Catalina, M, J Cot, AM Balu, JC Serrano-Ruiz and R Luque. 2011. Tailor-made biopolymers from leather waste valorisation. Green chemistry http://dx.doi.org/10.1039/c2gc16330f.
A versatile and potentially valuable natural material could be easily collected from the abundant waste produced when leather is made from animal hides, according to researchers from Spain who explain their novel process in the journal Green Chemistry.
Leather processing generates large amounts of remnant hides that are generally thrown away. But this solid waste is rich in a valuable and medically useful protein called collagen. This new method to recycle or reuse the waste alleviates the dumping, produces a necessary product and increases sustainable manufacturing.
Collagen is abundant in mammals and is an important part of muscle, tendons, ligaments, skin, guts, vessels and bone. The resilient, soft and flexible material does not trigger immune reactions, making it a rich resource for medical, cosmetics and veterinary applications. Collagen is used for implants, as sutures and in regenerative medicine – a field of medicine that grows new human cells, tissues or organs for transplant.
The researchers tested different extraction scenarios for their effect on the amount and quality of the collagen. They extracted the protein from two different types of processed cowhides to demonstrate the versatility of the technique.
The hides were cut, treated with acid and ground into a water solution. This process allowed the collagen molecules to dissolve in water. The collagen particles ranged in size from a few nanometers to a few dozen nanometers. Because size matters for collagen applications, the particles were filtered and separated according to their size.
To find the best method, they varied a number of factors, such as temperature, leather pieces, size after grinding, the nature of the acid, stir speed and type of water solution. The optimal results for yield came from an extraction using acetic acid – basically vinegar – for 24 hours at 25oC and a smaller particle size after grinding.
Next, they manipulated the extracted collagen molecules to determine their stability and mechanical properties. In fact, the use of collagen from leather is often limited because of the poor mechanical properties of the recovered collagen. Specifically, collagen must be rigid enough while not swelling too much when exposed to water. Here the researchers found a simple chemical treatment to render the collagen firm and stable.
From this method, they made several different kinds of materials – fibers, sponges, films, threads and gels – with rigidity and swelling in water properties necessary for biomedical applications.
The research is a good example of finding new ways to use a waste material for high value applications. More work will need to be done to compare the properties of these materials with commercial collagens. The next step will be to show the collagen source is reliable and free of contamination.
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