Integrated study of the structural and metabolic degeneration of skin during 4 degrees C storage in nutrient medium

Tissue conservation for transplantation

Pathophysiological changes that occur during ischemia and subsequent reperfusion cause damage to tissues procured for transplantation and also affect long-term allograft function and survival. The proper preservation of organs before transplantation is a must to limit these injuries as much as possible. For decades, static cold storage has been the gold standard for organ preservation, with mechanical perfusion developing as a promising alternative only recently. The current literature points to the need of developing dedicated preservation protocols for every organ, which in combination with other interventions such as ischemic preconditioning and therapeutic additives offer the possibility of improving organ preservation and extending it to multiple times its current duration. This review strives to present an overview of the current body of knowledge with regard to the preservation of organs and tissues destined for transplantation.

Comparative investigation of viability, metabolism and osteogenic capability of tissue-engineered bone preserved in sealed osteogenic media at 37 °C and 4 °C

Preservation of tissue-engineered (TE) bone is one of the key problems needed to be solved for its clinic application and industrialization. Traditional cryopreservation has been restricted because of the damages caused by ice formation and solution. Hypothermic preservation at 4 °C has been widely used for the preservation of transplanted organ despite potential negative effects on viability of cells and tissue. 37 °C is the best temperature for maintaining cellular bioactivities. However, 37 °C also has a potential negative effect on preserved cells due to consumption of nutrients and accumulation of by-products. No studies have reported which temperature is more suitable for the preservation of TE bone constructs. The current study explored the feasibility of preservation of TE bone constructs in sealed osteogenic media at 37 °C and 4 °C. Human bone marrow stromal cells (hBMSCs) were seeded into partially demineralized bone matrix (pDBM) scaffolds and cultured for 7 days to form TE bone constructs. The constructs were preserved in sealed osteogenic media at either 37 °C or 4 °C for 5, 7, 9 and 11 days, respectively. Growth kinetics, viability, metabolism and osteogenic capability were evaluated to explore the feasibility of preservation at 37 °C and 4 °C. The constructs cultured in osteogenic media at humidified 37 °C/5%CO2 served as the positive control. The results demonstrated that all the constructs preserved at 4 °C showed negative osteogenic capability at all time points with a much lower level of growth kinetics, viability and metabolism compared to the positive control. However, the constructs preserved at 37 °C showed good osteogenic capability within 7 days with a certain level of growth kinetics, viability and metabolism, although an obvious decrease in osteogenic capability was observed in the constructs preserved at 37 °C over 9 days. These results indicate that the preservation of TE bone constructs is feasible at 37 °C within 7 days in sealed osteogenic media.

Long-Term Preservation of Rat Skin Tissue by Epigallocatechin-3-O-Gallate

Skin grafts can be preserved by cryopreservation and refrigerated storage at 4°C. Epigallocatechin-3- O-gallate (EGCG) enhances the viability of stored skin grafts and also extends the storage time up to 7 weeks at 4°C. EGCG, the major polyphenolic constituent present in green tea, has potent antioxidant, antimicrobial, antiproliferative, and free radical scavenging effects. This study examined the effects of EGCG on skin cryopreservation. Skin sample biopsy specimens from GFP rats were previously treated with/without EGCG then moved to −196°C. Skin samples were transplanted to nude mice after 2, 8, and 24 weeks of preservation. Glucose consumption was measured after thawing to assess the metabolic activity. Two weeks later the transplanted skin grafts were excised and histologically analyzed. Histological examinations revealed the degeneration of the epidermal and dermal layers in all groups. In the EGCG groups, the grafts showed higher integrity in the epidermal layer and dermal matrix. The present findings suggest the future clinical usefulness of EGCG for skin preservation; however, the mechanism by which EGCG promotes skin preservation still remains unclear.

Penetration of Crystalline Powder Particles into Excised Human Skin Membranes and Model Gels from a Supersonic Powder Injector

The penetration of crystalline ibuprofen particles into excised human skin membranes and model target gels on actuation with the PowderJect ND1 ballistic needle-free injector has been examined. The deliverable dose of powder exiting the device is approximately 50% of the total cassette loading; the rest is lost via a gap forced open between the injector base and the surface of the target gel. It could be shown that substantial comminution of two different ibuprofen particle size fraction (38-53 microm, 53-75 microm) occurs within the injector on actuation. This resulted in an equiparation of the two initially different size fractions. Reduced comminution occurs with an ibuprofen/PVP (95:5) particulate formed by spray-drying/compaction/milling. On actuation into excised human skin membranes approximately 37% of cassette dose is recovered from the stratum corneum by stripping, and only 3% from the epidermis. It is concluded that powder delivery is mainly intra-epidermal with few particles fully breaching the stratum corneum. This is a consequence of the relative magnitude of the particle diameter (approximately 48 microm) and the stratum corneum thickness (approximately 10 microm). A 'soft' polyethylene glycol monolayer target gel gives the closest total percentage recovery of powder to that seen with the excised human skin membranes. Bilayer gels differentiated between surface impact/retention and penetration, but were difficult to handle. Powder penetration studies should therefore preferentially to be performed with human skin-membranes.

Guidelines on processing and clinical use of skin allografts

Processing methods used for banking of skin for subsequent therapeutic use depend on whether the skin is to retain viability or not. For viable skin grafts, sterilisation techniques cannot be applied, however antibiotics and antimycotics may be used to disinfect the tissue with respect to bacteria and fungi. Nevertheless, strict standards are applied to avoid disease transmission from donor to recipient involving donor medical history, donor testing for viral diseases, aseptic retrieval and processing, and control of storage temperature. Cryopreservation is the preferred method for long term storage of viable skin grafts. If viability is not required, then additional long term preservation methods may be used including deep-freezing, freeze-drying or high concentration solute preservation. All three methods work by reducing water activity. In addition it is possible to apply certain sterilisation techniques that have been shown not to damage the tissue. It is important that sterilisation methods are validated in accordance with precise definitions of sterilisation, and for the initial levels of "bioburden" expected to be present immediately prior to application of the sterilisation method. The application of improved and refined methodologies in accordance with defined standards has ensured improved graft performance while reducing risk to the recipient.

Storage media and temperature maintain normal anatomy of cadaveric human skin for transplantation to full-thickness skin wounds

Cadaveric human skin provides an optimal temporary cover after early excision of full-thickness burns; however, engraftment is reduced greatly by cryopreservation. Refrigerated skin is generally preferred because of its rapid revascularization, presumably caused by its greater viability. In this study, the effects of storage solutions, temperature, and the changing of the storage media on skin graft anatomy were evaluated as an indicator of graft viability. Split-thickness human skin grafts (0.012-0.015 mm) were retrieved from cadaveric donors and grafted to circumferential, full-thickness skin wounds on athymic mice. After clinical determination of engraftment 3 months after grafting, 6-mm punch biopsy samples of the human skin were harvested and separated into two groups. Biopsy samples were stored in either saline or Eagle's minimal essential medium. Media were not changed or were changed every 3 days. All groups were stored at either 4 degrees C or room temperature (RT). After 5, 10, and 21 days of storage, biopsy samples were grafted onto athymic mice for 20 days. The biopsy grafts were then collected and prepared for histologic scoring on a scale of +4 (normal anatomy) to 0 (no epithelial cells). Significant differences in histologic scores were found by the nonparametric Kruskal-Wallis test followed by Wilcoxon pairwise comparison. Skin stored in media maintained better histologic anatomy than skin in saline, suggesting better maintenance of viability. There was also better preservation of anatomy after storage at RT for 21 days with media changes every 3 days when compared to unchanged media and all conditions at 4 degrees C. These results support the hypothesis that increased availability of nutrients and increased storage temperature maintain higher viability of cadaveric human skin for transplantation to full-thickness cutaneous wounds.

Effect of storage and preservation methods on viability in transplantable human skin allografts

This study compared the metabolic activity of fresh skin samples to that of cadaver human skin allografts processed and stored by current tissue banking methods. We chose to use two metabolic assays as surrogate measures for viability in these grafts. Skin allografts stored either in liquid media at 4 degrees C for varying periods of time or stored by cryopreservation were quantitatively assessed for viability by tetrazolium reduction and oxygen consumption assays. These measurements were compared to viability assessments of fresh autograft skin. Human cadaver skin grafts, after procurement and just prior to further tissue bank processing, exhibited approximately 60% of the metabolic activity found in fresh skin samples obtained from living surgical donors. If allowed an overnight (18-24 h) incubation period at 37 degrees C, cadaver samples showed a recovery of their metabolic activity to 95% of that found in the autograft skin samples. When stored in liquid media at 4 degrees C, the cadaver skin declined steadily in cellular metabolic activity, arriving in less than 5 days storage at a measurement below that of cryopreserved skin. The cryopreserved skin was measured both immediately after thawing and dilution of cryoprotectant, as well as after equilibration and overnight incubation. Skin cryopreserved with dimethylsulfoxide Me(2)SO retained higher viability than glycerol cryopreserved skin. Residual concentrations of cryoprotectants were determined following typical recommendations for thawing and diluting skin allografts. The implications of these findings for transplantation and tissue banking are discussed.

Reduced engraftment and wound closure of cryopreserved cultured skin substitutes grafted to athymic mice

Cryopreservation of cultured skin substitutes is a requirement for establishment of banks of alternative materials for treatment of acute and chronic skin wounds. To determine whether cryopreservation of skin substitutes that contain cultured cells reduces their efficacy for wound closure, cell-biopolymer grafts were frozen, recovered into culture, and grafted to wounds on athymic mice. Grafts consisted of cultured human keratinocytes and fibroblasts attached to collagen-glycosaminoglycan substrates that were frozen in cell culture medium with 20% serum and 10% DMSO at a controlled rate and stored overnight in liquid nitrogen. After recovery into culture for 24 h, frozen or unfrozen (control) skin substitutes were grafted to full-thickness wounds on athymic mice. Wound area and surface electrical capacitance were measured at 2, 3, and 4 weeks after grafting at which time animals were sacrificed. Wounds were scored for presence of human cells by direct immunofluorescence staining with a monoclonal antibody to HLA-ABC. The data demonstrate that cell-biopolymer grafts are less efficacious after controlled-rate cryopreservation using 10% DMSO as a cryoprotectant. Frozen grafts at 4 weeks after surgery have significantly smaller wound areas, higher capacitance (wetter surface), and fewer healed wounds that contain human cells. The results suggest that these conditions for cryopreservation of cultured grafts reduce graft viability. Improved conditions for cryopreservation are required to maintain viability and efficacy of cultured skin substitutes after frozen storage.

A study of protein synthesis in cells cultured from involved psoriatic skin

Using histochemical techniques an abnormal programme of epidermal differentiation has been well documented in psoriasis. In order to characterise further the biochemistry of this process we have cultured dermal fibroblasts and epidermal keratinocytes from involved psoriatic skin. This has facilitated metabolic radiolabelling of skin cells and analysis of protein synthesis by two-dimensional polyacrylamide gel electrophoresis. The expression of keratin and differentiation markers was identical to that of normal keratinocytes, suggesting that psoriatic epidermal differentiation is not truncated in vitro as has been postulated to be the case in vivo. Low molecular mass components (5-8.5 kDa), previously shown to be upregulated in suprabasal keratinocytes, were detected in epidermal fractions from psoriatic skin enriched for basal cells. Of special interest was a component of 26 kDa, pI 5.9, which was highly upregulated in psoriatic as compared to normal cultured keratinocytes and was not detected in fibroblasts. These findings are in accord with a qualitatively abnormal pattern of differentiation for keratinocytes in the involved psoriatic epidermis.

The effects of biological wound dressings on the healing process

Three major biological dressings are available for the temporary closure of wounds: partial-thickness cadaveric human allograft skin, several forms of partial-thickness antibiotic-treated porcine xenograft skin, and human amnion. Generally, biological dressings reduce pain, close the wound to contamination and fluid loss, and prepare the wound bed for permanent closure, usually with autografts. The three types of biological dressings differ in their performance, with allograft skin being clearly superior in its wound maintenance and preparation characteristics, while porcine xenograft presents serious difficulties in incorporation into the wound bed and antigenic challenge to the recipient, and amnion is excessively fragile and tends to allow wound desiccation. The most serious potential liability of biological wound dressings is transmission of infection; however, the actual incidence of such transmission is extremely low. The advantages of physiological coverage provided by biological wound dressings greatly outweighs the chance for harm in the case of human allograft.

Effect of Solcoseryl on cadaveric split-skin oxygen consumption during 4 degrees C storage and in frozen biopsies

Oxygen consumption rate in cadaveric split-skin biopsies was investigated. Biopsies were harvested at different times postmortem and stored at different temperatures in either Solcoseryl (a protein-free bovine hemodialysate) or placebo-containing media. During the first week of storage Solcoseryl had no influence on oxygen consumption. However, in the second and third weeks the oxygen consumption was improved by Solcoseryl.

Development of a passive device for freezing large amounts of transplantable skin at one time in a -70 degrees C mechanical refrigerator

A simple device has been developed for the simultaneous cooling of up to 9120 cm2 of allograft skin in a flat package format. The device, named an insulated alternating-offset heat sink device, is composed of a stack of interleaved layers of 2.0-mm-thick packets of skin and 3.18-mm-thick aluminum heat sinks (each 33.0 cm long by 22.9 cm wide). Four skin packets are placed in a single layer on each heat sink plate, and the number of plates can be varied to accommodate different numbers of skin packets. Every heat sink protrudes 6.3 cm of its 33.0-cm length beyond the skin packets to make a fin for heat convection, but adjacent plates alternate the direction of their fin protrusion so that the layers of plates alternate in their 6.3-cm offset. Insulation layers of 2.54-cm-thick expanded polystyrene are placed on the exposed surfaces of the top and bottom heat sinks in the stack, and the stack is held together by rubber bands. The device is cooled in a -70 degrees C mechanical refrigerator. Maximal cooling rates of -1.8 degrees C min-1 are obtained for both 6- and 11-plate devices, and -3.0 degrees C min-1 for a 2-plate device. The exothermic temperature plateaus associated with skin cooled in these devices are 1.5-1.8 min in duration. Skin cooled by this technique maintains levels of glucose oxidation similar to those associated with skin cooled by liquid nitrogen vapor at a controlled rate of -1 degree C min-1, provided rapid warming is employed after -70 degrees C storage. The development of this device provides a method for the simple, low-cost cryopreservation of the large amounts of allograft skin obtained from a cadaveric donor.

Skin preservation at 4 degrees C: a species comparison

There are numerous experimental studies in the literature regarding skin storage and preservation. These studies are difficult to interpret due to the variety of storage techniques utilized and the number of different animal species used as skin donors. This study utilized a single cold storage protocol to test the effect of species variation on skin graft viability. Donor skin was obtained from five animal species and human surgical panniculectomy specimens. The skin was stored in modified Roswell Park Memorial Institute (RPMI) 1640 tissue culture media at 4 degrees C. Stored skin was transplanted to surgically created defects on athymic (nude) mice after specific storage intervals. Ten days after transplantation, the grafts were examined by gross and microscopic techniques. The viability of mouse, rat, and dog skin was significantly different from human skin, while stored rabbit and pig skin were similar to human skin. These results demonstrate the difficulty of applying the data of skin storage studies from nonhuman species to clinical practice. The data indicate that rabbit and pig skin may be used in laboratory studies of skin preservation at 4 degrees C with a strong likelihood that the results may be of clinical relevance in predicting the behavior of human skin under similar storage conditions.

The role of sampling in the detection of microbial contamination on cadaveric allograft skin used as a biological wound dressing

The availability of cryopreservation and low temperature storage techniques for cadaveric allograft skin allows it to be preserved while microbial assessments are made before its use as a temporary biological dressing on burn wounds. In a 300-donor, 5-year prospective study, we tested ten skin samples from defined areas on each donor for microbiological contamination. Although the skin from 52.3 per cent of the donors possessed some detectable residual microbial contamination after surgical body preparation and skin removal, such contamination was limited to an average of 1.4 areas per body, leaving 86 per cent of all skin obtained free from detectable contamination and suitable for use as biological wound dressings. The number of skin samples tested per donor body determined the accuracy of detection of the presence of contamination. Testing one skin sample per donor body yielded a correct skin assessment 92 per cent of the time, while testing five skin samples increased the accuracy to 96 per cent, and testing ten skin samples yielded a 99.9 per cent accuracy in detection of skin contamination. Thus, it is within the ability of a skin bank to set the limits of microbiological risk to patients receiving processed cadaveric allograft skin.

Cryopreservation of skin using an insulated heat sink box stored at -70 degrees C

The cooling of skin to a temperature of -70 degrees C was carried out by two methods: programmed controlled-rate (PCR) cooling at -1 degree C min-1 to -70 degrees C, and variable-rate cooling to -70 degrees C in an insulated heat sink box (IHSB). The IHSB was constructed of polystyrene and contained two aluminum heat sinks placed one on each side of flat packets of skin. The IHSB containing skin was cooled in a -70 degrees C constant-temperature refrigerator. When using the IHSB, the insulation provides a slow cooling rate while the paired heat sinks provide even heat flow across the top and bottom surfaces of the flat skin packets, minimizing the duration and potential damaging effects of the exothermic temperature plateau which occurs at the freezing point. When followed by 24-hr storage at -70 degrees C and warming at about 316 degrees C min-1, the IHSB cooling method was equivalent to the PCR method in generating a suitably slow cooling rate of -1 to -2 degrees C min-1, and maintaining about 80% of normal skin cell glucose metabolism. The development of the IHSB cooling system provides a method for the simple, cost-efficient cryopreservation of small amounts of autograft skin, such as those remaining from surgical procedures, and can also provide an allograft skin banking capability to any facility possessing a -70 degrees C refrigerator.

Variables determining the amount of microbial contamination on cadaveric allograft skin used as a biological wound dressing

The increased availability and use of cadaveric allograft skin as a temporary burn wound dressing has emphasized the need for a complete understanding of the parameters affecting the contamination level of this material. We undertook a prospective evaluation of the allograft skin obtained from 300 cadaveric donors over 5 years. We evaluated the contribution to skin contamination of eight parameters: sex, age, race, cause of death, elapsed time postmortem before skin removal, total refrigerated storage time of the skin prior to cryopreservation, donor body area from which the skin was removed, and choice of surgical operators or teams. The only parameters significantly related to skin contamination level were the choice of surgical operator or team which prepared the body and removed the skin (P = 0.0001) and the acceptance of skin from donors when the cause of death was unknown but presumed to be from natural causes (PNC) such as myocardial infarction or cerebral vascular accident (P = 0.006). In the case of the PNC deaths, there was only a small 3.4 per cent increase in bacterial contamination and no increase in fungi or yeast, while some surgical operators were associated with five-fold more bacterial contamination and nearly 13-fold more fungal contamination than other surgical operators. We conclude that the performance of surgical operators appears to be the major determinant of the microbiological cleanliness of skin from cadaveric allograft donors.

Optimum warming rates to maintain glucose metabolism in porcine skin cryopreserved by slow cooling

The optimum warming rate for cryopreserved skin (dimensions: 7.6 cm X 20 cm X 0.38 mm thick) folded double in a flat package format was tested using a recently developed quantitative assay of skin cell metabolism. The assay measured the metabolic conversion of glucose to carbon dioxide by intact partial-thickness skin. Skin cooled at a constant, controlled rate of -1 degree C min-1 to a temperature of -100 degrees C, and then rapidly transferred to -196 degrees C for overnight storage, could be optimally warmed at rates of 95-260 degrees C min-1 by immersion in 10-20 degrees C water. The amount of metabolic activity remaining in skin warmed at rates within this optimal range was 76-78% of normal. Slightly less than maximal metabolic activity, 71-75% of normal, resulted from warming rates of 292-458 degrees C min-1, obtained by immersion in 25-37 degrees C water. Skin metabolism remaining after warming rates of 30-53 degrees C min-1 (3-5 degrees C water) was 52-70% of normal, while that remaining after rates of 501-882 degrees C (40-65 degrees C water) was 0-47% of normal. These experiments establish practical upper and lower limits for post-cryopreservation warming rates employed to maintain skin cell metabolism, and the cellular viability which depends upon that metabolism.