Development of all polymer-based nanofluidic devices using replication technologies, which is a prerequisite for providing devices for a larger user base, is hampered by undesired substrate deformation associated with the replication of multi-scale structures. Therefore, most nanofluidic devices have been fabricated in glass-like substrates or in a polymer resist layer coated on a substrate. This letter presents a rapid, high fidelity direct imprinting process to build polymer nanofluidic devices in a single step. Undesired substrate deformation during imprinting was significantly reduced through the use of a polymer stamp made from a UV-curable resin. The integrity of the enclosed all polymer-based nanofluidic system was verified by a fluorescein filling experiment and translocation/stretching of λ-DNA molecules through the nanochannels. It was also found that the funnel-like design of the nanochannel inlet significantly improved the entrance of DNA molecules into nanochannels compared to an abrupt nanochannel/microfluidic network interface.
A novel biomass-mediated method to synthesize cellulose-stabilized silver nanoparticles (SNPs) and incorporate them into biocompatible/bioabsorbable poly-L-lactic acid (PLLA) for producing SNP-PLLA nanocomposite thin films was developed and the antimicrobial efficacy and biocompatibility of the SNP-PLLA films were studied. The formation and coating morphology of SNPs were characterized with UV-visible spectrophotometry and transmission electron microscopy (TEM), and the release rate of silver ion from the SNP-PLLA films was determined by inductively coupled plasma-optical emission spectrometry. Antimicrobial testing of the SNP-PLLA films performed with Staphylococcus aureus and Escherichia coli according to ISO 22196 standards demonstrated that the SNP-PLLA nanocomposite films with a SNP concentration of 700 ppm reduced colonies forming unit (CFU) counts by 99.8 and 99.99%, respectively. Despite the significant antimicrobial activity, the nanocomposite films with the same SNP concentration had little effect on the viability of human HeLa cells. This strategy that has been developed for the synthesis of nanoparticles and the formation of composite films demonstrates promise for reducing perioperative surgical site infections associated with indwelling devices.
A simple method was developed to obtain the polymerization shrinkage stress exerted on the sidewalls of resist/stamp interface in ultraviolet nanoimprint lithography. This method is based on the measurements of demolding force which is the sum of adhesion and friction forces. The mean polymerization shrinkage stress on the sidewalls can readily be decoupled from overall demolding force by independently measuring the friction coefficient, adhesion force and geometries of stamp structures. The polymerization shrinkage stress on the sidewalls is overall larger than adhesion and increases by adding more cross-linking agent to the resist composition. This indicates that in addition to lowering the adhesion at the resist/stamp interface, development of resists with low degrees of shrinkage during UV curing is critical to reducing demolding force. It was also found that the shrinkage stress depends not only on the resist composition but also the stamp structure. A pillar structured stamp leads to a larger stress than a stamp with gratings with identical depth and width.
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