DMD-based 3D printing is a powerful tool for making high-resolution biomimetic functional tissues and organs with various biomaterials for tissue engineering and regenerative medicine. A plethora of tissues have been fabricated using this technology including liver, heart, lung, kidney, blood vessels, cartilage, and placenta. In this article, we show prevascularization of the artificial tissue constructs using DMD-based 3D printing, which is essential to maintain the long term viability and function of a thick tissue. We also show a 3D printed biomimetic hepatic model that recapitulates the microarchitecture as well as the heterogeneous cell population of various cell types in the native liver tissue. It is important for the biomaterials to mimic the native microenvironment. Finally, we demonstrate that 3D printed tissue-specific decellularized extracellular matrix can improve cell response and behavior.
A major problem of current silicon thin film solar cells lies in low carrier collection efficiency due to short carrier diffusion length. Instead of improving the collection efficiency in a relatively thick solar cell, increasing light absorption while still keeping the active layer thin is an alternative solution. Absorption enhancement in a thin film Si solar cell by incorporating a two-dimensional periodic metallic nanopattern was investigated using three-dimensional finite element analysis. By studying the enhancement effect brought by different materials, dimensions, coverage, and dielectric environments of the metal nanopattern, we found that absorption enhancement occurs at wavelength range outside surface plasmons resonance of the nanostructures. The exploitation of the nanostructures also enhances the Fabry-Perot resonance in the active layer. It plays an important role in optimizing the absorption of the solar cell.
An aggressive pursuit for ever decreasing the minimum feature size in modern integrated circuit has lead to various challenges in nanofabrication. Finer feature size is very desirable in microelectronics and other applications for higher performance. However, it is difficult to achieve critical dimensions at sub-wavelength scale using traditional optical lithography techniques due to the optical diffraction limit. We developed several techniques to overcome this diffraction limit and simultaneously achieve massive, parallel patterning. One of the methods involves the principle of optical near-field enhancement between the spheres and substrate when irradiated by a laser beam, for obtaining the nano-features. Nonlinear absorption of the enhanced optical field between the spheres and substrate sample was believed to be the primary reason for the creation of nano-features. Also, we utilized the near-field enhancement around nanoridges and nanotips upon pulsed laser irradiation to produce line or dot patterns in nanoscale on gold thin films deposited on glass substrates. We demonstrated that the photolithography can be extended to a sub-wavelength resolution for patterning any substrate by exciting the surface plasmons on both metallic mask and a shield layer covering the substrate. We used laser-assisted photothermal imprinting method for directly nanopatterning carbon nanofiber-reinforced polyethylene nanocomposite.
A technique to create nanopatterns on hard-to-machine bulk silicon carbide (SiC) with a laser beam is presented. A monolayer of silica (SiO2) spheres of 1.76-µm and 640-nm diameter are deposited on the SiC substrate and then irradiated with an Nd:YAG laser of 355 and 532 nm. The principle of optical near-field enhancement between the spheres and substrate when irradiated by a laser beam is used for obtaining the nanofeatures. The features are then characterized using a scanning electron microscope and an atomic force microscope. The diameter of the features thus obtained is around 150 to 450 nm and the depths vary from 70 to 220 nm.
This paper presents an optimized method for microgyroscope design. A lumped dynamic model is presented to optimize the microgyroscope performances. The parameters are categorized into function variables and style variables to reduce optimization cost. The maximum sensitivity and minimum area of the device are selected and weighted as the combined multiple objective functions. The optimization is conducted with a solver in Excel 9.5TM Finite element simulation is used to verify these optimized results. Simulation results show good agreement with the calculation. The optimized microgyroscope was fabricated. The resonant characteristic from experiment is compared with the optimized results and simulation results.
Polymerase chain reaction (PCR) is a well-described method for selective identical replication of DNA molecules. In recent years, many micromachined PCR chips have been reported. These miniaturized PCR chips have great advantages such as a significant reduction in reagent costs and vastly reduced reaction time over the conventional PCR devices. In this paper a micro analysis system that will allow submicro-liter scale, continuous-flow PCR to be conducted in a glass chip has been presented. This glass chip is achieved through thermally bonding two pyrex 7740 glass wafers. One pyrex wafer is etched to form a 20-cycle microchannel of 80 micron wide and 30 micron deep. The other pyrex wafer with microheaters is thermally bonded to the microchannel wafer to produce a closed continuous microchannel for PCR. The total length of the microchannel is 0.5 m. The size of this device is 56 mm 'e 24 mm 'e 1 mm. Three reaction temperatures are controlled by three PID controllers. This PCR chip has a significant reagent reduction with a volume of less than 1 micro-liter. With 1 micro-liter reagent, we get total reaction time of 0.5 min to 3 min depending on various flow rates. This analysis chip is fabricated using standard micromachining techniques. The advantages of this chip include small quantities of reagent needed, high throughput, rapid thermal cycling, and batch micro-fabrication resulting in a significant cost reduction.
New lithographic, deposition, and etching tools for micro fabrication on planar silicon substrates have led to remarkable advances in miniaturization of silicon devices. However silicon is often not the substrate material of choice for applications in which there are requirements for electrically or thermally insulating substrates, low capacitance, resistance to corrosion, or hermetic sealing. Some of the MEMS packaging materials such as ceramics, polymers, and glass are currently being used to fabricate many microdevices. To support the rapid advancements of non-silicon MEMS it is necessary to introduce innovative techniques to process these MEMS packaging materials. In this study we present the application of pulsed laser ablation of ceramics, polymers and glass (MEMS packaging materials) to assist in fabrication of MEMS devices. Microstructuring of Al2O3 ceramic, polymers Poly-Vinyl-Alcohol (PVA), polystyrene (PS), and Pyrex glass were performed and studied by pulsed lasers at 193-nm, 266-nm and 308-nm wavelengths.
A dynamic model for a PZT actuated valveless micropump is presented in this work. The model couples PZT actuation with fluid flow in a flow chamber. Extended Bernoulli equation is used to describe flow dynamics in the inlet and outlet of the micropump. The dependence of the output pressure and flow rate on pump parameters is discussed. For low frequency actuation, the flow rate and back pressure increase as the PZT membrane thickness increases. The flow rate also increases for larger nozzle neck. The back pressure increases as the nozzle neck enlarges, reaches a maximum at about 80 microns, and then decreases when the nozzle neck keeps increasing. Such dependence becomes insignificant for nozzle neck larger than 200 microns. This model also predicts that the neck length has little influence on the back pressure and flow rate.
This work investigates the transient process of melting and microscale surface deformation upon pulsed Nd:YLF laser heating of Ni-P hard disk substrates. The laser pulse energy is in the range of 1.0 (mu) J to 5.0 (mu) J. The features produced by laser heating have a diameter of approximately 15 micrometers and height in the tens of nanometers range. A laser flash photography system is developed to visualize the transient topography development during the laser texturing process. The system has a nanosecond time resolution and sub-micron spatial resolution. A numerical analysis based on finite difference method is conducted to simulate the microscale energy transport and fluid glow. Comparison between the numerical and the experimental result helps to understand the physical mechanism of the process.