Placental Tissue

Placental membrane, with its critical role of protection and nourishment during fetal development, provides many unique properties that make it an ideal source tissue for a biologic scaffold¹. Placental membrane is a translucent structure that contains no blood vessels², nerves, muscles or lymph vessels³. The placental membrane is divided in two principal sections; the amnion and the chorion⁴. The amnion is a three layer structure with the innermost, epithelial layer contacting the amniotic fluid, the outermost layer, the mesenchymal layer attaching to the chorion and the intermediate basement membrane connecting the two⁵. The epithelial layer is comprised of a single layer of cuboid epithelial cells that are firmly attached to the basement membrane. The basement membrane has a high concentration of proteoglycans, especially heparin sulfate³, which make it permeable to amniotic macromolecules and help it to maintain the integrity of the entire amnion². The mesenchymal layer has three distinct sublayers; the compact layer, the fibroblast layer, and the spongy layer². The compact layer has a high collagen content that exists in aligned fibrils that provide the amnion with tensile strength and non-fibril collagens that attach to the basement membrane². The fibroblast layer is highly cellularized, containing amniotic mesenchymal cells, macrophages and fibroblast-like mesenchymal stem cells⁵. The spongy layer has proteogylcans and glycoproteins in a network of fibril collagen and provides only a loose connection to the chorion³. The chorion consists of four layers: cellular layer, reticular layer, pseudo-basement membrane, and trophoblast⁶. The cellular layer, composed of a fibroblast network, is in direct contact with the amnion⁷. The reticular layer, which accounts for most of the chorion’s thickness⁷, is constituted of a network of structural fibril proteins and cells that contribute to the placental barrier function⁸. The pseudo-basement membrane is a thin dense layer of connective tissue that is firmly attached to the reticular layer and sends anchoring fibers into the trophoblast⁶. The trophoblast layer consists of strata of trophoblasts the contact the maternal decidua⁹.

A primary function of the placental membrane is to provide a physiologic barrier to prevent desiccation³ and immunological barrier for the fetus, which is accomplished by expression of Human Leukocyte Antigen-G(HLA-G) by the trophoblast cells as opposed to other forms of HLA, which is maintained in the tissue². Placental membrane tissue exhibits anti-microbial properties due to the presence of β-3 defensins that act to prevent microbial colonization of the epithelial surface^2,5. Anti-inflammatory properties, based on the presence of interleukin-4 (IL-4), interleukin -10 (IL-10), TIMP-1, TIMP-2 and TIMP-4^3,10, of placental membranes are also beneficial to tissue healing. Placental membranes have shown clinical evidence of epithelialization^11-13 and the potential to heal without scarring¹⁴.

1. Shaifur Ra, M., et al., Properties and Therapeutic Potential of Human Amniotic Membrane. Asian Journal of Dermatology, 2015. 7(1): p. 1-12.

2. Niknejad, H., et al., Properties of the amniotic membrane for potential use in tissue engineering. Eur Cell Mater, 2008. 15: p. 88-99.

3. Mamede, A.C., et al., Amniotic membrane: from structure and functions to clinical applications. Cell Tissue Res, 2012. 349(2): p. 447-58.

4. Koob, T.J., et al., Cytokines in single layer amnion allografts compared to multilayer amnion/chorion allografts for wound healing. J Biomed Mater Res B Appl Biomater, 2015. 103(5): p. 1133-40.

5. Chopra, A. and B.S. Thomas, Amniotic Membrane: A Novel Material for Regeneration and Repair. J Biomim Biomater Tissue Eng, 2013. 18(1).

6. Bourne, G.L., The anatomy of the human amnion and chorion. Proc R Soc Med, 1966. 59(11 Part 1): p. 1127-8.

7. Bourne, G., The foetal membranes. A review of the anatomy of normal amnion and chorion and some aspects of their function. Postgrad Med J, 1962. 38: p. 193-201.

8. Jones, C.J.P. and H. Fox, Ultrastructure of the normal human placenta. Electron Microscopy Reviews, 1991. 4(1): p. 129-178.

9. Soares, M.J., K.M. Varberg, and K. Iqbal, Hemochorial placentation: development, function, and adaptations. Biol Reprod, 2018. 99(1): p. 196-211.

10. Hortensius, R.A. and B.A. Harley, Naturally derived biomaterials for addressing inflammation in tissue regeneration. Exp Biol Med (Maywood), 2016. 241(10): p. 1015-24.

11. Dua, H.S., et al., The amniotic membrane in ophthalmology. Surv Ophthalmol, 2004. 49(1): p. 51-77.

12. Subrahmanyam, M., Amniotic membrane as a cover for microskin grafts. Br J Plast Surg, 1995. 48(7): p. 477-8.

13. Ward, D.J. and J.P. Bennett, The long-term results of the use of human amnion in the treatment of leg ulcers. Br J Plast Surg, 1984. 37(2): p. 191-3.

14. Leavitt, T., et al., Scarless wound healing: finding the right cells and signals. Cell Tissue Res, 2016. 365(3): p. 483-93.