Femtosecond laser fabrication and characterization of microchannels and waveguides in methacrylate-based polymers

Femtosecond laser ablation is a promising method for producing polymeric microfluidic devices: it is a high precision processing technology resulting from an efficient energy deposition, while simultaneously minimizing heat conduction and thermal damage to the surrounding material. This work reports on the characterization of microchannels and waveguides fabricated by femtosecond laser technology in methacrylate-based polymers, precisely in thermoplastic poly(methyl methacrylate) (PMMA) and in a new material based on a high efficiency UV-curing process of methacrylic monomers bearing hydrophilic polyethylene glycol chains, namely tetraethylene glycol dimethacrylate and poly(ethylene glycol) methacrylate (PEG-MA). Microchannels in PMMA and PEG-MA, fabricated by parallel multi-scans, have sharp edges and low roughness, as investigated by Environmental Scanning Electron Microscopy and laser profilometer. Surface and physico-chemical properties after fs-laser processing were further studied by contact angle measurements and Attenuated Total Reflectance FTIR spectroscopy. Moreover, preliminary tests showed the refractive index of fs-laser PEG-MA exposed zones is different with respect to that of the surrounding polymer, suggesting that PEG-MA can be a good candidate to manufacture microfluidic devices containing integrated optic elements.     

Oxide nanocrystal based nanocomposites for fabricating photoplastic AFM probes

We report on the synthesis, characterization and application of a novel nanocomposite made of a negative tone epoxy based photoresist modified with organic-capped Fe(2)O(3) nanocrystals (NCs). The mechanical properties of the nanocomposite drastically improve upon incorporation of a suitable concentration of NCs in the polymer, without deteriorating its photolithography performance. High aspect ratio 3D microstructures made of the nanocomposite have been fabricated with a uniform surface morphology and with a resolution down to few micrometres. The embedded organic-capped Fe(2)O(3) NCs drastically increase the stiffness and hardness of the epoxy based photoresist matrix, making the final material extremely interesting for manufacturing miniaturized polymer based mechanical devices and systems. In particular, the nanocomposite has been used as structural material for fabricating photoplastic Atomic Force Microscopy (AFM) probes with integrated tips showing outstanding mechanical response and high resolution imaging performance. The fabricated probes consist of straight cantilevers with low stress-gradient and high quality factors, incorporating sharp polymeric tips. They present considerably improved performance compared to pure epoxy based photoresist AFM probes, and to commercial silicon AFM probes.     

Rheological properties and thermal transitions in millable polyurethane fluoroelastomers

A series of segmented polyurethane fluoroelastomers based on dimethylol‐terminated perfluoropolyethers (PFPEs), aliphatic diisocyanates and allyl functionality is presented. Depending on the type of diisocyanate monomer used, it was found that quite different prepolymer molecular weights were achieved. Thermal analysis by differential scanning calorimetry showed formation of polyphasic copolymers, either amorphous or semi‐crystalline depending on the monomer structure. Rheological measurements showed that much higher zero‐shear viscosity, a shorter Newtonian plateau and more marked shear thinning behaviour were achieved with polyurethanes based on hexamethylene diisocyanate (HDI) or H₁₂‐MDI monomers. Isothermal viscosity curves were fitted with either three‐ or two‐parameter empirical models, and relaxation times of the structures were estimated at the temperature of 120 °C. Copyright © 2004 Society of Chemical Industry     

SEAS, a secure e-voting protocol: Design and implementation

This paper presents SEAS, the Secure E-voting Applet System, a protocol for implementing a secure system for polling over computer networks, usable in distributed organizations whose members may range up to dozens of thousands. We consider an architecture requiring the minimum number of servers involved in the validation and voting phases. Sensus, [Cranor L, Cytron RK. Sensor: a security-conscious electronic polling system for the internet. In: Proceedings of HICSS'97. IEEE; 1997. p. 561–70], a well-known e-voting protocol, requires only two servers, namely a validator and a tallier. Even if satisfying most of the security requirements of an e-voting system, Sensus suffers from a vulnerability that allows one of the entities involved in the election process to cast its own votes in place of those that abstain from the vote. SEAS is a portable and flexible system that preserves the limited number of servers of Sensus, but it avoids the mentioned vulnerability. We propose a prototype implementation of SEAS based on Java applet and XML technology.     

The stethoscope. A potential source of nosocomial infection?

OBJECTIVE: To determine the relation between epidural injectate volume (ml/kg of body weight) and its craniad migration in calves and pigs. ANIMALS: 23 neonatal calves and 26 feeder pigs. PROCEDURE: Animals were randomly assigned to receive different volumes of new methylene blue (NMB, 1.2 mg/ml in 0.9% saline solution). Injections were made into the sacrococcygeal intervertebral space in calves and the lumbosacral intervertebral space in pigs, immediately after euthanasia. Sagittal sections of the spine were made at necropsy, and craniad migration of NMB was determined and rounded to the nearest intervertebral space. RESULTS: In calves treated with 0.05, 0.1, or 0.15 ml of NMB/kg, mean +/- SEM number of stained spinal segments was 5 +/- 0.3, 8 +/- 0.6, and 8 +/- 0.6, respectively. Craniad migration of NMB was significantly greater for 0.15 and 0.1 ml/kg volumes versus 0.05 ml/kg. In pigs treated with 0.05, 0.1, 0.2, of 0.3 ml of NMB/kg, mean number of stained spinal segments was 8 +/- 1.1, 8 +/- 0.9, 10 +/- 1.2, and 18 +/- 2.0. Craniad dye migration was significantly greater in the 0.3 ml/kg group versus the 3 lower volume groups. Linear regression performed on both sets of data after logarithmic transformation of spaces migrated to correct for non-normality was significant (P < 0.05), and R2 values of 0.49 and 0.55 were obtained for calves and pigs, respectively. CONCLUSIONS: There is a significant correlation between volume (ml/kg) of NMB injected in the epidural space and its craniad migration in calves and pigs. CLINICAL RELEVANCE: Results provide a basis for determination of volume of injectate to be given to reach a minimal desired level and should be a useful baseline for future investigations of epidural drug administration.