Effects of plasma treated PET and PTFE on expression of adhesion molecules by human endothelial cells in vitro

Long-term Outcomes of Polytetrafluoroethylene Bicuspid Pulmonary Valve Replacement

BACKGROUND

In 2016 we reported promising midterm outcomes of bicuspid pulmonary valve replacement using 0.1-mm polytetrafluoroethylene (PTFE) membrane. This follow-up study analyzes long-term outcomes and risk factors for reintervention and structural valve deterioration (SVD).

METHODS

We performed a retrospective review of the original 119 patients who underwent PTFE bicuspid pulmonary valve replacement. Median patient age was 16.9 years (range, 0.4-57.1). Reintervention was defined as any surgical or percutaneous catheter procedure on the PTFE valve. SVD was defined as development of a peak pressure gradient ≥ 50 mm Hg or at least a moderate amount of pulmonary regurgitation on follow-up echocardiography.

RESULTS

The median follow-up duration was 9.5 years. The survival rate was 96.5% at 5 and 10 years, with 2 early and 2 late mortalities. Freedom from reintervention was 90.0% at 5 years and 63.3% at 10 years. Freedom from SVD was 92.8% at 5 years and 51.1% at 10 years, with regurgitation the predominant mode (64.6%). Freedom from both reintervention and SVD at 5 and 10 years were 89.1% and 49.5%, respectively. Multivariable analysis identified smaller valve diameter (hazard ratio, 0.82; P < .001) and more than trivial pulmonary regurgitation at discharge (hazard ratio, 5.81; P < .001) as risk factors for reintervention or SVD.

CONCLUSIONS

Long-term results of the PTFE bicuspid pulmonary valve replacement were acceptable. However, improvements may be needed to reduce technical error and improve durability. Smaller valve diameter and more than trivial pulmonary regurgitation at discharge were risk factors for reintervention or SVD, warranting careful follow-up for timely reintervention.

Evaluating hydrophobic recovery of N2 and H2O(g) plasma modified silk fibroin films aged at ambient and elevated temperatures

Silk fibroin is a naturally derived polymer with great potential for biomedical use due to its strength, lack of immune response, and ability to biodegrade. The relatively hydrophobic nature of silk, however, can cause challenges with cell adhesion in vivo. Therefore, modification must be performed to improve the surface hydrophilicity, enhancing silk utility in the biomedical space. Low-temperature plasma (LTP) treatment is an established method for polymer modification and has the benefits of being a solvent-free, adaptable process. N₂ and H₂O(g) LTP treatments are both well-documented as strategies to enhance polar functional groups on a polymer's surface. However, many polymers tend to revert to their original hydrophobic state upon aging, reversing the effects of LTP modification. The hydrophobic recovery of N₂ and H₂O(g) LTP-modified silk has not been previously studied but has important implications for the uses and longevity of silk substrates in biomedical contexts. The goal of this study was to systematically evaluate the hydrophobic recovery of N₂ and H₂O(g) LTP-treated silk films. Films were LTP-modified using optimized plasma parameters (applied power, pressure, treatment time) and aged under both ambient and elevated temperature conditions up to 6 weeks after the initial treatment. Silk film surface properties were evaluated immediately after treatment and throughout the aging process using both water contact angle goniometry and x-ray photoelectron spectroscopy. LTP-treated silk films demonstrated a significant decrease in hydrophobicity compared to the untreated controls. Remarkably, both N₂ and H₂O(g) LTP modifications resulted in surfaces that retained hydrophilic properties over the 6 week aging period. Our findings represent a departure from what has been previously demonstrated in most LTP-modified synthetic polymers, suggesting that the secondary structure of silk fibroin plays a critical role in resisting hydrophobic recovery.

Critical Review on Sustainability in Denim: A Step toward Sustainable Production and Consumption of Denim

The exponential development in knowledge on the health and environmental concerns linked to conventional denim processing is directly responsible for the continuous increase in demand for the exploitation of sustainable denim. Research is essential to explore alternative methods to reduce the environmental impact caused by these industries. This review examines the many sustainable ways to produce denim, keeping in mind the problems that the denim industry is now facing in finding alternatives to conventional manufacturing practices. The most current advancements in environmentally friendly dyeing techniques for denim have been extensively discussed. These processes include the production of indigo from bacteria as well as different dyeing processes, such as digital spray, microbially assisted dyeing, and foam dyeing denim with indigo. In addition, this review covers the many environmentally friendly finishing methods for denim garments, such as ozone fading, e-flow, enzyme-based bleaching, water, laser fading, and so on. Finally, it is described how the chemical and mechanical processes used to finish denim might affect the amount of microplastics and microfibers released from the denim garment during domestic washing. As a result, the content presented in this review aims to address the importance of sustainable denim processing, that is, something that can be rethought, reevaluated, renewed, and restructured within the scope of conventional denim processes, while taking eco-responsible solutions for increased environmental sustainability into account.

Surface Coating of Polyurethane Films with Gelatin, Aspirin and Heparin to Increase the Hemocompatibility of Artificial Vascular Grafts

Purpose: A hemocompatible substrate can offer a wonderful facility for nitric oxide (NO) production by vascular endothelial cells in reaction to the inflammation following injuries. NO inhibits platelet aggregation this is especially critical in small-diameter vessels. Methods: The substrate films were made of polyurethane (PU) in a casting process and after plasma treatments, their surface was chemically decorated with polyethylene glycol (PEG) 2000, gelatin, gelatin-aspirin, gelatin-heparin and gelatin-aspirin-heparin. The concentrations of these ingredients were optimized in order to achieve the biocompatible values and the resulting modifications were characterized by water contact angle and Fourier transform infra-red (FTIR) assays. The values of NO production and platelet adhesion were then examined. Results: The water contact angle of the modified surface was reduced to 26±4^∘ and the newly developed hydrophilic chemical groups were confirmed by FTIR. The respective concentrations of 0.05 mg/ml and 100 mg/mL were found to be the IC50 values for aspirin and heparin. However, after the surface modification with aspirin, the bioactivity of the substrate increased in compared to the other experimental groups. In addition, there was a synergistic effect between these reagents for NO synthesis. While, heparin inhibited platelet adhesion more than aspirin. Conclusion: Because of the highly hydrophilic nature of heparin, this reagent was hydrolyzed faster than aspirin and therefore its influence on platelet aggregation and cell growth was greater. Taken together, the results give the biocompatible concentrations of both biomolecules that are required for endothelial cell proliferation, NO synthesis and platelet adhesion.

Potential of poly(alkylene terephthalate)s to control endothelial cell adhesion and viability

Poly(ethylene terephthalate) (PET) is known for its various useful characteristics, including its applicability in cardiovascular applications, more precisely as synthetic bypass grafts for large diameter (≥ 6 mm) blood vessels. Although it is widely used, PET is not an optimal material as it is not interactive with endothelial cells, which is required for bypasses to form a complete endothelium. Therefore, in this study, poly(alkylene terephthalate)s (PATs) have been studied. They were synthesized via a single-step solution polycondensation reaction, which requires mild reaction conditions and avoids the use of a catalyst or additives like heat stabilizers. A homologous series was realized in which the alkyl chain length varied from 5 to 12 methylene groups (n = 5-12). Molar masses up to 28,000 g/mol were obtained, while various odd-even trends were observed with modulated differential scanning calorimetry (mDSC) and rapid heat-cool calorimetry (RHC) to access the thermal properties within the homologous series. The synthesized PATs have been subjected to in vitro cell viability assays using Human Umbilical Vein Endothelial Cells (HUVECs) and Human Dermal Microvascular Endothelial Cells (HDMECs). The results showed that HUVECs adhere and proliferate most pronounced onto PAT_(n=9) surfaces, which could be attributed to the surface roughness and morphology as determined by atomic force microscopy (AFM) (i.e. R_q = 204.7 nm). HDMECs were investigated in the context of small diameter vessels and showed superior adhesion and proliferation after seeding onto PAT_(n=6) substrates. These preliminary results already pave the way towards the use of PAT materials as substrates to support endothelial cell adhesion and growth. Indeed, as superior endothelial cell interactivity compared to PET was observed, time-consuming and costly surface modifications of PET grafts could be avoided by exploiting this novel material class.

Considerations in the Development of Small-Diameter Vascular Graft as an Alternative for Bypass and Reconstructive Surgeries: A Review

BACKGROUND

Current design strategies for small diameter vascular grafts (< 6 mm internal diameter; ID) are focused on mimicking native vascular tissue because the commercially available grafts still fail at small diameters, notably due to development of intimal hyperplasia and thrombosis. To overcome these challenges, various design approaches, material selection, and surface modification strategies have been employed to improve the patency of small-diameter grafts.

REVIEW

The purpose of this review is to outline various considerations in the development of small-diameter vascular grafts, including material choice, surface modifications to enhance biocompatibility/endothelialization, and mechanical properties of the graft, that are currently being implanted. Additionally, we have taken into account the general vascular physiology, tissue engineering approaches, and collective achievements of the authors in this area. We reviewed both commercially available synthetic grafts (e-PTFE and PET), elastic polymers such as polyurethane and biodegradable and bioresorbable materials. We included naturally occurring materials by focusing on their potential application in the development of future vascular alternatives.

CONCLUSION

Until now, there are few comprehensive reviews regarding considerations in the design of small-diameter vascular grafts in the literature. Here-in, we have discussed in-depth the various strategies employed to generate engineered vascular graft due to their high demand for vascular surgeries. While some TEVG design strategies have shown greater potential in contrast to autologous or synthetic ePTFE conduits, many are still hindered by high production cost which prevents their widespread adoption. Nonetheless, as tissue engineers continue to develop on their strategies and procedures for improved TEVGs, soon, a reliable engineered graft will be available in the market. Hence, we anticipate a viable TEVG with resorbable property, fabricated via electrospinning approach to hold a greater potential that can overcome the challenges observed in both autologous and allogenic grafts. This is because they can be mechanically tuned, incorporated/surface-functionalized with bioactive molecules and mass-manufactured in a reproducible manner. It is also found that most of the success in engineered vascular graft approaching commercialization is for large vessels rather than small-diameter grafts used as cardiovascular bypass grafts. Consequently, the field of vascular engineering is still available for future innovators that can take up the challenge to create a functional arterial substitute.

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.

Immobilization of Enzymes on Flexible Tubing Surfaces for Continuous Bioassays

Immobilized enzymes can be used to catalyze biochemical reactions in a batch process, however, it is more difficult to use them in a continuous process. Herein, we develop an enzyme immobilization technique for flexible tubing surfaces, which can be used to catalyze biochemical reactions in a continuous process. In this technique, the tubing is first treated with (3-aminopropyl)triethoxysilane at 50 °C and baked at 100 °C in vacuum to form a network of reactive amine functional group on the inner tubing surface. Subsequently, dextran polyaldehyde, a polymeric cross-linker, is used to immobilize crude protease extract and catalase for hydrolyzing casein and degrading H₂O₂, respectively, in a continuous process. The immobilized proteases are highly stable even after a long-term storage at 4 °C. After 12 weeks of storage, 90% of the original protease activity can be preserved. Meanwhile, the immobilized catalase is able to degrade 0.1% H₂O₂ solution flowing at 5 μL/min. The immobilization technique is potentially useful for bioassays and industrial wastewater treatments when continuous processes are preferred.

Sialic Acid-Functionalized pH-Triggered Micelles for Enhanced Tumor Tissue Accumulation and Active Cellular Internalization of Orthotopic Hepatocarcinoma

Both targeted and stimuli-sensitive drug-delivery systems (DDSs) have been developed to augment antitumor effects. However, lack of knowledge regarding tumor tissue targeting and different effects of the stimuli-sensitive DDSs in orthotropic and ectopic tumors have impeded further advances in their clinical applications. Herein, we first reported a pH-triggered micelle with sialic acid (SA)-driven targeting ability (SA-poly(ethylene glycol)-hydrazone linker-doxorubicin (DOX), SPD). The SPD micelles encapsulated with DOX (SPDD) showed sustained drug release over 48 h in response to the pH gradient in vivo, slow under physical conditions and accelerated in the acid tumor microenvironment. In addition, the SPD micelles showed 2.3-fold higher accumulation in tumors after 48 h compared to the micelles lacking the SA moiety. The overexpression of E-selectin on the inflammatory vascular endothelial cells surrounding the tumors increased the accumulation of SPD micelles in tumor tissues, whereas that on the tumor cells increased the internalization of micelles. Consequently, SPDD micelles exerted remarkable antitumor effects in both orthotopic and ectopic models. Application of SPDD micelles in the in situ model reduced the tumor volume (77.57 mm³ vs 62.13 mm³) and metastasis after treatment for 25 days. These results suggest that SA-driven targeted DDS with a pH-responsive switch has the potential to treat hepatocarcinoma effectively both ectopically and orthotopically.

Promoting Endothelial Cell Affinity and Antithrombogenicity of Polytetrafluoroethylene (PTFE) by Mussel-Inspired Modification and RGD/Heparin Grafting

When used as small-diameter vascular grafts (SDVGs), synthetic biomedical materials like polytetrafluoroethylene (PTFE) may induce thrombosis and intimal hyperplasia due to the lack of an endothelial cell layer. Modification of the PTFE in an aqueous solution is difficult because of its hydrophobicity. Herein, aiming to simultaneously promote endothelial cell affinity and antithrombogenicity, a mussel-inspired modification approach was employed to enable the grafting of various bioactive molecules like RGD and heparin. This approach involves a series of pragmatic steps including oxygen plasma treatment, dopamine (DA) coating, polyethylenimine (PEI) grafting, and RGD or RGD/heparin immobilization. Successful modification in each step was verified via Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Plasma treatment increased the hydrophilicity of PTFE, thereby allowing it to be efficiently coated with dopamine. Grafting of dopamine, RGD, and heparin led to an increase in surface roughness and a decrease in water contact angle due to increased surface energy. Platelet adhesion increased after dopamine and RGD modification, but it dramatically decreased when heparin was introduced. All of these modifications, especially the incorporation of RGD, showed favorable effects on endothelial cell attachment, viability, and proliferation. Due to strong cell-substrate interactions between endothelial cells and RGD, the RGD/heparin-grafted PTFE demonstrated high endothelial cell affinity. This facile modification method is highly suitable for all hydrophobic surfaces and provides a promising technique for SDVG modification to stimulate fast endothelialization and effective antithrombosis.

Effects Of Gelatine-Coated Vascular Grafts On Human Neutrophils

The aim of the study was to investigate the immune-modulatory potential of commercially available PTFE and polyester vascular grafts with and without gelatine-coating. The biomaterial-cell-interaction was characterized by changes of established parameters such as PMN-related receptors/mediators, phagocytosis potential and capacity as well as the effect of an additional plasma-dependent modulation.

MATERIAL AND METHODS

By means of a standardized experimental in vitro model, various vascular graft material (PTFE/polyester/uncoated/gelatine-coated) was used for incubation with or without plasma and co-culturing with human neutrophile granulocytes (PMN) followed by analysis of representative receptors and mediators (CD62L, CD11b, CXCR2, fMLP-R, IL-8, Elastase, LTB4). Oxidative burst assessed phagocytosis capacity.

RESULTS

Comparing the vascular grafts, un-coated PTFE induced the lowest magnitude of cell stimulation whereas in case of gelatine-coating, cell response exceeded those of the other vascular grafts. This was also found comparing the polyester-based prosthetic material. Gelatine-coated polyester led to a more pronounced release of elastase than gelatine-coated PTFE and the uncoated materials. The results of oxidative burst indicated a reduced phagocytosis capacity in case of gelatine-coated polyester. Plasma incubation did also provide an impact on the cellular response. While in case of gelatine-coating, PMN-related receptor stimulation became lower, it increased by native polyester. The latter one did also induce more mediators such as IL-8 and LTB4 than gelatine-coated material.

CONCLUSIONS

There have been no extensive data on cell-cell interactions, cytokines and general histo-/hemocompatibility of human cells by the new generation of vascular grafts. It remains still open whether healing process and infectious resistance can be compromised by material-dependent over-stimulation or reduced phagocytosis potential of the immune cells of the primary unspecific immune response induced by gelatine-coated materials.

Emerging Trends in Abdominal Wall Reinforcement: Bringing Bio-Functionality to Meshes

Abdominal wall hernia is a recurrent issue world-wide and requires the implantation of over 1 million meshes per year. Because permanent meshes such as polypropylene and polyester are not free of complications after implantation, many mesh modifications and new functionalities have been investigated over the last decade. Indeed, mesh optimization is the focus of intense development and the biomaterials utilized are now envisioned as being bioactive substrates that trigger various physiological processes in order to prevent complications and to promote tissue integration. In this context, it is of paramount interest to review the most relevant bio-functionalities being brought to new meshes and to open new avenues for the innovative development of the next generation of meshes with enhanced properties for functional abdominal wall hernia repair.

Angiogenic tube formation of bovine aortic endothelial cells grown on patterns formed by H2/He plasma treatment of the plasma polymerized hexamethyldisiloxane film

Angiogenesis, the process to generate new vessels, is necessary for normal development in children as well as the wound healing and the tumor growth in adults. Therefore, it is physiologically and/or pathophysiologically significant to monitor angiogenesis. However, classical in vitro methods to evaluate angiogenesis take a long time and are expensive. Here, the authors developed a novel method to analyze the angiogenesis in a simple and economical way, using patterned films. In this study, the authors fabricated a plasma polymerized hexamethyldisiloxane (PPHMDSO) thin film deposited by capacitively coupled plasma chemical vapor deposition system with various plasma powers. The patterned PPHMDSO film was plasma treated by 10:90 H2/He mixture gas through a metal shadow mask. The films were characterized by water contact angle, atomic force microscopy, x-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy analyses. Our results show that the PPHMDSO film suppresses the cell adhesion, whereas surface modified PPHMDSO film enhances the cell adhesion and proliferation. From cell culture experiments, the authors found that the patterned film with 300 μm line interval was most efficient to evaluate the tube formation, a sapient angiogenic indicator. This patterned film will provide an effective and promising method for evaluating angiogenesis.

Enhanced adherence of mouse fibroblast and vascular cells to plasma modified polyethylene

Since the last decade, tissue engineering has shown a sensational promise in providing more viable alternatives to surgical procedures for harvested tissues, implants and prostheses. Biomedical polymers, such as low-density polyethylene (LDPE), high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE), were activated by Ar plasma discharge. Degradation of polymer chains was examined by determination of the thickness of ablated layer. The amount of an ablated polymer layer was measured by gravimetry. Contact angle, measured by goniometry, was studied as a function of plasma exposure and post-exposure aging times. Chemical structure of modified polymers was characterized by angle resolved X-ray photoelectron spectroscopy. Surface chemistry and polarity of the samples were investigated by electrokinetic analysis. Changes in surface morphology were followed using atomic force microscopy. Cytocompatibility of plasma activated polyethylene foils was studied using two distinct model cell lines; VSMCs (vascular smooth muscle cells) as a model for vascular graft testing and connective tissue cells L929 (mouse fibroblasts) approved for standardized material cytotoxicity testing. Specifically, the cell number, morphology, and metabolic activity of the adhered and proliferated cells on the polyethylene matrices were studied in vitro. It was found that the plasma treatment caused ablation of the polymers, resulting in dramatic changes in their surface morphology and roughness. ARXPS and electrokinetic measurements revealed oxidation of the polymer surface. It was found that plasma activation has a positive effect on the adhesion and proliferation of VSMCs and L929 cells.

Status and headway of the clinical application of artificial ligaments

The authors first reviewed the history of clinical application of artificial ligaments. Then, the status of clinical application of artificial ligaments was detailed. Some artificial ligaments possessed comparable efficacy to, and fewer postoperative complications than, allografts and autografts in ligament reconstruction, especially for the anterior cruciate ligament. At the end, the authors focused on the development of two types of artificial ligaments: polyethylene glycol terephthalate artificial ligaments and tissue-engineered ligaments. In conclusion, owing to the advancements in surgical techniques, materials processing, and weaving methods, clinical application of some artificial ligaments so far has demonstrated good outcomes and will become a trend in the future.

Separation and characterization of poly(tetrafluoroethylene) latex particles by asymmetric flow field flow fractionation with light-scattering detection

Poly(tetrafluoroethylene) (PTFE) latex particles have been analyzed and sorted according to size using asymmetric flow field flow fractionation (AF4) coupled with multiple-angle light scattering (MALS). Characterization of fractions by regular and depolarized dynamic light scattering confirmed that smaller particles elute prior to larger ones, as expected for field flow fractionation. The measured radii of the optically and geometrically anisotropic particles are consistent with those determined from transmission electron microscopy (TEM). A certain amount of heterogeneity remains in the fractions, but their uniformity for use as diffusion probes is improved. Full characterization of PTFE colloids will require a difficult assessment of the distribution, even within fractions, of the optical anisotropy. A general method to obtain number versus size distributions is presented. This approach is valid even when an online concentration detector is not available or ineffective. The procedure is adaptable to particles of almost any regular shape.

Grafting of a model protein on lactide and caprolactone based biodegradable films for biomedical applications

Thermoplastic biodegradable polymers displaying elastomeric behavior and mechanical consistency are greatly appreciated for the regeneration of soft tissues and for various medical devices. However, while the selection of a suitable base material is determined by mechanical and biodegradation considerations, it is the surface properties of the biomaterial that are responsible for the biological response. In order to improve the interaction with cells and modulate their behavior, biologically active molecules can be incorporated onto the surface of the material. With this aim, the surface of a lactide and caprolactone based biodegradable elastomeric terpolymer was modified in two stages. First, the biodegradable polymer surface was aminated by atmospheric pressure plasma treatment and second a crosslinker was grafted in order to covalently bind the biomolecule. In this study, albumin was used as a model protein. According to X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), albumin was efficiently immobilized on the surface of the terpolymer, the degree of albumin surface coverage (Γ_BSA) reached ~35%. Moreover, gel permeation chromatography (GPC) studies showed that the hydrolytic degradation kinetic of the synthesized polymer was slightly delayed when albumin was grafted. However, the degradation process in the bulk of the material was unaffected, as demonstrated by Fourier transform infrared (FTIR) analyses. Furthermore, XPS analyses showed that the protein was still present on the surface after 28 days of degradation, meaning that the surface modification was stable, and that there had been enough time for the biological environment to interact with the modified material.

Improvement of early cell adhesion on Thai silk fibroin surface by low energy plasma

Low energy plasma has been introduced to treat the surface of Thai silk fibroin which should be enhanced for cell adhesion due to its native hydrophobic surface. Plasma surface treatment could introduce desirable hydrophilic functionalities on the surface without using any chemicals. In this work, nitrogen glow discharge plasma was generated by a low energy AC50Hz power supply system. The plasma operating conditions were optimized to reach the highest nitrogen active species by using optical emission spectroscopy. X-ray photoelectron spectroscopy (XPS) revealed that amine, hydroxyl, ether, and carboxyl groups were induced on Thai silk fibroin surface after plasma treatment. The results on Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy confirmed that the plasma treated effects were only on the outermost layer since there was no change in the bulk chemistry. The surface topography was insignificantly changed from the detection with atomic force microscopy (AFM). The plasma-treated effects were the improved surface wettability and cell adhesion. After a 90-s treatment, the water contact angle was at 20°, while the untreated surface was at 70°. The early cell adhesion of L929 mouse fibroblast was accelerated. L929 cells only took 3h to reach 100% cell adhesion on 90 s N2 plasma-treated surface, while there was less than 50% cell adhesion on the untreated Thai silk fibroin surface after 6h of culture. The cell adhesion results were in agreement with the cytoskeleton development. L929 F-actin was more evident on 90 s N2 plasma-treated surface than others. It could be concluded that a lower energy AC50Hz plasma system enhanced early L929 mouse fibroblast adhesion on Thai silk fibroin surface without any significant change in surface topography and bulk chemistry.

Plasma-based biofunctionalization of vascular implants

Polymeric and metallic materials are used extensively in permanently implanted cardiovascular devices and devices that make temporary but often prolonged contact with body fluids and tissues. Foreign body responses are typically triggered by host interactions at the implant surface, making surface modifications to increase biointegration desirable. Plasma-based treatments are extensively used to modify diverse substrates; modulating surface chemistry, wettability and surface roughness, as well as facilitating covalent biomolecule binding. Each aspect impacts on facets of vascular compatibility including endothelialization and blood contact. These modifications can be readily applied to polymers such as Dacron® and expanded polytetrafluoroethylene, which are widely used in bypass grafting and the metallic substrates of stents, valves and pacemaker components. Plasma modification of metals is more challenging given the need for coating deposition in addition to surface activation, adding the necessity for robust interface adhesion. This review examines the evolving plasma treatment technology facilitating the biofunctionalization of polymeric and metallic implantable cardiovascular materials.

Nanopatterned polymer substrates promote endothelial proliferation by initiation of β-catenin transcriptional signaling

Control of endothelial phenotype involves a variety of signaling pathways and transcriptional regulators, including the junctional protein β-catenin. This multifunctional signaling molecule is part of adhesion contacts in the endothelium and is able to translocate into the nucleus to activate genetic programs and control proliferation and the fate of the cells. We investigated the influence of laser-generated nanopatterns on polymeric cell culture substrates on endothelial tissue architecture, proliferation and β-catenin signaling. For our experiments human microvascular endothelial cells or CD34(+) endothelial progenitor cells, isolated from human adipose tissue, were cultured on polyethylene terephthalate (PET) substrates with oriented nanostructures with lateral periodicities of 1.5 μm and 300 nm, respectively. The surface topography and chemistry of the PET substrates were characterized by electron microscopy, atomic force microscopy, water contact angle measurement and X-ray photoelectron spectroscopy. Analysis of cell phenotype markers as well as β-catenin signaling revealed that short-term culture of endothelial cells on nanostructured substrates generates a proliferative cell phenotype associated with nuclear accumulation of β-catenin and activation of specific β-catenin target genes. The effects of the nanostructures were not directly correlated with nanostructure-induced alignment of cells and were also clearly distinguishable from the effects of altered PET surface chemistry due to photomodification. In summary, we present a novel mechanism of surface topology-dependent control of transcriptional programs in mature endothelium and endothelial progenitor cells.

Synthesis of PECAM-1-specific 64Cu PET imaging agent: evaluation of myocardial infarction caused by ischemia-reperfusion injury in mouse

A PECAM-1 specific PET imaging agent, PECAM-1-Ab-DOTA-(64)Cu, was synthesized by conjugating the anti-mouse PECAM-1 antibody with 2,2',2",2"'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) and subsequent labeling with (64)Cu. Positron Emission Tomography (PET) was successfully performed in a mouse model of myocardial infarction (MI) induced by an ischemia/reperfusion (I/R) injury, indicating the elevated expression of PECAM-1.

Cluster Ion Beam Processing: Review of Current and Prospective Applications

Cluster ion beam processes which employ ions comprised of a few hundred to several thousand atoms are being developed into a new field of ion beam technology. The processes are characterized by low energy surface interaction effects, lateral sputtering phenomena and high-rate chemical reaction effects. This paper reviews the current status of studies of the fundamental cluster ion beam characteristics as they apply to nanoscale processing and present industrial applications. As new prospective applications, techniques are now being developed to employ cluster ions in surface analysis tools such as XPS and SIMS and to modify surfaces of bio-materials. Results related to these new projects will also be reviewed.

Tubular silk scaffolds for small diameter vascular grafts

Vascular surgeries such as coronary artery bypass require small diameter vascular grafts with properties that are not available at this time. Approaches using synthetic biomaterials have been not completely successful in producing non-thrombogenic grafts with inner diameters less than 6 mm, and there is a need for new biomaterials and graft designs. We propose silk fibroin as a microvascular graft material and describe tubular silk scaffolds that demonstrate improved properties over existing vascular graft materials. Silk tubes produced using an aqueous gel spinning technique were first assessed in vitro in terms of thrombogenicity (thrombin and fibrinogen adsorption, platelet adhesion) and vascular cell responses (endothelial and smooth muscle cell attachment and proliferation) in comparison with polytetrafluoroethylene (PTFE), a synthetic material most frequently used for vascular grafts. Silk tubes were then implanted into the abdominal aortas of Sprague-Dawley rats. At time points of 2 weeks and 4 weeks post implantation, tissue outcomes were assessed through gross observation (acute thrombosis, patency) and histological staining (H&E, Factor VIII, smooth muscle actin). Over the 4-week time period, we observed graft patency and endothelial cell lining of the lumen surfaces. These results demonstrate the feasibility of using silk fibroin as a vascular graft material and some advantages of silk tubes over the currently used synthetic grafts.

In vitro biocompatibility evaluation of surface-modified titanium alloys

The present work is aimed to evaluate the effects of a surface modification process on the biocompatibility of three vanadium-free titanium alloys with biomedical applications interest. Chemical composition of alloys investigated, in weight %, were Ti-7Nb-6Al, Ti-13Nb-13Zr, and Ti-15Zr-4Nb. An easy and economic method intended to improve the biocompatibiblity of these materials consists in a simple thermal treatment at high temperature, 750 degrees C, in air for different times. The significance of modification of the surface properties to the biological response was studied putting in contact both untreated and thermally treated alloys with human cells in culture, Human Umbilical Vein Endothelial Cells (HUVEC) and Human Peripheral Blood Mononuclear Cells (PBMC). The TNF-alpha release data indicate that thermal treatment improves the biological response of the alloys. The notable enhancement of the surface roughness upon oxidation could be related with the observed reduction of the TNF-alpha levels for treated alloys. A different behavior of the two cell lines may be observed, when adhesion molecules (ICAM-1 and VCAM-1 in HUVEC, ICAM-1, and LFA-1 in PBMC) were determined, PBMC being more sensitive than HUVEC to the contact with the samples. The data also distinguish surface composition and corrosion resistance as significant parameters for the biological response.