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Science and glue



Lab masters study nature, babies and tape for new ideas.



By Jack Kenny, Contributing Editor



Published October 14, 2013
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Let us now praise scientists. In the last issue, I wrote about a new self-adhesive patch whose chemical coatings make the wearer invisible to mosquitos. That is but one functional label technology that the folks in the lab coats are working on today. The practitioners of science study everything within reach with the aim of finding ways to improve and benefit life on earth. A great many of the studies reveal fascinating chemistries found in plants and animals, compounds such as adhesives and coatings that are critical to the lives of the creatures, and possibly of use to humans. Many such discoveries, when they become available for use, will be converted products.
Consider the bandage. Many of us get our blood checked on a regular basis, or donate blood. Tell me: Do you lose a few arm hairs when you rip that tape off? How many kids cry when it’s time to remove the Band-Aid?

A newborn doesn’t have an epidermis, the strong outer layer of skin. Medical tapes used to secure equipment such as monitors or respirators can cause damage when peeled off, including the removal of skin. In babies, such scarring can take months of care to heal.
Late last year, a research team at Brigham and Women’s Hospital (BWH), in Boston, MA, USA, published news that it had invented a quick-release tape that has both strong adhesive properties and a gentle release. The study was made in collaboration with The Institute for Pediatric Innovation and with Robert Langer at the Massachusetts Institute of Technology.

Traditional two-layer medical tapes have a polymer backing and an adhesive. The new tape has three layers.

“Current adhesive tapes that contain backing and adhesive layers are tailored to fracture at the adhesive-skin interface. With adults the adhesive fails leaving small remnants of adhesive on the skin, while with fragile neonate (baby) skin, the fracture is more likely to occur in the skin, causing significant damage,” says Jeffrey Karp, head of the research team at the BWH Division of Biomedical Engineering, Department of Medicine. “Our approach transitions the fracture zone away from the skin to the adhesive-backing interface, thus completely preventing any harm during removal.”

Early efforts focused on making weaker adhesives, which are less damaging to skin, but which do not hold devices securely. The new design incorporates an anisotropic (of unequal physical properties along different axes) adhesive interface between the backing and adhesive layers.

A standard medical tape backing is made of a thin sheet of polymer such as polyethylene terephthalate (PET). To create the new middle layer, the researchers coated the side that contacts the adhesive with a thin layer of silicone, forming a release liner. Adding this layer alone made it too easy for the tape to be pulled off, so they etched grid lines into the silicone with a laser, exposing some of the PET backing. The PET sticks to the adhesive layer more strongly, so the researchers can control the adhesion of the release liner by altering how much of the PET is revealed by the grid lines.

Once the backing is peeled off, any remaining adhesive left on the skin can safely be rolled off with a finger using a push-and-roll technique.

One glue, two victims
Consider the common house spider. The spider’s web is one of nature’s wonders, and for its size it is stronger than steel. Scientists have always examined spiders for their webs, their composition and their behaviors, and recently they have discovered an unusual talent of the house spider.

Biologists and polymer scientists at the University of Akron, Ohio, USA, have discovered that Parasteatoda tepidariorum has an unusual art. It manufactures one glue inside its body, but it employs two adhesive strengths in its webs, depending on the type of prey it hunts. The UA scientists report that the spiders use adhesive disks with a strong grip to anchor webs to ceilings and walls when they want to catch flying food; when prey is crawling on a surface, they give the adhesive disks a weak formulation.

Airborne insects have velocity, and the webs anchored with the strong adhesive formula are necessary to halt their flight and render them lunch. But when a walking insect makes contact with a surface-bound web, the weak adhesive grip snaps away from the ground, binding the prey and suspending it in the air. Dessert.

“We were intrigued by how cleverly spiders use silk to create a beautifully multifaceted adhesive and how they do so with very little glue,” says researcher Ali Dhinojwala, UA Department of Polymer Science chair and Morton Professor of Polymer Science. “It teaches us how to take something minimal and make the most of it – how to design an attachment to hold things together in unique ways.”

“When we made the discovery of the gumfoot adhesive disc that binds cobwebs lightly to the ground and compared it with the scaffolding adhesive discs, which attach cobwebs very firmly to walls and ceilings, we thought, ‘How is this spider using the same glue to design both a weak and a strong attachment disc?’,” says Vasav Sahni, a recent PhD graduate from the UA department of polymer science and currently a senior research engineer at 3M.

“What we have also discovered is a key design principle,” Sahni says. “It’s not a question of the inherent chemistry of the glue, but how the same glue can have different degrees of adhesion.”

A drop of water

3M’s Scotch tape, laser-thinned, captures water droplets for testing.
Consider Scotch tape. 3M’s indispensible creation continues to amaze. Manuel Ochoa, a doctoral student at Purdue University in West Lafayette, IN, USA, was collecting pollen when he learned that the tape curled when it was exposed to humidity. The tape is composed of a cellulose acetate sheet and an adhesive. The cellulose acetate absorbs water, but the adhesive repels it, so when the absorbent side expands, the adhesive stays the same, and the tape curls.

Smart thinkers at Purdue worked with this seemingly ordinary occurrence, and came up with a new product. They used a laser to machine the tape to one-tenth of its thickness, which enhanced the curling behavior. Then they formed little fingers a half-centimeter long from the tape. They manipulated the fingers into a small claw that can capture droplets of water. Researchers coated the fingers with magnetic nanoparticles so they could be collected with a magnet.

Water is a big issue, the biggest problem that humans face today and beyond. Water testing is a huge and costly business, and it can use every break that it can find. The little fingers of Scotch tape offer great promise to that industry.

Babak Ziaie, a Purdue professor of electrical and computer engineering and biomedical engineering, says that the discovery can be used to collect water samples for environmental testing. “It can be micromachined into different shapes and work as an inexpensive smart material that interacts with its environment to perform specific functions.”




The author is president of Jack Kenny Media, a communications firm specializing in the packaging industry, and is the former editor of L&NW magazine. He can be reached at jackjkenny@gmail.com.


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