The human amniotic membrane (AM) has been used in wound care for over a century. Amniotic membrane was first used therapeutically as a skin substitute material by John Staige Davis, MD. This procedure was performed at Johns Hopkins Hospital in 1910.
Structure and Function of the Amniotic Membrane
The amniotic membrane (AM) can easily be separated into two distinct layers: the amnion layer (fetal side) and the chorion layer (maternal side). The amnion is the avascular innermost layer of the amniotic membrane which surrounds and provides a physical protective barrier for the developing fetus and as the fetus grows in size, is exposed to amniotic fluid. The chorion is the vascular outer membrane that is in contact with the uterine wall and makes up the rest of the amniotic sac. Please note that only the amnion layer is used for PalinGen® Membranes, making them chorion free.
The amnion is a thin tissue measuring 0.02 – 0.05 mm in thickness and has three different layers:
- Epithelium
- Basement membrane
- Stroma (The stroma is composed of three layers – compact, fibroblast and intermediate (spongy).
In addition to acting as a physical protective barrier for the developing fetus, the amniotic membrane provides nutrients and immunological protection for the developing fetus. These properties play an important role in healing. The stroma contains the all-important fetal hyaluronic acid and cytokines necessary to reduce inflammation. In other words, amniotic membranes afford anti-inflammatory, anti-angiogenic, anti-microcrobial and anti-fibrotic properties.
If you examined the amniotic membrane under a microscope, you would find three different types of material: collagen and extracellular matrix, biologically active cells and regenerative molecules. The extracellular matrix provides structure and contains a number of specialized proteins, including proteoglycans, fibronectin, laminins and others. Several types of collagen add structural strength to the membrane. The biologically active cells function to regenerate new cellular materials within the lining of the membrane. Fibroblasts help to strengthen the tissue, and epithelial cells aid in the healing process via receptors on the cell surface. Regenerative molecules, which are important for growth and healing, are present in the amniotic membrane as well. These include numerous types of growth factors such as fibroblast growth factors and platelet-derived growth factors. Immunosuppressive cytokines prevent the amniotic membrane from being seen as “foreign” by both the mother and infant’s immune systems. There are also a number of specialized molecules, such as defensins which protect against bacterial infection.
Wound Healing Properties of Amniotic Membrane
The layers of amniotic membrane contain properties that each play an important role in healing. The amniotic membrane:
- contains a significant number of cytokines and essential growth factors
- reduces pain when applied to a wound
- increases and enhances the wound healing process
- has antibacterial properties
- is non-immunogenic (will not be seen as foreign material)
- provides a biological barrier
- provides a matrix for migration and proliferation of cells
- reduces inflammation
- reduces scar tissue formation
Dehydration of Amniotic Membrane Tissue
Historically, amniotic tissue was sterilized and stored at 4°C. Amniotic tissue could only be used for up to six weeks, at which point it was no longer useful. Now, this material can be cleansed, dehydrated and sterilized, which means that the shelf life of amniotic membrane has been greatly increased.
Composition of Amniotic Tissue
Amniotic Tissue Contain:
- Extracellular Matrix (ECM)
- Proteins
- Growth Factors
- Fibroblast Growth Factor (FGF)
- Epidermal Growth Factor (EGF)
- Platelet Derived Growth Factor (PDGF) A&B
- Vascular Endothelial Growth Factor (VEGF)
- Transforming Growth Factor beta (TGFβ)
- Cytokines
- Hyaluronic Acid
- Cellular Components
- Amino Acids
- Carbohydrates
THE BODY'S HEALING PROCESS
Healthy wound healing involves fibroblasts, the main connective tissue cells present in the body, and macrophages, which form in response to infection.
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DEVELOPMENT OF CHRONIC NON-HEALING WOUNDS
Chronic non-healing wounds are wounds that have failed to progress through a timely sequence of repair, or one that proceeds through the wound healing process without restoring anatomic and functional results. Typically, there is a physiologic impairment that slows or prevents wound healing. Although there is no clear consensus in the duration of a wound that defines chronicity, a range of 4 weeks to 3 months has been used to define chronic wounds in the literature. The Wound Healing Society classifies chronic wounds into 4 major categories: pressure ulcers, diabetic foot ulcers, venous ulcers, and arterial insufficiency ulcers.
When wound healing is impaired, there is usually not a single factor, but rather multiple contributing factors at play. This is due to the fact that there are overlapping mechanisms in normal wound healing that prevent a single factor from disrupting the process. However, when the wound healing process is disrupted and wound healing is impaired, chronic non-healing wounds will develop. In general, non-healing wounds share similar characteristics: high level of proteases, elevated inflammatory markers, low growth factor activity, and reduced cellular proliferation. There are several factors that affect wound healing and contribute to the pathogenesis of chronic wounds. Some of the common factors are infection, ischemia, metabolic conditions, immunosuppression, and radiation.
AMNION-DERIVED ALLOGRAFTS MAKE AN ATTRACTIVE WOUND BIOMATERIAL
Clinical Biotherapeutics is committed to the improvement of patient outcomes. PalinGen® Membrane and Hydromembrane are human allografts that provide a rich source of various biologically active factors involved in tissue regeneration and wound healing with anti-inflammatory, anti-bacterial, reepithelialization, and anti-fibrotic properties.
Two stages of inflammation. Acute inflammation is of Short Duration, whereas Chronic Inflammation is a long-lived Inflammatory Response.
