Skin in the game

A bioprinter that uses a patient’s own skin to repair injuries and burns could be a game changer in wound care, accelerating the delivery of treatment, and reducing costs for the patient and healthcare providers. The gold standard of wound repair is currently the skin graft, but the treatment is not without problems; it can be difficult to achieve adequate coverage of the wound, particularly if damage is extensive and there is a limited availability of healthy skin to harvest. Another option is to use donor skin, but this runs the risk of scar formation and the patient rejecting the donation. Cellular and non-cellular biological skin equivalents are commonly used as alternatives, but these usually involve multiple surgical procedures at a high cost.

A mobile skin-printing system that allows bilayered skin to be printed directly onto a wound has the potential to revolutionise how chronic, large or nonhealing wounds are treated and managed. Developed by researchers from the Wake Forest Institute for Regenerative Medicine, the bioprinting system is unique, offering onsite management of extensive wounds by scanning and measuring a wound to deposit cells exactly where they are needed to create new skin.

Skin has an important role in immunity; it protects the body against pathogens and excessive water loss, in addition to insulating and regulating temperature. Early treatment and rapid closure of acute and chronic wounds is essential for normal healing and the prevention of hypertrophic scarring – scars that have deposits of excessive amounts of collagen, and so appear raised.

Skin on skin

The skin is made up of several layers and shields the underlying muscles, bones, ligaments and internal organs. The major skin cells are dermal fibroblasts, which synthesise the extracellular matrix and collagen, and have a vital role in wound healing; and epidermal keratinocytes, which are the predominant cells in the outer layer of the skin, the epidermis.

Dermal fibroblasts and epidermal keratinocytes can easily be isolated from a small biopsy of uninjured tissue and expanded. The cells are then mixed into hydrogel and placed in a bioprinter.

“We take a handheld device used to scan the wound, which feeds data into the software,” says Sean Murphy, assistant professor of regenerative medicine, Wake Forest Institute for Regenerative Medicine. “We are using this data to tell the print heads which cells to deliver exactly where in the wound layer by layer. This process replicates and accelerates the formation of normal skin structure and function.”

Integrated imaging technology determines the topography of the wound and aids the precise in situ delivery of dermal fibroblasts and epidermal keratinocytes directly to the injured area, replicating the layered skin structure and function. The bioprinter is an inkjet printer that delivers controlled volumes of cells to predefined locations using thermal or acoustic forces to eject matter from the cartridge to the skin.

The technology is tailored to the individual patient’s needs, with their own cells dynamically contributing to wound healing by organising up front to start the healing process much faster. Using this method of wound repair could eradicate the need for uncomfortable skin grafts, which can also cause defects, especially for those suffering from burns or large wounds caused by diabetic or pressure ulcers, for example.

“Our skin-printing system has the potential to alleviate a lot of problems related to the treatment of wounds and burns,” says Murphy. “Currently, skin grafts are used and there is sometimes a limited availability of healthy skin to harvest, while skin grafts from donors risks immune rejection.

“Our system uses a patient’s own cells, taken from a small biopsy the size of a postage stamp, and expands those cells that actively contribute to the wound healing and formation of new skin.”

“What is unique about the technology is the mobility of the system,” explains Murphy, who is also assistant professor of biomedical engineering. It is designed to be wheeled right up to the bedside, which allows on-site management of wounds. The mobile aspect allows for delivery of cells directly into wounds, with an organisation that replicates healthy skin. This significantly accelerates wound healing and formation of new skin, compared with printing externally and manually placing printed tissue onto the patient.

“The mobile bioprinter has the potential to eliminate painful skin grafts and the disfigurement from scarring that patients currently endure,” he says. “Patients who received delayed treatments or under-performing treatments often experience extensive scarring that can result in long-term physiological defects, such as disfigurements and loss of range of motion.”

7million
Patients affected by chronic wounds, such as diabetic and pressure ulcers, or burn wounds in the US.
Journal of Functional Biomaterials

There are numerous potential applications of this technology. Chronic wounds, such as diabetic and pressure ulcers, and burn wounds affect more than seven million patients in the US alone with an annual expenditure of $25 billion. Full-thickness skin injuries are a major source of mortality and morbidity with an estimated 500,000 civilian burns treated each year. For military personnel, burn injuries account for between 10–30% of combat casualties.

Rapid response

The best response is seen with rapid treatments that result in closure and protection of wounds as fast as possible; this is especially important for the survival of patients with burn injuries. It is also crucial to prevent wounds worsening over time and causing further tissue damage.

“A mobile bioprinter that doctors could use to help heal these wounds with a patient’s own cells has many ramifications,” states Murphy. “Lives would be saved, doctors and patients have a better option, and there could be significant cost savings.”

Researchers have demonstrated proof of concept of the system by printing directly onto preclinical models. They were able to see new skin forming outward from the centre of the wound; furthermore, the skin was not rejected by the body.

“So far, we found that treatment with autologous fibroblasts and keratinocytes, delivered directly to specific locations of the wound, based on wound size and topology, resulted in the acceleration of wound healing and the formation of normal skin in situ,” explains Murphy.

The system was used to print a bilayered skin construct consisting of human fibroblasts and keratinocytes directly onto a full-thickness skin defect on a nude mouse. Researchers say this demonstrated the capabilities of the bioprinting system to deliver appropriate cell types and concentrations in a layered manner. The wound area was evaluated over a six-week period and showed rapid closure of the wound in the mice compared with the untreated and matrix controls.

In porcine models, wounds treated with autologous fibroblasts and keratinocytes performed better; they showed accelerated wound closure, reduced wound contraction and increased re-epithelialisation. Tissues had a dermal structure and composition similar to that of healthy skin, with extensive collagen deposition arranged in large, organised fibres, extensive mature vascular formation and a large number of proliferating keratinocytes.

“We have demonstrated the capabilities of our system to deliver allogeneic or autologous dermal fibroblasts and epidermal keratinocytes within a biological hydrogel to large full-thickness wounds. Wound treatment using our bioprinting system resulted in the quick and proper coverage of the wounds, which is crucial for maintaining homeostasis, wound closure, epithelialisation and scar prevention.”

The next step is to conduct a clinical trial in human subjects. Murphy says they are on the right track and moving through the regulatory processes necessary to do this. Future studies will use the bioprinting system to investigate the delivery of other biomaterials and cell types to further accelerate wound healing, reduce the requirement for biopsies and cell culture, and potentially provide an off-theshelf cartridge that can be used to rapidly treat patients whether they are in civilian hospitals or military field hospitals, states Murphy, with this eventually progressing to human clinical trials.

Bedside bioprinters capable of depositing cells directly into wounds such as pressure or diabetic ulcers and burns could represent a significant shift in the way injuries are treated. It has already been proven that the technology works in preclinical models; the next stage is to test the technology in humans. The printers have the potential to speed up the delivery of care – especially important when considering that rapid treatments produce the best results in terms of healing and wound protection. The mobility of the technology and its personalised nature could be a real revelation in on-site wound management.