Do Hoon Lee

Highly Sensitive and Flexible Strain Sensors Based on Patterned ITO Nanoparticle Channels

We demonstrate a highly sensitive and flexible bending strain sensor using tin-doped indium oxide (ITO) nanoparticles (NPs) assembled in line patterns on flexible substrates. By utilizing transparent ITO NPs without any surface modifications, we could produce strain sensors with adjustable gauge factors and optical transparency. We were able to control the dimensional and electrical properties of the sensors, such as channel height and resistance, by controlling the NP assembly speed. Furthermore, we were able to generate controlled gauge factor with values ranging from 18 to 157, which are higher than previous cases using metallic Cr NPs and Au NPs. The alignment of the ITO NPs in parallel lines resulted in low crosstalk between the transverse and longitudinal bending directions. Finally, our sensor showed high optical transmittance, up to ∼93% at 500 nm wavelength, which is desirable for flexible electronic applications.

MicroRNA signatures associated with thioacetamide-induced liver fibrosis in mice

Multiple etiologies of liver injury are associated with fibrosis in which the key event is the activation of hepatic stellate cells (HSCs). Although microRNAs (miRNAs) are reportedly involved in fibrogenesis, the complete array of miRNA signatures associated with the disease has yet to be elucidated. Here, deep sequencing analysis revealed that compared to controls, 80 miRNAs were upregulated and 21 miRNAs were downregulated significantly in the thioacetamide (TAA)-induced mouse fibrotic liver. Interestingly, 58 of the upregulated miRNAs were localized to an oncogenic miRNA megacluster upregulated in liver cancer. Differential expression of some of the TAA-responsive miRNAs was confirmed, and their human orthologs were similarly deregulated in TGF-β1-activated HSCs. Moreover, a functional analysis of the experimentally validated high-confidence miRNA targets revealed significant enrichment for the GO terms and KEGG pathways involved in HSC activation and liver fibrogenesis. This is the first comprehensive report of miRNAs profiles during TAA-induced mouse liver fibrosis. Graphical abstract We identified 80 upregulated miRNAs and 21 downregulated miRNAs associated with TAA-induced liver fibrosis in mice.

Engineered Phage Matrix Stiffness-Modulating Osteogenic Differentiation

Herein, we demonstrate an engineered phage mediated matrix for osteogenic differentiation with controlled stiffness by cross-linking the engineered phage displaying Arg-Gly-Asp (RGD) and His-Pro-Gln (HPQ) with various concentrations of streptavidin or polymer, poly(diallyldimethylammonium)chloride (PDDA). Osteogenic gene expressions showed that they were specifically increased when MC3T3 cells were cultured on the stiffer phage matrix than the softer one. Our phage matrixes can be easily functionalized using chemical/genetic engineering and used as a stem cell tissue matrix stiffness platform for modulating differential cell expansion and differentiation.

Biomimetic Materials and Structures for Sensor Applications

Diverse biological tissues and structures that often exhibit remarkable physical and chemical properties can be found throughout nature. Starting from very few and simple building blocks such as collagen fibrils, nature effortlessly makes hierarchical and complex structures which are often hard to imitate with the current top-down microfabrication techniques. With the recent development of diverse assembly methods of nanobiomaterials, we have started to build biomimetic structures with diverse optical, mechanical, and electrical properties using bottom-up approaches. The properties of such biomimetic materials, when exposed to certain physical or chemical stimuli, sometimes change enough and may be utilized for sensing applications. For example, some filamentous viruses can be assembled into colorful films on solid substrates, the colors of which can change when exposed to organic solvents and volatile organic compounds. These same films, when applied with mechanical pressure, can exhibit piezoelectric properties, where mechanical pressure can be transduced to electrical signals, allowing the utilization of these structures as mechanical force sensors. In this chapter, we will discuss the current state of the biomimetic materials and structures for sensor applications, giving emphasis on hierarchical structures based on fiber building blocks.