Improved endothelialization of titanium vascular implants by extracellular matrix secreted from endothelial cells

Physico-mechanical and biological evaluation of heparin/VEGF-loaded electrospun polycaprolactone/decellularized rat aorta extracellular matrix for small-diameter vascular grafts

Although the continuous development of small-diameter vascular grafts (SDVGs) (D < 5 mm) continues, most vascular grafts are made from synthetic polymers, which lead to serious complications from arteriosclerosis, thrombosis, and vascular ischemia. Here, to address these shortcomings, we combine synthetic polymers with natural decellularized small-diameter vessels and loaded with growth factor. We fabricated vascular grafts by electrospinning polycaprolactone (PCL) to decellularized rat aorta matrix (ECM) followed by heparin and vascular endothelial growth factor (VEGF) loading. In- vitro studies showed that PCL/ECM/VEGF vascular grafts, showed excellent hemocompatibility and biocompatibility properties. The vascular grafts implanted into the rat aorta revealed that the PCL/ECM/VEGF grafts promotes endothelial cells and smooth-muscle cells infiltration with a rate of FLK-1, ICAM1, and a-SMA distribution higher than that of the PCL and PCL/ECM vascular grafts at 2 weeks and 4 weeks after implantation. The PCL/ECM/VEGF vascular graft should be considered for potential small-diameter vascular grafts in clinical fields.

Tailoring ZE21B Alloy with Nature-Inspired Extracellular Matrix Secreted by Micro-Patterned Smooth Muscle Cells and Endothelial Cells to Promote Surface Biocompatibility

Delayed surface endothelialization is a bottleneck that restricts the further application of cardiovascular stents. It has been reported that the nature-inspired extracellular matrix (ECM) secreted by the hyaluronic acid (HA) micro-patterned smooth muscle cells (SMC) and endothelial cells (EC) can significantly promote surface endothelialization. However, this ECM coating obtained by decellularized method (dECM) is difficult to obtain directly on the surface of degradable magnesium (Mg) alloy. In this study, the method of obtaining bionic dECM by micro-patterning SMC/EC was further improved, and the nature-inspired ECM was prepared onto the Mg-Zn-Y-Nd (ZE21B) alloy surface by self-assembly. The results showed that the ECM coating not only improved surface endothelialization of ZE21B alloy, but also presented better blood compatibility, anti-hyperplasia, and anti-inflammation functions. The innovation and significance of the study is to overcome the disadvantage of traditional dECM coating and further expand the application of dECM coating to the surface of degradable materials and materials with different shapes.

Surface modification of polytetrafluoroethylene (PTFE) with a heparin-immobilized extracellular matrix (ECM) coating for small-diameter vascular grafts applications

Intimal hyperplasia, thrombosis formation, and delayed endothelium regeneration are the main causes that restrict the clinical applications of PTFE small-diameter vascular grafts (inner diameter < 6 mm). An ideal strategy to solve such problems is to facilitate in situ endothelialization. Since the natural vascular endothelium adheres onto the basement membrane, which is a specialized form of extracellular matrix (ECM) secreted by endothelial cells (ECs) and smooth muscle cells (SMCs), functionalizing PTFE with an ECM coating was proposed. However, besides ECs, the ECM-modified PTFE improved SMC growth as well, thereby increasing the risk of intimal hyperplasia. In the present study, heparin was immobilized on the ECM coating at different densities (4.89 ± 1.02 μg/cm2, 7.24 ± 1.56 μg/cm2, 15.63 ± 2.45 μg/cm2, and 26.59 ± 3.48 μg/cm2), aiming to develop a bio-favorable environment that possessed excellent hemocompatibility and selectively inhibited SMC growth while promoting endothelialization. The results indicated that a low heparin density (4.89 ± 1.02 μg/cm2) was not enough to restrict platelet adhesion, whereas a high heparin density (26.59 ± 3.48 μg/cm2) resulted in decreased EC growth and enhanced SMC proliferation. Therefore, a heparin density at 7.24 ± 1.56 μg/cm2 was the optimal level in terms of antithrombogenicity, endothelialization, and SMC inhibition. Collectively, this study proposed a heparin-immobilized ECM coating to modify PTFE, offering a promising means to functionalize biomaterials for developing small-diameter vascular grafts.

Novel Copper Nanoparticles Intercalated Polyurethane Heparin/Poly-L-Lysine Chelates Coated Stents: Viability Study for Coronary Vascular Cells and Aneurysms Treatments

Continuous delayed endothelium regeneration and continues thrombosis development designate a task for coronary artery stent rehabilitation. To progress the direct vascular cell behavior, aneurysms treatments and compatibility of cardiovascular implants novel copper intercalated polyurethane heparin/poly-L-lysine chelates treated stent has established in this report. The functional group modifications, structural characteristics, and stability of the chelates have investigated for polyurethane heparin: poly-L-lysine, copper intercalated polyurethane heparin/poly-L-lysine coated stents. The FTIR results showed the copper intercalation at 446 cmr and the Cu 2s peak at 932 eV from XPS also indicated that the successful coating of copper, polyurethane heparin, poly-L-lysine. The relative surface geomorphology of the chelates displayed the uniform Cu coating consisting of multilayer poly-L-lysine on the substrate. The stability and biocompatibility studies indicated the significantly enhanced performance with clot the APTT and TT periods as clotting and cell proliferation assessments. This type of composite proposes a stage on a stent external area for discerning track of vascular cell performance and aneurysms treatments with low side effects.

Bioactive and mechanically stable hydroxyapatite patterning for rapid endothelialization of artificial vascular graft

Polymeric vascular grafts have been widely used in the vascular regeneration field because of their ease of application. However, synthetic polymer grafts have the severe problem of low biocompatibility, which may cause delayed endothelialization and hyperplasia. In this study, we fabricated a linear hydroxyapatite (HA) pattern on a silicon wafer and then transferred the pattern to a poly(L-lactic)-acid (PLLA) film for use as a tubular vascular graft. The HA pattern with its characteristic needle-like shape was successfully embedded into the PLLA. The HA-patterned PLLA film exhibited superior mechanical stability compared with that of a HA-coated PLLA film under bending, elongation, and in vitro circulation conditions, suggesting its suitability for use as a tubular vascular graft. In addition, the HA pattern guided rapid endothelialization by promoting proliferation of endothelial cells and their migration along the pattern. The hemocompatibility of the HA-patterned PLLA was also confirmed, with substantially fewer platelets adhered on its surface. Overall, in addition to good mechanical stability, the HA-patterned PLLA exhibited enhanced biocompatibility and hemocompatibility compared with pure PLLA.

Nature-inspired extracellular matrix coating produced by micro-patterned smooth muscle and endothelial cells endows cardiovascular materials with better biocompatibility

Functionalizing cardiovascular biomaterials with an extracellular matrix (ECM) via in vitro decellularization has been applied as an effective method to improve the biocompatibility of implants.

Notoginsenoside Fc Accelerates Reendothelialization following Vascular Injury in Diabetic Rats by Promoting Endothelial Cell Autophagy

Interventional therapies, such as percutaneous transluminal angioplasty and endovascular stent implantation, are used widely for the treatment of diabetic peripheral vascular complications. Reendothelialization is an essential process in vascular injury following interventional therapy, and hyperglycemia in diabetes mellitus (DM) plays an important role in damaging endothelial layer integrity, leading to the retardance of reendothelialization and excessive neointimal formation. Notoginsenoside Fc (Fc), a novel saponin isolated from Panax notoginseng, effectively counteracts platelet aggregation. Nevertheless, the potential effects and molecular mechanisms of Fc on reendothelialization have yet to be explored. In this study, we present novel findings that show the benefit of Fc in accelerating reendothelialization and alleviating excessive neointimal formation following carotid artery injury in diabetic Sprague-Dawley rats in vivo. Simultaneously, the decreased autophagy of the injured carotid artery in diabetic rats was restored by Fc treatment. Our in vitro results also demonstrated that Fc promoted endothelial cell proliferation and migration under high-glucose treatment by increasing autophagy. In summary, this study supported the notion that Fc could accelerate reendothelialization following vascular injury in diabetic rats by promoting autophagy, suggesting that Fc may exert therapeutic benefits for early endothelial injury and restenosis following intervention in diabetes-associated vascular diseases.

Surface Modification with ECM-Inspired SDF-1α/Laminin-Loaded Nanocoating for Vascular Wound Healing

Surface biomimetic modification with extra-cellular matrix (ECM)-derived biomolecules is an emerging potential method of accelerating the healing of vascular stent lesions. However, insufficient capacity of the constructed biofunctional layer in maintaining its long-term efficiency and preventing thrombus and neointimal hyperplasia continue to be major limitations in clinical application. On the basis of the structure and function of ECM, in this study, we constructed a novel stromal cell-derived factor-1α (SDF-1α)/laminin-loaded nanocoating on the 316L stainless steel (SS) surface to provide improved function in modulation of vascular remodeling. The modified surface was found to control delivery of biomolecules and exhibit promising potential to provide stage-adjusted treatment after injury. An in vitro biocompatibility study suggested that the constructed layer may effectively prevent thrombosis formation by inhibiting platelet adhesion and activation, while accelerating endothelium regeneration by inducing endothelial cell (EC) migration and endothelial progenitor cell (EPC) aggregation. An in vivo animal test further demonstrated that the nanocoating may prevent thrombus and neointimal hyperplasia after implantation for 3 months. Therefore, the ECM-inspired nanocoating described in this study is a promising novel approach for vascular stent surface modification.

Effect of micropatterned TiO2 nanotubes thin film on the deposition of endothelial extracellular matrix: For the purpose of enhancing surface biocompatibility

The vascular endothelial cells (EC) extracellular matrix (ECM) on the biomaterial surface can significantly improve the blood compatibility and cell compatibility of the cardiovascular materials. In the present study, two types of micropatterned TiO2 nanotubes surfaces (gronano and toponano) were fabricated on the titanium surface by photolithography and two-step anodizing technology, for the purpose of enhancing the deposition and loading ability of the EC ECM. The effect of the micropatterned nanotubes on EC ECM deposition and loading was investigated by qualitative and quantitative characterizations of type IV collagen (CoIV). The blood compatibility of the deposited ECM layers was evaluated by platelet adhesion and activation tests, and the endothelialization function of the deposited ECM layers was investigated by EC culture for 3 days. As a result, there was more CoIV on the toponano surface compared with the control. Meanwhile, the ECM loaded toponano (ECM/toponano) possessed better blood compatibility and better endothelialization than the control. This ECM loaded micro-/nanocomposite thin film was anticipated for the potential application of the surface modification of cardiovascular devices based on its excellent biocompatibility.

Heart valve tissue engineering: how far is the bedside from the bench?

Heart disease, including valve pathologies, is the leading cause of death worldwide. Despite the progress made thanks to improving transplantation techniques, a perfect valve substitute has not yet been developed: once a diseased valve is replaced with current technologies, the newly implanted valve still needs to be changed some time in the future. This situation is particularly dramatic in the case of children and young adults, because of the necessity of valve growth during the patient's life. Our review focuses on the current status of heart valve (HV) therapy and the challenges that must be solved in the development of new approaches based on tissue engineering. Scientists and physicians have proposed tissue-engineered heart valves (TEHVs) as the most promising solution for HV replacement, especially given that they can help to avoid thrombosis, structural deterioration and xenoinfections. Lastly, TEHVs might also serve as a model for studying human valve development and pathologies.

Collagen-mimetic hydrogels promote human endothelial cell adhesion, migration and phenotypic maturation

This work evaluates the response of human aortic endothelial cells (HAECs) to thromboresistant collagen-mimetic hydrogel coatings toward improving the biocompatibility of existing "off-the-shelf" small-caliber vascular grafts. Specifically, bioactive hydrogels - previously shown to support α₁/α₂ integrin-mediated cell adhesion but to resist platelet activation - were fabricated by combining poly(ethylene glycol) (PEG) with a 120 kDa, triple-helical collagen-mimetic protein(Scl2-2) containing the GFPGER adhesion sequence. Analysis of HAECs seeded onto the resulting PEG-Scl2-2 hydrogels demonstrated that HAEC adhesion increased with increasing Scl2-2 concentration, while HAEC migration rate decreased over this same concentration range. In addition, evaluation of HAEC phenotype at confluence indicated significant differences in the gene expression of NOS3, thrombomodulin, and E-selectin on the PEG-Scl2-2 hydrogels relative to PEG-collagen controls. At the protein level, however, only NOS3 was significantly different between the PEG-Scl2-2 and PEG-collagen surfaces. Furthermore, PECAM-1 and VE-cadherin expression on PEG-Scl2-2 hydrogels versus PEG-collagen controls could not be distinguished at either the gene or protein level. Cumulatively, these data indicate the PEG-Scl2-2 hydrogels warrant further investigation as "off-the-shelf" graft coatings. In future studies, the Scl2-2 protein can potentially be modified to include additional extracellular matrix or cytokine binding sites to further improve endothelial cell responses.

Effect of tissue specificity on the performance of extracellular matrix in improving endothelialization of cardiovascular implants

Natural extracellular matrix (ECM) deposited in situ by cultured endothelial cells (ECs) has been proven effective in accelerating endothelialization of titanium (Ti) cardiovascular implants (CVIs) in our previous studies. In this study, the ECM deposited by smooth muscle cells (SMCs) was used in comparison to investigate the effects of tissue specificity of the ECM on the ability to accelerate endothelialization of CVIs. The results demonstrated that the ECM deposited by ECs and SMCs (EC-ECM, SMC-ECM, respectively) differed considerably in components and fibril morphology. Surface modification of Ti CVIs with both types of natural ECM was effective in improving their in vitro hemocompatibility and cytocompatibility simultaneously. However, the endothelialization of ECM-modified Ti CVIs in a canine model demonstrated a high tissue specificity of the ECM. Although the ECM deposited by SMCs (SMC-ECM) induced fewer platelet adhesion and sustained better growth and viability of ECs in vitro, its performance in accelerating in vivo endothelialization of Ti CVIs was extremely poor. In contrast, the ECM deposited by ECs (EC-ECM) led to complete endothelium formation in vivo.

Biomimetic modification of metallic cardiovascular biomaterials: from function mimicking to endothelialization in vivo

Biosystem-surface interactions play an important role in various biological events and determine the ultimate functionality of implanted devices. Endothelialization or mimicking of endothelium on the surface of cardiovascular materials is a promising way to solve the problems of material-induced thrombosis and restenosis. Meanwhile, a multifunctional surface design is needed as antithrombotic properties should be considered in the period when the implants are not yet completely endothelialized. In this article, we summarize some successful approaches used in our laboratory for constructing multifunctional endothelium-like surfaces on metallic cardiovascular biomaterials through chemical modification of the surface or by the introduction of specific biological molecules to induce self-endothelialization in vivo. Some directions on future research in these areas are also presented.

A novel in vitro model for preclinical testing of the hemocompatibility of intravascular stents according to ISO 10993-4

Subacute stent thrombosis, caused by undesired interactions between blood and the stent surface, is a major concern in the first few weeks following coronary artery stent implantation. The aim of this study was to establish a novel in vitro model for hemocompatibility testing of coronary artery stents according to ISO 10993-4. The model consists of a modified Chandler-Loop design with closed heparin-coated PVC Loops and a thermostated water bath. The tests were performed with anticoagulated human whole blood. After incubation in the loop, blood was analyzed for coagulation and inflammatory activation markers (TAT, β-TG, sP-selectin, SC5b-9 and PMN-elastase). Three different stent types with varying thrombogenicity were tested; statistically significant differences were found between the three stent types in measures of coagulation and platelet activation. The new Chandler-Loop model can be used as an alternative to animal and current in vitro models, especially for the determination of early events after stent implantation.