Scientists Create Dynamic Mechanical Materials

The scientists have unveiled a radically new approach for developing polymer nanocomposites which alter their mechanical properties when exposed to certain chemical stimuli.

In their new approach, the team used a biomimetic approach - or mimicking biology - copying nature's design found in the skin of sea cucumbers.

"These creatures can reversibly and quickly change the stiffness of their skin. Normally it is very soft, but, for example, in response to a threat, the animal can activate its 'body armor' by hardening its skin," explains one of the scientists. Marine biologists have shown in earlier studies that the switching effect in the biological tissue is derived from a distinct nanocomposite structure in which highly rigid collagen nanofibers are embedded in a soft connective tissue.

Building on their recent success on the fabrication of artificial polymer nanocomposites containing rigid cellulose nanofibers, the team mimicked the architecture nature 'designed' for the sea cucumbers and created artificial materials that display similar mechanical morphing characteristics.

The 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.

"We believe that electrodes that use mechanically adaptive polymer as substrate could alleviate this problem" explains one of the scientists. The development and testing of experimental microelectrodes that involve the new adaptive materials is currently underway. "That's why we designed our first materials to respond to water. This allows the rigid electrodes to become soft when implanted into the water-rich brain" he adds.; Source: Case Western Reserve University