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Micro Needles: No pain, great gain

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Posted January 7, 2014

It’s a common scene in doctor’s offices everywhere: a child refuses to roll up his sleeve for a routine vaccination; the needle will sting. But the days of the menacing hypodermic needle could be over.

Researchers are developing microneedles, a small patch of teeny tiny needles that can be used to administer medication and vaccines pain-free. The next generation of children may never know the anxiety triggered by a visit to the doctor. To them, a vaccine will simply be a small patch of miniscule cones pressed against their skin.

UBC’s Boris Stoeber is working on a method to fabricate inexpensive microneedles. Photo: Martin Dee.

UBC’s Boris Stoeber is working on a method to fabricate inexpensive microneedles. Photo: Martin Dee.

“Microneedles are being developed for comfort but they also allow for new concepts of medical treatment,” says Boris Stoeber, a professor of mechanical engineering and electrical and computer engineering.

No nerves, no pain, no problem

The goal of creating a painless drug delivery system using microneedles took off in the 1990s thanks to microelectromechanical systems or MEMS, an emerging field of engineering. It allowed scientists to explore ways to get medication and vaccines into the bloodstream without touching any nerves.

Skin is made of two layers, the epidermis and dermis. Microneedles are designed to puncture the outer epidermis layer, which acts as a protective shield, but not the dermis, which houses nerves and blood vessels. The drug is released into the epidermis and diffuses to the dermis and then the bloodstream.

While some researchers are developing solid microneedles that release drugs into the skin as they dissolve, Stoeber’s lab focuses on hollow microneedles, which are shaped like volcanoes, hollow cone or pillar-like structures. Size varies but they are mostly between 200-500 micrometres long and 50-80 micrometres in diameter, about the same diameter as a human hair. To get enough medication through such tiny structures, several microneedles are positioned on a small patch called an array.

Challenges

The first hollow microneedles were made of silicon but were expensive to produce. With their price tag, they could never be widely available.

This is where Stoeber’s lab comes in. They are working on a method to fabricate inexpensive microneedles that would be widely accessible. They’ve had some initial successes by creating a mold of cone-shaped micro-pillars and bathing it in polymer or plastic solution. As the solvent evaporates, the plastic microneedles form around the pillars.

As they get closer to finalizing a fabrication technique, they are also dealing with the next set of obstacles.

“There are still lots of unknowns. We’re not quite clear about the exact shape, the depth, or the process for delivering the drug,” he says. “Do you push it out with a high-speed impact or slowly let it diffuse out? These are things we have to investigate.”

A game changer for health care?

While the idea of a pain-free shot is exciting for adults and children who fear needles, there are other ways that microneedles can impact health care.

Replacing hypodermic needles with microneedles eliminates the process of injection and the risk of doing damage to nerves or blood vessels. With a simple patch anyone can administer certain drugs and vaccines. Self-administered needles could be hugely beneficial to people living in areas where access to medical professionals is limited.

Microneedles could also have a dramatic effect in the field of biosensing. As a postdoc Stoeber was involved in creating a microneedle-based concept to constantly monitor blood-glucose levels, a life-changing application for those living with diabetes. The days of pricking your fingers and worrying about blood sugar levels getting too high or too low in between checks would be gone.

For oncologists treating patients with cancer drugs, a similar microneedle application could allow them to monitor the concentration of medication in the patient’s blood. Stoeber has also teamed up with UBC colleagues in Dermatology and Pharmaceutical Sciences to examine whether microneedles will improve the effectiveness of drug delivery

“Microneedles can replace hypodermic needles for applications where injecting small volumes of drugs is sufficient” says Stoeber, Canada Research Chair in Microfluidics and Sensing Technology. “It’s exciting to try to solve fundamental problems with a very practical application.”

Not every graduate student successfully engineers a game-changing medical device or gets to observe a never before seen type of physics. But for Iman Mansoor and Ashkan Babaie, who study microfluidics in Boris Stoeber’s lab, this is part of their PhDs.

Mansoor was tasked with finding an inexpensive way to fabricate microneedles. He started by creating them out of a polymer, or plastic, material. A solution of the polymer and a solvent is mixed and set to dry on a mold containing an array of cone-shaped micro-pillars. As the solvent evaporates, the microneedles form out of the polymer material.

To make the microneedles stronger and more durable, Mansoor added a couple of steps to the fabrication process. He casts a conductive polymer layer on the mold that allows an electrical current to travel through, then he electroplates the mold with metal. The resulting microneedles are made of metal just like a hypodermic needle and an array costs about 10 cents.

While Mansoor honed in on the fabrication, Babaie is charged with understanding what is happening to the polymer solution as it dries into the volcanic microneedle shape. He works in the field of microfluidics, they study of how very small amounts of fluid flow. Microfluidics, an offshoot of MEMS, is essential for understanding the fabrication of the microneedle itself and for drug delivery.

Babaie looked for very small currents or flows forming during the evaporation process. Understanding how the solution of polymer moves during this step is crucial to refining the microneedle’s shape.

As expected, Babaie observed polymer solution flowing toward the micro-pillar structures as the solvent evaporated, creating the shape of the microneedle. But as he looked closer at the flow, he also noticed a small vortex forming at the base of the microneedle. This was something that had never been observed or reported before. He is conducting several experiments to characterize this vortex and understand its possible effects on microneedle’s shape and mechanical strength.

Source: UBC

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