Fabrication of guided-mode resonance elements by nanoimprint lithography.

This paper addresses utilization of nanoimprint lithography for fabrication of nanopatterned resonant photonic elements. These compact periodic films resonate sharply when illuminated with light. The attendant spectral and angular signatures are useful in design of photonic devices for various applications. It is of interest to design and optimize resonant leaky-mode elements with prescribed filtering, polarization, and security attributes. Applying nanoimprint lithography techniques, we fabricate prototype devices using polymer materials produced by Dymax Corporation. The initial prototypes are designed for use in the near-IR and telecommunications spectral regions. We apply holographic surface-relief gratings as master templates. With these templates, we have formed submasters in PDMS (polydimethylsiloxane) to function as imprint stamps for the soft lithography steps. Using these submasters, we fabricate periodic surfaces in UV-curable polymers with resonant films deposited on the surface by sputtering. Several example devices possessing resonance efficiencies exceeding 90% are presented along with their spectral and angular characteristics.

In vitro hemocompatibility studies of drug-loaded poly-(L-lactic acid) fibers.

Our objective was to evaluate the hemocompatibility of biodegradable stent fibers, employing a closed-loop circulation system filled with human blood. We also investigated the effects of the anti-inflammatory and anti-proliferative drugs curcumin and paclitaxel, incorporated into stent fibers. Fresh whole blood was circulated in four parallel closed-loop systems: the empty tube circuit (control) and tubes containing either a PLLA fiber coil (PLLA), a curcumin-loaded PLLA coil (C-PLLA) or a paclitaxel-loaded PLLA coil (P-PLLA). The influence of PLLA fiber, alone or loaded with drug incorporated during melt-extrusion, on leukocyte and platelet adhesion and activation was determined by flow cytometry. The effects of blood flow and fiber properties on cell deposition were assessed by scanning electron microscopy (SEM). The flow cytometry results clearly demonstrated that PLLA triggers blood cell activation at the site of deployment, as shown by increases in CD11b, CD62P and leukocyte-platelet aggregates, compared to controls. Curcumin and paclitaxel treatments both significantly reduced leukocyte and platelet activation and adhesion to PLLA fibers, as shown by flow cytometry and SEM. Activated leukocytes and platelets revealed significantly lower CD11b and CD62P receptor binding for C-PLLA compared with PLLA alone, and slightly lower for P-PLLA. Reductions in platelet-leukocyte aggregates were observed as well. In addition, there was less leukocyte and platelet adhesion to C-PLLA, compared with PLLA fiber controls, as shown by SEM. A continuous linear thrombus, composed of platelets, leukocytes, red blood cells and fibrin was occasionally detected along the line of tangency between the coil and the tube wall. Flow separation and eddying, proximal and distal to the line of tangency of coil and tube, is thought to contribute to this deposit. Curcumin was more effective than paclitaxel in reducing leukocyte and platelet activation and adhesion to PLLA stent fibers in this setting. However there was evidence of paclitaxel degeneration during melt extrusion that may have inhibited its effectiveness. Incorporation of the anti-inflammatory and anti-proliferative drug curcumin into bioresorbable stent fibers is proposed to prevent thrombosis and in-stent restenosis.