Originating from the times of ancient Rome, catgut sutures — created from the purified collagen of bovines, ovines, or caprines, but not felines — are noted for their strength and their capacity to naturally disintegrate within roughly three months. Despite the availability of synthetic absorbable sutures, catgut sutures remain in use across various surgical procedures. Now, engineers have created "smart" sutures, drawing inspiration from age-old sutures. These not only secure tissue but also sense inflammation and deliver drugs. These new sutures, based on animal tissue, are similar to the catgut sutures. However, in a modern adaptation, engineers have coated these sutures with hydrogels capable of being embedded with sensors, medication, or cells that release therapeutic molecules. Researchers anticipate that these sutures can assist patients with Crohn's disease in their recovery after intestinal surgery. Furthermore, the researchers suggest these sutures could also be modified for healing wounds or surgical cuts elsewhere in the body.

A team of engineers at Massachusetts Institute of Technology (MIT, Cambridge, MA, USA) set out to improve upon the pre-existing tissue-derived suture by creating a material that was not only tough and absorbable but also exhibited enhanced functionalities like sensing and drug delivery. These sutures could be of particular benefit for Crohn's disease patients requiring partial intestinal removal due to obstructions caused by severe scarring or inflammation. The operation involves rejoining the remaining ends of the intestine after a section has been removed. However, if the seal isn't secure, dangerous leaks could develop for the patient. Aiming to mitigate this risk, the MIT team sought to design a suture that could not only hold the tissue together but also detect inflammation — a potential indication of insufficient healing in the resealed intestines.

The researchers crafted their new sutures from pig tissue, which they "decellularized" with detergents to lower the likelihood of inflammation in the host tissue. This method resulted in a cell-free material known as "De-gut", comprising structural proteins like collagen and other biomolecules found in the extracellular matrix surrounding cells. After drying and twisting the tissue into strands, the team assessed its tensile strength, a measure of how much stretching the tissue can endure before breaking, and found it comparable to commercially available catgut sutures. It was also observed that the De-gut sutures induced much less immune response from the surrounding tissue compared to traditional catgut. The team then aimed to enhance the suture material with additional capabilities by coating the sutures with a layer of hydrogel, enabling the integration of various types of cargo — microparticles capable of sensing inflammation, different drug molecules, or living cells.

For the sensor application, the team engineered microparticles coated with peptides that are released when inflammation-linked enzymes known as MMPs are present in the tissue. These peptides can be detected using a simple urine test. The researchers also demonstrated that the hydrogel coating could transport drugs used for treating inflammatory bowel disease, including a steroid called dexamethasone and a monoclonal antibody known as adalimumab. These drugs were delivered via microparticles created from FDA-approved polymers such as PLGA and PLA, which help control the rate of drug release. The researchers suggest that this method could be tailored to deliver other types of drugs, like antibiotics or chemotherapy drugs.

Additionally, these smart sutures could be utilized to deliver therapeutic cells, such as stem cells. To investigate this, the researchers incorporated stem cells, engineered to express a fluorescent marker, into the sutures, finding that these cells remained viable for at least seven days when implanted in mice. These cells were also capable of producing vascular endothelial growth factor (VEGF), a growth factor that stimulates blood cell growth. The researchers are now focusing on further testing of these potential applications, as well as scaling up the production process for these sutures. They also plan to investigate the potential of using these sutures in body regions beyond the gastrointestinal tract.

“What we have is a suture that is bioderived and modified with a hydrogel coating capable of being a reservoir for sensors for inflammation, or for drugs such as monoclonal antibodies to treat inflammation,” said Giovanni Traverso, an associate professor of mechanical engineering at MIT, a gastroenterologist at Brigham and Women’s Hospital, and the senior author of the study. “Remarkably, the coating also has the capacity to retain cells that are viable for a prolonged period.” 

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