Microfabrication of Self-Oscillating Gel by Photolithography

Transcription

1 Microfabrication of Self-Oscillating Gel by Photolithography Y. Furuhata 1, M. ogawa 2, Y. Ito 2 and R. Yoshida 1 1 Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo Hongo, Bunkyo-ku, Tokyo, , Japan Phone/Fax: , furuhata@bmw.t.u-tokyo.ac.jp 2 Kanagawa Academy of Science and Technology, Japan Introduction: We have been studying the self-oscillating gel coupled with the oscillating reaction (the Belousov-Zhabotinsky (BZ) reaction) 1). The gel consists of the crosslinked poly(-isopropyl-acrylamide (IPAAm)) to which ruthenium tris(2,2 -bipyridine) (Ru(bpy) 3 ), a catalyst for BZ reaction, is covalently bonded. In this study, we have attempted microfabrication of self-oscillating gel by photolithography for application to micro-devices such as MEMS and µtas. Two photolithographic methods, (1) using photoinitiator and (2) using the polymer with azidophenyl groups, were employed to control the gel structure. Optimal conditions for microfabrication have been discussed by changing the concentration and composition of monomer solution and the intensity and time of photo-irradiation. Experimental: (1) Microfabrication using photoinitiator. IPAAm, Ru(bpy) 3 monomer,, -methylenebisacrylamide (MBAAm, 1.25mol%), and 2,2-dimethoxy-2-phenylacetophenone (photoinitiator) were dissolved in methanol. After purged with nitrogen gas, the solution was injected between glass plate and photomask plate separated by Teflon sheet (0.5mm). Polymerization was carried out by irradiating monochromatic light (370nm). (2) Microfabrication using photosensitive polymer. At first, poly(ipaam-co-acrylic acid-co-ru(bpy) 3 ) (molar ratio was 97:2:1) was synthesized in methanol (5mL, total monomer concentration 2.0M) containing 2,2 -azobisisobutyronitrile (AIB, 1mol% of total monomers) at 60 C for 24h. The resulting mixture was dialyzed against methanol and water, and then freeze-dried. Subsequently, this copolymer (100mg), 4-azidoaniline (30mg) and water-soluble carbodiimide (64mg) were dissolved in PBS (ph 7.0, 20mL), and the mixture was stirred at 4 C for 24h. The azidophenyl-amidated copolymer was obtained by dialyzing resulting mixture for 3 days against water and freeze-drying (Fig.1). Then this copolymer was dissolved in methanol (40mg/mL). The polymer solution was coated on glass or polystylene plate and dried up. The plate was then covered with a photomask and UV light was irradiated. Results and discussion: By both microfabrication method (1) and (2), several shapes of micrometer-sized gels with the same pattern as photomask were synthesized. As monomer and photoinitiator concentrations increase, the gelation time became shorter. Optimal condition for microfabrication (1) was obtained when the monomer concentration was 2.0M and light intensity was 1.5kW/cm 2. Fig.2 shows the lattice-shaped gel prepared by microfabrication (2). In oxidized state, the gel swelled more than in reduced state (Fig.3). Self-oscillation occurred and chemical wave propagation was observed as these gels were immersed in the substrate solution of BZ reaction. The self-oscillating behavior of the microgels was analyzed with comparing that of bulk gel. Reference: 1) R. Yoshida, K. Takei and T. Yamaguchi: Macromolecules, 36, 1759 (2003).

2 Microfabrication of Self-oscillating gel by Photolithography Y. Furuhata, M. ogawa, Y. ito, R. Yoshida 1) Tokyo Univ. 2) Kanagawa Academy of Science and Technology

3 A bs trac t We have been studying the self-oscillating gel coupled with the oscillating reaction (the Belousov-Zhabotinsky (BZ) reaction). The gel consists of the crosslinked poly(-isopropyl-acrylamide (IPAAm)) to which ruthenium tris(2,2õ-bipyridine) (Ru(bpy) catalyst for BZ reaction, is covalently bonded. In this study, we have attempted microfabrication of selfoscillating gel by photolithography for application to micro-devices such as MEMS and µtas. Two photolithographic methods, (1) using photoinitiator and (2) using the polymer with azidophenyl groups, were employed to control the gel structure. Optimal -condi tions for microfabrication have been discussed by changing the concentration and composition of monomer solution and the intensity and time of photo-irradiation.

4 Mechanism of Self-Oscillation for Polymer Gel Poly(IPAAm-co-Ru(bpy) 3 ) gel Transducer Belousov-Zhabotinsky (BZ) reaction Malonic acid Bromomalonic acid Br - Ru(bpy) 3 3+ Ru(bpy)3 2+ HBrO2 Products Reactants: MA, abro 3, HO 3 Catalyst: Ru(bpy) 3 2+ BrO3 - Gel size (diameter) [µm] Swelling curve Reduced state, Ru(II) Oxidized state, Ru(III) Difference of swelling ratio Temperature [ C] ( CH 2 CH ) ( CH 2 CH ) CH 2 CH x y 2+ / 3+ C O C O CH 3 H H CH 2 CH Ru H CH 3 CH 3 C O IPAAm Ru(bpy) 3 Self-oscillation Light intensity Gel size 10 µm Light; Ru(III) Dark; Ru(II) min Time CH Outer solution; CH R. Yoshida, et al.: J. Phys. Chem. A, 104, 7549 (2000). Mechanical Oscillation Redox Oscillation [MA]=0.0625M, [abro 3 ]=0.084M [HO 3 ]=0.6M, 20 C Heart muscle-emulating materials. Self-oscillating micropump or microactuator. 2

5 Microfabrication of Gels Miniaturization of the gel Improvement of response time (The response time of gel is proportional to the square of gel size) Application to the micro-devices (ex. Microactuator, µtas, MEMS) Technology of miniaturization -Synthetic technique- Suspension polymerization Emulsion polymerization (ex. Preparation of micro/nano gel particles) etc. -Lithography- Shape of gel can be easily changed. Photolithography Easy synthesis and simple device X-ray lithography (LIGA) 3D Microfabrication

6 Purpose of This Work We have attempted microfabrication of self-oscillating gel by photolithography for application to micro-devices such as MEMS and µtas. Two photolithographic methods were employed to control the gel structure. 1. Photolithography (1) Microfabrication using photo-initiator (2) Microfabrication using photosensitive polymer Optimal conditions for microfabrication have been discussed by changing the concentration and composition of monomer solution and the intensity and time of photo-irradiation. 2. X-ray lithography (LIGA) Preparation of Ciliary motion actuator made of selfoscillating gel (Artifitial Cilia)

7 1 -(1) Photolithography using photo-initiator Microfabrication Using Photo-Initiator Monomer solution (concentration; 2M) IPAAm Ru(bpy) 3 monomer (5 wt%) MBAAm (cross-linker) (1.25 mol%) Photo initiator (10 wt%) Methanol Monochromatic light (370nm) Photomask Spacer (thickness; 0.5 mm) Glass plate Photo initiator OCH 3 C OCH 3 C O 2,2,-Dimethoxy-2- phenylacetophenone The monomer solution was poured between the photomask and the glass. Photomask Glass plate Optimal conditions; Intensity: 1.0~1.5 mw/cm 2 Irradiation time: 3~5 min. Spacer

8 1 -(1) Photolithography using photo-initiator Micropatterning of Poly(IPAAm-co-Ru(bpy) 3 ) Gel Using Photo-Initiator. 500 µm Photomask Prepared gel Reduced state Oxidized state (in Ce(III) / HO 3 ) (in Ce(IV) / HO 3 ) d = 688 µm d = 785 µm

9 1 -(2) Photolithography using photosensitive polymer Microfabrication Using Photosensitive Polymer [Molar ratio] 94 : 1 : H-(CH 2 -CH) x (CH 2 -CH) y C=O CH 3 -H CH CH 3 CH 3 Ru (CH 2 -CH) z -H 2+ COOH + 3 H 2 PS or glass plate Polymer coating on a plate. Photomasking H-(CH 2 -CH) x C=O -H CH (CH 2 -CH) y CH 3 Ru Water soluble carbodiimide ph7.0, 4 C, 24hours (CH 2 -CH) z -H 2+ COH Washing UV irradiation itren reaction was occurred. - 3 groups bonded any carbon chain near it. CH 3 CH 3 4-azidophenylamidated poly(ipaam-co-ru(bpy) 3 ) 3 Gel pattern fixed on PS plate Detached microgels from glass plate

10 1 -(2) Photolithography using photosensitive polymer Micro-patterning of Poly(IPAAm-co-Ru(bpy)3) Gel Using Photosensitive Polymer [1] 200 µm Photomask (circle and square) Prepared gel (on PS plate) The minimum size for this microfabrication method = several µm

11 1 -(2) Photolithography using photosensitive polymer Micro-patterning of Poly(IPAAm-co-Ru(bpy) 3 ) Gel Using Photosensitive Polymer [2] 40µm 2µm Photomask (lattice-shaped) Prepared gel (on PS plate)

12 1 -(2) P hotolithography us ing photos ens itive polymer A F M Image of L attic e-s haped Mic rogel 500 [µm] [µm] 40 µm [µm] 3D image of A F M T hic knes s Å700 nm 80

13 1 -(2) Photolithography using photosensitive polymer Redox Changes of Poly(IPAAm-co-Ru(bpy) 3 ) Microgels Prepared by Photosensitive Polymer. 200 µm 100 µm Reduced state (at 20 C) Oxidized state (at 20 C) (in Ce(III) / HO 3 ) (in Ce(IV) / HO 3 )

14 1 -(2) Photolithography using photosensitive polymer Chemical Wave Propagation of Poly(IPAAm-co-Ru(bpy) 3 ) Microgel Prepared by Using Photosensitive Polymer 500 µm After 2 min. 3 min. 4 min. 5 min. 9 min. Outer solution: [MA]=0.09 M, [abro 3 ]=0.1 M, [HO 3 ]=0.4 M BZ reaction was occurred inside of the gel, and the chemical wave was propagated through the patterned gel arrangement.

15 2. X-ray lithography Preparation of Artificial Cilia by X-ray Lithography Photolithography 2D-microfabrication X-ray lithography 3D-microfabrication Concept of Artificial Cilia The propagation of chemical wave Moving deep X-ray lithography technique Exposure Development Au Evaporation i Electroplating X-ray PMMA Moving the photomask, X-ray was irradiated. The PMMA mold was too hard to takeout the gel, so the PDMS mold, the softer one, was prepared. PDMS molding PDMS De-molding Poly(IPAAm-co-Ru(bpy) 3 ) gel The propagation of chemical wave Lean the projections succesively

16 2. X-ray lithography The Gel Array Prepared by 3D-Microfabrication 240 µm 150 µm The projection array of gel with high aspect ratio 100 µm 300 µm The motio of the projection on BZ reaction was analyzed by image processing based on the video image. O. Tabata, H. Hirasawa, S. Aoki, R. Yoshida and E. Kokufuta: Sensors and Actuators A, 95, 234 (2002). O. Tabata, H. Kojima, T. Kasatani, Y. Isono and R. Yoshida: Proc. MEMS The motion of the gel projection Vertical coordinate [µm] Lateral coordinate [µm] The circular motion like a cilia

17 Summary < Microfabrication of self-oscillating gel > 1. Photolithography Several shapes of micrometer-sized gels were synthesized. Redox change of self-oscillating gel was observed and swelling change was measured. In the aqueous solution containing BZ substrates, self-oscillation accompanied by the propagation of chemical wave was achieved. 2. X-ray lithography (LIGA) The gel array with projections on surface was prepared. - Follow ing the propagation of chemical wave, the motion like a cilia wa observed. (Realization of artificial cilia.)