Micro-arc Oxidation Surface Research Articles

Enhanced SaOS-2 cell adhesion, proliferation and differentiation on Mg-incorporated micro/nano-topographical TiO2 coatings

Insufficient osteointegration still remains as one of the major problems associated with implant failures. Recently, modifying implant surface with hierarchical micro/nano-topography has attracted a great deal of attentions due to its stimulatory effect on osteogenesis. In the current work, micro-arc oxidation (MAO) was applied to create micro-scale topography on titanium substrate (referred as MAO surface). The MAO surface was mainly composed of porous TiO2 matrix distributed with CaSiO3 and CaO amorphous compounds. Subsequently, the hydrothermal treatment was employed to enable the formation of MgO nano-rods on MAO-fabricated surface (referred as MAO-HT surface). Thereafter, a post heat treatment was carried out for MAO-HT surface (referred as MAO-HT-800 surface). The rod-like nano-structures transformed to nano-particles after post heat treatment. The MAO-HT-800 surface exhibited significantly reduced release of Ca, Si and Mg ions compared to MAO-HT surface. In addition, the introduction of nano-structures onto MAO surface significantly increased surface hydrophilicity. Moreover, SaOS-2 cell behaviors such as adhesion, proliferation and differentiation in response to various surfaces basically followed the order: MAO surface < MAO-HT surface < MAO-HT-800 surface. The results indicate that modifying titanium surface with hierarchical micro/nano-topographies and tuning the morphological features of nano-structures could lead to enhanced osteogenesis.

Fabrication and in vitro properties of zinc-based superhydrophilic bioceramic coatings on zirconium

In this study, as the first step, the bioceramic coatings were fabricated on Zr (commercial pure zirconium) in calcium acetate and β‑calcium glycerophosphate salt-based electrolyte by MAO (micro arc oxidation). And then, as the second step, the Zn (zinc) thin film layer measured an average thickness of 5 nm was coated on the MAO surface by TE (thermal evaporation). The phase composition, surface and cross sectional morphology, elemental composition and wettability of the MAO and Zn-based MAO coatings were analyzed by powder-XRD and TF-XRD, SEM, EDS-mapping and contact angle goniometer, respectively. The phases of cubic-ZrO2, perovskite-CaZrO3 and HA (hydroxyapatite) were observed on the surfaces by powder and TF-XRD analyses. The morphology of the MAO surface was not changed by TE although the chemistry of it was different from the MAO surface. The surfaces of both coatings were porous and rough. The Zn was uniformly deposited through the whole surface. After TE process, the wettability of the surface decreased and the Zn-based surface exhibited superhydrophilicity compared to MAO surface. In vitro bioactivity test of both coatings were investigated by immersion test in SBF (simulated body fluid) up to 10 days. The bone like apatite layer (secondary apatite) on the Zn-based bioceramic surface was compact and uniform compared the one on the MAO surface although it was completely propagated through both surfaces. In vitro anti-bacterial test of both coatings were carried out by microbial adhesion for Gram positive and Gram negative bacteria. It was observed that the microbial adhesions of the Zn-based bioceramic surfaces were lower than ones of the MAO bioceramic surfaces for all Gram-positive and Gram-negative bacteria.

Characterization and in vitro properties of anti-bacterial Ag-based bioceramic coatings formed on zirconium by micro arc oxidation and thermal evaporation

In this study, at the first step, the commercial pure zirconium (Zr) was coated by micro arc oxidation (MAO) technique in solution, consisting of calcium acetate and β-calcium glycerophosphate salt. Then, silver (Ag) thin film layer that had an average thickness of 20nm was deposited on the MAO coated bioceramic surface by thermal evaporation (TE) technique. The phase structure, surface morphology, elemental composition and wettability of both Ag-coated and uncoated MAO coatings were characterized by powder-XRD and TF-XRD, SEM, EDX-mapping and contact angle goniometer, respectively. The powder and TF-XRD results indicated that cubic-zirconia, calcium zirconate and hydroxyapatite were detected on the surface after MAO and MAO+TE processes. Both coating surfaces were rough and porous. After TE process, Ag was homogeneously distributed on the surface. The Ag-based coated surface was hydrophobic compared to MAO surface. In vitro properties such as bioactivity and anti-bacterial tests of both coatings were investigated by soaking test in simulated body fluid (SBF) and bacterial formation, respectively. The apatite-forming abilities of both coatings were evaluated after soaking in SBF up to 10days. After soaking process, secondary apatite layer formed on the Ag-based MAO coatings was more homogenous and denser than one on the MAO surface, whereas secondary apatite structure was completely formed on both surfaces. Therefore, the bioactivity of the Ag-based MAO surfaces was significantly improved compared to the uncoated MAO coatings under SBF conditions. For 10 Gram-positive and Gram-negative bacteria, the bacterial adhesion of the Ag-based MAO coatings was considerably reduced compared to plain MAO surface.

Corrosion resistance of a superhydrophobic surface on micro-arc oxidation coated Mg-Li-Ca alloy

A superhydrophobic surface was successfully fabricated on micro-arc oxidation (MAO) coating on Mg-1Li-1Ca magnesium alloy via surface modification with stearic acid (SA). The microstructure, composition and superhydrophobic characteristics of the MAO/SA composite coatings were investigated by means of SEM, EDS, XRD, XPS, FT-IR, and contact angle (CA). The corrosion resistance of the coatings was assessed by potentiodynamic polarization, electrochemical impedance spectrum (EIS), and immersion test in 3.5 wt % NaCl solution. The results demonstrated that the morphology of the porous MAO surface was transformed to a novel petal-like clusters after modified with SA. The magnesium stearate and SA were deposited in/on the micro-pores and the surface of the MAO coating. The CA of the SA-modified surface reached 155.5°. The corrosion current density of the MAO/SA-7h coating decreased about three orders of the magnitude compared to the substrate. The SA-modified surface can provide a long-term corrosion protection for the Mg-1Li-1Ca alloy. Additionally, the coating formation mechanism as well as the corrosion mechanism were proposed and discussed.

The influence of direct laser metal sintering implants on the early stages of osseointegration in diabetic mini-pigs.

BackgroundHigh failure rates of oral implants have been reported in diabetic patients due to the disruption of osseointegration. The aim of this study was to investigate whether direct laser metal sintering (DLMS) could improve osseointegration in diabetic animal models.MethodsSurface characterizations were carried out on two types of implants. Cell morphology and the osteogenic-related gene expression of MG63 cells were observed under conditions of DLMS and microarc oxidation (MAO). A diabetes model in mini-pigs was established by intravenous injection of streptozotocin (150 mg/kg), and a total of 36 implants were inserted into the mandibular region. Micro-computed tomography (micro-CT) and histologic evaluations were performed 3 and 6 months after implantation.ResultsThe Ra (the average of the absolute height of all points) of MAO surface was 2.3±0.3 µm while the DLMS surface showed the Ra of 27.4±1.1 µm. The cells on DLMS implants spread out more podia than those on MAO implants through cell morphology analysis. Osteogenic-related gene expression was also dramatically increased in the DLMS group. Obvious improvement was observed in the micro-CT and Van Gieson staining analyses of DLMS implants compared with MAO at 3 months, although this difference disappeared by 6 months. DLMS implants showed a higher bone–implant contact percentage (33.2%±11.2%) at 3 months compared with MAO group (18.9%±7.3%) while similar results were showed at 6 months between DLMS group (42.8%±10.1%) and MAO group (38.3%±10.8%).ConclusionThe three-dimensional environment of implant surfaces with highly porous and fully interconnected channel and pore architectures can improve cell spreading and accelerate the progress of osseointegration in diabetic mini-pigs.

Phenolic Modified Ceramic Coating on Biodegradable Mg Alloy: The Improved Corrosion Resistance and Osteoblast-Like Cell Activity.

Magnesium alloys have great potential for developing orthopedic implants due to their biodegradability and mechanical properties, but the rapid corrosion rate of the currently-available alloys limits their clinical applications. To increase the corrosion resistance of the substrate, a protective ceramic coating is constructed by a micro-arc oxidation (MAO) process on ZK60 magnesium alloy. The porous ceramic coating is mainly composed of magnesium oxide and magnesium silicate, and the results from cell cultures show it can stimulate osteoblastic cell growth and proliferation. Moreover, gallic acid, a phenolic compound, was successfully introduced onto the MAO coating by grafting on hydrated oxide and chelating with magnesium ions. The gallic acid and rough surface of MAO altered the cell attachment behavior, making it difficult for fibroblasts to adhere to the MAO coating. The viability tests showed that gallic acid could suppress fibroblast growth and stimulate osteoblastic cell proliferation. Overall, the porous MAO coating combined with gallic acid offered a novel strategy for increasing osteocompatibility.

Characteristics of CeO2/ZrO2-HA composite coating on ZK60 magnesium alloy

Abstract

Early osseointegration of implants with cortex-like TiO2 coatings formed by micro-arc oxidation: A histomorphometric study in rabbits.

In our previous studies, a novel cortex-like TiO2 coating was prepared on Ti surface through micro-arc oxidation (MAO) by using sodium tetraborate as electrolyte, and the effects of the coating on cell attachment were testified. This study aimed to investigate the effects of this cortex-like MAO coating on osseointegration. A sand-blasting and acid-etching (SLA) coating that has been widely used in clinical practice served as control. Topographical and chemical characterizations were conducted by scanning electron microscopy, energy dispersive X-ray spectrometer, X-ray diffraction, contact angle meter, and step profiler. Results showed that the cortex-like coating had microslots and nanopores and it was superhydrophilic, whereas the SLA surface was hydrophobic. The roughness of MAO was similar to that of SLA. The MAO and SLA implants were implanted into the femoral condyles of New Zealand rabbits to evaluate their in-vivo performance through micro-CT, histological analysis, and fluorescent labeling at the bone-implant interface four weeks after surgery. The micro-CT showed that the bone volume ratio and mean trabecular thickness were similar between MAO and SLA groups four weeks after implantation. Histological analysis and fluorescent labeling showed no significant differences in the bone-implant contact between the MAO and SLA surfaces. It was suggested that with micro/nanostructure and superhydrophilicity, the cortex-like MAO coating causes excellent osseointegration, holding a promise of an application to implant modification.

Corrosion resistance and molecular dynamics behavior of the MAO/SAM composite coatings on magnesium alloy

To improve corrosion resistance of magnesium alloy AZ91D, y-Mercaptopropyltrimethoxysilane (MPTS) was assembled on the surface of micro-arc oxidation (MAO) treated magnesium alloy by self-assembly membrane (SAM) technique. The surface morphology and chemical components of the MAO/SAM composite coatings were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The corrosion resistance of samples was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy and total immersion tests in a 3.5 wt % NaCl solution. The measured EIS data were simulated by an equivalent circuit. Also the molecular dynamic simulation was used to study the adsorption behavior at the molecular level. The results showed that the surface of magnesium alloy was well covered by the MAO/SAM composite coatings with a better corrosion resistance. Chemical adsorption was formed between the organic molecules and the surface of the MAO coating. The approach presented here afforded an effective alternative for surface modification of magnesium-based materials to meet the many aspects of the application requirements.

Nanoscale modification of magnesium with highly textural lamellar nanosheets towards increasing the corrosion resistance and bioactivity

Abstract The present study aims to modify the surface of microarc oxidation (MAO) coated Mg using an alkaline fluoride solution so as to impart a nanoscale surface feature, which would be beneficial to improve the corrosion resistance and to promote a better bioactivity. The MAO coated Mg is modified with the formation of a highly textural lamellar nanosheet-like morphology after immersion in 0.1 M NaF (pH: 8.40) at 25 °C for 120 min, which completely covered the porous structure with the formation of nanosheets along with some agglomerated crystals. Thin film X-ray diffraction measurement, chemical composition analysis and Fourier transform infrared spectroscopy studies confirmed that the nanosheets are primarily Mg(OH)2 − xFx while the agglomerates are NaMgF3. The complete coverage of the porous structure by the modified layer along with the formation of Mg(OH)2 − xFx and NaMgF3 has enabled a better corrosion resistance for MAO coated Mg modified by NaF. The higher surface area of the nanosheets favoured nucleation of monocalcium phosphate anhydrous and newberyite, both of which are biologically relevant. The unique morphological feature of the modified surface helped to achieve an improved cell adhesion and proliferation of MC3T3-E1 osteoblast-like cells. The relative growth rate of both uncoated and coated Mg are > 75% on all the three days, fulfilled Grade 1 specification in terms of cytocompatibility as per ISO 10993-5 standard. The formation of nanoscale surface feature, improvement in corrosion resistance, better bioactivity and acceptable cytocompatibility point out that this methodology could be of immense help to modify the surface of Mg based absorbable implants.

Fabrication and characterization of hydrophobic microarc oxidation/poly-lactic acid duplex coating on biodegradable Mg–Ca alloy for corrosion protection

A double layer coating was prepared on biodegradable Mg–Ca alloy by microarc oxidation (MAO) followed by dip coating process. The results showed that hydrophobic poly-lactic acid (PLA) as a top layer with thickness of 37–40 μm provides significantly higher corrosion resistance in terms of corrosion current and charge transfer resistance, while the MAO coating alone (8–10 μm) exhibits lower corrosion resistance. However, both coating scenarios demonstrate better corrosion resistance compared with the uncoated Mg- 1.34wt% Ca alloy. Contact angle (CA) measurements showed that the double layer MAO/PLA coated sample presented hydrophobic properties with a CA of 95.30° which is higher than that of MAO coating (CA = 22.90°). The results also exhibit that hydrophobic PLA is effectively seals the porosities of the MAO layer providing effective protection for the biodegradable Mg alloy in the simulated body fluid (SBF) environment and improving the corrosion protection capacity of the MAO surface treatment.

Pulsed laser deposition of magnesium-containing bioactive glass film on porous Ti–6Al–4V substrate pretreated by micro-arc oxidation

Commercially pure Ti6Al4V (TC4) was pretreated by micro-arc oxidation (MAO) and then magnesium-containing bioactive glass thin film was successfully grown by pulsed laser deposition (PLD). After MAO and PLD treatments, the effects of MAO pretreatment and surface modification on the film bonding property and bioactivity were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and scratch tester. The results showed that the deposited film followed the surface relief of the porous MAO coating and strongly bonded to the substrate. And with increased immersion time in simulated body fluid (SBF), the lathlike and spherical apatites were generated and grown, indicating the surface-modified porous Ti6Al4V exhibit good bioactivity.

Layer-by-layer assembly of silver nanoparticles embedded polyelectrolyte multilayer on magnesium alloy with enhanced antibacterial property

Abstract Functionalization of magnesium alloy (Mg alloy) with multiple bioactivities is desired to obtain surfaces with improved biocompatibility and antibacterial property. In this article, an anticorrosive and antimicrobial coating was prepared on Mg alloy surface by layer-by-layer (LbL) assembly of polyelectrolytes. A polycationic copolymer (P(DOP- co -DMAEMA + )) bearing dopamine (DOP) and 2-(methacryloxy)ethyl trimethylammonium chloride (DMAEMA + ) was synthesized and deposited on the surface of micro-arc oxidation (MAO) treated Mg alloy substrate as the first layer. The presence of DOP units ensure a strong anchoring on Mg alloy substrate, and the –N + (CH 3 ) 3 groups are sources of positive charge, providing electrostatic interaction with polyanion electrolyte. Negatively charged colloidal silver particles were prepared by using dextran sulfate (DS) as a stabilizer to precede chemical reduction by dextrose and served as a polyanion electrolyte. The functional polyelectrolyte multilayered films were obtained by alternating deposition P(DOP- co -DMAEMA + ) and DS-stabilized silver colloid (DS-Ag) in a spin-assisted LbL assembly manner. The prepared nanosized silver colloids and functionalized Mg alloy were characterized by ultraviolet–visible (UV–vis) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Potentiodynamic polarization test confirmed that corrosion resistance of modified Mg alloy significantly increased and the fabricated polyelectrolyte multilayer films showed significant antibacterial activity.

Comparison of platelet adhesion behavior on pure titanium surfaces modified by different techniques

To evaluate the platelet adhesion ability on pure titanium surfaces modified with different techniques. Pure titanium specimens were treated with 5 different surface modification techniques, including machine polish (MP), dual acid-etch (DAE), sand blast-large grit and acid-etch (SLA), micro-arc oxidation (MAO) and anodized titania nanotube (TNT). The surface topographies of specimens were observed by scanning electron microscopy (SEM). Chemical compositions, surface roughness and static water contact angle of specimens were detected by energy dispersive spectrometer (EDS), laser scanning confocal microscope (LSCM) and contact angle analyzer respectively. Platelets were cultured on specimen surfaces for 30 min. The amount and viability of adhered platelets adhered were evaluated. Platelet distribution and morphology were observed by LSCM and SEM. Surface topographies of the five groups of specimens differed significantly. MP, DAE, SLA and MAO surfaces showed micro-scale topographies, while TNT surfaces showed nano-scale topography with nanotubes at the diameter of (80.46 ± 0.35) nm. The surface roughness of MAO was the highest among the 5 groups. TNT surfaces demonstrated the lowest roughness as well as the lowest static water contact angle as 13.55° ± 0.96°. The amount of platelets adhered on TNT surface was the greatest as (300 729 ± 8 325) platelet/µl and the viability was the highest (A450 value 2.14 ± 0.05). Platelet adhered intensively on TNT surfaces, forming pseudopodia, extending and connecting with each other. Surface properties of pure titanium affect platelet adhesion ability. Nano-scale topography can greatly improve platelet adhesion. Increased surface roughness and hydrophilicity can improve platelet adhesion ability.

Biological response of Sr-containing coating with various surface treatments on titanium substrate for medical applications

An implant requires a suitable surface to trigger osteointegration. The surface characteristics and chemical composition are important factors in this process. Plasma spraying and micro-arc oxidation can be used to fabricate rough and porous structures for medical applications. Strontium (Sr) has been shown to prevent osteoporosis in vitro and in vivo. However, few scientists have evaluated the biological response of Sr-containing coatings on different surface treatments. In this study, a sand-blasted (SB) surface (as the control), plasma-sprayed hydroxyapatite (HA) and Sr-substituted HA coatings (HAPS and SrHAPS, respectively), calcium phosphate and Sr-containing calcium phosphate micro-arc oxidation surface (CPM and SrCPM, respectively) were analyzed in terms of human osteoblastic cell (MG63) response. Sr was confirmed to be incorporated into the surface. SrHAPS and SrCPM specimens had higher cell responses than those of the HAPS and CPM groups, respectively. The cells cultured on SrCPM and SrHAPS specimens exhibited high proliferation and differentiation. However, CPM and SrCPM specimens stimulated more ECM-like structures than other specimens. The results show that Sr-containing coatings have good characteristics that enhance cell response. The SrCPM coating is a suitable implant surface treatment for clinical applications.

Structure and properties of compound coatings on Mg alloys by micro-arc oxidation/hydrothermal treatment

The compound coatings on Mg alloys have been successfully prepared by a two-step process of micro-arc oxidation (MAO) and hydrothermal treatment. The structure and composition of MAO coatings and compound coatings were studied by FESEM, XRD, EDS and XPS, respectively. The porous MAO layer on magnesium alloy comprised MgO and amorphous phosphate compounds. A hydrothermal layer with the thickness of around 4μm was deposited on the surface of MAO coating. The effects of pH value on the hydrothermal deposition mechanism were also proposed. At pH 5.6, the hydrothermal layer was flake-shaped, with the main crystalline of brushite (DCPD, CaHPO3⋅2H2O) and hydroxyapatite (HA, Ca5(PO4)3(OH)). At pH 9.4, the hydrothermal layer was rod-shaped with the main crystalline of HA. The corrosion resistance of the samples in simulation body fluid (SBF) solution was evaluated by Tafel curve and electrochemical impedance spectroscopy (EIS) measurement. The corrosion resistance of the compound coatings was improved by one order of magnitude than MAO coating and two orders of magnitude than Mg substrate, due to the excellent sealing effect and the increase of the thickness. The compound coating at pH 5.6 has a little greater thickness and more coverage than that at pH 9.4, therefore, the former had better corrosion resistance than the latter. Also, the hydrothermal treatment improves the apatite-induced ability of the samples in SBF solution under 37°C. Compared with MAO coating, the compound coatings presented great apatite-induced ability due to the hydrothermal treatment. The hydrothermal layer of the rod-like HA at pH 9.4 had better apatite-induced ability than that of the flake-like DCPD at pH 5.6.

Preparation and characterization of the micro-arc oxidation composite coatings on magnesium alloys

Abstract The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio, however the poor corrosion resistance limits the application in automobile industry. The Micro-arc Composite Ceramic (MCC) coatings on AZ91D magnesium alloys were prepared by Micro-arc Oxidation (MAO) and electrophoresis technologies. The microstructure, corrosion resistance, abrasion resistance, stone impact resistance and adhesion of MCC coatings were studied respectively. The cross section morphologies showed that the outer organic coating was filled into the hole on surface of MAO coating, and it acted as a shelter against corrosive products. The copper-accelerated acetic acid salt spray Test, abrasion resistance test, stone impact resistance test, thermal shock resistance test and adhesion test were used to evaluate the protective characterization by the third testing organization which approved by GM. The test results showed the composite coatings meet all the requirements. The MCC coating on Mg presents excellent properties, and it is a promising surface treatment technology on magnesium alloys for production vehicles.

Densification Behavior and Microstructure Evolution of Laser Surface Melting Processed Silicon-Containing Micro Arc Oxidation Coating

The present work investigated the effect of laser surface melting (LSM) process on micro arc oxidation (MAO) coating prepared in silicate electrolytes (Si-MAO) and aluminate electrolytes (Al-MAO). Plasma intensity of laser spots, element content and phase constituents of coatings were analyzed. During LSM remelting process, the formation of heat sources and micro molten pools on the surface of MAO coating were discussed. The results showed that the moderate plasma was formed more easily on the Si-MAO than Al-MAO coating, owing to the temperature threshold of melting oxide layer was decreased for silicon-containing MAO coating during LSM treatment. Besides, the Si-MAO coating of laser-treated had low porosity and smooth surface.

The adhesion and growth of both the human primary gingival epithelial cells and Streptococcus mutans on micro-arc oxidized titanium.

With good osseointegration properties, micro-arc oxidation has now gradually become the key point in basic research and clinical trials, but interface between the implant surface treated by micro-arc oxidation and gingival soft tissues has been seldom reported. The influences of micro-arc oxidation surface treatment on the biological behavior of primary human gingival epithelial cells (hGEC) and common pathogen Streptococcus mutans have been studied. MTT method was taken to test the adhesion and growth of hGEC on different treated surfaces. No significant changes were found between with or without MAO- treated surface. However, higher growth rate was observed in MAO group at first and third days, although it showed no significant difference at fifth and seventh day. Secretions of EGF of the cells grown on both surfaces were also no big changes (P > 0.05). RT-PCR showed adhesion gene of hGEC, E-cad on the first day of micro-arc oxidation surface treatment, expression level is higher than that of polishing group (P < 0.05), but no significant difference of the expression levels of Itgβ1, PCNA, and EGF. Finally, easier adhesion and high growth rate of Streptococcus mutans were found at MAO-treated surface (P < 0.05). In conclusion, our data suggested MAO-treated Ti surface may favor epithelial cell adhesion, but it also increase the risk of bacterial infection.

Bioactive coating with hierarchical double porous structure on titanium surface formed by two-step microarc oxidation treatment

The Ca, P, Si and Na incorporated bioactive coatings with double porous structure in macro (50–1000μm) and micro (0.6–2.0μm) scales have been successfully formed on Ti surface by a two-step treatment via microarc oxidation (MAO). The results reveal that the microarc oxidation and NO3− ion corrosion activated by plasma are the two key factors for the formation of macropores during the second MAO treatment. Meanwhile, the MAO processing current, mass loss, surface morphology and elemental concentration of the samples are significantly affected by the NaOH concentration in the electrolyte during the second treatment. With increasing of NaOH concentration from 5 to 20g/L, the mass loss of the two-step MAO treated (TMAO) samples first increases from 4.3 to 6.7%, then decreases to 4.7%. The number of macropores increases dramatically from 26 to 806mm−2, but the size of macropores declines gradually in a range of 1000–143μm with the varied NaOH concentration. Furthermore, an oxide film composed of Ti3O5 is formed on the macropore surface after treating in the electrolyte with 20g/L NaOH concentration. Additionally, the sample shows apatite inducing-ability evaluated in simulated body fluid immersion.