Girish Chitnis

Laser-treated hydrophobic paper: an inexpensive microfluidic platform

We report a method for fabricating inexpensive microfluidic platforms on paper using laser treatment. Any paper with a hydrophobic surface coating (e.g., parchment paper, wax paper, palette paper) can be used for this purpose. We were able to selectively modify the surface structure and property (hydrophobic to hydrophilic) of several such papers using a CO(2) laser. We created patterns down to a minimum feature size of 62±1 µm. The modified surface exhibited a highly porous structure which helped to trap/localize chemical and biological aqueous reagents for analysis. The treated surfaces were stable over time and were used to self-assemble arrays of aqueous droplets. Furthermore, we selectively deposited silica microparticles on patterned areas to allow lateral diffusion from one end of a channel to the other. Finally, we demonstrated the applicability of this platform to perform chemical reactions using luminol-based hemoglobin detection.

A Minimally Invasive Implantable Wireless Pressure Sensor for Continuous IOP Monitoring

This paper presents a minimally invasive implantable pressure sensing transponder for continuous wireless monitoring of intraocular pressure (IOP). The transponder is designed to make the implantation surgery simple while still measuring the true IOP through direct hydraulic contact with the intraocular space. Furthermore, when IOP monitoring is complete, the design allows physicians to easily retrieve the transponder. The device consists of three main components: 1) a hypodermic needle (30 gauge) that penetrates the sclera through pars plana and establishes direct access to the vitreous space of the eye; 2) a micromachined capacitive pressure sensor connected to the needle back-end; and 3) a flexible polyimide coil connected to the capacitor forming a parallel LC circuit whose resonant frequency is a function of IOP. Most parts of the sensor sit externally on the sclera and only the needle penetrates inside the vitreous space. In vitro tests show a sensitivity of 15 kHz/mmHg with approximately 1-mmHg resolution. One month in vivo implants in rabbits confirm biocompatibility and functionality of the device.

A batch-fabricated laser-micromachined PDMS actuator with stamped carbon grease electrodes

In this note, we report on the development of a batch-fabricated laser-micromachined elastomeric cantilever actuator composed of a polydimethylsiloxane (PDMS) bilayer (active/inactive) and soft-lithographically patterned conductive carbon grease electrodes. The described unimorph structure has a low actuation voltage and large out-of-plane displacement. For a 4 mm long, 1 mm wide, and 80 µm thick actuator, an out-of-plane displacement of 1.2 mm and a maximum force of 25 µN were measured using 450 V actuation voltage.

Ferrofluid-Impregnated Paper Actuators

In this paper, we report on an inexpensive method of fabricating miniature magnetic actuators using ferrofluid impregnated paper. Different types of papers (including soft tissue paper, cleanroom paper, Whatman-1 filter paper, printer paper, and newspaper) were loaded with oil-based ferrofluid, microma-chined by a CO2 laser and coated with a thin layer of parylene-C. The soaking capability of the different papers was investigated, with the soft tissue paper having the highest loading capacity, being able to absorb ferrofluid by as much as six times its original weight. Cantilever actuators fabricated from cleanroom and filter papers were able to generate the largest force (>; 40-mg equiva lent force), whereas the soft-tissue-paper cantilevers provided the greatest deflection (40° tip angle).

A thermophone on porous polymeric substrate

In this Letter, we present a simple, low-temperature method for fabricating a wide-band (>80 kHz) thermo-acoustic sound generator on a porous polymeric substrate. We were able to achieve up to 80 dB of sound pressure level with an input power of 0.511 W. No significant surface temperature increase was observed in the device even at an input power level of 2.5 W. Wide-band ultrasonic performance, simplicity of structure, and scalability of the fabrication process make this device suitable for many ranging and imaging applications.

Laser-assisted fabrication of batteries on wax paper

The functionality of paper-based diagnostic devices can be significantly enhanced by their integration with an on-board energy source. Here, we demonstrate the fabrication of paper-based electrochemical cells on wax paper using CO2 laser surface treatment and micromachining. A four cell zinc–copper battery shows a steady open-circuit voltage of ~3 V and can provide 0.25 mA for at least 30 min when connected to a 10 kΩ load. Higher voltages and current values can be obtained by adjusting the number and size of electrochemical cells in the battery without changing the fabrication process.

A Batch-Fabricated Single-Layer Elastomeric Actuator With Corrugated Surface

In this paper, we report on the first lasermicromachined batch-fabricated single-layer elastomeric actuator with a corrugated surface profile. The structural material of the cantilever actuator is a single [polydimethylsiloxane (PDMS)] layer, and electrodes are soft lithographically patterned conductive carbon grease. The asymmetric corrugated surface provides a bending moment in a single PDMS layer without the need for a second inactive layer. An actuator which is 5 mm long, 1 mm wide, and 80 μm thick can generate up to 2-mm out-of-plane displacement with zero applied force and 15 μN at zero deflection while consuming 20 μW of static power when actuated with 500 V.

In vivo brain electrophoresis – a novel method for chemotherapy of CNS diseases

Objective: The blood–brain barrier (BBB) is a protective mechanism that does its job superbly. So much so, that hitherto, brain chemotherapy has been limited by it. In fact, very few agents are effective against brain disease due to the inherent difficulties of penetrating the BBB. We describe a novel, extremely focused method for delivering drugs to specific diseased areas. This innovative method directly delivers putative substances to the pathological area, bypassing the BBB. Treatment of brain diseases could be improved by targeted, controlled delivery of therapeutic substances to diseased cerebral areas. Our described novel method – in vivo electrophoresis – achieves this. Methods: This technique was evaluated in beagles after craniotomy was performed and a custom-designed plate with electrodes inserted. The delivery of charged substances to selected areas with predictably guided movement was achieved via a created electrical field. Gadolinium, a compound unable to cross the BBB, was injected intracerebrally whereas an electrical field was created using the implanted electrodes surrounding the injection area. The electrical field-guided Gadolinium movement was evaluated using MRI. Results: Gadolinium was moved predictably using the created electrical field without complications. Conclusions: The experiment successfully demonstrated controlled movement of the substance. This technique can significantly change treatment of brain diseases because substances: i) may be moved in a controlled, predictable way – exponentially increasing therapeutic interactions with the target; and ii) no longer need to conform to constraints dictated by the BBB (molecular mass < 500 d; lipophilic), thereby increasing potential number of usable substances.

An ocular tack for minimally invasive continuous wireless monitoring of intraocular pressure

This paper presents a novel minimally invasive implantable pressure sensing transponder for continuous wireless monitoring of intraocular pressure (IOP). The transponder was designed to make the implantation and retrieval surgery simple while still measuring the true IOP through direct hydraulic contact with the intraocular space. Most parts of the sensor sit externally on the sclera and only a micro-needle penetrates inside the vitreous space through pars plana. In vitro tests showed a sensitivity of 15 kHz/mmHg with about 1 mmHg resolution. In vivo tests included one month implantation in rabbits, confirming the device biocompatibility and functionality.

Thermoelectric energy scavenging with temperature gradient amplification

In this paper, we demonstrate the application of fluorocarbon evaporative cooling in thermoelectric energy scavenging. The fabrication and performance characterization of a prototype micro-device is presented. The device consists of a thermoelectric generator mounted on a silicon substrate and encapsulated in a poly(dimethylsiloxane) chamber with a flexible cover. By filling the chamber with a fluorocarbon liquid of low boiling point (34°C), we were able to increase the body heat contact harvested energy by 226% compared to a device encapsulated in air. The availability of a variety of fluorocarbon liquids with different boiling points allows this harvesting amplification scheme to be used in a wide range of applications.