Micro and Nano Systems Letters最新文献

Preterm infants are prone to have higher risks of morbidity, disability and developmental delay compared to term infants. The primitive reflexes, inborn behaviors found in early life development, are shown to be a good tool to assess the integrity of the central nervous system of infants and to predict potential malfunctions. Among these reflexes, the non-nutritive sucking reflex plays an important role in indicating congenital abnormalities in brain development and feeding readiness, especially for premature infants. Conventionally, pediatricians evaluate the oral sucking power qualitatively based on their experiences, by using a gloved finger put inside the infant’s mouth. Thus, more quantitative solutions to assess the sucking power of preterm infants are necessary to support healthcare professionals in their evaluation procedures. Here, we developed a silver nanowire (AgNW)-based flexible pressure sensor to measure the non-nutritive sucking power of infants. The flexible sensor was fabricated using silver nanowires deposited on polydimethylsiloxane (PDMS) in a sandwich-like structure. The sensor based on the principle of strain gauge was attached to a ring-shaped connecting module, and then to a pacifier. The negative sucking pressure exerted by the infant deformed the sensor membrane, causing its electrical resistance to change without any contact between the infant’s mouth and the sensing element. The fabricated sensor was characterized and optimized to achieve both the suitable sensitivity and stability. Thanks to the excellent long-term electro-mechanical stability and high sensitivity, the developed sensor is expected to provide the means to quantitatively assess the non-nutritive sucking of infants, with a portable, low-cost, non-invasive and light-weight solution.

Recently, as the concentration of fine dust in the atmosphere has increased due to an increase in the use of fossil fuel power plants, automobiles, and factories, it has been increasingly important to measure fine dust in the atmosphere. This is because exposure to fine dust is closely related to the incidence of respiratory and cardiovascular diseases and eventually affects mortality. In this paper, we introduce a MEMS particle sensor based on the resonance frequency shift according to added particle mass. The actuation is driven by Aluminum nitride (AlN), and the total thickness is 2.8?μm. A laser doppler vibrometer (LDV), an optical measuring instrument, was used to measure the resonance frequency of the sensor. Airborne particles naturally were deposited on the sensor. To show the frequency shift according to the particle mass, the frequency shift was measured by dividing the case where the deposited particle mass was small and large. In each case, the frequency shift according to the deposited particle mass was predicted and compared with the frequency shift measured by LDV. It was shown that the deposited particle mass and frequency shift are proportional. The deposition of particulate mass was estimated by image analysis. The frequency shift caused by the particle mass deposited on the sensor was defined as the sensitivity of the sensor. The estimated sensitivity of the sensor is 0.219 to 0.354?kHz/pg.

Rapid diagnosis and treatment are required when blood clots build up in a blood vessel and clog up the vessel. This study proposes novel smart catheters that can simultaneously diagnose and treat blood vessel disease. This quick treatment increases survival probability and can prevent various complications. In the design of the smart catheters, Pt strain gauges can be used to measure the inside diameter of the vessel. This paper proposes a new fabrication process of the Pt strain gauges based on metal substrates made of Ni and Co alloy (referred to as “Ni-Co” in this paper). In the fabrication process, a Ni-Co thin film was deposited onto a silicon carrier wafer by electroplating and patterned into individual shapes by a liftoff process. Then, a multilayered Pt strain gauge consisting of insulation, adhesive layers, and Pt metallization was formed on the Ni-Co flexible substrate. Subsequently, the Pt strain gauges were peeled off from the carrier wafer by a new release process. To evaluate the performance of the strain gauges in terms of gauge factor and nonlinearity, tensile and compression tests were conducted by attaching Pt strain gauges to the constant stress beam.

Deep reactive-ion etching (DRIE) is commonly used for high aspect ratio silicon micromachining. However, scalloping, which is the result of the alternating Bosch process of DRIE, can cause many problems in the subsequent process and degrade device performance. In this work, we propose a simple and effective method to smoothen the scalloping of DRIE trenches. The proposed method utilizes sidewall dry etching by reactive-ion etching (RIE) based sulfur hexafluoride (SF₆) plasmas, following the DRIE process. To investigate the effect of the etch parameter on the scallop smoothing effect, the radio frequency (RF) power and gas flow are controlled. After the RIE treatment, the scallop smoothing effects were evaluated by measuring the average scallop depth under each condition. The scallop depth was reduced by 91% after implementing the scallop smoothing technique using RIE. Thus, our smoothening method based on SF₆ plasmas would provide broad availabilities and applicability in silicon micromachining with the simple low-temperature process.

To pierce through the skin and interact with the first biofluid available, microneedles should be mechanically strong. However, some polymers used to fabricate microneedles yield insufficient strength for the fabrication of arrays (PDMS, highly porous structures, etc.). To enhance mechanical properties, piercing materials can be used. They aim to pierce the skin evenly and dissolve quickly, clearing the way for underlying microneedles to interact with the interstitial fluid (ISF). Three materials—carboxymethyl cellulose (CMC), alginate, and hyaluronic acid (HA)—are discussed in this article. Low concentrations, for a quick dissolution while keeping enhancing effect, are used ranging from 1–5%(w/w) in deionized water. Their overall aspects, such as geometrical parameters (tip width, height, and width), piercing capabilities, and dissolution time, are measured and discussed. For breaking the skin barrier, two key parameters—a sharp tip and overall mechanical strength—are highlighted. Each material fails the piercing test at a concentration of 1%(w/w). Concentrations of 3%(w/w) and of 5%(w/w) are giving strong arrays able to pierce the skin. For the purpose of this study, HA at a concentration of 3%(w/w) results in arrays composed of microneedles with a tip width of 48?±?8?μm and pierced through the foil with a dissolution time of less than 2?min.

In this study, the spring constant of an accelerometer with a liquid-type proof mass was analyzed. Unlike a general solid-type microelectromechanical system accelerometer, the Laplace pressure is considered a restoring force in the analyzed accelerometer. Using a base excitation mathematical model, the sensor output could be estimated for a specific spring constant. Although the estimated sensor output data fit well with the experimental results, the spring constant of the device could also be determined dynamically (for oscillations below 5?Hz). Moreover, the damping constants could be inferred depending on whether sandblasting treatment was performed. Finally, the effects of the oscillation, surface condition, and volume of liquid metal droplets on the spring constant were analyzed.

With the increasing allergy cases worldwide, this study introduces a biodegradable microneedle system to facilitate allergy testing process. Dissolving microneedle provides a minimally invasive manner to go through skin barrier while avoiding needle phobia among patents, especially children. The microneedles were fabricated using copolymer polyvinylpyrrolidone-co-methacrylic acid (PVP-MAA) material. To ensure the successful insertion of microneedles into the skin, we tailored the mechanical strength of the copolymer by adjusting the weight ratio of two constituted polymers. A reservoir was designed to load allergy specimen for the allergy test. This system is expected to offer a simple and effective allergy testing that can facilitate the allergy testing protocol.

In this paper, we experimentally verified the length (L_ESC) and the concentration (c_ESC) of the extended space charge (ESC) layer in front of the electrical double layer (EDL) using the chronopotentiometric measurement and the equivalent circuit model analysis. From the experimentation, the coupled-response of the EDL and the ESC layer was discriminated from the contribution of electro-osmotic flow (EOF). In addition, we derived the potential differences across the ESC (V_ESC) layer using the circuit model of the ICP layer under rigorous consideration of ESC and EDL. As a result, we obtained that V_ESC was linearly proportional to the square of the applied current (i_applied). Hence, L_ESC and c_ESC were quantitatively provided, where L_ESC is linear to the i_applied and c_ESC is constant regardless of i_applied. Thus, this experimentation could not only clarify an essential ICP theory but also guide in ESC-based applications.

Conventional 3D printing methods require the addition of a supporting layer in order to accurately and reliably fabricate the desired final product. However, the use of supporting material is not economically viable, and during the process of removing the supporting material, the shape or the properties of the final product may be distorted. In our previous work, we proposed and demonstrated the concept of a new 3D printing method that utilizes the in situ light as a guide for the fabrication of freestanding overhanging structures without the need for supporting material. In this study, the influence of the light intensity on the diameter of the structure and the thickness of the layer produced per droplet is analyzed in order to identify the geometric range of structures that can be fabricated by the new 3D printing method. As the intensity of the light increased, the diameter of the structure also increased and the thickness of the layer per droplet decreased. This result is determined by a combination of factors; (1) the rebound motion of the photocurable droplet and (2) the surface area of the structure that needs to be covered.