An exploration of plastic deformation dependence of cell viability and adhesion in metallic implant materials.

The relationship between cell viability and adhesion behavior, and micro-deformation mechanisms was investigated on austenitic 316L stainless steel samples, which were subjected to different amounts of plastic strains (5%, 15%, 25%, 35% and 60%) to promote a variety in the slip and twin activities in the microstructure. Confocal laser scanning microscopy (CLSM) and field emission scanning electron microscopy (FESEM) revealed that cells most favored the samples with the largest plastic deformation, such that they spread more and formed significant filopodial extensions. Specifically, brain tumor cells seeded on the 35% deformed samples exhibited the best adhesion performance, where a significant slip activity was prevalent, accompanied by considerable slip-twin interactions. Furthermore, maximum viability was exhibited by the cells seeded on the 60% deformed samples, which were particularly designed in a specific geometry that could endure greater strain values. Overall, the current findings open a new venue for the production of metallic implants with enhanced biocompatibility, such that the adhesion and viability of the cells surrounding an implant can be optimized by tailoring the surface relief of the material, which is dictated by the micro-deformation mechanism activities facilitated by plastic deformation imposed by machining.

New limits on variation of the fine-structure constant using atomic dysprosium.

We report on the spectroscopy of radio-frequency transitions between nearly degenerate, opposite-parity excited states in atomic dysprosium (Dy). Theoretical calculations predict that these states are very sensitive to variation of the fine-structure constant α owing to large relativistic corrections of opposite sign for the opposite-parity levels. The near degeneracy reduces the relative precision necessary to place constraints on variation of α, competitive with results obtained from the best atomic clocks in the world. Additionally, the existence of several abundant isotopes of Dy allows isotopic comparisons that suppress common-mode systematic errors. The frequencies of the 754-MHz transition in 164Dy and 235-MHz transition in 162Dy are measured over the span of two years. The linear variation of α is α·/α=(-5.8±6.9([1σ]))×10(-17) yr(-1), consistent with zero. The same data are used to constrain the dimensionless parameter kα characterizing a possible coupling of α to a changing gravitational potential. We find that kα=(-5.5±5.2([1σ]))×10(-7), essentially consistent with zero and the best constraint to date.

Extreme nonlinear optics in a femtosecond enhancement cavity.

Intrinsic to the process of high-order harmonic generation is the creation of plasma and the resulting spatiotemporal distortions of the driving laser pulse. Inside a high-finesse cavity where the driver pulse and gas medium are reused, this can lead to optical bistability of the cavity-plasma system, accumulated self-phase modulation of the intracavity pulse, and coupling to higher-order cavity modes. We present an experimental and theoretical study of these effects and discuss their implications for power scaling of intracavity high-order harmonic generation and extreme ultraviolet frequency combs.

Power optimization of XUV frequency combs for spectroscopy applications [Invited].

We address technical impediments to the generation of high-photon flux XUV frequency combs through cavity-enhanced high harmonic generation. These difficulties arise from mirror damage, cavity nonlinearity, the intracavity plasma generated during the HHG process, and imperfect phase-matching. By eliminating or minimizing each of these effects we have developed a system capable of generating > 200 µW and delivering ~20 µW of average power for each spectrally separated harmonic (wavelengths ranging from 50 nm - 120 nm), to actual comb-based spectroscopy experiments.

Broadband phase noise suppression in a Yb-fiber frequency comb.

We report a simple technique to suppress high-frequency phase noise of a Yb-based fiber optical frequency comb using an active intensity noise servo. Out-of-loop measurements of the phase noise using an optical heterodyne beat with a cw laser show suppression of phase noise by ≥7 dB out to Fourier frequencies of 100 kHz with a unity-gain crossing of ∼700 kHz. These results are enabled by the strong correlation between the intensity and phase noise of the laser. Detailed measurements of intensity and phase noise spectra, as well as transfer functions, reveal that the dominant phase and intensity noise contribution above ∼100 kHz is due to amplified spontaneous emission or other quantum noise sources.

Total on-line analysis of a target protein from plasma by immunoextraction, digestion and liquid chromatography-mass spectrometry.

A total on-line analysis of a target protein from a plasma sample was made using a selective immunoextraction step coupled on-line to an immobilized enzymatic reactor (IMER) for the protein digestion followed by LC-MS/MS analysis. For the development of this device, cytochrome c was chosen as model protein due to its well-known sequence. An immunosorbent (IS) based on the covalent immobilization of anti-cytochrome c antibodies on a solid support was made and an immunoextraction procedure was carefully developed to assess a selective extraction of the target protein from plasma. For the first time, IS was easily coupled on-line with a laboratory-made IMER based on pepsin. The whole on-line device (IS-IMER-LC-MS/MS) allowed the quantification of cytochrome c from 8.5pmol to 1.7nmol in buffer medium. Finally, this device was applied to the analysis of only 85pmol of cytochrome c from plasma with a RSD value lower than 10% (n=3).

Evaluation of various immobilized enzymatic microreactors coupled on-line with liquid chromatography and mass spectrometry detection for quantitative analysis of cytochrome c.

An in-line procedure for protein analysis using a trypsin-based immobilized enzymatic reactor (IMER) coupled to LC-MS/MS has been developed. Various IMERs were synthesized and characterized by estimating the digestion yield of a pattern peptide in UV detection. Laboratory-made IMERs were optimized by studying the effect of different parameters as the nature of the functionalized immobilization support (silica, agarose), the amount of immobilized trypsin and the binding density. The potential of the laboratory-made IMERs were compared with a batch digestion and with a commercial trypsin-based IMER. The laboratory-made IMER based on CNBr-activated Sepharose showed the best performances in terms of digestion yields, digestion time, price and repeatability (RSD<4%). Cytochrome c was then digested on this IMER and used in-line with LC-MS. The target protein was easily recognized by the Mascot database until 17pmol injected.

Limit on the temporal variation of the fine-structure constant using atomic dysprosium.

Over 8 months, we monitored transition frequencies between nearly degenerate, opposite-parity levels in two isotopes of atomic dysprosium (Dy). These frequencies are sensitive to variation of the fine-structure constant (alpha) due to relativistic corrections of opposite sign for the opposite-parity levels. In this unique system, in contrast to atomic-clock comparisons, the difference of the electronic energies of the opposite-parity levels can be monitored directly utilizing a rf electric-dipole transition between them. Our measurements show that the frequency variation of the 3.1-MHz transition in (163)Dy and the 235-MHz transition in (162)Dy are 9.0+/-6.7 Hz/yr and -0.6+/-6.5 Hz/yr, respectively. These results provide a rate of fractional variation of alpha of (-2.7+/-2.6) x 10(-15) yr(-1) (1 sigma) without assumptions on constancy of other fundamental constants, indicating absence of significant variation at the present level of sensitivity.