Peptide-based strategies for enhanced cell uptake, transcellular transport, and circulation: Mechanisms and challenges.

Peptides are emerging as a new tool in drug and gene delivery. Peptide-drug conjugates and peptide-modified drug delivery systems provide new opportunities to avoid macrophage recognition and subsequent phagocytosis, cross endothelial and epithelial barriers, and enter the cytoplasm of target cells. Peptides are relatively small, low-cost, and are stable in a wide range of biological conditions. In this review, we summarize recent work in designing peptides to enhance penetration of biological barriers, increase cell uptake, and avoid the immune system. We highlight recent successes and contradictory results, and outline common emerging concepts and design rules. The development of sequence-structure-function relationships and standard protocols for benchmarking will be a key to progress in the field.

Rotation and alignment of anisotropic particles on nonplanar interfaces.

We study the alignment of micron-scale particles at air-water interfaces with unequal principle radii of curvature by optical microscopy. The fluid interface bends to satisfy the wetting conditions at the three phase contact line where the interface intersects the particle, creating deflections that increase the area of the interface. These deflections decay far from the particle. The far field interface shape has differing principle radii of curvature over length scales large compared to the particle. The deflections create excess area which depends on the angle of the particle with respect to the principle axes of the interface. We show that when particles create surface deflections with quadrupolar modes, the particles rotate to preferred orientations to minimize the free energy. In experiment, we focus on uniform surface energy particles, for which quadrupolar modes are forced by the particle shape. Analytical expressions for the torque and stable states are derived in agreement with experiment and confirmed computationally.

In situ study of the growth kinetics of individual island electrodeposition of copper.

The growth kinetics for individual islands during electrodeposition of copper have been studied using in situ transmission electron microscopy. We show that for sufficiently large overpotentials, the growth kinetics approach the rate laws expected for diffusion-limited growth of hemispherical islands, characterized by two distinct regimes. At short times, the island growth exponent is 0.5 as expected for diffusion-limited growth of uncoupled hemispherical islands, while at longer times, the growth exponent approaches 1/6 as expected for planar diffusion to the growing islands. These results provide the first direct measurements of the growth of individual islands during electrochemical deposition. However, quantitative comparison with rate laws shows that the island radii are smaller than predicted and the island densities are much larger than predicted, and we suggest that this is related to adatom formation and surface diffusion, processes which are not included in conventional growth models.

Poly(vinyl alcohol) : a potential matrix for glucose oxidase immobilization?

Considerable effort has been focused on the method of immobilizing glucose oxidase (GOD) for amperometric glucose biosensors since the technique employed may influence the available activity of the enzyme and thus affect the performance of the sensor. Narrow measuring range and low current response are still considered problems in this area. In this work, poly(vinyl alcohol)(PVA) was investigated as a potential matrix for GOD immobilization. GOD was entrapped in cross-linked PVA. The use of a PVA-GOD membrane as the enzymatic component of a glucose biosensor was found to be promising in both the magnitude of its signal and its relative stability over time. The optimum PVA-GOD membrane (cross-linking density of 0.06) was obtained through careful selection of the cross-linking density of the PVA matrix.

Poly(vinyl alcohol) : a potential matrix for glucose oxidase immobilization?

Considerable effort has been focused on the method of immobilizing glucose oxidase (GOD) for amperometric glucose biosensors since the technique employed may influence the available activity of the enzyme and thus affect the performance of the sensor. Narrow measuring range and low current response are still considered problems in this area. In this work, poly(vinyl alcohol)(PVA) was investigated as a potential matrix for GOD immobilization. GOD was entrapped in cross-linked PVA. The use of a PVA-GOD membrane as the enzymatic component of a glucose biosensor was found to be promising in both the magnitude of its signal and its relative stability over time. The optimum PVA-GOD membrane (cross-linking density of 0.06) was obtained through careful selection of the cross-linking density of the PVA matrix.

Fabrication of an all-polymer battery based on derivatized polythiophenes.

Conducting polymers that can be switched between an insulating neutral state and a conducting doped state are of interest for charge-storage applications such as secondary batteries. The authors report on the fabrication of an all-polymer battery incorporating derivatized polythiophene films electropolymerized onto graphite-coated polymeric supports and a polymer gel electrolyte film. The cells had discharge voltages of about 2.4 V and capacities of 9.5 to 11.5 mAh g-1. The elimination of any metallic components or liquids and the lightweight and flexible construction provide a unique alternative for secondary battery technology.

Fabrication and magnetic properties of arrays of metallic nanowires.

Arrays of ferromagnetic nickel and cobalt nanowires have been fabricated by electrochemical deposition of the metals into templates with nanometer-sized pores prepared by nuclear track etching. These systems display distinctive characteristics because of their one-dimensional microstructure. The preferred magnetization direction is perpendicular to the film plane. Enhanced coercivities as high as 680 oersteds and remnant magnetization up to 90 percent have also been observed.