CARLSBAD, CALIF. – For the estimated 10 million wounds that clinicians treat in the United States each year resulting from surgical procedures, trauma, burns, and other causes, the best outcome is a scar, a fibrotic dermis with a flattened epidermis that contains no sweat glands, no pilosebaceous units, and impaired nerve function.
But what if the outcome was skin regeneration instead of scar formation? At the annual symposium of the California Society of Dermatology & Dermatologic Surgery, Philip O. Scumpia, MD, PhD, described the .
“We’re preprogrammed to undergo scarring,” said Dr. Scumpia, associate professor of dermatology at the University of California, Los Angeles. “Tissue fibrosis is an evolutionary process” where a fibrotic matrix is deposited “as quickly as possible to close the gap caused by an injury,” he noted. “All of the cues in the normal wound healing process result in fibrosis, but we want to move from scarring to tissue regeneration. The goal is to make something that can shift from this evolutionary process, and it’s proven to be inherently difficult.”
Dr. Scumpia
Dr. Philip O. Scumpia
Common approaches to wound treatment include simple and advanced dressings, negative pressure, and hyperbaric oxygen. For wounds that persist beyond 30 days, advanced treatment options include decellularized grafts such as placental membranes, amniotic membranes, and acellular dermal matrices. “There are also cellularized grafts such as dressings that contain neonatal dermal fibroblasts,” which are expensive, said Dr. Scumpia, director of dermatopathology at the West Los Angeles VA Medical Center. “There are also semi-synthetic grafts such as single or double layer dermal replacement templates and synthetic dermal substitutes in the form of sheets or foam. All of these can help with wound coverage and help chronic wounds close on their own.”
Meanwhile, tissue regeneration – or efforts to restore tissue to its original functionality – include growth factors, stem cells, or replacement extracellular matrix (skin substitutes), or a combination. “Bioengineered dressings and bioengineered skin substitutes have shown modest improvement in wound healing but not tissue regeneration,” Dr. Scumpia said. “At best, we can accelerate scar formation and close the wound quicker, but nothing has been shown to regenerate tissue.”
Approaches to skin regeneration
Studies from the embryology literature have helped researchers develop better approaches to skin regeneration. For example, fetal skin heals without scarring when injured. “Hairs form from placodes, then sebaceous glands form, and fibroblasts that are part of the papillary mesenchymal body expressing special factors such as engrailed or CRABP1 drive hair follicle formation,” he said. “Many studies have shown that sonic hedgehog signaling, and Wnt/beta-catenin signaling can play a role in the development of new hair follicles. Also, fibroblasts in the dermis can drive hair follicle formation.”
Researchers are also learning about tissue regeneration from mouse models. For example, African spiny mice have been shown to heal regeneratively. “If you make wounds large enough on lab mice, the center heals regeneratively,” Dr. Scumpia said. “What’s interesting is that these same signals are present in embryonic hair follicle development. Why is this important? Who wants a hairy scar? It’s an organized structure that develops in the wound. That can help us understand what we need to put in so that our body regenerates on its own. In mouse models, the immune system has been shown to play a role in regeneration.”
Expanding on initial work conducted at UCLA, Dr. Scumpia and his colleagues founded San Diego-based Tempo Therapeutics, which is commercializing the MAP hydrogel to mimic the natural porosity and stiffness of skin. They sought to develop a new biomaterial, he said, noting that “the skin is porous on a microscale level, allowing cells to infiltrate different areas.” And the problem with existing biomaterials “is that they don’t incorporate into the skin very well,” he explained. “They’re usually stiff and rubbery and can cause a foreign body reaction, which can result in fibrous encapsulation and inflammation.”
The MAP hydrogel is composed of randomly packed “microsphere building blocks,” including an amino acid that promotes an immune response. When injected into a wound, the hydrogel forms a porous matrix in the tissue. Surface annealing locks in porosity and tissue grows into porous spaces, which avoids scar formation pathways and enables critical organs to regain function.
During in vivo tests, researchers observed decreases in inflammation compared with traditional hydrogels in the first 48 hours. “In mouse models, we found that if you inject in a hydrogel that has no porosity, the body tries to spit it out, and you have an immune reaction,” Dr. Scumpia said. “But when we used the MAP hydrogel, we found that cells can migrate through it, which allows wounds to heal quicker. When we added an antigen in the hydrogel trying to allow the hydrogel to degrade slower, it actually degraded more rapidly, but we found that new hair follicles formed in the center of these wounds, a hallmark of skin regeneration. My lab has been studying why this occurs and trying to use this to our advantage in other models.”
In an unpublished mouse burn wound model study, he and his colleagues excised a wound, but it never healed with regeneration in the center. “We don’t understand why,” he said. But when the researchers used the MAP gel in wounds of hairless mice, they observed the formation of sebaceous glands and hair follicles over the wound beds. “It’s an exciting finding to see hair follicles develop in the center of a wound,” Dr. Scumpia said. He noted that to date, use of the MAP hydrogel has demonstrated tissue regeneration in some of the 27 veterinary cases that have been performed, including for wounds following traumatic injuries or following tumor resections on paws that allowed the pets to avoid amputation.