New Discoveries

Pressure Ulcer Research, Part 1: Tissue Engineering Reveals New Research Possibilities

A major challenge facing complex rehab technology today is the demand for outcome measures — data to “prove” seating & mobility equipment produces successful results. Outcome measures are in demand partly due to pharmaceutical companies. Because conditions such as high cholesterol and depression are so common, drug manufacturers are able to roll out statistics on hundreds or thousands of patients who take part in their clinical trials.

In contrast, far fewer people use complex rehab technology (CRT) — and though they may have the same general diagnosis, their co-morbidities, past clinical issues and other circumstances make each CRT user a unique individual. What works for pharma companies is what funding sources have come to expect from the rest of healthcare as well…much to the challenge of seating & mobility providers and clinicians.

A New Approach to Research

Amit Gefen, Ph.D., is a professor of biomedical engineering at Tel Aviv University. At the International Seating Symposium in March, he talked about pressure ulcers — not just what causes them, but at what point and under what circumstances they occur. Gefen had just been published in Ostomy Wound Management — “Tissue Changes in Patients Following Spinal Cord Injury & Implications for Wheelchair Cushions & Tissue Loading.” He’d just co-authored, with his M.S. student Ayelet Levy and ROHO Inc. collaborator Kara Kopplin, an article in the Journal of Tissue Viability: “An Air-Cell-Based Cushion for Pressure Ulcer Protection Remarkably Reduces Tissue Stresses in the Seated Buttocks with Respect to Foams: Finite Element Studies.”

In an interview with Mobility Management, Gefen explained that he is not a seating & mobility clinician: “I have quite a different angle. My bachelor’s is in mechanical engineering; my master’s and my Ph.D. are in biomedical engineering. Very early, during my master’s research, I became interested in chronic wounds. It really started by looking at the foot skeleton and how it moves when we walk. But very quickly and certainly in my Ph.D. [work], it concerned mostly the soft tissues of the foot; the obvious medical application was to look at diabetic footwear. And this is how I became interested in chronic wounds.”

While studying chronic wounds, Gefen says he noticed a comparative lack of research in the field, “which is really almost neglected in terms of the research resources that we biomedical engineers see in fields like orthopaedics, cardiovascular, cancer. So I decided I would focus on that and try to bring the tools that mechanical engineers use, like computational modeling.

“Mechanical engineers use a lot of computational tools, computer tools, to try to describe how complex structures behave. So if you have a very complex machine — an engine or a bridge — that is subjected to combustion, wind, whatever, you can’t really take a pencil and a notebook and calculate those loads. You need to have a lot of computer power to solve all these complex equations that describe how this structure behaves.”

Borrowing the Tools of Engineers

Gefen explains that he applied the sort of computer simulations used by mechanical engineers “to look at how loads develop in tissues, not only on the surface of tissues, but also internally, where you can’t look.

“We sit on our two ischials basically, and these are really sharp objects. They are compressing all the soft tissues underneath them — the muscles, the fat, the skin. So we take a sharp object and what you have at the interface is a very concentrated load. You wouldn’t see that load on the surface. You would need something to look at the inside of the body to actually quantify that load and then see how these loads also change with regard to spinal cord injury subjects.”

While Gefen’s research would be applicable to wheelchair users with a range of diagnoses, as well as other chronic sitters, his first focus has been spinal cord injury.

“These are people with a life ahead of them potentially,” he says in explaining his choice. “These are not 80-year-old people at a terminal stage of their lives. Potentially if something can be done, [SCI patients] can [live to] be 80 years old.

“But one in 10 of them will die of pressure ulcers. That’s amazing to me because most of these patients get these spinal cord injuries when they are young: car accidents, motorcycle accidents, whatever.”

Motivated by those statistics — that spinal cord injuries generally happen to younger people, and that too many are succumbing to pressure ulcers — Gefen borrowed engineering tools for his research. But computational modeling alone, he says, wasn’t sufficient.

“Mechanical engineering helps me to look at loads inside the tissue, but that’s not enough, really,” he notes. “It can only tell you what the loads are. Is it 100mm of mercury or 200mm of mercury of pressure or 10 kilopascals or 100 kilopascals? What does it mean?”

Tissue Engineering Opens New Doors

By incorporating processes from other fields, notably biology, Gefen says researchers have created tissues via a process called tissue engineering. In a lab, cells in a culture dish are provided “the right stimuli. It could be mechanical stimuli, it could be electrical stimuli.”

With the appropriate biochemical environment, “these cells start to develop and differentiate into tissue-like structures and then into actual microscopic tissue pieces that you can set as a substitute for what we used to do 10 years ago with animals.”

Though the tissue engineering field is new — just 20 years old or so, says Gefen, who’s been involved from its early phase — the potential applications are far reaching, including creating replacements for failing human organs such as the heart, liver or kidneys. “It has many, many benefits. You can talk about the social and ethical aspects; I’m not going to go into that. The only thing I’m going to say is that when I’m applying a load to a tissue construct in a very well-controlled environment, I can see down to the level of individual cells, what these loads will do, how these loads will affect the cells.” Lab-generated tissues could open up a range of new possibilities for researchers. For example, testing the tissues could help to pinpoint “tissue injury thresholds” — that moment in time when tissues start to suffer injury due to the loads that they’re bearing. That sort of information would be much more difficult to achieve using traditional methods, since researchers couldn’t just leave human subjects in one position until tissue breakdown began. Applications in Patient Care & New Technologies

Armed with tissue injury threshold information, clinicians could work backward to determine when and how frequently patients should be repositioned to avoid injuries, as well as what type of cushion or mattress they should be using to increase their “safe sitting time” or “safe lying time.” Guidelines could be issued to tell employees in long-term care facilities how often to perform weight shifts, and which support surfaces should be prescribed per each condition or risk factor. “It’s not just what the research is saying, it’s also what the resources are [at facilities],” Gefen acknowledges. “But with that being said, we at least want to know what is happening in an ideal world. And then you can span it all the way through to technologies.”

So, it’s now possible to create healthy tissues in a lab. Is it also possible to create tissues that would emulate previous pressure ulcers or scarring?

“We’ve actually done that,” Gefen says. “That’s a very good point because the strength of doing computer simulations is you can’t look at all the conditions of all the patients in the world because that would take too much time and money, and they’re all unique. “One of the major strengths of computer simulation is that in the virtual environment, you can ask what if. So say I have a patient: What if that patient had a previous pressure ulcer? Let’s see how scars will affect internal tissue loading and the susceptibility to [future] pressure ulcers.” How about changing the ratios of muscle and fat within computer-simulated tissues, or reducing the thickness and elasticity of those skin tissues to emulate the skin of a geriatric or diabetic patient? “It has been done,” Gefen says. “All of that can be simulated.”

Coming up in Part 2: What Dr. Gefen’s research is uncovering about SCI patients, and how the research can be applied to new technology, including wheelchair seat cushions.

This article originally appeared in the June 2014 issue of Mobility Management.

About the Author

Laurie Watanabe is the editor of Mobility Management. She can be reached at

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