What biodegradable material possesses the hardness of conventional plastic?

What biodegradable material possesses the hardness of conventional plastic?

By Marija Jovic

The majority of biodegradable materials on the market today are being based on cellulose, a polysaccharide material derived from plants. These materials find wide spread applications in packaging, as containers for food or drinks, for example. However, the major drawback of these materials is their hardness, which is not as high as in conventional plastics. The Wyss Institute has developed a new material derived from the shells of crustaceans that can serve as a ‘hard’ biodegradable alternative to plastic.

The new material:

Researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University have developed a new material based on chitosan that is able to overcome these issues. Chitosan is a tough polysaccharide found in crustaceans’ shells, and is responsible for their toughness.

By studying complex interactions in the original biomaterial and then by recreating their unique chemistry and laminar design in the lab, it was possible to create the new material, named “Shrilk”. Shrilk is made by forming a laminate of chitosan and silk fibroin protein. This formation mimics the microarchitecture of a natural insect cuticle, thus providing the unique mechanical and chemical interactions giving rise to the unique mechanical and chemical properties.

Not only does the material have the strength of an aluminum alloy, but it is also two times lighter. The material is also clear, biocompatible, biodegradable, micromoldable and low-cost, as chitin (precursor of chitosan) is readily available as a shrimp waste product.

This material could be used in a variety of applications. As a cheap, environmentally safe alternative to plastic, it could be used to replace plastics in consumer products such as trash bags, packaging, and diapers that degrade quickly. And, as an exceptionally strong, biocompatible material, it could be used to create implantable foams, sutures and heal wounds that bear high loads, or as a scaffold for tissue regeneration.

How the chitin-based bioplastic was developed:

The original article was published in Advanced Materials by Dr. Javier G. Fernandez, and Dr. Donald Ingber. Three years after the first publication, the research continued by developing a method for large-scale manufacturing using a variation of this material. In the study, published in Macromolecular Materials & Engineering, the team used the shrimp shells but abandoned the silk in order to create an even cheaper, easier-to-make chitin-based bioplastic meant for manufacturing of everyday objects.

The key in doing so was in understanding the molecular geometry of chitosan, and that it is very sensitive to the method used to manufacture it. The idea and the goal were to fabricate the chitosan in a way that would preserve the integrity of its original molecular structure, thus preserving its strong mechanical properties.

After analyzing how factors such as temperature and concentration affect the mechanical properties of chitosan, the researchers were able to find “just right” conditions that would make it possible for the material to be processed using large scale manufacturing methods, such as traditional casting or injection molding manufacturing techniques. Adding wood flour helped in another issue the researchers were facing – shrinkage – which made chitosan maintain its original shape after the injection molding process. Using this know-how, it is now possible to manufacture complex three-dimensional (3D) shapes using chitin-based materials that can be made into robust items used in toys and cell phones for example.

In addition to that, the material does not present any threat to the environment, and to plant growth. In order to demonstrate that, the research team grew a California Blackeye pea plant in soil enriched with its chitosan bioplastic over a three-week period. The plastic material even released nitrogen-rich nutrients that efficiently supported plant growth.

The next step:

The next step is taking the technology out of the laboratory, and into a commercial application with an industry partner. The technology is available for licensing.

Image courtesy of pixabay.com

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