Evaluating sol-gel ceramic thin films for metal implant applications. I. Processing and structure of zirconia films on Ti-6AI-4V

Novel transparent zirconium-based hybrid material with multilayered nanostructures: studies of surface dewettability toward alkane liquids

We have successfully prepared unique inorganic-organic hybrid materials that demonstrate excellent transparency and dewettability toward various alkane liquids (n-hexadecane, n-dodecane and n-decane) without relying on conventional surface roughening and perfluorination. Such coatings were made using a novel family of hybrid materials generated by substituting carboxylic acids, with a range of alkyl chain lengths (CH(3)(CH(2))(x-2)COOH where x = total carbon number, i.e., 10, 12, 14, 16, 18, 22, or 24, into zirconium (Zr) tetra-propoxide complexes. This precursor was then mixed with acetic acid and spincast to produce transparent thin Zr-carboxylic acid (ZrCA(x)) hybrid films using a nonhydrolytic sol-gel process. Fourier transform infrared spectroscopy provided proof of Zr-O-Zr network formation in the films upon casting and also followed changes to the physical nature (liquid-like or solid-like) of the alkyl chain assemblies depending upon alkyl chain length. X-ray diffractometry revealed that the hybrid films prepared using the longer chain carboxylic acids (ZrCA(x≥18)) spontaneously self-assembled into lamella structures with d-spacings ranging from 29.5 to 32.7 Angstroms, depending on the length of the alkyl chain. On the other hand the remaining films (ZrCA(x<18)) showed no such ordering. Moreover, the dynamic dewetting behavior of our hybrid films with alkane liquids was also strongly affected by alkyl chain length. ZrCA(x) films with x = 12, 14, and 16 showed the best dynamic oleophobicity among the seven hybrid films. In particular, small volume alkane droplets (5 μL) could be easily set in motion to move across and off ZrCA(14) film surfaces without pinning at low tilt angles (~6°).

The optimal SAM surface functional group for producing a biomimetic HA coating on Ti

Commercial interest is growing in biomimetic methods that employ self assembled mono-layers (SAMs) to produce biocompatible HA coatings on Ti-based orthopedic implants. Recently, separate studies have considered HA formation for various SAM surface functional groups. However, these have often neglected to verify crystallinity of the HA coating, which is essential for optimal bioactivity. Furthermore, differing experimental and analytical methods make performance comparisons difficult. This article investigates and evaluates HA formation for four of the most promising surface functional groups: --OH, --SO(3)H, --PO(4)H(2) and --COOH. All of them successfully formed a HA coating at Ca/P ratios between 1.49 and 1.62. However, only the --SO(3)H and --COOH end groups produced a predominantly crystalline HA. Furthermore, the --COOH end group yielded the thickest layer and possessed crystalline characteristics very similar to that of the human bone. The --COOH end group appears to provide the optimal SAM surface interface for nucleation and growth of biomimetic crystalline HA. Intriguingly, this finding may lend support to explanations elsewhere of why human bone sialoprotein is such a potent nucleator of HA and is attributed to the protein's glutamic acid-rich sequences.

Electrolytic A12O3 coating on co-cr-mo implant alloys of hip prosthesis

The ceramic films over metallic implant surfaces have the potential to improve implant performance with respect to implant fixation, wear, or corrosion. In this study, the electrolytic Al2O3 coatings on F-1537 Co-Cr-Mo alloy were conducted in an aqueous solution of Al(NO3)3. Through the cycle polarization test in Hank's solution, it was found that the corrosion potential and protection potential of the alumina-coated were higher than that of the uncoated, and the corrosion current density was lower. The phase transformation of A12O3 film on Co-Cr-Mo alloy annealed at 800 K revealed todlite (5Al2O3 . H2O) and thetaAl2O3 (113) preferred orientation for 20 min, and thetaAl2O3 (200) preferred orientation with eta phase for 80 min. Scanning electron microscopy/energy dispersive spectroscopy observations after the scratch tests showed that the adhesion of the alumina films on Co-Cr-Mo alloy can load a stress over the yield strength (450 MPa) of Co-Cr-Mo alloy. The wear loss of ultra-high molecular-weight polyethylene to the Al2O3-coated specimen was eight times less than that to the uncoated. It is concluded that such Al2O3-coated films on Co-Cr-Mo implant alloy exhibit excellent quality in corrosion, adhesion, and wear for the application of hip prosthesis.

Evaluating sol-gel ceramic thin films for metal implant applications: III. In vitro aging of sol-gel-derived zirconia films on Ti-6Al-4V

Sol-gel-derived zirconia films were deposited onto polished Ti-6Al-4V substrates by dip-coating from an alkoxide precursor solution. No change in morphology of the zirconia film was observed after aging at 37 degrees C for 4-12 weeks in pH 4.0 buffer solution or Hanks' balanced salt solution (HBSS), although a precipitate predominantly composed of calcium phosphate was formed on those films aged in HBSS. X-ray diffraction identified the phase of the zirconia film as either cubic or tetragonal, and revealed no degradation to the monoclinic phase after aging. By a substrate straining test, the fracture strain of the coating was revealed to be 1.5%, above the yield strain of the titanium alloy substrate. At this strain level, through-thickness cracks formed in the coating where slip bands emerged from the substrate. Qualitatively, the adhesion of the film was sufficient to prevent gross delamination of the film at high strain levels, although small regions of delamination were caused by compressive buckling of the film. This behavior indicates generally good adhesion. No change in this behavior was observed after aging.

Evaluation of metal ion release and corrosion resistance of ZrO2 thin coatings on the dental Co-Cr alloys

OBJECTIVES

The aim of this study was to determine if electrolytic ZrO2 thin coatings increased the corrosion resistance and decreased the metal ion release of dental cobalt-chromium alloys.

METHODS

Dental Co-Cr alloys were electrolytically deposited with ZrO2 ceramic coatings using a 0.0625 M ZrO(NO3)2 solution, at various potentials, for 500 s. The electrolytic ZrO2 gel-coated specimens were annealed at 723 K for 1 h in air. Scanning electron microscopy (SEM) was used to observe the morphology of the ZrO2 ceramic coatings on Co-Cr alloys. A dynamic polarization test was used to compare the corrosion resistance of the ZrO2 coated and uncoated Co-Cr alloys in artificial saliva. Metal ion concentrations were determined with graphite furnace atomic absorption spectroscopy (AAS).

RESULTS

The SEM micrographs showed that the Co-Cr alloy can be coated with zirconia oxide at -0.7 V more homogeneously and more completely than at -1.5 V. The polarization curves indicated that the ZrO2 coating on Co-Cr alloys annealed at 723 K for 1 h in air exhibited better corrosion resistance in artificial saliva. The results of the AASs showed that the ZrO2-coated Co-Cr alloys decreased chromium ion release levels, as compared with the uncoated Co-Cr alloys. The scratch test indicated a good bond strength between the ZrO2 and Co-Cr alloy.

SIGNIFICANCE

The electrolytically deposited ZrO2 coatings on Co-Cr alloys may improve the corrosion resistance and decrease the release of metal ions. It is suggested that the electrolytic ZrO2 coating method could have a widespread application in dentistry in the future.