Medical Implants Could Soon Use New Plastic Biomaterials

Researchers from the University of Birmingham has developed a new thermoplastic biomaterial that is easy to process and shape as well as tough and strong.

This new plastic is a type of nylon which shape memory properties enable it to be stretched and molded but able to reform into its original shape when heated. In medical field where minimally invasive surgery techniques require additional flexibility in implant materials such as bone replacements, it’s particularly useful.

A team from the university’s school of chemistry was the one who developed this material. They investigated ways to use stereochemistry—a double bond in the backbone of the polymer chain—to manipulate the properties of polyesters and polyamides (nylons).

Now, there are a lot of biocompatible polymers we use in medicine. We see it in a form of tissue engineering to medical devices such as stents and the simplest one: sutures.

There has been progress in the area of resorbable or degradable materials that are broken down by the body over time. However, there are still only a handful of non-resorbable polymers for long-term use or applications.

The non-resorbable biomaterials widely available now like nylons have their own limitations. For example, metal implants can wear poorly and it can lead to particle fragments breaking off. On the other hand, composite materials can be difficult to process or come with hefty price tag.

In contrast, researchers can make this new material using standard chemistry techniques. Also, it offers a stable, long lasting option with tunable mechanical properties for different end products.

“This material offers some really distinctive advantages over existing products used to manufacture medical devices such as bone and joint replacements. We think it could offer a cost-effective, versatile and robust alternative in the medical device marketplace,” said senior researchers, Professor Andrew Dove.

Amorphous structure is a feature that gives a further advantage to the new material. “For many plastics, including nylon, the toughness is often dependent on their semi-crystalline structure, but this also makes them harder to shape and mold,”

“However, our new plastic is as tough as nylon, but without being crystalline so it is much easier to manipulate. We believe this is only possible due to the way we have used stereochemistry to control our design,” explained Josh Worch, the postdoctoral researcher who led the work.

heart valve replacement operations that use medical implant
heart valve replacement operations that use medical implant. Photo by Lena Gulenko Wikimedia Commons

Covered by a patent, the research team were able to design, produce the plastic, and test it in rats to prove its biocompatibility. They now plan to explore more ways to fine tune the material and its properties before going commercial.

New biomaterials are important because they could reduce implant rejection. A team from the University of Nottingham’s Schools of Pharmacy and Life Sciences has found that the surface shape and chemical composition of polymer materials can be changed to create materials that control the body’s immune response.

Therefore, new discoveries could help fight against rejection of medical devices. Future applications such as artificial joints, dental implants, and vascular implants could work better. The results of these recent studies have been published in Advanced Science and Matter.

Joints, stents, and dental implants are the most common medical devices that use biomaterials to restore function or completely replace diseased or damaged tissues.

Unfortunately, bodies are different and while some of us can accept these new foreign objects, others can’t. Common host reactions include responses such as inflammation, foreign body reaction (FBR), and fibrous capsule development which can result in the implant failing.

Reactions like these are caused by the activation of immune cells called monocytes and macrophages attaching to the implant surface. The physical features on the surface of a material or implant is known to have an influence to macrophage attachment.

“We are looking at ways to create materials that can be safely put inside the body without the immune system attacking it and causing rejection. To do this we are exploring materials that can control the immune response,” explained co-leader of the research, Professor Amir Ghaemmaghami.

“We have used high throughput screening technology to examine how the topography and chemical properties of a material can be used to design ‘immune-instructive’ surfaces for potential use in implants, which influence macrophage function and consequently the foreign body responses to biomaterials,” Ghaemmaghami continued.

New, eco-friendly sulfur polymers

polymer chain. Picture by SPT Paul Topham Wikimedia Commons
polymer chain. Picture by SPT Paul Topham Wikimedia Commons

Researchers at the University of Liverpool has been trying to develop new sulfur polymers that provide an environmentally friendly alternative to some traditional petrochemical based plastics. And they’ve made significant progress.

With his team, Dr. Tom Hasell, a University of Liverpool chemist and Royal Society Research Fellow, have published two papers which demonstrate practical and exciting developments for sulfur polymer technologies and application. In 2019 they reported a new catalytic process to make polymers out of sulfur. This new research was based on that.

I’ve just found this out, but sulfur is a waste product from many industrial processes. It’s only in recent years that a growing number of materials scientists have become interested in using it as an environmentally alternative to oil from which to manufacture plastics.

Aside of being plentiful, sulfur has another advantage of being more easily recyclable polymers.

Dr. Hasell and colleagues has made an exciting discovery that addresses the weakness of sulfur polymers, a factor that has limited its application. The paper, published in Angewandte Chemie and led by Ph.D. student Peiyao Yan, demonstrates that adding a second type of bonding, urethane bonds, to the materials increases the strength of sulfur polymers by up to 135 times.

It means that this second type of bonding can be controlled in terms of it’s a mount, and in turn controls the physical properties of the polymers.

Additionally, the researchers found that the strengthened sulfur polymers have shape-memory effects, meaning that they can be set in one shape, before being temporarily deformed into another.

When heated a little, they can remember their previous shape and go back to it. This setting process and temporary deformation can be repeated multiple times. This means that recycling this material is easier than conventional polymers.

Now, this is a first for sulfur polymers. Despite these unusual properties, the sulfur bonds of the polymers open up potential applications in areas such as soft robotics, self-repairing objects, and medicine. Perhaps in the future we can also have biomaterials for implants using sulfur polymers.

In a second paper published in Chemical Science, Dr. Hasell’s group teamed up with researchers at Flinders University in Australia. This time, they show that sulfur polymers could form rubber-like materials.

What’s special about them is that these rubber sulfur polymers could be easily self-repaired to their original strength within minutes, just by applying an amine catalyst that helps the bonds in the broken surfaces heal back together.

As a result, this new kind of rubber and catalyst can be used with low energy consumption to make flexible, repairable, sustainable objects—providing a very real and useful application for these new sulfur polymers.

“Both of these papers really show the potential of polymers made from waste sulfur to be a viable replacement material for some traditional petrochemical based plastics,” said Dr. Hasell.

“Not only as a substitute material, but as one that is easier to recycle, and has exciting new properties for materials chemists to explore. We are excited to see what ideas researchers have for using these new findings, in particular the memory shape and “re-programming” properties,” Hasell continued.



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