Showing papers by "Tingrui Pan published in 2009"

Direct projection on dry-film photoresist (DP2): Do-it-yourself three-dimensional polymer microfluidics

Abstract: In this paper, we present a novel rapid-prototyping process for out-of-cleanroom microfabrication of three-dimensional multilayer microfluidic structures with a 10 µm resolution, referred to as the Direct Projection on Dry-film Photoresist (DP2). A commercially available digital projector is customized to function as a direct mask generation and photo exposure system, while easy-processing photosensitive dry films are used as the microfluidic constructs. Multilayer alignments among maskless-patterned layers are reliably achieved by using a Software Alignment technique with less than 10 µm precision, which eliminates the use of mechanical travelling stage. The bonding between different layers of dry film, simply enabled by a plasma-assisted thermal lamination, offers an easy implementation for suspended multilayer microstructures. Development of a complex microfluidic chip from computer layout can thus be accomplished within an hour in a regular chemical or biological lab environment using this approach.

Measuring outlflow resistance/facility of an eye

Abstract: A measurement system takes measurements of intraocular pressure and displaced ocular volume for determination of aqueous outflow resistance A device with a πgid outer wall, a flexible inner wall, and an inflatable bladder in between is placed over the eye A pressure measurement system is coupled to the bladder and is configured to measure a pressure of fluid within the bladder A hydraulic unit is coupled to the bladder and configured to control a flow of fluid between the bladder and an external reservoir, and to measure a change of volume in the bladder created by the pressure applied to the eye Both the pressure measurement system and hydraulic unit are directly controlled by and communicated with a microprocessor/computer In addition, the microprocessor computes the outflow resistance of the eye as a function of the pressure in the bladder and the change of volume in the bladder over time.

Integrating sensing hydrogel microstructures into micropatterned hepatocellular cocultures.

Abstract: In this paper we describe a microfabrication-derived approach for defining interactions between distinct groups of cells and integrating biosensors with cellular micropatterns. In this approach, photoresist lithography was employed to micropattern cell-adhesive ligand (collagen I) on silane-modified glass substrates. Poly(ethylene glycol) (PEG) photolithography was then used to fabricate hydrogel microstructures in registration with existing collagen I domains. A glass substrate modified in this manner had three types of micrpatterned regions: cell-adhesive collagen I domains, moderately adhesive silanized glass regions, and nonadhesive PEG hydrogel regions. Incubation of this substrate with primary rat hepatocytes or HepG2 cells resulted in attachment of hepatic cells on collagen I domains with no adhesion observed on silane-modified glass regions or hydrogel domains. 3T3 fibroblasts added onto the same surface attached on the glass regions around the hepatocytes, completing the coculture. Significantly,...

Lab-on-a-print: from a single polymer film to three-dimensional integrated microfluidics

Abstract: With the major advances in soft lithography and polymer materials, use of microfluidic devices has attracted tremendous attention recently. A simple and fast micromachining process is highly in demand to prototype such a device efficiently and economically. In this paper, we first reported an out-of-cleanroom printing-based integrated microfabrication process, referred to as the lab-on-a-print (LOP), for rapid-prototyping three-dimensional microfluidics. Using this lab-on-a-print process, we demonstrated the potential to accomplish an entire design-to-fabrication cycle within an hour, including about 70 µm resolution of direct-lithography patterning, well-controlled polyimide wet etching, three-dimensional pattern alignment and multilayer wax thermal-fusion packaging. A microfluidic gradient generator was prepared and tested for validation of the lab-on-a-print microfabrication process.

Microfabrication of conductive PDMS on flexible substrates for biomedical applications

Abstract: In this paper, we present microfabrication of a novel photopatternable conductive PDMS material with silver powder as conductive filler and benzophenone as photosensitive component, employing standard photolithography approach. An array of miniaturized capacitive pressure sensors is micromachined onto flexible polymeric transparency using this approach. Highest conductivity of ∼104 S·m−1 and minimal feature resolution of 60 µm have been successfully achieved. In addition, a thermal compression step can mold the microfabricated device into a desired shape (e.g., contact lens). The unique combination of physical properties from both silver filler and PDMS matrix along with photopatternability makes the conductive PDMS composite an excellent material for biological and clinical sensing applications.

Non-adhesive PEG hydrogel nanostructures for self-assembly of highly ordered colloids

Abstract: In this paper, we report on the effect of patterned non-adhesive hydrogel nanosurfaces on the self-assembly of highly ordered colloids. Polyethylene glycol (PEG) hydrogel is employed as the substrate material in the study, for its desired non-adhesive property, and biocompatibility as well as photopatternability. Ultrafine PEG features are photopatterned onto glass substrates with minimal feature resolution of 500 nm using ultraviolet or deep ultraviolet exposure. By simply controlling the colloidal concentration of the nanoassembly solutions and the dimensions of the wells, a range of highly organized nanocolloidal patterns are formed inside the PEG wells. Unlike the traditional surface modification techniques, ours takes advantage of the unique non-adhesive property of PEG hydrogels to achieve extremely high selectivity in the pattern-assisted nanoassembly. Our experiments show that with oxygen plasma treatment, the non-adhesive property of the PEG surface deteriorates significantly, leading to non-selective assembly with complete surface coverage of nanocolloidal beads under the same processing condition. Therefore, benefiting from the unique non-adhesive surface property, the pattern-assisted nanoassembly method enables a highly predictable and robust process for colloidal nanofabrication, and the obtained nanocolloidal arrays with well organized patterns could potentially find applications in photonic crystal fabrication, biological sensing and analytical detection.

Micropattern-assisted nanoassembly: Ordered nanocolloidal array on PEG microstructures

Abstract: Assembly of colloidal arrays has attracted much attention over the past decade. Surface property and topology play important roles in the assembly of colloidal patterns and layers on various substrates. In this paper, we report on a novel micropattern-assisted nanoassembly (μPAN) method to organize highly ordered nanocolloidal arrays onto a nonfouling polymer surface. Polyethylene glycol (PEG) hydrogel is used as the substrate material in the study, for its desired biological properties, low surface energy and photopatternability. A high-density array of PEG microwells is first fabricated on glass substrates with the minimal feature resolution of 1 µm using photolithography method. By simply controlling the colloidal concentration of the dipping solution, the dimensions of the microwells and pulling speed of the substrate, various well organized nanocolloidal patterns are assembled inside the PEG microwells. In addition, the effect of surface property is experimentally investigated. After oxygen plasma treatment, the nonfouling property of the PEG surface deteriorates significantly, leading to a complete surface coverage of nanocolloidal beads. The novel μPAN method allows organizing highly ordered nanocolloidal arrays in a predictable and robust fashion, and has potential applications in photonic crystal fabrication, biological sensing, analytical detection and nanoassembly.