For thousands of years, silk has been treasured for its qualities as a beautiful material for elegant clothing. But scientists are exploiting the less obvious qualities of silk to develop versatile replacement parts for human eyes and knees.
The first word that comes to mind when you think of tang probably isn’t “strength,” but when it comes to toughness, pound for pound, smooth tang is tougher than steel. Few materials in the world equal the flexible fiber produced by the silkworm.
“Silk has immense potential to be developed into materials that have the same functional properties as healthy tissue, without any of the drawbacks of traditional implants,” said Dr Nick Skaer, chief executive of British biomedical company Orthox. “I am convinced that very soon – in the next few years – we will see very important clinical needs met by this versatile fiber.”
There are good reasons to turn silk into spare parts for the human body. This “super-fiber” is resistant, highly elastic, permeable to oxygen and water, biocompatible (is not rejected by the body during the transplant), stable and versatile (it can be transformed into a solid, a mesh or a gel). It is also able to block infection and promotes the regeneration of new tissues.
Weak at the knees
Dr. Skaer is part of FibroFix Cartilage, a research team focused on transforming silk into a knee cartilage substitute. Launching clinical trials in Hungary and the UK later this year in hopes that orthopedic implants will soon be available to European patients.
When the cartilage in the knee is damaged and people develop osteoarthritis (OA), they may be referred for knee replacement surgery (arthroplasty). The painful condition causes the bones in the joints to rub together and reduce mobility. It is also a widespread problem, with Europeans facing a 45% chance of developing osteoarthritis. The risk increases with age and weight. It is estimated that it costs European countries more than 7.2 billion euros and is increasing every year to treat osteoarthritis.
Knee replacement surgery has reasonably good results, but it is expensive, painful, and the recovery is long. It’s also complex and hard to fix if something goes wrong. Silk-based implants offer an enticing solution to these drawbacks.
FibroFix is made entirely of silk proteins (known as fibroin) which have mechanical properties almost identical to those of real cartilage. “It’s solid, it’s slippery like cartilage, and it deforms when you put pressure on it,” Dr. Skaer said.
Damaged cartilage is unable to repair itself easily and if left alone, a damaged knee will usually only get worse. FibroFix researchers have developed a way to extract and purify fibrofin and shape it into a suitable form for use as an implant.
This is inserted into the knee in a dry and compressed state. It quickly fills with fluid from the surrounding tissues which plumps it up to form a cushion-like barrier between the bones.
Critically, the porous material also supports tissue regeneration. The silk protein implant provides a scaffold on which bone and connective tissue can grow, so even slowly repairing cartilage begins to regenerate.
The advantages of the implant are twofold. “Once the implant is locked in place, you immediately regain function of your missing cartilage and you also get new, natural tissue that grows over time,” Dr. Skaer said.
Tests show that the implant surgery procedure is quick, postoperative pain is minimal, and recovery is straightforward. Dr. Skaer hopes for positive results in clinical trials. “We expect people to be on their feet soon after surgery and back to work quickly, which will be a big win for everyone,” he said.
Live long enough and the day will come when you need glasses. “Presbyopia affects precisely 100% of the population over the age of 45,” said Susana Marcos, research professor at the Spanish Institute of Optics (CSIC) and principal investigator of SILK-EYE.
The team working on SILK-EYE – an EU-funded project headquartered at Spain’s National Research Council in Madrid – has found a way to turn the protein silk fibroin into a transparent membrane that could one day be used to restore sight.
Presbyopia is the inability to focus on near objects. The condition is caused by hardening of the lens and gradually worsens with age. The standard treatment here is to invest in a pair of glasses or contact lenses. There is no treatment to restore the lost functionality of the young lens.
The goal is to develop a silk-based implant that will replace the hardened lens in a simple surgical procedure. The new membrane will change shape as it is pulled by the eye muscles to focus on near and far objects.
“We are doing well with this project,” said Professor Marcos. “We developed the silk membranes and refined the material so that it had the properties we wanted. It’s transparent, elastic, easy to work with, it has the right thickness and the right levels of permeability.
More work is needed, but the researchers have a clear goal in mind – Professor Marcos calls it the holy grail of ophthalmology – to restore older eyes to the capacity of their 20-year-old selves. “It’s on everyone’s mind in this field,” she said.
Silk-based corneal implants can also be used to replace vision correction laser surgery.
“Laser surgery (like LASIK) removes some corneal tissue, so your cornea becomes thinner,” Marcos said. “But surgery using silk would be additive – we would be adding the implant to what is already there, and therefore preserving the tissue.”
Worldwide, millions of people go blind as a result of corneal injury. It is a major public health issue. SILK-EYE researchers are working on affordable corneal implants and bandages to solve the problem.
The team has already successfully attached silk membranes to the corneal surface using an activated-light technique called photocollage – a technique that replaces the need for stitches.
Silk lens and corneal implant treatments come at a financial cost, but “we hope silk will be an affordable option for many people in Europe and around the world who are currently losing their sight due to widespread eye conditions,” said said Professor .Marcos.
The research in this article was funded by the EU. This article originally appeared in Horizon, the European research and innovation magazine.