Nanofiber coating prevents infections on prosthetic joints

One challenge with surgical implants is the risk of bacterial infection. Now researchers from Johns Hopkins Institute for NanoBioTechnology and the Johns Hopkins School of Medicine have developed a nano fiber coating that may help solve this problem. 

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A titanium implant (blue) without a nanofiber coating in the femur of a mouse. Bacteria are shown in red and responding immune cells in yellow. Credit: Lloyd Miller/Johns Hopkins Medicine

In a proof-of-concept study on mice, scientists at The Johns Hopkins University show that a novel coating they made with antibiotic-releasing nanofibers has the potential to better prevent at least some serious bacterial infections related to total joint replacement surgery.

A report on the study, published online the week of Oct. 24 in Proceedings of the National Academy of Sciences, was conducted on the rodents’ knee joints, but, the researchers say, the technology would have “broad applicability” in the use of orthopaedic prostheses, such as hip and knee total joint replacements, as well pacemakers, stents and other implantable medical devices. In contrast to other coatings in development, the researchers report the new material can release multiple antibiotics in a strategically timed way for an optimal effect.

“We can potentially coat any metallic implant that we put into patients, from prosthetic joints, rods, screws and plates to pacemakers, implantable defibrillators and dental hardware,” says co-senior study author Lloyd S. Miller, M.D., Ph.D., an associate professor of dermatology and orthopaedic surgery at the Johns Hopkins University School of Medicine.

Surgeons and biomedical engineers have for years looked for better ways —including antibiotic coatings — to reduce the risk of infections that are a known complication of implanting artificial hip, knee and shoulder joints.

Every year in the U.S., an estimated 1 to 2 percent of the more than 1 million hip and knee replacement surgeries are followed by infections linked to the formation of biofilms — layers of bacteria that adhere to a surface, forming a dense, impenetrable matrix of proteins, sugars and DNA. Immediately after surgery, an acute infection causes swelling and redness that can often be treated with intravenous antibiotics. But in some people, low-grade chronic infections can last for months, causing bone loss that leads to implant loosening and ultimately failure of the new prosthesis. These infections are very difficult to treat and, in many cases of chronic infection, prostheses must be removed and patients placed on long courses of antibiotics before a new prosthesis can be implanted. The cost per patient often exceeds $100,000 to treat a biofilm-associated prosthesis infection, Miller says.

Major downsides to existing options for local antibiotic delivery, such as antibiotic-loaded cement, beads, spacers or powder, during the implantation of medical devices are that they can typically only deliver one antibiotic at a time and the release rate is not well-controlled. To develop a better approach that addresses those problems, Miller teamed up with Hai-Quan Mao, Ph.D., a professor of materials science and engineering at the Johns Hopkins University Whiting School of Engineering, and a member of the Institute for NanoBioTechnology, Whitaker Biomedical Engineering Institute and Translational Tissue Engineering Center.

Over three years, the team focused on designing a thin, biodegradable plastic coating that could release multiple antibiotics at desired rates. This coating is composed of a nanofiber mesh embedded in a thin film; both components are made of polymers used for degradable sutures.

To test the technology’s ability to prevent infection, the researchers loaded the nanofiber coating with the antibiotic rifampin in combination with one of three other antibiotics: vancomycin, daptomycin or linezolid. “Rifampin has excellent anti-biofilm activity but cannot be used alone because bacteria would rapidly develop resistance,” says Miller. The coatings released vancomycin, daptomycin or linezolid for seven to 14 days and rifampin over three to five days. “We were able to deploy two antibiotics against potential infection while ensuring rifampin was never present as a single agent,” Miller says.

The team then used each combination to coat titanium Kirschner wires — a type of pin used in orthopaedic surgery to fix bone in place after wrist fractures — inserted them into the knee joints of anesthetized mice and introduced a strain of Staphylococcus aureus, a bacterium that commonly causes biofilm-associated infections in orthopaedic surgeries. The bacteria were engineered to give off light, allowing the researchers to noninvasively track infection over time.

Miller says that after 14 days of infection in mice that received an antibiotic-free coating on the pins, all of the mice had abundant bacteria in the infected tissue around the knee joint, and 80 percent had bacteria on the surface of the implant. In contrast, after the same time period in mice that received pins with either linezolid-rifampin or daptomycin-rifampin coating, none of the mice had detectable bacteria either on the implants or in the surrounding tissue.

“We were able to completely eradicate infection with this coating,” says Miller. “Most other approaches only decrease the number of bacteria but don’t generally or reliably prevent infections.”

After the two-week test, each of the rodents’ joints and adjacent bones were removed for further study. Miller and Mao found that not only had infection been prevented, but the bone loss often seen near infected joints — which creates the prosthetic loosening in patients — had also been completely avoided in animals that received pins with the antibiotic-loaded coating.

Miller emphasized that further research is needed to test the efficacy and safety of the coating in humans, and in sorting out which patients would best benefit from the coating — people with a previous prosthesis joint infection receiving a new replacement joint, for example.

The polymers they used to generate the nanofiber coating have already been used in many approved devices by the U.S. Food and Drug Administration, such as degradable sutures, bone plates and drug delivery systems.

In addition to Miller and Mao, the study’s authors are Alyssa Ashbaugh, Xuesong Jiang, Jesse Zheng, Andrew Tsai, Woo-Shin Kim, John Thompson, Robert Miller, Jonathan Shahbazian, Yu Wang, Carly Dillen, Alvaro Ordonez, Yong Chang, Sanjay Jain, Lynne Jones and Robert Sterling of The Johns Hopkins University.

Funding for this work was provided by a Nexus Award from the Johns Hopkins Institute for Clinical and Translational Research, which has been funded by the National Center for Advancing Translational Sciences and the National Institutes of Health Roadmap for Medical Research.

by Shawna Williams, shawna@jhmi.edu and Lauren Nelson, laurennelson@jhmi.edu

For press inquiries related to INBT, contact Mary Spiro, mspiro@jhu.edu

Fraley nets $500K Burroughs Wellcome Fund award for microfluidics work

Stephanie Fraley (Photo: Homewood Photography)

Stephanie Fraley (Photo: Homewood Photography)

A Johns Hopkins research fellow who is developing novel approaches to quickly identify bacterial DNA and human microRNA has won the prestigious $500,000 Burroughs Wellcome Fund (BWF) Career Award at the Scientific Interfaces. The prize, distributed over the next five years, helps transition newly minted PhDs from postdoctoral work into their first faculty positions.

Stephanie Fraley is a postdoctoral fellow working with Samuel Yang, MD, in Emergency Medicine/Infectious Disease at the Johns Hopkins School of Medicine and Jeff Wang, PhD, in Biomedical Engineering with appointments in the Whiting School of Engineering and the medical school. The goal of her work is to develop engineering technologies that can diagnose and guide treatment of sepsis, a leading cause of death worldwide, while simultaneously leading to improved understanding of how human cells and bacterial cells interact.

“Sepsis is an out of control immune response to infection,” Fraley said. “We are developing tools that are single molecule sensitive and can rapidly sort and detect bacterial and host response markers associated with sepsis. However, our devices are universal in that they can be applied to many other diseases.”

Fraley is using lab-on-chip technology, also known as microfluidics, to overcome the challenges of identifying the specific genetic material of bacteria and immune cells. Her technology aims to sort the genetic material down to the level of individual sequences so that each can be quantified with single molecule sensitivity.

“Bacterial DNA is on everything and contamination is everywhere, so trying to find the ones associated with sepsis is like the proverbial search for the needle in the haystack,” Fraley said. “With microfluidics, we can separate out all the bacterial DNA, so instead of a needle in a haystack, we have just the needles.”

Another advantage to Fraley’s novel technology is that it will assess all the diverse bacterial DNA present in a sample, without presuming which genetic material is important. “Bacteria are constantly evolving and becoming drug resistant,” she said. “With this technology, we can see all the bacterial DNA that is present individually and not just the strains we THINK we need to look for.”

Fraley’s award will follow her wherever her career takes her. The first two years of the prize fund postdoctoral training and that last three years help launch her professional career in academia. During the application process, she had to make a short presentation on her proposal to BWF’s panel of experts. “It was like the television show ‘Shark Tank’ but for scientists,” she laughs. “ The panelists gave me many helpful suggestions on my idea.”

Fraley earned her bachelor’s degree in chemical engineering from the University of Tennessee at Chattanooga and her doctorate in chemical and biomolecular engineering with Denis Wirtz, professor and director of Johns Hopkins Physical Sciences-Oncology Center. Wirtz is associate director for the Institute for NanoBioTechnology and Yang and Wang also are INBT affiliated faculty members.

BWF’s Career Awards at the Scientific Interface provides funding to bridge advanced postdoctoral training and the first three years of faculty service. These awards are intended to foster the early career development of researchers who have transitioned or are transitioning from undergraduate and/or graduate work in the physical/mathematical/computational sciences or engineering into postdoctoral work in the biological sciences, and who are dedicated to pursuing a career in academic research. These awards are open to U.S. and Canadian citizens or permanent residents as well as to U.S. temporary residents.