Rohit Modi

Generation of mesoscopic patterns of viable Escherichia coli by ambient laser transfer

We have generated mesoscopic patterns of viable Escherichia coli on Si(1 1 1), glass, and nutrient agar plates by using a novel laser-based transfer process termed matrix assisted pulsed laser evaporation direct write (MAPLE DW). We observe no alterations to the E. coli induced by the laser-material interaction or the shear forces during the transfer. Transferred E. coli patterns were observed by optical and electron microscopes, and cell viability was shown through green fluorescent protein (GFP) expression and cell culturing experiments. The transfer mechanism for our approach appears remarkably gentle and suggests that active biomaterials such as proteins, DNA and antibodies could be serially deposited adjacent to viable cells. Furthermore, this technique is a direct write technology and therefore does not involve the use of masks, etching, or other lithographic tools.

Direct writing of conformal mesoscopic electronic devices by MAPLE DW

Abstract We demonstrate a novel pulsed UV laser direct writing technique called MAPLE DW for the fabrication of conformal electronic devices. MAPLE DW (matrix assisted pulsed laser evaporation direct write) is a soft laser forward transfer technique that takes place in air and at room temperature. Specific experimental results for the deposition of Ag metal and BaTiO3 composite dielectrics with electrical quality comparable to conventional thick film deposition techniques will be given as well as a discussion of the relevant issues for further electronic device improvement. The mechanism of the MAPLE DW process that makes it applicable to a broad class of electronic materials and even biomaterials is also described.

Dielectric properties of oxide structures by a laser-based direct-writing method

Matrix-assisted pulsed laser evaporation direct-write (MAPLE-DW) is a laser-based method of directly writing mesoscopic patterns of electronic materials. Patterns of composite BaTiO 3 /SiO 2 /TiO 2 dielectric material were written onto Pt/Au interdigitated-electrode test structures, with precise control over final dielectric properties. Scanning electron microscopy indicates random close-packed structures of BaTiO 3 and SiO 3 particles, with interstitial spaces partially filled with titania. Depending on the BaTiO 3 :silica ratio, the dielectric constant ranged from 5 to 55 and followed a 4-component logarithmic rule of mixing. This work demonstrates that the transfer process and the final material properties of MAPLE-DW oxide materials are largely decoupled.

Laser direct writing of microbatteries for integrated power electronics

A novel laser-based process developed at the Naval Research Laboratory has been used to fabricate pseudocapacitors and microbatteries with tailored capacities for small electronic devices having size and/or weight restrictions. This process, called MAPLE DW (for matrix-assisted pulsed-laser evaporation direct write) can deposit rugged mesoscale (1 micrometers to 10 mm) electronic components over any type of substrate. A pulsed laser operating at 355 nm is used to forward transfer material from a tape-cast ribbon to a suitable substrate to form a precision design. With MAPLE DW, customized mesoscale electronic components can be produced, eliminating the need for multiple fabrication techniques and surface-mounted components. Direct write processing is especially attractive for the fabrication of micro-power sources and systems. The versatility of laser processing allows battery designs to be easily modified. Batteries and/or pseudocapacitors can be integrated with power management electronics to deliver a wide range of power outputs. By building power sources directly on electronic components, the weight of the power sources is decreased as the electronic substrate becomes part of the battery packaging and the lengths of interconnects are shortened, reducing conductor losses. RuOxHy pseudocapacitors deposited with MAPLE DW show good storage capacities. Pads of hydrous RuO2 having dimensions of 2.2 mm x 1.0 mm x 30 micrometers have been deposited in a planar configuration on gold current collectors. Rechargeable Zn/MnO2 alkaline microbatteries comprising of MnO2, Zn, an ethyl cellulose separator barrier layer and a KOH electrolyte have also been fabricated by MAPLE DW. The resulting structures with dimensions of 1.5 mm x 1.5 mm x 60 micrometers represent the first demonstration of a multilayer microbattery made by MAPLE DW. The performance of these prototypes are shown and the potential impact of MAPLE DW for the fabrication of novel microbattery systems for integrated power applications are discussed.

Matrix Assisted Pulsed Laser Evaporation-Direct Write (Maple-Dw): A New Method to Rapidly Prototype Organic and Inorganic Materials

This chapter overviews the Matrix Assisted Pulsed Laser Evaporation-Direct Write (MAPLE-DW) as a novel laser-based direct-write process that is capable of generating mesoscopic patterns ranging from 10μm to 5mm in feature size of any material, ranging from metals and ceramics to biological materials and polymers. The primary advantage of MAPLE-DW over similar direct-write methods is that any material that takes the form of a rheological fluid, polymer-based composite or fine powder can be directly written into mesoscopic patterns using MAPLE-DW. Therefore, MAPLE-DW offers wide range of flexibility in terms of starting raw materials. The chapter illustrates the methodology of the MAPLE-DW technique, along with the current understanding of the writing mechanism. . and the applications that include the direct writing of metals and ceramics, composite resistor, and phosphor patterns for display applications. Recent results on the direct writing of active proteins and two types of living cells, underscoring the utility of MAPLE-DW in the nascent field of engineered, biological-based mesoscale technology are reviewed as well.

MAPLE Direct Write (DW) patterning of Bio-active Ceramic Nanocomposites

A laser-based approach, Matrix Assisted Pulsed Laser Direct Write (MAPLE) technique is used to demonstrate two-dimensional direct writing of ceramics such as hydroxyl-apatite and zirconia, for developing inorganic scaffolds. We also demonstrate the patterning of live MG63 osteoblast cells onto various substrates. Our results show successful direct writing of ceramics and live cells concurrently, with a growth profile similar to that of as-deposited cells. After several days of growth, a live/dead assay shows live cells suggesting the biocompatibility of the ceramic and the viability of the process. This investigation demonstrates a novel method of developing heterogeneous tissue scaffolds, such as a cell-ceramic composite by CAD/CAM patterns.

Matrix Assisted Pulsed Laser Evaporation of Dexamethasone Thin Films

We have demonstrated deposition of dexamethasone thin films via matrix assisted pulsed laser evaporation (MAPLE). Infrared analysis revealed that dexamethasone thin films deposited by MAPLE and by drop casting had a similar absorbance spectra. AFM imaging of the MAPLE-deposited dexamethasone thin film revealed 2–10 μm punctuate ring-like structures. Deposited dexamethasone was tested for positive bioactivity by treating primary microglia cells with lipopolysacchride and measuring nitric oxide (NO) production. The successful deposition of dexamethasone thin films can be used on neural implants to prevent tissue injury and inflammatory response.