Developing defect-tolerant demolding process in nanoimprint lithography

Demolding, the process to separate stamp from molded resist, is most critical to the success of ultraviolet nanoimprint lithography (UV-NIL). In the present study we first investigated adhesion and demolding force in UV-NIL for different compositions of a model UV-curable resist containing a base (either tripropyleneglycol diacrylate with shorter chain length or polypropyleneglycol diacrylate with longer chain length), a cross-linking agent (trimethylolpropane triacrylate) and a photoinitiator (Irgacure 651). The demolding force was measured using a tensile test machine after imprinting the UV resist on a silicon stamp. In general, the shorter monomer shows a larger demolding force. Decreasing the cross-linking agent content from 49 to 0 wt% results in a decreased adhesion force at the resist/stamp interface thereby facilitating the demolding. Demolding stress in general is mainly generated due to shrinkage of the resist in the UV curing step and also adhesion and friction at the stamp/resist interface in the subsequent demolding step. In the second part of this study the effect of resist compositions on the stress generation was studied by numerical simulation of the curing and demolding steps in UV-NIL. Input parameters required for the simulation were determined experimentally. As the cross-linking agent content increases the fracture strength of the resist also increases. At the same time, shrinkage stress due to cure and also adhesion at the stamp/resist interface both increase. By normalizing the overall maximum local stress by the fracture stress of the resist, we found that there is an optimum for the cross-linking agent content that leads to the most successful imprinting. In the third part of our study a simple method was developed to obtain the polymerization shrinkage stress exerted on the sidewalls of resist/stamp interface in UV NIL. 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

Conversion of Industrial Waste and Wastewaters into Lipids Suitable for Biodiesel Production

The potential of oleaginous yeast Rhodotorula glutinis for the sustainable production of biodiesel feedstock via fermentation of lignocellulosic biomass in pulp and paper wastewater as a fermentation media was investigated. The overall objective was to increase the levels of lipid feedstock in oleaginous yeast in order to reduce biodiesel production cost. To meet sustainable production of biodiesel, industrial wastewater and waste lignocellulose biomass were used as cultivation media and carbon source, respectively. Pulp and paper wastewater effluent was selected as a source of water and nutrients for the production of microbial lipids due to its environmental pollution as it creates large volume of wastewater discharge with high chemical oxygen demand (COD). Since medium composition and process fermentation condition can significantly affect the fermentative performance of oleaginous microorganisms, to find the optimum cultivation condition, design of experiment combined with RSM optimization technique was performed, which has been shown to be successful to predict the optimum condition for the biomass and lipid production in batch fermentation. In addition, lignocellulosic biomass hydrolysate was used as a substrate to improve the cost associated with feedstock fermentation. Lignocellulosic hydrolysate, a product of degradation of lignocelllosic biomass, contains degradation by-products such as 5- hydroxymethylfurfural (HMF), furfural and acetic acid that are known as major inhibitors that influences microorganism growth process. Therefore, their impacts on the fermentative performance and lipid productivity of oleaginous yeast were explored. A detailed operating condition and equipment design for the process of biocrude production from pulp and paper wastewater on a commercial scale was developed. A technological assessment of the process was performed to evaluate their technical benefits and limitations. Results show that pulp and paper wastewater can be used as a cultivation media for the production of microbial lipids using R. glutinis. However, its carbon content has to be improved. Analysis of the design and cost of the process showed that acid hydrolysis process using paper mill sludge as lignocellulosic biomass required the smallest process equipment units but at a higher raw material cost compared to fermentation process

Complete plastic nanofluidic devices for DNA analysis via direct imprinting with polymer stamps

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 lambda-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.close131

Creativity and destructiveness in art and psychoanalysis

This paper focuses on the creativity of the patient in analysis and compares it to that of the artist. Taking artists’ descriptions of their practices as its starting point, the paper suggests that the relationship between patient and analyst parallels that between artist and medium. Psychoanalysis and artistic process can both be seen in terms of a complex interplay between oneness and separateness in which aggression and destructiveness play an essential part. The paper includes a discussion of different forms of aggression and destructiveness within the creative process with particular reference to Winnicott’s paper ‘The Use of an Object’ and Rozsika Parker’s ‘The Angel in the House’. It suggests that a consideration of artists’ creative processes can shed light both on the experience of the patient in analysis and on the role of the analyst in facilitating the development of the patient’s creativity

Sprayable antibacterial Persian gum-silver nanoparticle dressing for wound healing acceleration

Wound infection is considered a significant challenge in skin injuries. Sprayable antibacterial wound dressings are interesting alternatives to their traditional counterparts because of their facile preparation, ease-of-use, and the possibility of topical delivery of antibacterial materials. Herein, novel sprayable antibacterial dressings are formulated and reported. The dressings were developed by in-situ formation of Ag-nanoparticles (Ag-NPs) using Persian gum (PG) as a carbohydrate polymer. Several tests were conducted to investigate the effect of polymer concentration on the sprayablity, biocompatibility, and antibacterial activity of the dressings (PG/Ag-NPs). Results showed that formulations up to 2 wt.% PG/Ag-NPs could be sprayed properly and form intact films. Antibacterial evaluations also showed biocidal activity of 1% PG/Ag-NPs against Pseudomonas aeruginosa and Staphylococcus aureus. Cytotoxicity and in vivo full-thickness wound healing evaluation confirmed that 1% PG/ Ag-NPs spray was safe and improved wound healing process. All the results confirmed the high potential of formulated sprayable dressings for wound repair.Peer reviewe

Poly(3-hydroxybutyrate) Production from Natural Gas by a Methanotroph Native Bacterium in a Bubble Column Bioreactor

Reducing the total cost of poly(3-hydroxybutyrate) (PHB) production as an attractive substitute for conventional petrochemical plastics still remains an unsolved problem. The aim of this research was the screening of PHB-producing microorganisms and selection of the best suitable medium for microbial growth and PHB production from methane. A new isolated methanotroph for PHB production from natural gas was studied in different media. After selection of the suitable medium, the effect of five process variables (content of nitrogen source, disodium hydrogen phosphate, methane to air ratio, seed age, and pH) on PHB production was investigated in a bubble column bioreactor. Also, hydrodynamic and mass transfer factors (flow regime, mixing time, gas hold up, and kLa) were considered. At optimum operating conditions and engineering parameters in a bubble column, PHB content in the dried biomass reached 25 % w/w. The results showed that pH is the most important variable in the selected conditions

Bioinspired Processing:Complex Coacervates as Versatile Inks for 3D Bioprinting

3D bioprinting is a powerful fabrication technique in biomedical engineering, which is currently limited by the number of available materials that meet all physicochemical and cytocompatibility requirements for biomaterial inks. Inspired by the key role of coacervations in the extrusion and spinning of many natural materials, hyaluronic acid-chitosan complex coacervates are proposed here as tunable biomaterial inks. Complex coacervates are obtained through an associative liquid-liquid phase separation driven by electrostatic attraction between oppositely charged macromolecules. They offer bioactive properties as well as facile modulation of their mechanical properties through mild physicochemical changes in the environment, rendering them attractive for 3D bioprinting. Fine-tuning the salt concentration, pH, and molecular weight of the constituent polymers results in biomaterial inks that are printable in air and water. The biomaterial ink, initially a viscoelastic fluid, transitions into a viscoelastic solid upon printing due to dehydration (for printing in air) or due to a change in pH and ionic composition (for printing in water). Consequently, scaffolds printed using the complex coacervate inks are stable without the need for post-printing processing. Cell culture scaffolds fabricated in this way are cytocompatible and show long-term topological stability. These results pave the way to a new class of easy-to-handle tunable biomaterials for biofabrication

Effect of Dynamically Arrested Domains on the Phase Behavior, Linear Viscoelasticity and Microstructure of Hyaluronic Acid - Chitosan Complex Coacervates

Complex coacervates make up a class of versatile materials formed as a result of the electrostatic associations between oppositely charged polyelectrolytes. It is well-known that the viscoelastic properties of these materials can be easily altered with the ionic strength of the medium, resulting in a range of materials from free-flowing liquids to gel-like solids. However, in addition to electrostatics, several other noncovalent interactions could influence the formation of the coacervate phase depending on the chemical nature of the polymers involved. Here, the importance of intermolecular hydrogen bonds on the phase behavior, microstructure, and viscoelasticity of hyaluronic acid (HA)-chitosan (CHI) complex coacervates is revealed. The density of intermolecular hydrogen bonds between CHI units increases with increasing pH of coacervation, which results in dynamically arrested regions within the complex coacervate, leading to elastic gel-like behavior. This pH-dependent behavior may be very relevant for the controlled solidification of complex coacervates and thus for polyelectrolyte material design.</p

Impact of mitochondrial alternative oxidase expression on the response of Nicotiana tabacum to cold temperature

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87094/1/j.1399-3054.2011.01471.x.pd

Scalable Nanopillar Arrays with Layer‐by‐Layer Patterned Overt and Covert Images

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108683/1/adma201401246.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/108683/2/adma201401246-sup-0001-S1.pd