Effective indenter radius and frame compliance in instrumented indentation testing using a spherical indenter

We introduce a novel method to correct for imperfect indenter geometry and frame compliance in instrumented indentation testing with a spherical indenter. Effective radii were measured directly from residual indentation marks at various contact depths (ratio of contact depth to indenter radius between 0.1 and 0.9) and were determined as a function of contact depth. Frame compliance was found to depend on contact depth especially at small indentation depths, which is successfully explained using the concept of an extended frame boundary. Improved representative stress-strain values as well as hardness and elastic modulus were obtained over the entire contact depth

Conventional Vickers and true instrumented indentation hardness determined by instrumented indentation tests

We evaluate Vickers hardness and true instrumented indentation test (IIT) hardness of 24 metals over a wide range of mechanical properties using just IIT parameters by taking into account the real contact morphology beneath the Vickers indenter. Correlating the conventional Vickers hardness, indentation contact morphology, and IIT parameters for the 24 metals reveals relationships between contact depths and apparent material properties. We report the conventional Vickers and true IIT hardnesses measured only from IIT contact depths; these agree well with directly measured hardnesses within ±6% for Vickers hardness and ±10% for true IIT hardness

Nanomechanical behavior of biodegradable metallic glass for transient electrodes

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Pseudo-no-Reflow Phenomenon in Carotid Artery Stenting using FilterWire EX: Successful Recovery by Aspiration Thrombectomy

Distal protection devices such as FilterWire EX have been widely used in carotid artery stenting, however, the large amount of atherothrombotic debris entrapped in the filter could reduce or stop antegrade flow. We present a case of pseudo-no-reflow phenomenon after postdilatation of the stent in a patient with asymptomatic carotid artery stenosis. After several passes using an Export Aspiration catheter, normal flow in the internal carotid artery was restored. Aspiration thrombectomy can successfully recover pseudo-no-reflow phenomenon

Metastable polymer substrate for transient electronics

Transient electronics are designed to operate for programmed life times and then degrade leaving little to no trace behind. The initial work on transient electronics has been focused on biomedical applications in which the electronics are implanted, but eventually degrade and resorb into the body after the treatment is complete [1]. Biomedical transient electronics typically use a water soluble substrate, such as silk that slowly degrades as water diffuses into the substrate. However, the ability to more precisely program the lifetime of electronics and utilize other degradation stimuli would enable new applications in a variety of industries. Essential to this effort is the development of a new class of degradable substrates that can be triggered to degrade by exposure to a variety of environmental stimuli (e.g., mechanical stress, UV light, pH). In this study, we present a photodegradable transient substrate made of cyclic poly(phthalaldehyde) (PPA) doped with a photo-acid generator (PAG). Exposing the substrate to UV light generates acid through reaction of the PAG which then promotes the cleavage of the acetal backbone of PPA, leading to rapid film degradation. We monitored the degradation of the film using dynamic mechanical analysis and Fourier transform infrared spectroscopy. Results demonstrate that the polymer degrades into monomer and that the degradation rate is controlled by varying the concentration of PAG and the intensity of the UV source. In addition, electronic transistors, diodes, and resistors were fabricated from magnesium and silicon nanomembranes using our newly designed substrate. A combination of transfer-printing and electron-beam evaporation were used to demonstrate lithographic compatibility. We demonstrate electronic transience of a Mg resistor in as fast as 20 minutes with substantial physical degradation in 72 hours. REFERENCE [1] Hwang, S.-W., et. al. Science. 2012, 337, 1640

CVD-grown monolayer MoS2 in bioabsorbable electronics and biosensors

Transient electronics entails the capability of electronic components to dissolve or reabsorb in a controlled manner when used in biomedical implants. Here, the authors perform a systematic study of the processes of hydrolysis, bioabsorption, cytotoxicity and immunological biocompatibility of monolayer MoS2