Repeated Freezing Procedures Preserve Structural and Functional Properties of Amniotic Membrane for Application in Ophthalmology

Amnion-derived hydrogels as a versatile platform for regenerative therapy: from lab to market

In recent years, the amnion (AM) has emerged as a versatile tool for stimulating tissue regeneration and has been of immense interest for clinical applications. AM is an abundant and cost-effective tissue source that does not face strict ethical issues for biomedical applications. The outstanding biological attributes of AM, including side-dependent angiogenesis, low immunogenicity, anti-inflammatory, anti-fibrotic, and antibacterial properties facilitate its usage for tissue engineering and regenerative medicine. However, the clinical usage of thin AM sheets is accompanied by some limitations, such as handling without folding or tearing and the necessity for sutures to keep the material over the wound, which requires additional considerations. Therefore, processing the decellularized AM (dAM) tissue into a temperature-sensitive hydrogel has expanded its processability and applicability as an injectable hydrogel for minimally invasive therapies and a source of bioink for the fabrication of biomimetic tissue constructs by recapitulating desired biochemical cues or pre-defined architectural design. This article reviews the multi-functionality of dAM hydrogels for various biomedical applications, including skin repair, heart treatment, cartilage regeneration, endometrium regeneration, vascular graft, dental pulp regeneration, and cell culture/carrier platform. Not only recent and cutting-edge research is reviewed but also available commercial products are introduced and their main features and shortcomings are elaborated. Besides the great potential of AM-derived hydrogels for regenerative therapy, intensive interdisciplinary studies are still required to modify their mechanical and biological properties in order to broaden their therapeutic benefits and biomedical applications. Employing additive manufacturing techniques (e.g., bioprinting), nanotechnology approaches (e.g., inclusion of various bioactive nanoparticles), and biochemical alterations (e.g., modification of dAM matrix with photo-sensitive molecules) are of particular interest. This review article aims to discuss the current function of dAM hydrogels for the repair of target tissues and identifies innovative methods for broadening their potential applications for nanomedicine and healthcare.

Preparation of human amniotic membrane for transplantation in different application areas

The human amniotic membrane (hAM) is the inner layer of the placenta and plays protective and nutritional roles for the fetus during pregnancy. It contains multiple growth factors and proteins that mediate unique regenerative properties and enhance wound healing in tissue regeneration. Due to these characteristics hAM has been successfully utilized in ophthalmology for many decades. This material has also found application in a variety of additional therapeutic areas. Particularly noteworthy are the extraordinary effects in the healing of chronic wounds and in the treatment of burns. But hAM has also been used successfully in gynecology, oral medicine, and plastic surgery and as a scaffold for in vitro cell culture approaches. This review aims to summarize the different graft preparation, preservation and storage techniques that are used and to present advantages and disadvantages of these methods. It shows the characteristics of the hAM according to the processing and storage methods used. The paper provides an overview of the currently mainly used application areas and raises new application possibilities. In addition, further preparation types like extracts, homogenates, and the resulting treatment alternatives are described.

Monitoring of freezing patterns within 3D collagen-hydroxyapatite scaffolds using infrared thermography

The importance of cryopreservation in tissue engineering is unceasingly increasing. Preparation, cryopreservation, and storage of tissue-engineered constructs (TECs) at an on-site location offer a convenient way for their clinical application and commercialization. Partial freezing initiated at high sub-zero temperatures using ice-nucleating agents (INAs) has recently been applied in organ cryopreservation. It is anticipated that this freezing technique may be efficient for the preservation of both scaffold mechanical properties and cell viability of TECs. Infrared thermography is an instrumental method to monitor INAs-mediated freezing of various biological entities. In this paper, porous collagen-hydroxyapatite (HAP) scaffolds were fabricated and characterized as model TECs, whereas infrared thermography was proposed as a method for monitoring the crystallization-related events on their partial freezing down to -25 °C. Intra- and interscaffold latent heat transmission were descriptively evaluated. Nucleation, freezing points as well as the degree of supercooling and duration of crystallization were calculated based on inspection of respective thermographic curves. Special consideration was given to the cryoprotective agent (CPA) composition (Snomax®, crude leaf extract from Hippophae rhamnoides, dimethyl sulfoxide (Me₂SO) and recombinant type-III antifreeze protein (AFP)) and freezing conditions ('in air' or 'in bulk CPA'). For CPAs without ice nucleation activity, thermographic measurements demonstrated that the supercooling was significantly milder in the case of scaffolds present in a CPA solution compared to that without them. This parameter (ΔT, °C) altered with the following tendency: 10 Me₂SO (2.90 ± 0.54 ('in air') vs. 7.71 ± 0.43 ('in bulk CPA', P < 0.0001)) and recombinant type-III AFP, 0.5 mg/ml (2.65 ± 0.59 ('in air') vs. 7.68 ± 0.34 ('in bulk CPA', P < 0.0001)). At the same time, in CPA solutions with ice nucleation activity the least degree of supercooling and the longest crystallization duration (Δt, min) for scaffolds frozen 'in air' were documented for crude leaf homogenate (CLH) from Hippophae rhamnoides (1.57 ± 0.37 °C and 21.86 ± 2.93 min compared to Snomax, 5 μg/ml (2.14 ± 0.33 °C and 23.09 ± 0.05), respectively). The paper offers evidence that infrared thermography provides insightful information for monitoring partial freezing events in TECs when using different freezing containers, CPAs and conditions. This may further TEC-specific cryopreservation and optimization of CPA compositions with slow-nucleating properties.

Distribution of an analgesic palmitoylethanolamide and other N-acylethanolamines in human placental membranes

BACKGROUND

Human amniotic and amniochorionic membranes (AM, ACM) represent the most often used grafts accelerating wound healing. Palmitoylethanolamide, oleoylethanolamide and anandamide are endogenous bioactive lipid molecules, generally referred as N-acylethanolamines. They express analgesic, nociceptive, neuroprotective and anti-inflammatory properties. We assessed the distribution of these lipid mediators in placental tissues, as they could participate on analgesic and wound healing effect of AM/ACM grafts.

METHODS

Seven placentas were collected after caesarean delivery and fresh samples of AM, ACM, placental disc, umbilical cord, umbilical serum and vernix caseosa, and decontaminated samples (antibiotic solution BASE 128) of AM and ACM have been prepared. Ultra-high-performance liquid chromatography-tandem mass spectrometry was used for N-acylethanolamines analysis.

RESULTS

N-acylethanolamines were present in all studied tissues, palmitoylethanolamide being the most abundant and the anandamide the least. For palmitoylethanolamide the maximum average concentration was detected in AM (350.33 ± 239.26 ng/g), while oleoylethanolamide and anandamide were most abundant in placenta (219.08 ± 79.42 ng/g and 30.06 ± 7.77 ng/g, respectively). Low levels of N-acylethanolamines were found in serum and vernix. A significant increase in the levels of N-acylethanolamines (3.1-3.6-fold, P < 0.001) was observed in AM when the tissues were decontaminated using antibiotic solution. The increase in decontaminated ACM was not statistically significant.

CONCLUSIONS

The presence of N-acylethanolamines, particularly palmitoylethanolamide in AM and ACM allows us to propose these lipid mediators as the likely factors responsible for the anti-hyperalgesic, but also anti-inflammatory and neuroprotective, effects of AM/ACM grafts in wound healing treatment. The increase of N-acylethanolamines levels in AM and ACM after tissue decontamination indicates that tissue processing is an important factor in maintaining the analgesic effect.

Questions about Residual Cell Viability in Cryopreserved Human Amniotic Membrane and Its Impact on Clinical Applications

We questioned the relevance of evaluating residual cell viability in human amniotic membrane (hAM) after its cryopreservation since cell survival is controversial and its ability to act as a matrix (including the presence of growth factors and cytokines) appears to be most important for tissue regeneration purposes. We also discussed the usefulness of osteodifferentiating amniotic cells in whole hAM for bone repair applications. We have evidence that determining residual cell viability after cryopreservation and hAM osteodifferentiation is not justified.

Possible important roles of galectins in the healing of human fetal membranes

The fetal membranes healing is a complex and dynamic process of replacing devitalized and missing cellular structures and tissue layers. Multiple cells and extracellular matrices, and cell differentiation, migration and proliferation may participate in restoring the integrity of damaged tissue, however this process still remains unclear. Therefore, there is a need to identify and integrate new ideas and methods to design a more effective dressing to accelerate fetal membrane healing. This review explores the function and role of galectins in the inflammatory, epithelial mesenchymal transition, proliferative migration, and remodeling phases of fetal membrane healing. In conclusion, the preliminary findings are promising. Research on amnion regeneration is expected to provide insight into potential treatment strategies for premature rupture of membranes.

Cryopreservation of human amniotic membrane for ocular surface reconstruction: a comparison between protocols

PURPOSE

To compare the effects on adhesive and structural properties of newer preservation conditions to those obtained with an established, standardized protocol (dimethyl sulfoxide at -180 °C). In attempt to simplify and enhance the safety of the procedure, we tested dextran-based freezing medium and a dry condition (no medium) at temperatures of -80 °C.

METHODS

Five patches of human amniotic membrane were obtained from three different donors. For each donor, five preservation condition were tested: dimethyl sulfoxide at -180 °C, dimethyl sulfoxide at -80 °C, dextran-based medium at -180 °C, dextran-based medium at -80 °C and dry freezing at -80 °C (no medium). At the end of four months storage period, adhesive properties and structure were analyzed.

RESULTS

None of the newer preservation protocols showed differences in adhesive and structural properties of the tissues. The stromal layer always kept its adhesiveness, while both structure and basement membrane were not altered by any the preservation protocol.

CONCLUSIONS

Switching from liquid nitrogen cryopreservation to -80 °C would reduce manipulation, simplify the procedure, making it also cheaper. The use of dextran-based freezing medium or no medium at all (dry condition) would avoid the potential toxicity of the dimethyl sulfoxide-based freezing media.

Effect of Amniotic Membrane/Collagen-Based Scaffolds on the Chondrogenic Differentiation of Adipose-Derived Stem Cells and Cartilage Repair

Objectives: Repairing articular cartilage damage is challenging. Clinically, tissue engineering technology is used to induce stem cell differentiation and proliferation on biological scaffolds to repair defective joints. However, no ideal biological scaffolds have been identified. This study investigated the effects of amniotic membrane/collagen scaffolds on the differentiation of adipose-derived stem cells (ADSCs) and articular cartilage repair.

Methods: Adipose tissue of New Zealand rabbits was excised, and ADSCs were isolated and induced for differentiation. An articular cartilage defect model was constructed to identify the effect of amniotic membrane/collagen scaffolds on cartilage repair. Cartilage formation was analyzed by imaging and toluene blue staining. Knee joint recovery in rabbits was examined using hematoxylin and eosin, toluidine, safranine, and immunohistochemistry at 12 weeks post-operation. Gene expression was examined using ELISA, RT-PCR, Western blotting, and immunofluorescence.

Results: The adipose tissue was effectively differentiated into ADSCs, which further differentiated into chondrogenic, osteogenic, and lipogenic lineages after 3 weeks’ culture in vitro. Compared with platelet-rich plasmon (PRP) scaffolds, the amniotic membrane scaffolds better promoted the growth and differentiation of ADSCs. Additionally, scaffolds containing the PRP and amniotic membrane efficiently enhanced the osteogenic differentiation of ADSCs. The levels of COL1A1, COL2A1, COL10A1, SOX9, and ACAN in ADSCs + amniotic membrane + PRP group were significantly higher than the other groups both in vitro and in vivo. The Wakitani scores of the ADSC + amniotic membrane + PRP group were lower than that in ADSC + PRP (4.4 ± 0.44**), ADSC + amniotic membrane (2.63 ± 0.38**), and control groups (6.733 ± 0.21) at week 12 post-operation. Osteogenesis in rabbits of the ADSC + amniotic membrane + PRP group was significantly upregulated when compared with other groups. Amniotic membranes significantly promoted the expression of cartilage regeneration-related factors (SOX6, SOX9, RUNX2, NKX3-2, MEF2C, and GATA4). The ADSC + PRP + amniotic membrane group exhibited the highest levels of TGF-β, PDGF, and FGF while exhibiting the lowest level of IL-1β, IL6, and TNF-α in articular cavity.

Conclusion: Amniotic membrane/collagen combination-based scaffolds promoted the proliferation and cartilage differentiation of ADSCs, and may provide a new treatment paradigm for patients with cartilage injury.

Various administration forms of decellularized amniotic membrane extract towards improving corneal repair

Amniotic membrane (AM) transplantation is often used as a treatment for corneal repair, but AM is prone to dissolving and shedding after surgery; multiple transplants will cause pain and financial burden. In this work, human amniotic membrane was firstly decellularized to obtain an AM extracellular matrix (dAM). This dAM was homogenized and extracted to obtain the dAM extract (simplified as dAME). Different forms of administration for corneal injury were performed as liquid drops (diluted dAME), in situ gels (using temperature-dependent Poloxamer 407 as the matrix), and tablets (poly(vinyl alcohol) as the matrix). The cytocompatibility of dAME was evaluated using corneal epithelial cells, corneal stromal cells and fibroblasts as cell models. The results showed that dAME is biocompatible to all these cells. Cells exhibited normal morphology and growth state at a dAME concentration of up to 160 μg mL^-1. In vivo, dAME exhibited increased wound healing efficiency in severe corneal injury, being characterized with a shorter healing time for epithelium and a faster recovery for stromal opacity and thickness, compared with those of the control eyes. Different forms of administration have different effects on corneal repair; among them, in situ gels achieved the best therapeutic efficiency. Their biological mechanism was detected via quantitative real-time polymerase chain reaction (qRT-PCR) technology. It was confirmed that dAME plays important roles in promoting the mRNA expression of leucine-rich and immunoglobulin-like domains 1 (LRIG1) and in inhibiting the mRNA of transforming growth factor-β1 (TGF-β1).

Characterization of Cryopreserved Canine Amniotic Membrane

Amniotic membrane is an effective corneal reconstruction material in veterinary surgery. Cryopreserved amniotic membrane is widely used in practice. Properties of cryopreserved canine amniotic membranes are currently not well studied. This study aimed to compare three properties between canine amniotic membranes cryopreserved for 7 days and 30 days, including tensile strength, transparency, and cell viability. After their respective cryopreservation time, stress-strain curves of the cryopreserved membranes' tensile strength were assessed using a universal testing machine. Both groups produced J-shaped stress-strain curves with statistically comparable parameters, including maximum stress, strain, and Young's modulus. The percentage of cell viability was observed by trypan blue staining under a light microscope. Membrane transparency was tested with a spectrophotometer. Transparency tests showed high levels of light transmission and low haze, with no statistical difference between groups. Cell viability was statistically lower in the 30-day cryopreserved group. Tensile strength and transparency of cryopreserved CAM were not significantly impeded for up to 30 days. For CAM to be used as an alternative corneal transplant material in veterinary and regenerative medicine, further research on cell biology, biomechanical properties of the membrane, and cell viability should be conducted.

Proteome Composition of Bovine Amniotic Membrane and Its Potential Role in Corneal Healing

Purpose

To investigate the protein profile of bovine amniotic membranes (bAM) and to determine putative associations between protein composition in bAM and known corneal healing pathways.

Methods

The bAM were acquired from normal full-term births (n = 10), processed, and stored at -80°C for two days. Subsequently, the frozen membranes were thawed at room temperature and prepared for proteomic exploration using high-resolution liquid chromatography-mass spectrometry, followed by bioinformatics analysis. Recently identified corneal healing pathways were contrasted with protein profiles and pathways present in bAM.

Results

The analyses identified 2105 proteins, with an interactive network of 1271 nodes (proteins) and 8757 edges (interactions). The proteins with higher betweenness centrality measurements include microfibril-associated protein 4, HSD3B1, CAPNS1, ATP1B3, CAV1, ANXA2, YARS, and GAPDH. The top four pathways in Kyoto Encyclopedia of Genes and Genomes were ribosome, metabolic pathway, spliceosome, and oxidative phosphorylation. The bAM and cornea shared abundant proteins, genome ontology, and signaling pathways.

Conclusions

The high-throughput proteomic profile of the bAM demonstrated that numerous proteins present in the cornea are also present in this fetal membrane. Our findings collectively demonstrate the similarity between bAM and the cornea's protein composition, supporting our hypothesis that bAM can be used to treat corneal diseases.

Concentrations of tissue inhibitor of matrix metalloproteinase-1 and hyaluronic acid in canine amniotic membranes cryopreserved for different time points and its effects in dogs with complicated corneal ulcers

OBJECTIVES

To determine the concentrations of total protein (TP), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and hyaluronic acid (HA) in amniotic membranes (AMs) harvested from placentas of bitches of different ages and cryopreserved for different time points. The outcomes of complicated corneal defects of dogs repaired with AMs stored for the same time points were also evaluated.

PROCEDURES

Ten cryopreserved canine AMs were stored for short term (2-50 days), middle term (92-210 days), or long term (256-357 days). TP was quantified by Bradford's test, whereas TIMP-1 and HA were quantified by ELISA. Twenty-one dogs that had an AM transplantation to restore deep or perforating corneal wounds were selected.

RESULTS

TIMP-1 levels were lower in AMs cryopreserved for middle term (p = .02) and long term (p = .0009), when compared to AMs stored for short term. TP (p = .39) and HA (p = .18) concentrations in AMs did not differ among the storage time. TIMP-1 concentration in AMs correlated with storage time (R = -.65, p < .0001), while TP (R = -.33, p = .07) and HA concentrations did not (R = -.15, p = .41). The age of donors did not correlate with the components evaluated in the AMs. Corneal defects repaired with AMs stored for short term healed sooner than the ones repaired with AMs stored for middle (p < .01) and long term (p = .02). Additionally, TIMP-1 levels in AMs correlated negatively with the epithelization time (R = -.62, p = .002). Graft opacity was severe in 55% of cases. However, the HA levels in AMs correlated negatively with the opacification score (R = -.47, p = .03). Vision was observed in more patients who presented deep ulcers and descemetoceles, than in the ones with perforations (p = .004).

CONCLUSIONS

TIMP-1 concentration in canine AMs significantly decreased over a year storage time, while TP and HA concentrations did not change during the same period. The age of donors did not correlate with the components evaluated in the AMs. Complicated corneal defects repaired with AMs cryopreserved for short term healed sooner and tended to be less opaque; however, satisfactory to optimal outcomes were achieved even in the eyes repaired with AMs stored for up to a year.

Freeze-Dried Versus Cryopreserved Amniotic Membranes in Corneal Ulcers Treated by Overlay Transplantation: A Case-Control Study

PURPOSE

The purpose of this study was to assess cryopreserved amniotic membrane (C-AM) versus chorion-free freeze-dried amniotic membrane (FD-AM) overlay transplantation for corneal ulcers in a French tertiary ophthalmology hospital.

METHODS

Between March and July 2020, when C-AMs were not available because of the COVID-19 pandemic, 28 corneal ulcers underwent FD-AM overlay transplantation and were retrospectively compared with 22 corneal ulcers treated with C-AM during the same period in 2018. All patients had at least 3 months of follow-up, and those who underwent combined surgeries were excluded. Ulcers were assessed at baseline and then at 72 hours, 1 month, and 3 months. Population demographics, follow-up time, ulcer etiologies, epithelial defect size, ulcer depth, and complications were also recorded.

RESULTS

Baseline characteristics and clinical features of both groups were comparable. There was no statistically significant difference in the number of overlay AM transplantations (P = 0.52) or early detachments (P = 0.57). At 3 months, the corneal healing rate was almost the same in both groups (89% and 91% for FD-AM and C-AM, respectively; P = 0.87). Complications were equally uncommon (11% and 9%, respectively; P = 0.92). In logistic regression, the type of the membrane did not influence corneal healing at 1 month (P = 0.42) or 3 months (P = 0.99), regardless of the depth of the ulcer. However, whatever the type of AM used, the deeper the ulcer was, the less likely it was to heal at 3 months (P = 0.02).

CONCLUSIONS

This is the first study that provides positive insight into the effectiveness of FD-AM compared with C-AM when used as overlay transplantation for treating corneal ulcers.

Surgical Application of Human Amniotic Membrane and Amnion-Chorion Membrane in the Oral Cavity and Efficacy Evaluation: Corollary With Ophthalmological and Wound Healing Experiences

Due to its intrinsic properties, there has been growing interest in human amniotic membrane (hAM) in recent years particularly for the treatment of ocular surface disorders and for wound healing. Herein, we investigate the potential use of hAM and amnion-chorion membrane (ACM) in oral surgery. Based on our analysis of the literature, it appears that their applications are very poorly defined. There are two options: implantation or use as a cover material graft. The oral cavity is submitted to various mechanical and biological stimulations that impair membrane stability and maintenance. Thus, some devices have been combined with the graft to secure its positioning and protect it in this location. This current opinion paper addresses in detail suitable procedures for hAM and ACM utilization in soft and hard tissue reconstruction in the oral cavity. We address their implantation and/or use as a covering, storage format, application side, size and number, multilayer use or folding, suture or use of additional protective covers, re-application and resorption/fate. We gathered evidence on pre- and post-surgical care and evaluation tools. Finally, we integrated ophthalmological and wound healing practices into the collected information. This review aims to help practitioners and researchers better understand the application of hAM and ACM in the oral cavity, a place less easily accessible than ocular or cutaneous surfaces. Additionally, it could be a useful reference in the generation of new ideas for the development of innovative protective covering, suturing or handling devices in this specific indication. Finally, this overview could be considered as a position paper to guide investigators to fulfill all the identified criteria in the future.

Electrospun PCL/PLA Scaffolds Are More Suitable Carriers of Placental Mesenchymal Stromal Cells Than Collagen/Elastin Scaffolds and Prevent Wound Contraction in a Mouse Model of Wound Healing

Mesenchymal stem/stromal cells (MSCs) exert beneficial effects during wound healing, and cell-seeded scaffolds are a promising method of application. Here, we compared the suitability of a clinically used collagen/elastin scaffold (Matriderm) with an electrospun Poly(ε-caprolactone)/poly(l-lactide) (PCL/PLA) scaffold as carriers for human amnion-derived MSCs (hAMSCs). We created an epidermal-like PCL/PLA scaffold and evaluated its microstructural, mechanical, and functional properties. Sequential spinning of different PCL/PLA concentrations resulted in a wide-meshed layer designed for cell-seeding and a dense-meshed layer for apical protection. The Matriderm and PCL/PLA scaffolds then were seeded with hAMSCs, with or without Matrigel coating. The quantity and quality of the adherent cells were evaluated in vitro. The results showed that hAMSCs adhered to and infiltrated both scaffold types but on day 3, more cells were observed on PCL/PLA than on Matriderm. Apoptosis and proliferation rates were similar for all carriers except the coated Matriderm, where apoptotic cells were significantly enhanced. On day 8, the number of cells decreased on all carrier types except the coated Matriderm, which had consistently low cell numbers. Uncoated Matriderm had the highest percentage of proliferative cells and lowest apoptosis rate of all carrier types. Each carrier also was topically applied to skin wound sites in a mouse model and analyzed in vivo over 14 days via optical imaging and histological methods, which showed detectable hAMSCs on all carrier types on day 8. On day 14, all wounds exhibited newly formed epidermis, and all carriers were well-integrated into the underlying dermis and showing signs of degradation. However, only wounds treated with uncoated PCL/PLA maintained a round appearance with minimal contraction. Overall, the results support a 3-day in vitro culture of scaffolds with hAMSCs before wound application. The PCL/PLA scaffold showed higher cell adherence than Matriderm, and the effect of the Matrigel coating was negligible, as all carrier types maintained sufficient numbers of transplanted cells in the wound area. The anti-contractive effects of the PCL/PLA scaffold offer potential new therapeutic approaches to wound care.

Human Amniotic Membrane: A review on tissue engineering, application, and storage

Human amniotic membrane (hAM) has been employed as scaffolding material in a wide range of tissue engineering applications, especially as a skin dressing and as a graft for corneal treatment, due to the structure of the extracellular matrix and excellent biological properties that enhance both wound healing and tissue regeneration. This review highlights recent work and current knowledge on the application of native hAM, and/or production of hAM-based tissue-engineered products to create scaffolds mimicking the structure of the native membrane to enhance the hAM performance. Moreover, an overview is presented on the available (cryo) preservation techniques for storage of native hAM and tissue-engineered products that are necessary to maintain biological functions such as angiogenesis, anti-inflammation, antifibrotic and antibacterial activity.