From the poster titled: Active tunable release of therapeutics

through the nanochannel Delivery System (nDS)

Giacomo Bruno, R. Thomas Geninatti, and Alessandro Grattoni

Department of Nanomedicine, Houston Methodist Research Institue, Houston, TX 77030

Abstract

The nanochannel Delivery System (nDS) leverages a nanofluidic membrane manufactured with high accuracy silicon microfabrication techniques for the sustained, zero-order release of drugs. Therapeutic release has been maintained at clinically relevant dosages for periods ranging from weeks to months. However, drug release from the nDS is passively controlled and diffusion-based, limiting its employment to constant delivery applications. Here, we present the next generation of nDS (nDS2) implants which demonstrated active control of therapeutic release through application of a low voltage potential (< 2 V) between the inlet and outlet of the membrane’s fluidic channels. Platinum electrodes were deposited on the membrane surfaces and electrical behavior, degradation, chip communication and biocompatibility of the altered membrane were evaluated. This nDS2 has the potential to enable successful development of actively tunable implantable delivery devices.

nDS Platform

The nanochannel Delivery System (nDS) membranes were manufactured using high precision silicon microfabrication techniques, achieving passive long-term zero-order release through nanoconfinement and limiting diffusive drug release from an implantable reservoir. The nanochannels within these membranes constrain diffusion through dimensional confinement and surface-to-molecule interactions which dominate nanoscale analyte diffusion (1).

nDS Platform

Prototypes of the control unit and implant circuit were developed in our lab based on CC2541 microcontrollers (Texas Instruments).

nDS2 Fabrication

Silicon wafers (700 µm thick) were coated by chemical vapor deposition (CVD) with a 1.7 µm SiN film. Three separate methods were employed to integrate the electrodes on the chip surface: i) electron beam (e-beam) deposition of a Pt film, ii) sputter deposition of a Pt coat, and iii) laminated Pt foil. For i) and ii), a SiO2 (250 nm) substrate was deposited on the SiN surface in the presence of argon plasma to ensure a defect-free dielectric layer. Then, a Ti adhesion layer was formed prior to the final Pt film. Ti (10 nm) and Pt (60 nm) layers were deposited at three different angles of deposition with respect to the substrate surface (30°, 45° and 90°), achieving equal layer thicknesses perpendicular to the substrate. For iii) Pt foils (100 µm thickness) were obtained from Sigma Aldrich and laser-cut to a 6 mm x 6 mm square shape.

Electrodes Characterization and Communication Test

Electrodes were characterized in terms of electrical behavior, degradation, and biocompatibility. Electrical behavior was evaluated through electrical impedance spectroscopy (EIS). Franks’ model of electrode-electrolyte interface (2) was employed to calculate the parameters of electrical capacity, leakage resistance, and surface roughness. Atomic force microscopy (AFM) and inductively coupled plasma mass spectroscopy (ICP-MS) were utilized to quantify degradation. Biocompatibility was assessed by measuring cell viability through an MTT assay.

Electrodes Characterization and Communication Test

Degradation values. A) degradation values over time, B) degradation values under active (1.5 V) and passive (0 V) conditions, C) degradation values at room temperature (23°C) and accelerated conditions (90°C). The asterisk (*) highlight a P<0.05

Electrodes Characterization and Communication Test

Electrical Impedence Spectroscopy of different electrodes over time in both PBS solution and in cell colture

Electrodes Characterization and Communication Test

MTT cell proliferation assay for the platinum electrodes with no voltage (passive mode) and 1.5 V (active mode) configurations

Electrodes Characterization and Communication Test

ICP-MS for the quantification of the electrodes degradation over time

The deposited electrodes prove similar in electrical behavior to the Pt foils in the LF and HF regimes once constant impedance is considered. Degradation tests showed that the electrodes present high integrity and biorobustness. ICP-MS results showed negligible degradation. MTT results are preliminary indications of the biocompatibility. The implant prototypes were tested for RF-communication. Successful communications were achieved at and below the distance 0.9 m (in water) and 1.5 m (on rats).

Release

• Based on the results, we selected the 45° e-beam deposition method as the ideal approach to fabricate Pt electrodes on the surfaces of pre-microfabricated, 200 nm nanochannel membranes. By tu-ning an electrical potential between the electrodes in the range of -1.5 VDC to +1.5 VDC, elec-trophoretic control of dendritic fullerene 1 (DF-1) was achieved.

Release

A) Schematics of the custom release testing apparatus. (B) nDS membrane with electron beam deposited electrodes placed onto the polyether ether ketone (PEEK) body of the diffusion testing apparatus. PEEK was used as it is nonconductive. (C) nDS membrane assembly with Pt-foil electrodes, e, and silicon gaskets, g.

Conclusions

The second generation of nDS implant technology has been developed. The first tunable release from the nanochannel membrane has been demonstrated. Further in vitro and in vivo studies will be necessary to develop effective active tunable release from the implant. The capability of this nanotechnology platform to temporally control the diffusive release of molecules offers potential solutions in management of several chronic diseases such as cancer, heart disease, circadian dysfunction, hypertension, and pain, as well as directly enabling modern treatment regimens such as chronotherapy.

References

1. Cosentino, C. et al. (2005). Dynamic model of biomolecular diffusion through two-dimensional nanochannels. The journal of physical chemistry. B 109, 7358-7364.

2. W. Franks, I. Schenker, P. Schmutz and A. Hierlemann, Impedance Characterization and Modeling of Electrodes for Biomedical Applications. IEEE Trans Biomed Eng 52(7): 1295-1302 (2005)

Acknowledgements

The authors are thankful to Jeff Schmulen for his expertise on nanofabrication, Dr. R. Lyle Hood and Dr. Eugenia Nicolov for laboratory assistance, and NanoMedical Systems, Inc. (Austin, TX) for provision of the nDS membranes.