The researchers used recombinant techniques to manufacture the small, synthetic SRT molecule used to produce eco-friendly thermoplastics. Image: © Adriás Bago
A team of researchers from Penn State have studied squid to develop an eco-friendly thermoplastic that could be used for 3D printing applications. Squids are normally used for producing dyes and inks, and are also eaten as food.
Most of the companies looking into this type of material have focused on synthetic plastics. Synthetic plastics are not rapidly deployable for field applications, and more importantly, they are not eco-friendly.
Melik C. Demirel, professor of engineering science and mechanics at Penn State
Squid ring teeth (SRT) have a protein complex that was studied by Demirel and his team of researchers. This material is a natural thermoplastic, however, a large number of squid and a huge effort is required for extracting the material.
We have the genetic sequence for six squid collected around the world, but we started with the European common squid.
Melik C. Demirel, professor of engineering science and mechanics at Penn State
The team of researchers studied the genetic sequence of the protein complex molecule. They attempted to synthesize different types of proteins from this complex molecule. Among these some of the proteins demonstrated stable thermal response, while other proteins were not thermoplastics. The researchers synthesized a SRT protein that had the smallest known molecular weight and this was found to be a thermoplastic.
Fossil fuel sources such as crude oil are used for manufacturing most types of plastics. Synthetic oils are used to produce some high-end plastics. Typically, thermoplastics are polymer materials. These materials can be melted, formed and solidified as the same thermoplastic material without any degradation in its material properties.
The thermoplastic derived from SRT can be heated, molded or extruded as a thermoplastic for fabrication or it can be dissolved in acetic acid or similar solvents that can be used for film casting. This material can be used as the source material for making complex geometric structures using 3D printing machines.
The researchers employed recombinant techniques for producing the synthetic SRT molecule. The SRT protein genes were than inserted into E. coli. These harmless bacteria then produced the plastic molecules as a part of their routine activity. These plastic molecules were then removed. For this part of the project, Demirel collaborated with Wayne Curtis, professor of chemical engineering along with their students.
The next generation of materials will be governed by molecular composition -- sequence, structure and properties.
Demirel
The thermoplastic material that was created by the researchers is a semi-crystalline material that can be soft or rigid. It is a wet adhesive that enables it to stick even under wet conditions. The material also demonstrates a very high tensile strength. Furthermore, the thermoplastic protein demonstrates an assortment of tunable properties that would allow it to be modified to suit specific requirements for production. This thermoplastic can be used for cosmetic and medical application as it is a protein.
"Direct extraction or recombinant expression of protein based thermoplastics opens up new avenues for materials fabrication and synthesis, which will eventually be competitive with the high-end synthetic oil based plastics," the researchers report.
Istvan Albert, associate professor of biochemistry and molecular biology; Huihun Jung, graduate student in engineering science and mechanics; Aswathy Sebastian, Bioinformatics Consulting Center; Sergio Florez, graduate student in chemical engineering; and Abdon Pena-Francesch were other researchers who took part in this study.
The Army Research Office and the Office of Naval Research have provided support for this study.
This research has been published in the peer-reviewed scientific journal, Advanced Functional Materials. This study illustrates the cover of the current issue.
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