Read an exclusive excerpt from Silk: A History in Three Metamorphoses

And that was very different, Vollrath found, from the enormous Pinna nobilis mollusc and its mussel-like relatives, whose byssus threads are not actually spun, but blow-moulded in the foot, and then flipped out. That extrusion moulding of the byssus thread, the way Pinna makes it, ‘that is very sophisticated precisely because they are not spun. They grow.’ Indeed, in 2014, threads like that of Pinna nobilis had been used by another group of scientists at the University of California, Santa Barbara as the inspiration for creating a new polymer that could not only repair itself − ‘self-heal’ − if damaged, but do so underwater, under conditions in which adhesives would normally struggle to set.

Vollrath’s main focus, however, would remain on his spiders. And then he also began working with the silk of the wild tasar moth, the Antheraea. He chose the Antheraea rather than the Bombyx because wild silkworms evolved independently from the domesticated Bombyx mori silkworm. While the Bombyx lost much that it would need to survive in the wild along the road to its domestication, wild moths continued adapting to cope with the trials of their natural environments. Adaptations occurred to protect their delicate, succulent silkworm pupae as they metamorphosed, defenceless, from the threats of physical attack from animals; from bacteria and other organisms that might bring disease; and from the endless other dangers to which they might be exposed. As a result, those silk fibres of the Antheraea displayed breaking stress and toughness of the same magnitude as spider major ampullate silks − that is, the coveted properties of the dragline silk of spiders that had so diligently avoided being farmed. Vollrath’s early interest was in collecting and studying silks simply to understand the science and properties of the material rather than to make anything with it. As word of his research spread, he says, ‘slowly you have people asking, well, what can we do with it? Then you collaborate with people who actually will try to make things.’ One of those things would become materials made from silk, and destined for the repair of damaged structures inside the human body. Having tested them in the laboratory, and finding them to be effective for such repair, Vollrath’s silk innovations went into the clinic, at least as far as human trials, in which his silk was tested for use in the repair of cartilage. But it did not successfully get past those trials, and, therefore, never made it onto the general market. Despite this, because of its efficacy, it has since been used in nerve repair procedures in humans, an outcome that was only possible in cases of ‘compassionate use’, which means that it was adopted for use as a treatment option despite being unauthorized. That sort of application of a product still under development is only permitted under strict conditions, and only in patients who have a disease with no satisfactory, authorized therapies, and who cannot enter clinical trials. ‘So you can’t really publish that’, Vollrath says. Publishing experiments is how science progresses, so that others can understand what Vollrath had done, exactly how he did it, and try to do it them-selves, as a check on the validity of what might otherwise be nothing more than one laboratory’s claim. Added to which, compassionate use will be restricted to a small number of patients. To say with any good probability that a treatment is effective usually requires closer to one hundred patients, and ideally even more than that. Nevertheless, the small number of patients who did have their nerves repaired using silk implants has been followed up. And it seems to work − but, Vollrath still cautions, ‘you have to do it in proper trials. Or people do not trust it.’ Even if a small proportion of people have an immune response to it, he says, ‘even if it’s one per cent, we would consider it small, but if you roll it out to ten thousand or one hundred thousand people, then one per cent is a lot of people, so you have to be so careful. Someone’s quality of life is so important. Putting the silk in looks like it will work from animal trials, but humans have a very sophisticated immune system.’

That great advantage of silk, as harnessed by Genghis Khan in the East and Dr George Emory Goodfellow in the Wild West, is that it is an animal protein; that it is already related to the keratin protein that we produce and possess; that it can, therefore, easily be integrated into our own bodies; that it is biodegradable − all these can also become an immense disadvantage if that silk ends up triggering an unmanageable immune response once implanted inside a human. And if the silk were to integrate into our tissues, triggered an immune response and then could not be separated out, that would be unconscionable.

(Excerpted with permission from Silk: A History in Three Metamorphoses by Aarathi Prasad, published by HarperCollins; 2023)