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Feiqiao Yu - One of the best experts on this subject based on the ideXlab platform.

  • NEMS - Integration of slanted tether check-valves for high Pressure applications
    2011 6th IEEE International Conference on Nano Micro Engineered and Molecular Systems, 2011
    Co-Authors: Feiqiao Yu
    Abstract:

    We present a new approach to assemble multiple parylene check-valves to create a new device for high Pressure microfluidic applications. By assembling several residual-stress-enhanced slanted tether check-valves in series, the Cracking Pressure of several psi can be easily achieved. The valve is modeled by extended valve theory considering the unsteady flow effect at the beginning of ckeck-covering plate's opening. A new equivalent diode model is also proposed to analyze and predict the check-valves' microfluidic behavior. Check-valves with thermally pre-stressed slanted tethers are chosen due to its remarkable high Cracking Pressure of each single check-valve. The slanted tethers are made using linearized partial exposure lithography technique and the tensile stress of the tethers is controlled by annealed in different temperatures. The size of each packaged single check-valve can be as small as 2 mm in length and 850 µm in diameter and the final packaged device with several integrated check-valves is capable of regulating Pressure up to several psi. The testing result shows a higher Cracking Pressure with more check-valves, proving the series additivity of this model and integration. With its small size and high Pressure regulating capability, the new check-valve system can be used to perform high Pressure control application where the implantation space is limited. Different kind of parylene check-valves can also be combined to reach different Pressure range using this packaging approach.

  • Integration of slanted tether check-valves for high Pressure applications
    2011 6th IEEE International Conference on Nano Micro Engineered and Molecular Systems, 2011
    Co-Authors: Feiqiao Yu
    Abstract:

    We present a new approach to assemble multiple parylene check-valves to create a new device for high Pressure microfluidic applications. By assembling several residual-stress-enhanced slanted tether check-valves in series, the Cracking Pressure of several psi can be easily achieved. The valve is modeled by extended valve theory considering the unsteady flow effect at the beginning of ckeck-covering plate's opening. A new equivalent diode model is also proposed to analyze and predict the check-valves' microfluidic behavior. Check-valves with thermally pre-stressed slanted tethers are chosen due to its remarkable high Cracking Pressure of each single check-valve. The slanted tethers are made using linearized partial exposure lithography technique and the tensile stress of the tethers is controlled by annealed in different temperatures. The size of each packaged single check-valve can be as small as 2 mm in length and 850 μm in diameter and the final packaged device with several integrated check-valves is capable of regulating Pressure up to several psi. The testing result shows a higher Cracking Pressure with more check-valves, proving the series additivity of this model and integration. With its small size and high Pressure regulating capability, the new check-valve system can be used to perform high Pressure control application where the implantation space is limited. Different kind of parylene check-valves can also be combined to reach different Pressure range using this packaging approach.

  • NEMS - Ex Vivo implantation study of minimally invasive glaucoma drainage device
    2010 IEEE 5th International Conference on Nano Micro Engineered and Molecular Systems, 2010
    Co-Authors: Feiqiao Yu, Sınav Saati, Rohit Varma, Mark S. Humayun
    Abstract:

    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.

  • NEMS - Stiction of parylene C to silicon surface measured using blister tests
    2010 IEEE 5th International Conference on Nano Micro Engineered and Molecular Systems, 2010
    Co-Authors: Feiqiao Yu, Po-jui Chen
    Abstract:

    Micro-fabricated biocompatible check valves are integral parts of many implantable micro-fluidic devices. The Cracking Pressure of check valves is usually controlled by stiction between polymeric films and the underlying substrate. The following paper presents the first comprehensive study of stiction between parylene and silicon surfaces. The valves are fabricated using surface micromachining with parylene C as the structural material. Deep Reactive Ion Etching (DRIE) is used to create through holes in the wafer for the passage of fluids. Blister test is employed to calculate stiction. From experimental results, stiction between parylene C and silicon surfaces is found to be 2.59 J/m2, which is comparable to the stiction between silicon and other polymeric thin films.

  • Cracking Pressure control of parylene checkvalve using slanted tensile tethers
    2010 IEEE 23rd International Conference on Micro Electro Mechanical Systems (MEMS), 2010
    Co-Authors: Feiqiao Yu
    Abstract:

    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.

Po-jui Chen - One of the best experts on this subject based on the ideXlab platform.

  • NEMS - Stiction of parylene C to silicon surface measured using blister tests
    2010 IEEE 5th International Conference on Nano Micro Engineered and Molecular Systems, 2010
    Co-Authors: Feiqiao Yu, Po-jui Chen
    Abstract:

    Micro-fabricated biocompatible check valves are integral parts of many implantable micro-fluidic devices. The Cracking Pressure of check valves is usually controlled by stiction between polymeric films and the underlying substrate. The following paper presents the first comprehensive study of stiction between parylene and silicon surfaces. The valves are fabricated using surface micromachining with parylene C as the structural material. Deep Reactive Ion Etching (DRIE) is used to create through holes in the wafer for the passage of fluids. Blister test is employed to calculate stiction. From experimental results, stiction between parylene C and silicon surfaces is found to be 2.59 J/m2, which is comparable to the stiction between silicon and other polymeric thin films.

  • Parylene stiction
    2010 IEEE 23rd International Conference on Micro Electro Mechanical Systems (MEMS), 2010
    Co-Authors: Feiqiao Yu, Po-jui Chen
    Abstract:

    This paper presents a preliminary study into stiction between parylene C and substrate surfaces for biocompatible check-valve applications. During fabrication, parylene C is used as the structural material for the check-valve. The substrate surfaces studied include Au, Al, Si, parylene C, XeF2 treated Si, and silicon dioxide. Stiction between different surfaces is created after sacrificial photoresist etching. Then, the stiction is measured using blister tests, and stiction mechanisms for different materials are investigated. The devices are released with different recipes to examine their effects. Finally, the results of the study reveal methods to control the Cracking Pressure of parylene check-valves.

  • Stiction of parylene C to silicon surface measured using blister tests
    2010 IEEE 5th International Conference on Nano Micro Engineered and Molecular Systems, 2010
    Co-Authors: Feiqiao Yu, Po-jui Chen
    Abstract:

    Micro-fabricated biocompatible check valves are integral parts of many implantable micro-fluidic devices. The Cracking Pressure of check valves is usually controlled by stiction between polymeric films and the underlying substrate. The following paper presents the first comprehensive study of stiction between parylene and silicon surfaces. The valves are fabricated using surface micromachining with parylene C as the structural material. Deep Reactive Ion Etching (DRIE) is used to create through holes in the wafer for the passage of fluids. Blister test is employed to calculate stiction. From experimental results, stiction between parylene C and silicon surfaces is found to be 2.59 J/m2, which is comparable to the stiction between silicon and other polymeric thin films.

  • Floating-Disk Parylene Microvalves for Self-Pressure-Regulating Flow Controls
    Journal of Microelectromechanical Systems, 2008
    Co-Authors: Po-jui Chen, Damien C Rodger, Mark S. Humayun
    Abstract:

    This paper presents the first parylene-based floating-disk microvalve with self-Pressure-regulating characteristics for various microfluidic applications. By incorporating a free-floating disk diaphragm with no anchoring/tethering structures to constrain its movement, the microvalve realizes configurable Pressure-based flow-shunting functions in a stand-alone fashion. Its passive operation eliminates the need for power sources or the external actuation of the device. A multilayer polymer surface-micromachining technology is utilized for device fabrication by exploiting parylene C (poly-chloro-p-xylylene) as the biocompatible structural material for high mechanical compliance as compared with other conventional thin-film materials. Experimental results successfully demonstrate that the in-channel microvalves control water flows in the following two different shunt designs: 1) a nearly ideal regular check valve with zero forward-Cracking Pressure, zero reverse leakage, and 1.25 times1013 - 2.09 times 1013 Nldrs/m5 (0.03-0.05 psildrmin/muL, 1.55-2.59 mmHgldrmin/muL) of fluidic resistance; and 2) a Pressure-bandpass check valve with 0-100 mmHg and 0-10 muL/min of Pressure and flow rate regulation ranges, respectively, as well as 4.88 ×1013 Nldrs/m5 (0.12 psi middotmin/muL, 6.08 mmHg middotmin/muL) of fluidic resistance in the forward conductive region. Such a biocompatible and implantable microvalve has the great potential of being integrated in microfluidic systems to facilitate effective microflow control for lab-on-a-chip and biomedical applications. [2008-0055].

  • microfluidic valve having free floating member and method of fabrication
    2007
    Co-Authors: Yuchong Tai, Po-jui Chen, Damien C Rodger, Mark S. Humayun
    Abstract:

    Micro check valves having a free-floating member for controlling flow of fluid in microfluidic and biomedical applications and methods of fabrication. A micro check valve includes a valve seat, a valve cap that contacts the valve seat and an untethered floating member that can move between the valve seat and the valve cap. Certain micro check valves have zero Cracking Pressure and no reverse leakage. Certain other valves may be configured to permit flow of fluid within a Pressure range. The floating member can be solid or define an orifice, and the valve seat can have one or two levels. Valves can be configured to allow fluid to flow when the floating member is pushed by fluid against the valve cap or against the valve seat. The valve seat may be silicon or another material that is compatible with micromachining processes, and the valve cap and the floating member may be a polymer such as Parylene.

J C Galvez - One of the best experts on this subject based on the ideXlab platform.

  • modelling of concrete cover Cracking due to non uniform corrosion of reinforcing steel
    Construction and Building Materials, 2017
    Co-Authors: Santiago Guzman, J C Galvez
    Abstract:

    Abstract This paper addresses the modelling of non-uniform corrosion in reinforced concrete. An uneven distribution of rust around the perimeter of the rebar is considered which represents the most common situation in real concrete structures and, especially, when they are exposed to a chloride environment. A comparison with the conventional approach based on a uniform corrosion and expansion Pressure around the rebar is performed in both Cracking Pressure and Cracking radial displacement terms. As a result, surface Cracking appears much earlier in the case of non-uniform corrosion with corresponding vertical surface displacements being rather higher, with such an effect becoming more evident as cover increases. Finally, distinct Cracking patterns are derived through the proposed embedded cohesive crack model by means of a practical example.

Mark S. Humayun - One of the best experts on this subject based on the ideXlab platform.

  • NEMS - Ex Vivo implantation study of minimally invasive glaucoma drainage device
    2010 IEEE 5th International Conference on Nano Micro Engineered and Molecular Systems, 2010
    Co-Authors: Feiqiao Yu, Sınav Saati, Rohit Varma, Mark S. Humayun
    Abstract:

    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.

  • Ex Vivo implantation study of minimally invasive glaucoma drainage device
    2010 IEEE 5th International Conference on Nano Micro Engineered and Molecular Systems, 2010
    Co-Authors: Feiqiao Yu, Sınav Saati, Rohit Varma, Mark S. Humayun
    Abstract:

    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 passive MEMS drug delivery pump for treatment of ocular diseases
    Biomedical Microdevices, 2009
    Co-Authors: Ronalee Lo, Rajat N. Agrawal, Sınav Saati, Po Ying Li, Mark S. Humayun, Ellis Meng
    Abstract:

    An implantable manually-actuated drug delivery\r\ndevice, consisting of a refillable drug reservoir, flexible\r\ncannula, check valve, and suture tabs, was investigated as a new approach for delivering pharmaceuticals to treat chronic ocular diseases. Devices are fabricated by molding and bonding three structured layers of polydimethylsilox-ane. A 30 gauge non-coring needle was used to refill the reservoir; this size maximized the number of repeated refills while minimizing damage to the reservoir. The check valve Cracking Pressure was 76±8.5 mmHg (mean ± SE, =4);the valve sustained > 2000 mmHg of reverse Pressure without leakage. Constant delivery at 1.57±0.2µL/sec and 0.61±0.2µL/sec (mean ± SE, =4) under 500 mmHg and\r\n250 mmHg of applied Pressure, respectively, was obtained in benchtop experiments. The valve closing time constant was 10.2 s for 500 mmHg and 14.2 s for 250 mmHg. Assembled devices were successfully demonstrated in benchtop,ex vivo , and in vivo experiments.

  • Floating-Disk Parylene Microvalves for Self-Pressure-Regulating Flow Controls
    Journal of Microelectromechanical Systems, 2008
    Co-Authors: Po-jui Chen, Damien C Rodger, Mark S. Humayun
    Abstract:

    This paper presents the first parylene-based floating-disk microvalve with self-Pressure-regulating characteristics for various microfluidic applications. By incorporating a free-floating disk diaphragm with no anchoring/tethering structures to constrain its movement, the microvalve realizes configurable Pressure-based flow-shunting functions in a stand-alone fashion. Its passive operation eliminates the need for power sources or the external actuation of the device. A multilayer polymer surface-micromachining technology is utilized for device fabrication by exploiting parylene C (poly-chloro-p-xylylene) as the biocompatible structural material for high mechanical compliance as compared with other conventional thin-film materials. Experimental results successfully demonstrate that the in-channel microvalves control water flows in the following two different shunt designs: 1) a nearly ideal regular check valve with zero forward-Cracking Pressure, zero reverse leakage, and 1.25 times1013 - 2.09 times 1013 Nldrs/m5 (0.03-0.05 psildrmin/muL, 1.55-2.59 mmHgldrmin/muL) of fluidic resistance; and 2) a Pressure-bandpass check valve with 0-100 mmHg and 0-10 muL/min of Pressure and flow rate regulation ranges, respectively, as well as 4.88 ×1013 Nldrs/m5 (0.12 psi middotmin/muL, 6.08 mmHg middotmin/muL) of fluidic resistance in the forward conductive region. Such a biocompatible and implantable microvalve has the great potential of being integrated in microfluidic systems to facilitate effective microflow control for lab-on-a-chip and biomedical applications. [2008-0055].

  • microfluidic valve having free floating member and method of fabrication
    2007
    Co-Authors: Yuchong Tai, Po-jui Chen, Damien C Rodger, Mark S. Humayun
    Abstract:

    Micro check valves having a free-floating member for controlling flow of fluid in microfluidic and biomedical applications and methods of fabrication. A micro check valve includes a valve seat, a valve cap that contacts the valve seat and an untethered floating member that can move between the valve seat and the valve cap. Certain micro check valves have zero Cracking Pressure and no reverse leakage. Certain other valves may be configured to permit flow of fluid within a Pressure range. The floating member can be solid or define an orifice, and the valve seat can have one or two levels. Valves can be configured to allow fluid to flow when the floating member is pushed by fluid against the valve cap or against the valve seat. The valve seat may be silicon or another material that is compatible with micromachining processes, and the valve cap and the floating member may be a polymer such as Parylene.

Byung Hwan Oh - One of the best experts on this subject based on the ideXlab platform.

  • effects of non uniform corrosion on the Cracking and service life of reinforced concrete structures
    Cement and Concrete Research, 2010
    Co-Authors: Bong Seok Jang, Byung Hwan Oh
    Abstract:

    The purpose of this study is to explore the effects of non-uniform corrosion on Cracking behavior of concrete cover. The effects of non-uniform corrosion distribution, cover-to-rebar diameter ratio, and concrete compressive strength on the Cracking Pressure of concrete cover were studied. The present study indicates that the Pressures to cause Cracking of concrete cover under non-uniform corrosion conditions are much smaller than those under uniform corrosion case. The Cracking Pressure decreases up to about 60% depending upon the types of non-uniform corrosion distributions. It was also shown that cover-to-rebar diameter ratio and concrete compressive strength affect greatly the Cracking Pressure of concrete cover. Realistic equations on the Cracking Pressure of concrete cover were derived. The comparisons of analysis results with the test data on the Cracking Pressure of concrete cover show fairly good agreement. Finally, the effect of non-uniform corrosion on the service life of concrete structures was discussed.