Imaging material properties of biological samples with a Force Feedback Microscope

Mechanical properties of biological samples have been imaged with a \textit{Force Feedback Microscope}. Force, force gradient and dissipation are measured simultaneously and quantitatively, merely knowing the AFM cantilever spring constant. Our first results demonstrate that this robust method provides quantitative high resolution force measurements of the interaction The little oscillation imposed to the cantilever and the small value of its stiffness result in a vibrational energy much smaller than the thermal energy, reducing the interaction with the sample to a minimum. We show that the observed mechanical properties of the sample depend on the force applied by the tip and consequently on the sample indentation. Moreover, the frequency of the excitation imposed to the cantilever can be chosen arbitrarily, opening the way to frequency-dependent studies in biomechanics, sort of spectroscopic AFM investigations

Spectroscopic investigation of local mechanical impedance of living cells

The mechanical properties of PC12 living cells have been studied at the nanoscale with a Force Feedback Microscope using two experimental approaches. Firstly, the local mechanical impedance of the cell membrane has been mapped simultaneously to the cell morphology at constant force. As the force of the interaction is gradually increased, we observed the appearance of the sub-membrane cytoskeleton. We shall compare the results obtained with this method with the measurement of other existing techniques. Secondly, a spectroscopic investigation has been performed varying the indentation of the tip in the cell membrane and consequently the force applied on it. In contrast with conventional dynamic atomic force microscopy techniques, here the small oscillation amplitude of the tip is not necessarily imposed at the cantilever first eigenmode. This allows the user to arbitrarily choose the excitation frequency in developing spectroscopic AFM techniques. The mechanical response of the PC12 cell membrane is found to be frequency dependent in the 1 kHz - 10 kHz range. The damping coefficient is reproducibly observed to decrease when the excitation frequency is increased.Comment: 8 pages, 8 figure

Meccanopercezione e controllo posturale negli alberi

Gli alberi costruiscono una struttura autoportante capace di rimanere eretta mentre cresce in un ambiente con una grandissima variabilit\ue0 a livello dei carichi meccanici. Questa capacit\ue0 \ue8 dovuta in parte ad un disegno meccanico e a materiali adeguati e in parte, come negli animali, al fatto che adattano la crescita della struttura scheletrica alle condizioni di carico e regolano la postura con movimenti attivi e dinamici. Si propone un approfondimento sui diversi meccanismi di meccanopercezione nelle piante e sulla fondamentale importanza che questo meccanismo ricopre nel controllo posturale della pianta durante la crescita. La risposta ad uno stimolo meccanico a livello dell\u2019intera pianta passa attraverso la sua percezione a livello dei meccanismi fisiologici delle singolo cellule. Si vuole porre particolare attenzione sui possibili candidati come recettori dello stimolo meccanico, sul possibile ruolo della parete cellulare come fonte di informazione dello stato di tensione nei tessuti, alla trasduzione del segnale e alla sua interazione con altri segnali che influenzano il controllo della postura della pianta, come ad esempio gli stimoli gravitropici

Determining the Surface-To-Bulk Progression in the Normal-State Electronic Structure of Sr2RuO4 by Angle-Resolved Photoemission and Density Functional Theory

In search of the potential realization of novel normal-state phases on the surface of Sr2RuO4 - those stemming from either topological bulk properties or the interplay between spin-orbit coupling (SO) and the broken symmetry of the surface - we revisit the electronic structure of the top-most layers by ARPES with improved data quality as well as ab-initio LDA slab calculations. We find that the current model of a single surface layer (\surd2x\surd2)R45{\deg} reconstruction does not explain all detected features. The observed depth-dependent signal degradation, together with the close quantitative agreement with LDA+SO slab calculations based on the LEED-determined surface crystal structure, reveal that (at a minimum) the sub-surface layer also undergoes a similar although weaker reconstruction. This points to a surface-to-bulk progression of the electronic states driven by structural instabilities, with no evidence for Dirac and Rashba-type states or surface magnetism.Comment: 4 pages, 4 figures, 1 table. Further information and PDF available at: http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/articles.htm

Antitumor activity of the ERK inhibitor SCH772984 [corrected] against BRAF mutant, NRAS mutant and wild-type melanoma.

BackgroundIn melanoma, dysregulation of the MAPK pathway, usually via BRAF(V600) or NRAS(Q61) somatic mutations, leads to constitutive ERK signaling. While BRAF inhibitors are initially effective for BRAF-mutant melanoma, no FDA-approved targeted therapies exist for BRAF-inhibitor-resistant BRAF(V600), NRAS mutant, or wild-type melanoma.MethodsThe 50% inhibitory concentration (IC50) of SCH772984, a novel inhibitor of ERK1/2, was determined in a panel of 50 melanoma cell lines. Effects on MAPK and AKT signaling by western blotting and cell cycle by flow cytometry were determined.ResultsSensitivity fell into three groups: sensitive, 50% inhibitory concentration (IC50) < 1 μM; intermediately sensitive, IC50 1-2 μM; and resistant, >2 μM. Fifteen of 21 (71%) BRAF mutants, including 4 with innate vemurafenib resistance, were sensitive to SCH772984. All three (100%) BRAF/NRAS double mutants, 11 of 14 (78%) NRAS mutants and 5 of 7 (71%) wild-type melanomas were sensitive. Among BRAF(V600) mutants with in vitro acquired resistance to vemurafenib, those with MAPK pathway reactivation as the mechanism of resistance were sensitive to SCH772984. SCH772984 caused G1 arrest and induced apoptosis.ConclusionsCombining vemurafenib and SCH722984 in BRAF mutant melanoma was synergistic in a majority of cell lines and significantly delayed the onset of acquired resistance in long term in vitro assays. Therefore, SCH772984 may be clinically applicable as a treatment for non-BRAF mutant melanoma or in BRAF-mutant melanoma with innate or acquired resistance, alone or in combination with BRAF inhibitors

Immunomodulation by imiquimod in patients with high-risk primary melanoma.

Imiquimod is a synthetic Toll-like receptor 7 (TLR7) agonist approved for the topical treatment of actinic keratoses, superficial basal cell carcinoma, and genital warts. Imiquimod leads to an 80-100% cure rate of lentigo maligna; however, studies of invasive melanoma are lacking. We conducted a pilot study to characterize the local, regional, and systemic immune responses induced by imiquimod in patients with high-risk melanoma. After treatment of the primary melanoma biopsy site with placebo or imiquimod cream, we measured immune responses in the treated skin, sentinel lymph nodes (SLNs), and peripheral blood. Treatment of primary melanomas with 5% imiquimod cream was associated with an increase in both CD4+ and CD8+ T cells in the skin, and CD4+ T cells in the SLN. Most of the CD8+ T cells in the skin were CD25 negative. We could not detect any increases in CD8+ T cells specifically recognizing HLA-A(*)0201-restricted melanoma epitopes in the peripheral blood. The findings from this small pilot study demonstrate that topical imiquimod treatment results in enhanced local and regional T-cell numbers in both the skin and SLN. Further research into TLR7 immunomodulating pathways as a basis for effective immunotherapy against melanoma in conjunction with surgery is warranted