Researchers from Rutgers University, New Jersey, have created bioinspired, programmable microneedles that enhance tissue adhesion using Projection micro-stereolithography (PµSL).
Influenced by the microhooks of parasites, barbed stingers of honeybees, and quills of porcupines, 4D printed backward-facing barbs were fabricated and designed to deform horizontally to be minimally invasive upon tissue contact. Howon Lee, the senior author of the study published in Advanced Functional Materials, explained:
“We think our 4D printed microneedle array will allow for more robust and sustained use of minimally invasive, pain-free and easy-to-use microneedles for delivering drugs, healing wounds, biosensing, and other soft tissue applications.”
Bioinspired 4D printed needles
According to the researchers, hypodermic needles are prone to cause pain, scarring, and infection. As they are widely used in hospitals and labs for the extraction of blood and injection of drugs, these risks are rather common. Microneedles have been looked at as a solution as they are short, thin, minimally invasive, and negate pain and the risk of infection.
Nonetheless, regarding drug delivery, microneedles do not exhibit strong adhesion to tissues. The study states, “Typical micromanufacturing techniques for microneedle fabrication yield a smooth and plain side profile, which inevitably results in weak tissue adhesion. Some living creatures in nature have developed interesting solutions to achieve strong tissue adhesion in the microscopic length-scale.”
The Rutgers team observed that the barbed stinger of a honeybee demonstrates exhibits 70 times stronger adhesion force than a barbless acupuncture needle. Moreover, a natural quill of North American porcupine having microscopic backward-facing deployable barbs was recognized to display three times higher tissue adhesion compared to its barbless counterpart. These creatures, as well as the microhooks of parasites, were used to form 4D printed microneedles with curving structures.
Adding movement to microneedles
4D printing refers to 3D printing object which has programmable movement or shapeshifting qualities. The transformable element of these barbed microneedles arise when they are immersed in ethanol for rinsing after the PµSL process. The uncured monomers in the bottom portion of the barbs diffuse out leaving behind loose spaces, causing them to face the opposite direction after insertion.
Using chicken muscle tissue as a soft tissue model, the researchers achieved 18 times stronger tissue adhesion with these microneedles when compared to barbless needles. “We demonstrated control of thickness and bending curvature of the barbs by controlling light exposure time and material composition of the precursor solution,” the study concludes.
“4D Printing of a Bioinspired Microneedle Array with Backward‐Facing Barbs for Enhanced Tissue Adhesion” is co-authored by Daehoon Han, Riddish S. Morde, Stefano Mariani, Antonino A. La Mattina, Emanuele Vignali, Chen Yang, Giuseppe Barillaro, and Howon Lee.
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Featured image shows 4D printed microneedles featuring backward-facing barbs that interlock with tissue when inserted, enhancing adhesion. Photo via Rutgers University.