## 5 Trends in the Development of Barrier Membranes  
### Amiotic and Chorionic Membranes  
Amiotic and chorionic membranes are biological membranes, which means that they are bio-absorbable and compatible with tissues. The human placenta is essential in the development and survival of the fetus, ensuring physical and biological protection [141]. The amniotic membrane consists of a thick basal membrane and an avascular stromal matrix; this is the innermost layer of the placenta. Chorion forms the outer end of the sac and is made up of several types of collagen and bioactive components of cell adhesion [142]. Amiotic and chorionic membranes have been used in transplant surgery, proving healing, anti-inflammatory and antibacterial properties [143]. Membrane harvesting is usually done from healthy pregnant patients; caesarean section is preferred because vaginal birth placentas may be contaminated [141]. After harvesting, the collected placenta is placed in a sterile transport medium; to obtain the amniotic membrane, the amnion is separated from the underlying chorion along their natural plane of cleavage. Subsequently, the amniotic membrane is abundantly irrigated with a saline solution containing streptomycin, penicillin, neomycin and amphoteric prior to storage [143]. Methods of preserving the amniotic membrane include cryopreservation, lyophilization or air drying. Cryopreservation results in an improved retention of proteins and growth factors compared to lyophilization [144], but cryopreservation can affect the viability of cells in the amniotic membrane [145]. After lyophilization or air drying, it is necessary to sterilize the membrane with the help of gamma radiation [146] or with peracetic acid [147]. The amniotic membrane contains type IV, V and VI collagen as well as proteins (fibronectin, laminin, proteoglycans, glycosaminoglycans) [148]. The amniotic membrane contains laminin 5, a protein that stimulates the cell adhesion of gingival epithelial cells, collagen types I, II, IV, V and VI, platelet-derived growth factor, fibroblast growth factor and TGF-\(\beta\)[149]. Perlecan found in the amniotic membrane plays an important role in binding growth factors and interacts with various cell adhesion molecules [150]. Histologically, the chorionic membrane consists of three layers: reticulate, basal membrane and trophoblastic. Collagen types I, III, IV, V, VI and VII, as well as proteoglycans are found in the crosslinked layer; the basal membrane contains type IV collagen, fibronectin and laminin [151]. Inhibitors of matrix metalloproteinases have been identified in the chorion, factors that can inhibit inflammatory status and stop collagen degradation [152]. Given these aspects, amniotic and chorion structures offer potential for use as barrier membranes in GTR and GBR. Such membranes have antibacterial and antifungal properties, minimize wound inflammation and provide a protein-rich matrix that allows cells to migrate more easily [153]. Moreover, the harvesting technique is relatively simple; by hydration with the blood, the membrane becomes malleable [142]. Major limitations include the risk of cross-contamination, as well as their fragility [151]. Ambiotic and chorionic membranes have been shown to be effective in bone neo-formation in periodontal defects, on canine [154] and human [155] subjects. [PERSON] et al. used an amniotic membrane in combination with an alloplastic biphasic bone substitute (60% hydroxyapatite, 40% tricalcium phosphate) to treat infrabony defects; this membrane generated similar results to porcine-derived collagen membrane in terms of postoperative healing and the amount of newly formed bone [155]. [PERSON] et al. [156] used an ammio-chorionic membrane to treat infrabony defects, observing significant improvements of clinical parameters (probing depth and loss of periodontal clinical attachment) at 12 months [156].