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Biodegradable Microfabricated Plug-Filters forGlaucoma Drainage DevicesTeimour MalekiBirck Nanotechnology Center, Purdue University, tmalekij@purdue.edu

Girish ChitnisBirck Nanotechnology Center, Purdue University, gchitnis@purdue.edu

Jun Hyeong ParkBirck Nanotechnology Center, Purdue University, park1@purdue.edu

Louis B. CantorIndiana University-Purdue University Indianapolis

Babak ZiaieBirck Nanotechnology Center, Purdue University, bziaie@purdue.edu

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Maleki, Teimour; Chitnis, Girish; Park, Jun Hyeong; Cantor, Louis B.; and Ziaie, Babak, "Biodegradable Microfabricated Plug-Filtersfor Glaucoma Drainage Devices" (2012). Birck and NCN Publications. Paper 1190.http://docs.lib.purdue.edu/nanopub/1190

IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 59, NO. 6, JUNE 2012 1507

Biodegradable Microfabricated Plug-Filtersfor Glaucoma Drainage Devices

Teimour Maleki*, Member, IEEE, Girish Chitnis, Jun Hyeong Park, Louis B. Cantor,and Babak Ziaie, Senior Member, IEEE

Abstract—We report on the development of a batch fabricatedbiodegradable truncated-cone-shaped plug filter to overcome thepostoperative hypotony in nonvalved glaucoma drainage devices.Plug filters are composed of biodegradable polymers that disap-pear once wound healing and bleb formation has progressed pastthe stage where hypotony from overfiltration may cause complica-tions in the human eye. The biodegradable nature of device elimi-nates the risks associated with permanent valves that may becomeblocked or influence the aqueous fluid flow rate in the long term.The plug-filter geometry simplifies its integration with commercialshunts. Aqueous humor outflow regulation is achieved by control-ling the diameter of a laser-drilled through-hole. The batch com-patible fabrication involves a modified SU-8 molding to achievetruncated-cone-shaped pillars, polydimethylsiloxane micromold-ing, and hot embossing of biodegradable polymers. The developedplug filter is 500 μm long with base and apex plane diametersof 500 and 300 μm, respectively, and incorporates a laser-drilledthrough-hole with 44-μm effective diameter in the center.

Index Terms—Biodegradable plug-filter, glaucoma drainage de-vice (GDD), hot embossing, laser drilling, micromolding.

I. INTRODUCTION

S EVERAL ocular diseases that cause increased intraocularpressure (IOP) and ultimately result in decreased visual

field are collectively termed high-tension glaucoma. ElevatedIOP (normal IOP is typically between 10 and 21 mmHg) maydamage the optic nerve and result in permanent blindness. Ac-cording to National Institutes of Health approximately 120 000individuals are blind from glaucoma that accounts for 9% to12% of all cases of blindness in the United States. The rate of

Manuscript received February 1, 2011; revised June 5, 2011 and November4, 2011; accepted November 13, 2011. Date of publication December 16, 2011;date of current version May 18, 2012. This work was supported in part by theOffice of the Vice-President for Research at the Purdue University and the In-diana University School of Medicine, and an unrestricted grant from Researchto Prevent Blindness. Asterisk indicates corresponding author.*T.Maleki is with the Birck Nanotechnology Center, Purdue University,West

Lafayette, IN 47906 USA (e-mail: tmalekij@purdue.edu).G. Chitnis is with the School of Mechanical Engineering, Purdue University,

West Lafayette, IN 47906 USA (e-mail: gchitnis@purdue.edu).J. H. Park and B. Ziaie are with the School of Electrical and Computer

Engineering, Purdue University, West Lafayette, IN 47906 USA (e-mail:park1@purdue.edu; bziaie@purdue.edu).L. B. Cantor is with the Department of Ophthalmology, Eugene and Marilyn

Glick Eye Institute, Indiana University, School of Medicine, Indianapolis, IN47906 USA (e-mail: lcantor@iupui.edu).Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TBME.2011.2179031

glaucoma blindness is mainly attributed to the failure of earlydiagnosis and the limitations of the available treatment options.The treatment provided for glaucoma is highly dependent on

the progression of the disease. If the initial treatment with med-ication and/or laser surgery is not satisfactory, more invasivemethods such as trabeculectomy and implantation of glaucomadrainage devices (GDDs) are performed [1]. The basic conceptof all theGDDs currently available is very similar to theMoltenoimplant, first introduced in 1969 [2]. GDDs include a tube thatis connected to an equatorial plate under the conjunctiva. Thistube would create an alternate aqueous pathway from the ante-rior chamber (AC) that shunts the aqueous humor out of the eyeto the end plate located in the equatorial region of the globe.The diverted aqueous humor is then removed through intercel-lular spaces and the lymphatic system. The use of GDDs as analternative to trabeculectomy and cyclodestructive proceduresin the management of glaucoma is increasing [3].The GDDs currently used in glaucoma management can be

classified into two main groups: 1) nonvalved devices that in-clude Molteno (Molteno Ophthalmic Limited, Dunedin, NewZealand) and Baerveldt glaucoma implant (Abbott Medical Op-tics Inc., Abbott Park, IL). These devices contain a tube withoutany active resistance to regulate the outflow; and 2) valved de-vices that include the Ahmed glaucoma valve (NewWorldMed-ical, Rancho Cucamonga, CA) and the Krupin slit valve (HoodLaboratories, Pembroke, MA). The second group incorporatesa valve at the end of the tube that results in some restrictionof outflow to the drainage plate [4]. It has been shown that thevalved Ahmed glaucoma implant may not be as effective asthe nonvalved devices (Molteno and Baerveldt) at lowering theIOP [5]–[8]. Goulet et al. demonstrated a significant rise in theIOP after 2 years with the Ahmed valve in spite of medicationsused to control the pressure. In the same time period, they alsoobserved a higher failure ratewith theAhmed valve as comparedto the Baerveldt shunts [5].Nonvalved implants might be better in the long term but they

inherently pose a higher risk of early postoperative hypotonydue to excessive outflow since these implants rely on woundhealing and fibrous bleb formation at the endplate to regulatethe aqueous drainage. Once established, this fibrous capsulationprovides sufficient resistance to outflow and control over IOP.The size of the end plate surface area and the thickness of thefibrous bleb determine the amount of fluidic resistance throughthe device. However, it takes a few weeks for the fibrous bleb toform. During this time period aqueous humor drains passivelythrough the silicone tube without any measurable restriction.This problem of hypotony due to excessive drainage may lead

0018-9294/$31.00 © 2012 IEEE

1508 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 59, NO. 6, JUNE 2012

Fig. 1. (a) Plug-filter inserted in a Baerveldt implant’s tube to regulate theoutflow and (b) 3-D schematic of the microfabricated plug filter.

to a flat AC in the eye, choroidal effusions, hemorrhage, or otherpostoperative complications. There have been several attemptsto address this problem by including a degradable suture withthe tube and modifying the silicone tube exit to create a slitvalve [9]–[13]. Suturing the tube during operation requires ad-ditional surgical manipulation and extends the operative time,whereas a slit valve (similar to the Krupin slit valve) is a per-manent modification that might affect the fluid flow rate in thelong term. Other ligation techniques involve the placement ofa nonabsorbable suture within the tube lumen that then mustbe removed postoperatively, usually in the physician’s office.Hence, it is desirable to have a mechanism that would limit theoutflow at the early stages after surgery and vanish after blebformation has begun.In this paper, we report the development of a microfabricated

biodegradable plug filter to address the aforementioned prob-lems. This plug filter regulates the postoperative flow rate bycontrolling the tube resistance and would degrade within a fewweeks following the surgery.

II. DESIGN AND FABRICATION PROCESS

A. Design

Fig. 1(a) shows a Baerveldt implant with a biodegradablefilter plug inserted into its inlet silicone tube. It is instructive tocalculate the pressure drop across the tube, if no flow restrictor

is employed. Flow rates in the microtube are small enough toassume laminar flow, so the pressure drop due to friction fora cylindrical tube can be calculated by the Hagen–Poiseuilleequation [14]:

ΔP =8ηLQ

πr4 (1)

where ΔP is pressure drop across the tube, η is dynamic vis-cosity, L is length of the tube, Q is the flow rate, and r is theradius of the tube. Baerveldt implant contains a 0.30-mm innerdiameter silicone tube that is 32mm long [15].When this deviceis implanted in the eye, unless the flow is restricted prior to thebleb formation, the pressure difference between the two sidesof the tube (AC versus the atmosphere) will be 0.027 mmHg,causing severe hypotony (assuming a aqueous humor viscosityand flow rate of 6.92 × 10−4 kg/m.s [16] and 2 μL/min [17],respectively). Based on simple geometrical and fluid dynamicsarguments, introducing a 500-μm long cylindrical plug with a24-μmdiameter through hole in the tube can reduce the pressurein the AC to the normal physiological range of 15–20 mmHg.

B. Fabrication Process

Fig. 1(b) demonstrates the 3-D schematic of the plug-filter.It has a truncated-cone-shaped geometry to facilitate insertioninto the tube of commercial GDDs. The diameter and the lengthof the laser-drilled hole in the middle of the plug filter regulatethe aqueous outflow after GDD implantation.The fabrication process for the plug filter is depicted in Fig. 2.

First, a truncated-cone-shaped micropillar array was fabricatedusing SU-8 (2100 series, Microchem Corporation, Newton,MA) photoresist. Since achieving 500-μm thickness with a sin-gle spin coat is challenging, three layers of repeated applica-tion followed by soft bake prior to the UV exposure were usedto achieve the desired height [see Fig. 2(a)]. Then, the triple-layered SU-8 was overexposed from the backside through a1-mm thick glass mask (6000mJ/cm2 UV exposure dose) [seeFig. 2(b)]. This backside overexposure results in SU-8 pillarswith a smooth sidewall at a certain angle [18] [see Fig. 2(c)].The fabricated SU-8 mold was then treated with tridecafluoro-(1,1,2,2, tetrahydrooctyl)-1-trichlorosilane (United ChemicalTechnologies, Inc., PA) vapor to ease the removal of the subse-quent polydimethylsiloxane (PDMS) layer. PDMSwas next castagainst the mold and cured at 110 ◦C for 20 min [see Fig. 2(d)].After peeling off the PDMS from the SU8mold [see Fig. 2(e)]

biodegradable plug-filters were fabricated by hot embossing.This was accomplished by pouring polymer powder on top ofthe mold and heating it up to 140 ◦C in vacuum for 3 h [seeFig. 2(f)]. Due to the high viscosity of the biodegradable poly-mer, this vacuum heating is necessary to ensure that the polymerfills the holes completely and replaces the trapped air. After-ward, the PDMS mold was removed from the vacuum, placedon top of a hotplate (140 ◦C), and biodegradable polymer wassqueezed between the PDMS mold and another PDMS layerby applying 25-kPa pressure [see Fig. 2(g)]. This step is re-quired for removing excess biodegradable polymer from thesurface of the PDMSmold and separating individual plug filters[see Fig. 2(h)]. Finally, CO2 laser (Resonetics, Nashua, NH)

MALEKI et al.: BIODEGRADABLE MICROFABRICATED PLUG-FILTERS FOR GLAUCOMA DRAINAGE DEVICES 1509

Fig. 2. Fabrication process for the truncated plug-filter: (a) SU-8 coating ona glass slide, (b) masked backside exposure, (c) SU-8 truncated-cone shapedpillars, (d) PDMS casting against the master mold, (e) PDMS mold peel off,(f) filling the PDMS mold by the biodegradable polymer, (g) removal of theexcess polymer by applying pressure at high temperatures, (h) isolated cone-shaped biodegradable pillars, and (i) laser drilling of through-hole at the centerof the cone.

micromachining was used to drill a 24-μm diameter flow-regulating through-hole at the center of plug filter [see Fig. 2(i)].Due to the high viscosity of biodegradable polymers, even

at temperatures well above their glass transition (140–150 ◦C),both vacuum and high temperature are required to completelyfill the PDMS mold. Fig. 3(a) shows an SEM image of a con-ical frustum-shaped SU-8 micropillar, with a base diameter of500μm and an apex diameter of 300μm fabricated by the mod-ified back-side exposure method [see Fig. 2(b) and (c)]. Anoptical image of an array of the microfabricated plug filters inthe PDMS mold before laser drilling is shown in Fig. 3(b). Theplug filters were laser drilled without removing them from themold, so the PDMSmold acted as a package for the final device.

Fig. 3. (a) SEM image of a SU-8 micropillar, (b) optical image of the batchfabricated plug-filter array in the PDMS mold, (c) SEM of a single plug filterafter laser drilling, (d) SEM of two filters showing different diameter holes inthe base (left) and apex (right) planes.

Fig. 3(c) shows an SEM image of the final plug filter made ofpolylactic-co-glycolic acid (PLGA) after laser drilling (a 40-μmdiameter laser-drilled hole is clearly visible in the center of theapex plane of the plug filter).It is important to mention two complications regarding the

fabrication of the filter plug. As is clear from Fig. 3, althoughthe SU8 mold is a truncated cone, the final plug has a morerounded upper face. This is due to the high viscosity of meltedpolymer solution and the fact that even in vacuum and at hightemperatures and pressures, it is difficult to completely fill thePDMS mold, and the surface tension of the melted polymerrounds the top surface to some extent. This is not very criticalas long as the cone shape is preserved and the plug can be easilyinserted into the tube. Another complication has to do withlaser drilling the polymer. Although we originally designed thethrough-hole to be 24μm in diameter, laser drilling was notcalibrated well enough to achieve the targeted dimension. Thiscan be remedied by performing several test runs in order tooptimize the laser power for targeted dimension. In addition,the base plane where the beam first hits the polymer will havea larger diameter hole that that of the apex plane where thebeam exits [see Fig. 3(d)]. In our case, the apex plane (exit) holediameter was 40μm, whereas the base plane (entrance) had an85-μm diameter hole. This tapering effect is well known and isanticipated when one drills a high aspect ratio hole with laser.

III. MATERIALS AND METHODS

We tested two different structural materials for fabricationof the biodegradable plug filter: PLGA (5050 DLG 4A, Sur-Modics Pharmaceuticals Inc., AL) and poly-lactic-acid (PLA),(100 DL 7 E, SurModics Pharmaceuticals Inc., AL). It is in-structive to compare the mechanical and degradation proper-ties of these two structural materials that are summarized in

1510 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 59, NO. 6, JUNE 2012

TABLE IGLASS TRANSITION TEMPERATURE AND DEGRADATION TIMES

FOR 100% PLA AND 50/50 PLGA

Fig. 4. (a) Schematic of the PLGA plug-filter coated with a polymer withhigher glass transition temperature, (b)–(d) batch compatible coating process,(e) optical image of the plug filter before coating, and (e) optical image of thesame plug-filter after coating with epoxy.

Table I. As can be seen, by increasing the DL-lactide ratio in thePLGA, the glass transition temperature increased at the expenseof longer degradation times. This is a well-known property ofPLGA copolymers. For 100% PLA with a glass transition tem-perature of 56–60 ◦C, the degradation time is about 5–6 monthsthat is longer that what is required for the bleb formation. How-ever, one can adjust the glass transition/degradation time of thebiodegradable polymers by controlling their molecular weightand the end groups [19].As will be discussed in Section IV, neither of these polymers

can be used as the structural materials of the plug filter. One canuse an alternative approach to overcome the low glass transitionof the PLGA by coating the outer area of the plug filter with abiocompatible polymer such as SU-8, parylene, or an epoxy [seeFig. 4(a)]. This outer shell will provide mechanical support tothe filter and prevent clogging of the holes. We coated the plugfilter with SU-8 (UV-curing adhesive) by spinning the resist ona glass slide and rolling the plug filter against its surface (theshell thickness can be adjusted by controlling the spin rate).However, to make the process batch compatible, a mold can befabricated in silicon as depicted in Fig. 4(b). The mold can thenbe coatedwith PLA, SU-8, or UV-curing adhesive [see Fig. 4(c)]followed by stamping the plug filters against the coated mold[see Fig. 4(d)]. Fig. 4(e) and (f) shows optical images of theplug filter before and after coating with 50-μm thick UV-curableadhesive (Henkel, CT), respectively.After fabrication, the plug filter was inserted into the open

end side of a commercial Baerveldt implant silastic tube [see

Fig. 5. (a)Optical image of a plug filter inserted in aGDD’s tube. (b) Truncatedshape of the plug filter simplifies its insertion with a tweezer.

Fig. 6. (a) Block diagram of the test setup, (b) optical image of the setup, and(c) magnified image of the plug filter under the test.

Fig. 5(a)]. Due to the conical shape of the plug filter, insertioncan be simply done using a forceps [see Fig. 5(b)].

In vitro testingwas conducted using phosphate buffered saline(PBS) (Sigma-Aldrich Company, MO) in a 37 ◦C silicone oilbath to simulate the aqueous humor and body temperature. Inthis setting, the syringe pump acts as the aqueous humor inflowand the flask containing the valve serves as a sub-Tenon space.Fig. 6(a) shows the block diagram of the test setup. PBS solutionwas pumped into the GDD tube having a plug filter at constant

MALEKI et al.: BIODEGRADABLE MICROFABRICATED PLUG-FILTERS FOR GLAUCOMA DRAINAGE DEVICES 1511

Fig. 7. Back pressure versus time for a PLGA plug filter with no hole.

flow rate (2–3μL/min) and backpressure was monitored usingthe MPX2010GP (Freescale,TX) pressure sensor. The pressuresensor was calibrated to account for the resulting hydraulic pres-sure caused by submerging the filter in the water. Labjack U12(Labjack Corp. CO) was used for data acquisition. An opticalphotograph of the test setup is shown in Fig. 6(b). A magnifiedimage is illustrated in Fig. 6(c), showing a needle connected tothe GDD device floating in PBS solution. The upper left inset ofthis picture shows a closeup of the GDD device while the upperright inset shows the filter lodged inside the tube.

IV. RESULTS AND DISCUSSION

After successful fabrication of the plug filter, the first ex-periment was designed to confirm that the plug filter does notmove inside the silastic tube at elevated pressures that can occurif the central hole is clogged. For this purpose, we inserted aPLGA plug filter with no hole in the silicone tube and PBS waspumped into the tube at the constant flow rate of 3μL/min at37 ◦C while the resulted pressure was monitored by computer.Fig. 7 demonstrates the resulted backpressure versus time. Asdepicted in the graph, pressure rose continuously until the pointof a sudden drop due to pressure-created leaks in the test setup.We did not observe any movement during this period indicatingthat the plug filter can withstand pressures up to 160 mmHg.The slow rise time of the pressure in Fig. 7 is due to the airgap between the liquid and the pressure sensor. This is requiredsince liquid cannot come into contact with the membrane of thepressure sensor.In the next step, we calibrated the pressure versus flow rate

of the plug filters using a room temperature setup. Fig. 8 showsflow rate versus pressure characteristics of plug filters made ofPLGA having two holes, each with an apex and bases diametersof 40 and 85μm, respectively.Testing different filters resulted in similar characteristics

showing the reproducibility of the experiment. However, as canbe seen from the graph, flow rate at the pressure of interest(15–20 mmHg) is much higher than the expected value (30–40μL/min as opposed to the physiological rate of 3μL/min).This is mainly due to the large hole sizes of the plug filters. Asillustrated in (1), flow rate is proportional to the fourth power ofthe hole’s diameter, which explains the resulted high flow ratesin plug filters having holes with twice the diameter. In an effort

Fig. 8. Flow rate versus pressure characteristics of plug filters made of 50/50PLGA having an effective diameter of 44μm.

Fig. 9. Back pressure versus time for a PLGA plug filter with two holes.

to limit the flow rate, multiple plug filters can be used in series.As expected, this will increase the pressure drop in proportionto the number of devices (1). Based on these sets of experi-ments, we can define an effective hole diameter of 44μm. Thisincorporates the effect of tapering due to laser microdrilling.After calibration, we continued the characterization of the

PLGA plug filter having two laser-drilled holes by inserting aplug filter into a silicone tube, pumping PBS with constant flowrate of 3μL/min PBS at 37 ◦C, andmonitoring the backpressure.The pressure versus time is shown in Fig. 9. As can be seen, theplug filter regulated the pressure for up to 2 days. However, thepressure started to rise after that, and elevated pressures above600mmHg popped out the plug filter from the tube. Observationof the filter under an optical microscope revealed that the plugfilter was completely deformed and the holes were collapsed.This deformation can be explained by the low glass transitiontemperature of PLGA (42–48 ◦C, see Table I). Furthermore,PBS acted as a plasticizer and lowered the glass transition tem-perature even further, softening the PLGA at 37 ◦C. Since thediameter of the plug filter was chosen to be larger than the innerdiameter of the GDD tube, a circumferential mechanical stresson the filter resulted in mechanical collapse of the holes in thesoftened PLGA.One method to overcome the softening problem is to change

the structural material of the plug filter. We explored other

1512 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 59, NO. 6, JUNE 2012

Fig. 10. Back pressure versus time for a PLA plug filter with one hole.

Fig. 11. Back pressure versus time for a PLGA plug filter coated with(a) epoxy, and (b) SU-8.

commercially available biodegradable polymers with a higherglass transition temperature that can be used as the plug-filter’sstructural material. As shown in Table I, PLA has a higher glasstransition temperature (56–60 ◦C). We also laser drilled onlyone hole in plug filters (rather than two holes in the previoussamples) in an attempt to increase the flow resistance and raisethe backpressure. Fig. 10 shows the pressure versus time graphof the new filter, when tested in similar condition and PBS flowrate was set to 2μL/min. As can be seen, pressure was regu-lated and no increase in the pressure was observed for up to 15days. However, pressure is lower than the desired value (15–20 mmHg) that is attributed to the larger hole size (effectivediameter of 38 μm) than what was initially designed (24 μm).The long degradation time of the PLA complicates the use ofthis polymer as the structural material and increases the risk as-sociated with clogging with inflammatory and red blood cells.We also explored a second method to address the softening

problem by creating a thin supporting shell around the plug filter[see Fig. 4(a)] with a biocompatible material. Fig. 11 shows the

pressure versus time graphs of the plug filter coated with UV-curable adhesive [see Fig. 11(a)], and SU-8 [see Fig. 11(b)],when tested with PBS at flow rate of 2μL/min. As can be seenin both cases, the pressure was regulated (no increase in thepressure was observed) for up to 45 days due to the stiffer outershell layer. The spikes in the pressure are attributed to alteringthe dynamics of the system when we introduced more PBS tothe system as the syringe ran out of PBS.

V. CONCLUSION

In conclusion, a biodegradable plug filter was developedto test the feasibility of flow control in nonvalved glaucomadrainage devices. A batch-compatible fabrication process flowfor fabrication of a self-packaged plug filter was discussed. Atruncated-cone-shaped geometry was chosen to simplify the in-sertion of the plug filter into the GDD’s tube. In vitro resultsshowed that plug filter made of PLA was capable of regulatingthe pressure for more than 15 days. However, plug filters madeof 50/50 PLGA showed softening at body temperature resultingin the collapse of the through-hole after insertion into the tube.To address the softening issue in the PLGA plug filters, theywere coated with SU-8 or UV-curing adhesive. These coatedstructures were capable of regulating the pressure up to 45 daysthat is long enough for bleb formation.Although the degradation period of the selected biodegrad-

able polymer (50/50 PLGA) is 3–4weeks (see Table I) biodegra-dation kinetics can vary from few weeks to several months de-pending on numerous factors including device geometry. Thedegradation scheme of PLGA is bulk rather than surface erosionthatmeans polymer breakdown takes place throughout the entiresample. This implies a sharp drop in pressure after plug-filterdegradation rather than a continuous pressure loss throughoutthe process (see Figs. 10 and 11).Further research is needed to optimize the size of the hole

in order to achieve desirable IOP regulation. In addition, it isdesirable to adjust the PLA/PGA composition to attain an ap-propriate glass transition/degradation time ratio. Finally, it isworth mentioning that inflammatory or red blood cells releasedinto the aqueous humor after the operation could potentiallyclog the hole in the plug filter (although the possibility is lowdue to the large diameter of the hole, 24μm). If clogging occursduring this period, eye drops or ablation of the plug filter withlaser can be used to reduce the IOP and open the drainage path.

ACKNOWLEDGMENT

Authors would like to thank Mr. K. Kadziauskas of AbbottMedical Optics, CA for providing us with GDD devices.

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Teimour Maleki (M’09) received the B.Sc. degree inbiomedical engineering from the Amirkabir Univer-sity of Technology, Tehran, Iran, in 2000, the M.Sc.degree in electrical engineering from the Universityof Tehran, Tehran, Iran, in 2003, and the Ph.D. degreein electrical engineering from the Purdue University,West Lafayette, IN, in 2010.He is currently a Research Assistance Professor

in the Birck Nanotechnology Center, Purdue Univer-sity. His research interest includes the developmentof micro/nanodevices and implantable microsystems

for healthcare.

Girish Chitnis received the Bachelor’s degree inmechanical engineering from the Indian Institute ofTechnology Bombay, Mumbai, India, in 2007. Since2007, he has been working toward the Ph.D. degreein engineering with the School of Mechanical Engi-neering, Purdue University, West Lafayette, IN.His research interests include microelectrome-

chanical systems and their biomedical applications.

Jun Hyeong Park received the B.S. degree inelectrical engineering from Purdue University, WestLafayette, IN, in 2009, where he is currently workingtoward the Ph.D. degree in electrical engineeringwiththe School of Electrical and Computer Engineering.His research interests include MEMS devices

for drug delivery and biosensor using biodegradablepolymers.

Louis B. Cantor completed his undergraduate andgraduate medical education in 1984 from IndianaUniversity.He is the Jay C. and Lucile L. Kahn Professor and

Chair of the Department of Ophthalmology, EugeneandMarilyn Glick Eye Institute at Indiana UniversitySchool of Medicine. He was an ophthalmology res-ident at Indiana University. In 1985, he completedhis glaucoma fellowship at Wills Eye Hospital inPhiladelphia under the direction of George L. Spaeth.He joined the Indiana University Department of Oph-

thalmology as Director of the Glaucoma Service in 1985. From 1986 to 1989,he also served as Chief of Ophthalmology at Wishard Memorial Hospital (In-dianapolis, Indiana). In 1996, he assumed the additional role as Director of theOphthalmology Residency Program for the department. In 1999, he attained therank of Professor of Ophthalmology.Dr. Cantor was appointed Secretary for Ophthalmic Knowledge for the

American Academy of Ophthalmology beginning in January 2007. He is alsoan Associate Examiner for the American Board of Ophthalmology.

Babak Ziaie (A’95–M’00–SM’07) received thePh.D. degree in electrical engineering from the Uni-versity of Michigan, Ann Arbor, in 1994.From 1995 to 1999, he was a Postdoctoral Fellow

and an Assistant Research Scientist with the Centerfor IntegratedMicrosystems, University ofMichigan.From 1999 to 2004, he was subsequently with theDepartment of Electrical and Computer Engineering,University of Minnesota, Twin Cities, as an Assis-tant Professor. Since January 2005, he has been withthe School of Electrical and Computer Engineering,

Purdue University, West Lafayette, IN, where he is currently a Full Professor.His research interests include related to the biomedical applications of micro-and nanoelectromechanical systems (BioMEMS/BioNEMS).