Rapid 3D Patterning of Poly(acrylic acid) Ionic Hydrogel for Miniature pH Sensors

Zhang

Adv Materials Technologies

et al. 2018

Self Cite

healthcare applications. However, the structures of OTFTs are relatively complex, which makes their fabrication process rigid and costly. Therefore, there is still enduring enthusiasm to develop new wearable pressure sensors to enhance their merits, such as high sensitivity, wide operation range, flexibility, economic fabrication, and deployment costs. [7c] Several mechanisms have been used to fabricate pressure sensors, such as piezoelectricity, [3a,10] capacitance, [1b,f,11] triboelectricity, [12] and piezoresistivity. [1c,e,13] Among them, piezoresistivity-type pressure sensors have the advantages of simple structure, low-cost, and convenient read-out, and thus have been drawn incredible attention to the development of flexible devices. To sustain large deformation, this type of flexible pressure sensor is commonly fabricated by elastic polymer materials, such as polydimethylsiloxane (PDMS), [1c,13a] polyurethane (PU), [1h] and even polypyrrole (PPy). [1d] Although such devices have shown their impressive performances, the sensitivities of those sensors are still not very high and/or their operation ranges are not wide enough for many applications. [8b] For example, the pressure sensor fabricated by Park et al. [1e] using Au-coated PDMS as the active matrix has a sensitivity of 2 kPa −1 under a pressure lower than 220 Pa. When the pressure increases above 220 Pa, its sensitivity starts to drop, and it will eventually reach saturation when the pressure reaches 3.5 kPa. Based on quantum tunneling effect, Lee et al. [1h] demonstrated a pressure sensor using a PU matrix mixed with sea-urchin shaped metal nanoparticles, and improved the sensitivity to 2.46 kPa −1 . However, its high sensitivity can be achieved only when the pressure is lower than 1 kPa. It will decrease to 0.055 kPa −1 when the applied pressure is above 10 kPa.One of the promising solutions to this issue is to adopt elastic hydrogels, which have significantly lower modulus of elasticity, for flexible pressure sensing applications. Using hollow-sphere microstructured PPy hydrogel, Bao and co-workers [1d] achieved a remarkable leap of sensitivity to an unprecedently high level of 133.1 kPa −1 . However, the high sensitivity can only sustain at the pressure up to 30 Pa. It will decrease significantly to 0.05 kPa −1 when the pressure goes above 10 kPa. Therefore, a remaining challenge is how to develop flexible pressure sensors with both high sensitivity and wide operation range. This problem might be solved by using hydrogel with high stretchability and toughness. Suo and co-workers [14] demonstrated a Elastic hydrogels have recently attracted remarkable attention because of their unique mechanical and stimulus-responsive properties. In this work, a novel elastic supramolecular hydrogel for wearable pressure sensors is developed by photocrosslinking polyacrylamide (PAAm) through covalent bonds and hydrogen bonds as well as ionic bonds in the presence of poly(acrylic acid) and Ca 2+ . Gold nanowires (Au NWs) are homogeneously mingled with...

Section: Resultsmentioning

confidence: 99%

Micropatterned Elastic Gold‐Nanowire/Polyacrylamide Composite Hydrogels for Wearable Pressure Sensors

Zhang

Adv Materials Technologies

et al. 2018

Self Cite

“…Among them, digital micromirror device (DMD) maskless lithography eliminates the cost of mask production and increases lithography flexibility as compared to typical masklithography. The exposure light source for SU-8 is usually the I-line (365 nm) [17][18][19][20] of a high-power mercury lamp which has the disadvantages of a large spectral range, short life, high power consumption, and pollution. The light-emitting diode (LED) is widely used in DMD lithography because of the characteristics of a single spectrum, energy saving, long life and no pollution.…”

Section: Introductionmentioning

confidence: 99%

Multi-layer lithography using focal plane changing for SU-8 microstructures

Chen

Zhou

Zheng

et al. 2020

Mater. Res. Express

In this paper, we report on a type of SU-8 microstructure with vertical sidewalls used for polydimethydiloxane (PDMS) microchannels. Multi-layer lithography using focal plane changing approach is proposed to expose the SU-8 photoresist based on a digital micromirror device (DMD) maskless lithography system. We used a light-emitting diode source with a wavelength of 405 nm. The thickness of the SU-8 is divided into multi-layers according to the depth of focus. Each layer corresponds to a depth of focus, and then, a virtual mask is designed for the layer. Finally, each layer is exposed to changes in the focal plane. The results indicate that the actual profile of the SU-8 mold shows good agreement with the design profile without any T-profiles. Additionally, there is better linewidth in the proposed method compared with multi-exposure by a single fixed focal plane. The PDMS microchannels result also demonstrate the stability of the SU-8 mold.

Macromolecular Bioscience

“…Nevertheless, most of them were designed for the intracellular pH detection and placed in the low nanometer size range. Besides fluorescent sensors, optical polymeric sensors in the micrometer range were also developed to detect the pH change …”

Section: Introductionmentioning

confidence: 99%

Synthesis and Validation of Functional Nanogels as pH‐Sensors in the Hair Follicle

Dimde

Sahle

Wycisk

et al. 2017

Patzelt et al. have described the size-dependent uptake of 100-1000 nm sized nanoparticles into the HF. Mediumsized nanoparticles (500-700 nm) achieved a maximum in penetration depth, [4] due to the surface structure of the hair and the hair follicle. Particles that are of the same size thickness of the keratin cells (530 nm in human hair and 320 nm in porcine hair) can be easily transported into the HF. The movements of the hair acts as a pumping system. Thus, the optimum size is also dependent on the species. [5,6] But even if the particles penetrate into the HF, they will not pass the follicular barrier. Consequently, the particles could be used as a transport system for drugs. Particles in the required nanoscale range can be produced in various ways. [7][8][9] A possibility to achieve particles in the nanometer range is the synthesis of nanogels which exist of crosslinked polymer chains and form 3D nanosized networks. [10,11] They can be prepared by mini [12][13][14][15] and microemulsion. [16,17] In this case reactive macromolecules are templated into stabilized droplets and then reacted to the desired nanoparticles. However, high energy input by ultrasonication or large amounts of surfactants are needed to stabilize the droplet reactors. To avoid these harsh In the present study, a pH responsive dendritic polyglycerol nanogel (dPG-NG) is developed to measure the pH values inside the hair follicle (HF) using an ex vivo porcine ear model. The macromolecular precursors are labeled with a pH sensitive indodicarbocyanine dye (pH-IDCC) and a control dye (indocarbocyanine dye: ICC) and crosslinked via a mild and surfactantfree Thiol-Michael reaction using an inverse nanoprecipitation method. With this method, it is possible to prepare tailor-made particles in the range of 100 nm to 1 µm with a narrow polydispersity. The dPG-NGs are characterized using dynamic light scattering, nanoparticle tracking analysis, and atomic force microscopy. Systematic analysis of confocal microscope images of histological sections of the skin enables accurate determination of the pH gradient inside the HF. The results show that these novel pH-nanosensors deeply penetrate the skin via the follicular pathway and the pH of the pig hair follicles increase from 6.5 at the surface of the skin to 7.4 in deeper areas of the HF. The pH-nanosensor shows no toxicity potentials.