Under the fluorescent lights of Harbor City General’s outpatient clinic, a tray of electrodes, saline pads and tiny labeled vials became the centerpiece of a standing-room lesson Friday: in iontophoresis, drugs don’t all travel the same way, even when the same battery powers the patch.

The session, led by biomedical engineer Dr. Priya Nanduri and dermatology nurse educator Luis Ortega, was prompted by a spike in staff questions after the hospital expanded its iontophoretic options for localized pain control and anti-inflammatory delivery.

“People hear ‘electric drug delivery’ and picture one thing — like the current is a conveyor belt,” Nanduri told the group, gesturing toward a demo rig humming quietly at a low setting. “In practice, there are two main rides. One is a push. The other is a sweep.”

Two mechanisms, two everyday pictures

Nanduri framed the distinction with analogies that drew nods from nurses who said they were tired of vendor jargon.

• Electromigration (the ‘push’): “Think of like charges repelling,” she said. “It’s the way two magnets with the same pole won’t sit together. The electrode of the same charge as the drug acts like that stubborn magnet — it pushes the charged drug away and into the skin.”

• Electroosmosis (the ‘sweep’): Ortega compared it to water moving through a sponge. “Skin has tiny pathways,” he said, holding up a porous training pad. “When the current runs, fluid can drift through those pathways. If the fluid is moving, it can carry along passengers — even ones that aren’t charged — like leaves floating in a slow stream.”

The analogies mattered, Ortega said later, because “staff don’t dose with equations — they dose with intuition.”

A compact ‘total flux’ breakdown, as the team uses it

Rather than writing formulas on a whiteboard, Nanduri offered a simple running tally she said her lab uses when troubleshooting why a patch underperforms.

“In our notes, total delivery into the skin is the sum of a few pieces,” she said, listing them in plain terms:

• Baseline seepage: what would drift in without current (the “background” movement).
• Electromigration: the electric push on charged molecules.
• Electroosmosis: the current-driven fluid flow that can carry solutes as riders.

“When delivery is lower than expected, it’s usually because one of those pieces is smaller than we assumed,” she said.

Directionality guide: who goes where — and who can hitch a ride

A common source of confusion, speakers said, is assuming polarity alone answers every question. Nanduri described a “directionality guide” the hospital is adding to its internal protocol sheet.

• Cations (positively charged): “They’re repelled by the anode or the cathode?” a therapist asked.

  “Repelled by the electrode with the same sign,” Nanduri replied. “So cations are pushed away from the positive electrode (anode) and into the skin beneath it.”

• Anions (negatively charged): “Same idea,” she said. “Anions are pushed away from the negative electrode (cathode) and into the skin beneath it.”

• Neutral solutes (no net charge): Here, Ortega said, the workshop’s biggest “aha” moment tends to land.

  “Neutrals don’t get the electric push,” he said. “But if the current sets up fluid flow, neutrals can still move because they ride with that moving fluid. That’s electroosmosis — the hitchhiking effect.”

In the demo, Ortega added a neutral dye to a training membrane and asked staff to predict its movement. “Half the room said, ‘It won’t go anywhere,’” he said. “Then they watched it creep along with the flow.”

What changes the balance between push and sweep

In a short Q-and-A, clinicians asked why two drugs can behave so differently under the same settings.

Nanduri said the balance is shaped by what the solute is and what the skin is.

On the drug side:

• Charge: “If it’s strongly charged at skin pH, electromigration can dominate,” she said. “If it’s neutral, you’re mostly betting on flow.”
• Size: “Bigger molecules are harder to move through tight pathways,” Ortega said. “They may need more help from fluid flow — or may simply not fit well.”
• Ionic mobility: Nanduri described it as “how easily the ion moves when the field is on.” Some ions “respond quickly” and others “drag along,” she said.

On the skin side:

• Fixed charge: “Skin isn’t a blank filter,” Nanduri said. “It carries fixed charges that can encourage fluid flow in one overall direction during current.”
• Pore pathways: Ortega pointed to sweat ducts and hair follicles on a diagram taped to the cart. “Those pathways can act like express lanes,” he said, adding that their availability varies by site and patient.
• Hydration: “Hydration changes conductivity and opens up pathways,” Ortega said. “A dry site can turn a good plan into a slow trickle.”

A physical therapist in attendance, Jenna Cho, said she plans to adjust her prep routine. “I didn’t realize how much the ‘sweep’ depends on hydration,” she said. “That’s something I can control before I ever change the current.”

Common misconceptions (callout)

What staff kept getting wrong — and what the workshop corrected

• “Neutrals can’t move.” Neutrals may not be pushed by charge, speakers said, but they can still be carried along by electroosmotic flow.
• “Polarity alone determines everything.” Polarity matters for electromigration, Nanduri said, but skin properties and fluid flow can amplify, blunt or even overshadow the simple “like charges repel” story.
• “More current always means more delivery.” Ortega cautioned that comfort limits, skin irritation risk and shifting pathway behavior can mean the relationship is “not a straight line in real patients.”

A small change in language, a big change in troubleshooting

By the end of the hour, the workshop’s refrain had condensed into a practical checklist.

“When a patch doesn’t work, don’t just ask, ‘Did we pick the right polarity?’” Nanduri told the room. “Ask: Are we relying on push, sweep, or both — and what did the skin allow today?”

Harbor City General said it will roll out a one-page bedside guide next month and add a short competency module for new staff. Ortega, stacking the demo pads back into their case, said the goal is less mystery and more predictable care.

“If you know which ride your drug is taking,” he said, “you’re less likely to chase the wrong fix.”