Hollow microneedle array fabrication using a rational design to prevent skin clogging in transdermal drug delivery.

Microneedle (MN) technology is promising to replace hypodermic needles for practical use and painless drug delivery. However, the complex top-down fabrication process of functional MN arrays is a bottleneck that hinders their widespread use. Here, we fabricate the tapered hollow MN array using a unique bi-level-tip by combining strain-engineering and capillary self-assembly of carbon nanotube (CNT) microstructures. Strain-engineering facilitated by the offset pattern of the catalyst enables the growth of bent, bi-level CNT microstructures while capillary self-assembly helps in constituting the tapered geometry of MNs. The bottom-up fabrication that consists of only two standard photolithography steps and CNT growth to form the scaffold of MNs followed by a polymer (polyimide) reinforcement step to impart mechanical stiffness to MNs provides scalable and fewer processing steps. The tapered shape of the MN allows an 8 times smaller force to pierce and penetrate the skin compared to the straight MN. The liquid delivery rate of the bi-level-tip MN is measured to be 26% better than the flat tip MN of the same lumen size as its geometry reduces skin clogging effect at the needle tip. In addition, cytotoxicity tests verify that the polyimide reinforced CNT-MNs are biocompatible for future in vivo applications.

Morphological Versatility in the Self-Assembly of Val-Ala and Ala-Val Dipeptides.

Since the discovery of dipeptide self-assembly, diphenylalanine (Phe-Phe)-based dipeptides have been widely investigated in a variety of fields. Although various supramolecular Phe-Phe-based structures including tubes, vesicles, fibrils, sheets, necklaces, flakes, ribbons, and wires have been demonstrated by manipulating the external physical or chemical conditions applied, studies of the morphological diversity of dipeptides other than Phe-Phe are still required to understand both how these small molecules respond to external conditions such as the type of solvent and how the peptide sequence affects self-assembly and the corresponding molecular structures. In this work, we investigated the self-assembly of valine-alanine (Val-Ala) and alanine-valine (Ala-Val) dipeptides by varying the solvent medium. It was observed that Val-Ala dipeptide molecules may generate unique self-assembly-based morphologies in response to the solvent medium used. Interestingly, when Ala-Val dipeptides were utilized as a peptide source instead of Val-Ala, we observed distinct differences in the final dipeptide structures. We believe that such manipulation may not only provide us with a better understanding of the fundamentals of the dipeptide self-assembly process but also may enable us to generate novel peptide-based materials for various applications.

Anemone-like nanostructures for non-lithographic, reproducible, large-area, and ultra-sensitive SERS substrates.

The melt-infiltration technique enables the fabrication of complex nanostructures for a wide range of applications in optics, electronics, biomaterials, and catalysis. Here, anemone-like nanostructures are produced for the first time under the surface/interface principles of melt-infiltration as a non-lithographic method. Functionalized anodized aluminum oxide (AAO) membranes are used as templates to provide large-area production of nanostructures, and polycarbonate (PC) films are used as active phase materials. In order to understand formation dynamics of anemone-like structures finite element method (FEM) simulations are performed and it is found that wetting behaviour of the polymer is responsible for the formation of cavities at the caps of the structures. These nanostructures are examined in the surface-enhanced-Raman-spectroscopy (SERS) experiment and they exhibit great potential in this field. Reproducible SERS signals are detected with relative standard deviations (RSDs) of 7.2-12.6% for about 10,000 individual spots. SERS measurements are demonstrated at low concentrations of Rhodamine 6G (R6G), even at the picomolar level, with an enhancement factor of ∼10(11). This high enhancement factor is ascribed to the significant electric field enhancement at the cavities of nanostructures and nanogaps between them, which is supported by finite difference time-domain (FDTD) simulations. These novel nanostructured films can be further optimized to be used in chemical and plasmonic sensors and as a single molecule SERS detection platform.

Pluronic polymer capped biocompatible mesoporous silica nanocarriers.

A facile self-assembly method is described to prepare PEGylated silica nanocarriers using hydrophobic mesoporous silica nanoparticles and a pluronic F127 polymer. Pluronic capped nanocarriers revealed excellent dispersibility in biological media with cyto- and blood compatibilities.

A new multiresponsive drug delivery system using smart nanogels.

This paper addresses the synthesis and characterization of a novel temperature- and pH-responsive nanogel system based on poly(vinylcaprolactam-co-2-dimethylaminoethyl methacrylate) [P(VCL-co-DMAEMA)] by using a surfactant-free emulsion polymerization procedure for the multiresponsive drug delivery of hydrophobic drugs. The effects of solvent, monomer, pH, and temperature were studied to tailor the average particle hydrodynamic diameters and the polydispersity index of the final particles. According to dynamic light-scattering measurements, the obtained nanogels show a narrow particle-size distribution and their hydrodynamic diameters can be varied from 81 to 368 nm. The nanogels display a re-entrant phase-transition state, and the equilibrium volume swelling ratio of the nanogels decreases drastically down to 47 °C and then increases up to 65 °C. In addition, the nanogels show pH-dependent behavior. They exhibit a maximum size at pH 5.0. Rhodamine B (RhB) was chosen as a model compound for drug loading and release studies from P(VCL-co-DMAEMA) on the basis of particles in different phosphate buffer solutions at different temperatures. The temperature/pH-dependent cumulative release and ultrasound-enhanced pulsatile release properties were investigated for RhB-loaded nanogels for long-term and one-shot delivery. The nanogels display efficient delivery for both long-term and one-shot delivery systems. We provide here a proof of concept for the novel use of multiresponsive nanogels having an overall size below 200 nm as a cargo system for hydrophobic drugs and for controlled release mediated by temperature/pH and ultrasound.

Extremely fast and highly selective detection of nitroaromatic explosive vapours using fluorescent polymer thin films.

A novel sensing material based on pyrene doped polyethersulfone worm-like structured thin film is developed using a facile technique for detection of nitroaromatic explosive vapours. The formation of π-π stacking in the thin fluorescent film allows a highly sensitive fluorescence quenching which is detectable by the naked eye in a response time of a few seconds.

Preparation of a novel polymer-modified si surface for DNA immobilization.

The design of a novel polymer-modified overlayer composed of PPAPE and GPMS on a silicon wafer for immobilization of DNA molecules is described. After hydroxylation of Si(100) surfaces, GPMS molecules were self-assembled onto these surfaces. PPAPE molecules were then covalently attached to the epoxy-terminated surfaces. The incubation time and concentration of PPAPE was found to effect both layer thickness and water CA. The type of organic solvent and the pH were found to change the nature of the PPAPE-modified surface for DNA immobilization. It is concluded that PPAPE-modified surfaces show advantages for DNA immobilization by electrostatic interactions between DNA molecules and positively charged free amino groups of the PPAPE-modified surfaces at the appropriate pH values.