Characteristics of amniotic membranes
The human placenta consists of a placental lobe and a placental sac. The placental sac is made up of 2 adjacent membranes, the amnion and chorion, which extend from the chorionic plate and the umbilical cord. These membranes contain the amniotic fluid and surround and protect the fetus during development. The amnion membrane consists of a layer of epithelial cells, a basement membrane, and an underlying avascular stromal layer containing mesenchymal cells and mesenchymal stem cells. Structurally, the stromal layer contains collagen types I, III, IV, V, and VI as well as laminins, proteoglycans, and fibronectin. The chorion membrane sits beneath the amnion and consists of a reticular layer, a basement membrane, and the underlying trophoblast. The reticular layer contains a similar set of structural proteins as found in the amniotic stromal layer, albeit with a different distribution, while the trophoblast is enriched for laminins and fibronectin.
The collagens and other fibrous protein components in the extracellular matrix (ECM) of the amniotic membranes provide a structural scaffold to support proliferation and regeneration. These tissues also contain growth factors, which modulate the immune response, control inflammation, inhibit matrix metalloproteinases production, support angiogenesis, promote ECM production and tissue proliferation, and assist in tissue remodeling.
The dHAM used is available in both an amnion membrane configuration (WX45) and a chorion-based membrane configuration (WX200). These membranes are processed by the technology and designed to resorb and incorporate faster, so their biologic components can work quicker.
The technology is designed to better preserve the tissue’s natural biomechanical structure by scientifically controlling moisture levels versus traditional heat-baking or freeze-drying (lyophilization) systems; it also avoids the use of harsh chemical rinses or crosslinking agents. Further, while some amniotic membranes are marketed as “immune-privileged” based on the natural properties of the placentas, the technology allografts have been proven to be able to suppress an active immune response in vitro,15 which is instrumental in modulating inflammation and potentially reducing the risk of rejection and graft failure.
History of clinical use
Historically, most clinical reports16-20 on the use of placental tissues have discussed the use of amniotic membranes for an array of clinical applications since the 1920s.These uses include general surgery,21,22 corneal surgery,23-25 plastic surgery,26 burn and wound care,27-36 sports medicine,34-37 foot and ankle procedures,38,39 spine and dural repair,40-46 nerve wrap or dural covering,40,43,46 and tendon repair.37,38
Methods
The study was reviewed by Midlands Institutional Review Board (IRB) for approval, and they ruled this pilot retrospective study review of existing patient records was exempt from IRB review in accordance with 45CFR46.101B. The data collected were without identifiers or links to identifiers. In addition, the investigator conducted the records review, and as the patients’ clinician, he had access to their records as part of routine clinical care. Twenty patients were selected for inclusion in a retrospective cohort study from the authors’ patient population at a single clinical site. Male and female patients were randomly selected without bias to gender. Patients were identified as having a chronic ulceration involving the venous system of the lower extremities, a chronic DFU or ulcer of autoimmune origin nonvenous and nondiabetic. All patients were initially screened using the ankle-brachial index (ABI), medical history, and chronicity of wound of longer duration than 4 weeks. Inclusion criteria included VLUs and DFUs with a minimum of 4 weeks nonhealing, and other wound types not attributed to either venous leg or diabetic foot wounds. Exclusion criteria included acute infection, use of prior cellular-tissue products for wounds (CTPs), or ABI less than 0.6.
Patients underwent a run-in period of 2 weeks, where standard of care (SOC) was used to clear the wound of bioburden. The dHAM was applied at weeks 1 (2 weeks post run-in), 3, and 5, if necessary. Wound measurements and photographs of the wound were recorded weekly. Data were collected through a standard form in each patient’s medical record to improve reliability and reproducibility. The data extraction was performed by the author and to reduce bias; reduction of bias was performed by selecting patients whose wounds already were established and in temporal sequence.