Coatings & surface treatment Coatings & surface treatment Stick it to F
scar tissue
The build-up of scar tissue around implants is a common reason for their failure. But engineers at MIT might have found a way to tackle this problem – coating devices with a hydrogel adhesive, which causes the device to bind to the surrounding tissues so the immune system won’t attack it. Natalie Healey explores the potential of this approach.
rom pacemakers to drug delivery systems, implantable medical devices have improved millions of lives worldwide. Yet despite their benefits, they face a persistent hurdle – foreign body reactions, in particular scar tissue formation around the device. When the immune system detects a foreign object, the resulting scar tissue produced (known as a fibrous capsule) can lead to implant failure and put patients at risk. However, researchers are exploring innovative adhesives to tackle the problem, which could enhance the longevity and reliability of medical implants. “Fibrous capsule formation around implants is a big problem,” says mechanical engineer Xuanhe Zhao from the Massachusetts Institute of Technology in Boston, US. “It is ubiquitous around devices in the body, causing a significant portion of implant failures.” This often necessitates additional surgeries, prolongs patient recovery, and, in severe cases, leads to the failure of life-saving devices. These complications also drive up healthcare costs due to additional time-intensive procedures and resource demands. For example, severe fibrous capsule formation around breast implants can cause discomfort, pain and distortion of the implant’s shape, sometimes requiring surgical removal or replacement. In 2020, more than 58,000 breast implant reoperations were done in the US due to the scar tissue becoming hard and starting to contract, reports a 2021 paper in the journal Cells. Similarly, scarring around drug delivery implants reduces the medicine’s efficacy. In pacemakers or other cardiac devices, fibrous capsules can obstruct the function of pacing leads, potentially causing device failure, Zhao adds. With his team’s adhesive, Zhao hopes to overcome these problems, so implants can do their job without inciting the immune system.
Immune attack
Preventing scar tissue formation isn’t easy. The body’s immune system is a double-edged sword. It might protect us from harmful invaders, but it can also overreact to interventions designed to improve health. When an implant is inserted into the body, the immune system marks it out as a foreign object. This triggers an inflammatory response and the body can then begin to encapsulate the implant with a layer of fibrous tissue, in an attempt to isolate it from the surrounding tissue. But what if the implant could bind straight to those surrounding tissues, preventing scar tissue from forming? That’s the thinking behind the MIT team’s approach. Biomedical engineers have been trying to address the problem of fibrous capsule formation for many years, says Zhao. But in 2019, his team made a nature-inspired breakthrough, originally developed to help seal wounds. Designing an adhesive to stick two dry surfaces together is relatively straightforward, thanks to forces like hydrogen bonds and electrostatic interactions. However, achieving this kind of instant adhesion is much harder with wet surfaces, such as body tissues. The water between the surfaces acts as a barrier, stopping the molecules from connecting. So while tissue adhesives have many potential benefits (such as reducing pain and faster application) over traditional methods like sutures or staples for sealing wounds, the options we currently have often fall short. Animals like mussels, barnacles and spiders have developed natural adhesives that work effectively in wet
62 Medical Device Developments /
www.medicaldevice-developments.com
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