Daily Clinical News – New adhesive hydrogel coatings extend the life of pacemakers and medical implants – Surgical techniques

New self-adhesive hydrogel coatings extending the life of pacemakers and medical implants

Authors: HospiMedica International staff authors
Posted on May 28, 2024

When medical devices such as pacemakers are implanted in the body, they often trigger an immune response that causes scar tissue to build up around the device. Scarring, called fibrosis, can interfere with the operation of the devices and require their removal. To solve this problem, engineers discovered a simple and universal method to prevent fibrosis by coating the devices with a hydrogel adhesive. This coating bonds the devices to the tissue and protects them from attacks by the immune system.

The adhesive developed by engineers from the Massachusetts Institute of Technology (MIT, Cambridge, MA, USA) consists of cross-linked polymers called hydrogels. It resembles surgical tape that was previously developed to seal internal wounds. The researchers determined that other hydrogel adhesives could also protect against fibrosis and anticipate that this approach could be applied not only to pacemakers but also to sensors and devices that deliver drugs or therapeutic cells. Over the years, the team has developed a range of adhesives for medical use, including double-sided and single-sided tapes, useful for repairing surgical incisions or internal damage. These adhesives work by quickly absorbing moisture from moist tissues via polyacrylic acid, a superabsorbent material found in diapers. Once moisture is absorbed, chemical groups called NHS esters in polyacrylic acid form permanent bonds with proteins on the tissue surface in a process that takes about five seconds.

Photo: Coating implantable devices with a hydrogel adhesive eliminates the build-up of scar tissue around them (Image courtesy of ilusmedical/Shutterstock)

A few years ago, the team began investigating whether this type of adhesive could also hold medical implants in place and prevent fibrosis. To evaluate this, they coated polyurethane devices with glue and implanted them in various places, such as the abdominal wall, colon, stomach, lungs or heart of rats. When removed a few weeks later, no scar was visible. Further experiments in additional animal models consistently demonstrated a lack of fibrosis at the site of implantation of adhesive-coated devices lasting up to three months. The team performed bulk RNA sequencing and fluorescence imaging to analyze the animals’ immune response and found that initially immune cells such as neutrophils infiltrated the implant site. However, these attacks quickly stopped before any scarring could develop.

This adhesive has potential applications in coatings for epicardial pacemakers – devices placed on the heart to regulate heart rate. MIT researchers found that after adhesive-coated wires were implanted into rats, the wires worked effectively for at least three months without scarring. They also experimented with a hydrogel adhesive containing chitosan, a natural polysaccharide that similarly prevented fibrosis in animal studies. In contrast, two commercially available tissue adhesives they tested did not prevent fibrosis because they eventually detached from the tissue, allowing the immune system to resume its attack. In another experiment, researchers coated the implants with a hydrogel adhesive and then immersed them in a solution that stripped the polymers of their adhesive properties while maintaining their overall chemical composition. After implantation and fixation with sutures, fibrosis occurred, indicating that the researchers believe that the mechanical interaction between the adhesive and tissue plays a key role in preventing immune attacks.

“The dream of many research groups and companies is to implant something into the body that the body will not see in the long run, and the device will be able to perform a therapeutic or diagnostic function. Now we have such an ‘invisibility cloak’ and it is very general: there is no need for a drug or a special polymer,” said MIT professor Xuanhe Zhao.

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