OK, I think that headline includes all the topics I write about plus my faves: biodegradable and composite materials, plus robotic and 3D printing assembly technologies. What more could I want for an almost-Christmas blog?
The best part is, it's all true: An MIT research team has invented what they see as a solution to the need for biodegradable 3D-printable materials made from something besides petroleum-based sources. The team, members of MIT's Mediated Matter Group, includes graduate students Laia Mogas-Soldevila and Jorge Duro-Royo, as well as Neri Oxman, associate professor of media arts and sciences. They developed a water-based robotic fabrication method as both an alternative design approach and an enabling technology for additive manufacturing (AM), using biodegradable hydrogel composites.
The team's research "focuses on the combination of expanding the dimensions of the fabrication envelope, developing structural materials for additive deposition, incorporating material-property gradients, and manufacturing architectural-scale biodegradable systems," they write in the abstract to an article describing their work in the Journal of 3D Printing and Additive Manufacturing.
A robotically controlled AM extrusion system operating at room temperature produces large-scale 3D objects made of biodegradable composites. These composites combine various concentrations of naturally occurring hydrogels, such as chitosan, with other organic aggregates. The team points out that, in addition to biodegradability, natural materials can also have mechanical properties that are equivalent to, or even better than, human-made materials. For example, some shell is tougher than engineered ceramics, like the insanely strong mantis shrimp claw that's inspired aerospace-grade carbon composite, and some wood has the strength of steel.
Mentioning chitosan is interesting because that material has appeared in others' work on compostable bioplastics. Chitosan is derived from chitin, a long chain polysaccharide that gives rigidity and toughness to the exoskeleton of insects and the hard shells of crustaceans like shrimp. It can be found naturally in discarded shrimp shells.
The MIT team points out that natural polysaccharides like chitin, along with natural polymers, are renewable resources that occur in huge quantities, and that polysaccharides are highly diverse both structurally and functionally. Chitosan, for instance, has been used to make biodegradable scaffolds for bone tissue engineering, and has been injection-molded using epoxy resin molds to make compostable items like cups. It's also used as a resin matrix in some industrial fiber-based composites.
The team's syringe extrusion system uses either a single nozzle or multiple, parallel nozzles fed by high-capacity material repositories, and materials can either be pre-mixed or combined on-the-fly at the nozzle. Objects created by the volume-driven system can either be dissolved in water and then recycled within a few minutes. Or they can be chemically stabilized to moisture, making them capable of storing water, or hydration-induced shape changes, or releasing nutrients while biodegrading. Applications include fully recyclable products or temporary architectural components with graded mechanical and optical properties.
The volume-driven system is portable at 8.8 lb fully loaded with syringes and deposition material, and can be attached to a CNC machine. Experiments were done using a 6-axis KUKA Agilus KR1100 robotic arm, for precision and repeatability, to build objects measuring 37.9 inch x 19.7 inch. Preliminary results showed consistent volumetric flow rates, graded properties, and feature sizes varying from sub-millimeter scale to macro scale, and graded properties. Next steps will include improving the nozzle to more precisely combine on-the-fly mixing of materials, redesigning the 3D printer as a pneumatic extrusion system for more complex extrusion paths, and investigating cellulose fiber reinforcement of materials for better mechanical properties.
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