Speakers

Polymer MEMS Devices for Biomedical Applications

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Jong-Hyun Lee
Gwangju Institute of Science and Technology (GIST)
Nov. 30 10:10~10:40

Abstract

The MEMS (Micro Electro Mechanical Systems) technologies have been widely applied in various biomedical fields to meet their requirements of minimal invasiveness and accurate diagnosis/surgery. Especially, polymer-based MEMS devices have many advantages over conventional Si MEMS in terms of compliance, disposability, and cost for biomedical applications. The paper deals with the polymer MEMS devices that have been recently developed for glaucoma drainage device, anti-reflux ureteral stent, actuatable microneedle array for drug delivery etc.

[Glaucoma drainage device]

A polymeric micro check valve for a glaucoma drainage device (GDD) was developed for precise regulation of intraocular pressure (IOP) and effective aqueous humor turnover (AHT). The pedestal, slightly elevated by selective coating of a parylene C film, induces pre-stress in the thin valve membrane, which enhances the predictability of the cracking pressure. The GDD comprises a cannula and a normally closed polymeric micro check valve, which are made of PDMS, a biocompatible polymer, with three layers: top (cover), intermediate (thin valve membrane), and bottom (base plate). A feedback channel, located between the top and intermediate layers, prevents reverse flow by feeding the pressure of the outlet channel back to the thin valve membrane. To achieve a precise cracking pressure and sufficient drainage of humor for humans, the thicknesses of the valve membrane and parylene C film are designed to be 58 μm and 1 μm, respectively. The experimental results show that the cracking pressure of the fabricated GDD lies within the range of normal IOP (1.33–2.67 kPa). The forward flow rate (drainage rate), 4.3 ± 0.9 μL/min at 2.5 kPa, is adequate to accommodate the rate of AHT in a normal human eye (2.4 ± 0.6 μL/ min). The reverse flow was not observed when a hydrostatic pressure of up to 4 kPa was applied to the outlet and the feedback channel.

[Anti-reflux ureteral stent]

An anti-reflux ureteral stent was fabricated to effectively prevent backward flow with a negligible reduction in forward flow. The stent comprised a 7F Double-J (DJ) stent and a polymeric flap valve. Two types of stent were prepared for in vitro tests: DJ stents with (1) an uncoated valve (UCV) stent and (2) a parylene C coated valve (PCV) stent for enhanced biocompatibility. The flow characteristics of each stent were evaluated considering flow direction, parylene coating, and stent side holes, and were compared to the intact DJ stent. The forward flow rate for the distal portion of the UCV and PCV stents was 9.8 mL/min and 7.8 mL/min at applied pressure of 15 cm H2O (normal anterograde pressure in patients with stents), respectively. Backward flow rate for the distal portion of the UCV and PCV stents was decreased by 28 times and 8 times at applied pressure of 50 cm H2O (maximum bladder pressure), respectively, compared with the distal portion of the intact DJ stent. Forward flow rates of whole stents were 22.2mL/min (UCV stent) and 20.0mL/min (PCV stent) at applied pressure of 15 cm H2O, and backward flow rates of whole UCV and PCV stents were decreased by 8.3 times and 4.0 times at applied pressure of 50 cm H2O, respectively, compared with the intact DJ stent. In vivo Study Using a Porcine Model showed that the flap valve-attached ureteral stent effectively prevented VUR under conditions of elevated intravesical pressure without urinary obstruction.

[Actuatable microneedle array]

A movable microneedle array, which can be switched on–off electrically, was fabricated. Unlike conventional microneedle arrays, which are usually fixed on substrates, the active microneedle array can move in and out by thermopneumatic force, so that drugs can be delivered or body liquid can be extracted through the skin surface (epidermis) only when needed. The active microneedle array consists of four layers: an air microchamber, a microfluidic channel, a microneedle array, and a protection layer. These four layers are made of PDMS and SU-8, and are assembled together on a glass substrate. As the microheater (Ti/Pt), integrated with a temperature sensor, heats up the air inside the microchamber, the microchamber volume expands, moving the microneedle array in the outward direction. The microfluidic channel layer acts as not only a fluidic path but also a mechanical support for the microneedle array. The microneedle array moves out to 413 mm, which distance is sufficient to deliver drugs or extract body liquid through the skin surface. The measured actuation force was 40 mN when the initial gap between the microneedle tip and the force gauge was 50 mm. Operation conditions for successful skin penetration using the fabricated movable microneedle array were confirmed in the experimental study using chicken flesh.

 

Education

  • 1986, KAIST (Ph.D. – Mechanical Engineering)
  • 1983, KAIST (M.S. – Mechanical Engineering)
  • 1981, Seoul National University (B.S. – Mechanical Design)

 

Professional Career

  • 2005.09, Present Professor, GIST
  • 2004.09, 2005.08 Visiting Professor (Univ. of Cincinnati, USA)
  • 2000.06, 2004.08 Associate Professor, Professor, GIST
  • 1999.01, 2000.05 Principle Investigator, ETRI

 

Awards and Honors

  • 2007-Present, Member, Advisory committee of the Korean MEMS Conference
  • 2004, General chair, Steering committee of the Korean MEMS Conference
  • 2003, Chairman, Program committee of the Korean MEMS Conference
  • 2003.8-Present, Member, Evaluation committee of UNITEF