Interacción

Th e n DS2 de vice w as c onceptualized to ac hieve a m anipulable rele ase profi le i n d rug t herapy. A n electrode w as i ntegrated i nto t his de vice. A n app lied c urrent ac ross t he ele ctrodes c ontrols t he

Nanochannels Entry flow chamber (a)

(b) (c)

Entry port

Input finger

Glass top substrate Silicon bottom substrate

Nanochannels

Input/output fingers Anchor points

Exit port

Anchor points Exit flow chamber

Output finger

FIGURE 6.13 nDS1g Microchip: (a) a 3-D schematic view of the device, (b) a picture of a fabricated nDS1g device showing anchor points, input/output fi ngers, and nanochannels. Th ese features can be seen through the glass-top substrate, (c) a fl uid front showing Iso-propyl-alcohol (IPA) fl ow through an nDS1g device. Th e color shadow in the n anochannels i s t he mov ing fl uid f ront. (R eprinted f rom Si nha, P. M . 2 005. Na noengineered i mplantable devices for controlled drug delivery, Ph.D. Th e sis, Th e Ohio State University. With permission.)

electrokinetic fl ow of molecules of interest through this device. Th ese electrodes could be connected to an external circuit that can be a p re-programmable circuit, a w ireless circuit, or a f eedback control circuit for a b iological response (Sinha, 2005). A s chematic diagram of an nDS2 device is shown in Figure 6.14a. Th ese devices are made up o f a b ottom silicon substrate and a top g lass substrate. Th e bottom substrate has many similar features to the nDS1 device. In addition to the advantages mentioned earlier, use of a top g lass substrate in nDS2 provides insulation. Electrodes are integrated in the top glass substrate, and the insulating properties of glass prevents any short-circuit between the two elec-trodes. As with nDS1 and nDS1g the nanochannels exist between the two bonded wafer surfaces. A top view of the device is shown in Figure 6.14b. Locations of three cross sections are marked as A, B, and C in this fi gure. Cross-sectional views at t hese locations are shown in Figure 6.14c. Cross-section A shows the internal features including entry/exit fl ow chambers, input/output fi ngers, nanochannels, anchor points, anchor regions, and spacer regions. Cross-section B s hows the glass seal around the electrodes to p revent fl uid le aking f rom t he en try/exit fl ow c hambers to t he c ontact pad re gions.

Cross-section C shows the bonding pad regions. Th e top substrate has electrode contact chambers that are fabricated to expose the electrodes to the fl uid. Th ese chambers are aligned with the entry and exit fl ow chambers on the bottom silicon substrate. Th e top g lass substrate also has an entry port that is etched a ll t he w ay t hrough t he w afer, a nd a ligns w ith one of t he ele ctrode c ontact c hambers. Th e bottom substrate contains the rest of the features. Th e nanochannel height and applied current between the electrodes defi ne the delivery rate. Th e design and fabrication details of this device are described elsewhere (Sinha, 2005).

Contact pad Entry port

Exit port Electrodes Glass top substrate Silicon bottom substrate

Electrode Deposited oxide

C (c) (b)

(a)

B

A

Electrode

A B C Entry flow chamber

Nanochannels Input finger

Output finger Exit flow chamber Anchor points

Anchor points

Connecting cables

FIGURE 6.14 (See color insert following page 10-24.) nDS2 Microchip: (a) a 3-D schematic view of the device, (b) a top v iew of t he device. Th ere are three cross-section locations marked as A, B, and C i n this fi gure, cross- sectional views at these locations are shown in (c). (Reprinted from Sinha, P. M. 2005. Nanoengineered implantable devices for controlled drug delivery, Ph.D. Th e sis, Th e Ohio State University. With permission.)

6.3.2.2 Diffusion Studies

Diff usion characteristics of nDS1 were initially investigated using glucose as a model molecule. Th ese studies suggested that these devices (60 nm and 100 nm channel size) permit the release of glucose in a linear fashion, in accordance with “zero-order” kinetics for the period investigated (Sinha et al., 2004;

Lesinski et al., 2005). Figure 6.15a shows glucose release profi le from a 100 nm device. Next, it was tested whether the pore size (100 nm) of the nDS devices would permit the diff usion of functionally active IFN-α. For this, diff usion chambers containing the nDS were mounted on individual wells of a Costar Transwell p late, to w hich a s olution c ontaining 1 9 μg/mL I FN-α ( equivalent to 5 .94 × 1011 μM) was added. Plates were incubated at room temperature with gentle shaking. Aliquots from the bottom chamber of the Costar Transwell plate were removed daily (days 0–7), snap frozen and stored at −80°C until they were analyzed for IFN-α content by commercial ELISA (R&D Systems, Inc.). Release profi le for IFN-α also demonstrated sustained release for the period investigated (Figure 6.15b). Further studies using phosphorylated STAT1 (P-STAT1) a s a m arker of I FN-α ac tivity i n v iable PBMCs a nd t umor cells confi rmed that functionally active IFN-α could diff use through the nDS1 microchip. By w ay of comparison, subcutaneous administration of IFN-α-2b (3 M IU/m²) to a melanoma patient resulted in an Fsp of 1.56 in PBMCs harvested 1 h posttherapy (Figure 6.16). Th is suggested that nDS microchips used in t his study were capable of ad ministering physiologically relevant doses of IFN-α directly to

0

FIGURE 6.15 (a) Release profi les from nDS mounted in Costar diff usion chambers mounted on t he wells of a transwell plate. Glucose release (depicted as percent released) was measured on a daily basis using the Glucose-SL assay (Diagnostic Chemicals Limited) for 7 days. Data shown were derived from experiments utilizing three inde-pendent devices; (b) IFN-α release from the nDS. Th e release profi le was measured as explained above and quanti-tated by a commercially available IFN-α ELISA (R & D Systems). Data shown were derived from experiments using three independent devices. (With kind permission from Springer Science+Business Media: Lesinski, G. B. et al., 2005. Biomed. Microdevices 7(1): 71–79. Copyright 2005.)

the t umor m icroenvironment, a nd t herefore, c ould b e u sed to de velop a lternative s trategies for t he treatment of unresectable tumors (Lesinski et al., 2005). It is also important to mention here that IFN-α used for these studies was the same that is used for IV injections in clinical practice.

Nanochannel microchips described here h ave the capability of integration of electronics on board and, therefore, can be used for pre-programmed and remote-activated (drug on demand) delivery of drugs. Further, this technology off ers advantages in the scalability of the manufacturing process and exquisite device reproducibility. Additionally, these systems do not re quire the development of novel formulations for d rugs. Th erefore, a lready approved FDA formulations can be used i n t hese devices potentially re sulting i n faster c linic t ranslation of t his te chnology. C ommercial de velopment of t his technology for therapeutic use is currently being done by NanoMedical Systems (Houston, TX).

Cell type: PBMC

FIGURE 6.16 IFN-α diff uses through nDS and exhibits functional activity. (a, b) Th e functional ability of IFN-α released from the nDS was confi rmed by measuring P-STAT1 in PBMCs or MEL 39 tumor cells in the bottom well of transwell plates mounted with Costar diff usion chambers containing the nDS (as shown in Figure 16.5). Clear histograms represent PBS-treated PBMCs and shaded histograms represent PBMCs responding to IFN-α diff using through t he n DS. (c) P-STAT1 le vels i n PBMCs of a p atient w ith m alignant me lanoma h arvested i mmediately before and 1 hour aft er subcutaneous administration of 3 M IU/m² of IFN-α2b. Th e M1 marker denotes the mea-sured region, which was set based on a background staining from an isotype control antibody. All data were derived from at le ast 1 0,000 e vents gat ed on t he l ymphocyte p opulation. ( With k ind p ermission f rom Spr inger Science+Business Media: Lesinski, G. B. et al., 2005. Biomed. Microdevices 7(1): 71–79. Copyright 2005.)