Surface engineering of cardiovascular stent with endothelial cell selectivity for in vivo re-endothelialisation

Pro-endothelialization of nitinol alloy cardiovascular stents enhanced by the programmed assembly of exosomes and endothelial affinity peptide

Stent implantation is one of the most effective methods for the treatment of atherosclerosis. Nitinol stent is a type of stent with good biocompatibility and relatively mature development; however, it cannot effectively achieve long-term anticoagulation and early endothelialization. In this study, nitinol surfaces with the programmed assembly of heparin, exosomes from endothelial cells, and endothelial affinity peptide (REDV) were fabricated through layer-by-layer assembly technology and click-chemistry, and then exosomes/REDV-modified nitinol interface (ACC-Exo-REDV) was prepared. ACC-Exo-REDV could promote the rapid proliferation and adhesion of endothelial cells and achieve anticoagulant function in the blood. Besides, ACC-Exo-REDV had excellent anti-inflammatory properties and played a positive role in the transformation of macrophage from the pro-inflammatory to anti-inflammatory phenotype. Ex vivo and in vivo experiments demonstrated the effectiveness of ACC-Exo-REDV in preventing thrombosis and hyperplasia formation. Hence, the programmed assembly of exosome interface could contribute to endothelialization and have potential application on the cardiovascular surface modification to prevent stent thrombosis and restenosis.

Vascular tissue reconstruction by monocyte subpopulations on small-diameter acellular grafts via integrin activation

Although the clinical application of cell-free tissue-engineered vascular grafts (TEVGs) has been proposed, vascular tissue regeneration mechanisms have not been fully clarified. Here, we report that monocyte subpopulations reconstruct vascular-like tissues through integrin signaling. An Arg-Glu-Asp-Val peptide-modified acellular long-bypass graft was used as the TEVG, and tissue regeneration in the graft was evaluated using a cardiopulmonary pump system and porcine transplantation model. In 1 day, the luminal surface of the graft was covered with cells that expressed CD163, CD14, and CD16, which represented the monocyte subpopulation, and they exhibited proliferative and migratory abilities. RNA sequencing showed that captured cells had an immune-related phenotype similar to that of monocytes and strongly expressed cell adhesion-related genes. In vitro angiogenesis assay showed that tube formation of the captured cells occurred via integrin signal activation. After medium- and long-term graft transplantation, the captured cells infiltrated the tunica media layer and constructed vascular with a CD31/CD105-positive layer and an αSMA-positive structure after 3 months. This finding, including multiple early-time observations provides clear evidence that blood-circulating monocytes are directly involved in vascular remodeling.

A paradigm for high-throughput screening of cell-selective surfaces coupling orthogonal gradients and machine learning-based cell recognition

The combinational density of immobilized functional molecules on biomaterial surfaces directs cell behaviors. However, limited by the low efficiency of traditional low-throughput experimental methods, investigation and optimization of the combinational density remain daunting challenges. Herein, we report a high-throughput screening set-up to study biomaterial surface functionalization by integrating photo-controlled thiol-ene surface chemistry and machine learning-based label-free cell identification and statistics. Through such a strategy, a specific surface combinational density of polyethylene glycol (PEG) and arginine-glutamic acid-aspartic acid-valine peptide (REDV) leads to high endothelial cell (EC) selectivity against smooth muscle cell (SMC) was identified. The composition was translated as a coating formula to modify medical nickel-titanium alloy surfaces, which was then proved to improve EC competitiveness and induce endothelialization. This work provided a high-throughput method to investigate behaviors of co-cultured cells on biomaterial surfaces modified with combinatorial functional molecules.

Functionalization of in vivo tissue-engineered living biotubes enhance patency and endothelization without the requirement of systemic anticoagulant administration

Vascular regeneration and patency maintenance, without anticoagulant administration, represent key developmental trends to enhance small-diameter vascular grafts (SDVG) performance. In vivo engineered autologous biotubes have emerged as SDVG candidates with pro-regenerative properties. However, mechanical failure coupled with thrombus formation hinder translational prospects of biotubes as SDVGs. Previously fabricated poly(ε-caprolactone) skeleton-reinforced biotubes (PBs) circumvented mechanical issues and achieved vascular regeneration, but orally administered anticoagulants were required. Here, highly efficient and biocompatible functional modifications were introduced to living cells on PB lumens. The 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy (DMPE)-PEG-conjugated anti-coagulant bivalirudin (DPB) and DMPE-PEG-conjugated endothelial progenitor cell (EPC)-binding TPS-peptide (DPT) modifications possessed functionality conducive to promoting vascular graft patency. Co-modification of DPB and DPT swiftly attained luminal saturation without influencing cell viability. DPB repellent of non-specific proteins, DPB inhibition of thrombus formation, and DPB protection against functional masking of DPT's EPC-capture by blood components, which promoted patency and rapid endothelialization in rat and canine artery implantation models without anticoagulant administration. This strategy offers a safe, facile, and fast technical approach to convey additional functionalization to living cells within tissue-engineered constructs.

Poly(2-methoxyethyl acrylate) coated bioprosthetic heart valves by copolymerization with enhanced anticoagulant, anti-inflammatory, and anti-calcification properties

Commercial glutaraldehyde (Glut) cross-linked bioprosthetic heart valves (BHVs) fabricated from the pericardium have become the most popular choice for treating heart valve diseases. Nevertheless, thrombosis, inflammation and calcification might lead to structural valve degeneration (SVD), which limited the durability of BHVs. Herein, to improve the biocompatibility of BHVs, we fabricated a poly-(2-methoxyethyl acrylate) (PMEA) coated porcine pericardium (PMEA-PP) through grafting PMEA to the porcine pericardium (PP) that was pre-treated with Glut and methacrylated polylysine. PMEA coating mitigated the side effects caused by aldehyde residues. It was shown that the PMEA coating reduced cytotoxicity and inflammation reactions and improved endothelialization potential, and its hydrophilic surface improved the anti-thrombotic properties of PPs. And the PMEA coating significantly reduced the calcification of PPs. This strategy promoted the endothelialization potential and improve the anti-thrombosis and anti-calcification properties of BHVs, and is expected to overcome the defects of commercial BHVs.

Effectiveness of Direct Laser Interference Patterning and Peptide Immobilization on Endothelial Cell Migration for Cardio-Vascular Applications: An In Vitro Study

Endothelial coverage of an exposed cardiovascular stent surface leads to the occurrence of restenosis and late-stent thrombosis several months after implantation. To overcome this difficulty, modification of stent surfaces with topographical or biochemical features may be performed to increase endothelial cells’ (ECs) adhesion and/or migration. This work combines both strategies on cobalt-chromium (CoCr) alloy and studies the potential synergistic effect of linear patterned surfaces that are obtained by direct laser interference patterning (DLIP), coupled with the use of Arg-Gly-Asp (RGD) and Tyr-Ile-Gly-Ser-Arg (YIGSR) peptides. An extensive characterization of the modified surfaces was performed by using AFM, XPS, surface charge, electrochemical analysis and fluorescent methods. The biological response was studied in terms of EC adhesion, migration and proliferation assays. CoCr surfaces were successfully patterned with a periodicity of 10 µm and two different depths, D (≈79 and 762 nm). RGD and YIGSR were immobilized on the surfaces by CPTES silanization. Early EC adhesion was increased on the peptide-functionalized surfaces, especially for YIGSR compared to RGD. High-depth patterns generated 80% of ECs’ alignment within the topographical lines and enhanced EC migration. It is noteworthy that the combined use of the two strategies synergistically accelerated the ECs’ migration and proliferation, proving the potential of this strategy to enhance stent endothelialization.

Double-Network Hydrogel Armored Decellularized Porcine Pericardium as Durable Bioprosthetic Heart Valves

Heart valves have extraordinary fatigue resistance which beat ≈3 billion times in a lifetime. Bioprosthetic heart valves (BHVs) made from fixed heteroplasm that are incrementally used in heart valve replacement fail to sustain the expected durability due to thrombosis, poor endothelialization, inflammation, calcification, and especially mechanical damage induced biocompatibility change. No effective strategy has been reported to conserve the biological properties of BHV after long-term fatigue test. Here, a double-network tough hydrogel is introduced, which interpenetrate and anchor into the matrix of decellularized porcine pericardium (dCell-PP) to form robust and stable conformal coatings and reduce immunogenicity. The ionic crosslinked hyaluronic acid (HA) network mimics the glycocalyx on endothelium which improves antithrombosis and accelerates endothelialization; the chemical crosslinked hydrophilic polyacrylamide (PAAm) network further enhances antifouling properties and strengthens the shielding hydrogels and their interaction with dCell-PP. In vitro and rabbit ex vivo shunt assay demonstrate great hemocompatibility of polyacrylamide/HA hydrogel hybrid PP (P/H-PP). Cell experiments and rat subcutaneous implantation confirm satisfactory endothelialization, biocompatibility, and anticalcification properties. For hydrodynamic experiment, P/H-PP gains full mark at different flow conditions and sustains excellent biomechanical and biological properties after 200 000 000 cycles. P/H double-network hydrogel armoring dCell-PP is a promising progress to extend BHV durability for clinical implantation therapy.

Applying Principles of Regenerative Medicine to Vascular Stent Development

Stents are a widely-used device to treat a variety of cardiovascular diseases. The purpose of this review is to explore the application of regenerative medicine principles into current and future stent designs. This review will cover regeneration-relevant approaches emerging in the current research landscape of stent technology. Regenerative stent technologies include surface engineering of stents with cell secretomes, cell-capture coatings, mimics of endothelial products, surface topography, endothelial growth factors or cell-adhesive peptides, as well as design of bioresorable materials for temporary stent support. These technologies are comparatively analyzed in terms of their regenerative effects, therapeutic effects and challenges faced; their benefits and risks are weighed up for suggestions about future stent developments. This review highlights two unique regenerative features of stent technologies: selective regeneration, which is to selectively grow endothelial cells on a stent but inhibit the proliferation and migration of smooth muscle cells, and stent-assisted regeneration of ischemic tissue injury.

Label-Free and In Situ Identification of Cells via Combinational Machine Learning Models

Cell identification and counting in living and coculture systems are crucial in cell interaction studies, but current methods primarily rely on complicated and time-consuming staining techniques. Here, a label-free method to precisely recognize, identify, and instantly count cells in situ in coculture systems via combinational machine learning models s presented. A convolutional neural network (CNN) model is first used to generate virtual images of cell nuclei based on unlabeled phase-contrast images. Coordinates of all the cells are then returned according to the virtual nucleus images using two clustering algorithms. Finally, phase-contrast images of single cells are cropped based on the coordinates and sent into another CNN model for cell-type identification. This combinational approach is highly automatic and efficient, which requires few to no manual annotations of images in the training phase. It shows practical performance in different cell culture conditions including cell ratios, densities, and substrate materials, having great potential in real-time cell tracking and analyzing.

miR-22 eluting cardiovascular stent based on a self-healable spongy coating inhibits in-stent restenosis

The in-stent restenosis (IRS) after the percutaneous coronary intervention contributes to the major treatment failure of stent implantation. MicroRNAs have been revealed as powerful gene medicine to regulate endothelial cells (EC) and smooth muscle cells (SMC) in response to vascular injury, providing a promising therapeutic candidate to inhibit IRS. However, the controllable loading and eluting of hydrophilic bioactive microRNAs pose a challenge to current lipophilic stent coatings. Here, we developed a microRNA eluting cardiovascular stent via the self-healing encapsulation process based on an amphipathic poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, PCEC) triblock copolymer spongy network. The miR-22 was used as a model microRNA to regulate SMC. The dynamic porous coating realized the uniform and controllable loading of miR-22, reaching the highest dosage of 133 pmol cm-2. We demonstrated that the sustained release of miR-22 dramatically enhanced the contractile phenotype of SMC without interfering with the proliferation of EC, thus leading to the EC dominating growth at an EC/SMC ratio of 5.4. More importantly, the PCEC@miR-22 coated stents showed reduced inflammation, low switching of SMC phenotype, and low secretion of extracellular matrix, which significantly inhibited IRS. This work provides a simple and robust coating platform for the delivery of microRNAs on cardiovascular stent, which may extend to other combination medical devices, and facilitate practical application of bioactive agents in clinics.

Vascular Polyurethane Prostheses Modified with a Bioactive Coating-Physicochemical, Mechanical and Biological Properties

This study describes a method for the modification of polyurethane small-diameter (5 mm) vascular prostheses obtained with the phase inversion method. The modification process involves two steps: the introduction of a linker (acrylic acid) and a peptide (REDV and YIGSR). FTIR and XPS analysis confirmed the process of chemical modification. The obtained prostheses had a porosity of approx. 60%, Young's Modulus in the range of 9-11 MPa, and a water contact angle around 40°. Endothelial (EC) and smooth muscle (SMC) cell co-culture showed that the surfaces modified with peptides increase the adhesion of ECs. At the same time, SMCs adhesion was low both on unmodified and peptide-modified surfaces. Analysis of blood-materials interaction showed high hemocompatibility of obtained materials. The whole blood clotting time assay showed differences in the amount of free hemoglobin present in blood contacted with different materials. It can be concluded that the peptide coating increased the hemocompatibility of the surface by increasing ECs adhesion and, at the same time, decreasing platelet adhesion. When comparing both types of peptide coatings, more promising results were obtained for the surfaces coated with the YISGR than REDV-coated prostheses.

A promising potential candidate for vascular replacement materials with anti-inflammatory action, good hemocompatibility and endotheliocyte-cytocompatibility: phytic acid-fixed amniotic membrane

Due to its excellent biocompatibility and anti-inflammatory activity, amniotic membrane (AM) has attracted much attention from scholars. However, its clinical application in vascular reconstruction was limited for poor processability, rapid biodegradation, and insufficient hemocompatibility. A naturally extracted substance with good cytocompatibility, phytic acid (PA), which can quickly form strong and stable hydrogen bonds on the tissue surface, was used to crosslink decellularized AM (DAM) to prepare a novel vascular replacement material. The results showed that PA-fixed AM had excellent mechanical strength and resistance to enzymatic degradation as well as appropriate surface hydrophilicity. Among all samples, 2% PA-fixed specimen showed excellent human umbilical vein endothelial cells (HUVECs)-cytocompatibility and hemocompatibility. It could also stimulate the secretion of vascular endothelial growth factor and endothelin-1 from seeded HUVECs, indicating that PA might promote neovascularization after implantation of PA-fixed specimens. Also, 2% PA-fixed specimen could inhibit the secretion of tumor necrosis factor-αfrom co-cultured macrophages, thus might reduce the inflammatory response after sample implantation. Finally, the results ofex vivoblood test andin vivoexperiments confirmed our deduction that PA might promote neovascularization after implantation. All the results indicated that prepared PA-fixed DAM could be considered as a promising small-diameter vascular replacement material.

Influences of Stent Design on In-Stent Restenosis and Major Cardiac Outcomes: A Scoping Review and Meta-Analysis

Thanks to the developments in implantable biomaterial technologies, invasive operating procedures, and widespread applications especially in vascular disease treatment, a milestone for interventional surgery was achieved with the introduction of vascular stents. Despite vascular stents providing a solution for embolisms, this technology includes various challenges, such as mechanical, electro-chemical complications, or in-stent restenosis (ISR) risks with long-term usage. Therefore, further development of biomaterial technologies is vital to overcome such risks and problems. For this purpose, recent research has focused mainly on the applications of surface modification techniques on biomaterials and vascular stents to increase their hemocompatibility. ISR risk has been reduced with the development and prevalent usage of the art technology stent designs of drug-eluting and biodegradable stents. Nevertheless, their problems have not been overcome completely. Furthermore, patients using drug-eluting stents are faced with further clinical challenges. Therefore, the bare metal stent, which is the first form of the vascular stent technology and includes the highest ISR risk, is still in common usage for vascular treatment applications. For this reason, further research is necessary to solve the remaining vital problems. In this scoping review, stent-based major cardiac events including ISR are analyzed depending on different designs and material selection in stent manufacturing. Recent and novel approaches to overcome such challenges are stated in detail.

Development of In Vitro Endothelialised Stents - Review

Endovascular treatment is prevalent as a primary treatment for coronary and peripheral arterial diseases. Although the introduction of drug-eluting stents (DES) dramatically reduced the risk of in-stent restenosis, stent thrombosis persists as an issue. Notwithstanding improvements in newer generation DES, they are yet to address the urgent clinical need to abolish the late stent complications that result from in-stent restenosis and are associated with late thrombus formation. These often lead to acute coronary syndromes with high mortality in coronary artery disease and acute limb ischemia with a high risk of limb amputation in peripheral arterial disease. Recently, a significant amount of research has focused on alternative solutions to improve stent biocompatibility by using tissue engineering. There are two types of tissue engineering endothelialisation methods: in vitro and in vivo. To date, commercially available in vivo endothelialised stents have failed to demonstrate antithrombotic or anti-stenosis efficacy in clinical trials. In contrast, the in vitro endothelialisation methods exhibit the advantage of monitoring cell type and growth prior to implantation, enabling better quality control. The present review discusses tissue-engineered candidate stents constructed by distinct in vitro endothelialisation approaches, with a particular focus on fabrication processes, including cell source selection, stent material composition, stent surface modifications, efficacy and safety evidence from in vitro and in vivo studies, and future directions.

Challenges and strategies for in situ endothelialization and long-term lumen patency of vascular grafts

Vascular diseases are the most prevalent cause of ischemic necrosis of tissue and organ, which even result in dysfunction and death. Vascular regeneration or artificial vascular graft, as the conventional treatment modality, has received keen attentions. However, small-diameter (diameter < 4 mm) vascular grafts have a high risk of thrombosis and intimal hyperplasia (IH), which makes long-term lumen patency challengeable. Endothelial cells (ECs) form the inner endothelium layer, and are crucial for anti-coagulation and thrombogenesis. Thus, promoting in situ endothelialization in vascular graft remodeling takes top priority, which requires recruitment of endothelia progenitor cells (EPCs), migration, adhesion, proliferation and activation of EPCs and ECs. Chemotaxis aimed at ligands on EPC surface can be utilized for EPC homing, while nanofibrous structure, biocompatible surface and cell-capturing molecules on graft surface can be applied for cell adhesion. Moreover, cell orientation can be regulated by topography of scaffold, and cell bioactivity can be modulated by growth factors and therapeutic genes. Additionally, surface modification can also reduce thrombogenesis, and some drug release can inhibit IH. Considering the influence of macrophages on ECs and smooth muscle cells (SMCs), scaffolds loaded with drugs that can promote M2 polarization are alternative strategies. In conclusion, the advanced strategies for enhanced long-term lumen patency of vascular grafts are summarized in this review. Strategies for recruitment of EPCs, adhesion, proliferation and activation of EPCs and ECs, anti-thrombogenesis, anti-IH, and immunomodulation are discussed. Ideal vascular grafts with appropriate surface modification, loading and fabrication strategies are required in further studies.

Biodegradable phosphorylcholine copolymer for cardiovascular stent coating

Phosphorylcholine (PC) based polymer coatings with excellent biocompatibility have shown successful commercialization in drug-eluting stents. However, poor degradability represents a challenge in the application of biodegradable stents. Herein, a biodegradable phosphorylcholine copolymer is developed based on one-step radical ring-opening polymerization (RROP). This copolymer was synthesized by copolymerization of a PC unit, degradable ester (2-methylene-1,3-dioxepane, MDO) unit and non-degradable butyl methacrylate (BMA) unit, which showed ratio controllability by changing the monomer ratio during polymerization. We demonstrated that the copolymer with the ratio of 34% MDO, 19% MPC and 47% BMA could form a stable coating by ultrasonic spray, and showed good blood compatibility, anti-adhesion properties, biodegradability, and rapamycin eluting capacity. In vivo study revealed its promising application as a biodegradable stent coating. This work provides a facile path to add biodegradability into PC based polymers for further bio-applications.

Endothelial Cell-Mediated Gene Delivery for In Situ Accelerated Endothelialization of a Vascular Graft

As an urgently needed device for vascular diseases, the small-diameter vascular graft is limited by high thrombogenicity in clinical applications. Rapid endothelialization is a promising approach to construct an antithrombogenic inner surface of the vascular graft. The main bottleneck for rapid endothelialization is the adhesion, migration, and proliferation of endothelial cells (ECs) in situ of the small-diameter vascular graft. Herein, we innovatively fabricated an intelligent gene delivery small-caliber vascular graft based on electrospun poly(lactic acid-co-caprolactone) and gelatin for rapid in situ endothelialization. The graft surface was co-modified with EC adhesive peptide of Arg-Glu-Asp-Val (REDV) and responsive gene delivery system. REDV can selectively adhere ECs onto the graft surface; subsequently, the overexpressed matrix metalloproteinase by ECs can effectively cleave the linker peptide GPQGIWGQ-C; and finally, the gene complexes were intelligently and enzymatically released from the graft surface, and thereby, the gene can efficiently transfect ECs. Importantly, this enzymatically releasing gene surface has been proven to be safe and temporarily stable in blood flow owing to the biotin-avidin interaction to immobilize gene complexes on the inner surface of vascular grafts through the GPQGIWGQ-C peptide linker. It has the advantage of specifically adhering the ECs to the surface and smartly transfecting them with high transfection efficiency. The co-modified surface has been demonstrated to accelerate the luminal endothelialization in vivo, which might be attributed to the synergistic effect of REDV and effective gene transfection. Particularly, the intelligent and responsive gene release surface will open a new avenue to enhance the endothelialization of blood-contacting devices.

Electrochemically deposition of catechol-chitosan hydrogel coating on coronary stent with robust copper ions immobilization capability and improved interfacial biological activity

Establishing a facile and versatile strategy to confer coronary stent with improved interfacial biological activity is crucial for novel cardiovascular implants. Developing a coating with NO release ability catalyzed by metal ions, such as copper, will be highly advantageous for the functionalized surface modification of metal stents. However, most available strategies involve drawbacks of low efficiency, complex processes, and toxic chemicals. Therefore, in this study, we report a green and facile electrobiofabrication method to construct the bioactive hydrogel coating by combining chitosan, catechol groups and copper ions on coronary stent and titanium surfaces. Experimental results demonstrated that the chitosan hydrogel coating can be precisely controlled synthesis via electrochemical deposition and serves as a versatile platform for copper ions immobilization. Additionally, mussel-inspired catechol groups could be chemically grafted on chitosan chains to further enhance the film mechanical properties and binding abilities of copper ions. Moreover, in vitro cell biocompatibility and catalyzed NO-generation activity have also been accessed and which suggesting great possibilities for biomedical applications. Therefore, by coupling the electrobiofabrication approach and multi-functionalities of the hybrid film, this report would advance the development of biomimetic hydrogel coating for vascular engineering (e.g., coronary stent) and other biomedical devices.

The impact of antifouling layers in fabricating bioactive surfaces

Bioactive surfaces modified with functional peptides are critical for both fundamental research and practical application of implant materials and tissue repair. However, when bioactive molecules are tethered on biomaterial surfaces, their functions can be compromised due to unwanted fouling (mainly nonspecific protein adsorption and cell adhesion). In recent years, researchers have continuously studied antifouling strategies to obtain low background noise and effectively present the function of bioactive molecules. In this review, we describe several commonly used antifouling strategies and analyzed their advantages and drawbacks. Among these strategies, antifouling molecules are widely used to construct the antifouling layer of various bioactive surfaces. Subsequently, we summarize various structures of antifouling molecules and their surface grafting methods and characteristics. Application of these functionalized surfaces in microarray, biosensors, and implants are also introduced. Finally, we discuss the primary challenges associated with antifouling layers in fabricating bioactive surfaces and provide prospects for the future development of this field. STATEMENT OF SIGNIFICANCE: The nonspecific protein adsorption and cell adhesion will cause unwanted background "noise" on the surface of biological materials and detecting devices and compromise the performance of functional molecules and, therefore, impair the performance of materials and the sensitivity of devices. In addition, the selection of antifouling surfaces with proper chain length and high grafting density is also of great importance and requires further studies. Otherwise, the surface-tethered bioactive molecules may not function in their optimal status or even fail to display their functions. Based on these two critical issues, we summarize antifouling molecules with different structures, variable grafting methods, and diverse applications in biomaterials and biomedical devices reported in literature. Overall, we expect to shed some light on choosing the appropriate antifouling molecules in fabricating bioactive surfaces.

Surface Modification of Intraocular Lens with Hydrophilic Poly(Sulfobetaine Methacrylate) Brush for Posterior Capsular Opacification Prevention

Purpose: The intraocular lens (IOL) is a common, yet important, implantable device used in treatment of cataract in clinics. However, the unexpected adhesion of postoperative residual lens epithelial cells (LECs) often causes serious complications, such as posterior capsular opacification (PCO), which lead to vision loss again. In this investigation, a poly(sulfobetaine methacrylate) (PSBMA) brush coating was fabricated on an IOL to generate a hydrophilic surface coating on the IOL for enhanced cell adhesion resistance so as to decrease PCO incidence. Methods: The PSBMA brush coating on the IOL surface was fabricated using surface-initiated reversible addition-fragmentation chain transfer polymerization. X-ray photoelectron spectroscopy (XPS) was used to demonstrate the surface coating preparation. The water contact angle (WCA) measurement was used to test surface hydrophilicity. In vitro LEC culture was use to evaluate the cell behavior on the IOL material surfaces, with or without PSBMA coating modification. Finally, animal cataract surgeries were carried out to evaluate in vivo biocompatibilities and anti-PCO effects. Results: The XPS and WCA measurements illustrate successful surface modification and good surface hydrophilicity. The in vitro cell culture results show that the hydrophilic PSBMA polymer brush coating evidently decreases adhesion and proliferation of LECs. Results of the in vivo cataract surgery with intraocular implantation show that PSBMA modification on the IOL surface does not induce side effects in nearby tissues, whereas posterior capsular hyperplasia can be evidently reduced. Conclusion: The PSBMA brush surface-modified IOL has good in vivo biocompatibility and it can effectively reduce the incidence of postoperative PCO.

Intelligent H2S release coating for regulating vascular remodeling

Coronary atherosclerotic lesions exhibit a low-pH chronic inflammatory response. Due to insufficient drug release control, drug-eluting stent intervention can lead to delayed endothelialization, advanced thrombosis, and unprecise treatment. In this study, hyaluronic acid and chitosan were used to prepare pH-responsive self-assembling films. The hydrogen sulfide (H₂S) releasing aspirin derivative ACS14 was used as drug in the film. The film regulates the release of the drug adjusted to the microenvironment of the lesion, and the drug balances the vascular function by releasing the regulating gas H₂S, which comparably to NO promotes the self-healing capacity of blood vessels. Drug releasing profiles of the films at different pH, and other biological effects on blood vessels were evaluated through blood compatibility, cellular, and implantation experiments. This novel method of self-assembled films which H₂S in an amount, which is adjusted to the condition of the lesion provides a new concept for the treatment of cardiovascular diseases.

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PH-responsive self-assembling films were used to intelligently release the drugs at atherosclerotic lesions.

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As a gaseous signaling molecule, H₂S donor ACS14 was loaded into the films used in the field of cardiovascular disease treatment.

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H₂S can help to regulate vascular remodeling and balance the vascular function.

Versatile Cell-Specific Ligand Arrangement System onto Desired Compartments of Biodegradable Matrices for Site-Selective Cell Adhesion Using DNA Tags

A promising approach for the regeneration of tissues or organs with three-dimensional hierarchical structures is the preparation of scaffold-cell complexes that mimic these hierarchical structures. This requires an effective technique for immobilizing cell-specific ligands at arbitrarily chosen positions on matrices. Here, we report a versatile system for arranging cell-specific ligands onto desired compartments of biodegradable matrices for site-selective cell arrangement. We utilized the specific binding abilities of specific DNAs, immobilizing them as tags to arrange cell-recognition ligands at desired areas of the matrices by specific binding with cell-recognition ligand-DNA conjugates. We synthesized poly(l-lactide) (PLLA), a biodegradable polymer, with an oligo-DNA (trimer of deoxyguanosine: dG₃) attached via a poly(ethylene glycol) (PEG) spacer to generate dG₃-PEG-b-PLLA. The peptides Arg-Gly-Asp-Ser (RGDS) and Arg-Glu-Asp-Val (REDV) were chosen as cell-recognition ligands and were attached to an adapter DNA (aDNA), which can specifically bind to the dG₃ moiety through G-quadruplex formation. The obtained dG₃-PEG-b-PLLA was deposited on a small spot of the PLLA film, and the aDNA-RGDS or aDNA-REDV conjugate was added on the film to immobilize these ligands at the spot. We confirmed the specific adhesion of L929 cells (a mouse fibroblast cell line) and human umbilical vein endothelial cells (HUVECs) on the small areas coated with dG₃-PEG-b-PLLA in the presence of aDNA-RGDS and aDNA-REDV, respectively, even after applying shear stress by flowing medium across the spot. Cell-specific attachment of the target cells was effectively achieved in a spatially controlled manner. This technique has the potential for the construction of cell-scaffold complexes that mimic the hierarchical structures of natural organs and may represent a breakthrough in realizing regenerative medicine and tissue engineering of complex organs.

Enzyme Mimics for the Catalytic Generation of Nitric Oxide from Endogenous Prodrugs

The highly diverse biological roles of nitric oxide (NO) in both physiological and pathophysiological processes have prompted great interest in the use of NO as a therapeutic agent in various biomedical applications. NO can exert either protective or deleterious effects depending on its concentration and the location where it is delivered or generated. This double-edged attribute, together with the short half-life of NO in biological systems, poses a major challenge to the realization of the full therapeutic potential of this molecule. Controlled release strategies show an admirable degree of precision with regard to the spatiotemporal dosing of NO but are disadvantaged by the finite NO deliverable payload. In turn, enzyme-prodrug therapy techniques afford enhanced deliverable payload but are troubled by the inherent low stability of natural enzymes, as well as the requirement to control pharmacokinetics for the exogenous prodrugs. The past decade has seen the advent of a new paradigm in controlled delivery of NO, namely localized bioconversion of the endogenous prodrugs of NO, specifically by enzyme mimics. These early developments are presented, successes of this strategy are highlighted, and possible future work on this avenue of research is critically discussed.

Bioclickable and mussel adhesive peptide mimics for engineering vascular stent surfaces

Thrombogenic reaction, aggressive smooth muscle cell (SMC) proliferation, and sluggish endothelial cell (EC) migration onto bioinert metal vascular stents make poststenting reendothelialization a dilemma. Here, we report an easy to perform, biomimetic surface engineering strategy for multiple functionalization of metal vascular stents. We first design and graft a clickable mussel-inspired peptide onto the stent surface via mussel-inspired adhesion. Then, two vasoactive moieties [i.e., the nitric-oxide (NO)-generating organoselenium (SeCA) and the endothelial progenitor cell (EPC)-targeting peptide (TPS)] are clicked onto the grafted surfaces via bioorthogonal conjugation. We optimize the blood and vascular cell compatibilities of the grafted surfaces through changing the SeCA/TPS feeding ratios. At the optimal ratio of 2:2, the surface-engineered stents demonstrate superior inhibition of thrombosis and SMC migration and proliferation, promotion of EPC recruitment, adhesion, and proliferation, as well as prevention of in-stent restenosis (ISR). Overall, our biomimetic surface engineering strategy represents a promising solution to address clinical complications of cardiovascular stents and other blood-contacting metal materials.

Nitric Oxide-Producing Cardiovascular Stent Coatings for Prevention of Thrombosis and Restenosis

Cardiovascular stenting is an effective method for treating cardiovascular diseases (CVDs), yet thrombosis and restenosis are the two major clinical complications that often lead to device failure. Nitric oxide (NO) has been proposed as a promising small molecule in improving the clinical performance of cardiovascular stents thanks to its anti-thrombosis and anti-restenosis ability, but its short half-life limits the full use of NO. To produce NO at lesion site with sufficient amount, NO-producing coatings (including NO-releasing and NO-generating coatings) are fashioned. Its releasing strategy is achieved by introducing exogenous NO storage materials like NO donors, while the generating strategy utilizes the in vivo substances such as S-nitrosothiols (RSNOs) to generate NO flux. NO-producing stents are particularly promising in future clinical use due to their ability to store NO resources or to generate large NO flux in a controlled and efficient manner. In this review, we first introduce NO-releasing and -generating coatings for prevention of thrombosis and restenosis. We then discuss the advantages and drawbacks on releasing and generating aspects, where possible further developments are suggested.

Different influence of sulfated chitosan with different sulfonic acid group sites on HUVECs behaviors

The vascularization within the scaffold is still a significant challenge in tissue engineering applications. Sulfated chitosan (SCS) as an amazing substance have been used in tissue engineering to stimulate angiogenesis. However, it is not clear whether they have difference in the ability to promote vascularization of SCS with different sulfonic acid group sites. The aim of this study was to evaluate human umbilical vein endothelial cells (HUVECs) viability and differentiation in vitro, affected by three types of sulfated chitosan' i.e. 2-N-6-O-sulfated chitosan (2,6-SCS), 3'6-O-sulfated chitosan (3,6-SCS) and 6-O-sulfated chitosan (6-SCS). The results are showed that all the SCS possesses excellent biological properties to promote HUVECs viability and proliferation. Especially, 2,6-SCS promotes desirable intracellular nitric oxide secretion and capillary tube formation. Meanwhile, 2,6-SCS up-regulate the related gene and protein expression compared with other sulfonic acid group sites SCS and heparin. Therefore, 2,6-SCS is a promising substitute material for angiogenesis and as aqueous formulation can be employed to fabrication functionalization scaffold surface with promoted angiogenesis.

Cellular attachment behavior on biodegradable polymer surface immobilizing endothelial cell-specific peptide

Small-caliber artificial blood vessels with inner diameters of smaller than 4 mm have not been put into practical use because of early thrombus formation and graft occlusion. To realize small-caliber artificial blood vessels with anti-thrombus property and long-term patency, one of the promising approaches is endothelialization of the lumen by tissue engineering approaches. Integrin α4β1 on the endothelial cell membrane is known to act as a receptor for Arg-Glu-Asp-Val (REDV) tetra-peptide, and this peptide can be used as a specific ligand to introduce endothelial cell attachment onto the surfaces of polymer scaffold. In this study, biodegradable polymer surface immobilizing REDV peptide were prepared, and the specific attachment of endothelial cells on it was investigated as a preliminary study for tissue-engineered small-caliber blood vessels in a future application. We synthesized copolymer of ε-caprolactone and depsipeptide having reactive carboxylic acid side-chain groups (PGDCL), and REDV peptide was attached to the copolymer to give PGDCL-REDV. The attachment of human umbilical vein endothelial cells (HUVECs) were investigated for the blend polymer film prepared by mixing PGDCL and PGDCL-REDV. The obtained blend polymer films exhibited sequence- and cell-specific HUVECs attachment through REDV peptide recognition. This technique should be useful not only to obtain artificial blood vessels which induce endothelialization and but also to provide biodegradable scaffolds with specific ligands immobilized surfaces for tissue regeneration.

A potential strategy for in-stent restenosis: Inhibition of migration and proliferation of vascular smooth muscle cells by Cu ion

The in-stent restenosis (ISR) often happens after the implantation of metal stents, including both bare metal stents (BMSs) and drug-eluting stents (DESs). Drug release from DESs could reduce significantly the occurrence of ISR but also suppress the revascularization and cause thrombosis. In this study, the effect of Cu ion in a range of 0 to 500 μM on the migration and proliferation of rat aortic smooth muscle cells (RASMCs) was investigated by a series of in vitro experiments including wound-healing assay, cell viability assay and flow cytometric analysis. It has been found that the critical concentration of Cu ion should be at least 250 μM in order to significantly inhibit the migration of RASMCs and the proliferation of RASMCs were impeded by every dose of Cu ion used in this study. In addition, the protein level of caspase-3 was upregulated by 250 μM and 500 μM Cu²⁺ exposure, which might be the main reason for RASMCs apoptosis. Thus, it is proposed that ISR might be prevented by the constant release of Cu ion.

Layer-by-Layer Deposition of Hyaluronan and Quercetin-Loaded Chitosan Nanoparticles onto Titanium for Improving Blood Compatibility

Surface modification is an effective way to improve the hemocompatibility of biomaterials. Quercetin has significant anticoagulation and antithrombotic effects, and thus it is a promising candidate agent for the surface modification of blood-contacting materials. In this study, quercetin was successfully encapsulated in tripolyphosphate–chitosan nanoparticles (TCs) based on the ionic gelation of chitosan with tripolyphosphate (TPP) anions. Then, hyaluronan acid (HA)/quercetin-loaded TPP–chitosan nanoparticle (QTCs) films, in addition to HA/TCs films, were prepared separately using an electrostatic layer-by-layer self-assembly technique. The encapsulation of quercetin in the chitosan nanoparticles was confirmed by UV spectra. The quercetin-loaded multilayer coatings were also successfully self-assembled, as confirmed by the UV spectra and contact angle measurements. Platelet adhesion experiments were carried out with platelet-enriched plasma so as to evaluate the blood compatibility of the different samples. There were many platelets on the surfaces of the glass and HA/TC-coated titanium, which were partially activated but not aggregated. Meanwhile, many more platelets were observed on the uncoated titanium surfaces, most of which developed pseudopodia. By contrast, the platelet adhesion and activation were reduced remarkably on the surface of the HA/QTC-coated titanium. These results showed that the multilayer coatings containing quercetin could act as potential biomaterials to improve the anticoagulation performance of blood-contacting materials.

Mussel-inspired "built-up" surface chemistry for combining nitric oxide catalytic and vascular cell selective properties

Specific selectivity of vascular cells and antithrombogenicity are crucial factors for the long-term success of vascular implants. In this work, a novel concept of mussel-inspired "built-up" surface chemistry realized by sequential stacking of a copper-dopamine network basement, followed by a polydopamine layer is introduced to facilitate the combination of nitric oxide (NO) catalysis and vascular cell selectivity. The resultant "built-up" film allowed easy manipulation of the content of copper ions and the density of catechol/quinone groups, facilitating the multifunctional surface engineering of vascular devices. For example, the chelated copper ions in the copper-dopamine network endow a functionalized vascular stent with a durable release of NO via catalytic decomposition of endogenous S-nitrosothiol. Meanwhile, the catechol/quinone groups on the film surface allow the facile, secondary grafting of the REDV peptide to develop a selectivity for vascular cells, as a supplement to the functions of NO. As a result, the functionalized vascular stent perfectly combines the functions of NO and REDV, showing excellent antithrombotic properties and competitive selectivity toward the endothelial cells over the smooth muscle cells, hence impressively promotes re-endothelialization and improves anti-restenosis in vivo. Therefore, the first mussel-inspired "built-up" surface chemistry can be a promising candidate for the engineering of multifunctional surfaces.

Bioinspired, Artificial, Small-Diameter Vascular Grafts with Selective and Rapid Endothelialization Based on an Amniotic Membrane-Derived Hydrogel

Clinical application of the amniotic membrane (AM) in vascular reconstruction was limited by poor processability, rapid biodegradation, and insufficient hemocompatibility. In this work, decellularized AM was digested to a thermosensitive hydrogel and densely cross-linked in the nanoscale as "enhanced" collagenous fibers. Via N-(3-dimehylaminopropyl)-N'-ethylcarbodiimide and N-hydroxysuccinimide (EDC/NHS) catalysis, REDV was further grafted to simulate anticoagulant substances on naturally derived blood vessels. This modification approach endowed AM with rapid endothelialization and rare vascular restenosis. Through adjusting the fixation condition, the pore size and mechanical stability of the fiber network were approximate to those of natural tissues and precisely designed to fit for cell adhesion. AM was synchronously fixed by alginate dialdehyde (ADA) and EDC/NHS, forming a "double-cross-linked" stable structure with significantly improved mechanical strength and resistance against enzymic degradation. The hemolytic and platelet adhesion test indicated that ADA/REDV-AM could inhibit hemolysis and coagulation. It also exhibited excellent cytocompatibility. It selectively accelerated adsorption and migration of endothelial cells (ECs) while impeding adhesion and proliferation of smooth muscle cells (SMCs). It maintained EC superiority in competitive growth and avoided thrombosis in vivo. Furthermore, its property of promoting reconstruction and repair of blood vessels was proved in an animal experiment. Overall, the present study demonstrates that ADA/REDV-AM has potential application as a small-diameter artificial vascular intima with rapid endothelialization and reduced SMC/platelet adhesion.

Hierarchical Capillary Coating to Biofunctionlize Drug-Eluting Stent for Improving Endothelium Regeneration

The drug-eluting stent (DES) has become one of the most successful and important medical devices for coronary heart disease, but yet suffers from insufficient endothelial cell (EC) growth and intima repair, eventually leading to treatment failure. Although biomacromolecules such as vascular endothelial growth factor (VEGF) would be promising to promote the intima regeneration, combining hydrophilic and vulnerable biomacromolecules with hydrophobic drugs as well as preserving the bioactivity after harsh treatments pose a huge challenge. Here, we report on a design of hierarchical capillary coating, which composes a base solid region and a top microporous region for incorporating rapamycin and VEGF, respectively. The top spongy region can guarantee the efficient, safe, and controllable loading of VEGF up to 1 μg/cm² in 1 minute, providing a distinctive real-time loading capacity for saving the bioactivity. Based on this, we demonstrate that our rapamycin-VEGF hierarchical coating impressively promoted the competitive growth of endothelial cells over smooth muscle cells (ratio of EC/SMC~25) while relieving the adverse impact of rapamycin to ECs. We further conducted the real-time loading of VEGF on stents and demonstrate that the hierarchical combination of rapamycin and VEGF showed remarkable endothelium regeneration while maintaining a very low level of in-stent restenosis. This work paves an avenue for the combination of both hydrophobic and hydrophilic functional molecules, which should benefit the next generation of DES and may extend applications to diversified combination medical devices.

Endothelium-Mimicking Multifunctional Coating Modified Cardiovascular Stents via a Stepwise Metal-Catechol-(Amine) Surface Engineering Strategy

Stenting is currently the major therapeutic treatment for cardiovascular diseases. However, the nonbiogenic metal stents are inclined to trigger a cascade of cellular and molecular events including inflammatory response, thrombogenic reactions, smooth muscle cell hyperproliferation accompanied by the delayed arterial healing, and poor reendothelialization, thus leading to restenosis along with late stent thrombosis. To address prevalence critical problems, we present an endothelium-mimicking coating capable of rapid regeneration of a competently functioning new endothelial layer on stents through a stepwise metal (copper)-catechol-(amine) (MCA) surface chemistry strategy, leading to combinatorial endothelium-like functions with glutathione peroxidase-like catalytic activity and surface heparinization. Apart from the stable nitric oxide (NO) generating rate at the physiological level (2.2 × 10^-10 mol/cm²/min lasting for 60 days), this proposed strategy could also generate abundant amine groups for allowing a high heparin conjugation efficacy up to ∼1 μg/cm², which is considerably higher than most of the conventional heparinized surfaces. The resultant coating could create an ideal microenvironment for bringing in enhanced anti-thrombogenicity, anti-inflammation, anti-proliferation of smooth muscle cells, re-endothelialization by regulating relevant gene expressions, hence preventing restenosis in vivo. We envision that the stepwise MCA coating strategy would facilitate the surface endothelium-mimicking engineering of vascular stents and be therefore helpful in the clinic to reduce complications associated with stenosis.

Co–Cr–Mo alloy binding peptide as molecular glue for constructing biomedical surfaces

The mechanical properties of Co–Cr–Mo (CCM) alloys are advantageous in various biomedical applications. However, because of their bioinert surface, CCM alloys exhibit poor endothelial cell attachment properties; thus, problems of biocompatibility remain. In this study, we aimed to improve the biocompatibility of the CCM alloy surface using solid-binding peptides. We selected peptides with high binding affinity for cast CCM alloy surfaces through in vitro evolution by the phage display method. The peptides were functionalized on the CCM alloy surfaces by simple immersion in the peptide solution. The peptide bound to both cast and 3D-printed CCMs with the same affinity. The peptides linked to the amino acid motif that promotes cell adhesion, and improved the attachment of endothelial cells on the 3D-printed CCM in serum and serum-free conditions. Hence, CCM-binding peptides are attractive tools for constructing a biofunctional surface on CCM-based biodevices.

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.

Co-immobilization of ACH11 antithrombotic peptide and CAG cell-adhesive peptide onto vascular grafts for improved hemocompatibility and endothelialization

Surface modification by conjugating biomolecules has been widely proved to enhance biocompatibility of small-caliber artificial vascular grafts. In this study, we aimed at developing a multifunctional vascular graft that provides not only good hemocompatibility but also in situ rapid endothelialization. Herein, a vascular graft (inner diameter ∼2 mm) was fabricated by electrospinning with poly(lactic acid-co-caprolactone) and gelatin, and then biofunctionalized with antithrombotic peptide with sequence LTFPRIVFVLG (ACH₁₁) and cell adhesion peptide with sequence CAG through adhesive poly(dopamine) coating. We developed this graft with the synergistic properties of low thrombogenicity and rapid endothelialization. The successful grafting of both CAG and ACH₁₁ peptides was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface micromorphology of the modified surfaces was observed by field emission scanning electron microscopy. Our results demonstrated that the multifunctional surface suppressed the denaturation of absorbed fibrinogen, hindered coagulation factor Xa activation, and inhibited platelet adhesion and aggregation. Importantly, this modified surface could selectively enhance endothelial cells adhesion, proliferation and release of nitric oxide. Upon in vivo implantation of 6 weeks, the multifunctional vascular graft showed improved patency and superior vascular endothelialization. Overall, the results effectively demonstrated that the co-immobilization of ACH₁₁ and CAG provided a promising method for the improvement of hemocompatibility and endothelialization of vascular grafts. STATEMENT OF SIGNIFICANCE: Electrospun small-caliber vascular grafts are increasingly used to treat cardiovascular diseases. Despite their success related to their good biodegradation and mechanical strength, they have some drawbacks, such as low hemocompatibility and endothelialization. The single-function ligands are insufficient to modify surface with both good hemocompatibility and rapid endothelialization simultaneously. Therefore, we functionalized electrospun vascular graft by novel antithrombotic peptide and cell-adhesive peptide to construct superior anticoagulation and ECs-selective adhesion surface in present study. The multifunctional vascular grafts benefit for high long-term patency and rapid endothelialization.

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.