A flash of light. Ethereal blue and purple sparks and plumes, shooting like a laser beam until it hits the surface where it dances and branches gracefully like bolts of lightning. The mesmerizing sight is accompanied by an incongruently harsh, high-pitched crackle, like powerful electricity ripping through metal. “You see how it changes?” says Dr. Theresa Freeman loudly over the sound of the machine, the wonder in her eyes still visible behind the reflection of the bright light in her glasses. “That is the incredible thing about plasma, it can change composition entirely depending on the parameters I set and the surface it strikes.”
A Passion for Curiosity
An unconventional journey led Dr. Theresa Freeman to become a pioneer in the field of plasma medicine, taking on the unknown with creative thinking.
Dr. Freeman’s excitement is contagious, and one can’t help but be drawn into this world of possibilities that plasma – the fourth state of matter – represents. By making observations grounded in her wealth of knowledge of cell biology, Dr. Freeman - associate professor of orthopedic surgery - has traversed the boundaries of physics and engineering to uncover novel insights and drive the development of biomedical applications of plasma devices. Among dozens of research firsts, Dr. Freeman demonstrated that plasma can enhance both stem cells and their environment to promote bone and cartilage formation, resulting in the potential use of plasma in wound healing and orthopedic surgery. She hopes to make more major advancements in the field with a new NIH grant, leading a tripartite partnership of researchers from the U.S., the Republic of Ireland and Northern Ireland to study how plasma can be used to treat bone infection.
This project represents a flourishing chapter in Dr. Freeman’s research, but her career path towards the unlikely field of plasma medicine has been filled with ups and downs, and twists and turns. Curiosity, creativity, and a commitment to mentoring the next generation has marked her unconventional path.
The Start of an Unconventional Path
“Ever since I was a kid, I’ve had this natural curiosity,” recounts Dr. Freeman. “I was always asking – ‘Why?’ and ‘How?’”
This curiosity drew her to the sciences, particularly biology. She excelled in the subject and continued to nurture her passion in college, at the University of Sciences in Philadelphia. There she got her first taste of laboratory research, doing a brief project under Dr. Ara DerMarderosian, trying to isolate the active pharmacological component in a Nyssa sylvatica, or the black gum berry. But that would be the extent of her exposure to research for a while. After graduating college in 1983, with a BS in Biology, she became a high school teacher of biology and chemistry. During that time, she got married and two years later, after her son was born, she became a lab instructor at Burlington County Community College.
It was then that her path started to turn, when she met a woman professor; most of Dr. Freeman’s professors in college had been men. “They had seemed aloof and elite,” she remembers, “so I really never identified being a professor as a career path.” Observing this woman, who also had a PhD and treated her like a peer, was a big deal. The two formed a friendship, and Dr. Freeman found a role model she never knew she needed. “It was so important to be able to relate with her, it made me think – if she can do it, I can do it too.” In the fall of 1992, even though it had been almost ten years since graduating college, Dr. Freeman applied for and got a graduate teaching assistantship at Rutgers University, where she would pursue her PhD.
A Delayed, But Deep, Dive into the Cell
In those 10 years, the whole field of molecular biology had been discovered, making her graduate school classes quite challenging – but Dr. Freeman was excited to learn. She eventually joined a lab that studied the cell nucleus and became enamored with cell biology. “It was so cool to see the way cells are so dynamic and how they act as individuals, yet work together,” she says.
She studied why and how chromosomes - the thread-like structures that carry our genetic material - were organized in the nucleus. Soon she was spending hours in a dark microscope room, seeing a nucleus lit up by fluorescent painting probes –a new technique that allowed her to fluorescently label specific chromosomes different colors and track their positions as cell activities changed. With this new tool, she made fresh observations of well-known cellular processes like cell division. Her thesis work described how chromosome positions in the nucleus were carefully orchestrated; the findings were published in Science, one of the most prestigious scientific journals. This would be the first example of Dr. Freeman’s ability to use innovation to push the boundaries of scientific questions, master new techniques and expose her keen eye for interesting observations.
A schematic from Dr. Freeman's publication in Science depicting the arrangement of chromosomes in human cells.
“I am always reminding my students now, it’s all about keeping an open mind to experimental outcomes,” explains Dr. Freeman. “Something that might seem like an aberration might turn out to be a new discovery.”
Even with her family responsibilities, Dr. Freeman finished her master’s and PhD degrees in four years. “I was the only person in my PhD cohort with a family,” she says. “My classmates were perhaps more up to date on the state of science, but those 10 years delay gave me valuable life experience – I was more mature, confident in my abilities, organized, and having young kids meant that I was very efficient with my time.”
From Genetic Codes to Computer Codes
After just under a year as a postdoc, she translated her experience in microscopy and analysis to her first faculty position at the University of Pennsylvania in 1997. She was a research assistant professor in the department of molecular genetics, and assistant director of the cell morphology core at the University’s Institute of Human Gene Therapy. The late 90’s were a pivotal time for the field of gene therapy, a treatment that uses genetic material encoding proteins to change the course of a disease.
A newspaper clip about Dr. Freeman's work at the Institute of Human Gene Therapy at University of Pennsylvania.
“I loved it, unfortunately it was impossible to fit everything into regular working hours and I was missing too many family dinners,” reflects Dr. Freeman. “I hadn’t anticipated finishing my PhD or getting a faculty job so quickly, and the kids were still very young. Ultimately, I felt I had to find a job where I could better balance family life with work.”
So after only a year in her faculty position, Dr. Freeman decided to pursue a job in industry as an applications scientist, which provided more flexibility. “I could work from home and make my own schedule of when to visit clients, and still attend all the kids’ activities,” she says.
As part of her work, she assisted clients in academia and the pharmaceutical industry in analyzing images captured through microscopy. True to her ability quickly learn a new technique, Dr. Freeman taught herself to write visual basic code and create custom analysis programs. But after seven years, the novelty of this work started to wear off. “As someone who has always been driven by challenges, I knew I needed a change,” says Dr. Freeman, “and I really missed academic research.”
On a chance visit with clients in the department of orthopaedic research at Jefferson, they inquired if she knew anyone who had imaging skills and a background in cell biology. She didn’t think twice, and immediately asked if they would consider her; it felt like a perfect fit and couldn’t have come at a better time – Dr. Freeman was ready for her return to academia.
Returning to Academia, the Bare Bones of it
In 2004, Dr. Freeman was hired as a research associate at Jefferson. This return to academia not only came with a big cut in pay and free time, but Dr. Freeman found herself starting from the lowest rung of the ladder, in a completely new field. “I didn’t know anything about orthopedics,” she says. “It was a steep learning curve. Fortunately, the department was such a welcoming, inclusive and collaborative group.”
One of Dr. Freeman’s mentors and collaborators in the department was Irving Shapiro, BDS, PhD, professor and director of the Tissue Engineering and Regenerative Medicine Training program.
“Dr. Freeman is a brilliant scientist,” says Dr. Shapiro. “When she joined the department, she brought with her a broad knowledge base, impressive microscopy skills and an immense grasp of the latest technology and how to apply it to the tissues we’re studying.”
Dr. Freeman with Dr. Irving Shapiro.
“I’m a cell biologist, and luckily everything has a cell,” says Dr. Freeman. “Bone cells are called osteocytes and I was immediately drawn to the bone’s ability to remodel and regenerate in response to injury or disease.”
In particular, she was fascinated by reactive species and how they could promote bone regeneration. Reactive species, more commonly known as free radicals, are created when electrons hit molecules like water or carbon dioxide and break them up into smaller molecules. Some common examples of reactive species are peroxide, ozone and nitric oxide.
Free radicals often have a bad reputation – they are what antioxidants defend against and why we’re often told to load up on antioxidant-rich foods like leafy greens and dark chocolate. But, actually, “they play an important role in the cell, as signaling molecules,” says Dr. Freeman. Cells have a kind of sensor that monitors the level of reactive species – at lower, normal levels, beneficial signaling cascades are always running to keep the cell going. However, if reactive species levels get too high, the sensor activates, turning on signaling cascades that can kill the cell to protect against DNA damage.
“When we are young the set-point on the sensor is high. As we age, inflammation and oxidative stress build up in our body, making it much easier to hit the set-point and turn on those destructive pathways, resulting in diseases like osteoarthritis,” says Dr. Freeman. She became interested in how to change the set-point and manipulate reactive species in cells. A fortuitous meeting with investigators at The Drexel Plasma Institute in 2010 took Dr. Freeman’s research onto yet another path.
Pioneer of Plasma
Plasma is the fourth state of matter, along with liquid, solid and gas. When gas molecules are hit by electrons, they breakdown into ions that produce plasma– a gaseous mixture of reactive species and charged particles or ions. Plasma is all around us – a crack of lightning, a neon sign on the side of the road, a plasma TV and the sun.
“Plasma is usually very hot – not so surprising since it’s what makes up the sun,” says Alexander Fridman, PhD, renowned plasma scientist, physicist and director of The Drexel Plasma Institute. “Using a generator that could rapidly switch energy levels, we were able to generate a cold or non-thermal, plasma where all the heat is kept inside the charged particles, instead of being emitted. This type of plasma can safely be used on human skin and tissues.”
“We knew the technology had potential applications in medicine and biology, but that was not our expertise,” continues Dr. Fridman. “We happened to meet with Dr. Freeman at a local research meeting, and we immediately decided to work together. She was so enthusiastic and had so many creative ideas for how to use this technology.”
Plasma is a rich source of reactive species and energy. “But it’s important to understand that just blasting a cell with plasma doesn’t mean it will do what you want. Each cell type reacts differently,” explains Dr. Freeman. “So, one part of the challenge is understanding the cellular biology and physiology, which is my expertise, and the other part is understanding the components and energy of plasma, which I had to learn.”
Orthopedic infection is a significant clinical problem and one of Dr. Freeman’s early experiments with plasma was to determine if it could be used to kill bacteria, without harming healthy mammalian cells. She found something quite unexpected. While the plasma didn’t selectively kill off bacteria, she found that low levels of plasma could actually stimulate cells to grow and differentiate. Based on this data, Dr. Freeman was awarded the first NIH R01 grant to study plasma medicine and determine if plasma treated stem cells could be used to promote regeneration, pushing Jefferson to the forefront of the field.
“Over the last 10 years, Dr. Freeman has become a pioneer in the field of plasma medicine,” says Dr. Shapiro. “Much of what we know today about how plasma affects biological tissue is thanks to her efforts.” She has published research on the use of plasma in a range of applications - destroying cancer cells, limb regeneration, bone formation, orthopedic infection and wound healing. She has collaborated with researchers across the world, including Jean-Michel Pouvesle, PhD, who nominated her for The Plasma Medicine Award in 2018.
“We come from two very different worlds,” says Dr. Pouvesle. “She is a biologist, I am a physicist; it can be difficult to understand each other. But she knows how to overcome this barrier, unlike many scientists who speak such a specialized language. She is able to so deftly extrapolate her knowledge and ideas across fields and be a bridge between biology and physics and engineering. Because of her, the future of plasma medicine is vibrant with possibilities.”
A Dedicated Mentor to the Next Generation
For her part, Dr. Freeman credits a key part of building that bridge to Natalie Chernets, who was a PhD student at the time in the Drexel Plasma Institute. “She became a sort of translator between the two worlds. I taught her the biological aspects, and she taught me the physics concepts. Together, we grew our understanding of what plasma can do in a biological context.”
Dr. Chernets ended up doing a joint thesis in Dr. Freeman’s lab and stayed on as a postdoctoral fellow. “I was very impressed with Dr. Freeman's ability to guide both the theoretical and practical aspects of research,” says Dr. Chernets. “She knows how each piece of equipment in her lab works and can troubleshoot if it malfunctions. This is a very unique strength in a thesis advisor.” She adds, “At the time that I met Dr. Freeman, I had no female mentors. It was so refreshing to be able to talk about our experiences as women in science, life outside of academia, and just have a different comfort level than what I had with male mentors.”
Dr. Freeman with Dr. Natalie Chernet, on the day Dr. Freeman was awarded the Elizabeth Bingham Mentoring Award.
Dr. Freeman’s unconventional career trajectory bolstered Dr. Chernets when she herself had a child during the last year of her PhD. “If it wasn’t for Dr. Freeman’s support, I very likely would have dropped out of grad school,” recalls Dr. Chernets. “There were days when childcare fell through during an important deadline, Dr. Freeman would welcome me into her home and take care of my child while I wrote. I’ve never experienced that level of support. Another time, we were going to a conference in San Antonio, and bad weather forced my flight to land in Austin. I was pregnant at the time and she was concerned for my safety, so she rented a car and picked me up from Austin. She goes above and beyond - it will always stay with me.”
Mentorship has been a cornerstone of Dr. Freeman’s time at Jefferson. She took on directing the Summer Undergraduate Research Program (SURP) in Jefferson’s College of Life Sciences, which aims to give rising college seniors opportunities to experience research in a wide range of biomedical fields, and provide a stepping-stone to graduate school.
Dr. Freeman with her lab assistants Lilith Elmore and Lauren Israel.
She has been particularly committed to the advancement of women in science, fueled in part by her own rapport with the woman professor she met back in community college. “It is so impactful for people to see themselves in a position that might seem closed off to them.”
It is tough being a woman in STEM, she adds, recalling the many micro-aggressions and slights she’s faced over the years. “On top of that, there are the added challenges that come with balancing academia and family life,” she says. “I try providing a lift up over some hurdles that bar talented young women from succeeding in STEM. Actually in many ways, their successes give me greater satisfaction than my own, because if I help them, and they pass it forward, the successes become exponential.”
Her mentorship has been so impactful that in 2016, she was selected for the Elizabeth Bingham Mentoring Award. It’s an honor presented by the Philadelphia Chapter of American Women in Science (AWIS) to a distinguished scientist who has significantly influenced the advancement of women in science. Dr. Chernets was among several women in the lab who nominated her. “I am proud to say, I stay in touch with all of them and they have gone on to become exceptional women with successful careers,” Dr. Freeman extolls like a proud mom.
