The Israel National Skin Bank: Quality Assurance and Graft Performance of Stored Tissues

Clinical Impact of Cryopreservation on Split Thickness Skin Grafts in the Porcine Model

Vital, genetically engineered, porcine xenografts represent a promising alternative to human cadaveric allografts (HCA) in the treatment of severe burns. However, their clinical value would be significantly enhanced if preservation and long-term storage-without the loss of cellular viability-were feasible. The objective of this study was to examine the direct impact of cryopreservation and the length of storage on critical in vivo and in vitro parameters, necessary for a successful, potentially equivalent substitute to HCA. In this study, vital, porcine skin grafts, continuously cryopreserved for more than 7 years were compared side-by-side to otherwise identically prepared skin grafts stored for only 15 minutes. Two major histocompatibility complex (MHC)-controlled donor-recipient pairs received surgically created deep-partial wounds and subsequent grafting with split-thickness porcine skin grafts, differentiated only by the duration of storage. Clinical and histological outcomes, as well as quantification of cellular viability via a series of 3-4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) assays, were assessed. No statistically significant differences were observed between skin grafts cryopreserved for 15 minutes vs 7 years. Parametric distinctions between xenografts stored for short- vs long-term durations could not be ascertained across independent clinical, histological, or in vitro evaluative methods. The results of this study validate the ability to reliably preserve, store, and retain the essential metabolic activity of porcine tissues after cryopreservation. Plentiful, safe, and readily accessible inventories of vital xenografts represent an advantageous solution to numerous limitations associated with HCA, in the treatment of severe burns.

Platelet-Rich Plasma for Skin Graft Storage: An Experimental Study Using Rabbit Ears

BACKGROUND

Storage of surplus grafts for later use is one of the standard procedures used in plastic surgery. For the delayed use of skin grafts, various methods and media have been investigated for short-term storage. This study aimed to investigate the effect of platelet-rich plasma (PRP) skin graft storage on the survival of skin grafts obtained from rabbit ears.

MATERIALS AND METHODS

Twelve rabbits were used in this study. A total of 12 skin grafts measuring 1 × 1 cm were obtained from the inner surfaces of the rabbits' ears. The grafts were stored at +4°C in saline, Hartmann's, and PRP media. On days 3, 7, 10, and 14, the grafts were implanted into the ears in areas measuring 1 × 1 cm where the skin, cartilage, and perichondria were excised. After the implantation of the grafts, the survival rates were evaluated by measuring the graft areas on day 0, day 10, and day 30.

RESULTS

The graft survival rate decreased as the storage period increased in all 3 of the media. The decrease in survival rate was higher in the grafts that were stored in the Hartmann's media in comparison with the saline and PRP media, and the difference was statistically significant. The decrease in graft survival was similar between the storage in saline and PRP media; however, the differences were statistically insignificant.

CONCLUSIONS

Although in vitro criteria are important for evaluating graft survival, in vivo studies showing the graft take rate in the recipient area are required. When the in vivo criteria are evaluated, the use of PRP is not superior to the use of saline for graft storage. However, additional studies are required to evaluate the effects of PRP media on graft quality.

Skin graft storage in platelet rich plasma (PRP)

Storage of skin grafts for later use is one of the standard applications in surgery. It is the most preferred method to maintain at +4°C in refrigeration after wrapping the surplus grafts into sterile gauze pad moistened with saline. Although there are many studies on the storage of skin grafts, less is known about storing skin grafts with PRP. Twenty-five pieces of 1 × 1 cm² partial thickness skin graft were harvested from 12 patients during the reduction mammoplasty operation. Twenty-four grafts were divided into 4 groups, and each group consisted of 6 grafts, 1 graft was analyzed as Day 0. Grafts in Group 1, 2, and 3 were wrapped by sterile gauze pad moistened by either saline (Group 1) or Hartman (Group 2) or PRP (Group 3). Grafts were analyzed macroscopically and microscopically. There were no significant differences between media for the first 10 days. Decrease in viability was less in saline and PRP wrapped grafts at 20 day, viability decreased significantly in all environments after 20 days. Although there was no significant difference in saline or PRP storage, it was observed macroscopically that the grafts stored in the PRP appeared better.

Feasibility study of the sterilization of pigskin used as wound dressings by neutral electrolyzed water

BACKGROUND

Neutral electrolyzed water (NEW) is considered to be a high-level biodegradable disinfectant with sporicidal, bactericidal, and virucidal activity. It has also been reported to accelerate wound healing; thus, it is particularly attractive for the elimination or minimization of the microbial population of skin grafts to be used as wound dressings.

METHODS

Pigskins were sterilized with different concentrations of NEW and with different methods. The feasibility of pigskin sterilization by NEW was evaluated through microbiological analyses, viability assays, histologic assessments, contact cytotoxicity assays, and extract cytotoxicity assays.

RESULTS

NEW has strong bactericidal effects on pigskin microorganisms, does not change skin graft histologic properties, and has no cytotoxicity; however, skin viability was significantly reduced after NEW treatment.

CONCLUSION

Although NEW treatment is a very safe and effective method for nonviable pigskin dressing sterilization, to obtain a complete sterilization of pigskin grafts, available chlorine concentration of NEW as well as sterilization time and methods should be optimized.

The viability change of pigskin in vitro

BACKGROUND

It is widely recognised that take of grafts is strongly influenced by tissue viability. Although porcine skin is currently the most widely used xenograft, the viability change of pigskin in vitro has not been extensively studied. The purpose of this study was to assess the change of the viability of Bama miniature pigskin after harvest and cryopreservation, and to set up a guideline for pigskin preservation and storage that would allow the skin to retain the highest viability after treatment and still be used in the clinical applications.

METHODS

Harvested pigskin grafts were divided into five groups: normal saline medium/4 degrees C (group 1), Dulbecco's minimum essential medium (DMEM)/4 degrees C (group 2), normal saline medium/25 degrees C (group 3), DMEM/25 degrees C (group 4) and cryopreserved (group 5). In our experiment, the viability was investigated by 3-(4,5)-dimethylthiazol-2,5-diphenyl tetrasolium bromide (MTT) salt assay. We also evaluated the transplantation performance of preserved skin in different conditions by using a rat recipient model, in which primary take was evaluated by gross observation and predetermined histological criteria after 7 days.

RESULTS

Skin stored at 4 degrees C showed a very slow viability decrease with time. The sample showed a viability decrease of about 70% after 3 days in normal saline and 4 days in DMEM medium. Nevertheless, skin stored in DMEM at 25 degrees C underwent a viability increase during the first 4h and then decreased gradually to about 70% after 20 h, while the viability declined very quickly for skin grafts stored in normal saline medium at 25 degrees C, and maintained the same viability only within 6h of preservation. On the other hand, cryopreserved skin has been shown to maintain a level of skin metabolism equal to 77% of the fresh sample when measured immediately after thawing, and the viability remained about 70% after 6h at 25 degrees C and 2 days at 4 degrees C in DMEM. The graft performance of skin specimens with 70% viability of fresh skin stored in different conditions has not shown statistical significance compared with fresh pigskin.

CONCLUSIONS

Based on these results, we suggest that the conservation period of fresh pigskin should not exceed 72 or 96 h when stored in normal saline or DMEM at 4 degrees C, and should not exceed 6 or 18 h when stored in normal saline or DMEM at 25 degrees C. Cryopreserved pigskin should be stored in DMEM for a maximum period of 48 h at 4 degrees C and 6h at 25 degrees C after thawing.

Effects of different preservation solutions on skin graft epidermal cell viability and graft performance in a rat model

This study sought to evaluate the viable epidermal cell count of skin stored at 4 degrees C in different media, and to determine the longest time that grafts could be stored and still be used for clinical application of skin grafts. Harvested rat skin grafts were divided into four groups: saline (group 1), Roswell Park Memorial Institute-1,640 solution (RPMI) (group 2), University of Wisconsin solution (UW) (group 3), and Histidine-tryptophan-ketoglutarate solution (HTK) (group 4). After the designated storage time (7, 14, 21, 28, or 35 days), grafts were divided into two parts. Skin grafts (3 cm x 3 cm) were then autotransplanted onto full-thickness circular wound beds. Percentages of viable keratinocytes (PVK) declined significantly for skin grafts stored in UW, HTK, and saline solutions (Kruskal-Wallis, P<0.05), while there was an insignificant decline in the PVK of skin grafts stored in RPMI until the 28th day of storage (Kruskal-Wallis, P>0.05). Compared with UW, HTK, and saline, grafts stored in RPMI had significantly higher percentages of PCNA at the 14th and 21st days of storage (Mann-Whitney U-test, P<0.05). Grafts stored in RPMI had significantly lower apoptosis rates than did grafts stored in UW or HTK (P<0.05). Based on these results, we conclude that RPMI-1640 provides a better environment for skin grafts by increased quality and survival time of skin grafts, as assessed by both microscopic and macroscopic investigations.

Performance and safety of skin allografts

Skin preservation for transplantation began almost 200 years ago with the pioneering work of Baronio (cited by in Ref. ). Since that time, hundreds of papers have been published on the preservation of skin for later application in wound treatment. This interest stems from the excellent clinical results obtained with skin as a permanent autograft or temporary allograft for wound cover, coupled with the relative ease of preservation and storage methods. The general recognition of the need for human skin allografts has stimulated the establishment of banking facilities and research to improve the methods for harvesting, processing, storage, and subsequent evaluation of transplantation performance.