Biological Mechanism of Hydrolyzed Sponge-Mediated Stratum Corneum Penetration and Its Transdermal Permeation-Enhancing Efficacy:In Vitro and In Vivo Study

Imagine your skin is like a super-tough castle wall, designed to keep everything out. The very top layer, called the stratum corneum, is the castle's main gatekeeper. It's so good at its job that it blocks almost all medicines, especially the big, heavy ones (like proteins) or the water-loving ones that hate oil. Usually, getting a drug past this wall is like trying to sneak a piano through a mouse hole—it just doesn't work.

Scientists have tried to build tiny, artificial needles (made of silicon) to poke holes in this wall, creating little tunnels for the medicine to slip through. But a team of researchers asked: What if we used nature's own needles instead?

They turned to hydrolyzed sponge spicules (SHS). Think of these as microscopic, needle-like shards harvested from a specific type of sponge (Haliclona sp.). These aren't just random bits of dirt; they are sharp, cylindrical needles, about 80–120 μm long and 8–15 μm wide, made of silica (glass-like material).

The Big Surprise: It's Not Just a Puncture

The researchers expected these sponge needles to work just like the silicon ones: poke a hole, let the drug in, and move on. But they discovered something much cooler.

The paper explicitly rules out the idea that sponge spicules work only by making physical holes. If they were just boring holes, they should have performed exactly the same as the silicon needles. But they didn't. The sponge needles were 1.5 times better at getting drugs through, especially for the tricky big and oily molecules.

Why? Because the sponge needles do a "double-tap":

1. Physical Puncture: They physically poke high-density micro-channels through the skin wall.
2. Biological Magic: They also send a temporary signal to the skin cells to loosen up their "security guards."

The "Loose Security" Analogy

Imagine the skin cells are like bricks in a wall, held together by mortar (lipids) and locked doors (tight junction proteins called claudin-1 and occludin).

• The Silicon Needle: Just punches a hole in the wall. The doors and mortar around the hole stay locked and tight.
• The Sponge Needle: Punches the hole and tells the doors to unlock for a little while.

The study found that after using the sponge needles, the expression of those "lock" proteins (claudin-1 and occludin) dropped significantly. At 12 hours after treatment, the levels of these proteins were down to about 31.5% and 40.2% of normal, respectively. This temporary "unlocking" created extra pathways for drugs to slip through the gaps between cells, not just through the holes.

How Well Did It Work?

The researchers tested this with four different "model drugs" (fake medicines with different sizes and properties) and compared the sponge needles to silicon needles and a "do nothing" control.

• For the Oily Drug (Protoporphyrin IX): The sponge needles boosted the amount of drug getting through by 12.3 times compared to doing nothing. The silicon needles only managed 8.1 times.
• For the Big Protein (BSA, 66.5 kDa): This is a huge molecule that usually can't get through at all. The sponge needles boosted it by 6.1 times, while silicon only got 4.0 times.
• For Small Water-Loving Drugs: Even for these, the sponge needles were better, boosting permeation by 5.8 to 9.2 times.

The paper suggests that the more "oily" (hydrophobic) the drug is, the better the sponge needles work, with a strong link between the drug's oiliness and how well it got through.

Is It Safe? Will the Castle Stay Broken?

A major concern with poking holes in skin is: Does the wall stay broken?
The paper measured this carefully. They found that the skin's barrier function (measured by how much water escapes, called TEWL) did get temporarily damaged. It went from a normal 8.3 ± 1.2 g/m²/h up to 21.7 ± 2.8 g/m²/h on day 3 of treatment.

But here is the good news: The skin heals itself fast.

• By 24 hours after stopping the treatment, the barrier started fixing itself.
• By 48 hours, it was mostly back to normal.
• By 72 hours, the barrier was fully restored, with water loss back to 9.2 ± 1.5 g/m²/h (statistically the same as the start).

The paper also checked if the sponge needles were toxic. They tested them on mouse cells and found the cells were still 80% alive (a safety grade of 1), and when tested on rabbit skin, the irritation was "very mild" and gone within 24 hours.

What the Paper Does NOT Say

It's important to know what this study didn't prove.

• It did not prove this works on human skin yet. All the tests were on rats, mice, and rabbits.
• It did not prove this cures diseases in people. It only proved it helps drugs get through the skin in a lab and in animals.
• It did not say the sponge needles are perfect for everyone. The authors suggest that for people with already damaged skin (like eczema or psoriasis), the results might be different because their "castle walls" are already broken.

The Bottom Line

This study suggests that hydrolyzed sponge spicules are a powerful, natural tool for delivering medicine through the skin. They work better than artificial silicon needles because they combine physical poking with a temporary, reversible biological loosening of the skin's barriers.

The magic happens quickly (within 30 minutes to form channels) and heals quickly (within 48–72 hours). While it's not a cure-all for every skin condition yet, it offers a fascinating new way to think about how we can sneak medicines past our body's toughest guards.