions. The adsorption properties varied with the ratio of calcined kaolin to hydroxyapatite. These properties for post-formed samples were different from those in powdered form. Post-formed samples showed higher fluoride adsorption. The maximum fluoride adsorption capacity and efficiency of the post-formed samples (calcined kaolin) at pH 3 were 1.74 F− mg/g and 87%, respectively. The sorption of fluoride of hydroxyapatite and mixed calcined kaolin/hydroxyapatite powders was found to have the form of the Langmuir isotherm, which indicates a monolayer adsorption on the adsorbent surface. Isotherms of calcined kaolin powder, post-formed calcined kaolin and mixed calcined kaolin/hydroxyapatite samples followed the Freundlich isotherm, which indicates multilayer adsorption on a heterogenous adsorbent surface.

The rapid age growth in most of the developed countries leads to application of artificial joints such as knee joints and hip joints. The properties of titanium alloy such as light weight, high strength and good biocompatibility make it a suitable material for wide usage as artificial joints. However, titanium alloy cannot directly adhered with human bone; thus, bonds or coating are required. Plasma-sprayed hydroxyapatite (HAp) is widely used as a coating to bond artificial Ti-6Al-4V implants with human bone. The contact slip mainly occurs at the HAp-Ti-6Al-4V interface which also known as possible delamination interface in hip joint artificial implant. The coating fretting fatigue delamination condition can lead to contact slip at HAp coating-Ti-6Al-4V interface which will accelerate HAp coating fretting wear behavior. This paper presents the influence of normal loading, fatigue loading and delamination length on contact slip distributions at HAp coating-Ti-6Al-4V interface through finite element based methodology. A simple FE contact configuration model consist of contact pad, HAp coating and Ti-6Al-4V substrate is examined under static simulation. The predicted results revealed that lower normal load with higher maximum fatigue loading condition could promote more contact slip distribution. The contact slip is also increased with increasing delamination length. The induced contact slip can accelerates fretting wear behavior of HAp coating.

This study aims at clarifying the effects of delamination on fretting wear behaviors of plasma-sprayed hydroxyapatite coating. Plasma-sprayed hydroxyapatite (HAp) coating has been widely used as a bond between human bone with artificial metallic implants in order to smoothly transmit loads by gaits. However, HAp coating is susceptible to be failed due to brittle fracture, fatigue cracks, wears by fretting or corrosion etc. Wear particles made by fretting are concerned for activating inflammatory reactions at surrounding organs, which lead to loosening of implants or subsequent failures. Delamination in interfaces of HAp coating can accelerate the wear behaviors in fretting fatigue. Moreover, adhesive conditions between human bone with artificial implants can affect such the delamination / wear behaviors of HAp coating. Adhered contact surfaces between human bone with artificial implants are practically believed to suppress such wear behaviors. However, no experimental study to observe the behaviors has been conducted. An in-situ observation system of fretting fatigue was facilitated. The in-situ observations revealed that higher stress amplitudes and lower contact pressures promoted growth rates of delamination. Furthermore, delamination between HAp coating with metal substrates could accelerate the wear amounts from both the artificial human bone and HAp coatings. Adhered contact conditions between contact pads with coated substrates demonstrated lower delamination growth rates in HAp coating. Even in the cases of adhered contacts conditions, delaminaion continued propagations, which indicated that wear behaviors would occur once delamination reached a certain length. Finite element analyses also revealed that delamiantion length in HAp coating could mainly promote wear behaviors of HAp coating.

Purpose: Peri-implantitis is an important biologic complication that can lead to implant failure. Proper treatment should effectively kill bacteria, not harm the implant surface, and promote regeneration. Recently, photocatalytic coating without antibiotics or external agents was proposed to be an alternative to antibiotic therapy. The aim of this study was to evaluate the photocatalytic antibacterial effect of a new titanium implant coating made from hydroxyapatite-tryptophan complex and gray titania, which was activated by two visible lights. Materials and Methods: Titanium alloy substrate was plasma sprayed with hydroxyapatite (80 wt%) and dititanium trioxide (20 wt%) and then pressed with tryptophan. Three bacteria related to peri-implantitis, Porphyromonas gingivalis, Tannerella forsythia, and Aggregatibacter actinomycetemcomitans, were used in this study. Six conditions were tested: (1) control group (only bacteria), (2) photocatalytic sample in darkness (bacteria and coated sample in darkness), (3) red laser for 15 minutes (bacteria irradiated with photoactivated disinfection [PAD] light, 650-nm wavelength), (4) broadband light-emitting diode (LED) for 15 minutes (bacteria irradiated with broadband LED, peak wavelength at 470 nm), (5) photocatalysis by red laser for 15 minutes (bacteria and coated sample irradiated with PAD light), and (6) photocatalysis by broadband LED for 15 minutes (bacteria and coated sample irradiated with broadband LED). After 15 minutes of irradiation, photocatalytic antibacterial effects were evaluated by total viable bacterial count, adenosine triphosphate (ATP) assay, and LIVE/DEAD assay. Results: The number of all bacteria tested was significantly decreased by the photocatalytic effect of both visible light sources (P < .05). For P gingivalis, viable bacteria of lethal photosensitization groups were also significantly decreased (P < .05), especially when using the broadband LED. However, the coating material itself did not have antibacterial properties without light activation. There was no significant difference in ATP among groups (P > .05). LIVE/DEAD staining showed that red fluorescent bacterial cells were present in photocatalytic groups from the two light sources. Conclusion: Photoactivated hydroxyapatite-tryptophan complex and gray titania as a photocatalytic coating has antibacterial effects on bacteria associated with periimplantitis. [ABSTRACT FROM AUTHOR]

Hydroxyapatite particles (HAp) have been widely used by many dental implant systems as an implant coating material because of their osteoconductive properties. This study aimed at improving the antibacterial effect of HAp as a substitute for antibiotic agents which can increase drug resistance. HAp/gray titania was selected as the coating material for on the titanium alloy substrate due to its antibacterial properties after photocatalytic reaction. When combined with amino acids, HAp can form a fluorescent complex which enhances this property. Before clinical application, this new coating should be examined for cytotoxic effects against biological cells or tissues. Therefore, L929 mouse fibroblasts were used to represent fibrous tissue surrounding dental implant. After performing a 6-day alamarBlue assay, the new coating method using hydroxyapatite-tyrosine complex with gray titania on titanium alloy surface can be said to have no influence on the growth of fibroblasts. [ABSTRACT FROM AUTHOR]

This paper describes evaluation process of bending strengths of plasma-sprayed hydroxyapatite (HAp) coatings. Plasma-sprayed HAp coatings are widely used in the fields of medical implant in order to improve the biocompatibility of substrate alloys in vivo. Their strength is normally evaluated by indentation-fracture method (IF method) or shearing tests. However, these results are considerably varied because of the pores on the surfaces of coatings and to accurately discuss the quality of coatings, the effects of pore size distributions on their strengths must be considered. The maximum pore size was then predicted using extreme statistics and modified Saltycov's method. In order to calculate fracture toughness of the specimen, indentation fracture method (IF) was applied. Fracture probability model were then used to determine the strength of the coating layers. [ABSTRACT FROM AUTHOR]

To clarify hydroxyapatite (HAp) nanocrystal formation based on the interfacial interactions with organic molecules is important for controlling the dispersion states/shapes of HAp and understanding the biomineralization mechanism. In this study, the effects of cetyltrimethylammonium bromide (CTAB) micelles on the HAp nanocrystal formation process were investigated through both the morphosynthesis technique and the molecular orbital calculations. The HAp nanocrystals synthesized in the presence of CTAB exhibited a controlled rod-like shape and subsequently grew up by a thermal treatment to be larger-sized nanocrystals at a well-dispersed state. It was also found that the CTAB micelles strained and disordered at the higher temperature effectively induced heterogeneous nucleation to initiate the nucleation/growth processes. In contrast, HAp nanocrystals synthesized without CTAB exhibited irregular-shaped and aggregated nanocrystals, which are due to dominantly occurring homogeneous nucleation. According to the molecular orbital calculations, the cationic N atom of the CTAB molecule strongly interacted with the Ca ion in the a-plane as well as the hydroxyl/phosphate groups in the c-plane of HAp via ionic/covalent bonding (e.g., only ionic bonding at the closer interfacial distance at 1.0 Å), leading to effective nucleation on the micelle surfaces. Therefore, a possible reason for the rod-like and well-dispersed nanocrystal formation is due to the heterogeneous nuclei formation/growth on the N atoms of CTAB micelles and subsequent fusion growth among the CTAB micelle-directed inorganic-organic complexes in the confined spaces. The present results will be applicable for designing tailored HAp morphologies based on inorganic-organic hybrid interaction systems. [ABSTRACT FROM AUTHOR]