Monitoring, banking, and clinical use of amnion as a burn wound dressing

Skin and skin substitutes in burn management

Early burn excision has reduced the mortality from major burns. This practice presents the problem of wound coverage after excision, since the availability of autologous donor sites is limited in very large burns. This article reviews the methods available for covering burn wounds. Methods of expanding autologous skin are discussed as well as techniques using allogeneic tissue and xenograft. Newer synthetic skin substitutes have become an important advance and are also described. Cultured skin replacements are also discussed along with their shortfalls. The treatment of a patient with major burns may require the use of many different skin substitutes, as none is entirely satisfactory on its own.

Preservation methods of allografts and their (lack of) influence on clinical results in partial thickness burns

Allografts, cadaver skin and amnion membrane are considered the golden standard in the management of partial thickness burns. However, debate on whether the tissue needs to be viable is on-going, since many believe that viable grafts result in better healing. The objective of this literature survey was to analyse the evidence on the method of preservation of allografts (cadaver skin or amnion membrane, glycerol, cryopreservation, lyophilisation) having a clinical impact on the healing of partial thickness burns. The survey focussed on preservation techniques and clinical outcomes (reepithelialisation) in partial thickness burns, as well as on differences in viability, immunogenicity and antimicrobial properties of the preservation methods. Most studies on allograft treatment of partial thickness burns are observational, with only one study of a (historical) comparative nature. A true meta-analysis was not performed and the results of this survey are observational in nature as well: they indicate that there is no evidence that viability of the graft influences healing outcomes. Thus, instead of viability, other aspects, such as intrinsic antimicrobial safety of the preservation method and cost should be the primary criteria for the choice of preservation method to be used for allografts.

Transplantation of Preserved Human Amniotic Membrane for Bladder Augmentation in Rats

Although gastrointestinal segments have been widely used for bladder reconstruction, they are not ideal because of the possible complications. Searches have therefore continued for an alternative material for augmentation. Here, we performed bladder augmentation in rats using human amniotic membrane (hAM). Morphologically, the hAM-augmented bladder revealed regeneration of urothelium, detrusor smooth muscle, and nerve fibers within 3 months post-operatively. In our functional evaluation of bladder strips, we compared hAM-augmented bladders with bladders augmented using small intestinal submucosa (SIS). For example, at 6 months post-operatively, contractions of the following size (as a percentage of the responses in the control-bladder group) were obtained in response to high potassium, carbachol, and electrical field stimulation, respectively: hAM 22% vs SIS 15%, hAM 15% vs SIS 7%, hAM 5.3% vs SIS 1.3% (no significant differences, hAM vs SIS). Both hAM- and SIS-augmented bladders displayed adequate capacity and compliance. The present results indicate that, for bladder augmentation, hAM can be used as a scaffold and is comparable in this respect with SIS. hAM can be more easily obtained than SIS and requires little preparation, and its use raises few ethical questions. Hence, hAM may represent a new therapeutic alternative for urological reconstructions.

Biocompatible collagen scaffolds from a human amniotic membrane: physicochemical and in vitro culture characteristics

A reconstituted collagen membrane from human amnion has been investigated as a source of collagen matrix, which could be used as a substratum for culturing human fibroblasts. The suitability of pepsin-solubilized reconstituted human amniotic membrane, before and after cross-linking with chitosan, as a dermal matrix for culturing fibroblast was assessed by morphologic, physicochemical, cytotoxic and histochemical methods. Measurement of thermodynamic behaviour, by differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA), and tensile strength suggested that the cross-linked membrane had sufficient elasticity to serve as an efficient dermal substrate for in vitro culture of fibroblasts. Fibroblasts cultured on the chitosan cross-linked collagen membrane had good adherence, retaining their morphology as indicated by microscopic analysis. Proliferation of fibroblasts. observed on this membrane affirms its non-toxic nature. These results support the application of reconstituted human amniotic collagen membrane as collagenous scaffolds to culture fibroblasts in vitro.

Skin resurfacing for the burned patient

It has been estimated that 2 million people per year have burns requiring medical attention in the United States. The available and expert clinicians in dedicated burn centers around the country have cared successfully for these patients and given them a second chance at a functional life. It still behooves current-day plastic surgeons to be knowledgeable and adept in their care, not only because they may be called upon at times to manage some of the smaller acute burns, but also because many of the general principles of burn reconstruction and wound management are relevant to other areas of general plastic surgery. Acute burns should be dealt with like any other major trauma with the ABCs of aggressive resuscitation and airway management. Like any other wound, debridement and nutrition are important (i.e., early escharectomy of the burn wound and enteral nutrition during the hypermetabolic state). Early coverage of the open wound is essential to limit bacterial colonization and prevent infection and to reduce fluid and electrolyte and heat loss. If autografts are not available immediately, temporary coverage with one of the above-mentioned barrier materials should be used. Still, autografts, when available, should be the burn surgeon's first choice. Donor sites may be reharvested to provide more autograft than was anticipated with large-percentage TBSA burns. Physicians should keep in mind the advantages (and disadvantages) of using the scalp and back. As far as research and technological advances in the area of plastic surgery, burn surgery may be the most progressive, with the evolution of biologic tissue-engineered skin substitutes and the research of growth factors in healing. Further improvements in tissue engineering and technology should result in even more effective skin substitutes and hence better functional and aesthetic outcomes with economic efficiency in large burns.

Bacterial contamination of amniotic membrane

AIM

In the light of interest being shown in amniotic membrane grafts for use in ocular surgery, this study aims to identify the bacterial contaminants commonly found on placental membranes from both caesarean and vaginal deliveries.

METHODS

Samples of placental membrane were taken following both elective caesarean and normal vaginal deliveries. Bacterial contaminants were identified.

RESULTS

All samples were contaminated. A greater number of different species were recovered from the vaginal deliveries, including several which were actually or potentially pathogenic.

CONCLUSION

There is a greater risk of contamination from pathogenic bacteria on placentas from vaginal deliveries. It is recommended that amnion for use in ocular surface procedures should be retrieved only from placentas following elective caesarean deliveries.

Identification of antiangiogenic and antiinflammatory proteins in human amniotic membrane

PURPOSE

To identify the potential antiangiogenic and antiinflammatory proteins expressed in human amniotic membrane tissue.

METHODS

Human amniotic epithelial and mesenchymal cells were isolated from human amniotic membranes by sequential trypsin and collagenase digestion. Total RNAs were harvested from freshly obtained human amniotic epithelial and mesenchymal cells. Antiangiogenic and antiinflammatory proteins were detected by the reverse transcriptase-polymerase chain reaction (RT-PCR) technique and further confirmed by DNA sequencing of PCR-amplified transcripts. The distribution of tissue inhibitors of metalloproteinase (TIMPs) were studied further by immunohistochemistry performed on paraffin-embedded amniotic membrane tissue.

RESULTS

RT-PCR results showed that both human amniotic epithelial and mesenchymal cells express interleukin-1 receptor antagonist, all four TIMPs, collagen XVIII, and interleukin-10. Thrombospondin-1 was expressed in all of the epithelial cell specimens and in one out of five mesenchymal cell specimens. Furthermore, immunohistochemistry studies performed on freshly prepared amniotic membrane confirmed that all members of the TIMP family were present in epithelial and mesenchymal cells as well as in the compact layer of the amniotic stroma. In cryopreserved amniotic membranes, positive staining was seen in residual amniotic cells and stroma.

CONCLUSIONS

Human amniotic membrane epithelial and mesenchymal cells express various antiangiogenic and antiinflammatory proteins. Some of those proteins also were found in amniotic membrane stroma. These findings may explain in part the antiangiogenic and antiinflammatory effects of amniotic membrane transplantation.

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.

Amniotic membrane as a biological dressing in the management of burns

This report details observations in 90 patients with dermal depth burns treated using amniotic membrane. The patients were divided into three subgroups: superficial dermal, intermediate dermal and deep dermal burns diagnosed clinically. All patients were dressed with amniotic membrane which was changed daily. The amniotic membrane relieved the discomfort of dressing changes, postoperative pain and oozing and allowed rapid epithelialization and early healing in superficial and intermediate depth dermal burns. In deep dermal burns the membrane was dissolved because of slough in the burn wound. After removal of the slough the amniotic membrane helped in rapid regeneration of epithelium and early healing.