A radically new approach for developing polymer nano composites which alter their mechanical properties, particularly stiffness and strength, in a programmed fashion, when exposed to certain chemical stimuli has taken shape. The materials were designed to change from hard plastic of a CD case to a soft rubber when brought in contact with water. The new materials are tailored to respond specifically to water and to exhibit minimal swelling, so they don't soak up water like a sponge. The team mimicked the architecture nature 'designed' for the sea cucumbers and created artificial materials that display similar mechanical morphing characteristics.
Using a biomimetic approach, an interdisciplinary team of researchers from the departments of macromolecular science and engineering and biomedical engineering at the Case School of Engineering and the Louis Stokes Cleveland Department of Veterans Affairs Medical Center has published ground-breaking work on a new type of polymer that displays chemoresponsive mechanic adaptability - meaning the polymer can change from hard to soft plastic and vice versa in seconds when exposed to liquid by mimicking biology, copying nature's design found in the skin of sea cucumbers. Sea cucumbers can reversibly and quickly change the stiffness of their skin. Normally their skin is very soft, but, in response to a threat, the animal can activate its 'body armor' by hardening its skin. Marine biologists have shown in earlier studies that the switching effect in the biological tissue is derived from a distinct nano composite structure in which highly rigid collagen nano fibers are embedded in a soft connective tissue. The stiffness is mediated by specific chemicals that are secreted by the animal's nervous system and which control the interactions among the collagen nano fibers. When connected, the nano fibers form a reinforcing network which increases the overall stiffness of the material considerably, when compared to the disconnected (soft) state.

The Case Western Reserve/VA team is specifically interested in using such dynamic mechanical materials in biomedical applications, for example as adaptive substrates for intracortical microelectrodes. These devices are being developed as part of 'artificial nervous systems' that have the potential to help treat patients that suffer from medical conditions such as Parkinson's disease, stroke or spinal cord injuries, i.e. disorders in which the body's interface to the brain is compromised. A problem observed in experimental studies is that the quality of the brain signals recorded by such microelectrodes usually degrades within a few months after implantation, making chronic applications challenging. One hypothesis for this failure is that the high stiffness of these electrodes, which is required for their insertion, causes damage to the surrounding, very soft brain tissue over time. The development and testing of experimental microelectrodes that involve the new adaptive materials is currently underway.