A source of friction | Eurek alert!

Many soft biomedical devices, such as silicone implants and contact lenses, operate in direct contact with living cells and tissues. They can be designed to adjust their shape or appearance, or to improve their interactions inside the body. A problem with such devices is that soft implant surfaces can induce inflammation by unintentionally increasing friction as the outer surface of the device slides against living cells and tissues.

Angela Pitenis, an assistant professor in the Department of Materials at UC Santa Barbara, received a prestigious Early CAREER award from the National Science Foundation (NSF) to study this problem, with a view to improving medical devices used by millions of people. every year. The NSF Faculty Early Career Development program, which encourages young faculty to pursue cutting-edge research and advance excellence in education, will provide Pitenis with nearly $600,000 in funding over five years.

“The Early CAREER award is a huge honour,” said Pitenis, who works to better understand interface phenomena, such as friction, adhesion and wear, between soft materials and living cells. “As an experimenter, research support is essential. This award provides funding for a dedicated Ph.D. student researcher, essential reagents and refill fees for use of shared experimental facilities and funding for outreach programs focused on science communication and broadening participation of underrepresented and underserved groups in science, technology, engineering and mathematics. I am very happy that the NSF supports my research directions and my role as a teacher-researcher.

“I offer my sincere congratulations to Professor Angela Pitenis on receiving the prestigious NSF Early CAREER Award,” said Tresa Pollock, Acting Dean of the UCSB College of Engineering (COE) and Alcoa Distinguished Professor of Materials. “It continues a strong and growing tradition of our stellar young faculty receiving national recognition for their innovative research. We look forward to seeing her continued success on this project and those she will pursue in the future.

Pitenis’ project, “Dynamics of Fragile Interactions,” fills a gap in the knowledge and understanding of lubrication, or the reduction of friction and resistance to motion in soft aqueous gels, and in biotribology, which is l study of friction, wear and lubrication in biological systems.

“My project is inspired by the need for soft biological materials that allow lubrication, despite persistent and far-reaching tribological challenges, such as the mechanical stresses that are created when surfaces interact in relative motion,” said Pitenis, who has joined the UCSB Materials Department in 2018.

The project is guided by the hypothesis that slippery surfaces in nature reduce friction through a delicate balance of fracturing and rapid cross-linking between macromolecules in aqueous solutions. It is a phenomenon that occurs in the ocular tear film, which physically separates the sensitive surfaces of the cornea and the eyelid by a distance of about 5 micrometers (µm). Although the tear film is over 90% water – a poor technical lubricant – it provides robust biological lubrication over tens of thousands of blinks each day. In this system, biology has engineered elegant networks of gelling proteins, called mucins, to enable resilience through frailty.

“By easily fracturing when sliding and then quickly recovering when at rest, the fragile gel networks act as mechanical fuses that rapidly dissipate high stresses and protect underlying cells and tissues,” Pitenis said. “Our project will contribute to explaining the mechanics of aqueous gels in biological lubrication, which could lead to the engineering of more reliable, responsive, resilient and responsible biotribological interfaces.”

Since biological materials are often difficult to obtain in large quantities and subject to high variability from sample to sample, the Pitenis lab will design synthetic models of biological gels using high-grade hydrogels. in water, which are cross-linked three-dimensional networks of water-swollen hydrophilic polymer chains.

“These model materials can provide fundamental insights into the complex lubricating mechanisms of biological interfaces like tear film aqueous gel networks,” she said.

Researchers at the Pitenis lab will also use its custom-built scientific instruments, called tribometers, to measure friction and normal forces when sliding synthetic transparent gels, and will use optical microscopy techniques to study interfacial phenomena. Observation of the contact will allow researchers to improve their understanding of the mechanics and dynamics of the interface.

“Resilience in the face of fragility is an emerging concept,” said Pitenis. “While many studies in materials science over the past few decades have focused on ways to make soft materials stronger and more resistant to fracture, these characteristics may actually impair lubrication. Establishing that brittle interfaces offer robust protection and low friction will extend the study of the dynamics of fragile interfaces to many fields focused on soft materials, including biology, chemistry, physics, mechanics and medicine.

In addition to demonstrating self-healing surface gel layers that dynamically re-gel during recovery, the lab will explore the incorporation of degradable chemicals into the gels with the goal of recycling synthetic polymers and products made from them. of materials.

Pitenis also plans to use the CAREER award to increase the participation and retention of women and minority English learners in STEM by engaging in local community outreach and participating in the Research and Development Partnership Program. Education in Materials (PREM) from UCSB’s Materials Research Laboratory. . PREM offers ten-week summer research internships for students at UCSB and the University of Texas at El Paso.

“I’m especially excited to work with undergraduates because they add tremendous value to research labs, often by asking deceptively simple yet endlessly complicated questions that can trigger in-depth research discussions and sometimes even new research projects!” said Pitenis, who also plans to pursue international collaborations with the University of Alberta and the University of Leeds.

Pitenis is among ten junior College of Engineering faculty members who have received CAREER awards since April 2020. UCSB ranks first among public universities for the percentage of eligible junior faculty who have received the awards from 2017 to 2021.

“I am extremely grateful to my graduate and undergraduate students who have kept me motivated and inspired during a global pandemic,” Pitenis added. “I hope this award will encourage students to consider careers in research, education and scholarship.”


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