A type of natural polymer, cellulose is the main component of plant cell walls, and it's increasingly been finding use as an eco-friendly, biocompatible 3D-printing material. Now, scientists have devised a method of printing complex objects with a higher cellulose content than ever.
The new technique was developed via a collaboration between the ETH Zurich research institute and the Swiss Federal Laboratories for Materials Science and Technology (Empa).
It begins with a "printing ink" composed of nothing other than water and six to 14 percent cellulose particles and fibers. These nanoscale cellulose bits are suspended within the water, giving the ink a gel-like consistency. Utilizing a process known as "direct ink writing," the material is extruded from a printer nozzle in successive layers, gradually building up a three-dimensional object.
That item is subsequently placed in a bath of organic solvents. This causes the object to shrink and densify, as the cellulose particles react to the solvent by aggregating together. The now-smaller object is then removed from the bath, allowing any solvent still within it to evaporate.
Next, it's soaked in a solution that contains a photosensitive plastic precursor, which seeps into the cellulose "scaffold" that makes up the object. When the item is subsequently exposed to ultraviolet light, the precursor changes into solid plastic.
This results in a finished composite product that is up to 27 percent cellulose by volume – according to ETH Zurich, this is a record for additive printing. Based on the type of plastic precursor used, the objects can be either hard and rigid or soft and flexible, depending on their intended application.
So far, the technology has been used to create a number of relatively small, delicate objects – if their wall thickness is greater than 5 mm when initially printed, distortions can occur as they shrink. Once developed further, the process could conceivably be utilized in the production of items such as cartilage-replacement implants or customized product packaging.
The research is described in a paper that was recently published in the journal Advanced Functional Materials.
Source: ETH Zurich
