Jeffrey Chun-Hui Lin

Highly flexible, transparent and patternable parylene-C superhydrophobic films with high and low adhesion

This paper reports the first parylene-C based superhydrophobic films with high or low adhesion for potential droplet-based microfluidics. By creating hierarchical dual-scale micro/nanostructures and applying various plasma treatments, both biomimetic designs of lotus leaf effect with high contact angle and low adhesion, and petal effect with high contact angle but high adhesion, are demonstrated. Due to parylenes properties, these superhydrophobic films are highly flexible and transparent. Moreover, selective patterning of hydrophilic and superhydrophobic areas on a single film is also achieved. The combination of flexibility, transparency, selective patterning and simple fabrication makes our superhydrophobic films compare favorably to other designs.

Minimally Invasive Parylene Dual-Valved Flow Drainage Shunt for Glaucoma Implant

A parylene-enabled microvalved shunt implant for glaucoma drainage is presented in this paper. Enabled by the dual-checkvalve operation, this device can physically drain the extra intraocular fluid and regulate the intraocular pressure (IOP) within the normal range (15-20 mmHg). Improved surgical features, in addition to the functional/microfluidic components, such as parylene-tube carrier and anchors, are also incorporated in such device to realize minimally invasive suture-less implantation, suitable for practical in vivo use. With the optimized micromachining and post-fabrication process procedures, the developed implant is the first checkvalved glaucoma drainage device (GDD), which is passive, consumes no additional power, and functions without any circuit involved to pursue its medical application.

Feeling the Pressure: A Parylene-Based Intraocular Pressure Sensor

Intraocular pressure (IOP) is important for the prevention and treatment of certain human eye diseases. For example, glaucoma is the second leading cause of blindness in the world according to the World Health Organization [1]. The majority of glaucoma patients have an IOP >; 20 mmHg (compared with a normal IOP of 10 mmHg), which could damage patients optic nerves in the backside of the eye and cause irreversible blindness. Currently, there is no cure for glaucoma, but with early diagnosis and proper treatment, the visual loss can be slowed or eliminated. Due to the lack of other symptoms or pain, and the eyes ability to compensate for loss of peripheral vision, many glaucoma patients are unaware of the diseases development until it is severe. In fact, only half of the patients in the United States are aware of having glaucoma. Therefore, early diagnosis and treatment are important to prevent blindness. Thus, a device to diagnose early-stage glaucoma is in demand.

High quality factor parylene-based intraocular pressure sensor

A new concept of the intraocular pressure (IOP) sensor design and its implantation approach are presented in this paper. A parylene-based sensing part with about 30 μm in thickness was fabricated, and then integrated with an implantation tube attached to sensors backside pressure access hole. During the implantation, only the implantation tube was implanted into the anterior chamber to fulfill minimally invasive implantation. The IOP sensor membrane is thin and flexible so that it can attach to the cornea. Because the sensing area was exposed outside to the air all the time, the quality factor can be kept at 27-30 to maintain the sensing distance during the whole testing pressure range. The sensitivity is obtained as high as 542 ppm/mmHg while the responsivity is about 205 kHz/mmHg, which is suitable for biomedical applications.

Creep of parylene-C film

The glass transition temperature of as-deposited parylene-C is first measured to be 50°C with a ramping-temperature-dependent modulus experiment. The creep behavior of parylene-C film in the primary and secondary creep region is then investigated below and above this glass transition temperature using a dynamic mechanical analysis (DMA) machine Q800 from TA instruments at 8 different temperatures: 10, 25, 40, 60, 80, 100, 120 and 150°C. The Burgers model, which is the combined Maxwell model and Kelvin-Voigt model, fits well with our primary and secondary creep data. Accordingly, the results show that theres little or no creep below the glass transition temperature. Above the glass transition temperature, the primary creep and creep rate increases with the temperature, with a retardation time constant around 6 minutes.

Viscoplasticity of parylene-C film at body temperature

As parylene-C, a thermal plastic, has been extensively used as an implant material, its viscoplastic behavior at body temperature has never been systematically studied. Presented here is the first extensive in vitro study of the viscoplastic behaviors of 20-μm-thick parylene-C film at 37°C. The viscoplastic behaviors are investigated by uniaxial tensile tests at different strain rates (Figure 2), cyclic loading/unloading test (Figure 3) abrupt strain rate changing (Figure 4), creep-recovery (Figure 5), and stress-relaxation (Figure 6). There are three major conclusions here. First, below a stress of 2.5MPa, no observable viscoplastic behavior of 20-μm-thick parylene-C is found. Secondly, parylene-C film is a strain (or stress) and strain-rate dependent viscoplastic material. Thirdly, Burgers model is adequate to describe both creep and stress relaxation behaviors. In addition, the rate of the creep recovery (modeled with a single time constant) and stress relaxation (modeled with two time constants) decreases with increasing applied stress and/or strain.

Fluorescent Labeling, Sensing and Differentiation of Leukocytes from Undiluted Whole Blood Samples

In this paper, we demonstrated leukocyte labeling, sensing and differentiation from undiluted human whole blood samples with microfabricated devices. A challenging issue in leukocyte sensing from blood samples is the required high dilution level, which is used mainly to prevent interference from the overwhelmingly outnumbered erythrocytes. Dilution is undesirable for micro hemacytometers. It not only increases sample volume and processing time, but also requires mixing and buffer storage for on- chip implementation. Unlike commercial bulk instruments and previous efforts by other groups, we completely eliminated the requirement for dilution by staining leukocytes specifically with fluorescent dye acridine orange (AO) in undiluted human whole blood and then sensing them in microfluidic devices. Green fluorescent signal centered at 525 nm was used for leukocyte count and red fluorescent signal centered at 650 nm was used for leukocyte differentiation. Throughput of one hundred leukocytes per second was achieved, which means operation time for one sample only requires several seconds.

Cracking pressure control of parylene checkvalve using slanted tensile tethers

MEMS check valves with fixed cracking pressures are important in micro-fluidic applications where the pressure, flow directions and flow rates all need to be carefully controlled. This work presents a new surface-micromachined parylene check valve that uses residual thermal stress in the parylene to control its cracking pressure. The new check valve uses slanted tethers to allow the parylene tensile stress to apply a net downward force on the valving seat against the orifice. The angle of the slanted tethers is made using a gray-scale mask to create a sloped sacrificial photoresist with the following tether parylene deposition. The resulted check valves have both the cracking pressures and flow profiles agreeable well with our theoretical analysis.

Ex Vivo implantation study of minimally invasive glaucoma drainage device

We present in this paper the first ex vivo implantation results of our minimally invasive glaucoma drainage device (GDD.) The GDD is designed to treat glaucoma patients by draining out their extraneous aqueous humor out of the anterior chamber utilizing a MEMS micro-fluidic normally closed (NC) check valve. The NC check valve is encapsulated in protective tubing made from parylene C, which has been proved to be biocompatible in implantation. A new packaging and a bench-top testing procedure is established to characterize the integrated GDD prior to its implantation into enucleated porcine eyes. Pre-implanted characterization curve demonstrates a cracking pressure of 10–20 mmHg of the NC check valve, which agrees with our theoretical design. Ex vivo implantation results show that cracking pressure is measured as 24 mmHg by unloading the eye pressure. The little offset of the cracking pressure comes from the differences between the in vitro and ex vivo testing environments. The hysteresis behavior of the NC check valve is also examined during implantation and is presented here.

A simple all-parylene in-channel pop-up checkvalve with controllable cracking pressure

We present here a new surface-micromachined, all-parylene (para-xylylene), in-channel, normally-closed pop-up checkvalve with a designable cracking pressure. The cracking pressure is created by the mechanical residual tensile stress introduced by a popping mechanism. Moreover, an even higher cracking pressure can be achieved by thermal annealing before popping, which adds another degree of freedom to control the cracking pressure. The checkvalves can be easily micro machined combined with parylene channels to form a fully independent micro fluidic regulating system. A testing chip is designed to test the fabricated device sealed with photoresist which can be released by acetone afterward. This work demonstrated a cracking pressure of 0.17 psi by the popping and 0.32 psi by the combined thermal annealing (at 140°C) and popping. The final device is designed as 6 mm long, which is useful for heath care or any biomedical applications.