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Researchers use 3D printed skin to close wounds

The material containing hair follicle precursors may have implications for more natural-looking reconstructive surgery

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According to researchers from Penn State, who recently harnessed fat cells and supporting structures from clinically procured human tissue to precisely correct injuries in rats, fat tissue holds the key to 3D printing layered living skin and potentially hair follicles. The advancement could have implications for reconstructive facial surgery and even hair growth treatments for humans.

In February, the US Patent and Trademark Office granted the team a patent for the bioprinting technology it developed and used in the study – the findings of which were published in Bioactive Materials.

“Reconstructive surgery to correct trauma to the face or head from injury or disease is usually imperfect, resulting in scarring or permanent hair loss,” said Ibrahim T. Ozbolat, professor of engineering science and mechanics, biomedical engineering, and neurosurgery at Penn State, who led the international collaboration. “With this work, we demonstrate bioprinted, full-thickness skin with the potential to grow hair in rats. That’s a step closer to being able to achieve more natural-looking and aesthetically pleasing head and face reconstruction in humans.”

While scientists have previously 3D bioprinted thin layers of skin, Ozbolat and his team are the first to intraoperatively print a full, living system of multiple skin layers, including the bottom-most layer or hypodermis. Intraoperatively refers to the ability to print the tissue during surgery, meaning the approach may be used to more immediately and seamlessly repair damaged skin. The top layer – the epidermis that serves as visible skin – forms with support from the middle layer on its own, so it doesn’t require printing. The hypodermis, made of connective tissue and fat, provides structure and support over the skull.

“The hypodermis is directly involved in the process by which stem cells become fat,” said Ozbolat. “This process is critical to several vital processes, including wound healing. It also has a role in hair follicle cycling, specifically in facilitating hair growth.”

The researchers started with human adipose – or fat – tissue obtained from patients undergoing surgery at Penn State Health Milton S. Hershey Medical Center. Collaborator Dino J. Ravnic, associate professor of surgery in the Division of Plastic Surgery at Penn State College of Medicine, led his lab in obtaining the fat for extraction of the extracellular matrix – the network of molecules and proteins that provides structure and stability to the tissue – to make one component of the bioink.

Ravnic’s team also obtained stem cells, which have the potential to mature into several different cell types if provided the correct environment, from the adipose tissue to make another bioink component. Each component was loaded into one of three compartments in the bioprinter. The third compartment was filled with a clotting solution that helps the other components properly bind onto the injured site.

“The three compartments allow us to co-print the matrix-fibrinogen mixture along with the stem cells with precise control,” said Ozbolat. “We printed directly into the injury site with the target of forming the hypodermis, which helps with wound healing, hair follicle generation, temperature regulation, and more.”

The researchers achieved both the hypodermis and dermis layers, with the epidermis forming within two weeks by itself.

“We conducted three sets of studies in rats to better understand the role of the adipose matrix, and we found the co-delivery of the matrix and stem cells was crucial to hypodermal formation,” said Ozbolat. “It doesn’t work effectively with just the cells or just the matrix – it has to be at the same time.”

It was also found that the hypodermis contained down growths – the initial stage of early hair follicle formation. According to the researchers, while fat cells do not directly contribute to the cellular structure of hair follicles, they are involved in their regulation and maintenance.

“In our experiments, the fat cells may have altered the extracellular matrix to be more supportive for down-growth formation,” said Ozbolat. “We are working to advance this, to mature the hair follicles with controlled density, directionality, and growth.”

According to Ozbolat, the ability to precisely grow hair in injured or diseased sites of trauma can limit how natural reconstructive surgery may appear. He said that this work offers a ‘hopeful path forward’, especially in combination with other projects from his lab involving printing bone and investigating how to match pigmentation across a range of skin tones.

“We believe this could be applied in dermatology, hair transplants, and plastic and reconstructive surgeries – it could result in a far more aesthetic outcome,” said Ozbolat. “With the fully automated bioprinting ability and compatible materials at the clinical grade, this technology may have a significant impact on the clinical translation of precisely reconstructed skin.”

The National Institutes of Health and the Scientific and Technological Research Council of Türkiye supported this work.

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