Sangkwon Han

Biomimetic Microfingerprints for Anti‐Counterfeiting Strategies

An unclonable, fingerprint-mimicking anti-counterfeiting strategy is presented that encrypts polymeric particles with randomly generated silica film wrinkles. The generated wrinkle codes are as highly unique as human fingerprints and are technically irreproducible. Superior to previous physical unclonable functions, codes are tunable on demand and generable on various geometries. Reliable authentication of real-world products that have these microfingerprints is demonstrated using optical decoding methods.

Fine-tuned grayscale optofluidic maskless lithography for three-dimensional freeform shape microstructure fabrication

This article presents free-floating three-dimensional (3D) microstructure fabrication in a microfluidic channel using direct fine-tuned grayscale image lithography. The image is designed as a freeform shape and is composed of gray shades as light-absorbing features. Gray shade levels are modulated through multiple reflections of light in a digital micromirror device (DMD) to produce different height formations. Whereas conventional photolithography has several limitations in producing grayscale colors on photomask features, our method focuses on a maskless, single-shot process for fabrication of freeform 3D micro-scale shapes. The fine-tuned gray image is designed using an 8-bit grayscale color; thus, each pixel is capable of displaying 256 gray shades. The pattern of the UV light reflecting on the DMD is transferred to a photocurable resin flowing through a microfluidic channel. Here, we demonstrate diverse free-floating 3D microstructure fabrication using fine-tuned grayscale image lithography. Additionally, we produce polymeric microstructures with locally embedded gray encoding patterns, such as grayscale-encoded microtags. This functional microstructure can be applied to a biophysical detection system combined with 3D microstructures. This method would be suitable for fabricating 3D microstructures that have a specific morphology to be used for particular biological or medical applications.

Direct, rapid antimicrobial susceptibility test from positive blood cultures based on microscopic imaging analysis

For the timely treatment of patients with infections in bloodstream and cerebrospinal fluid, a rapid antimicrobial susceptibility test (AST) is urgently needed. Here, we describe a direct and rapid antimicrobial susceptibility testing (dRAST) system, which can determine the antimicrobial susceptibility of bacteria from a positive blood culture bottle (PBCB) in six hours. The positive blood culture sample is directly mixed with agarose and inoculated into a micropatterned plastic microchip with lyophilized antibiotic agents. Using microscopic detection of bacterial colony formation in agarose, the total time to result from a PBCB for dRAST was only six hours for a wide range of bacterial concentrations in PBCBs. The results from the dRAST system were consistent with the results from a standard AST, broth microdilution test. In tests of clinical isolates (n = 206) composed of 16 Gram-negative species and seven Gram-positive species, the dRAST system was accurate compared to the standard broth microdilution test, with rates of 91.11% (2613/2868) categorical agreement, 6.69% (192/2868) minor error, 2.72% (50/1837) major error and 1.45% (13/896) very major error. Thus, the dRAST system can be used to rapidly identify appropriate antimicrobial agents for the treatment of blood stream infection (BSI) and antibiotic-resistant strain infections.

Lithographic resolution enhancement of a maskless lithography system based on a wobulation technique for flow lithography

We present a method for improving the lithographic resolution of digital micromirror devices for flow-lithography using a wobulation technique. While maintaining the area of UV exposure, the lithographic resolution was improved using a wobulation technique, which is a large screen display technique that enhances resolution via overlapping pixels by half a pixel. The edges of a diagonal pattern in a microstructure were smoothly generated with additional sub-patterns compared to conventional single pattern-exposure. In addition, the surface roughness of the microstructure was improved because the gaps between pixels were filled by the overlapping patterns.

Direct rapid antibiotic susceptibility test (dRAST) for blood culture and its potential usefulness in clinical practice

Purpose. The direct rapid antibiotic susceptibility test (dRAST), based on analysing changes in bacterial micro‐colonies under antibiotic conditions, detects antibiotic resistance within 6 h of direct smear examination results. This study aimed to assess the accuracy of dRAST and evaluate its potential usefulness for improving selection of appropriate antibiotic in real clinical practice settings. Methodology. We evaluated the accuracy of dRAST by comparing the antibiotic treatments that should have been administered based on dRAST results and the broth microdilution (BMD) test and its potential usefulness via simulation. Result. For 49/52 (94.2 %) patients with Gram‐positive bacteraemia and 66/67 (98.5 %) patients with Gram‐negative bacteraemia, antibiotics indicated by dRAST results were the same as those indicated by the BMD test. Among 34 patients with ineffective and suboptimal treatment, 19 (55.9 %) of patients could have received optimal treatment 1 to 2 days earlier with dRAST results. Among 33 patients given unnecessary broad‐spectrum antibiotics, 1 to 2 days earlier de‐escalation could have been possible for 27 (81.8 %) patients based on dRAST results. Conclusion. The introduction of dRAST could increase the use of optimal antibiotics and reduce unnecessary broad‐spectrum antibiotic use in the early period of bacteraemia.

Hierarchical shape-by-shape assembly of microparticles for micrometer-scale viral delivery of two different genes

Understanding tissue engineering using a bottom-up approach has been hindered by technical limitations because no platform can demonstrate the controlled formation of a heterogeneous population of cells in microscale. Here, we demonstrate hierarchical shape-by-shape assembly of virus-laden particles into larger ones to transfect two different genes on the seeded cells. We show that smaller daughter particles with different sizes and shapes can be assembled into the matching indentations of larger parent particles with different sizes and shapes. Then, we transfected a population of cells with two different gene-transfecting viruses, each of which was laden on the parent or daughter particles.

Clinical Evaluation of QMAC-dRAST for Direct and Rapid Antimicrobial Susceptibility Test with Gram-Positive Cocci from Positive Blood Culture Bottles

QuantaMatrix Inc., Institutes of Entrepreneurial BioConvergence, Seoul National University, Department of Electrical and Computer Engineering, Seoul National University, Department of Transdisciplinary Studies, Seoul National University, Department of Laboratory Medicine, Seoul National University Hospital, Seoul National University Hospital Biomedical Research Institute, Seoul National University Hospital, Seoul, Korea