Conformal Zn-Benzene Dithiol Thin Films for Temperature-Sensitive Electronics Grown via Industry-Feasible Atomic/Molecular Layer Deposition Technique.

The atomic/molecular layer deposition (ALD/MLD) technique combining both inorganic and organic precursors is strongly emerging as a unique tool to design exciting new functional metal-organic thin-film materials. Here, this method is demonstrated to work even at low deposition temperatures and can produce highly stable and conformal thin films, fulfilling the indispensable prerequisites of today's 3D microelectronics and other potential industrial applications. This new ALD/MLD process is developed for Zn-organic thin films grown from non-pyrophoric bis-3-(N,N-dimethylamino)propyl zinc [Zn(DMP)2] and 1,4-benzene dithiol (BDT) precursors. This process yields air-stable Zn-BDT films with appreciably high growth per cycle (GPC) of 4.5 Å at 60 °C. The Zn/S ratio is determined at 0.5 with Rutherford backscattering spectrometry (RBS), in line with the anticipated (Zn─S─C6H6─S─)n bonding scheme. The high degree of conformality is shown using lateral high-aspect-ratio (LHAR) test substrates; scanning electron microscopy (SEM) analysis shows that the film penetration depth (PD) into the LHAR structure with cavity height of 500 nm is over 200 µm (i.e., aspect-ratio of 400). It is anticipated that the electrically insulating metal-organic Zn-BDT thin films grown via the solvent-free ALD/MLD technique, can be excellent barrier layers for temperature-sensitive and flexible electronic devices.

Nondestructive fluorescence-based quantification of threose-induced collagen cross-linking in bovine articular cartilage.

Extensive collagen cross-linking affects the mechanical competence of articular cartilage: it can make the cartilage stiffer and more brittle. The concentrations of the best known cross-links, pyridinoline and pentosidine, can be accurately determined by destructive high-performance liquid chromatography (HPLC). We explore a nondestructive evaluation of cross-linking by using the intrinsic fluorescence of the intact cartilage. Articular cartilage samples from bovine knee joints were incubated in threose solution for 40 and 100 h to increase the collagen cross-linking. Control samples without threose were also prepared. Excitation-emission matrices at wavelengths of 220 to 950 nm were acquired from the samples, and the pentosidine and pyridinoline cross-links and the collagen concentrations were determined using HPLC. After the threose treatment, pentosidine and lysyl pyridinole (LP) concentrations increased. The intrinsic fluorescence, excited below 350 nm, decreased and was related to pentosidine [r = -0.90, 240/325 nm (excitation/emission)] or LP (r = -0.85, 235/285 nm) concentrations. Due to overlapping, the changes in emission could not be linked specifically to the recorded cross-links. However, the fluorescence signal enabled a nondestructive optical estimate of changes in the pentosidine and LP cross-linking of intact articular cartilage.

Optical spectral reflectance of human articular cartilage - relationships with tissue structure, composition and mechanical properties.

The information from spectral reflectance of articular cartilage has been related to the integrity of the tissue. This study explores more in detail the interrelations between the cartilage composition, structure and mechanical properties, and optical spectral reflectance. Using human osteochondral samples the reflectance spectral images of articular cartilage were captured and analyzed by using CIELAB color space as well as principal component analysis. With both analysis methods statistically significant correlations were observed between the reflectance and histological integrity, as assessed by Mankin scoring, tissue proteoglycan content and dynamic modulus. In thick human cartilage, the reflectance was found to be independent of the cartilage thickness, suggesting negligible influence of the underlying subchondral bone. Based on the present results diagnostically relevant information on cartilage quality can be extracted using optical spectral reflectance measurements. These measurements could be feasible during arthroscopic surgery when more in-depth information of the properties of articular cartilage is needed.

Optical spectral imaging of degeneration of articular cartilage.

Osteoarthritis (OA) is a common musculoskeletal disorder often diagnosed during arthroscopy. In OA, visual color changes of the articular cartilage surface are typically observed. We demonstrate in vitro the potential of visible light spectral imaging (420 to 720 nm) to quantificate these color changes. Intact bovine articular cartilage samples (n=26) are degraded both enzymatically using the collagenase and mechanically using the emery paper (P60 grit, 269 microm particle size). Spectral images are analyzed by using standard CIELAB color coordinates and the principal component analysis (PCA). After collagenase digestion, changes in the CIELAB coordinates and projection of the spectra to PCA eigenvector are statistically significant (p<0.05). After mechanical degradation, the grinding tracks could not be visualized in the RGB presentation, i.e., in the visual appearance of the sample to the naked eye under the D65 illumination. However, after projecting to the chosen eigenvector, the grinding tracks are revealed. The tracks are also seen by using only one wavelength, i.e., 469 nm, however, the contrast in the projection image is 1.6 to 2.5 times higher. Our results support the idea that the spectral imaging can be used for evaluation of the integrity of the cartilage surface.