Combinatorial coating of adhesive polypeptide and anti-CD34 antibody for improved endothelial cell adhesion and proliferation

Development of a universal, oriented antibody immobilization method to functionalize vascular prostheses for enhanced endothelialization for potential clinical application

BACKGROUND

Thrombosis is a common cause of vascular prosthesis failure. Antibody coating of prostheses to capture circulating endothelial progenitor cells to aid endothelialization on the device surface appears a promising solution to prevent thrombus formation. Compared with random antibody immobilization, oriented antibody coating (OAC) increases antibody-antigen binding capacity and reduces antibody immunogenicity in vivo. Currently, few OAC methods have been documented, with none possessing clinical application potential.

RESULTS

Dopamine and the linker amino-PEG8-hydrazide-t-boc were successfully deposited on the surface of cobalt chromium (CC) discs, CC stents and expanded polytetrafluoroethylene (ePTFE) grafts under a slightly basic condition. CD34 antibodies were immobilized through the reaction between aldehydes in the Fc region created by oxidation and hydrazides in the linker after t-boc removal. CD34 antibody-coated surfaces were integral and smooth as shown by scanning electron microscopy (SEM), had significantly reduced or no substrate-specific signals as revealed by X-ray photoelectron spectroscopy, were hospitable for HUVEC growth as demonstrated by cell proliferation assay, and specifically bound CD34 + cells as shown by cell binding testing. CD34 antibody coating turned hydrophobic property of ePTFE grafts to hydrophilic. In a porcine carotid artery interposition model, a confluent monolayer of cobblestone-shaped CD31 + endothelial cells on the luminal surface of the CD34 antibody coated ePTFE graft were observed. In contrast, thrombi and fibrin fibers on the bare graft, and sporadic cells on the graft coated by chemicals without antibodies were seen.

CONCLUSION

A universal, OAC method was developed. Our in vitro and in vivo data suggest that the method can be potentially translated into clinical application, e.g., modifying ePTFE grafts to mitigate their thrombotic propensity and possibly provide for improved long-term patency for small-diameter grafts.

CD34 Antibody-Coated Biodegradable Fiber Membrane Effectively Corrects Atrial Septal Defect (ASD) by Promoting Endothelialization

Biodegradable materials are a next-generation invention for the treatment of congenital heart diseases. However, the corresponding technology used to develop ideal biomaterials still presents challenges. We previously reported the first biodegradable atrial septal defect (ASD) occluder made of poly-lactic acid (PLLA). Unfortunately, the PLLA occluder had a limited endothelialization effect. In this study, the surface of the occluder membrane was coated with sericin/CD34 antibodies to promote the growth of endothelial cells and the regeneration of defective tissue and enhance the repair of the atrial septal defect. The physicochemical properties of the coat on the surface of the fiber membrane were characterized. The sericin coat successfully covered the fiber surface of the membrane, and the thickness of the membrane increased with the sericin concentration. The swelling rate reached 230%. The microscopic observation of fluorescently labeled CD34 antibodies showed that the antibodies successfully attached to the fiber membrane; the fluorescence intensity of PLLA-SH5 was particularly high. The in vitro experiment showed that the PLLA-SH-CD34 fiber membrane was biocompatible and promoted the adhesion and proliferation of endothelial cells. According to our findings, the PLLA-SH-CD34 membrane provides a theoretical and technical basis for the research and development of novel biodegradable occluders.

Attachment of endothelial colony-forming cells onto a surface bearing immobilized anti-CD34 antibodies: Specific CD34 binding versus nonspecific binding

Cardiovascular disease is a leading cause of death worldwide; however, despite substantial advances in medical device surface modifications, no synthetic coatings have so far matched the native endothelium as the optimal hemocompatible surface for blood-contacting implants. A promising strategy for rapid restoration of the endothelium on blood-contacting biomedical devices entails attracting circulating endothelial cells or their progenitors, via immobilized cell-capture molecules; for example, anti-CD34 antibody to attract CD34+ endothelial colony-forming cells (ECFCs). Inherent is the assumption that the cells attracted to the biomaterial surface are bound exclusively via a specific CD34 binding. However, serum proteins might adsorb in-between or on the top of antibody molecules and attract ECFCs via other binding mechanisms. Here, we studied whether a surface with immobilized anti-CD34 antibodies attracts ECFCs via a specific CD34 binding or a nonspecific (non-CD34) binding. To minimize serum protein adsorption, a fouling-resistant layer of hyperbranched polyglycerol (HPG) was used as a "blank slate," onto which anti-CD34 antibodies were immobilized via aldehyde-amine coupling reaction after oxidation of terminal diols to aldehydes. An isotype antibody, mIgG1, was surface-immobilized analogously and was used as the control for antigen-binding specificity. Cell binding was also measured on the HPG hydrogel layer before and after oxidation. The surface analysis methods, x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, were used to verify the intended surface chemistries and revealed that the surface coverage of antibodies was sparse, yet the anti-CD34 antibody grafted surface-bound ECFCs very effectively. Moreover, it still captured the ECFCs after BSA passivation. However, cells also attached to oxidized HPG and immobilized mIgG1, though in much lower amounts. While our results confirm the effectiveness of attracting ECFCs via surface-bound anti-CD34 antibodies, our observation of a nonspecific binding component highlights the importance of considering its consequences in future studies.

Strategies for improving endothelial cell adhesion to blood-contacting medical devices

The endothelium is a critical mediator of homeostasis on blood-contacting surfaces in the body, serving as a selective barrier to regulate processes such as clotting, immune cell adhesion, and cellular response to fluid shear stress. Implantable cardiovascular devices including stents, vascular grafts, heart valves, and left ventricular assist devices are in direct contact with circulating blood and carry a high risk for platelet activation and thrombosis without a stable endothelial cell (EC) monolayer. Development of a healthy endothelium on the blood-contacting surface of these devices would help ameliorate risks associated with thrombus formation and eliminate the need for long-term anti-platelet or anti-coagulation therapy. Although ECs have been seeded onto or recruited to these blood-contacting surfaces, most ECs are lost upon exposure to shear stress due to circulating blood. Many investigators have attempted to generate a stable EC monolayer by improving EC adhesion using surface modifications, material coatings, nanofiber topology, and modifications to the cells. Despite some success with enhanced EC retention in vitro and in animal models, no studies to date have proven efficacious for routinely creating a stable endothelium in the clinical setting. This review summarizes past and present techniques directed at improving the adhesion of ECs to blood-contacting devices.

Single and multi-functional coating strategies for enhancing the biocompatibility and tissue integration of blood-contacting medical implants

Device-associated clot formation and poor tissue integration are ongoing problems with permanent and temporary implantable medical devices. These complications lead to increased rates of mortality and morbidity and impose a burden on healthcare systems. In this review, we outline the current approaches for developing single and multi-functional surface coating techniques that aim to circumvent the limitations associated with existing blood-contacting medical devices. We focus on surface coatings that possess dual hemocompatibility and biofunctionality features and discuss their advantages and shortcomings to providing a biocompatible and biodynamic interface between the medical implant and blood. Lastly, we outline the newly developed surface modification techniques that use lubricant-infused coatings and discuss their unique potential and limitations in mitigating medical device-associated complications.

Engineering blood vessels and vascularized tissues: technology trends and potential clinical applications

Vascular tissue engineering has the potential to make a significant impact on the treatment of a wide variety of medical conditions, including providing in vitro generated vascularized tissue and organ constructs for transplantation. Since the first report on the construction of a biological blood vessel, significant research and technological advances have led to the generation of clinically relevant large and small diameter tissue engineered vascular grafts (TEVGs). However, developing a biocompatible blood-contacting surface is still a major challenge. Researchers are using biomimicry to generate functional vascular grafts and vascular networks. A multi-disciplinary approach is being used that includes biomaterials, cells, pro-angiogenic factors and microfabrication technologies. Techniques to achieve spatiotemporal control of vascularization include use of topographical engineering and controlled-release of growth/pro-angiogenic factors. Use of decellularized natural scaffolds has gained popularity for engineering complex vascularized organs for potential clinical use. Pre-vascularization of constructs prior to implantation has also been shown to enhance its anastomosis after implantation. Host-implant anastomosis is a phenomenon that is still not fully understood. However, it will be a critical factor in determining the in vivo success of a TEVGs or bioengineered organ. Many clinical studies have been conducted using TEVGs, but vascularized tissue/organ constructs are still in the research & development stage. In addition to technical challenges, there are commercialization and regulatory challenges that need to be addressed. In this review we examine recent advances in the field of vascular tissue engineering, with a focus on technology trends, challenges and potential clinical applications.

Epithelial sealing effectiveness against titanium or zirconia implants surface

The aims of implant treatment now involve not only restoration of mastication function, but also recovery of esthetics. Currently, zirconia is widely used as an esthetic material for implant abutment. Therefore, it is very important to understand the efficacy of zirconia for epithelial sealing as an implant material. We compared the effects of materials on the sealing of the peri-implant epithelium (PIE) to titanium (Ti) or zirconia (Zr) implants, for application to clinical work. Maxillary first molars were extracted from rats and replaced with Ti or Zr implants. The sealing of the PIE to the implants was evaluated with immunohistochemistry observation and HRP analysis. The morphological and functional changes in rat oral epithelial cells (OECs) cultured on Ti or Zr plates were also evaluated. After 4 weeks, the PIE on the Ti and Zr implants showed similar structures. The Zr implants appeared to form a weak epithelial seal at the tissue-implant interface, and exhibited markedly less adhesive structures than the Ti implants under electron microscopic observation. In the in vitro experiments, decreased expression levels of adhesion proteins were observed in OECs cultured on Zr plates compared with those cultured on Ti plates. In addition, the cell adherence on Zr plates was reduced, while the cell migration was low on Ti plates. Zr is a better choice for an esthetic implant material, but needs further improvement for integration with the epithelial wound healing process around a dental implant. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Lubricant-Infused Surfaces with Built-In Functional Biomolecules Exhibit Simultaneous Repellency and Tunable Cell Adhesion

Lubricant-infused omniphobic surfaces have exhibited outstanding effectiveness in inhibiting nonspecific adhesion and attenuating superimposed clot formation compared with other coated surfaces. However, such surfaces blindly thwart adhesion, which is troublesome for applications that rely on targeted adhesion. Here we introduce a new class of lubricant-infused surfaces that offer tunable bioactivity together with omniphobic properties by integrating biofunctional domains into the lubricant-infused layer. These novel surfaces promote targeted binding of desired species while simultaneously preventing nonspecific adhesion. To develop these surfaces, mixed self-assembled monolayers (SAMs) of aminosilanes and fluorosilanes were generated. Aminosilanes were utilized as coupling molecules for immobilizing capture ligands, and nonspecific adhesion of cells and proteins was prevented by infiltrating the fluorosilane molecules with a thin layer of a biocompatible fluorocarbon-based lubricant, thus generating biofunctional lubricant-infused surfaces. This method yields surfaces that (a) exhibit highly tunable binding of anti-CD34 and anti-CD144 antibodies and adhesion of endothelial cells, while repelling nonspecific adhesion of undesirable proteins and cells not only in buffer but also in human plasma or human whole blood, and (b) attenuate blood clot formation. Therefore, this straightforward and simple method creates biofunctional, nonsticky surfaces that can be used to optimize the performance of devices such as biomedical implants, extracorporeal circuits, and biosensors.

Tissue Engineering at the Blood-Contacting Surface: A Review of Challenges and Strategies in Vascular Graft Development

Tissue engineered vascular grafts (TEVGs) are beginning to achieve clinical success and hold promise as a source of grafting material when donor grafts are unsuitable or unavailable. Significant technological advances have generated small-diameter TEVGs that are mechanically stable and promote functional remodeling by regenerating host cells. However, developing a biocompatible blood-contacting surface remains a major challenge. The TEVG luminal surface must avoid negative inflammatory responses and thrombogenesis immediately upon implantation and promote endothelialization. The surface has therefore become a primary focus for research and development efforts. The current state of TEVGs is herein reviewed with an emphasis on the blood-contacting surface. General vascular physiology and developmental challenges and strategies are briefly described, followed by an overview of the materials currently employed in TEVGs. The use of biodegradable materials and stem cells requires careful control of graft composition, degradation behavior, and cell recruitment ability to ensure that a physiologically relevant vessel structure is ultimately achieved. The establishment of a stable monolayer of endothelial cells and the quiescence of smooth muscle cells are critical to the maintenance of patency. Several strategies to modify blood-contacting surfaces to resist thrombosis and control cellular recruitment are reviewed, including coatings of biomimetic peptides and heparin.

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.

Poly(ethylmethacrylate-co-diethylaminoethyl acrylate) coating improves endothelial re-population, bio-mechanical and anti-thrombogenic properties of decellularized carotid arteries for blood vessel replacement

Decellularized vascular scaffolds are promising materials for vessel replacements. However, despite the natural origin of decellularized vessels, issues such as biomechanical incompatibility, immunogenicity risks and the hazards of thrombus formation, still need to be addressed. In this study, we coated decellularized vessels obtained from porcine carotid arteries with poly (ethylmethacrylate-co-diethylaminoethylacrylate) (8g7) with the purpose of improving endothelial coverage and minimizing platelet attachment while enhancing the mechanical properties of the decellularized vascular scaffolds. The polymer facilitated binding of endothelial cells (ECs) with high affinity and also induced endothelial cell capillary tube formation. In addition, platelets showed reduced adhesion on the polymer under flow conditions. Moreover, the coating of the decellularized arteries improved biomechanical properties by increasing its tensile strength and load. In addition, after 5 days in culture, ECs seeded on the luminal surface of 8g7-coated decellularized arteries showed good regeneration of the endothelium. Overall, this study shows that polymer coating of decellularized vessels provides a new strategy to improve re-endothelialization of vascular grafts, maintaining or enhancing mechanical properties while reducing the risk of thrombogenesis. These results could have potential applications in improving tissue-engineered vascular grafts for cardiovascular therapies with small caliber vessels.

Surface Coating of Polytetrafluoroethylene with Extracellular Matrix and Anti-CD34 Antibodies Facilitates Endothelialization and Inhibits Platelet Adhesion Under Sheer Stress

Expanded polytetrafluoroethylene (ePTFE) polymers do not support endothelialization because of nonconductive characteristics towards cellular attachment. Inner surface modification of the grafts can improve endothelialization and increase the long-term patency rate of the ePTFE vascular grafts. Here we reported a method of inner-surface modification of ePTFE vascular graft with extracellular matrix (ECM) and CD34 monoclonal antibodies (CD34 mAb) to stimulate the adhesion and proliferation of circulating endothelial progenitor cells on ePTFE graft to enhance graft endothelialization. The inner surface of ECM-coated ePTFE grafts were linked with CD34 mAb in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC/NHS) solution and the physicochemical properties, surface morphology, biocompatibility, and hemocompatibility of the grafts were studied. The hydrophilicity of CD34 mAb-coated graft inner surface was significantly improved. Fourier transform infrared spectroscopy analysis confirmed ECM and CD34 mAb cross-linking in the ePTFE vascular grafts with our method. Scanning electron microscopy analysis showed protein layer covering uniformly on the inner surface of the modified grafts. The cell-counting kit-8 (CCK-8) assay confirmed that the modified graft has no obvious cytotoxicity. The modified graft showed a low hemolytic rate (0.9%) in the direct contact hemolysis test, suggesting the modification improved hemocompatibility of biopolymers. The modification also decreased adhesion of platelets, while significantly increased the adhesion of endothelial cells on the grafts. We conclude that our method enables ePTFE polymers modification with ECM and CD34 mAb, facilitates endothelialization, and inhibits platelet adhesion on the grafts, thus may increase the long-term patency rate of the prosthetic bypass grafts.

Tailoring biomaterial surface properties to modulate host-implant interactions: implication in cardiovascular and bone therapy

Host body response to a foreign medical device plays a critical role in defining its fate post implantation. It is thus important to control host-material interactions by designing innovative implant surfaces. In the recent years, biochemical and topographical features have been explored as main target to produce this new type of bioinert or bioresponsive implants. The review discusses specific biofunctional materials and strategies to achieve a precise control over implant surface properties and presents possible solutions to develop next generation of implants, particularly in the fields of bone and cardiovascular therapy.

Contrasting biofunctionalization strategies for the enhanced endothelialization of biodegradable vascular grafts

Surface modification of biodegradable vascular grafts is an important strategy to improve the in situ endothelialization of tissue engineered vascular grafts (TEVGs) and prevent major complications associated with current synthetic grafts. Important strategies for improving endothelialization include increasing endothelial cell mobilization and increased endothelial cell capture through biofunctionalization of TEVGs. The objective of this study was to assess two biofunctionalization strategies for improving endothelialization of biodegradable polyester vascular grafts. These techniques consisted of cross-linking heparin to graft surfaces to immobilize vascular endothelial growth factor (VEGF) or antibodies against CD34 (anti-CD34Ab). To this end, heparin, VEGF, and anti-CD34Ab attachment and quantification assays confirmed the efficacy of the modification strategy. Cell attachment and proliferation on these groups were compared to unmodified grafts in vitro and in vivo. To assess in vivo graft functionality, the grafts were implanted as inferior vena cava interpositional conduits in mice. Modified vascular grafts displayed increased endothelial cell attachment and activity in vivo, according to microscopy techniques, histological results, and eNOS expression. Inner lumen diameter of the modified grafts was also better maintained than controls. Overall, while both functionalized grafts outperformed the unmodified control, grafts modified with anti-CD34Ab appeared to yield the most improved results compared to VEGF-loaded grafts.

Effect of low voltage AC fields on cardiovascular implants

Coronary Artery Stents have been the preferred form of treatment for vascular occlusive disease, due to the minimally invasive surgical procedure, post-operative recovery time and cost, when compared to open coronary bypass surgery. The cellular response upon applying an AC electric field to type 316LM Stainless Steel stent mimics was investigated in this paper. The highest RBC adhesion was observed at voltages higher than 88 mV and lower than 74 mV. Their unique alignment along the lines of fracture on the stent surface at 88 mV was a phenomenon caused by an increase in electrical conductivity in these regions. Being able to control RBC adhesion may have various clinical implications such as inhibition of thrombus formation, and provide a basis to analyse whether electric fields may be applied to cancer therapy as well.

Biological effects of anti-CD34-coated ePTFE vascular grafts. Early in vivo experimental results

Aim of the study

To assess the biological activity of anti-CD34 antibody-coated ePTFE vascular prostheses.

Material and methods

Indium¹¹¹-labeled autologous thrombocytes were administered to 5 anesthetized pigs after the placement of femoral arterial and venous catheters. An arterio-venous fistula, created by the random interposition of 4 different ePTFE grafts (A = dry control, B = dry anti-CD34, C = wet control, D = wet anti-CD34), was blood perfused for 0, 10, 30, 60 and 120 minutes. Radioactivity of each graft was measured and expressed in cpm/mg. Morphological studies were performed to assess intraluminal deposition.

Results

The median radioactivity of graft B was significantly higher than that of graft A after 60 min (1074 vs. 18; p = 0.021) and 120 min (1990 vs. 25; p = 0.043) of perfusion. Similarly, graft D was significantly more active than graft C (60 min: 1388 vs. 26; p = 0.021 and 120 min: 2780 vs. 23; p = 0.021). Histological and SEM results confirmed the radio-labeling in-vivo studies by showing significantly more protein/cell and platelet depositions (p = 0.012).

Conclusions

Anti-CD34-coated ePTFE grafts bound significantly more platelets/cells and proteins than their uncoated counterparts, confirming the bioactivity of the antibody. This process is time-dependent and matches the morphological results. The anti-CD34 coating may enhance temporal and spatial endothelialization of vascular grafts and, thus, possibly improve clinical results by providing direct endothelial progenitor cell (EPC) adhesion/entrapment or by creating a biocompatible protein-thrombocyte/cell layer that indirectly enhances migration and further proliferation of EPCs.

A novel three-dimensional adipose-derived stem cell cluster for vascular regeneration in ischemic tissue

BACKGROUND AIMS

Stem cells are one of the most powerful tools in regeneration medicine. However, many limitations remain regarding the use of adult stem cells in clinical applications, including poor cell survival and low treatment efficiency. We describe an innovative three-dimensional cell mass (3DCM) culture that is based on cell adhesion (basic fibroblast growth factor-immobilized substrate) and assess the therapeutic potential of 3DCMs composed of human adipose tissue-derived stromal cells (hASCs).

METHODS

For formation of a 3DCM, hASCs were cultured on a substrate with immobilized fibroblast growth factor-2. The angiogenic potential of 3DCMs was determined by immunostaining, fluorescence-activated cell sorting and protein analysis. To evaluate the vasculature ability and improved treatment efficacy of 3DCMs, the 3DCMs were intramuscularly injected into the ischemic limbs of mice.

RESULTS

The 3DCMs released various angiogenic factors (eg, vascular endothelial growth factor and interleukin-8) and differentiated into vascular cells within 3 days in normal medium. Blood vessel and tissue regeneration was clearly observed through visual inspection in the 3DCM-injected group. hASC injection slowed limb necrosis after treatment, but 50% of the mice ultimately had limb loss within 28 days. Most mice receiving 3DCMs had limb salvage (89%) or mild limb necrosis (11%).

CONCLUSIONS

3DCM culture promotes the efficient vascular differentiation of stem cells, and 3DCM transplantation results in the direct vascular regeneration of the injected cells and an improved therapeutic efficacy.

Synthetic ePTFE grafts coated with an anti-CD133 antibody-functionalized heparin/collagen multilayer with rapid in vivo endothelialization properties

An anti-CD133 antibody multilayer functionalized by heparin/collagen on an expanded polytetrafluoroethylene (ePTFE) graft was developed to accelerate early endothelialization. The surface modification of ePTFE grafts demonstrated that the multilayer is stable in static incubation and shaking conditions and that the anti-CD133 antibodies were successfully cross-linked onto the surface. Blood compatibility tests revealed that the coimmobilized heparin/collagen films in the presence or absence of anti-CD133 antibodies prolonged the blood coagulation time and that there was less platelet activation and aggregation, whereas the hemolysis rate was comparable with the bare ePTFE grafts. Cellular proliferation was not inhibited, as the heparin/collagen synthetic vascular grafts coated with CD133 antibody showed little cytotoxicity. The endothelial cells adhered well to the modified ePTFE grafts during a cell adhesion assay. A porcine carotid artery transplantation model was used to evaluate the modified ePTFE grafts in vivo. The results of histopathological staining and scanning electron microscopy indicated that the anti-CD133 antibody was able to accelerate the attachment of vascular endothelial cells onto the ePTFE grafts, resulting in early rapid endothelialization. The success of the anti-CD133 antibody-functionalized heparin/collagen multilayer will provide an effective selection system for the surface modification of synthetic vascular grafts and improve their use in clinical applications.

Promotive effect of insulin-like growth factor-1 for epithelial sealing to titanium implants

Improvement of oral epithelial adhesion to titanium (Ti) may significantly enhance the efficacy of dental implants. Here, we investigated whether insulin-like growth factor-1 (IGF-1) improved the sealing of the peri-implant epithelium (PIE) around the implant. Right maxillary first molars were extracted from rats and replaced with experimental implants. After 4 weeks of IGF-1 treatment, the implant-PIE interface exhibited a band of immunoreactive laminin-332 (Ln-5), similar to the tooth-junctional epithelium interface, that was partially absent in the untreated group. Immunoelectron microscopy showed a characteristic Ln-5-positive band including hemidesmosomes at both the apical and upper portions of the implant-PIE interface in the IGF-1-treated group. We also investigated the effects of IGF-1/PI3K inhibitors on the dynamics of rat oral epithelial cells (OECs) grown on Ti plates. In OECs cultured with IGF-1, adhesion protein expression increased, cell adherence to Ti plates was higher, and proliferation was faster, whereas migration and apoptosis were induced in the absence of IGF-1 or in the presence of both IGF-1 and a PI3K inhibitor. These data suggest that PI3K mediates the promotive effects of IGF-1, and that IGF-1 is effective at enhancing epithelial integration around Ti implants.

Strategies and techniques to enhance the in situ endothelialization of small-diameter biodegradable polymeric vascular grafts

Due to the lack of success in small-diameter (<6 mm) prosthetic vascular grafts, a variety of strategies have evolved utilizing a tissue-engineering approach. Much of this work has focused on enhancing the endothelialization of these grafts. A healthy, confluent endothelial layer provides dynamic control over homeo-stasis, influencing and preventing thrombosis and smooth muscle cell proliferation that can lead to intimal hyperplasia. Strategies to improve endothelialization of biodegradable polymeric grafts have encompassed both chemical and physical modifications to graft surfaces, many focusing on the recruitment of endothelial and endothelial progenitor cells. This review aims to provide a compilation of current and developing strategies that utilize in situ endothelialization to improve vascular graft outcomes, providing a context for the future directions of vascular tissue-engineering strategies that do not require preprocedural cell seeding.

Combination coating of chitosan and anti-CD34 antibody applied on sirolimus-eluting stents can promote endothelialization while reducing neointimal formation

Background

Circulating endothelial progenitor cells (EPCs) capture technology improves endothelialization rates of sirolimus-eluting stents (SES), but the problem of delayed re-endothelialization, as well as endothelial dysfunction, has still not been overcome. Therefore, we investigated whether the combination coating of hyaluronan-chitosan (HC) and anti-CD34 antibody applied on an SES (HCASES) can promote endothelialization, while reducing neointimal formation and inflammation.

Methods

Sirolimus-eluting stents(SES), anti-CD34 antibody stents (GS) and HC-anti-CD34 antibody combined with sirolimus-eluting stents (HCASES) were deployed in 54 normal porcine arteries and harvested for scanning electron microscopy (SEM) and histological analysis. The ratio of endothelial coverage above the stents was evaluated by SEM analysis at 7, 14 and 28 days. The percentage of in-stent stenosis was histologically analyzed at 14 and 28 days.

Results

SEM analysis at 7 days showed that endothelial strut coverage was increased in the HCASES group (68±7%) compared with that in the SES group (31±4%, p=0.02). At 14 days, stent surface endothelialization, evaluated by SEM, showed a significantly higher extent of endothelial coverage above struts in the GS (95 ± 2%) and the HCASES groups (87±4%) compared with that in the SES group (51±6%, p=0.02). Histological examination showed that the percentage of stenosis in the HCASES group was not significantly different to that of the SES and GS groups (both p> 0.05). At 28 days, there was no difference in the rates of endothelial coverage between the HCASES and GS groups. The HCASES group showed less stenosis than that in the GS group (P < 0.05), but it was not significantly different from the SES group (P=0.068).

Conclusions

SEM and histology demonstrated that HCASESs can promote re-endothelialization while enhancing antiproliferative effects.

Improvement of interfacial adhesion of biodegradable polymers coated on metal surface by nanocoupling

A method of securing the adhesion of biodegradable polymer coating was investigated for drug-eluting metal stents, using surface-initiated ring-opening polymerization (SI-ROP) of L-lactide. Introduction of oligolactide on the stainless steel (SS) surface was successful and the thickness of the oligolactide grafts remained on the nanometer scale, as determined by ellipsometry. The presence of an oligolactide graft was also identified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) and electron spectroscopy for chemical analysis (ESCA). On top of the grafts, poly(D,L-lactide-co-glycolide) (PLGA) coating was carried out on different substrates such as SS control, plasma-treated SS, and lactide-grafted (referred to as a nanocoupled) SS using electrospraying. When the adhesion forces were measured with a scratch tester, the nanocoupled SS showed the strongest interfacial adhesion between polymer coating layer and metal substrate. The outcome of the peel-off test was also consistent with the result of the scratch test. When degradation behavior of the polymer coating in vitro was examined for up to 4 weeks in a continuous fluid flow, the SEM images demonstrated that polymer degradation was obvious due to hydration and swelling of the polymer matrix. Although the matrix completely disappeared after 4 weeks for SS control and plasma-treated substrates, the nanocoupled SS was persistent with some polymer matrix. In addition, the release profiles of SRL-loaded PLGA coating appeared slightly different between control and nanocoupled groups. This work suggested that the concept of nanocoupling remarkably improved the interfacial adhesion stability between metal surface and polymer layer and controlled drug release, and showed the feasibility of drug-eluting stents.

Ureteral stents: new ideas, new designs

Ureteral stents represent a minimally invasive alternative to preserve urinary drainage whenever ureteral patency is deteriorated or is under a significant risk to be occluded due to extrinsic or intrinsic etiologies. The ideal stent that would combine perfect long-term efficacy with no stent-related morbidity is still lacking and stent usage is associated with several adverse effects that limit its value as a tool for long-term urinary drainage. Several new ideas on stent design, composition material and stent coating currently under evaluation, foreseen to eliminate the aforementioned drawbacks of ureteral stent usage. In this article we review the currently applied novel ideas and new designs of ureteral stents. Moreover, we evaluate potential future prospects of ureteral stent development adopted mostly by the pioneering cardiovascular stent industry, focusing, however, on the differences between ureteral and endothelial tissue.