A better bond: McMaster team chemically re-engineers silicone to unlock new applications in medicine

“An interdisciplinary research team at McMaster has engineered a material that has all the flexibility and strength of silicone used in medical applications, but also resists clotting and doesn’t provoke the human body into rejecting it. Polydimethylsiloxane, or PDMS, is already everywhere in modern medicine, from cochlear and breast implants to tubing and catheters. Its bulk properties as a tough and stretchy rubber give silicone immense versatility, but its surface properties are a problem: It’s hydrophobic, prone to triggering clotting when in contact with blood, and can provoke the body to wall it off in fibrous capsules, which can lead to long-term complications. McMaster researchers created the new material, which stays “clean” longer, by redesigning the silicone network and forming chemical bonds to an ultra-hydrophilic, antifouling polymer. “Even really good medical-grade silicones can activate platelets over time and start the clotting cascade,” says Todd Hoare, Professor of Chemical Engineering. “What’s different here is the coating doesn’t just sit on top — it forms chemical bonds to the silicone, creating a stable interface that shuts down one of the pathways blood uses to clot.” The groundbreaking work, led by PhD candidate Norma Garza Flores and supported by an NSERC Alliance grant, was published this month in Advanced Healthcare Materials . Chemistry advanced by conversations and curiosity The road to this point has been five years in the making and took a serendipitous moment to advance the science. In the Arthur Bourns Building on campus, the Hoare Lab, including graduate student Eva Mueller, had developed a library of anti-fouling polymers from hydrogel projects. Next door, chemist Mike Brook and his colleague Robert Bui were pioneering dynamic silicone networks, primarily for application on rubber to try to make it more reusable. It took a casual hallway conversation between former PhD students in both labs to identify the opportunity: If the silicone’s bonds could rearrange, maybe the polymers could bond rather than just sit on top. Work quickly got underway. To test the effectiveness of their new approach, Hoare called up Jeff Weitz, a blood expert in the Faculty of Health Sciences with a cross-appointment in Bioengineering. Within half an hour, he had an invitation to bring over samples for hemocompatibility testing. “This kind of interdisciplinarity and open-door collaboration is one of McMaster’s real strengths,” says Hoare. “It’s the norm here, not the exception, and it drives new discoveries and innovations.” Brook, who has been at McMaster for more than 40 years, strongly agrees. He points to the 23 McMaster professors, 10 outside of his own discipline, with whom he has co-authored papers as evidence of the university’s collaborative culture. In human plasma tests run with Weitz’s team at the Thrombosis and Atherosclerosis Research Institute, the modified silicone shut down a major clotting pathway that is typically activated on PDMS. “We used pooled human plasma to get more accurate results,” says Garza Flores. “And the same trend held in a living organism: The bonded polymer silicone drew fewer immune cells, formed thinner capsules and deposited less collagen at the interface compared to unmodified controls, all signs of a reduced foreign body response.” Applications and opportunities Silicone has always had the feel and flexibility that surgeons value — properties that, in theory, make it attractive for vascular grafts and valves. But in practice, poor blood compatibility kept PDMS on the sidelines for those jobs. “Silicone’s mechanics can be designed to be flexible and expandable for artificial vessels, but blood compatibility has been a barrier,” Hoare says. “With our approach, there’s potential down the road to use the materials in vascular applications.” Ultimately, improved compatibility means expanded opportunities for medical applications and a reduction in adverse effects. Garza Flores is also exploring contact lens concepts with collaborators in McMaster Engineering Dean Heather Sheardown’s C20/20 group; a separate line of work reflecting how widely a truly biocompatible silicone could reach. A marathon, not a sprint For Garza Flores, this research marks a pivotal moment in her McMaster journey. She first came to McMaster from Mexico as a Mitacs-funded undergraduate intern for four months in 2019. “I really liked the culture of the Hoare lab and was eager to return for graduate studies,” she says. “I’ve always been interested in tissue engineering and making materials more biocompatible.” Seven years later, Garza Flores mentors McMaster undergraduate researchers who’ve helped strengthen the mechanics of the new silicone while preserving its antifouling performance. “It’s been tremendously rewarding to realize what I hoped to achieve back as an intern,” says Garza Flores. “The work has potential to transform the medical field.” The Hoare Lab team continues to make breakthroughs in their silicone-polymer work, making mechanical improvements to further prove the effectiveness of their findings. With a PCT patent filed and a startup venture on the way, the team is continuing to advance their innovation with the hope of seeing it progress to clinical trials. 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