Fabrication of Size- and Shape- Controllable Mixed-Scale PDMS Channel Networks Including 3D Microfunnels

Department of Mechanical EngineeringIn this thesis, a novel batch fabrication technology for a mixed-scale PDMS (Polydimethylsilane) channel networks using carbon- micro electromechanical systems (MEMS) and single molding process is introduced. Nanofabrication has been used in broad research fields including single electron memories, multiple tunnel junction (MTJ) devices, micro electromechanical systems (MEMS) sensors, and nanofluidic devices. Nanofluidic channel networks are crucial parts in various applications such as DNA electrophoresis, bio sensors, molecular preconcentration, ionic transport nanofluidic diodes, desalination, nanofludic transistors because of their unique phenomena including ion concentration polarization, ion rectification effect, nanocapillarity and electrical double layer overlap. However, the research on the nanofluidics has been limited because of the lack of simple and cost-effective nanofabrication technologies. Microfabrication technologies that are compatible with nanofabrication processes also needs to be developed so as to integrate microfluidic channels with nanochannels, because the microchannels guide sample fluid into and out of the nanochannels and thus mixed-scale channel networks are the basic architecture of the nanofluidic devices. However, the fabrication of mixed-scale channel networks is limited by difficult alignment processes between nanostructures and microstructures, high fabrication cost, and time consuming and complex processes. These limitations can be overcame by utilizing carbon-MEMS technology and single polymer molding process. A mixed-scale carbon structure as the mold of a Poly (dimethylsiloxane) (PDMS) channel network was fabricated using conventional UV lithography and pyrolysis. A single molding process using multi-layers of hard PDMS and soft PDMS completes the fabrication of mixed-scale PDMS channel networks including 55-nm-high and 441-nm-wide nanochannels. The quality of the PDMS molding process was evaluated using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The surface energy of the pyrolyzed carbon mold could be modulated by controlling pyrolysis temperature resulting in high surface energy. As a result, a single carbon mold could replicate PDMS channel networks more than 40 times without anti-adhesion coating. The hermetic sealing and uniformity of the PDMS nanochannel were evaluated by filling the mixed-scale PDMS channel networks with fluorescein isothiocyanate (FITC). The properties of PDMS nanochannels were characterized by measuring I-V relationship in KCl solution. Except for the simple fabrication of the complex carbon mold, the pyrolysis process also enabled the formation of smoothly tapered mold side wall because of good adhesion between the photoresist and substrate, and volume reduction in pyrolysis. As a result, 3-D funnels could be integrated at the entrance and exit of the nanochannel. By this novel 3-D funnel structure, efficient entrapment of a single micro particle at the entrance of a nanochannel was enabled. It is expected that the mixed-scale PDMS channel networks with 3D-funnels can be applied to nanoelectroporation for efficient cell transfectionope

An Energy-Efficient Secure Scheme in Wireless Sensor Networks

We propose an energy-efficient security scheme in wireless sensor networks. The proposed scheme converts sensing data using TinyMD5, which is a variation of MD5, a one-way hash function, and can solve the collision problem of hash value that occurs when MD5 is modified. In addition, it strengthens security capabilities by transmitting data through multiple paths after conversion with TinyMD5 and divides the data to make decryption of the original data difficult. To show the superiority of the proposed algorithm, we compare it with the existing schemes through simulations. The performance evaluation results show that the proposed scheme maintains security better than the existing scheme, improving the communication cost and the network lifetime

Syntheses of 3-[(Alkylamino)methylene]-6-methyl-1Hpyridine-2,4-diones, Fluorescence Probes 3-Substituted 7-Methyl-6H-pyrano[3,2-c]pyridine-2,5-diones, and Tetrahydro-6H-2,10-dioxa-9-azaanthracen-1-ones

Various condensation and ring-closing reactions were used for the syntheses of 3-[(alkylamino)methylene]-6-methylpyridine-2,4(1H,3H)-diones, bicyclic pyridinones, and tricyclic morpholinopyrones. For instance, 3-[(dialkylamino)methylene]-6-methylpyridine-2,4(1H,3H)-diones were synthesized from the condensation of dialkylamines and 3-formyl-4-hydroxy-6-methylpyridin-2(1H)-one. 3-Formyl-4-hydroxy-6-methylpyridin-2(1H)-one, derived from 3-formyl-4-hydroxy-6-methylpyridin-2(1H)-one, was used to construct a number of bicyclic pyridinones via a one-pot Knoevenagal and intramolecular lactonization reaction. Tricyclic morpholinopyrones were assembled from a dialkylation reaction involving a dinucleophile, 3-amino-4-hydroxy-6-methyl-2H-pyran-2-one, and a dielectrophile, trans-3,6-dibromocyclohexene. Depending on the reaction conditions, isomers of the tricyclic molecules can be selectively produced, and their chemical structures were unequivocally determined using single-crystal X-ray analyses and 2D COSY spectroscopy. The fluorescently active bicyclic pyridinone compounds show longer absorption (368–430 nm; maximum) and emission wavelengths (450–467 nm) than those of 7-amino-4-methylcoumarin (AMC; λ[subscript abs,max] = 350 nm; λ[subscript em] = 430 nm) suggesting these molecules, such as 3-(2-aminoacetyl)-7-methyl-2H-pyrano[3,2-c]pyridine-2,5(6H)-dione, can be employed as fluorescence activity based probes for tracing biological pathways

A trust approach for sharing research reagents

The core feature of trusts-holding property for the benefit of others-is well suited to constructing a research community that treats reagents as public goods

Long-term survival benefits of intrathecal autologous bone marrow-derived mesenchymal stem cells (Neuronata-R®: lenzumestrocel) treatment in ALS: Propensity-score-matched control, surveillance study

ObjectiveNeuronata-R® (lenzumestrocel) is an autologous bone marrow-derived mesenchymal stem cell (BM-MSC) product, which was conditionally approved by the Korean Ministry of Food and Drug Safety (KMFDS, Republic of Korea) in 2013 for the treatment of amyotrophic lateral sclerosis (ALS). In the present study, we aimed to investigate the long-term survival benefits of treatment with intrathecal lenzumestrocel.MethodsA total of 157 participants who received lenzumestrocel and whose symptom duration was less than 2 years were included in the analysis (BM-MSC group). The survival data of placebo participants from the Pooled-Resource Open-Access ALS Clinical Trials (PROACT) database were used as the external control, and propensity score matching (PSM) was used to reduce confounding biases in baseline characteristics. Adverse events were recorded during the entire follow-up period after the first treatment.ResultsSurvival probability was significantly higher in the BM-MSC group compared to the external control group from the PROACT database (log-rank, p < 0.001). Multivariate Cox proportional hazard analysis showed a significantly lower hazard ratio for death in the BM-MSC group and indicated that multiple injections were more effective. Additionally, there were no serious adverse drug reactions found during the safety assessment, lasting a year after the first administration.ConclusionThe results of the present study showed that lenzumestrocel treatment had a long-term survival benefit in real-world ALS patients

Servicescape Factors Which Influence Tourists’ Behavioral Intentions to Repeat Visits to Horse-Based Tourism Attractions in Texas

A popular attraction in Texas is a horse attraction, including county and state fairs, horse races, horse shows, horse tours, rodeo and livestock shows, and trail drives/rides (Office of the Governor, Economic Development & Tourism, 2010). The purpose of this study will be (a) to understand the under-explored area of tourists’ perception of the servicescape in horse-based tourism; (b) to investigate tourists’ perceived quality of the impact of the servicescape on emotions; and (c) to examine the relationships among perceived servicescape, emotions and behavioral intentions of visitors to horseback riding attractions in Texas. The findings of the study will provide information to horse-based service providers/tourism attractions and contribute to the development, operations, and marketing strategies of horse-based tourism

Fabrication of a monolithic carbon mold for producing a mixed-scale PDMS channel network using a single molding process

We introduce a novel batch fabrication technique of a monolithic carbon mold for producing a mixed-scale polydimethylsiloxane (PDMS) channel network consisting of nanochannels and microchannels with micro-pillars. Nano- fluidics has attracted much attention because of their distinguishing properties. However, the research on the nanofluidics is limited by complex nanofabrication techniques. In this paper, a mixed-scale monolithic carbon mold was simply fabricated using a batch carbon-MEMS process consisting of two successive UV-lithography processes and a single pyrolysis. Then, PDMS channel networks was completed by soft molding process. By modulating pyrolysis conditions, the surface energy of the pyrolyzed carbon mold could be optimized for efficient PDMS channel demolding

Mixed-scale channel networks including Kingfisher-beak-shaped 3D microfunnels for efficient single particle entrapment

Reproducible research results for nanofluidics and their applications require viable fabrication technologies to produce nanochannels integrated with microchannels that can guide fluid flow and analytes into/out of the nanochannels. We present the simple fabrication of mixed-scale polydimethylsiloxane (PDMS) channel networks consisting of nanochannels and microchannels via a single molding process using a monolithic mixed-scale carbon mold. The monolithic carbon mold is fabricated by pyrolyzing a polymer mold patterned by photolithography. During pyrolysis, the polymer mold shrinks by ???90%, which enables nanosized carbon molds to be produced without a complex nanofabrication process. Because of the good adhesion between the polymer mold and the Si substrate, non-uniform volume reduction occurs during pyrolysis resulting in the formation of curved carbon mold side walls. These curved side walls and the relatively low surface energy of the mold provide efficient demolding of the PDMS channel networks. In addition, the trigonal prismatic shape of the polymer is converted into to a Kingfisher-beak-shaped carbon structure due to the non-uniform volume reduction. The transformation of this mold architecture produces a PDMS Kingfisher-beak-shaped 3D microfunnel that connects the microchannel and the nanochannel smoothly. The smooth reduction in the cross-sectional area of the 3D microfunnels enables efficient single microparticle trapping at the nanochannel entrance; this is beneficial for studies of cell transfection.clos

Development of the batch fabrication technique using carbon-MEMS for mixed-scale channel networks including tapered 3D microfunnels

This paper reports a novel fabrication technique of a monolithic carbon mold for producing a mixedscale PDMS channel network consisting of nano- and microchannels. Nanofluidic has attracted much attention because of their distinguishing properties. A mixed-scale carbon mold was simply fabricated using a carbon-MEMS process. A soft lithography was used to complete mixed-scale channel networks. Because of anisotropic volume reduction in pyrolysis, vertical polymer side walls were converted into smoothly tapered carbon side walls. Therefore, 3D carbon microfunnel naturally can be converted from triangular prism polymer structure. PDMS microfunnel can guide fluid and particle to entrance of nanochannel more efficiently