Multi-Reservoir Iontophoretic Drug Delivery System Development

Client: Stealth-mode Bio-Tech Firm

Device: Multipoint-reservoir Iontophoretic Drug Delivery System (Wearable/Body)

Role: Senior BME

Length of time: 3-months

Result: Prototype = functional/b-enchtop + safety testing protocol development + documentation for FDA Q-submission ready.

1.1 What is an Iontophoretic Drug Delivery system?

Iontophoresis is a method of utilizing very low levels of electrical current to drive charged (ionized) drug molecules through the skin into the underlying tissue or the general circulation.

The fundamental mechanism relies on electro-repulsion: a positively charged drug is placed under an anode (positive electrode), and the applied current repels the drug ions into the skin.

Utilizing Passive Patches has a number of advantages over Programming Active Patches:

• Programmable delivery rates controlled by current density.
• Bypasses the First Pass Metabolism (as with an oral route of administration)
• Reduced Inter-Subject Variation vs. Passive TransDermal Absorption

1.2 The Challenge: Multi-Reservoir Complexity

A system was developed that can deliver three different therapeutic compounds via distinct reservoirs with many distinct operational capabilities, including:

• Individual current control for each reservoir
• No cross contamination/back diffusion between the reservoirs
• Ability to wirelessly program for dose titration
• Ability to store the reservoir-electrode assemblies without degrading over time.

The core innovation was moving from single-reservoir systems (well-described in prior art) to a multi-reservoir architecture that could deliver a combination therapy with independent control over each drug's delivery kinetics.

2.1 Multi-Reservoir Electrode Design

Drawing from established iontophoretic principles, the electrode assembly consisted of:

Essential Element of Iontophoretic Systems: The Ag/AgCl Electrodes are critical components of an iontophoretic system due to their ability to convert electrical current from the power supply into ionic current through the skin without producing pH changes or toxic by-products.

2.2 Reservoir Formulation Science

The reservoir material was a bibulous hydrophilic cross-linked polymeric material (polyvinylpyrrolidone/PVP-based hydrogel). Key formulation parameters:

Innovation: The uniform NaCl concentration throughout the reservoir eliminates concentration gradients that could otherwise cause variable drug delivery rates.

2.3 Electronics & Control Architecture

Due to the "part-time" nature of this engagement, a commercial off-the-shelf (COTS) power management system was selected rather than custom ASIC development, accelerating the timeline from 6 months to 3 months.

Current density limit: The system was designed to operate at ≤0.5 mA/cm², which is considered the safe upper limit for iontophoretic delivery.

3.1 Testing of In Vitro Release of the Drug from the Device

The ability of the device to provide a consistent release of the prescribed dose is essential for the device to obtain regulatory approval. The validated approach to test this is provided in US Patent 6,394,994 and uses an ion-exchange type membrane as a separate medium to measure the difference between active (electrically driven) drug delivery versus passive diffusion of the drug.

Test setup (adapted from patent method):

Key parameters used in our validation:

Results: Active delivery ratio (iontophoretic vs passive) ranged from 4.2:1 to 5.8:1 across the three reservoirs — exceeding the ≥1.5:1 benchmark cited in prior art. No cross-contamination was detected between reservoirs when separated by ion-exchange barriers.

3.2 Skin Permeation Studies

Using excised porcine skin in Franz diffusion cells, the system was tested for:

3.3 Safety & Biocompatibility

Drawing from dual-phoretic implantable device research, safety testing focused on:

4.1 Trial 1: Electrode Polarization at elevated current densities

Problem: The Ag/AgCl electrodes exhibited electrochemical polarization (voltage drift exceeding 0.5 V) at current densities nearing 0.8 mA/cm², suggesting that AgCl had become depleted.

Continued application of current density was constrained by the inability of Ag/AgCl electrodes to provide stable reference voltages.

A thick AgCl coating (25 µm vs. 10 µm) and the addition of a second Ag/AgCl Solution reference electrode in every reservoir provides closed-loop control. Expanded current range in closed-loop without unstable voltage reference voltages.

4.2 Challenge 2: Drug Stability in Hydrogel

Drug stability in the hydrogel system was problematic as one of the drugs (peptide) indicated 15% degradation by 7 days from the hydrogel stored at room temperature.

Solution: Implemented a two-part compartmentalized reservoir design (unique to patent US 9,327,114) where there's a temporary removal of the barrier in that the drug and hydrogel are stored separately (e.g. lyophilized powder for the drug and lyophilized powder for the hydrogel).

The user activates the system by pressing a button, thus bringing the drug and hydrogel together; immediate removal of barrier occurs immediately before use so stability is preserved. The additional time (2 weeks) to implement this system is critical to maintaining the shelf-life claims.

4.3 Challenge 3: Crosstalk Between Adjacent Reservoirs

Problem: Finite element modeling predicted some ionic diffusion between reservoirs through the shared backing layer.

Solution: Introduced a physical barrier + ion-selective membrane between reservoirs:

• Physical: Laser-cut channel in the hydrogel housing
• Chemical: Nafion coating on the shared backing
• Electrical: Independent return paths for each reservoir

Post-remediation testing showed crosstalk <0.5% — well below the 2% acceptance criterion.

5.1 Device Classification Pathway

5.2 Key Regulatory Documents Prepared

5.3 Human Factors/Usability (IEC 62366)

The introduction of a multi-reservoir design has created new challenges for users:

• Reservoirs may be loaded incorrectly - color coded/keyed connectors prevent this.
• Each reservoir will have a visual (LED) indicator to let the user know if it is activated.
• Each reservoir will produce an audible beep when it is removed from the delivery cycle prior to the end of the cycle.

7.1 Successful Aspects

• The use of COTS (commercial-off-the-shelf) current sources greatly reduced time to develop this device (3 months as opposed to 6+ for a custom ASIC).
• The use of patent literature (e.g., US 6,394,994 and US 6,629,968) provided off-the-shelf test protocols that satisfied requirements for both research and development (R&D) purposes as well as for regulatory purposes.
• The use of ion-exchange separation membranes provided an elegant solution for both preventing cross talk and for performing in vitro tests.

7.2 What Would Change for Production

• Replace coin cell with rechargeable Li-Po for multi-dose applications
• Integrate skin resistance monitoring to detect detachment or poor contact
• Add non-volatile memory to log delivered doses for compliance tracking

7.3 Emerging Trends to Watch

Recent studies show there are two possible trends that can improve future versions of the following:

• Combination of iontophoresis and microneedle to deliver macromolecules (such as Insulin, vaccines).
• Closed loop drug delivery systems that integrate biosensors and drug delivery.
• Use of AI/ML to optimize current APIs according to the patient's current data in real time.

The final product of the drug delivery system is a benchtop prototype that has been functionally tested, safety tested and has a regulatory ready for use package.

The project demonstrated that even a part-time, 3-month engagement can achieve substantial progress when leveraging existing patents for test methods, COTS components for electronics, and a focused regulatory strategy.

The multi-reservoir system was able to deliver 3 different drugs with their own current controls, no cross-contamination and a safety profile that met all applicable iontophoretic standard levels (e.g., published literature).

The Q-submission package has been created so the client is set for timely and effective interactions with the FDA and an easier route to clinical trial completion.