Controlling Supramolecular Structures of Drugs by Light.

Controlling physicochemical properties of light-unresponsive drugs, by light, prima facie, a paradox approach. We expanded light control by ion pairing light-unresponsive salicylate or ibuprofen to photoswitchable azobenzene counterions, thereby reversibly controlling supramolecular structures, hence the drugs' physicochemical and kinetic properties. The resulting ion pairs photoliquefied into room-temperature ionic liquids under ultraviolet light.

Photo-induced structural modification of silk gels containing azobenzene side groups.

Azobenzene modification of Bombyx mori silkworm silk creates a photo-responsive 'azosilk' biomaterial, allowing for 3D laser patterning. Written regions fluoresce, and become fluid-filled raised 'micro-blisters' with a 10-fold photo-softening effect of the modulus. Patterning is facile and versatile, with potential applications as soft tunable materials for dynamic cell guidance and microfluidics.

High-resolution nanomechanical analysis of suspended electrospun silk fibers with the torsional harmonic atomic force microscope.

Atomic force microscopes have become indispensable tools for mechanical characterization of nanoscale and submicron structures. However, materials with complex geometries, such as electrospun fiber networks used for tissue scaffolds, still pose challenges due to the influence of tension and bending modulus on the response of the suspended structures. Here we report mechanical measurements on electrospun silk fibers with various treatments that allow discriminating among the different mechanisms that determine the mechanical behavior of these complex structures.

Photoresponsive retinal-modified silk-elastin copolymer.

The chimeric proteins, silk-elastin-like protein polymers (SELPs), consist of repeating units of silk and elastin to retain the mechanical strength of silk, while incorporating the dynamic environmental sensitivity of elastin. A retinal-modified SELP was prepared, modified, and studied for photodynamic responses. The protein was designed, cloned, expressed, and purified with lysine present in the elastin repeats.

Osteoblastic differentiation and stress response of human mesenchymal stem cells exposed to alternating current electric fields.

Background: Electric fields are integral to many biological events, from maintaining cellular homeostasis to embryonic development to healing. The application of electric fields offers substantial therapeutic potential, while optimal dosing regimens and the underlying mechanisms responsible for the positive clinical impact are poorly understood.

Methods: The purpose of this study was to track the differentiation profile and stress response of human bone marrow derived mesenchymal stem cells (hMSCs) undergoing osteogenic differentiation during exposure to a 20 mV/cm, 60 kHz electric field.

Supercontinuum trap stiffness measurement using a confocal approach.

We report a novel method for characterizing the stiffness of white light supercontinuum tweezers, in which the nonlinear photonic crystal fiber used for supercontinuum generation is also utilized as an effective confocal pinhole to track the motion of a trapped bead and as a scan head to realize rapid scanning of the optical trap. By measuring the phase of the bead's motion in following the trap, a lateral stiffness value of about 7.9 μN/m was obtained with supercontinumm power of about 75 mW.

Bioactive silk protein biomaterial systems for optical devices.

Silk-based biomaterial systems have been previously explored for a variety of medical and nonmedical materials needs. The unique biophysical features of silks provide options to generate highly tailored structures and morphologies with this unique family of fibrous proteins. To exploit these features, we have optimized the all aqueous processing of silk fibroin into novel surface nanopatterned protein materials.

Microscopic flow measurements with optically trapped microprobes.

The use of optical tweezers to measure micrometer-resolution velocity fields in fluid flow is demonstrated as an extension of a scanning confocal viscosity microscope. This demonstration is achieved by detection of the motion of an optically trapped microsphere in an oscillating laser trap. The technique is validated by comparison with an independent video-based measurement and applied to obtain a two-dimensional map of the flow past a microscopic wedge.

Imaging microscopic viscosity with confocal scanning optical tweezers.

The techniques of confocal microscopy and optical tweezers have shown themselves to be powerful tools in biological and medical research. We combine these methods to develop a minimally invasive instrument that is capable of making hydrodynamic measurements more rapidly than is possible with other devices. This result leads to the possibility of making scanning images of the viscosity distribution of materials around biopolymer-producing cells.

Simple fabrication technique for rapid prototyping of seamless cylindrical microchannels in polymer substrates.

This article presents a simple and novel method for the fabrication of cylindrical microchannels in polymer or biopolymer substrates. This process results in highly regular, cylindrical microchannels, suitable both to the transport of liquid and the transmission of light. This method eliminates issues associated with positioning tolerances characteristic of conventional fabrication techniques, such as soft lithography.

Terahertz parametric generation photonic band gap structure with negligible structural dispersion in the optical range.

We present a photonic band gap (PBG) structure (or nonlinear photonic crystal) design for terahertz (THz) wave parametric generation, whose component materials have a small refractive index difference in the near infrared and a large index difference for THz waves. The structural dispersion of such a PBG structure is strong in the THz range but negligible in the optical range. The former allows the phase-matched pump wavelength to be placed in the near infrared to eliminate two-photon absorption of the pump and signal beams.

Cascaded nonlinear difference-frequency generation of enhanced terahertz wave production.

Cascaded nonlinear optical interactions are analyzed for their potential to overcome quantum-defect related limitations on the efficiency of terahertz wave difference-frequency generation. The dispersion of ZnTe permits phase-matched production of a series of Stokes lines from two initial near-infrared beams. As the pump beams run down the Stokes ladder, the number of terahertz photons continually increases.

Measuring microscopic viscosity with optical tweezers as a confocal probe.

We demonstrate, what is to the best our knowledge, a new method for studying the motion of a particle trapped by optical tweezers; in this method the trapping beam itself is used as a confocal probe. By studying the response of the particle to periodic motion of the tweezers, we obtain information about the medium viscosity, particle properties, and trap stiffness. We develop the mathematical model, demonstrate experimentally its validity for our system, and discuss advantages of using this method as a new form of scanning photonic force microscopy for applications in which a high spatial and temporal resolution of the medium viscosity is desired.