In this interview, Professor Wendelin Stark speaks to AZoM about a new gelatin-based yarn his research group have been developing. It is hoped that this yarn will find application in the medical industry thanks to its biocompatible nature.
Spools of the gelatin-based yarn. P. R. Stoessel and W. J. Stark/ETH Zurich
What inspired you to produce a new biopolymer?
As a result of their high disposability and their persistence, synthetic polymers are becoming discredited more and more. There is a broad consensus that biodegradable polymers should be promoted.
Unfortunately, successful biopolymers such as polylactic acid (PLA) rely on sugar or starch as raw material. Thus, they may compete with the food chain and endanger food security. To my understanding, it is beneficial to produce biopolymers from monomers or macromolecules extracted from waste streams.
Actually, we have not developed a new biopolymer in this project. Quite the contrary: we have chosen to process an extremely old and well-known protein (gelatin) into fibers.
Why have you chosen to work with gelatin?
Gelatin is one of the most abundant agricultural waste proteins. It is derived from collagen which is the main structural protein in the skin, bones and tendons of vertebrates. With that it is largely available from meat industry by-products. Around 25 million tons of such by-products are globally accumulated per year.
The threads are passed over ethanol-soaked rolls. P. R. Stoessel and W. J. Stark/ETH Zurich
How do you produce the yarn?
To produce a spinning dope, gelatin is mixed with water and 2-propanol. Upon heating, this ternary mixture undergoes a phase-separation. The lower, gelatin-rich phase – basically a protein precipitate – is then extruded through six nozzles, the filaments are guided via two rollers through air and taken up on a conveyor belt. With this set-up around 200 m·min-1 filaments are produced.
The fibers can either be used as monofilaments or the whole fiber roving can be hand-twisted into 2-ply yarns. The yarns produced in our studies consist of around 1,000 monofilaments (each 20-25 µm diameter).
What kind of properties does this material provide?
The fibers have a very smooth surface which results in an attractive luster. Moreover, the interior of the fibers is filled with cavities, yielding a porosity of 30 %. The latter is extremely interesting in terms of light-weight fibers or thermal insulation.
How strong is the material?
The strongest gelatin fibers produced in our studies are wet-spun monofilaments. These fibers exhibit tensile strengths of around 180 MPa, elastic moduli of 3800 MPa and nearly 40 % strain at break. These values are very similar to the tensile properties measured for natural sheep wool.
Gelatin is obviously soluble in water – how have you overcome this property to make a stable and long lasting yarn?
We have chosen a three step procedure: (1) we added multi-functional epoxides to the spinning mixture. After spinning, the yarns were heat treated to obtain a good reactivity between the amino-groups of the protein (lysine) and the epoxide. (2)
Furthermore, the yarns were treated with gaseous formaldehyde to further improve the crosslinking degree. (3) In an attempt to mimic the hydrophobic nature of sheep wool, we applied an impregnation with lanolin, the natural sheep wool wax. With these treatments we could significantly reduce the water uptake of the gelatin yarns from around 1’200 % to 200 %, allowing for multiple swelling and drying cycles of the yarns.
A prototype mitten made from the yarn on the right, next to one made from merino wool. P. R. Stoessel and W. J. Stark/ETH Zurich
You mentioned that you are looking into medical applications as collagen is biocompatible – are there benefits to this yarn over materials currently used?
The extraction of native collagen is a very expensive procedure. To our knowledge, large-scale spinning of collagen fibers has not yet been achieved. Moreover, it is known that many processing steps such as electrospinning strongly degrade the collagen.
Our spinning process is able to produce relevant amounts of gelatin fibers with simple equipment and harmless solvents at a low price (approximately 15-20 $ per kg of fibers). This competitive cost structure combined with the biocompatibility and versatility of gelatin fibers motivate to assess the application of the fibers in medical applications.
What kind of further development is necessary?
The next stages of development fully depend on the chosen application. To find out where to apply the fibers we are in close contact with industry.
If the gelatin yarns are of interest to the biomedical sector, we will consider carrying out cell studies and optimizing the fibers for e.g. the application in a wound dressing. If the fibers prove to be valuable in the textile sector, we will further work on the improvement of the fibers’ wet strength and study the processability on conventional spinning machinery.
Overall, we are curious to find out in which direction this project will lead.
About Professor Wendelin Stark
Wendelin J. Stark (1976) received his Master in Chemistry in 2000 from ETH Zurich, followed by a PhD in Mechanical Engineering in 2002, also from ETH Zurich.
In 2004 he founded the Functional Materials Laboratory within the Departments of Chemistry and Applied Bioscience at the ETH Zurich.
His research group pursues application-oriented research at the interface of chemistry with material science and medicine.
He has published over 200 papers and 30 patents. Over 20 nanoparticle containing products have been commercialized in currently 4 spin-off companies from the research group.
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