A material inspired by the proteins in squid ring teeth could lead to new self-healing and flexible medical devices, according to researchers in the US. The synthetic material, developed from repeated sequences of proteins, could lead to fast and biocompatible proton conductors for medical implants and devices.
With proton conduction being ubiquitous in nature and having many applications in energy and electronic technologies, the team from Pennsylvania State University, NIST and the University of Maryland investigated flexible and self-healing medical devices that work on protons in the same way as biological systems. While proton transfer remains crucial to fuel cell production, cells currently use ion-transfer membranes that are made from polymers and not biocompatible.
However, the polymers shown in this study, as reported in Chemistry of Materials [Pena-Francesch et al. Chem. Mater. (2018) DOI: 10.1021/acs.chemmater.7b04574], are not only biocompatible but also self-healing, flexible and stretchable. They are bio-synthetically made by selecting the DNA sequences, so their manufacture can be programmed with varying conductivity and flexibility.
“Our goal is to understand the design rules of biological proton conductors so that we can create a synthetic protein that is as good as a non-biocompatible proton conductor”Melik Demirel
While protein-based proton conductors are not quite as powerful or efficient as polymer conductors, the study explored ways to optimize the proton conductivity. Squid ring teeth proteins, which are comprised of amino acids, involve numerous tandem repeats – short series of molecules that are arranged to repeat themselves any number of times – in their molecular make-up. Here, the team developed squid-inspired proteins with 4, 7, 11 and 25 repeats, before creating films from the materials.
Tandem-repeat proteins and arrays exhibit a wide range of structures and functions. It was found that increasing the number of tandem repeats raised the proton conductivity of the proteins, while various combinations of amino acids reduced proton conductivity. Also, as the proteins tend to be composed of an amorphous section and a crystalline section, stretching the polymer increased the conductivity in the direction of the stretch but not perpendicularly, as well as to realign the crystalline segments to conduct more effectively.
Although the dependence of mechanical properties on repeat numbers has been studied extensively, the relationship between transport properties and tandem repeats had been relatively uncharted until now. As researcher Melik Demirel said, “Our goal is to understand the design rules of biological proton conductors so that we can create a synthetic protein that is as good as a non-biocompatible proton conductor”. The material could lead to new directions in materials science and also life sciences, particularly in synthetic biology and biotechnology with the help of DNA technology.