Biologically-Inspired Patterned and Coated Adhesives for Medical Devices

The challenge of having a medical device robustly and reversibly adhere to a tissue in a minimally-invasive way during a clinical procedure is significant and has yet to be solved. Materials that could perform this adhesion would be valuable for use in a wide array of devices, including wired and wireless endoscopes for gastrointestinal interventions; cardiovascular devices such as mobile robots that transverse the heart surface or fixation devices for open heart surgery; and for adhering craniectomy devices to the skull during decompressive treatment. Fibrillar patterned adhesives inspired by the micro- and nano-scale structures on the feet of geckos have been widely studied and synthesized and have shown great potential for reversible adhesion in dry environments. Preliminary work has also been conducted to enhance the adhesion of these materials in wet conditions by coating them with polymers that include dopamine methacrylamide (DMA), a synthetic sticky polymer inspired by the material found naturally in the holdfasts of mussels. These coated materials demonstrated wet adhesion enhancement at the nano-scale, but not at the macro-scale and not when compared to unpatterned materials. In this work, we take previously-developed gecko-inspired patterned arrays of fibers with mushroom-shaped tips which have demonstrated enhanced adhesion with respect to unpatterned materials in dry conditions and coat them with these same synthetic mussel-inspired polymers to enhance adhesion in fully-submerged wet environments. DMA-containing polymers were synthesized through a multistep process and applied to an array of micro-scale polyurethane fibers by stamping. Material samples were tested in a custom-built adhesion measurement system in contact with a 6 mm glass hemisphere in both dry and wet conditions. Flat DMA-stamped samples demonstrated as much as 7 times enhancement over uncoated samples, while patterned, coated samples demonstrated as much as 23 times adhesion enhancement. The sample also maintained 65% of its adhesive ability over 100 test cycles. These materials are the first to demonstrate reversible fibrillar adhesion in wet conditions at the macro-scale with respect to both unpatterned and uncoated materials on non-flat surfaces using intermolecular forces instead of suction forces. Versatile reversible materials capable of adhering to non-flat surfaces in wet conditions should continue to be studied for their value for a wide array of medical device applications.