Anticoagulant and antiplatelet agents: their clinical and device application(s) together with usages to engineer surfaces

Layer-by-layer assembly of thin organic films on PTFE activated by cold atmospheric plasma

An air diffuse coplanar surface barrier discharge is used to activate the surface of polytetrafluoroethylene (PTFE) samples, which are subsequently coated with polyvinylpyrrolidone (PVP) and tannic acid (TAN) single, bi- and multilayers, respectively, using the dip-coating method. The surfaces are characterized by X-ray Photoelectron Spectroscopy (XPS), Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM). The XPS measurements show that with plasma treatment the F/C atomic ratio in the PTFE surface decreases, due to the diminution of the concentration of CF2 moieties, and also oxygen incorporation through formation of new C–O, C=O and O=C–O bonds can be observed. In the case of coated samples, the new bonds indicated by XPS show the bonding between the organic layer and the surface, and thus the stability of layers, while the gradual decrease of the concentration of F atoms with the number of deposited layers proves the creation of PVP/TAN bi- and multi-layers. According to the ATR-FTIR spectra, in the case of PVP/TAN multilayer hydrogen bonding develops between the PVP and TAN, which assures the stability of the multilayer. The AFM lateral friction measurements show that the macromolecular layers homogeneously coat the plasma treated PTFE surface.

Is there an alternative to systemic anticoagulation, as related to interventional biomedical devices?

To reduce the toxic effects, related clinical problems and complications such as bleeding disorders associated with systemic anticoagulation, it has been hypothesized that by coating the surfaces of medical devices, such as stents, bypass grafts, extracorporeal circuits, guide wires and catheters, there will be a significant reduction in the requirement for systemic anticoagulation or, ideally, it will no longer be necessary. However, current coating processes, even covalent ones, still result in leaching followed by reduced functionality. Alternative anticoagulants and related antiplatelet agents have been used for improvement in terms of reduced restenosis, intimal hyperphasia and device failure. This review focuses on existing heparinization processes, their application in clinical devices and the updated list of alternatives to heparinization in order to obtain a broad overview, it then highlights, in particular, the future possibilities of using heparin and related moieties to tissue engineer scaffolds.

Bioactive technologies for hemocompatibility

The contact of any biomaterial with blood gives rise to multiple pathophysiologic defensive mechanisms such as activation of the coagulation cascade, platelet adhesion and activation of the complement system and leukocytes. The reduction of these events is of crucial importance for the successful clinical performance of a cardiovascular device. This can be achieved by improving the hemocompatibility of the device materials or by pharmacologic inhibition of the key enzymes responsible for the activation of the cascade reactions, or a combination of both. Different strategies have been developed during the last 20 years, and this article attempts to review the most significant, by dividing them into three main categories: bioinert or biopassive, biomimetic and bioactive strategies. With regard to bioactive strategies, particular attention is given to heparin immobilization and recent related technologies. References from both scientific literature and commercial sites are provided. Future development and studies are suggested.

Zwitterionic poly(2-oxazoline)s as promising candidates for blood contacting applications

The hemocompatibility and cytotoxicity of zwitterionic poly(2-oxazoline)s are investigated.

Biomechanics and biocompatibility of the perfect conduit-can we build one?

No currently available conduit meets the criteria for an ideal coronary artery bypass graft. The perfect conduit would combine the availability and complication-free harvest of a synthetic vessel with the long-term patency performance of the internal mammary artery. However, current polymer conduits suffer from inelastic mechanical properties and especially poor surface biocompatibility, resulting in early loss of patency as a coronary graft. Approaches to manufacture an improved conduit using new polymers or polymer surfaces, acellular matrices, or cellular constructs have to date failed to achieve a commercially successful alternative. Elastin, by mimicking the native extracellular environment as well as providing elasticity, provides the 'missing link' in vascular conduit design and brings new hope for realization of the perfect conduit.

Alternative conduits for microvascular anastomoses

Thrombotic events in vascular substitutes are the main cause of obliteration of most microvascular prostheses and subsequent failure of microvascular anastomoses. The development of new biomaterials for vascular replacement aims to obtain an ideal graft for microvascular surgery. Completely bioresorbable vascular prostheses with the capacity to induce regeneration and growth of a new vascular segment seem to overcome the limitations of contemporary artificial prostheses, mostly made of artificial materials and lacking the capacity to grow and be remodeled. Autologous vessels are currently the most used material for small-diameter arterial replacement. Immune acceptance is a major advantage offered by this technique, but the time required is a limitation in emergency surgery. The need for a prosthetic graft that would have the same properties as a small-diameter conduit has led investigators to pursue many avenues in vascular biology. This article details the development of microvascular synthetic prostheses, clarifying the current status and the future aims.

Synthesis, spectroscopic characterization and biological evaluation studies of Schiff's base derived from naphthofuran-2-carbohydrazide with 8-formyl-7-hydroxy-4-methyl coumarin and its metal complexes

Metal complexes of the type ML(2), where M=Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and L=Schiff's base derived from the condensation of naphthofuran-2-carbohydrazide with 8-formyl-7-hydroxy-4-methyl coumarin have been synthesized. The chelation of the complexes have been elucidated in the light of analytical, IR, UV-vis, (1)H NMR, mass, ESR spectral data, thermal and magnetic studies. The measured molar conductance values indicate that, the complexes are non-electrolytic in nature. The redox behavior of one of the synthesized metal complexes was investigated by cyclic voltammetry. The Schiff's base and its metal complexes have been screened for their in vitro antibacterial and antifungal activities by MIC method. The DNA cleavage activities of all the complexes were studied by agarose gel electrophoresis method. In addition, the free ligand along with its complexes has been studied for their antioxidant activity.

Bergapten induces ER depletion in breast cancer cells through SMAD4-mediated ubiquitination

ERα function is crucial for the development of normal mammary gland as well as in the process of progression of breast cancer cells. Signals that target receptor levels contribute to regulate estrogens effects in the cells. An intricate cross-regulation has been documented between ERα and TGF-β down-stream molecules: SMAD2, SMAD3, and SMAD4, that can bind ERα and regulate their signaling. Thus, identification of natural anticancer drugs able to influence the latter molecule might provide alternative choices for breast cancer treatment. Taking into account our previous published data we wanted to study the effect of 5-Methoxypsoralen (bergapten) on ERα and on TGF-β pathway. We reported that bergapten, a coumarin containing compound, effectively depletes ERα in MCF-7 breast cancer sensitive cells and in tamoxifen-resistant clone. The decrease of ERα protein after bergapten treatment results from the ubiquitine-proteasome pathway as demonstrated by the use of MG-132. IP experiments with ER antibody, demonstrated that the protein has physical interaction with SMAD4 and poly-ubiquitine and the amount of ubiquitinated receptor, linked to SMAD4, is greater under bergapten. The crucial role played by SMAD4, in this process, emerges from the observation that in breast cancer cells, silencing of SMAD4, resulted in increased expression of endogenous ERα in both control and bergapten-treated cells, compared to wild- type cells. The same results were confirmed in siRNA TGF-β RII cells. The results suggest a novel negative regulation of ERα by TGF-β/SMAD4 in breast cancer cells and indicate that the SMAD4 protein is involved in the degradation of ERα induced by bergapten. We propose that bergapten may efficiently act as a natural antitumoral agent, able to deplete ERα from breast cancer tamoxifen-sensitive and resistant cells, thereby retraining the effect of membrane signals targeting ERα and in such way its mitogenic potentiality.

Sustained release of heparin on enlarged-pore and functionalized MCM-41

Mesoporous silica MCM-41 and SBA-15 were chosen to study the adsorption and release of bulky biomolecule heparin, in order to develop new heparin controlled delivery system and expand the application of mesoporous materials in life science. To explore how the structure of support such as pore size and surface state affects the accommodation and release of heparin, we used decane as swelling agent to enlarge pores of MCM-41, introduced amino groups for improving the biocompatibility of support, and controllably retained templates in the as-synthesized sample. The influence of modification on the structure of samples was investigated by XRD and N(2) adsorption-desorption, whereas their performance of adsorbing and releasing heparin was assessed with that of toluidine blue method. Both enlarged pore and organic modification significantly promoted the adsorption and prolonged the release of heparin in MCM-41, and the release was characterized with a three-stage release model. The mechanism of heparin release from mesoporous material was studied by fitting the release profiles to the theoretical equation. As expected, some mesoporous composites could release heparin in the long term with tuned dosage.

Surface chemistry to minimize fouling from blood-based fluids

Upon contact with bodily fluids/tissues, exogenous materials spontaneously develop a layer of proteins on their surface. In the case of biomedical implants and equipment, biological processes with deleterious effects may ensue. For biosensing platforms, it is synonymous with an overwhelming background signal that prevents the detection/quantification of target analytes present in considerably lower concentrations. To address this ubiquitous problem, tremendous efforts have been dedicated over the years to engineer protein-resistant coatings. There is now extensive literature available on stealth organic adlayers able to minimize fouling down to a few ng cm(-2), however from technologically irrelevant single-protein buffered solutions. Unfortunately, few coatings have been reported to present such level of performance when exposed to highly complex proteinaceous, real-world media such as blood serum and plasma, even diluted. Herein, we concisely review the surface chemistry developed to date to minimize fouling from these considerably more challenging blood-based fluids. Adsorption dynamics is also discussed.

Surface modification of biomaterials: a quest for blood compatibility

Cardiovascular implants must resist thrombosis and intimal hyperplasia to maintain patency. These implants when in contact with blood face a challenge to oppose the natural coagulation process that becomes activated. Surface protein adsorption and their relevant 3D confirmation greatly determine the degree of blood compatibility. A great deal of research efforts are attributed towards realising such a surface, which comprise of a range of methods on surface modification. Surface modification methods can be broadly categorized as physicochemical modifications and biological modifications. These modifications aim to modulate platelet responses directly through modulation of thrombogenic proteins or by inducing antithrombogenic biomolecules that can be biofunctionalised onto surfaces or through inducing an active endothelium. Nanotechnology is recognising a great role in such surface modification of cardiovascular implants through biofunctionalisation of polymers and peptides in nanocomposites and through nanofabrication of polymers which will pave the way for finding a closer blood match through haemostasis when developing cardiovascular implants with a greater degree of patency.

Small-caliber vascular prosthesis prototype based on controlled release of heparin from mesochannels and its enhanced biocompatibility

A novel small-caliber vascular prosthesis prototype is proposed on the basis of a new heparin release system, that is, the controlled delivery of heparin from mesochannels. Fabrication of mesochannels on artificial biomaterials is successfully achieved through epitaxial growth of mesoporous silica nanoparticles on expanded polytetrafluoroethylene grafts, and thus heparin can be immobilized through a space limitation effect, thereby avoiding the loss of bioactivity and enabling long-lasting release. The adsorption and release of heparin are controlled by adjusting the adsorbate-adsorbent interaction through tailoring the mesostructure. Owing to the continuous and sustained release of heparin, the performances of artificial vessels are greatly improved, thus paving a new way to prepare functional blood-contacting biomaterials with high biocompatibility.

Coumarin-trioxane hybrids: synthesis and evaluation as a new class of antimalarial scaffolds

First synthesis of novel coumarin-trioxane hybrids is reported. The synthesis was achieved via condensation of β-hydroxyhydroperoxides with coumarinic-aldehydes in presence of p-toluenesulfonic acid in good yields and the novel hybrids were evaluated for their antimalarial activity both in vitro and in vivo.

A silver nanocomposite biomaterial for blood-contacting implants

Cardiovascular implants must resist infection and thrombosis. A nanocomposite polymeric material [polyhedral-oligomeric-silsesquioxane-poly(carbonate-urea)urethane; POSS-PCU] demonstrates ideal properties for cardiovascular applications. Silver nanoparticles or nanosilver (NS) are recognized for efficient antibacterial properties. This study aims to determine the influence of NS integrated POSS-PCU on thrombogenicity. Silver nitrate was reduced with dimethylformamide and stabilized by the inclusion of fumed silica nanoparticles to prevent aggregation of NS and were incorporated into POSS-PCU to form a range of POSS-PCU-NS concentrations (by weight); 0.20% (NS16), 0.40% (NS32), 0.75% (NS64), and 1.50% (NS128). Surface wettability was determined with sessile-drop water contact angles. Platelets were introduced onto test samples and Alamar Blue (AB), mitochondrial-activity assay, quantified the degree of platelet adhesion whilst platelet-factor-4 (PF4) ELISA quantified the degree of platelet activation. Thromboelastography (TEG) determined the profiles of whole blood kinetics while hemolysis assay demonstrated the degree of blood compatibility. Increasing levels of NS induced greater hydrophilicity. A concentration dependant decrease in platelet adhesion and activation was observed with AB and PF4 readings, respectively. TEG demonstrated that the antithrombogenic properties of POSS-PCU were retained with POSS-PCU-NS16, and enhanced with POSS-PCU-NS32, but was reduced with POSS-PCU-NS64 and POSS-PCU-NS128. POSS-PCU-NS64 and POSS-PCU-NS128 demonstrated a hemolytic tendency, but no hemolysis was observed with POSS-PCU-NS16 and POSS-PCU-NS32. Overall, POSS-PCU-NS32 rendered potent antithrombogenic properties.

Creation of a blood-compatible surface: a novel strategy for suppressing blood activation and coagulation using a nitroxide radical-containing polymer with reactive oxygen species scavenging activity

Various polymeric materials have been used in medical devices, including blood-contacting artificial organs. Contact between blood and foreign materials causes blood cell activation and adhesion, followed by blood coagulation. Concurrently, the activated blood cells release inflammatory cytokines together with reactive oxygen species (ROS). We have hypothesized that the suppression of ROS generation plays a crucial role in blood activation and coagulation. To confirm this hypothesis, surface-coated polymers containing nitroxide radical compounds (nitroxide radical-containing polymers (NRP)) were designed and developed. The NRP was composed of a hydrophobic poly(chloromethylstyrene) (PCMS) chain to which 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) moieties were conjugated via condensation reaction of the chloromethyl groups in PCMS with the sodium alcoholate group of 4-hydroxy-TEMPO. Blood compatibility was investigated by placing NRP-coated beads in contact with rat whole blood. The amount of ROS generated on PCMS-coated beads used as a control increased significantly with time, while NRP-coated beads suppressed ROS generation. It is interesting to note that the suppression of inflammatory cytokine generation by NRP-coated beads was shown to be significantly higher than that by PCMS-coated beads. Both platelet and leukocyte adhesion to the beads were suppressed with increasing TEMPO incorporation in the polymer. These results confirm that the suppression of ROS by NRP prevents inflammatory cytokine generation, which in turn results in the suppression of blood activation and coagulation on the beads.

Covalent attachment of multilayers on poly(tetrafluoroethylene) surfaces

These studies demonstrate a new approach of producing multifunctionalized coatings on poly(tetrafluoroethylene) (PTFE) surfaces by covalent attachments of multilayers (CAM) of heparin (HP) and poly(ethylene glycol) (PEG). This process can be universally applied to other covalently bonded species and was facilitated by microwave plasma reactions in the presence of maleic anhydride which, upon ring-opening and hydrolysis, provided covalent attachment of COOH groups to PTFE. These studies showed that alternating layers of PEG and HP can be covalently attached to COOH-PTFE surfaces, and the volume concentration and surface density of PEG and HP on the PTFE surface achieved by the CAM were 7.02-6.04 × 10(-3) g/cm(3) (2.1-1.8 × 10(-7) g/cm(2)) and 9.3-8.7 × 10(-3) g/cm(3) (2.8-2.6 × 10(-7) g/cm(2)), respectively. The CAM process may serve numerous applications when the covalent modification of inert polymeric substrates is required and particularly where the presence of bioactive species for biocompatibility enhancement is desirable.

Anti-fouling bioactive surfaces

Bioactive surfaces refer to surfaces with immobilized bioactive molecules aimed specifically at promoting or supporting particular interactions. Such surfaces are of great importance for various biomedical and biomaterials applications. In the past few years, considerable effort has been made to create bioactive surfaces by forming specific biomolecule-modified surfaces on a non-biofouling "base" or "background". Hydrophilic and bioinert polymers have been widely used as anti-fouling layers that resist non-specific protein interactions. They can also serve as "spacers" to effectively move the immobilized biomolecule away from the surface, thus enhancing its bioactivity. In this review we summarize several successful approaches for the design and preparation of bioactive surfaces based on different types of anti-fouling/spacer materials. Some perspectives on future research in this area are also presented.

The artificial endothelium

As the world of critical care medicine advances, extracorporeal therapies (ECC) have become commonplace in the management of the high risk intensive care patient. ECC encompasses a wide variety of technologies from hemodialysis, continuous renal replacement therapy (CRRT) and plasmapheresis, to cardiopulmonary bypass (CPB), extracorporeal life support (ECLS) and hepatic support. The development of internal man made organs is the next step with ventricular assist devices and artificial lungs. As we advance the technologies with smaller devices, and more intricate circuitry, we lack the keystone necessary to control the blood-biomaterial interface. For the last 50 years much has been learned about surface induced thrombosis and attempts have been made to prevent it with alternative systemic anticoagulation, circuitry surface modifications, or a combination of both. Despite these efforts, systemic or regional anticoagulation remain necessary for both laboratory and clinical application of ECC. As such, the development of an endothelial-like, biomimetic surface to reduce or perhaps even eliminate the blood activation/thrombus formation events that occur upon exposure to artificial surfaces is paramount.

Synthesis and in vitro evaluation of novel coumarin-chalcone hybrids as potential anticancer agents

A series of coumarin-chalcone hybrids have been synthesized and evaluated for their in vitro cytotoxicity against a panel of four human cancer cell lines and normal fibroblasts (NIH3T3). Among 21 compounds screened, three compounds (23, 25 and 26) showed IC(50) range from 3.59 to 8.12 μM. The most promising compound 26 showed around 30-fold more selectivity towards C33A (cervical carcinoma) cells over normal fibroblast NIH3T3 cells with an IC(50) value of 3.59 μM.

Current Strategies in Cardiovascular Biomaterial Functionalization

Prevention of the coagulation cascade and platelet activation is the foremost demand for biomaterials in contact with blood. In this review we describe the underlying mechanisms of these processes and offer the current state of antithrombotic strategies. We give an overview of methods to prevent protein and platelet adhesion, as well as techniques to immobilize biochemically active molecules on biomaterial surfaces. Finally, recent strategies in biofunctionalization by endothelial cell seeding as well as their possible clinical applications are discussed.

Development of cardiovascular bypass grafts: endothelialization and applications of nanotechnology

There is a critical clinical need for small-diameter bypass grafts, with applications involved in the coronary artery and lower limb. Commercially available materials give rise to unfavorable responses when in contact with blood and subjected to low-flow hemodynamics and, thus, are nonideal as small-diameter bypass grafts. Optimizing the mechanical properties to match both the native artery and the graft surfaces has received keen attention. Endothelialization of bypass grafts is considered a protective mechanism where the biochemicals produced from endothelial cells exert a range of favorable responses, including antithrombotic, noninflammatory responses and inhibition of intimal hyperplasia. In situ endothelialization is most desirable. Nanotechnology approaches facilitate all aspects of endothelialization, including endothelial progenitor cell mobilization, migration, adhesion, proliferation and differentiation. 'Surface nanoarchitecturing mechanisms', which mimic the natural extracellular matrix to optimize endothelial progenitor cell interaction and controlled delivery of various factors in the form of nanoparticles, which can be combined with gene therapy, are of keen interest. This article discusses the development of bypass grafts, focusing on the optimization of the biological properties of mechanically suitable grafts.

Biofunctionalization of biomaterials for accelerated in situ endothelialization: a review

The higher patency rates of cardiovascular implants, including vascular bypass grafts, stents, and heart valves are related to their ability to inhibit thrombosis, intimal hyperplasia, and calcification. In native tissue, the endothelium plays a major role in inhibiting these processes. Various bioengineering research strategies thereby aspire to induce endothelialization of graft surfaces either prior to implantation or by accelerating in situ graft endothelialization. This article reviews potential bioresponsive molecular components that can be incorporated into (and/or released from) biomaterial surfaces to obtain accelerated in situ endothelialization of vascular grafts. These molecules could promote in situ endothelialization by the mobilization of endothelial progenitor cells (EPC) from the bone marrow, encouraging cell-specific adhesion (endothelial cells (EC) and/or EPC) to the graft and, once attached, by controlling the proliferation and differentiation of these cells. EC and EPC interactions with the extracellular matrix continue to be a principal source of inspiration for material biofunctionalization, and therefore, the latest developments in understanding these interactions will be discussed.

Assessment of the potential of progenitor stem cells extracted from human peripheral blood for seeding a novel vascular graft material

OBJECTIVE

A novel nanocomposite has recently been developed based on polyhedral oligomeric silsesquioxane attached by direct reaction onto a urethane segment, as a potential vascular graft material; its trade name is UCL-Nano. The UCL-Nano has been demonstrated to have similar viscoelastic properties to the walls of a natural artery, to be resistant to degradation and to be able to sustain endothelial cell seeding. Human peripheral blood contains both circulating endothelial cells and endothelial progenitor cells, which may be suitable for conduit seeding. The aim of this study was to develop a system with the potential to deliver an endothelial cell-seeded bypass graft in a realistic time frame.

MATERIALS AND METHODS

Endothelial progenitor cells and circulating endothelial cells were isolated from human peripheral blood and were characterized by fluorescent-activated cell sorting, reverse transcriptase-polymerase chain reaction and immunohistochemistry. Isolated cells were seeded on nanocomposite and were maintained in culture for 35 days.

RESULTS

The UCL-Nano was successfully seeded with cells and a confluent cell layer was achieved after 14-day culture. Cells remained viable and confluent on the nanocomposite for 35 days.

CONCLUSION

In conclusion, these results suggest that this process has potential both for a realistic and achievable two-stage seeding process for vascular bypass grafts and for the potential development of a device, with the aim of achieving in situ seeding once implanted.

Metal oxide surface charge mediated hemostasis

Blood coagulates faster upon contact with polar glasslike surfaces than on nonpolar plastic surfaces; this phenomenon is commonly termed the glass effect. However, the variable hemostatic response that we report here for contact-activated coagulation by different metal oxides, all of which are polar substrates, requires a refinement of this simple polarity model of how inorganic metal oxides activate the intrinsic pathway of blood coagulation. To our knowledge, the role of metal oxide surface charge as determined at the physiological pH and Ca2+ concentration of blood has not been previously investigated. We find that basic oxides with an isoelectric point above the pH of blood are anticoagulant while acidic oxides with an isoelectric point below the pH of blood are procoagulant. Using a thromboelastograph, we find that the onset time for coagulation and rate of coagulation post-initiation depend on both the sign and the magnitude of the initial surface charge density of the metal oxide. This work presents a useful strategy based on a quantifiable material parameter to select metal oxides to elicit a predictable and tunable biological response when they are in contact with blood.

Addressing thrombogenicity in vascular graft construction

Thrombosis is a major cause of poor patency in synthetic vascular grafts for small diameter vessel (< 6 mm) bypass. Arteries have a host of structural mechanisms by which they prevent triggering of platelet activation and the clotting cascade. Many of these are present in vascular endothelial cells. These mechanisms act together with perpetual feedback at different levels, providing a constantly fine-tuned non-thrombogenic environment. The arterial wall anatomy also serves to promote thrombosis as a healing mechanism when it has been severely injured. Surface modification of synthetic graft surfaces to attenuate the coagulation cascade has reduced thrombosis levels and improved patency in vitro and in animal models. Success in this endeavor is critically dependent on the methods used to modify the surface. Platelets adhere to positively charged surfaces due to their own negative charge. They also preferentially attach to hydrophobic surfaces. Therefore synthetic graft development is concerned with hydrophilic materials with negative surface charge. However, fibrinogen has both hydrophilic and hydrophobic binding sites-amphiphilic materials reduce its adhesion and subsequent platelet activation. The self-endothelializing synthetic graft is an attractive proposition as a confluent endothelial layer incorporates many of the anti-thrombogenic properties of arteries. Surface modification to promote this has shown good results in animal models. The difficulties experienced in achieving spontaneous endothelialisation in humans have lead to the investigation of pre-implantation in vitro endothelial cell seeding. These approaches ultimately aim to result in novel synthetic grafts which are anti-thrombogenic and hence suitable for coronary and distal infrainguinal bypass.

Development of small-diameter vascular grafts

INTRODUCTION

Cardiovascular disease, including coronary artery and peripheral vascular pathologies, is the leading cause of mortality in the United States and Western countries. There is a pressing need to develop small-diameter vascular vessels for bypass surgery and other vascular reconstructive procedures. Tissue engineering offers the prospect of being able to meet the demand for replacement of diseased vessels. Significant advances have been made in recent studies and provide confidence that success is attainable. For instance, a completely cellular approach culturing cells into tissue sheets and wrapping these layers was able to form a layered cellular vascular graft with impressive strength.

METHODS/RESULTS

In our experiments, decellularization and heparin immobilization grafts from porcine tissues implanted in a canine model could be repopulated from the host cells, indicating the grafts' potential to develop into living tissues that can adapt and respond to changes in the body.

CONCLUSIONS

This review summarizes the current status of vascular grafts used clinically, updates the most recent developments on vascular tissue engineering, and discusses the challenges for the future.

Novel thromboresistant materials

The development of a clinically durable small-diameter vascular graft as well as permanently implantable biosensors and artificial organ systems that interface with blood, including the artificial heart, kidney, liver, and lung, remain limited by surface-induced thrombotic responses. Recent breakthroughs in materials science, along with a growing understanding of the molecular events that underlay thrombosis, has led to the design and clinical evaluation of a variety of biologically active coatings that inhibit components of the coagulation pathway and platelet responses by surface immobilization or controlled release of bioactive agents. This report reviews recent progress in generating synthetic thromboresistant surfaces that inhibit (1) protein and cell adsorption, (2) thrombin and fibrin formation, and (3) platelet activation and aggregation.

UV surface modification of a new nanocomposite polymer to improve cytocompatibility

A novel modified nanocomposite was studied for the adhesion and proliferation of the human umbilical vein endothelial cell (HUVEC) line EA.hy926. The nanocomposite under investigation was poly(carbonate-urea)urethane with silsesquioxane nano-cages, here in the form of a mixture of two polyhedral oligomeric silsesquioxanes. The nanocomposite surfaces were exposed to ultraviolet (UV) light of a Xe(*)(2)-excimer lamp at a wavelength of 172 nm in an ammonia atmosphere. The effects of the irradiation were characterized by atomic force and scanning electron microscopy (AFM, SEM), X-ray photo-electron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) using an attenuated total reflection (ATR) device and measurements of advancing water contact angle (CA). The irradiation resulted in the introduction of new hydrophilic N- and O-containing groups into the surface, which was initially amphiphilic, while surface morphology remained mainly unchanged. Slight chemical changes were also observed for the silsesquioxane nano-cages at the surface. Onto the untreated and irradiated samples HUVECs were seeded and grown for various durations in culture. Standard tissue-culture polystyrene (PS) was employed as a positive control to check the efficiency of the cell-culture methods. Viability and proliferation of the cells were then assessed using a non-radioactive assay. Compared to the untreated nanocomposite polymer, irradiation times of at least 5 min resulted in a significantly increased cell proliferation between 3 and 8 days after seeding with the HUVEC line EA.hy926.

Tissue engineering of small intestine--current status

Short bowel syndrome (SBS) has always posed a great threat to patients and has been one of the biggest challenges for doctors due to its high morbidity and mortality. So far, parenteral nutrition (PN) and small bowel transplantation remain the only viable therapeutic options. However, sepsis and liver failure associated with PN and limited availability of the donor organs and high graft rejection rates associated with transplantation have limited their use to a nonpermanent solution. Clearly, there is a need for an alternative therapy whereby increasing the absorptive surface area would help neonates and adults suffering from permanent intestinal failure. Techniques such as sequential intestinal lengthening are being explored in animal models with little success. Attempts to engineer small intestine since the late 1980s have achieved varying degrees of success in animal models with evolving refinements in biotechnology. The most encouraging results so far have been the generation of intestinal neomucosa in the form of cysts when intestinal epithelial organoid units isolated from neonatal rats were seeded onto biodegradable polymers before implantation in syngeneic adult rats' omentum. Although still experimental, continued attempts worldwide using cultured stem cells and improved polymer technology offer promise to provide an off-the-shelf artificial intestine as a novel therapy for patients with SBS. This article reviews the current status of progress in the field of small intestinal tissue engineering and addresses various types of cell sources and scaffold material having potential to be used in this field.

PEG-hirudin/iloprost Coating of Small Diameter ePTFE Grafts Effectively Prevents Pseudointima and Intimal Hyperplasia Development

OBJECTIVES

Small diameter PTFE grafts are prone to thrombosis and intimal hyperplasia development. Heparin graft coating has beneficial effects but also potential drawbacks. The purpose of this study was to evaluate the experimental efficacy of PEG-hirudin/iloprost coated small caliber PTFE grafts.

METHODS

Thirty-six femoro-popliteal ePTFE grafts (expanded polytetrafluoroethylene, diameter 4 mm) were inserted into 18 pigs. Grafts were randomised individually for each leg and grouped for 3 groups. Group I consisted of native ePTFE grafts, group II were grafts coated with a polylactide polymer (PLA) without drugs and group III grafts were coated with PLA containing a polyethylene glycol (PEG)-hirudin/iloprost combination. The follow-up period was 6 weeks. Patency rates were calculated and development of pseudointima inside the grafts was noted. Thickness of intimal hyperplasia at the distal anastomoses was measured using light microscopy.

RESULTS

Patency rates for group I were 6/9 (67%), for group II 9/10 (90%) and 12/12 (100%) for group III. In groups I and II there was a significant reduction of blood flow proximal to the graft at graft harvest, to 29+/-12 and 28+/-20 ml/min respectively (both p<0.01 versus preoperative value), whilst in group III blood flow, 99+/-21 ml/min, remained at the preoperative level. Subtotal stenosis due to development of pseudointima was noted in each of the native and PLA coated grafts but not in group III grafts. Intimal hyperplasia at the distal anastomosis was lowest in group III.

CONCLUSIONS

The PEG-hirudin/iloprost coating of ePTFE prostheses effectively reduced pseudointima and intimal hyperplasia development and led to superior graft patency.