Developing small-diameter vascular grafts with human amniotic membrane: long-term evaluation of transplantation outcomes in a small animal model

Biofabrication of small-diameter vascular graft with acellular human amniotic membrane: a proof-of-concept study in pig

Expanded polytetrafluoroethylene (ePTFE) grafts are Food and Drug Administration approved and effective for large vessel surgeries but face challenges in smaller vessels (Inner Diameter, ID ⩽ 6 mm) due to reduced blood flow and higher risks of thrombosis, stenosis, and infection. This study developed a vascular graft with an ID of 6 mm from decellularized human amniotic membrane (DAM graft) and compared its performance to ePTFE grafts in a porcine carotid artery model for one month. DAM grafts retained key extracellular matrix structures and mechanical properties post-decellularization, with customizable layers and stiffness to meet specific clinical needs. DAM grafts demonstrated successful carotid artery replacement, showing good surgical feasibility, patency, and post-operative recovery in all animals. In contrast to ePTFE grafts, which exhibited significant neointimal hyperplasia (NIH), poor endothelialization, and inflammation, DAM grafts displayed organized endothelial coverage, smooth muscle alignment, and reduced inflammation, minimizing NIH, thrombosis, and graft failure. These findings position DAM grafts as a promising alternative to synthetic grafts, especially for small-diameter applications. Future research should focus on improving endothelialization, exploring molecular mechanisms, and assessing long-term outcomes to further optimize DAM grafts for clinical use.

Decellularization of human iliac artery: A vascular scaffold for peripheral repairs with human mesenchymal cells

This work presents strong evidence supporting the use of decellularized human iliac arteries combined with adipose tissue-derived stem cells (hASCs) as a promising alternative for vascular tissue engineering, opening the path to future treatments for peripheral artery disease (PAD). PAD is a progressive condition with high rates of amputation and mortality due to ischemic damage and limited graft options. Traditional synthetic grafts often fail due to poor integration, while autologous grafts may be unsuitable for patients with compromised vascular health. This study explores the potential of decellularized human iliac arteries as scaffolds for vascular grafts, focusing on preserving extracellular matrix (ECM) ultrastructure while minimizing immunogenic response. A perfusion-based protocol with enzymatic and detergent agents effectively removed cellular material, resulting in scaffolds with preserved ECM architecture, including organized collagen and elastin fibers. To assess scaffold bioactivity, hASCs were seeded onto the decellularized ECM, demonstrating high viability. Structural assessments, including histological staining and mechanical testing, confirmed that decellularized arteries retained their hierarchical structure and exhibited increased stiffness, suggesting an adaptive realignment of ECM fibers. Thermal and ultrastructural analyses further showed that decellularized scaffolds maintained stability and integrity comparable to native tissue, underscoring their durability for clinical applications. The human iliac artery shows potential as a vascular scaffold due to its accessibility and the ability to support the viability of hASC. Future research will emphasize in vivo validation and strategies for functional recellularization to evaluate the clinical viability of these engineered vascular grafts.

Rapid Preparation of Collagen/Red Blood Cell Membrane Tubes for Stenosis-Free Vascular Regeneration

Extracellular matrix (ECM)-based small-diameter vascular grafts (SDVGs, inner diameter (ID) < 6 mm) hold great promise for clinical applications. However, existing ECM-based SDVGs suffer from limited donor availability, complex purification, high cost, and insufficient mechanical properties. SDVGs with ECM-like structure and function, and good mechanical properties were rapidly prepared by optimizing common materials and preparation, which can improve their clinical prospects. Here, we rapidly prepared an electrospinning film-collagen/red blood cell membrane-genipin hydrogel tube (ES-C/Rm-G-ht, ID = 2 mm) by the combination of the cross-linking of genipin, plastic compression, electrospinning, and rolling without a biological adhesive, which had a shorter preparation time of less than 17 h compared to the existing ECM-based SDVGs (preparation time of 4-18 weeks). ES-C/Rm-G-ht exhibited a layered honeycomb-like structure and demonstrated the ECM-like functions to promote the proliferation and migration of endothelial cells, and prevent thrombus and inflammation. Furthermore, ES-C/Rm-G-ht, possessing sufficient mechanical strength, showed high patency, rapid endothelialization (95%), good regeneration of smooth muscle cell layers and ECM, and effective antistenosis capability after implantation in the rabbit's carotid artery for 31 days. This work provides a straightforward, cost-effective, and promising strategy to prepare SDVGs with ECM-like structure and function, which is an ideal alternative for vascular grafts and autologous vessels in the current clinic.

Vascular Damage and Repair - Are Small-Diameter Vascular Grafts Still the "Holy Grail" of Tissue Engineering?

Cardiovascular diseases are the most important cause of morbidity and mortality in the civilized world. Stenosis or occlusion of blood vessels leads not only to events that are directly life-threatening, such as myocardial infarction or stroke, but also to a significant reduction in quality of life, for example in lower limb ischemia as a consequence of metabolic diseases. The first synthetic polymeric vascular replacements were used clinically in the early 1950s. However, they proved to be suitable only for larger-diameter vessels, where the blood flow prevents the attachment of platelets, pro-inflammatory cells and smooth muscle cells on their inner surface, whereas in smaller-diameter grafts (6 mm or less), these phenomena lead to stenosis and failure of the graft. Moreover, these polymeric vascular replacements, like biological grafts (decellularized or devitalized), are cell-free, i.e. there are no reconstructed physiological layers of the blood vessel wall, i.e. an inner layer of endothelial cells to prevent thrombosis, a middle layer of smooth muscle cells to perform the contractile function, and an outer layer to provide innervation and vascularization of the vessel wall. Vascular substitutes with these cellular components can be constructed by tissue engineering methods. However, it has to be admitted that even about 70 years after the first polymeric vascular prostheses were implanted into human patients, there are still no functional small-diameter vascular grafts on the market. The damage to small-diameter blood vessels has to be addressed by endovascular approaches or by autologous vascular substitutes, which leads to some skepticism about the potential of tissue engineering. However, new possibilities of this approach lie in the use of modern technologies such as 3D bioprinting and/or electrospinning in combination with stem cells and pre-vascularization of tissue-engineered vascular grafts. In this endeavor, sex-related differences in the removal of degradable biomaterials by the cells and in the behavior of stem cells and pre-differentiated vascular cells need to be taken into account. Key words: Blood vessel prosthesis, Regenerative medicine, Stem cells, Footprint-free iPSCs, sr-RNA, Dynamic bioreactor, Sex-related differences.

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.

An increase in Wharton's jelly membrane osteocompatibility by a genipin-cross-link

Wharton's Jelly (WJ) has attracted significant interest in the field of tissue healing thanks to its biological properties, including antibacterial activity and immunomodulation. However, due to the fast degradation and poor mechanical behavior in biological environment, its application in bone regeneration is compromised. Here, we proposed to use genipin as an efficient cross-linking agent to significantly improve the elasticity and the enzymatical stability of the WJ matrix. The degree of cross-linking, linear elastic moduli, and collagenase resistance varied over a wide range depending on genipin concentration. Furthermore, our results highlighted that an increase in genipin concentration led to a decreased surface wettability, therefore impairing cell attachment and proliferation. The genipin cross-linking prevented rapid in vitro and in vivo degradation, but led to an adverse host reaction and calcification. When implanted in the parietal bone defect, a limited parietal bone regeneration to the dura was observed. We conclude that genipin-cross-linked WJ is a versatile medical device however, a careful selection is required with regards to the genipin concentration.

Challenges and advances in materials and fabrication technologies of small-diameter vascular grafts

The arterial occlusive disease is one of the leading causes of cardiovascular diseases, often requiring revascularization. Lack of suitable small-diameter vascular grafts (SDVGs), infection, thrombosis, and intimal hyperplasia associated with synthetic vascular grafts lead to a low success rate of SDVGs (< 6 mm) transplantation in the clinical treatment of cardiovascular diseases. The development of fabrication technology along with vascular tissue engineering and regenerative medicine technology allows biological tissue-engineered vascular grafts to become living grafts, which can integrate, remodel, and repair the host vessels as well as respond to the surrounding mechanical and biochemical stimuli. Hence, they potentially alleviate the shortage of existing vascular grafts. This paper evaluates the current advanced fabrication technologies for SDVGs, including electrospinning, molding, 3D printing, decellularization, and so on. Various characteristics of synthetic polymers and surface modification methods are also introduced. In addition, it also provides interdisciplinary insights into the future of small-diameter prostheses and discusses vital factors and perspectives for developing such prostheses in clinical applications. We propose that the performance of SDVGs can be improved by integrating various technologies in the near future.

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.