Bio-composites reinforced with unique coral collagen fibers: Towards biomimetic-based small diameter vascular grafts

Fabric-Enhanced Vascular Graft with Hierarchical Structure for Promoting the Regeneration of Vascular Tissue

Natural blood vessels have completed functions, including elasticity, compliance, and excellent antithrombotic properties because of their mature structure. To replace damaged blood vessels, vascular grafts should perform these functions by simulating the natural vascular structures. Although the structures of natural blood vessels are thoroughly explored, constructing a small-diameter vascular graft that matches the mechanical and biological properties of natural blood vessels remains a challenge. A hierarchical vascular graft is fabricated by Electrospinning, Braiding, and Thermally induced phase separation (EBT) processes, which could simulate the structure of natural blood vessels. The internal electrospun structure facilitates the adhesion of endothelial cells, thereby accelerating endothelialization. The intermediate PLGA fabric exhibits excellent mechanical properties, which allow it to maintain its shape during long-term transplantation and prevent graft expansion. The external macroporous structure is beneficial for cell growth and infiltration. Blood vessel remodeling aims to combine a structure that promotes tissue regeneration with anti-inflammatory materials. The results in vitro demonstrated that it EBT vascular graft (EBTVG) has matched the mechanical properties, reliable cytocompatibility, and the strongest endothelialization in situ. The results in vitro and replacement of the resected artery in vivo suggest that the EBTVG combines different structural advantages with biomechanical properties and reliable biocompatibility, significantly promoting the stabilization and regeneration of vascular endothelial cells and vascular smooth muscle cells, as well as stabilizing the blood microenvironment.

Three-dimensional printing and decellularized-extracellular-matrix based methods for advances in artificial blood vessel fabrication: A review

Blood vessels are the tubes through which blood flows and are divided into three types: millimeter-scale arteries, veins, and capillaries as well as micrometer-scale capillaries. Arteries and veins are the conduits that carry blood, while capillaries are where blood exchanges substances with tissues. Blood vessels are mainly composed of collagen fibers, elastic fibers, glycosaminoglycans and other macromolecular substances. There are about 19 feet of blood vessels per square inch of skin in the human body, which shows how important blood vessels are to the human body. Because cardiovascular disease and vascular trauma are common in the population, a great number of researches have been carried out in recent years by simulating the structures and functions of the person's own blood vessels to create different levels of tissue-engineered blood vessels that can replace damaged blood vessels in the human body. However, due to the lack of effective oxygen and nutrient delivery mechanisms, these tissue-engineered vessels have not been used clinically. Therefore, in order to achieve better vascularization of engineered vascular tissue, researchers have widely explored the design methods of vascular systems of various sizes. In the near future, these carefully designed and constructed tissue engineered blood vessels are expected to have practical clinical applications. Exploring how to form multi-scale vascular networks and improve their compatibility with the host vascular system will be very beneficial in achieving this goal. Among them, 3D printing has the advantages of high precision and design flexibility, and the decellularized matrix retains active ingredients such as collagen, elastin, and glycosaminoglycan, while removing the immunogenic substance DNA. In this review, technologies and advances in 3D printing and decellularization-based artificial blood vessel manufacturing methods are systematically discussed. Recent examples of vascular systems designed are introduced in details, the main problems and challenges in the clinical application of vascular tissue restriction are discussed and pointed out, and the future development trends in the field of tissue engineered blood vessels are also prospected.

Optimization of Electrospun Bilayer Vascular Grafts through Assessment of the Mechanical Properties of Monolayers

Small-diameter vascular grafts must be obtained with the most appropriate materials and design selection to harmoniously display a variety of features, including adequate tensile strength, compliance, burst strength, biocompatibility, and biodegradability against challenging physiological and hemodynamic conditions. In this study, monolayer vascular grafts with randomly distributed or radially oriented fibers are produced using neat, blended, and copolymer forms of polycaprolactone (PCL) and poly(lactic acid) (PLA) via the electrospinning technique. The blending ratio is varied by increasing 10 in the range of 50-100%. Bilayer graft designs are realized by determining the layers with a random fiber distribution for the inner layer and radial fiber orientation for the outer layer. SEM analysis, wall thickness and fiber diameter measurements, tensile strength, elongation, burst strength, and compliance tests are done for both mono- and bilayer scaffolds. The findings revealed that the scaffolds made of neat PCL show more flexibility than the neat PLA samples, which possess higher tensile strength values than neat PCL scaffolds. Also, in blended samples, the tensile strength values do not show a significant improvement, whereas the elongation values are enhanced in tubular samples, depending on the blending ratio. Also, neat poly(l-lactide-co-caprolactone) (PLCL) samples have both higher elongation and strength values than neat and blended scaffolds, with some exceptions. The blended specimens comprising a combination of PCL and PLA, with blending ratios of 80/20 and 70/30, exhibited the most elevated burst pressures. Conversely, the PLCL scaffolds demonstrated superior compliance levels. These findings suggest that the blending approach and fiber orientation offer enhanced burst strength, while copolymer utilization in PLCL scaffolds without fiber alignment enhances their compliance properties. Thus, it is evident that using a copolymer instead of blending PCL and PLA and combining the PLCL layer with PCL and PLA monolayers in bilayer vascular graft design is promising in terms of mechanical and biological properties.

Toward a mechanically biocompatible intervertebral disc: Engineering of combined biomimetic annulus fibrosus and nucleus pulposus analogs

Intervertebral disc (IVD) degeneration and accompanying lower back pain impose global medical and societal challenges, affecting over 600 million people worldwide. The IVD complex fibrocartilaginous structure is responsible for the spine biomechanical function. The nucleus pulposus (NP), composed of swellable glycosaminoglycan (GAG), transfers compressive loads to the surrounding fiber-reinforced annulus fibrosus (AF) lamellae, which stretches under tension. Together, these substructures allow the IVD to withstand extremely high and complex loads. Key to mimic the complete disc must consider the properties of its substructures. This study presents three novel substructures-a biomimetic silk-reinforced composite lamella for the AF, a GAG analog for the NP, and a novel biomimetic combined AF-NP construct. The biomimetic AF demonstrates nonlinear, hyperelastic, and anisotropic behavior similar to the native human AF, while the NP analog demonstrates mechanical behavior similar to the human NP. The synergized biomimetic AF-NP demonstrates similar behavior to the unconfined NP, with significantly increased deformations indicating improved performance. Validation of the AF-NP construct mechanics using a finite element model yields results compatible with native human IVD under various physiological loadings. The ability of our AF-NP construct to mimic the native IVD offers a revolutionary concept for the potential development of a fully functional IVD.

Adipose-Derived Stem Cells in Reinforced Collagen Gel: A Comparison between Two Approaches to Differentiation towards Smooth Muscle Cells

Scaffolds made of degradable polymers, such as collagen, polyesters or polysaccharides, are promising matrices for fabrication of bioartificial vascular grafts or patches. In this study, collagen isolated from porcine skin was processed into a gel, reinforced with collagen particles and with incorporated adipose tissue-derived stem cells (ASCs). The cell-material constructs were then incubated in a DMEM medium with 2% of FS (DMEM_part), with added polyvinylalcohol nanofibers (PVA_part sample), and for ASCs differentiation towards smooth muscle cells (SMCs), the medium was supplemented either with human platelet lysate released from PVA nanofibers (PVA_PL_part) or with TGF-β1 + BMP-4 (TGF + BMP_part). The constructs were further endothelialised with human umbilical vein endothelial cells (ECs). The immunofluorescence staining of alpha-actin and calponin, and von Willebrand factor, was performed. The proteins involved in cell differentiation, the extracellular matrix (ECM) proteins, and ECM remodelling proteins were evaluated by mass spectrometry on day 12 of culture. Mechanical properties of the gels with ASCs were measured via an unconfined compression test on day 5. Gels evinced limited planar shrinkage, but it was higher in endothelialised TGF + BMP_part gel. Both PVA_PL_part samples and TGF + BMP_part samples supported ASC growth and differentiation towards SMCs, but only PVA_PL_part supported homogeneous endothelialisation. Young modulus of elasticity increased in all samples compared to day 0, and PVA_PL_part gel evinced a slightly higher ratio of elastic energy. The results suggest that PVA_PL_part collagen construct has the highest potential to remodel into a functional vascular wall.

Fabrication of mechanical skeleton of small-diameter vascular grafts via rolling on water surface

Mimicking the multilayered structure of blood vessels and constructing a porous inner surface are two effective approaches to achieve mechanical matching and rapid endothelialization to reduce occlusion in small-diameter vascular grafts. However, the fabrication processes are complex and time consuming, thus complicating the fabrication of personalized vascular grafts. A simple and versatile strategy is proposed to prepare the skeleton of vascular grafts by rolling self-adhesive polymer films. These polymer films are directly fabricated by dropping a polymer solution on a water surface. For the tubes, the length and wall thickness are controlled by the rolling number and position of each film, whereas the structure and properties are tailored by regulating the solution composition. Double-layer vascular grafts (DLVGs) with microporous inner layers and impermeable outer layers are constructed; a microporous layer is formed by introducing a hydrophilic polymer into a polyurethane (PU) solution. DLVGs exhibit a J-shaped stress-strain deformation profile and compliance comparable to that of coronary arteries, sufficient suture retention strength and burst pressure, suitable hemocompatibility, significant adhesion, and proliferation of human umbilical vein endothelial cells. Freshly prepared PU tubes exhibit good cytocompatibility. Thus, this strategy demonstrates potential for rapid construction of small-diameter vascular grafts for individual customization.

The mechanical behavior of silk-fibroin reinforced alginate hydrogel biocomposites - Toward functional tissue biomimetics

Soft tissues are constructed as fiber-reinforced composites consisting of structural mechanisms and unique mechanical behavior. Biomimetics of their mechanical behavior is currently a significant bioengineering challenge, emphasizing the need to replicate structural and mechanical mechanisms into novel biocomposite designs. Here we present a novel silk-based biocomposite laminate constructed from long natural silk and fibroin fibers embedded in an alginate hydrogel matrix. Controlling the mechanical features of these laminates were studied for different fiber volume fractions (VF) and orientations using unidirectional tensile tests. Three material systems were investigated having different fiber orientations: longitudinal (0°), transverse (90°), and cross-plied (0/90°). The general behavior of the biocomposite laminates was anisotropic hyperelastic with large deformations. Longitudinal fibroin laminates have shown a tensile modulus of 178.55 ± 14.46 MPa and tensile strength of 18.47 ± 2.01 MPa for 0.48 VF. With similar VF, cross-plied fibroin laminates demonstrated structural shielding ability, having a tensile modulus and tensile strength of 101.73 ± 8.04 MPa and 8.29 ± 1.63 MPa for only a third of the VF directed in the stretching direction. The stress-strain behavior was in a similar range to highly stiff native human soft tissues such as ligament and meniscus. These findings demonstrate the potential of the fibroin fiber-reinforced biocomposites to mimic the mechanics of tissues with a quantitatively controlled amount of fibers and designed spatial arrangement. This can lead to new solutions for the repair and replacement of damaged functional and highly stiff soft tissues.

Hydrogel-complexed small-diameter vascular graft loaded with tissue-specific vascular extracellular matrix components used for tissue engineering

Tissue engineering is thought to the most promising strategy to develop successful small diameter vascular grafts (SDVG) to meet clinical demand. The introduction of natural substances into the SDVG made from synthetic biomaterials can improve the biocompatibility to promote the regeneration of SDVG in vivo. Due to that natural materials from different sources may have property deviation, it is vital to determine the source of natural materials to optimize SDVG fabrication for tissue engineering applications. In this study, bioactive SDVGs were prepared via coating of heparin-modified poly-(ε-caprolactone) scaffolds with a precursor solution containing vascular extracellular matrix (VECM) components and subsequent in situ gelation. The mechanical properties, degradation behaviors, and morphologies of the SDVGs were thoroughly characterized and evaluated. Cell experiments demonstrated the in vitro tissue specificity of the VECM that could promote the proliferation of endothelial cells better than skin-derived collagen. Furthermore, three types of SDVGs, SDVGs with blank hydrogel, SDVGs with skin-derived collagen, and SDVGs with vascular extracellular matrix (VECM-SDVGs), were implanted into the abdominal aorta of rats for one month. The explanted SDVGs were then comprehensively evaluated using hematoxylin and eosin, Masson, von Kossa staining, and immunohistochemical staining for CD31, α-SMA, and MHC. The results showed that the VECM-SDVGs showed the best endothelium regeneration, appropriate intima regeneration, and no calcification, indicating the in vivo specificity of the fabricated VECM-SDVGs. Thus, long-term implantation of VECM-SDVGs was performed. The results showed that a complete endothelial layer formed after 6 months of implantation, and the amount of contractile SMCs in the regenerative smooth muscle layer approached the amount of native aorta at the 12th month. Consequently, relying on vascular tissue specificity, VECM-SDVGs can modulate the regenerative behavior of the implanted SDVGs in vivo to achieve satisfactory vascular regeneration both in short- and long-term implantation.

Review of Polymeric Biomimetic Small-Diameter Vascular Grafts to Tackle Intimal Hyperplasia

Small-diameter artificial vascular grafts (SDAVG) are used to bypass blood flow in arterial occlusive diseases such as coronary heart or peripheral arterial disease. However, SDAVGs are plagued by restenosis after a short while due to thrombosis and the thickening of the neointimal wall known as intimal hyperplasia (IH). The specific causes of IH have not yet been deduced; however, thrombosis formation due to bioincompatibility as well as a mismatch between the biomechanical properties of the SDAVG and the native artery has been attributed to its initiation. The main challenges that have been faced in fabricating SDAVGs are facilitating rapid re-endothelialization of the luminal surface of the SDAVG and replicating the complex viscoelastic behavior of the arteries. Recent strategies to combat IH formation have been mostly based on imitating the natural structure and function of the native artery (biomimicry). Thus, most recently, developed grafts contain a multilayered structure with a designated function for each layer. This paper reviews the current polymeric, biomimetic SDAVGs in preventing the formation of IH. The materials used in fabrication, challenges, and strategies employed to tackle IH are summarized and discussed, and we focus on the multilayered structure of current SDAVGs. Additionally, the future aspects in this area are pointed out for researchers to consider in their endeavor.

Serum miR-96-5p is a novel and non-invasive marker of acute myocardial infarction associated with coronary artery disease

Acute myocardial infarction (AMI) is a severe cardiovascular disease. AMI associated with coronary artery disease (AMI-CAD) is a subtype of AMI, composed of AMI patients caused by CAD. This study aimed to evaluate the diagnostic value of miR-96-5p in AMI induced by coronary artery disease. Expression of miR-96-5p and BCL2L13 was evaluated by serum samples and cells utilizing Western blot and RT-qPCR assays. The diagnostic value of miR-96-5p in AMI-CAD was analyzed with a receiver operating characteristic (ROC) curves. The correlation between miR-96-5p and BCL2L13 was examined by Spearman's correlation analysis. The level of oxidative stress and apoptosis were estimated via relative commercial kit, flow cytometry apoptosis assay and TUNEL staining assay. Our study discovered that miR-96-5p was down-regulated while BCL2L13 was up-regulated in patients with AMI-CAD. miR-96-5p was a potential diagnostic parameter, which may help distinguish AMI-CAD patients from healthy controls. In vitro experiments, miR-96-5p expression was down regulated while BCL2L13 was up-regulated in hypoxic cardiomyocytes. After confirming the targeted link of miR-96-5p to BCL2L13 using luciferase reporter and RNA pull down assays, we discovered that miR-96-5p overexpression may restore oxidative stress and cell apoptosis induced by hypoxia treatment in H9c2 cells; meanwhile, co-transfection with BCL2L13 overexpressing plasmid might partly countervail the ameliorative effects of miR-96-5p on oxidative stress and apoptosis. Collectively, miR-96-5p may function as a potential diagnostic biomarker for AMI-CAD patients, and the up-regulation of miR-96-5p would ameliorate AMI-associated cardiomyocytes injury by targeting BCL2L13, hence contributing to the clinical treatment of AMI-CAD.

Bioengineering artificial blood vessels from natural materials

Bioengineering an effective, small diameter (<6 mm) artificial vascular graft for use in bypass surgery when autologous grafts are unavailable remains a persistent challenge. Commercially available grafts are typically made from plastics, which have high strength but lack elasticity and present a foreign surface that triggers undesirable biological responses. Tissue engineered grafts, leveraging decellularized animal vessels or derived de novo from long-term cell culture, have dominated recent research, but failed to meet clinical expectations. More effective constructs that are readily translatable are urgently needed. Recent advances in natural materials have made the production of robust acellular conduits feasible and their use increasingly attractive. Here, we identify a subset of natural materials with potential to generate durable, small diameter vascular grafts.