Amniotic 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]. Amniotic 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 amphotericin 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-β [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].

Amniotic and chorionic membranes have been shown to be effective in bone neo-formation in periodontal defects, on canine [154] and human [155] subjects. Venkatesan 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]. Holtzclaw et al. [156] used an amnio-chorionic membrane to treat infrabony defects, observing significant improvements of clinical parameters (probing depth and loss of periodontal clinical attachment) at 12 months [156]. Another study compared the effects of lyophilized amniotic membrane and collagen membrane on newly formed bone density; the bone density of defects treated with amniotic membrane was higher than the sites where no barrier membrane was used and equivalent to the density obtained with collagen membrane (p < 0.05) at 3 weeks [157].

The amniotic membrane has also been used successfully in periodontal muco-gingival surgery; the association of the amniotic membrane with repositioned flaps has generated favorable results in covering the gingival recessions and in increasing the thickness of the attached gingiva [158,159].

An amniotic membrane with different potential areas of use was patented (US6326019B1) [160], but its usage was directed mainly in skin and mucosal grafting. Actishield™ (Wright Medical, Memphis, TN, USA) was also developed, but with main indication for orthopedic surgery. Up to date, there is no approved commercial amniotic/chorionic membrane for periodontal tissue regeneration. Nevertheless, in all types of membranes, Quality by Design principles and regulations have been introduced in order to obtain benefits of an integrated and risk-free approach to the industrialization process in membranes manufacturing [55].

Platelet concentrates have been a research topic for more than 20 years; platelet-rich plasma, discovered in the late 1990s, was the result of centrifugation of blood harvested on the spot from the patient, offering good advantages in oral and maxillofacial surgery [161]. This procedure, on the other hand, had disadvantages related to the use of anticoagulants that could interfere with the healing process. Subsequently, a new product without anticoagulant was developed, platelet-rich fibrin (PRF). PRF has been shown to significantly increase the potential for tissue regeneration, favoring the slow and gradual release of growth factors trapped in its fibrin matrix [162].

PRP has been used primarily for soft tissue regeneration rather than osteogenesis and requires more blood than PRF. PRP is centrifuged at a higher rate, causing all heavy white blood cells and stem cells to sink to the base of the tube, not being collected in the sample [163]. Further research has found that a higher platelet concentration with the inclusion of white blood cells and stem cells in the sample would be even more therapeutic. The inclusion of white blood cells helped prevent postoperative infection, and the presence of stem cells generated an obvious capacity for regeneration. PRF is centrifuged at a slower rate, which causes a higher concentration of white blood cells, stem cells and platelets to remain in the middle plasma layer. Thus, PRF has a platelet concentration almost double that of blood. Platelets are involved in the release of growth and clotting factors. If the release of the growth factor occurs rapidly in the case of PRP, it is slow for PRF, with an average duration of 7–10 days postoperatively [164].

PRF has also proven effective in treating gingival recessions. Anilkumar et al. [167] compared PRF and connective tissue grafting with lateral repositioned flap to cover Miller class II recessions. Recession coverage was complete for 91% of patients treated with PRF, compared with 66% for those treated with a connective graft [167]. Jankovic et al. [168], in a treatment of Miller class I or II recessions, compared the results of the use of PRF membranes and connective tissue graft, combined with coronally repositioned flaps and connective tissue graft. The parameters studied were the size of the recession, attachment gain, the height of the keratinized gingiva, the pocket depth, the quality and speed of wound healing and the patient’s discomfort; clinical parameters were evaluated at baseline and after 12 months. The results were similar between the use of a PRF membrane and a connective graft. The authors noted that although the amount of acquired keratinized tissue is higher with the connective graft, PRF provided better healing and less discomfort to the patient [168]. Thus, PRF may be an interesting, effective and relatively low-cost option, but further studies are needed on larger study groups in order to establish accurate protocols.

Three-dimensional printing aims to generate an individualized 3D object, according to a design developed by software (computer aided design—CAD), by depositing the chosen material layer by layer. Three-dimensional technology already has applications in various fields, such as the production of anatomical models and surgical guides or regenerative medicine. There are multiple methods of 3D printing, including fusion deposition modeling (FDM), stereolithography (SLA) or selective laser sintering (SLS), but FDM remains the technique of choice for bioprinting [169]. The biomaterials used include hydrogels in combination with living cells and/or growth factors, natural and synthetic bioplastics, proteins, polymer biomolecules and ceramics [170].

Natural biomaterials used in 3D printing techniques include collagen, agarose, alginate, chitosan, silk, gelatin, cellulose, hyaluronic acid and fibrin [171], and synthetic biomaterials include PLA, PGA, PLGA and PCL [172,173]. Decellularized matrix components containing both conserved cellular elements and specific signaling factors of high importance in regenerative processes can also be used, because the latter can guide the cells of the resident tissue or provide the host cells with the necessary instructions for tissue regeneration [174].

Tayebi et al. tested a 3D-printed membrane of sodium elastin/gelatin/hyaluronate in vitro; the membrane has shown good mechanical properties as well as a stimulation of fibroblast proliferation [10]. Bai et al. [175] developed an individualized membrane with 3D-printed titanium mesh; various types of titanium mesh designed with different diameters, and thicknesses were tested based on their mechanical strength by a three-point bending test and FEA. According to the authors, the mechanical properties of the titanium mesh increased when the thickness decreased (0.5 mm to 0.3 mm); by increasing mesh diameter (3 mm to 5 mm), the mechanical properties of the mesh decreased [175].

A time dimension was added to 3D technology, with the appearance of being 4D; 3D printed construction thus changes, resulting in a transition in shape, structure and function [176]. This technology is based on intelligent biomaterials that have the ability to undergo changes as a result of exposure to various stimuli (temperature, pH, humidity, electric or magnetic fields, light, sound or a combination thereof) [177]. Thus, 4D bioprinting offers new directions for the development of tissue reconstruction techniques.