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Nov 29, 2017 | By David

Bio-based materials are becoming more important to 3D printing, for a number of reasons. A major factor is the relatively small impact they have on the environment, as they are sustainable, non-polluting and relatively cheap and safe to produce. They also boast a number of unique properties that set them apart from similar artificial materials. One of the most exciting recent breakthroughs in the bio-material field is cellulose nanofibrils, made from the fundamental building block of plant matter. Sweden's Chalmers University of Technology and the VTT Technical Research Centre of Finland have been experimenting with their use for a variety of different applications.

Cellulose nanofibrils are the smallest fibres that cellulose can be decomposed into, and they tend to be made from wood or as a side product from agriculture or food production. The fibres are mixed with water to form a paste, which can then be used as 3D printing material.  When dried, this paste forms structures that have high levels of mechanical strength as well as being bio-degradable.

The cross-links between fibrils can be easily manipulated to make structures that are more porous, more rigid or more flexible, according to requirements. This flexibility was previously a major stumbling block for bio-based materials, as the printed structures would get progressively harder as they dried. Some significant progress has now been made on this front. According to Professor Paul Gatenholm of Chalmers University in Gothenburg, ''The drying process is critical... We have developed a process in which we freeze the objects and remove the water by different means as to control the shape of the dry objects. It is also possible to let the structure collapse in one direction, creating thin films.’'

The list of applications that the VTT has for nano-cellulose is extensive, and covers a lot of ground. The Center develops 3D printing technology for modifying textiles, mock-ups, and indoor decoration elements, as well as medical applications in wound care. The indoor decorations will be the first commercially available application. Nanofibrils are used to expand the range of possible surface patterns used when creating decorations.

As for the medical applications, this is where the use of cellulose becomes particularly interesting. In collaboration with the University of Tampere, in a project funded by The Academy of Finland, the VTT is developing 3D printed adhesive bandages that can help promote the re-growth of skin cells around a wound. This is achieved due to the extra flexibility of the healed wound area. According to VTT’s senior scientist Panu Lahtinen, ‘‘By using nanocellulose, we have succeeded in creating 3D structures that absorb liquids three times more efficiently than the dressings commonly used in wound care’’

‘Smart’ wound dressings are also in development, with nano-cellulose being a key part of the technology. In combination with printed electronics and a protein used in wound care, the 3D printed nano-cellulose structure is able to measure the healing of the wound in real time. Data about temperature or bioimpedance can be gathered and transmitted wirelessly to a computer for analysis by medical professionals.

The latter two pioneering applications are exciting, but as yet not possible to implement by hospitals, as cellulose nano-fibrils haven’t been officially approved for medical use. At the Chalmers University, work has been going into the development of electrically conductive structures made of cellulose nano-fibrils, and this is something that should have potential for more widespread use. Using two gels together, one conductive and one non-conductive, and controlling the drying process, researchers have been able to produce three-dimensional circuits. With their flexibility, electrical conductivity, and organic basis, these circuits could have a huge range of applications. A couple suggested by Gatenholm are sensors that can be integrated into packaging, and wearable textiles that would be capable of converting body heat into electricity.

 

 

Posted in 3D Printing Materials

 

 

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