Different complex surfaces of polyethyleneglycol (PEG) and REDV ligand to enhance the endothelial cells selectivity over smooth muscle cells

Biomimetic Approaches in Scaffold-Based Blood Vessel Tissue Engineering

Cardiovascular diseases remain a leading cause of mortality globally, with atherosclerosis representing a significant pathological means, often leading to myocardial infarction. Coronary artery bypass surgery, a common procedure used to treat coronary artery disease, presents challenges due to the limited autologous tissue availability or the shortcomings of synthetic grafts. Consequently, there is a growing interest in tissue engineering approaches to develop vascular substitutes. This review offers an updated picture of the state of the art in vascular tissue engineering, emphasising the design of scaffolds and dynamic culture conditions following a biomimetic approach. By emulating native vessel properties and, in particular, by mimicking the three-layer structure of the vascular wall, tissue-engineered grafts can improve long-term patency and clinical outcomes. Furthermore, ongoing research focuses on enhancing biomimicry through innovative scaffold materials, surface functionalisation strategies, and the use of bioreactors mimicking the physiological microenvironment. Through a multidisciplinary lens, this review provides insight into the latest advancements and future directions of vascular tissue engineering, with particular reference to employing biomimicry to create systems capable of reproducing the structure-function relationships present in the arterial wall. Despite the existence of a gap between benchtop innovation and clinical translation, it appears that the biomimetic technologies developed to date demonstrate promising results in preventing vascular occlusion due to blood clotting under laboratory conditions and in preclinical studies. Therefore, a multifaceted biomimetic approach could represent a winning strategy to ensure the translation of vascular tissue engineering into clinical practice.

Surface Modification of PEEKs with Cyclic Peptides to Support Endothelialization and Antithrombogenicity

Synthetic polymers are often utilized in the creation of vascular devices, and need to possess specific qualities to prevent thrombosis. Traditional strategies for this include surface modification of vascular devices through covalent attachment of substrates such as heparin, antiplatelet agents, thrombolytic agents, or hydrophilic polymers. One promising prosthetic material is polyether ether ketone (PEEK), which is utilized in various FDA-approved medical devices, including vascular and endovascular prostheses. We hypothesized that surface modification of biologically inert PEEK can help improve its endothelial cell affinity and reduce its thrombogenic potential. To evaluate this, we developed an effective surface-modification approach with unique cyclic peptides, such as CCHGGVRLYC and CCREDVC. We treated the PEEK surface with ammonia plasma, which introduced amine groups onto the PEEK surface. Subsequently, we were able to conjugate these peptides to the plasma-modified PEEKs. We observed that cyclic CCHGGVRLYC conjugated on prosthetic PEEK not only supported endothelialization, but minimized platelet adhesion and activation. This technology can be potentially applied for in vivo vascular and endovascular protheses to enhance their utility and patency.

Covalently Grafted Peptides to Decellularized Pericardium: Modulation of Surface Density

The covalent functionalization of synthetic peptides allows the modification of different biomaterials (metallic, polymeric, and ceramic), which are enriched with biologically active sequences to guide cell behavior. Recently, this strategy has also been applied to decellularized biological matrices. In this study, the covalent anchorage of a synthetic peptide (REDV) to a pericardial matrix decellularized via Schiff base is realized starting from concentrated peptide solutions (10^-4 M and 10^-3 M). The use of a labeled peptide demonstrated that as the concentration of the working solution increased, the surface density of the anchored peptide increased as well. These data are essential to pinpointing the concentration window in which the peptide promotes the desired cellular activity. The matrices were extensively characterized by Water Contact Angle (WCA) analysis, Differential Scanning Calorimetry (DSC) analysis, geometric feature evaluation, biomechanical tests, and preliminary in vitro bioassays.

Multifunctional nanoparticle-VEGF modification for tissue-engineered vascular graft to promote sustained anti-thrombosis and rapid endothelialization

Purpose: The absence of a complete endothelial cell layer is a well-recognized reason leading to small-diameter tissue-engineered vascular graft failure. Here we reported a multifunctional system consisting of chitosan (CS), Arg-Glu-Asp-Val (REDV) peptide, heparin, and vascular endothelial growth factor (VEGF) to achieve sustained anti-thrombosis and rapid endothelialization for decellularized and photo-oxidized bovine internal mammary arteries (DP-BIMA). Methods: CS-REDV copolymers were synthesized via a transglutaminase (TGase) catalyzed reaction. CS_-REDV-Hep nanoparticles were formed by electrostatic self-assembly and loaded on the DP-BIMA. The quantification of released heparin and vascular endothelial growth factor was detected. Hemolysis rate, platelets adhesion, endothelial cell (EC) adhesion and proliferation, and MTT assay were performed in vitro. The grafts were then tested in a rabbit abdominal aorta interposition model for 3 months. The patency rates were calculated and the ECs regeneration was investigated by immunofluorescence staining of CD31, CD144, and eNOS antibodies. Results: The nanoparticle-VEGF system (particle size: 61.8 ± 18.3 nm, zeta-potential: +13.2 mV, PDI: .108) showed a sustained and controlled release of heparin and VEGF for as long as 1 month and exhibited good biocompatibility, a lower affinity for platelets, and a higher affinity for ECs in vitro. The nanoparticle-VEGF immobilized BIMA achieved 100% and 83.3% patency in a rabbit abdominal interposition model during 1 and 3 months, respectively, without any thrombogenicity and showed CD31, CD144, eNOS positive cell adhesion as early as 1 day. After 3 months, CD31, CD144, and eNOS positive cells covered almost the whole luminal surface of the grafts. Conclusion: The results demonstrated that the multifunctional nanoparticle-VEGF system can enhance the anti-thrombosis property and promote rapid endothelialization of small-diameter tissue-engineered vascular grafts. Utilizing nanoparticles to combine different kinds of biomolecules is an appropriate technology to improve the long-term patency of small-diameter tissue-engineered vascular grafts.

A Polymeric Strategy Empowering Vascular Cell Selectivity and Potential Application Superior to Extracellular Matrix Peptides

Endothelialization of vascular implants plays a vital role in maintaining the long-term vascular patency. In situ endothelialization and re-endothelialization is generally achieved by selectively promoting endothelial cell (EC) adhesion and, meanwhile, suppressing smooth muscle cell (SMC) adhesion. Currently, such EC versus SMC selectivity is achieved and extensively used in vascular-related biomaterials utilizing extracellular-matrix-derived EC-selective peptides, dominantly REDV and YIGSR. Nevertheless, the application of EC-selective peptides is limited due to their easy proteolysis, time-consuming synthesis, and expensiveness. To address these limitations, a polymeric strategy in designing and finding EC-selective biomaterials using amphiphilic β-peptide polymers by tuning serum protein adsorption is reported. The optimal β-peptide polymer displays EC versus SMC selectivity even superior to EC-selective REDV peptide regarding cell adhesion, proliferation, and migration of ECs versus SMCs. Study of the mechanism indicates that surface adsorption of bovine serum albumin, an abundant and anti-adhesive serum protein, plays a critical role in the ECs versus SMCs selectivity of β-peptide polymer. In addition, surface modification of the optimal β-peptide polymer effectively promotes the endothelialization of vascular implants and inhibits intimal hyperplasia. This study provides an alternative strategy in designing and finding EC-selective biomaterials, implying great potential in the vascular-related biomaterial study and application.

Recent advances in inhibiting atherosclerosis and restenosis: from pathogenic factors, therapeutic agents to nano-delivery strategies

Due to dominant atherosclerosis etiology, cardiovascular diseases (CVDs) remain the leading cause of morbidity and mortality worldwide. In clinical trials, advanced atherosclerotic plaques can be removed by angioplasty and vascular...

Recent strategies for improving hemocompatibility and endothelialization of cardiovascular devices and inhibition of intimal hyperplasia

Cardiovascular diseases have become one of the leading causes of mortality worldwide. Stents and artificial grafts have been used to treat cardiovascular diseases. Thrombosis and restenosis seriously impact clinical outcome...

A zwitterionic hydrogel coated titanium surface with high-efficiency endothelial cell selectivity for rapid re-endothelialization

Coronary stent implantation is an effective procedure for percutaneous coronary intervention treatment. However, its long-term safety and efficacy are still hindered by the in-stent restenosis and late thrombus formation. Herein, an anti-biofouling and endothelial cell selective zwitterionic hydrogel coating was developed to simultaneously enhance the nonspecific resistance and rapid re-endothelialization of the titanium surface. An endothelial cell selective peptide, REDV, could be simply conjugated on the zwitterionic carboxybetaine (CB) hydrogel to prepare the REDV/CB coating. It was found that the REDV/CB hydrogel layer maintained antifouling properties, which could inhibit the protein adsorption, bacterial adhesion, platelet activation and aggregation, and smooth muscle cell proliferation. More importantly, the co-culture study confirmed that the conjugated REVD peptide could specifically capture endothelial cells and promote their migration and proliferation, and simultaneously decrease the adhesion and proliferation of smooth muscle cells. Therefore, the antifouling and endothelial cell selective coating proposed in this work provides a promising strategy to develop an intravascular stent for promoted re-endothelialization and inhibited neointimal hyperplasia in clinical applications.

Local Delivery of Dual MicroRNAs in Trilayered Electrospun Grafts for Vascular Regeneration

Globally growing problems related to cardiovascular diseases lead to a considerable need for synthetic vascular grafts. For small-caliber vascular prosthesis, it remains essential to fulfill rapid endothelialization, inhibit intimal hyperplasia, and prevent calcification for keeping patency. To modulate vascular regeneration, herein, we developed a bioactive trilayered tissue-engineered vascular graft encapsulating both microRNA-126 and microRNA-145 in the fibrous inner and middle layers, respectively. In vitro cell activities demonstrated that the trilayered electrospun membranes had significant biological advantages in enhanced growth and intracellular nitric oxide production of vascular endothelial cells, modulation of phenotypes of vascular smooth muscle cells (SMCs), and restraint of calcium deposition through fast-releasing microRNA-126 and slow-releasing microRNA-145. Histological and immunofluorescent analyses of in vivo implantation in a rat abdominal aorta interposition model suggested that the dual-microRNA-loading trilayered electrospun graft exerted a positive effect on accelerating endothelialization, improving contractile SMC regeneration, and promoting normal extracellular matrix formation. Meanwhile, the local bioactivity of microRNA-126 and microRNA-145 in the trilayered vascular graft could regulate inflammation and depress calcification possibly by facilitating transformation of macrophages into the anti-inflammatory M2 phenotype. These findings indicated that the trilayered electrospun graft by local delivery of dual microRNAs could be possibly used as a bioactive substitute for replacement of artificial small-caliber blood vessels.

Combinatorial functionalization with bisurea-peptides and antifouling bisurea additives of a supramolecular elastomeric biomaterial

The bioactive additive toolbox to functionalize supramolecular elastomeric materials expands rapidly. Here we have set an explorative step toward screening of complex combinatorial functionalization with antifouling and three peptide-containing additives in a bisurea-based supramolecular system. Thorough investigation of surface properties of thin films with contact angle measurements, X-ray photoelectron spectroscopy and atomic force microscopy, was correlated to cell-adhesion of endothelial and smooth muscle cells to apprehend their respective predictive values for functional biomaterial development. Peptides were presented at the surface alone, and in combinatorial functionalization with the oligo(ethylene glycol)-based non-cell adhesive additive. The bisurea-RGD additive was cell-adhesive in all conditions, whereas the endothelial cell-specific bisurea-REDV showed limited bioactive properties in all chemical nano-environments. Also, aspecific functionality was observed for a bisurea-SDF1α peptide. These results emphasize that special care should be taken in changing the chemical nano-environment with peptide functionalization. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1725-1735.

Endothelialization of cardiovascular devices

Blood-contacting surfaces of cardiovascular devices are not biocompatible for creating an endothelial layer on them. Numerous research studies have mainly sought to modify these surfaces through physical, chemical and biological means to ease early endothelial cell (EC) adhesion, migration and proliferation, and eventually to build an endothelial layer on the surfaces. The first priority for surface modification is inhibition of protein adsorption that leads to inhibition of platelet adhesion to the device surfaces, which may favor EC adhesion. Surface modification through surface texturing, if applicable, can bring some hopeful outcomes in this regard. Surface modifications through chemical and/or biological means may play a significant role in easy endothelialization of cardiovascular devices and inhibit smooth muscle cell proliferation. Cellular engineering of cells relevant to endothelialization can boost the positive outcomes obtained through surface engineering. This review briefly summarizes recent developments and research in early endothelialization of cardiovascular devices. STATEMENT OF SIGNIFICANCE: Endothelialization of cardiovascular implants, including heart valves, vascular stents and vascular grafts is crucial to solve many problems in our health care system. Numerous research efforts have been made to improve endothelialization on the surfaces of cardiovascular implants, mainly through surface modifications in three ways - physically, chemically and biologically. This review is intended to highlight comprehensive research studies to date on surface modifications aiming for early endothelialization on the blood-contacting surfaces of cardiovascular implants. It also discusses future perspectives to help guide endothelialization strategies and inspire further innovations.

Effects of a Bioactive SPPEPS Peptide on Chondrogenic Differentiation of Mesenchymal Stem Cells

A synthetic 'chondroinductive' biomaterial that could induce chondrogenesis without the need for growth factors, extracellular matrix, or pre-seeded cells could revolutionize orthopedic regenerative medicine. The objective of the current study was thus to introduce a synthetic SPPEPS peptide and evaluate its ability to induce chondrogenic differentiation. In the current study, dissolving a synthetic chondroinductive peptide candidate (100 ng/mL SPPEPS) in the culture medium of rat bone marrow-derived mesenchymal stem cells (rBMSCs) elevated collagen type II gene expression compared to the negative control (no growth factor or peptide in the cell culture medium) after 3 days. In addition, proteomic analyses indicated similarities in pathways and protein profiles between the positive control (10 ng/mL TGF-β₃) and peptide group (100 ng/mL SPPEPS), affirming the potential of the peptide for chondroinductivity. Incorporating the SPPEPS peptide in combination with the RGD peptide in pentenoate-functionalized hyaluronic acid (PHA) hydrogels elevated the collagen type II gene expression of the rBMSCs cultured on top of the hydrogels compared to using either peptide alone. The evidence suggests that SPPEPS may be a chondroinductive peptide, which may be enhanced in combination with an adhesion peptide.

Surface modification of polyvinyl alcohol (PVA)/polyacrylamide (PAAm) hydrogels with polydopamine and REDV for improved applicability

Developing a small-diameter vascular graft with a satisfactory performance in terms of mechanical and biological properties remains a challenging issue because of comprehensive requirements from clinical applications. Polyvinyl alcohol (PVA)/polyacrylamide (PAAm) hydrogels exhibit many desirable characteristics for small-diameter vascular grafts because of their tunable mechanical properties, especially high compliance. However, poor cells adhesion hinders their application for endothelialization in situ. Therefore, in the present work, polydopamine (PDA) and tetrapeptide Arg-Glu-Asp-Val (REDV) were used to functionalize the hydrogels surface and improve cells adhesion. A series of characterizations were systematically conducted to examine the applicability of coated hydrogels to small-diameter vascular grafts. Results showed that bare and coated hydrogels have appropriate structural stability, and no significant differences in tensile properties could be found after being coated with PDA or PDA-REDV. The hydrophilicity of the hydrogels decreased with the coatings of PDA and especially PDA-REDV to improve protein adsorption, porcine iliac artery endothelial cells (PIECs) adhesion, viability, proliferation, and spreading on the hydrogels. Lower hemolysis percentages and higher blood clotting index values were attained for the hydrogels, suggesting their satisfactory hemocompatibility. Overall, the present work provided insights into the development of a novel hydrogel-based small-diameter vascular graft. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:117-127, 2020.

Target regulation of both VECs and VSMCs by dual-loading miRNA-126 and miRNA-145 in the bilayered electrospun membrane for small-diameter vascular regeneration

Clinical utility of small-diameter vascular grafts is still challenging in blood vessel regeneration owing to thrombosis and intimal hyperplasia. To cope with the issues, modulation of gene expression via microRNAs (miRNAs) could be a feasible approach by rational regulating physiological activities of both vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). Our previous studies demonstrated that individually loaded miRNA-126 (miR-126) or miRNA-145 (miR-145) in the electrospun membranes showed the tendency to promote vascular regeneration. In this work, the bilayered electrospun graft in 1.5-mm diameter was developed by emulsion electrospinning to dual-load miR-126 and miR-145 for target regulation of both VECs and VSMCs, respectively. Accelerated release of miR-126 was achieved by introducing poly(ethylene glycol) in the inner electrospun poly(ethylene glycol)-b-poly(l-lactide-co-caprolactone) ultrafine fibrous membrane, reaching 61.3 ± 1.2% of the cumulative release in the initial 10 days, whereas the outer electrospun poly(l-lactide-co-glycolide) membrane composed of microfibers fulfilled prolonged release of miR-145 for about 56 days. In vivo tests suggested that dual-loading with miR-126 and miR-145 in the bilayered electrospun membranes could modulate both VECs and VSMCs for rapid endothelialization and hyperplasia inhibition as well. It is reasonably expected that dual target-delivery of miR-126 and miR-145 in the electrospun vascular grafts has effective potential for small-diameter vascular regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 371-382, 2019.

Toward endothelialization via vascular endothelial growth factor immobilization on cell-repelling functional polyurethanes

We screened a family of nonspecific cell-repelling polyurethanes (PUs) whose backbones are attached with epoxy group-terminated polyethylene glycol (PEG) side chains. Water incubation of the PU films (with 9.2-31.1 wt % PEG) caused a surface enrichment of PEG chains where vascular endothelial growth factor (VEGF) was grafted by forming secondary amine linkages between VEGF molecules and the PEG spacer. These linkages are still ionizable similar to original primary amines in VEGF, thereby retaining the original charge distribution on VEGF macromolecules. This charge conservation together with PEG steric repulsion helped to preserve VEGF conformation and bioactivity. The PU substrates with suitable hard segments contents and VEGF surface densities can selectively induce endothelial cells (ECs) adhesion and proliferation toward endothelialization. Moreover, the PU substrates, even grafted with fibrinogen (Fg), cannot trigger platelet adhesion and deformation, suggesting an inactive conformation of the grafted Fg. Thus enough antithrombogenicity of the PU substrates could be expected before full endothelialization. These PU materials might be applied onto the lumens of vascular grafts, potentially stimulating luminal endothelialization in vivo. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 965-977, 2019.

Improving functional re-endothelialization of acellular liver scaffold using REDV cell-binding domain

Engineering of functional vascularized liver tissues holds great promise in addressing donor organ shortage for transplantation. Whole organ decellularization is a cell removal method that retains the native vascular structures of the organ such that it can be anastomosed with the recipient circulation after recellularization with healthy cells. However, a main hurdle to successful implantation of bioengineered organ is the inability to efficiently re-endothelialize the vasculature with a functional endothelium, resulting in blood clotting which is the primary cause of failure in early transplant studies. Here, we present an efficient approach for enhancing re-endothelialization of decellularized rat liver scaffolds by conjugating the REDV cell-binding domain to improve attachment of endothelial cells (EC) on vascular wall surfaces. In order to facilitate expression and purification of the peptide, REDV was fused with elastin-like peptide (ELP) that confers thermally triggered aggregation behavior to the fusion protein. After validating the adhesive properties of the REDV-ELP peptide, we covalently coupled REDV-ELP to the blood vasculature of decellularized rat livers and seeded EC using perfusion of the portal vein. We showed that REDV-ELP increased cell attachment, spreading and proliferation of EC within the construct resulting in uniform endothelial lining of the scaffold vasculature. We further observed that REDV-ELP conjugation dramatically reduced platelet adhesion and activation. Altogether, our results demonstrate that this method allowed functional re-endothelialization of liver scaffold and show great potential toward the generation of functional bioengineered liver for long-term transplantation.

STATEMENT OF SIGNIFICANCE

There is a critical need for novel organ replacement therapies as the grafts for transplantation fall short of demand. Recent advances in tissue engineering, through the use of decellularized scaffolds, have opened the possibility that engineered grafts could be used as substitutes for donor livers. However, successful implantation has been challenged by the inability to create a functional vasculature. Our research study reports a new strategy to increase efficiency of endothelialization by increasing the affinity of the vascular matrix for endothelial cells. We functionalized decellularized liver scaffold using elastin-like peptides grafted with REDV cell binding domain. We showed that REDV-ELP conjugation improve endothelial cell attachment and proliferation within the scaffold, demonstrating the feasibility of re-endothelializing a whole liver vasculature using our technique.

Design and Applications of Cell-Selective Surfaces and Interfaces

Tissue regeneration involves versatile types of cells. The accumulation and disorganized behaviors of undesired cells impair the natural healing process, leading to uncontrolled immune response, restenosis, and/or fibrosis. Cell-selective surfaces and interfaces can have specific and positive effects on desired types of cells, allowing tissue regeneration with restored structures and functions. This review outlines the importance of surfaces and interfaces of biomaterials with cell-selective properties. The chemical and biological cues including peptides, antibodies, and other molecules, physical cues such as topography and elasticity, and physiological cues referring mainly to interactions between cells-cells and cell-chemokines or cytokines are effective modulators for achieving cell selectivity upon being applied into the design of biomaterials. Cell-selective biomaterials have also shown practical significance in tissue regeneration, in particular for endothelialization, nerve regeneration, capture of stem cells, and regeneration of tissues of multiple structures and functions.

Surface modification and endothelialization of polyurethane for vascular tissue engineering applications: a review

Cardiovascular implants, especially vascular grafts made of synthetic polymers, find wide clinical applications in the treatment of cardiovascular diseases. However, cases of failure still exist, notably caused by restenosis and thrombus formation. Aiming to solve these problems, various approaches to surface modification of synthetic vascular grafts have been used to improve both the hemocompatibility and long-term patency of artificial vascular grafts. Surface modification using hydrophilic molecules can enhance hemocompatibility, but this may limit the initial vascular endothelial cell adhesion. Therefore, the improvement of endothelialization on these grafts with specific peptides and biomolecules is now an exciting field of research. In this review, several techniques to improve surface modification and endothelialization on vascular grafts, mainly polyurethane (PU) grafts, are summarized, together with the recent development and evolution of the different strategies: from the use of PEG, zwitterions, and polysaccharides to peptides and other biomolecules and genes; from in vitro endothelialization to in vivo endothelialization; and from bio-inert and bio-active to bio-mimetic approaches.

Peptide-Functionalized Polyurethane Coatings Prepared via Grafting-To Strategy to Selectively Promote Endothelialization

Endothelialization, formation of endothelial cells (ECs) layer on cardiovascular implant surface, is considered an ideal approach to prevent restenosis (renarrowing of blood vessel mainly due to the accumulation of proliferated vascular smooth muscle cells, SMCs) and thrombosis. In this study, the possibility of using polyurethane (PU) as a coating platform for functionalization with peptide to enhance endothelialization on implants is explored. PUs are synthesized through metal-free organocatalytic polymerization followed by chemical conjugation with an EC-specific REDV peptide through thiol-ene reaction. Meanwhile, the free isocyanate groups of PU allow for covalent grafting of REDV-functionalized PU (PU/REDV) to silanize implant materials (nitinol and PET). PU/REDV coating with peptide grafting density of ≈2 nmol cm^-2 selectively accommodates primary human umbilical vein ECs (HUVECs) and retards spreading of primary human umbilical artery SMCs (HUASMCs). In addition, a layer of HUVECs is formed within 3 d on PU/REDV-coated surfaces, while proliferation of HUASMCs is inhibited. The selectivity is further confirmed by coculture of HUVECs and HUASMCs. Moreover, the PU/REDV-coated surfaces are less thrombogenic as evidenced by reduced number and activity of adhered platelets. Therefore, PU/REDV can be potentially used as a coating of cardiovascular implants to prevent restenosis and thrombosis by promoting endothelialization.

Regulation of macrophage polarization and promotion of endothelialization by NO generating and PEG-YIGSR modified vascular graft

As an effective clinic treatment for cardiovascular disease, vascular transplantation gains much acceptance recently. However, due to the acute thrombosis and intimal hyperplasia, long-term failure of synthetic grafts after implanted in small diameter blood vessel decelerates its commercial use. The continued acute inflammation and delayed endothelialization have been considered as fundamental reasons. To enhance the adhesion and organization of endothelial cells (ECs) and improve the vascular remodeling process, we have constructed a vascular graft based on electrospun polycaprolactone (PCL) matrix, on which organoselenium-immobilized polyethyleneimine (SePEI) for in situ nitric oxide (NO) generation and hyaluronic acid (HA) grafted with poly (ethylene glycol) (PEG) modified Tyr-Ile-Gly-Ser-Arg (YIGSR) for antifouling and EC adhesion were deposited through electrostatic layer-by-layer assembly. The in vitro results showed that SePEI deposited on the grafts could catalyze stable generation of NO. After in situ implantation in rats for 4 and 8weeks, the graft promoted the transformation of macrophages into an anti-inflammatory phenotype (M2), which helped endothelium remodeling. YIGSR on the outmost layer facilitated more rapid and organized EC adhesion compared to PCL and non-modified grafts. PEG polymer chain on the outmost layer mitigated nonspecific adsorption of undesirable blood components. In our study, we first demonstrated the regulation of macrophage polarization by an NO-generating vascular graft. The results indicated that the approach of anti-inflammatory macrophage polarization and enhanced endothelialization through NO generation and PEG-modified YIGSR in our study may provide a new perspective for the clinic application of cell-free small-diameter vascular grafts.

Multifunctional Gene Carriers with Enhanced Specific Penetration and Nucleus Accumulation to Promote Neovascularization of HUVECs in Vivo

Recently, gene therapy has attracted much attention, especially for the treatment of vascular disease. However, it is still challenging to develop the gene carriers with high biocompatibility as well as highly efficient gene delivery to overcome multiple barriers. Herein, a frequently used cell-penetrating peptide PKKKRKV (TAT) was selected as a functional sequence of the gene carrier with distinctive cell-penetrating ability. REDV peptide with selectively targeting function for endothelial cells (ECs) and nuclear localization signals (NLS) were integrated with this TAT peptide to obtain a highly efficient gene delivery system with ECs specificity and nucleus accumulation capacity. Besides, the glycine sequences with different repeat numbers were inserted into the above integrated peptide. These glycine sequences acted as a flexible spacer arm to exert the targeting, cell-penetrating, and nucleus accumulation functions of each functional peptide. Three tandem peptides REDV-G_m-TAT-G_m-NLS (m = 0, 1, and 4) complexed with pZNF580 plasmid to form gene complexes. The results of hemocompatibility and cytocompatibility indicated that these peptides and gene complexes were nontoxic and biocompatible. The internalization efficiency and mechanism of these gene complexes were investigated. The internalization efficiency was improved as the introduction of targeting REDV and glycine sequence, and the REDV-G₄-TAT-G₄-NLS/pZNF580 (TP-G4/pZNF580) complexes showed the highest cellular uptake among the gene complexes. The TP-G4/pZNF580 complexes also presented significantly higher internalization efficiency (∼1.36 times) in human umbilical vein endothelial cells (HUVECs) than human umbilical artery smooth muscle cells. TP-G4/pZNF580 complexes substantially promoted the expression of pZNF580 by confocal live cell imaging, gene delivery efficiency, and HUVECs migration assay. The in vitro and in vivo revascularization ability of transfected HUVECs was further enhanced obviously. In conclusion, these multifunctional REDV-G_m-TAT-G_m-NLS peptides offer a promising and efficacious delivery option for neovascularization to treat vascular diseases.

Multilayer Choline Phosphate Molecule Modified Surface with Enhanced Cell Adhesion but Resistance to Protein Adsorption

Choline phosphate (CP), which is a new zwitterionic molecule, and has the reverse order of phosphate choline (PC) and could bind to the cell membrane though the unique CP-PC interaction. Here we modified a glass surface with multilayer CP molecules using surface-initiated atom-transfer radical polymerization (SI-ATRP) and the ring-opening method. Polymeric brushes of (dimethylamino)ethyl methacrylate (DMAEMA) were synthesized by SI-ATRP from the glass surface. Then the grafted PDMAEMA brushes were used to introduce CP groups to fabricate the multilayer CP molecule modified surface. The protein adsorption experiment and cell culture test were used to evaluate the biocompatibility of the modified surfaces by using human umbilical veinendothelial cells (HUVECs). The protein adsorption results demonstrated that the multilayer CP molecule decorated surface could prevent the adsorption of fibrinogen and serum protein. The adhesion and proliferation of cells were improved significantly on the multilayer CP molecule modified surface. Therefore, the biocompatibility of the material surface could be improved by the modified multilayer CP molecule, which exhibits great potential for biomedical applications, e.g., scaffolds in tissue engineering.

Star-shaped copolymer grafted PEI and REDV as a gene carrier to improve migration of endothelial cells

A transfection process of EA.hy926 cells treated by REDV peptide targeted micelles/pDNA complexes.

Comb-shaped polymer grafted with REDV peptide, PEG and PEI as targeting gene carrier for selective transfection of human endothelial cells

Several REDV peptide molecules are covalently linked onto an amphiphilic block copolymer to obtain REDV-modified polycationic polymer as a gene carrier with targeting function. The targeting gene complexes show high cell recognition and binding affinity to human endothelial cells.

Multi-targeting peptides for gene carriers with high transfection efficiency

Non-viral gene carriers for gene therapy have been developed for many years.

Materials and surface modification for tissue engineered vascular scaffolds

Although vascular implantation has been used as an effective treatment for cardiovascular disease for many years, off-the-shelf and regenerable vascular scaffolds are still not available. Tissue engineers have tested various materials and methods of surface modification in the attempt to develop a scaffold that is more suitable for implantation. Extracellular matrix-based natural materials and biodegradable polymers, which are the focus of this review, are considered to be suitable materials for production of tissue-engineered vascular grafts. Various methods of surface modification that have been developed will also be introduced, their impacts will be summarized and assessed, and challenges for further research will briefly be discussed.

Substrate-mediated delivery of gene complex nanoparticles via polydopamine coating for enhancing competitiveness of endothelial cells

Substrate-mediated delivery of functional plasmid DNA (pDNA) has been proven to be a promising strategy to promote competitiveness of endothelial cells (ECs) over smooth muscle cells (SMCs), which is beneficial to inducing fast endothelialization of implanted vascular devices. Thus, it is of great importance to develop universal approaches with simplicity and easiness to immobilize DNA complex nanoparticles on substrates. In this study, the bioinspired polydopamine (PDA) coating was employed in immobilization of DNA complex nanoparticles, which were composed of protamine (PrS) and plasmid DNA encoding with hepatocyte growth factor (HGF-pDNA) gene. We demonstrated that the DNA complex nanoparticles can be successfully immobilized onto the PDA surface. Consequently, the HGF expression of both ECs and SMCs were significantly improved when they cultured on the DNA complex nanoparticles-immobilized substrates. Furthermore, EC proliferation was specifically promoted due to bioactivity of HGF, leading to an enhancement of EC competitiveness over SMCs. Our findings demonstrated the substrate-mediated functional gene nanoparticle delivery through PDA coating as a simple and efficient approach. It may hold great potential in the field of interventional cardiovascular implants.

Endothelialization of polyurethanes: Surface silanization and immobilization of REDV peptide

The paper presents method for chemical immobilization of arginine-glutamic acid-aspartic acid-valine (REDV) peptide on polyurethane surface. The peptide has been covalently bonded using silanes as a spacer molecules. The aim of this work was to investigate the proposed modification process and assess its biological effectiveness, especially in contact with blood and endothelial cells. Physicochemical properties were examined in terms of wettability, atomic composition and density of introduced functional groups and peptide molecules. Experiments with blood showed that material coating reduced number of surface-adhered platelets and fibrinogen molecules. In contrast to polyurethane (PU), there were no blood components deposited on REDV-modified materials (PU-REDV); fibrinogen adsorption on PU-REDV surface has been strongly reduced compared to PU. Analysis of cell adhesion after 1, 2, 3, 4, and 5 days of culture showed a significant increase of the cell-coated area on PU-REDV compared to PU. However, an intense cell growth appeared also on the control surface modified without the addition of REDV. Thus, the positive effect of REDV peptide on the adhesion of HUVEC could not be unequivocally confirmed.

Surface PEGylation of intraocular lens for PCO prevention: An in vivo evaluation

Posterior capsular opacification (PCO) is a common complication in cataract surgery. The development of PCO is attributed to the combination of adhesion, migration, proliferation, and transdifferentiation of the residual lens epithelial cells (LEC) onto the interface of intraocular lens (IOL) material and lens posterior, in which the initial adhesion is the beginning step and plays important roles. In the present study, hydrophilic polyethylene glycol (PEG) was immobilized onto IOL surface via plasma-aided chemical grafting procedure. The attenuated total reflection - Fourier transform infrared (ATR-FTIR) and contact angle (CA) - measurements indicate the successful surface PEGylation, as well as the excellent hydrophilicity of the surfaces. Compared with pristine IOL, the PEGylation does not influent its optical property, whereas the initial adhesion of LEC is greatly inhibited. In vivo ocular implantation results show that the PEGylated IOL presents good in vivo biocompatibility, and can effectively prevent the PCO development.

A novel biliary stent coated with silver nanoparticles prolongs the unobstructed period and survival via anti-bacterial activity

Symptomatic biliary stricture causes life-threatening complications, such as jaundice, recurrent cholangitis and secondary biliary cirrhosis. Fully covered self-expanding metal stents (FCSEMSs) are gaining acceptance for treatments of benign biliary stricture and palliative management of malignant biliary obstructions. However, the high rate of FCSEMS obstruction limits their clinic use. In this study, we developed a novel biliary stent coated with silver nanoparticles (AgNPs) and investigated its efficacy both in vitro and in vivo. We first identified properties of the AgNP complex using ultraviolet detection. The AgNP complex was stable without AgNP agglomeration, and Ag abundance was correspondingly increased with an increased bilayer number. The AgNP biliary stent demonstrated good performance in the spin-assembly method based on topographic observation. The AgNP biliary stent also exhibited a long-term anti-coagulation effect and a slow process of Ag⁺ release. In vitro anti-bacteria experiments indicated that the AgNP biliary stent exhibited high-efficiency anti-bacterial activity for both short- and long-term periods. Importantly, application of the AgNP biliary stent significantly prolonged the unobstructed period of the biliary system and improved survival in preclinical studies as a result of its anti-microbial activity and decreased granular tissue formation on the surface of the anastomotic biliary, providing a novel and effective treatment strategy for symptomatic biliary strictures.

REDV–polyethyleneimine complexes for selectively enhancing gene delivery in endothelial cells

Gene therapy provides a new strategy for promoting endothelialization, and rapid endothelialization has attracted increasing attention for inhibiting thrombosis and restenosis in artificial vascular implants.

Effect of Polyelectrolyte Film Stiffness on Endothelial Cells During Endothelial-to-Mesenchymal Transition

Endothelial-to-mesenchymal transition (EndMT), during which endothelial cells (ECs) transdifferentiate into mesenchymal phenotype, plays a key role in the development of vascular implant complications such as endothelium dysfunction and in-stent restenosis. Substrate stiffness has been confirmed as a key factor to influence EC behaviors; however, so far, the relationship between substrate stiffness and EndMT has been rarely studied. Here, ECs were cultured on the (poly(L-lysine)/hyaluronate acid) (PLL/HA) multilayer films with controlled stiffness for 2 weeks, and their EndMT behaviors were studied. We demonstrated that ECs lost their markers (vWf and CD31) in a stiffness-dependent manner even without supplement of growth factors, and the softer film favored the maintaining of EC phenotype. Further, induced by transforming growth factor β1 (TGF-β1), ECs underwent EndMT, as characterized by losing their typical cobblestone morphology and markers and gaining smooth muscle cell markers (α-smooth muscle actin and calponin). Interestingly, stronger EndMT was observed when ECs were cultured on the stiffer film. Collectively, our findings suggest that substrate stiffness has significant effects on EndMT, and a softer substrate is beneficial to ECs by keeping their phenotype and inhibiting EndMT, which presents a new strategy for surface design of vascular implant materials.

REDV Peptide Conjugated Nanoparticles/pZNF580 Complexes for Actively Targeting Human Vascular Endothelial Cells

Herein, we demonstrate that the REDV peptide modified nanoparticles (NPs) can serve as a kind of active targeting gene carrier to condensate pZNF580 for specific promotion of the proliferation of endothelial cells (ECs). First, we synthesized a series of biodegradable amphiphilic copolymers by ring-opening polymerization reaction and graft modification with REDV peptide. Second, we prepared active targeting NPs via self-assembly of the amphiphilic copolymers using nanoprecipitation technology. After condensation with negatively charged pZNF580, the REDV peptide modified NPs/pZNF580 complexes were formed finally. Due to the binding affinity toward ECs of the specific peptide, these REDV peptide modified NPs/pZNF580 complexes could be recognized and adhered specifically by ECs in the coculture system of ECs and human artery smooth muscle cells (SMCs) in vitro. After expression of ZNF580, as the key protein to promote the proliferation of ECs, the relative ZNF580 protein level increased from 15.7% to 34.8%. The specificity in actively targeting ECs of the REDV peptide conjugated NPs/pZNF580 complexes was still retained in the coculture system. These findings in the present study could facilitate the development of actively targeting gene carriers for the endothelialization of artificial blood vessels.