Skin cell gun

The skin cell gun is an experimental device for the treatment of second degree burns developed by Joerg C. Gerlach and colleagues of the Department Of Surgery at the University of Pittsburgh’s McGowan Institute for Regenerative Medicine. With this technique, individual adult stem cells from the patient's uninjured skin are applied to the wound cite, where they differentiate into normal skin. (The conventional methods use solid layers of tissue, not disaggregated cells.) The hope is that with the skin cell gun, damaged skin tissue can be regenerated more quickly than with traditional methods.

Operation

Stem cells from a biopsy of the patient's healthy skin are isolated, placed into a sterile syringe with a fitted nozzle, and sprayed directly through the nozzle into the wound. Using computer precision, the gun distributes cells at a uniform velocity throughout the wound. Then, a temporary artificial wound capillary system is applied. A tube is attached to each end of the dressings, one doing the work of an artery and the other of a vein. A bioreactor is attached to this artificial vascular system to provide nutrition such as glucose, sugar, amino acids, antibiotics and electrolytes; and support the fragile skin stem cells until they start to grow and generate new skin.

The newly introduced stem cells are able to regenerate and differentiate into their respective parts in a matter of days. The first phase of gathering the patient’s stem cells, creating a solution, and applying the stem cells takes approximately 1.5–2 hours. Within a week, the wound dressing procedure allows the stem skin cells to fully generate normal skin, and after a couple of months the skin regains its color and texture.

Natural Skin Healing Process

The natural skin healing process is a grouping of the mechanisms that allows the skin to repair itself after a tear, burn or other injury. For healthy skin, the epidermis and dermis layers, together form a protective barrier that shields the inner body. Once that barrier is broken, the normal healing process is set in motion. Wound healing generally has three different stages: the inflammatory stage, the proliferative stage and the remodeling stage. Once the skin is damaged, a series of interrelated events take place in close succession in order to repair the skin. Within minutes after the an injury occurs, blood platelets collect at the site of injury to form a clot. This clot limits bleeding at the injury site. The inflammatory phase causes bacteria and debris to be removed from the wound, and signals are released that result in the division of cells for repair. The proliferative phase is shown by the formation of new tissue at the injury site, the replacement of new skin at the site and the general shrinking and eventual disappearance of the wound. New blood vessels are also established during the healing process. The wound is made smaller by myofibroblasts, which hold on to the edges of the wound and slowly get smaller by a system similar to the contraction of muscle cells. When cellular repair is complete unneeded cells are disposed of through apoptosis.

Past Approaches

The skin cell gun is not the first ground-breaking method used to treat burns. The genesis of tissue engineered products as skin substitutes began more than 20 years ago with improved culture methods for the growth of keratinocytes, and the production of natural and synthetic matrices used as delivery systems for cells or cell products.

Keratinocytes are epidermal cells that synthesize keratin and other proteins. They are formed from undifferentiated (basal) cells and comprise 95% of the epidermis. Access to populations of keratinocytes that can be grown and expanded in vitro and still serve as stem cells subsequent to transplant is a requirement for producing epidermal skin substitutes.

The overall goal of tissue engineering is the recapitulation of normal skin and normal skin function. As such, any epidermal replacement must restrict trans-epidermal water loss, limit bodily damage induced by environmental chemical and physical insults, and minimize microbial load. Any dermal replacement must provide epidermal support, neovascularization, and functional pliability. Some of the most popular methods of skin regeneration are as follows:

1. Rheinwald and Green experimented with treating whole skin with trypsin to separate the epidermis from the dermis and to disaggregate the epidermal cells, which were then grown on a feeder layer of lethally irradiated mouse cells in a complex culture medium. Three to four weeks later, confluent stratified sheets of epidermal keratinocytes were available for grafting.
2. Cultured epithelial autografts (CEA) began to move into mainstream use for deep partial-thickness injury, full-thickness burn injury, and congenital nevi in 1988. When allowed to grow in a lab setting, individual keratinocytes produce colonies that fuse and form a multilayered epithelium. When these keratinocyte cultures are incubated with Dipase II, the epithelial tissue detaches itself from the surface of the culture vessel and is readily available as a skin substitute.
3. Skin glue has been used to successfully treat deep partial and full-thickness burn injuries. Histologically normal epidermis has been shown to develop in situ.
4. The direct application of keratinocyte cell suspensions has also shown promise. When delivered within a fibrin spray, keratinocytes promote the closure of deep partial and full-thickness burns, and of chronic wounds. The fibrin helps secure even placement of the keratinocytes. The keratinocyte spray technology is being commercialized for human use pending clinical trials and regulatory approvals (ReCell®, CellSpray®, CellSpray®XP).
5. “Acellular dermal substitutes have been evaluated for their ability to jumpstart neodermis formation and to provide a matrix compatible with reepithelialization and neovascularization.”
   1. De-epidermized dermis is structurally identical to dermis and can be purchased as Alloderm ®. It can be used in conjunction with either STSG or CEA. De-epidermized dermis offers the advantage of being able to support engraftment of thin rather than thick STSG.
   2. Dermal matrix molecules require extensive remodeling to achieve normal dermal structure. Sold as Integra®, the pore size of the matrix is designed to be sufficient to allow fibroblast and endothelial cell migration to occur, and for the product to be remodeled by invading host cells. Neodermis is formed in about 3 weeks, at which time the silastic layer readily detaches. As with de-epidermized dermis, to achieve permanent wound closure, the treated area must be grafted with either a thin STSG or with CEA.

Comparison to traditional methods

Whereas it takes mere hours to prepare and administer stem cells with the stem cell gun, it takes 2-3 weeks to produce a skin sheet and harvest it from an external lab. Once the skin sheet has been attached to the wound, blisters form under the newly attached skin, pushing the sheet up, damaging the wound and increasing the risk of infection. The skin cell gun applies its stem cells directly to the patient's cells, which alleviates the concern of further tissue damage. The artificial vascular system network also provides a reliable source of protection to the skin stem cells. After the wound has been treated, it takes months for the skin sheet to heal over, yet only days for the skin cell gun to fulfill its function. Reducing the fragility of the cells and time frame of the operation by cleverly employing differentiated stem skin cells in such a way that offers a renewable source of replacement is an essential component of the skin cell gun’s capability.

Applications

The method is only applicable to a small minority of burn victims. Patients who have incurred second-degree burns are generally the only ones offered the treatment because they still contain a foundation of skin on the dermis level in which the skin cells can attach to and grow. Third-degree burns, however, completely deprive victims of both their epidermis and dermis skin levels, which exposes the tissue surrounding the muscles. The skin cell gun has not progressed to the point where it can be used for such advanced wounds, and these patients must seek more traditional treatment methods. The skin cell gun is generally not used for burn victims with anything less than a second-degree burn either. First degree-burns still maintain portions of the epidermis and can readily heal on their own, thus they do not needing this expensive technology.

Currently, the skin cell gun's applications have not been extended to include the regeneration of skin lost due to other injuries or skin diseases. It is also limited in that it is only effective immediately following the burn incident.

Results

Since 2008 the skin cell gun has been under development trying to make it function correctly and heal a patient in the most efficient and fastest way possible. To date, over a dozen patients have been treated with this gun and have recovered successfully. However, this skin cell gun only currently works for second degree burns, but with more extensive research, the hope of it treating third degree burns is not too far off. Right now patients have been treated with a preliminary prototype and the final prototype is still going through studies as it is not FDA approved just yet. Currently being worked on is how not to injure the stem cells during the spraying procedure and the bases on medical disposables. This treatment is only for recently burned victims; it will not work for those who suffered the injury a few months prior. Scars or acne cannot be healed either.

A few days are required for the wounds to internally heal with this new process; but after those few days, the wound still looks damaged. The skin will not start to look as it did before the injury until months afterward. Because pigment cells are so much deeper in the part of the skin than keratinocytes are, pigment cells need much more time to develop.

Benefits and side effects

The average healing patients for second degree burns takes weeks, which the skin cell gun reduces to days. Traditional skin grafting can be risky, in that chances for infection are relatively high. The skin cell gun alleviates this concern because the increased speed in which the wound heals directly correlates to the decreased time the wound can be vulnerable to infection. Although it takes several months for the skin to regain the exact texture and color before the incident, harmful side effects that can result from an open wound are not a factor.

Applying the skin cells is quick and doesn't harm the patient because only a thin layer of the patients’ healthy skin is extracted from the body into the aqueous spray. The electronic spray distributes the skin cells uniformly without damaging the skin cells, and patients feel as if they are sprayed with salt water.

Because the skin cells are replicas of the patient’s own cells, the skin that is regenerated looks more natural than skin grown from traditional methods. During recovery, the skin cells grow into fully functional layers of the skin, including the dermis, epidermis, and blood vessels. The regenerated skin leaves little scarring. The basic idea of optimizing regenerative healing techniques to damaged biological structures demonstrated by the skin cell gun in the future may also be applied to engineering reconstruction of vital organs, such as the heart and kidneys.

There are major limitations: the method will not work on deep burns that go through bone and muscle, specifically below the dermis. As of 2011, only several dozen patients have been treated; it remains an experimental, not a proven method. The skin cell gun is still in its early prototyping stage, since it has only treated a dozen patients in Germany and the US, compared to over 50,000 treated with Dermagraft ® bioengineered skin substitute. There is thus a lack of published peer reviewed clinical evidence, and no knowledge of long-term stability of the newly generated skin.