Enhanced functions of vascular cells on nanostructured Ti for improved stent applications

Vascular tissue possesses numerous nanostructured surface features, but most metallic vascular stents proposed to restore blood flow are smooth at the nanoscale. Thus, the objective of the present study was to determine in vitro vascular cell functions on nanostructured titanium (Ti) compared to conventional commercially pure (c.p.) Ti. Results of this study showed for the first time greater competitive adhesion of endothelial versus vascular smooth muscle cells on nanostructured Ti compared to conventional Ti after 4 hours. Moreover, when cultured separately, increased endothelial and vascular smooth muscle cell density was observed on nanostructured Ti compared to conventional c.p. Ti after 1, 3, and 5 days; endothelial cells formed confluent monolayers before vascular smooth muscle cells on nanostructured Ti. Results also showed greater total amounts of collagen and elastin synthesis by vascular cells when cultured on nanostructured Ti. Since a major mode of failure of conventional vascular stents is the overgrowth of smooth muscle cells compared to endothelial cells, these results suggest that while the functions of both types of vascular cells were promoted on nanostructured c.p. Ti, endothelial cell functions (of particular importance, cell density or confluence) were enhanced over that of vascular smooth muscle cells. Thus, the present in vitro study showed that vascular stents composed of nanometer c.p. Ti particles may invoke advantageous cellular responses for improved stent applications.     

Mechanism(s) of increased vascular cell adhesion on nanostructured poly(lactic-co-glycolic acid) films

Studies have shown that poly(lactic-co-glycolic acid) (PLGA) films with nanometer surface features promote vascular endothelial and smooth muscle cell adhesion. The objective of this in vitro research was to begin to understand the mechanisms behind this observed increase in vascular cell adhesion. Results provided evidence that nanostructured PLGA adsorbed significantly more vitronectin and fibronectin from serum compared to conventional (or those not possessing nanometer surface features) PLGA. When separately preadsorbing both vitronectin and fibronectin, increased vascular smooth muscle and endothelial cell density was observed on nanostructured (compared to conventional) PLGA. Additionally, blocking of cell-binding epitopes of fibronectin and vitronectin significantly decreased vascular cell adhesion on nanostructured (compared to conventional) PLGA. For this reason, results of the present in vitro study demonstrated that cell adhesive proteins adsorbed in different quantities and altered bioactivity on nanostructured compared to conventional PLGA topographies, which (at least in part) may account for the documented increased vascular cell adhesion on nanostructured PLGA. In this manner, this study continues to provide evidence for the promise of nanostructured PLGA in vascular tissue engineering applications.     

PLGA nanometer surface features manipulate fibronectin interactions for improved vascular cell adhesion

The largest cause of mortality in the Western world is atherosclerotic vascular disease. Many of these diseases require synthetic vascular grafts; however, their patency rate is only 30% in small (<6 mm) diameter vascular grafts after 5 years of implantation. In an effort to increase small diameter vascular graft success, researchers have been designing random nanostructured surface features which enhance vascular cell functions. However, for the present study, highly-controllable, nanostructured features on poly(lactic-co-glycolic acid) (PLGA) surfaces were formulated. To create ordered nanostructured roughness on PLGA surfaces, either 500, 200, or 100 nm polystyrene nanospheres were separately placed onto mica. These were then used as a template for creating an inverse poly(dimethylsiloxane) mold which was utilized to cast PLGA. Compared to all other PLGA films formulated, AFM results demonstrated greater initial fibronectin spreading on PLGA which possessed spherical 200 nm features. Compared to smooth PLGA, PLGA with 500 or 100 nm surface features, results further showed that PLGA with 200 nm spherical features promoted vascular cell (specifically, endothelial, and smooth muscle cell) adhesion. In this manner, the present study demonstrated a specific nanometer surface feature size that promoted fibronectin spreading and subsequent vascular cell adhesion; criteria critical to vascular graft success.     

The role of nanometer and sub-micron surface features on vascular and bone cell adhesion on titanium

The quantified contribution of pure nanometer (features less than 100 nm in both the lateral and vertical scale) and sub-micron (features larger than 100 nm in the lateral scale) surface structures on the adhesion of vascular (endothelial) and bone (osteoblasts) cells were demonstrated in this study. Compared with flat titanium surfaces, sub-micron surface features led to a 27% increase in surface energy and promoted endothelial cell adhesion density by 200%. In addition, nanometer surface features also led to a 10% increase in surface energy and a 50% increase in endothelial cell adhesion density compared to flat titanium surfaces. Using aligned patterns of such features on titanium, it was clearly identified that both endothelial and bone cells selectively adhered onto sub-micron and nanometer surface features by 400% and 50% more than onto flat regions, respectively. Thus, the surface patterns developed in this study clearly confirmed that sub-micron to nanometer titanium surface features enhanced cytocompatibility properties for both endothelial and bone cells. Although sub-micron features on titanium had the highest surface energy and the greatest cell adhesion densities, nanometer surface features in this study were more efficient surface features increasing both surface energy and cell adhesion more with respect to smaller changes in surface area and surface roughness (compared to sub-micron surface features on titanium which had considerably larger changes in surface area and surface roughness).     

Decreased platelet adhesion and enhanced endothelial cell functions on nano and submicron-rough titanium stents

Endothelialization of a vascular stent is a critical step to prevent late stent thrombosis. In this study, electron beam deposition was utilized to create different scales of roughness on titanium stents, including flat features (F-Ti), a mixture of nanometer and submicron features (S-Ti), and nanometer features (N-Ti). The role of stent surface roughness on initial protein adsorption, platelet adhesion, rat aortic endothelial cell adhesion, migration, and nitric acid/endothelin-1 secretion was investigated in vitro. Results revealed the highest endothelial cell attachment on S-Ti after 4?h. Moreover, under flow conditions, the endothelial cell layer remained the most intact on S-Ti. These results were positively correlated with improved vitronectin adsorption on S-Ti. Endothelial cells also showed the fastest migration on S-Ti of all the samples over a 96?h time period. Endothelial cells on S-Ti exhibited the highest nitric acid/endothelin-1 ratio of all the samples, indicating potentially the best antithrombic endothelial cellular phenotype. This study also revealed the lowest platelet adhesion on S-Ti of all the samples. In summary, without using pharmaceutical agents, significantly less platelet and greater endothelial responses on nanometer to submicron rough titanium were observed in this study compared to flat titanium and, thus, nanometer to submicron surface features on titanium should be further studied for vascular stent applications.     

Nanostructured polymer/nanophase ceramic composites enhance osteoblast and chondrocyte adhesion

Osteoblast (bone-forming cell) and chondrocyte (cartilage-synthesizing cell) adhesion on novel nanostructured polylactic/glycolic acid (PLGA) and titania composites were investigated in the present in vitro study. Nanostructured polymers were created by chemically treating micron-structured PLGA with select concentrations of NaOH for various periods of time. Dimensions of ceramics were controlled by utilizing either micron or nanometer grain size titania. Compared with surfaces with conventional or micron surface roughness dimensions, results provided the first evidence of increased osteoblast and chondrocyte adhesion on 100 wt% PLGA films with nanometer polymer surface roughness dimensions. Results also confirmed other literature reports of enhanced osteoblast adhesion on 100 wt% nanometer compared with conventional grain size titania compacts; however, the present study provided the first evidence that decreasing titania grain size into the nanometer range did not influence chondrocyte adhesion. Finally, osteoblast and chondrocyte adhesion increased on 70/30 wt% PLGA/titania composites formulated to possess nanosurface rather than conventional surface feature dimensions. The present study, thus, provided evidence that these nanostructured PLGA/titania composites may possess the ability to simulate surface and/or chemical properties of bone and cartilage, respectively, to allow for exciting alternatives in the design of prostheses with greater efficacy.     

Nanotextured titanium surfaces for enhancing skin growth on transcutaneous osseointegrated devices

A major problem with transcutaneous osseointegrated implants is infection, mainly due to improper closure of the implant–skin interface. Therefore, the design of transcutaneous osseointegrated devices that better promote skin growth around these exit sites needs to be examined and, if successful, would clearly limit infection. Due to the success already demonstrated for orthopedic implants, developing surfaces with biologically inspired nanometer features is a design criterion that needs to be investigated for transcutaneous devices. This study therefore examined the influence of nanotextured titanium (Ti) created through electron beam evaporation and anodization on keratinocyte (skin-forming cell) function. Electron beam evaporation created Ti surfaces with nanometer features while anodization created Ti surfaces with nanotubes. Conventional Ti surfaces were largely micron rough, with few nanometer surface features. Results revealed increased keratinocyte adhesion in addition to increased keratinocyte spreading and differences in keratinocyte filopodia extension on the nanotextured Ti surfaces prepared by either electron beam evaporation or anodization compared to their conventional, unmodified counterparts after 4 h. Results further revealed increased keratinocyte proliferation and cell spreading over 3 and 5 days only on the nanorough Ti surfaces prepared by electron beam evaporation compared to both the anodized nanotubular and unmodified Ti surfaces. Therefore, the results from this in vitro study provided the first evidence that nano-modification techniques should be further researched as a means to possibly improve skin growth, thereby improving transcutaneous osseointegrated orthopedic implant longevity.     

In vitro hemocompatibility and vascular endothelial cell functionality on titania nanostructures under static and dynamic conditions for improved coronary stenting applications

The usefulness of nanoscale topography in improving vascular response in vitro was established previously on hydrothermally modified titanium surfaces. To propose this strategy of surface modification for translation onto clinically used metallic stents, it is imperative that the surface should be also hemocompatible: an essential attribute for any blood-contacting device. The present in vitro study focuses on a detailed hemocompatibility evaluation of titania nanostructures created through an alkaline hydrothermal route on metallic Ti stent prototypes. Direct interactions of TiO₂ nanocues of various morphologies with whole blood were studied under static conditions as well as using an in vitro circulation model mimicking arterial flow, with respect to a polished Ti control. Nanomodified stent surfaces upon contact with human blood showed negligible hemolysis under constant shear and static conditions. Coagulation profile testing indicated that surface roughness of nanomodified stents induced no alterations in the normal clotting times, with insignificant thrombus formation and minimal inflammatory reaction. Endothelialized nanomodified Ti surfaces were found to inhibit both activation as well as aggregation of platelets compared with the control surface, with the endothelium formed on the nanosurfaces having an increased expression of anti-thrombogenic genes. Such a nanotextured Ti surface, which is anti-thrombogenic and promotes endothelialization, would be a cost-effective alternative to drug-eluting stents or polymer-coated stents for overcoming in-stent restenosis.     

The adhesive properties of endothelial cells on endovascular stent coated by substrates of poly-l-lysine and fibronectin

Optimizing endothelial cell growth and adhesion on the surface of metallic stents implanted in the vascular system is a fundamental issue in understanding and improving their long-term biocompatibility. The ability of the endothelial cell to attach and adhere to the luminal stent surface as well as the capacity to withstand the significant shear stress associated with blood flow are important determinants. The adhesive characteristics of human umbilical vein endothelial cellsectin (HUVEC) on stent surfaces coated with either Poly-L-Lysine (PLL) or fibron (FN) were compared with uncoated controls. Increasing concentrations of PLL and FN were measured using a micropipette aspiration system. The adhesivenamic properties of HUVECs under static flow conditions were compared to a dy environment on endovascular stents using a parallel-plate-flow chamber. A scanning electron microscope picture was used to measure the number and the adhesive cell ratio as well as the percentage of surface coverage of stent by endothelial cells. The adhesive forces of HUVECs on foreign surfaces coated with PLL and FN were higher compared to uncoated surfaces, and were dependent on incr ing concentrations. These coatings resulted in significant increase of the adhesive force of HUVECs. The influence of substrates on the adhesion of the endothelial cell monolayer under static or dynamic flow conditions was highly significant compared with controls (p<0.01). No significant differences were observed between PLL and FN substrates. Both PLL and FN coated surfaces can significantly increase the adhesion and growth of HUVECs on metallic stent surfaces.     

Fibroblast adhesion to micro- and nano-heterogeneous topography using diblock copolymers and homopolymers

Polymeric substrates of different surface chemistry and length scales were found to have profound influence on cell adhesion. The adhesion of fibroblasts on surfaces of oxidized polystyrene (PS), on surfaces modified with random copolymers of PS and poly(methyl methacrylate) [P(S-r-MMA)] with topographic features, and chemically patterned surfaces that varied in lateral length scales from nanometers to microns were studied. Surfaces with heterogeneous topographies were generated from thin film mixtures of a block copolymer, PS-b-MMA, with homopolymers of PS and PMMA. The two homopolymers macroscopically phase separated and, with the addition of diblock copolymer, the size scales of the phases decreased to nanometer dimensions. Cell spreading area analysis showed that a thin film of oxidized PS surface promoted adhesion whereas a thin film of P(S-r-MMA) surface did not. Fibroblast adhesion was examined on surfaces in which the lateral length scale varied from 60 nm to 6 microm. It was found that, as the lateral length scale between the oxidized PS surfaces decreased, cell spreading area and degree of actin stress fiber formation increased. In addition, scanning electron microscopy was used to evaluate the location of filopodia and lamellipodia. It was found that most of the filopodia and lamellipodia interacted with the oxidized PS surfaces. This can be attributed to both chemical and topographic surface interactions that prevent cells from interacting with the P(S-r-MMA) at the base of the topographic features.     

Selective adhesion and growth of vascular endothelial cells on bioactive peptide nanofiber functionalized stainless steel surface

Metal-based scaffolds such as stents are the most preferred treatment methods for coronary artery disease. However, impaired endothelialization on the luminal surface of the stents is a major limitation occasionally leading to catastrophic consequences in the long term. Coating the stent surface with relevant bioactive molecules is considered to aid in recovery of endothelium around the wound site. However, this strategy remains challenging due to restrictions in availability of proper bioactive signals that will selectively promote growth of endothelium and the lack of convenience for immobilization of such signaling molecules on the metal surface. In this study, we developed self-assembled peptide nanofibers that mimic the native endothelium extracellular matrix and that are securely immobilized on stainless steel surface through mussel-inspired adhesion mechanism. We synthesized Dopa-conjugated peptide amphiphile and REDV-conjugated peptide amphiphile that are self-assembled at physiological pH. We report that Dopa conjugation enabled nanofiber coating on stainless steel surface, which is the most widely used backbone of the current stents. REDV functionalization provided selective growth of endothelial cells on the stainless steel surface. Our results revealed that adhesion, spreading, viability and proliferation rate of vascular endothelial cells are remarkably enhanced on peptide nanofiber coated stainless steel surface compared to uncoated surface. On the other hand, although vascular smooth muscle cells exhibited comparable adhesion and spreading profile on peptide nanofibers, their viability and proliferation significantly decreased. Our design strategy for surface bio-functionalization created a favorable microenvironment to promote endothelial cell growth on stainless steel surface, thereby providing an efficient platform for bioactive stent development for long term treatment of cardiovascular diseases.     

Investigation of surface endothelialization on biomedical nitinol (NiTi) alloy: Effects of surface micropatterning combined with plasma nanocoatings

Plasma nanocoated films with trimethylsilane-oxygen monomers showed outstanding biocompatibility in our previous studies. In this study, endothelialization on biomedical nitinol alloy surfaces was systematically investigated. Our study focuses on elucidating the effects of surface micropatternings with micropores and microgrooves combined with plasma nanocoating. Plasma nanocoatings with controlled thickness between 40 and 50 nm were deposited onto micropatterned nitinol surface in a direct current plasma reactor. Bovine aortic endothelial cells were cultured in vitro on these nitinol samples for 1, 3 and 5 days. It was found that rougher surfaces could enhance cell adhesion compared with the smoother surfaces; the surfaces patterned with micropores showed much more endothelialization than microgrooved surface after a 3 days culture. The cell culture results also showed that plasma nanocoatings significantly further increased cell proliferation and cell adhesion on the micropatterned nitinol surfaces, as compared with non-plasma nanocoated surface of nitinol samples. The surface micropatternings combined with plasma nanocoatings could improve the cell adhesion and accelerate surface endothelialization after implantation of intravascular stents, which is expected to reduce in-stent restenosis.     

Endothelial and vascular smooth muscle cell function on poly(lactic-co-glycolic acid) with nano-structured surface features

Biomaterials that successfully integrate into surrounding tissue should match not only the tissue's mechanical properties, but also its topography. The cellular response to a biomaterial may be enhanced in synthetic polymer formulations by mimicking the surface roughness created by the associated nano-structured extra-cellular matrix components of natural tissue. As a first step towards this endeavor, the goal of the present in vitro study was to use these design parameters to develop a synthetic, nano-structured, polymeric biomaterial that promotes cell adhesion and growth for vascular applications. In a novel manner, poly(lactic-co-glycolic acid) (PLGA) (50/50wt% mix) was synthesized to possess a range (from micron to nanometer) of surface features. Reduction of surface features was accomplished by treating conventional PLGA with various concentrations of NaOH for select periods of time. Results from cell experiments indicated that, compared to conventional PLGA, NaOH treated PLGA enhanced vascular smooth muscle cell adhesion and proliferation. However, PLGA prepared by soaking in NaOH decreased endothelial cell adhesion and proliferation compared to conventional PLGA. After further investigation, this finding was determined to be a result of chemical (and not topographical) changes during polymer synthesis. Surface chemistry effects were removed while retaining nano-structured topography by using polymer/elastomer casting methods. Results demonstrated that endothelial and smooth muscle cell densities increased on nano-structured cast PLGA. For these reasons, the present in vitro study provided the first evidence that nano-structured surface features can significantly improve vascular cell densities; such design criteria can be used in the synthesis of the next-generation of more successful tissue-engineered vascular grafts.     

Immobilization of heparin/poly-l-lysine nanoparticles on dopamine-coated surface to create a heparin density gradient for selective direction of platelet and vascular cells behavior

Restenosis, thrombosis formation and delayed endothelium regeneration continue to be problematic for coronary artery stent therapy. To improve the hemocompatibility of the cardiovascular implants and selectively direct vascular cell behavior, a novel kind of heparin/poly-l-lysine (Hep/PLL) nanoparticle was developed and immobilized on a dopamine-coated surface. The stability and structural characteristics of the nanoparticles changed with the Hep:PLL concentration ratio. A Hep density gradient was created on a surface by immobilizing nanoparticles with various Hep:PLL ratios on a dopamine-coated surface. Antithrombin III binding quantity was significantly enhanced, and in plasma the APTT and TT times as coagulation tests were prolonged, depending on the Hep density. A low Hep density is sufficient to prevent platelet adhesion and activation. The sensitivity of vascular cells to the Hep density is very different: high Hep density inhibits the growth of all vascular cells, while low Hep density could selectively inhibit smooth muscle cell hyperplasia but promote endothelial progenitor cells and endothelial cell proliferation. These observations provide important guidance for modification of surface heparinization. We suggest that this method will provide a potential means to construct a suitable platform on a stent surface for selective direction of vascular cell behavior with low side effects.     

Corrosion behavior and biocompatibility of nanostructured TiO2 film on Ti6Al4V

The corrosion behavior and cell adhesion property of nanostructured TiO2 films deposited electrolytically on Ti6Al4V were examined in the present in vitro study. The nanostructured TiO2 film deposition on Ti6Al4V was achieved via peroxoprecursors. SEM micrographs exhibit the formation of amorphous and crystallite TiO2 nanoparticles on Ti6Al4V before and after being annealed at 500 degrees C. Corrosion behavior of TiO2-deposited and uncoated Ti6Al4V was evaluated in freely aerated Hank's solution at 37 degrees C by the measurement and analysis of open-circuit potential variation with time, Tafel plots, and electrochemical impedance spectroscopy. The electrochemical results indicated that nano-TiO2 coated Ti6Al4V showed a better corrosion resistance in simulated biofluid than uncoated Ti6Al4V. Rat bone cells and human aortic smooth muscle cells were grown on these substrates to study the cellular responses in vitro. The SEM images revealed enhanced cell adhesion, cell spreading, and proliferation on nano-TiO2 coated Ti6Al4V compared to those grown on uncoated substrates for both cell lines. These results suggested that nanotopography produced by deposition of nanostructured TiO2 onto Ti alloy surfaces might enhance corrosion resistance, biocompatibility, and cell integration for implants made of Ti alloys.     

Patterned biofunctional designs of thermoresponsive surfaces for spatiotemporally controlled cell adhesion, growth, and thermally induced detachment

In the present study, we report advanced patterned biofunctionalization of thermoresponsive surfaces for achievement of spatiotemporally controlled cell adhesion, growth, and thermally induced detachment. These patterned biofunctional thermoresponsive surfaces were prepared using dual surface modification techniques: electron beam-induced surface patterning of carboxyl-functional thermoresponsive polymers with appropriate metal masks and following site-selective biofunctionalization with biomolecules, the cell adhesive peptide (RGDS) and/or the cell growth factor (insulin; INS). Patterned co-immobilization of RGDS-INS onto thermoresponsive surfaces dominated site-selective cell adhesion and growth along with patterned biofunctional domains in the serum-free culture. Spatiotemporal detachment of sparsely adherent and confluent cells from these patterned biofunctional thermoresponsive surfaces were both achieved only by reducing temperature. Furthermore, RGDS-INS-patterned thermoresponsive surfaces also successfully demonstrated the selective fabrication and recovery of either contiguous monolayer or mesh-like designed monolayer tissue constructs on the identical surfaces. Thus, patterned biofunctional designs would be utilized for the creation and harvest of biomimetic-designed vascular networks having sufficient biofunctional activities in facilitated cell sheet engineering and regenerative medicine.     

Fabrication of endothelial progenitor cell (EPC)-seeded intravascular stent devices and in vitro endothelialization on hybrid vascular tissue

Rapid re-endothelialization at an atherosclerotic lesion after balloon inflation or stent deployment may be essential for reducing or preventing local thrombus formation and restenosis. In order to prevent these complications via enhanced rapid re-endothelialization, we fabricated two types of endothelial progenitor cell (EPC)-seeded intravascular stent devices. One was a photocured gelatin-coated metallic stent, and the other was a microporous thin segmented polyurethane (SPU) film-covered stent on which photocured gelatin was coated. Both devices were seeded with ex vivo expanded EPCs obtained from canine peripheral blood. Seeded EPCs formed confluent monolayers onto surfaces of both photocured gelatin-coated stent struts and SPU film, and a majority of cells remained on surfaces of stents after stent expansion. The EPC-seeded stent was expanded in a tubular hybrid vascular medial tissue composed of vascular smooth muscle cells and collagen as an arterial media mimic. After 7-day culture, EPCs, which migrated from the stent struts, proliferated and endothelialized the luminal surfaces of the hybrid vascular medial tissue. This in vitro pilot study prior to in vivo experiments suggests that on-stent cell delivery of EPCs may be novel therapeutic devices for re-endothelialization or endothelium lining or paving at an atherosclerotic arterial wall, resulting in the prevention of on-stent thrombus formation and in-stent restenosis, as well as the rapid formation of normal tissue architecture.     

Polymers with nano-dimensional surface features enhance bladder smooth muscle cell adhesion

Previous studies investigating the design of synthetic bladder wall substitutes have involved polymers with micro dimensional structures. Since the body is made up of nano-structured components (e.g., extracellular matrix proteins), the focus of the present in vitro study was to design nano-structured polymers for use as synthetic bladder constructs that mimic the topography of natural bladder tissue. In order to complete this task, novel nano-structured biodegradable polymeric films of poly-lactic-co-glycolic-acid (PLGA), poly-ether-urethane (PU), and poly-caprolactone (PCL) were fabricated and separately treated with various concentrations of NaOH (for PLGA and PCL) and HNO(3) (for PU) for select time periods. These treatments reduced the polymer surface feature dimensions from conventional micron dimensions to biologically inspired nanometer dimensions. Select cytocompatibility properties of these biomaterials were tested in vitro. Results provide the first evidence that adhesion of bladder smooth muscle cells is enhanced as polymer surface feature dimensions are reduced into the nanometer range. In addition, surface analysis results reveal that the polymer nanometer surface roughness is the primary design parameter that increases bladder smooth muscle cell adhesion. For this reason, the "next generation" of tissue-engineered bladder constructs with increased efficacy should contain surfaces with nanometer (as opposed to micron) surface features.     

Platelet inhibition and endothelial cell adhesion on elastin-like polypeptide surface modified materials

Platelet adhesion and activation are important early markers of biomaterial blood compatibility, while surfaces that promote enhanced endothelial cell adhesion and eNOS expression are strategic targets for long term vascular graft applications. Materials surface modified with fluorinated surface modifiers, containing peptides inspired from elastin cross-linking domains, have been used for the cross-linking of elastin-like polypeptide 4 (ELP4) macromolecules onto polyurethane surfaces. In the present study, ELP4 modified polyurethanes were evaluated in vitro to assess platelet adhesion, microparticle formation and bulk platelet activation following blood-material interactions. Reduced platelet adhesion and bulk platelet activation were observed following contact between reconstituted human blood and the ELP4 materials, relative to the uncoated base polyurethane controls. ELP4 modified materials also promoted endothelial cell adhesion and retention over a period of one week and showed that the endothelial cells exhibited an organized actin cytoskeleton and enhanced endothelial nitric oxide synthase (eNOS) expression relative to the control surfaces. These results indicate that polyurethane elastomers modified with ELP4 covalently bound to fluorinated surface modifiers provide a promising approach for endowing synthetic elastomers with both reduced blood platelet activation properties and enhanced endothelial cell adhesion for potential use in vascular graft applications.     

T cell interaction with ICAM-1-deficient endothelium in vitro: transendothelial migration of different T cell populations is mediated by endothelial ICAM-1 and ICAM-2.

The trafficking of T lymphocytes is carefully regulated by adhesive interactions with the vascular endothelium. Depending on their maturation and activation stage, T lymphocytes exhibit distinctive patterns of homing and recirculation, which is at least partly due to the selective expression of cell adhesion molecules (CAM) on the T cell surface. In order to define whether the differential usage of CAM during the steps of transendothelial migration is involved in organ-specific recirculation of different T cell subsets we compared the interaction of three different T cell populations with mouse endothelioma cell lines in vitro. Using a novel approach, where we directly compared T cell interaction with ICAM-1-deficient endothelium to wild-type endothelium, we recently demonstrated that endothelial ICAM-1 and ICAM-2 play a key role in mediating the transendothelial migration of CD4(+) memory T cells. Here we show that endothelial ICAM-1 and ICAM-2 are equally required for the transendothelial migration of other T cell populations such as thymocytes and T lymphoma cells, which differ from CD4(+) memory T cells in their maturation and activation stage, as well as in their surface expression of adhesion molecules. Our data therefore demonstrate that transendothelial migration of different T cell populations is mediated by the same endothelial CAM, i.e. ICAM-1 and ICAM-2, and thus subset-specific interaction of T cells with endothelial cells must be regulated prior to transendothelial migration.