Younghyun Cho

Controlled release of an anti-cancer drug from DNA structured nano-films

We demonstrate the generation of systemically releasable anti-cancer drugs from multilayer nanofilms. Nanofilms designed to drug release profiles in programmable fashion are promising new and alternative way for drug delivery. For the nanofilm structure, we synthesized various unique 3-dimensional anti cancer drug incorporated DNA origami structures (hairpin, Y, and X shaped) and assembled with peptide via layer-by-layer (LbL) deposition method. The key to the successful application of these nanofilms requires a novel approach of the influence of DNA architecture for the drug release from functional nano-sized surface. Herein, we have taken first steps in building and controlling the drug incorporated DNA origami based multilayered nanostructure. Our finding highlights the novel and unique drug release character of LbL systems in serum condition taken full advantages of DNA origami structure. This multilayer thin film dramatically affects not only the release profiles but also the structure stability in protein rich serum condition.

Polymer Nanotubules Obtained by Layer‐by‐Layer Deposition within AAO‐Membrane Templates with Sub‐100‐nm Pore Diameters

The preparation and features of nanotubes consisting of various materials have attracted signifi cant attention over the past few years because of their potential applications in microelectronics, biosensors, drug-delivery systems, and many other fi elds. The layer-by-layer (LbL) deposition technique on templates has been one of the most popular methods for the formation of nanotubes. Any size and shape of template can be utilized and the desired amount of various materials including polyelectrolytes, [ 1,2 ] biomolecules, [ 3,4 ]

Layer-by-layer assembled stimuli-responsive nanoporous membranes

Stimuli-responsive materials that could change their properties and structures in response to external stimuli have recently received much attention owing to their many potential applications in biosensors, drug delivery systems, actuation devices, and many others. Among various preparation methods to realize these goals, layer-by-layer (LbL) assembly, based on polyelectrolytes leading to swellable multilayers, is a powerful processing method because it can be applied to substrates of any shape and size and, at the same time, the multilayer films assembled under specific conditions show a strong swelling behavior that can be modulated in response to post-treatment conditions. For molecular-level filtration, the pore size of membranes containing cylindrical pores should be less than tens of nanometers. However, it has been regarded as a challenging task to uniformly deposit polyelectrolytes on the sidewalls of nanoporous membranes with sub-100 nm pore diameters based on the LbL deposition method due to the well-known entropic entrance barrier problem. In the present study, by introducing pH-sensitive poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) multilayers into nanoscaled pores with less than 100 nm diameter, we could additionally reduce and control the pore diameter of anodic aluminum oxide (AAO) membranes by adjusting the post-pH treatment, yielding smart ultrafiltration (UF) or nanofiltration (NF) membranes with various cutoffs realized in one membrane. Based on pH-sensitive nanopores in membranes, the translocation behavior of small spherical molecules as well as linear polymers through the stimuli-responsive membranes has been studied in detail.

Multilayer Thin Film Coatings Capable of Extended Programmable Drug Release: Application to Human Mesenchymal Stem Cell Differentiation

The promise of cellular therapy lies in healing damaged tissues and organs in vivo as well as generating tissue constructs in vitro for subsequent transplantation. Postnatal stem cells are ideally suited for cellular therapies due to their pluripotency and the ease with which they can be cultured on functionalized substrates. Creating environments to control and successfully drive their differentiation toward a lineage of choice is one of the most important challenges of current cell-based engineering strategies. In recent years, a variety of biomaterials platforms have been prepared for stem cell cultures, primarily to provide efficient delivery of growth or survival factors to cells and a conductive microenvironment for their growth. Here, we demonstrate that repeating tetralayer structures composed of biocompatible poly(methacrylic acid), poly(acrylamide), and poly(ethylene oxide)-block-poly(ε-caprolactone) micelles arrayed in layer-by-layer films can serve as a payload region for dexamethasone delivery to human mesenchymal stem cells (MSCs). This architecture can induce MSC differentiation into osteoblasts in a dose-dependent manner. The amount of Dex loaded in the films is controlled by varying the deposition conditions and the film thickness. Release of Dex is tuned by changing the amount of covalent cross-linking of multilayers via thermal treatments. The multilayer architecture including payload and cell-adhesion region introduced here are well suited for extended cell culture thus affording the important and protective effect of both Dex release and immobilization. These films may find applications in the local delivery of immobilized therapeutics for biomedical applications, as they can be deposited on a wide range of substrates with different shapes, sizes, and composition.

Toward Mass Producible Ordered Bulk Heterojunction Organic Photovoltaic Devices

A strategy to fabricate nanostructured poly(3-hexylthiophene) (P3HT) films for organic photovoltaic (OPV) cells by a direct transfer method from a reusable soft replica mold is presented. The flexible polyfluoropolyether (PFPE) replica mold allows low-pressure and low- temperature process condition for the successful transfer of nanostructured P3HT films onto PEDOT/PSS-coated ITO substrates. To reduce the fabrication cost of masters in large area, we employed well-ordered anodic aluminum oxide (AAO) as a template. Also, we provide a method to fabricate reversed nanostructures by exploiting the self-replication of replica molds. The concept of the transfer method in low temperature with a flexible and reusable replica mold obtained from an AAO template will be a firm foundation for a low-cost fabrication process of ordered OPVs.

Online Scalability Characterization of Data-Parallel Programs on Many Cores

We present an accurate online scalability prediction model for data-parallel programs on NUMA many-core systems. Memory contention is considered to be the major limiting factor of program scalability as data parallelism limits the amount of synchronization or data dependencies between parallel work units. Reflecting the architecture of NUMA systems, contention is modeled at the last-level caches of the compute nodes and the memory nodes using a two-level queuing model to estimate the mean service time of the individual memory nodes. Scalability predictions for individual or co-located parallel applications are based solely on data obtained during a short sampling period at runtime; this allows the presented model to be employed in a variety of scenarios. The proposed model has been implemented into an open-source OpenCL and the GNU OpenMP runtime and evaluated on a 64-core AMD system. For a wide variety of parallel workloads and configurations, the evaluations show that the model is able to predict the scalability of data-parallel kernels with high accuracy.

Adaptive Space-Shared Scheduling for Shared-Memory Parallel Programs

Space-sharing is regarded as the proper resource management scheme for many-core OSes. For today’s many-core chips and parallel programming models providing no explicit resource requirements, an important research problem is to provide a proper resource allocation to the running applications while considering not only the architectural features but also the characteristics of the parallel applications.

Efficient Checkpointing of Live Virtual Machines

The ability to save the state of a running virtual machine (VM) for later restoration is an important tool for home, server, and virtual desktop cloud (VDC) environments in order to achieve optimal and balanced hardware utilization. With guest memory sizes of four to eight gigabytes being the norm the time- and space-overhead of storing VM checkpoints still prevents an effective use of the technique. This work presents a method for fast and space-efficient checkpointing of VMs. Based on the observation that operating systems cache disk blocks in memory, the proposed technique transparently intercepts I/O operations and maintains an up-to-date mapping of memory pages and disk blocks containing identical data. At a checkpoint, those memory pages are excluded from the checkpoint image leading to a significant reduction of both the time and space required to take a checkpoint of a running VM. The broad applicability and good performance of the proposed method is demonstrated by an extensive set of experiments. We have implemented the technique for para-virtualized (PV), PVHVM, and fully-virtualized (HVM) guests in the Xen hypervisor. In comparison with an unmodified Xen hypervisor, experiments with Linux and Windows guests, on average, achieve a 86, 76, 53, and 47 percent reduction in the stored data and a 73, 62, 47, and 38 percent shorter time required to take a checkpoint for PV, PVHVM, HVM Linux, and HVM Windows guests, respectively.

Maximizing system utilization via parallelism management for co-located parallel applications

With an increasing number of cores and memory controllers in multiprocessor platforms, co-location of parallel applications is gaining on importance. Key to achieve good performance is allocating the proper number of threads to co-located applications. This paper presents NuPoCo, a framework for automatically managing parallelism of co-located parallel applications on NUMA multi-socket multi-core systems. NuPoCo maximizes the utilization of CPU cores and memory controllers by dynamically adjusting the number of threads for co-located parallel applications. Evaluated with various scenarios of co-located OpenMP applications on a 64-core AMD and a 72-core Intel machine, NuPoCo achieves a reduction of the total turnaround time by 10-20% compared to the default Linux scheduler and an existing parallelism management policy focusing on CPU utilization only.

On-the-fly workload partitioning for integrated CPU/GPU architectures

Integrating CPUs and GPUs on the same die provides new opportunities for optimization, especially for irregular data-parallel workloads that fail to fully exploit the computational power of the GPU. Such workloads benefit from a proper partitioning between the CPU and the GPU. This paper presents an on-the-fly workload partitioning technique for irregular workloads on integrated architectures. Unlike existing work, no prior analysis of the workload is required. GPU kernels and input data are analyzed and optimized at runtime. The technique executes work chunks of similar load on the GPU and assigns irregular chunks to the CPU. Evaluated with various irregular workloads, the method achieves a 1.4x--7.1x speedup over GPU execution on AMD and Intel processors.