Synthesizing Squid-Based Thermoplastics

Jan 27, 2016

by Mark Crawford ASME.org

Now squid has more than just table appeal. Researchers at Penn State University have developed a thermoplastic from squid proteins that is remarkably versatile and can be used in 3D printing.

"Most companies interested in thermoplastics have focused on synthetic plastics," states Melik C. Demirel, professor of engineering science and mechanics at Penn State University and leader of the research team. "Synthetic plastics are, however, not rapidly deployable for field applications and, more importantly, are not ecofriendly."

This innovative research is the result of a broader approach that Demirel terms “genomechanics” which brings together engineering mechanics, genomics, large-scale computation, materials science and design, and manufacturing. The research involved four phases:

  1. Discovery: the extraction and sequencing of genomic information to identify elastomeric proteins.
  2. Synthesis: the process that produces the high-strength proteins.
  3. Properties: computational simulations of molecular structures are designed and linked to experimental properties.
  4. Biomimicry: scale-up of the process is performed in a biodegradable, but less expensive, polymer to produce high-volume materials.

“Compared to polymers manufactured from fossil fuels and synthetic oils, biosynthetic polymers are ecofriendly, biodegradable, lightweight, can be fabricated at room temperature, have gene-sequenced tunable strength and properties, and lend themselves to low-energy and low-cost manufacturing processes,” says Demirel. “We are opening up a new field of material property design based on tunable genetic sequencing-structure-property relationships.”

Unique Physical Properties

Following this four-point protocol, Demirel and his team have researched a novel fibrious protein—squid ring teeth (SRT)—for the last four years. SRT protein exhibits an unusual and reversible transition from a solid to a rubber and can be thermally shaped into any 3D geometry (for example, fibers, colloids, and thin films). “We have demonstrated that SRT has excellent mechanical, structural, and optical properties, in both wet and dry conditions, which exceed most natural and synthetic polymers,” he adds.

When cut in half, the SRT-based plastic sticks itself back together with a drop of water. Image: Demirel Lab at Penn State University

Demirel is also impressed by the self-repair ability of this protein. For example, his team was able to cut a SRT sample in half and repair it by applying pressure and warm water (view video).

Most plastics are derived from fossil fuel sources like crude oil. Thermoplastics have properties that allow them to be melted, formed, and cooled without degrading the material’s unique physical properties. The SRT team created is semi-crystalline and can be rigid or soft. It also shows a very high tensile strength. Another interesting characteristic is that, as a wet adhesive, it sticks to other materials, even if it is wet, expanding the possibilities of combining it with other materials for specialized manufacturing purposes.

SRT is a versatile material that can be dissolved in a simple solvent like acetic acid and used in film casting, or it can be extruded or injection-molded like other thermoplastic materials. Results also show that SRT can be used as a 3D printing material to create products with complex, geometric shapes and features.

Fortunately, squids do not need to be collected and sacrificed to make SRT, which can be manufactured synthetically using recombinant gene technology. SRT protein genes are inserted into E. coli bacteria, which then produce SRT molecules as part of their normal biological functions. The thermoplastic is then harvested from the E. coli environment.

Moving Forward

The discovery of this remarkable thermoplastic material shows how new classes of functional biomimetic materials can be synthesized and manufactured through an understanding of how nature customizes biomolecules to createfunctional materials with tailored physical properties. Because it is a protein, SRT can be used for medical or cosmetic applications where biocompatibility is of top concern.

"The next generation of materials will be governed by molecular composition: sequence, structure, and properties," says Demirel. "Direct extraction or recombinant expression of protein-based thermoplastics opens up new avenues for materials fabrication and synthesis. Eventually these materials will be competitive with the high-end, synthetic, oil-based plastics. On a broader scale, I envisage applications of genomechanics in high-performance textiles, green cosmetics, medical implants, biosensing, and combatting bioterrorism, among many others.”

Mark Crawford is an independent writer.

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We are opening up a new field of material property design based on tunable genetic sequencing-structure-property relationships.Prof. Melik C. Demirel, Penn State University