Kang Wei | The Ohio State University (original) (raw)

Adaptive Optics by Kang Wei

Liquid lens offers a simple solution to achieve tunable optical powers. This approach, however, s... more Liquid lens offers a simple solution to achieve tunable optical powers. This approach, however, suffers from deteriorated resolution at high diopters. In this study, a plano-convex liquid lens with aspherical cross-section is developed. Such configuration allows for the lens profiles at high diopters to be close to spherical shapes by alleviating the edge-clamping effects. Resolution tests of a 6mm lens with optimized asphericity exhibit improved resolutions in both center and peripheral regions at 40 and 100 diopters than the lenses with planar membranes. It shows that aspherical membranes can improve the resolving power of liquid lenses at high diopters, thus providing a new route of optimizing the imaging performance of adaptive liquid lenses for various applications.

Unlike traditional focalization that recruits multiple moving lens elements to adjust focus, liqu... more Unlike traditional focalization that recruits multiple moving lens elements to adjust focus, liquid lenses deliver adaptive focusing by simply tuning the surface profile of liquid or the elastomer that encloses liquid. Its simple and compact configuration, low cost, and actuation efficiency promise wide industrial, medical, and consumer applications. Dielectric elastomers (DEs), one type of commercially available soft active material, have been a good fit for creating adaptive optics. In this Letter, we present an adaptive, membrane-sealed liquid lens hydrostatically coupled to a concentric annular DE actuator. Electric actuation deforms the annular DE, which induces fluid transmission between the lens part and the actuation part for lens actuation. The maximum measured focal range was from 25.4 to 105.2 mm within 1.0 kV, which significantly outperforms the existing DE-actuated liquid lenses and eliminates the need for prestraining. The lens also enables varied focal ranges by simply adjusting its initial surface sagitta, providing flexibility for practical imaging applications.

Insect compound eyes and human camera eyes are two exquisite optical systems created by nature. T... more Insect compound eyes and human camera eyes are two exquisite optical systems created by nature. The compound eye boasts an angle of view (AOV) up to 180° thanks to its hemispherical arrangement of hundreds of prime microscale lenses. The camera eye, on the other hand, can change shape to focus on objects at various depths, yet accepts light within a smaller AOV. Imitations of either imaging system have been abundant but with limited success. Here, we describe a reconfigurable polymeric optofluidic device that combines the architectural merits of both vision mechanisms, featuring a large AOV (up to 120°) with adaptive focusing capabilities (from 0 to 275 diopter (D)). This device consists of bi-layered microfluidics: an array of millimeter-sized fluidic lenses is integrated into the top layer and arranged on an elastomeric membrane embedded within the bottom layer. The membrane can be deformed from a planar surface into a series of dome-shaped geometries, rearranging individual fluidic lenses in desired curvilinear layouts. Meanwhile, each fluidic lens can vary its radius of curvature for a monocular depth sensation. Such a design presents a new perspective of tunable optofluidics for a broad range of applications , such as robotic vision and medical laparoendoscopy, where adaptive focalization with a large viewing angle is a clear advantage.

We report an adaptive optofluidic lens system that configures an elastomer-liquid singlet lens wi... more We report an adaptive optofluidic lens system that configures an elastomer-liquid singlet lens with 10 mm in diameter and a pair of elastomer-liquid binocular lenses where each single lens is with 3 mm in diameter for switchable two-dimensional (2D) and three-dimensional (3D) imaging. The singlet and the binoculars share the same optical channel and are arranged axially with the image sensor. The singlet enables 2D imaging with higher resolution, while the binoculars help to generate a stereoscopic image pair for 3D vision and depth perception. This study addresses the current difficulties of implementing both stereoscopic imaging capability and high optical resolution into small imaging devices, such as laparoendoscopes and miniaturized autofocus/zoom systems.

We present a smartphone based microscope using elastomer liquid lens as the objective to achieve ... more We present a smartphone based microscope using elastomer liquid lens as the objective to achieve adjustable magnification without lens displacement or replacement. The microscope is small enough to fit into a pocket wallet and can work with smartphone cameras. Instead of using an elastomer membrane with a constant thickness, a membrane with a varied thickness profile is used to reduce the working pressure for improved reliability. Compared to the existing smartphone based microscopes, this microscope allows adjustable magnification without the needs for compromising the miniaturization. It thus promises potential applications in point-of-care diagnostics and other on-chip optical inspections.

We present a membrane sealed fluidic lens that is hydrostatically connected to a concentric ring-... more We present a membrane sealed fluidic lens that is hydrostatically connected to a concentric ring-shaped electroactive elastomer. Electrical activation deforms the ring-shaped elastomer, which induces fluid passage between the lens part and the actuation part of the membrane. This changes the lens's shape and therefore the focal length. The focal length ranges from 25.4 mm to 105.2 mm can be obtained with a voltage bias of 1.0 kV. Comparing to the existing fluidic lenses driven by electroactive polymers, this lens has a wider range of refractive power at a significantly lower actuation voltage. Our device finds applications in miniaturized optical components where adaptive focalization is paramount.

Most of currently employed laparoscopes use a single and non-tunable solid lens to visualize the ... more Most of currently employed laparoscopes use a single and non-tunable solid lens to visualize the surgical environment during minimal invasive interventions. These devices are limited due to the loss of depth perception, fixed view direction and narrow field-of-view (FOV). In this study, a three-dimensional deformable liquid lens array with adaptive focusing and directional view capability is developed. Miniature liquid lenses sealed by deformable membranes are arranged on a flexible substrate. During the operation, the flexible substrate where the liquid lenses reside is driven by hydraulic pressure and bulges into different curvatures, which results in the maximal angular difference of the optical axes of individual lenses in the array from 0 o to 45 o. The focal length of each lens can be simultaneously tuned from 64.3mm to 2.1mm. At the directional view of 45 o and focal length of 2.1mm, the overall FOV exceeds 150 o. This work promises the potential of directional and wide angle laparoscopic imaging where space constraint is a concern.

Biomedical Microdevices by Kang Wei

Remote controlled capsule (RCC) has been extensively used in the field of site-specific drug deli... more Remote controlled capsule (RCC) has been extensively used in the field of site-specific drug delivery. It is a potent tool to study the regional drug absorption of the gastrointestinal (GI) tract that provides pharmaceutical scientists with significant pharmacokinetics data for oral drug formulation development. In present investigations, a patented novel RCC has been devised based on micro-electronic mechanical system (MEMS) technology. Micro-thrusters were for the first time exploited as drug release actuators of RCCs. As the micro-thruster is ignited by a radio frequency (RF) signal, the thrust force generated by the propellants pushes the piston forward and leads to a rapid and complete expulsion of therapeutic agents from the capsule. The micro-thruster merely consumes 120 mW for ignition and the duration time of drug release is decreased to less than 1 s. The feasibility of the novel RCC was evaluated through animal experiments in beagles using aminophylline as the model drug. The novel RCC developed is a promising alternative for site-specific drug delivery in human GI tract.

A novel solid propellant microthruster has been developed and used as the actuation assembly of a... more A novel solid propellant microthruster has been developed and used as the actuation assembly of a patented remote controlled capsule (RCC). It produces sufficient gas pressure to empty the drug reservoir within the RCC. A MEMS-based microigniter works as the critical component of the miniaturized thruster that houses the detonating agent – diazodintrophenol (DDNP) and the propellant – black powder. Ignition and combustion tests were performed to justify its feasibility and reliability. Results demonstrated that 166 mW power consumption led to one successful combustion and that complete and rapid drug release was achieved when the propellant ranged from 16 mg to 20 mg. The RCC integrated with the microthruster could provide a promising alternative for site-specific drug delivery in human GI tract.

In clinical practice, examination of the hemorrhagic spot (HS) remains difficult. In this paper, ... more In clinical practice, examination of the hemorrhagic spot (HS) remains difficult. In this paper, we describe a remote controlled capsule (RCC) micro-system with an automated, color-based sensor to identify and localize the HS of the gastrointestinal (GI) tract. In vitro testing of the detecting sensor demonstrated that it was capable of discriminating mimetic intestinal fluid (MIF) with and without the hemoglobin (Hb) when the concentration of Hb in MIF was above 0.05 g/ml. Therefore, this RCC system is able to detect the relatively accurate location of the HS in the GI tract.

A system is described here that can noninvasively control the navigation of freely behaving rat v... more A system is described here that can noninvasively control the navigation of freely behaving rat via ultrasonic, epidermal and LED photic stimulators on the back. The system receives commands from a remote host computer to deliver specified electrical stimulations to the hearing, pain and visual senses of the rat respectively. The results demonstrate that the three stimuli work in groups for the rat navigation. We can control the rat to proceed and make right and left turns with great efficiency. This experiment verified that the rat was able to reach a setting destination in the way of cable with the help of a person through the appropriate coordination of the three stimulators. The telemetry video camera mounted on the head of the rat also achieved distant image acquisition and helped to adjust its navigation path over a distance of 300 m. In a word, the non-invasive motion control navigation system is a good, stable and reliable bio-robot.

We report an on-board microfluidic pump driven by magnetic stir bar that can be integrated into t... more We report an on-board microfluidic pump driven by magnetic stir bar that can be integrated into the micro-total-analysis systems (µTAS) without micro-to-macro connection. Rotational magnetic field causes the spinning of the magnetic stir bar that generates centrifugal force to propel the flow. The pump controls both the flow rate and flow direction when positioned on specific locations of a magnetic stir plate set at varied spin velocities.

Micro and Nanofabrication by Kang Wei

Periodic micro/nanostructures with the characteristic dimensions at single or two length scales h... more Periodic micro/nanostructures with the characteristic dimensions at single or two length scales have manifested their strengths in providing contact cues to regulate cell alignment and motility, creating diffractive gratings for wavelength selection and pulse compression, and producing tailored surface wettability and adhesion. The currently used lithographic and surface wrinkling methods often require substantial use of special fabrication facilities and a cleanroom environment, and are accompanied by complicated fabrication processes. This paper systematically examines a facile benchtop wrinkling process to produce periodic micro/nanostructures and hierarchical topographies on elastomeric substrates in a general wet laboratory. Atmospheric electric discharge generated by a hand-held corona surface treater produces a rigid thin film atop an elastomeric foundation containing an initial tensile strain. Periodic sinusoidal wrinkled deformations with tailored wavelengths and amplitudes form spontaneously upon stress removal. This process is compatible with commercial tensile test machines and can create elastomeric micro/nanowrinkled structures within minutes. It can also be coupled with softlithography and/or photolithography to generate hierarchical wrinkled topographies with various degrees of anisotropy. This work provides a technical basis for versatile manufacturing of periodic and hierarchical wrinkled topographies at different length scales for various applications.

Silica nanoparticles coating and sintering is a widely-used approach for creating hydrophobic and... more Silica nanoparticles coating and sintering is a widely-used approach for creating hydrophobic and super-hydrophobic surfaces. The role of substrate material in this process, however, has not been thoroughly investigated. In this work, the role of substrate material is examined by measuring surface wettability of three different substrate materials (glass, polyimide and copper) under systematically varied conditions. These surfaces are modulated from hydrophilic (water contact angle (WCA) < 90 •) to superhydrophobic (WCA > 150 •) by coating and sintering silica nanoparticles, followed by assembling a layer of fluorine compound. Static WCA characterization shows that surface wettability is not solely dependent on the concentration of the coating colloidal, but is also on the substrate material. In particular, copper substrate exhibits a larger WCA than glass and polyimide substrates. Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and Atomic Force Microscopy (AFM) characterizations show that the substrate material-dependent wettability is attributed to thermal-induced nanostructures on the copper surface, which contributes to the hierarchical micro-/nano-topography. This finding is important for designing hydrophobic/superhydrophobic surfaces comprised of different materials, especially those that would experience thermal cycles in surface functionalization and subsequent use.

This paper reports an electrical discharge assisted surface wrinkling process to produce hierarch... more This paper reports an electrical discharge assisted surface wrinkling process to produce hierarchical and anisotropic surface patterns on polymethylsiloxane (PDMS). Highly ordered sinusoidal wrinkles with tailored height (h) and wavelength (λ) are fabricated by surface modification of a uniaxially pre-strained PDMS using a hand-held corona discharger followed by strain relaxation. The resulting nanoscale wrinkles overlay on 1) microwrinkled substrate and 2) reflowed microstructures to create anisotropic and hierarchical surface topographies. This electrical discharge assisted wrinkling process for creating multi-scale roughness is accessible in general wet lab environments. Such structures have broad applications in optical gratings, cell mechanics studies, and micro/nanofluidics.

A benchtop process is reported to create and pattern nanowrinkling structures on the polydimethyl... more A benchtop process is reported to create and pattern nanowrinkling structures on the polydimethylsiloxane (PDMS) surface. Electrical discharge generates a rigid thin film on a uniaxially strained PDMS foundation using a hand-held corona tester. Subsequent relaxation leads to surface wrinkling with varied wavelength dependent on the exposure time. Those nanowrinkles are directed either parallel or orthogonal to linear PDMS microstructures by manipulating the strain field during wrinkling. Compared to E-beam evaporation, UV exposure, or focused ion beam for surface wrinkling, this wet bench process avoids the use of costly equipment and greatly reduces turnaround fabrication cycle. INTRODUCTION Periodic micro/nanoscale polymer structures are widely used in optical gratings, cell alignment guidance, and micro/nanofluidics. One popular method to create such structures is to utilize mechanical buckling instability. To this end, a rigid thin layer is often deposited on a solid support made of compliant materials such as polystyrene (PS), polydimethylsiloxane (PDMS), or shape memory polymers. Upon compression the thin layer undergoes buckling and self-organizes into microscale or nanoscale wrinkles. Effective approaches of micro/nano wrinkle formation include metal evaporation or sputtering on elastomeric films, UV-ozone irradiation or oxygen plasma treatment of mechanically stretched polymer substrates, and exposure of polymer substrates to focused ion beam (FIB) [1]. Special facilities are essential in these processes for creating the rigid thin layer on the solid foundation. The limited accessibility of these facilities and the associated long processing time, however, compromises the manufacturing efficacy. In this study we report an alternative method using a hand-held corona tester, which can create ordered micro/nanowrinkles within a few minutes on a wet laboratory benchtop. The need for cleanroom environment or expensive facilities is eliminated. This method also allows easy integration with conventional microfabrication to create hierarchical micro/nanostructures.