Advances in keratinocyte delivery in burn wound care

Abstract

This review gives an updated overview on keratinocyte transplantation in burn wounds concentrating on application methods and future therapeutic cell delivery options with a special interest in hydrogels and spray devices for cell delivery. To achieve faster re-epithelialisation of burn wounds, the original autologous keratinocyte culture and transplantation technique was introduced over 3 decades ago. Application types of keratinocytes transplantation have improved from cell sheets to single-cell solutions delivered with a spray system. However, further enhancement of cell culture, cell viability and function in vivo, cell carrier and cell delivery systems remain themes of interest. Hydrogels such as chitosan, alginate, fibrin and collagen are frequently used in burn wound care and have advantageous characteristics as cell carriers. Future approaches of keratinocyte transplantation involve spray devices, but optimisation of application technique and carrier type is necessary.

Keywords: Burn injury; Cell transplantation; Hydrogels; Spray application; Wound healing.

Graphical abstract

Fig. 1

Layers and function of the skin. The uppermost layer of the skin is the epidermis. The epidermis consists of 5 main layers described from deep to superficial: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. The epidermis has two distinct functions: a protective barrier function against trauma and fighting off pathogens as well as a controlling function regulating body temperature, fluid and electrolyte balance. Other functions of the epidermis include production of vitamin D, pigmentation, providing mechanical strength and it has a role in cutaneous immune function.

Fig. 2

Keratinocyte differentiation and markers. Diagram is showing differentiation of keratinocytes in the epidermis with expression of stratification markers. Basal keratinocytes express Keratin 5, keratin 14 and keratin 15. When keratinocytes differentiate they move upwards into the suprabasal layers: stratum spinosum, stratum granulosum and finally stratum corneum. Differentiating keratinocytes express specific markers in each epidermal layer.

Fig. 3

Role of keratinocytes in re-epithelialisation. Schematic illustration of a skin injury with keratinocytes as key cells. Keratinocytes are activated via pro-inflammatory cytokines and growth factors released in the wound bed. Once activated, keratinocytes from the wound edges and dermal appendages migrate over the provisional matrix and finally close the defect in a process called epithelization. When the basal layer is spared from injury, basal keratinocytes can support this process by upward migration as occurs in non-injured skin. Activated keratinocytes communicate with other cell types present in the epidermis. Epithelial cells proliferate and differentiate to achieve a stratified epithelium with restoration of the barrier function of the skin. Maturation of the wound continues over a period of several months with fibroblasts remodeling the underlying dermis.

Fig. 4

Burn wound coverage with cultured epithelial autografts applied in sheets. In this example, successful burn wound healing in about 2 weeks was achieved when the sheets were removed a week after application. a) Deep second degree burn in the back of a 29-year old patient after excision of the burn b) application of cultured keratinocyte sheets c) removal of sheets 8 days after surgery and d) complete healing 16 days after surgery.

Fig. 5

Spray delivery of cultured keratinocytes to enhance burn wound healing. In this example, a mixed depth burn to the abdomen was treated with solely sprayed cultured keratinocytes (no additional mesh grafting) 27 days after injury. The wound was considered to have healed completely 10 days after treatment. Unfortunately, long term outcomes in terms of scar quality were not available for this patient.

Fig. 6

Methods of autologous keratinocyte transplantation to burn wounds. In patients with burn injury keratinocytes can be isolated from a small skin biopsy as illustrated above. The autologous keratinocytes can be cultured and delivered to the wound bed of the patient by several methods. First to be developed was a sheet of cultured epithelial cells, thereafter a single cell suspension applied to the wound by dripping from a syringe and latest development is application of cultured or uncultured cells in single-suspension with a spray device.