Substrate dependance, temperature dependance and temperature sensitivity and resolution of doped-silicon microcantilevers

This thesis aims to characterize microcantilevers with integrated heater-thermometers. This research concentrates on characterization for use in data storage, sensing, surface science, and nano-manufacturing. The rst objective seeks to understand the speci c thermal interactions between a heated microcantilever tip and various substrates. The experiments investigate thermal conductance, thermal time constant, and temperature-dependant adhesion force between and cantilever tip and substrates of silicon, quartz, and polyimide. The second objective is to utilize a heated microcantilever as a heater-thermometer. The experiments investigate the thermal calibration sensitivity and resolution under steady and periodic conditions near room-temperature. The results were compared to the Raman spectroscopy, which measures the local temperature at the cantilever tip

Magnetic field tuning of mechanical properties of ultrasoft PDMS-based magnetorheological elastomers for biological applications

We report tuning of the moduli and surface roughness of magnetorheological elastomers (MREs) by varying applied magnetic field. Ultrasoft MREs are fabricated using a physiologically relevant commercial polymer, SylgardTM 527, and carbonyl iron powder (CIP). We found that the shear storage modulus, Young\u27s modulus, and root-mean-square surface roughness are increased by ∼41×, ∼11×, and ∼11×, respectively, when subjected to a magnetic field strength of 95.5 kA m−1. Single fit parameter equations are presented that capture the tunability of the moduli and surface roughness as a function of CIP volume fraction and magnetic field strength. These magnetic field-induced changes in the mechanical moduli and surface roughness of MREs are key parameters for biological applications

The effect of polymer stiffness on magnetization reversal of magnetorheological elastomers

Ultrasoft magnetorheological elastomers (MREs) offer convenient real-time magnetic field control of mechanical properties that provides a means to mimic mechanical cues and regulators of cells in vitro. Here, we systematically investigate the effect of polymer stiffness on magnetization reversal of MREs using a combination of magnetometry measurements and computational modeling. Poly-dimethylsiloxane- based MREs with Young’s moduli that range over two orders of magnitude were synthesized using commercial polymers SylgardTM 527, Sylgard 184, and carbonyl iron powder. The magnetic hysteresis loops of the softer MREs exhibit a characteristic pinched loop shape with almost zero remanence and loop widening at intermediate fields that monotonically decreases with increasing polymer stiffness. A simple two-dipole model that incorporates magneto-mechanical coupling not only confirms that micrometer-scale particle motion along the applied magnetic field direction plays a defining role in the magnetic hysteresis of ultrasoft MREs but also reproduces the observed loop shapes and widening trends for MREs with varying polymer stiffnesses

Retroviral matrix and lipids, the intimate interaction

Retroviruses are enveloped viruses that assemble on the inner leaflet of cellular membranes. Improving biophysical techniques has recently unveiled many molecular aspects of the interaction between the retroviral structural protein Gag and the cellular membrane lipids. This interaction is driven by the N-terminal matrix domain of the protein, which probably undergoes important structural modifications during this process, and could induce membrane lipid distribution changes as well. This review aims at describing the molecular events occurring during MA-membrane interaction, and pointing out their consequences in terms of viral assembly. The striking conservation of the matrix membrane binding mode among retroviruses indicates that this particular step is most probably a relevant target for antiviral research

Optomechanical measurement of the stiffness of single adherent cells

Recent advances in mechanobiology have accumulated strong evidence showing close correlations between the physiological conditions and mechanical properties of cells. In this paper, a novel optomechanical technique to characterize the stiffness of single adherent cells attached on a substrate is reported. The oscillation in a cell\u27s height on a vertically vibrating reflective substrate is measured with a laser Doppler vibrometer as apparent changes in the phase of the measured velocity. This apparent phase shift and the height oscillation are shown to be affected by the mechanical properties of human colorectal adenocarcinoma cells (HT-29). The reported optomechanical technique can provide high-throughput stiffness measurement of single adherent cells over time with minimal perturbation

Biodegradable Monocrystalline Silicon Photovoltaic Microcells As Power Supplies For Transient Biomedical Implants

Bioresorbable electronic materials serve as foundations for implantable devices that provide active diagnostic or therapeutic function over a timeframe matched to a biological process, and then disappear within the body to avoid secondary surgical extraction. Approaches to power supply in these physically transient systems are critically important. This paper describes a fully biodegradable, monocrystalline silicon photovoltaic (PV) platform based on microscale cells (microcells) designed to operate at wavelengths with long penetration depths in biological tissues (red and near infrared wavelengths), such that external illumination can provide realistic levels of power. Systematic characterization and theoretical simulations of operation under porcine skin and fat establish a foundational understanding of these systems and their scalability. In vivo studies of a representative platform capable of generating ≈60 µW of electrical power under 4 mm of porcine skin and fat illustrate an ability to operate blue light-emitting diodes (LEDs) as subdermal implants in rats for 3 d. Here, the PV system fully resorbs after 4 months. Histological analysis reveals that the degradation process introduces no inflammatory responses in the surrounding tissues. The results suggest the potential for using silicon photovoltaic microcells as bioresorbable power supplies for various transient biomedical implants

Integrated cantilever-based biosensors for the detection of chemical and biological entities

Microcantilever sensors can be largely divided by the operation mode and the measurement environment. The operation mode of microcantilever sensors can be either the static mode based on the cantilever deflection or the dynamic mode based on the resonant frequency. The measurement environment often determines the type of sample entities and limits the sensitivity of the microcantilever sensor. The measurement environment can be in vacuum, in air, or in liquid. In this chapter, the microcantilever sensors in each category will be reviewed and one exemplary work will be discussed in further detail

Biophysical properties of human breast cancer cells measured using silicon MEMS resonators and atomic force microscopy

10.1039/c4lc01179aLab on a Chip - Miniaturisation for Chemistry and Biology153839-84

Self-heating in piezoresistive cantilevers

We report experiments and models of self-heating in piezoresistive microcantilevers that show how cantilever measurement resolution depends on the thermal properties of the surrounding fluid. The predicted cantilever temperature rise from a finite difference model is compared with detailed temperature measurements on fabricated devices. Increasing the fluid thermal conductivity allows for lower temperature operation for a given power dissipation, leading to lower force and displacement noise. The force noise in air is 76% greater than in water for the same increase in piezoresistor temperature