Adhesion and proliferation of human endothelial cells on photochemically modified polytetrafluoroethylene

Fabrication Scaffold with High Dimensional Control for Spheroids with Undifferentiated iPS Cell Properties

Spheroids are expected to aid the establishment of an in vitro-based cell culture system that can realistically reproduce cellular dynamics in vivo. We developed a fluoropolymer scaffold with an extracellular matrix (ECM) dot array and confirmed the possibility of mass-producing spheroids with uniform dimensions. Controlling the quality of ECM dots is important as it ensures spheroid uniformity, but issues such as pattern deviation and ECM drying persist in the conventional microstamping method. In this study, these problems were overcome via ECM dot printing using a resin mask with dot-patterned holes. For dot diameters of φ 300 μm, 400 μm, and 600 μm, the average spheroid diameters of human iPS cells (hiPSCs) were φ 260.8 μm, 292.4 μm, and 330.7 μm, respectively. The standard deviation when each average was normalized to 100 was 14.1%. A high throughput of 89.9% for colony formation rate to the number of dots and 89.3% for spheroid collection rate was achieved. The cells proliferated on ECM dots, and the colonies could be naturally detached from the scaffold without the use of enzymes, so there was almost no stimulation of the cells. Thus, the undifferentiated nature of hiPSCs was maintained until day 4. Therefore, this method is expected to be useful in drug discovery and regenerative medicine.

Design considerations of benchtop fluid flow bioreactors for bio-engineered tissue equivalents in vitro

One of the major aims of bio-engineering tissue equivalents in vitro is to create physiologically relevant culture conditions to accurately recreate the cellular microenvironment. This often includes incorporation of factors such as the extracellular matrix, co-culture of multiple cell types and three-dimensional culture techniques. These advanced techniques can recapitulate some of the properties of tissue in vivo, however fluid flow is a key aspect that is often absent. Fluid flow can be introduced into cell and tissue culture using bioreactors, which are becoming increasingly common as we seek to produce increasingly accurate tissue models. Bespoke technology is continuously being developed to tailor systems for specific applications and to allow compatibility with a range of culture techniques. For effective perfusion of a tissue culture many parameters can be controlled, ranging from impacts of the fluid flow such as increased shear stress and mass transport, to potentially unwanted side effects such as temperature fluctuations. A thorough understanding of these properties and their implications on the culture model can aid with a more accurate interpretation of results. Improved and more complete characterisation of bioreactor properties will also lead to greater accuracy when reporting culture conditions in protocols, aiding experimental reproducibility, and allowing more precise comparison of results between different systems. In this review we provide an analysis of the different factors involved in the development of benchtop flow bioreactors and their potential biological impacts across a range of applications.

Development of a Simple Spheroid Production Method Using Fluoropolymers with Reduced Chemical and Physical Damage

Establishing an in vitro–based cell culture system that can realistically simulate in vivo cell dynamics is desirable. It is thus necessary to develop a method for producing a large amount of cell aggregates (i.e., spheroids) that are uniform in size and quality. Various methods have been proposed for the preparation of spheroids; however, none of them satisfy all requirements, such as cost, size uniformity, and throughput. Herein, we successfully developed a new cell culture method by combining fluoropolymers and dot patterned extracellular matrix substrates to achieve size-controlled spheroids. First, the spheroids were spontaneously formed by culturing them two-dimensionally, after which the cells were detached with a weak liquid flow and cultured in suspension without enzyme treatment. Stable quality spheroids were easily produced, and it is expected that the introduction and running costs of the technique will be low; therefore, this method shows potential for application in the field of regenerative medicine.

Surface Modification of PLLA, PTFE and PVDF with Extreme Ultraviolet (EUV) to Enhance Cell Adhesion

Recently, extreme ultraviolet (EUV) radiation has been increasingly used to modify polymers. Properties such as the extremely short absorption lengths in polymers and the very strong interaction of EUV photons with materials may play a key role in achieving new biomaterials. The purpose of the study was to examine the impact of EUV radiation on cell adhesion to the surface of modified polymers that are widely used in medicine: poly(tetrafluoroethylene) (PTFE), poly (vinylidene fluoride) (PVDF), and poly-L-(lactic acid) (PLLA). After EUV surface modification, which has been performed using a home-made laboratory system, changes in surface wettability, morphology, chemical composition and cell adhesion polymers were analyzed. For each of the three polymers, the EUV radiation differently effects the process of endothelial cell adhesion, dependent of the parameters applied in the modification process. In the case of PVDF and PTFE, higher cell number and cellular coverage were obtained after EUV radiation with oxygen. In the case of PLLA, better results were obtained for EUV modification with nitrogen. For all three polymers tested, significant improvements in endothelial cell adhesion after EUV modification have been demonstrated.

Responses of endothelial cells, smooth muscle cells, and platelets dependent on the surface topography of polytetrafluoroethylene

In this study, the effect of different structures (flat, expanded, and electrospun) of polytetrafluoroethylene (PTFE) on the interactions of endothelial cells (ECs), smooth muscle cells (SMCs), and platelets was investigated. In addition, the mechanisms that govern the interactions between ECs, SMCs, and platelets with different structures of PTFE were discussed. The surface characterizations showed that the different structures of PTFE have the same surface chemistry, similar surface wettability and zeta potential, but uniquely different surface topography. The viability, proliferation, morphology, and phenotype of ECs and SMCs interacted with different structures of PTFE were investigated. Expanded PTFE (ePTFE) provided a relatively better surface for the growth of ECs. In case of SMC interactions, although all the different structures of PTFE inhibited SMC growth, a maximum inhibitory effect was observed for ePTFE. In case of platelet interactions, the electrospun PTFE provided a better surface for preventing the adhesion and activation of platelets. Thus, this study demonstrated that the responses of ECs, SMCs, and platelets strongly dependent on the surface topography of the PTFE. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2291-2304, 2016.

Engineering and functionalization of biomaterials via surface modification

Recent progress pertaining to the surface treatment of implantable macro-scale biomaterials and using micro- and nano-biomaterials for disease diagnosis and drug/gene delivery is reviewed.

Effects of macro- versus nanoporous silicon substrates on human aortic endothelial cell behavior

Human aortic endothelial cells play a key role in the pathogenesis of atherosclerosis, which is a common, progressive, and multifactorial disease that is the clinical endpoint of an inflammatory process and endothelial dysfunction. Study and development of new therapies against cardiovascular disease must be tested in vitro cell models, prior to be evaluated in vivo. To this aim, new cell culture platforms are developed that allow cells to grow and respond to their environment in a realistic manner. In this work, the cell adhesion and morphology of endothelial cells are investigated on functionalized porous silicon substrates with two different pore size configurations: macroporous and nanoporous silicon. Herein, we modified the surfaces of porous silicon substrates by aminopropyl triethoxysilane, and we studied how different pore geometries induced different cellular response in the cell morphology and adhesion. The cell growth over the surface of porous silicon becomes an attractive field, especially for medical applications. Surface properties of the biomaterial are associated with cell adhesion and as well as, with proliferation, migration and differentiation.

Surface modification of polymers for biocompatibility via exposure to extreme ultraviolet radiation

Polymeric biomaterials are being widely used for the treatment of various traumata, diseases and defects in human beings due to ease in their synthesis. As biomaterials have direct interaction with the extracellular environment in the biological world, biocompatibility is a topic of great significance. The introduction or enhancement of biocompatibility in certain polymers is still a challenge to overcome. Polymer biocompatibility can be controlled by surface modification. Various physical and chemical methods (e.g., chemical and plasma treatment, ion implantation, and ultraviolet irradiation etc.) are in use or being developed for the modification of polymer surfaces. However an important limitation in their employment is the alteration of bulk material. Different surface and bulk properties of biomaterials are often desirable for biomedical applications. Because extreme ultraviolet (EUV) radiation penetration is quite limited even in low density mediums, it could be possible to use it for surface modification without influencing the bulk material. This article reviews the degree of biocompatibility of different polymeric biomaterials being currently employed in various biomedical applications, the surface properties required to be modified for biocompatibility control, plasma and laser ablation based surface modification techniques, and research studies indicating possible use of EUV for enhancing biocompatibility.

The in vivo blood compatibility of bio-inspired small diameter vascular graft: effect of submicron longitudinally aligned topography

Background

Cardiovascular disease is the leading cause of deaths worldwide and the arterial reconstructive surgery remains the treatment of choice. Although large diameter vascular grafts have been widely used in clinical practices, there is an urgent need to develop a small diameter vascular graft with enhanced blood compatibility. Herein, we fabricated a small diameter vascular graft with submicron longitudinally aligned topography, which mimicked the tunica intima of the native arterial vessels and were tested in Sprague–Dawley (SD) rats.

Methods

Vascular grafts with aligned and smooth topography were prepared by electrospinning and were connected to the abdominal aorta of the SD rats to evaluate their blood compatibility. Graft patency and platelet adhesion were evaluated by color Doppler ultrasound and immunofluorescence respectively.

Results

We observed a significant higher patency rate (p = 0.021) and less thrombus formation in vascular graft with aligned topography than vascular graft with smooth topography. However, no significant difference between the adhesion rates on both vascular grafts (smooth/aligned: 0.35‰/0.12‰, p > 0.05) was observed. Moreover, both vascular grafts had few adherent activated platelets on the luminal surface.

Conclusion

Bionic vascular graft showed enhanced blood compatibility due to the effect of surface topography. Therefore, it has considerable potential for using in clinical application.

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.

Binding of the cell adhesive protein tropoelastin to PTFE through plasma immersion ion implantation treatment

The interaction of proteins and cells with polymers is critical to their use in scientific and medical applications. In this study, plasma immersion ion implantation (PIII) was used to modify the surface of polytetrafluorethylene (PTFE), enabling the covalent binding of a cell adhesive protein, tropoelastin, without employing chemical linking molecules. Tropoelastin coating of untreated or PIII treated PFTE simultaneously promoted and blocked cell interactions respectively, i.e. PIII treatment of the PTFE surface completely inverses the cell interactive properties of bound tropoelastin. This activity persisted over long term storage of the PIII treated surfaces. The integrin binding C-terminus of tropoelastin was markedly less solvent exposed when bound to PIII treated PTFE than untreated PTFE, accounting for the modulation of cell adhesive activity. This presents a new methodology to specifically modulate cell behavior on a polymer surface using a simple one step treatment process, by adjusting the adhesive activity of a single extracellular matrix protein.

Enhancing Endothelial Cell Retention on ePTFE Constructs by siRNA-Mediated SHP-1 Gene Silencing

Polymeric vascular grafts hold great promise for vascular reconstruction, but the lack of endothelial cells renders these grafts susceptible to intimal hyperplasia and restenosis, precluding widespread clinical applications. The purpose of this study is to establish a stable endothelium on expanded polytetrafluoroethylene (ePTFE) membrane by small interfering RNA (siRNA)-induced suppression of the cell adhesion inhibitor SH2 domain-containing protein tyrosine phosphatase-1 (SHP-1). Human umbilical vein endothelial cells (HUVECs) were treated with scrambled siRNA as a control or SHP-1 specific siRNA. Treated cells were seeded onto fibronectin-coated ePTFE scaffolds and exposed to a physiological range of pulsatile fluid shear stresses for 1 h in a variable-width parallel plate flow chamber. Retention of cells was measured and compared between various shear stress levels and between groups treated with scrambled siRNA and SHP-1 specific siRNA. HUVECs seeded on ePTFE membrane exhibited shear stress-dependent retention. Exposure to physiological shear stress (10 dyn/cm2) induced a reduction in the retention of scrambled siRNA treated cells from 100% to 85% at 1 h. Increased shear stress (20 dyn/cm2) further reduced retention of scrambled siRNA treated cells to 55% at 1 h. SHP-1 knockdown mediated by siRNA enhanced endothelial cell retention from approximately 60% to 85% after 1 h of exposure to average shear stresses in the range of 15–30 dyn/cm2. This study demonstrates that siRNA-mediated gene silencing may be an effective strategy for improving the retention of endothelial cells within vascular grafts.

Seeding density matters: extensive intercellular contact masks the surface dependence of endothelial cell-biomaterial interactions

The effects of seeding density have often been overlooked in evaluating endothelial cell-biomaterial interactions. This study compared the cell attachment and proliferation characteristics of endothelial cells on modified poly (L: -lactic acid) (PLLA) films conjugated to gelatin and chitosan at low and high seeding densities (5,000 and 50,000 cells/cm(2)). During the early stage (2 h) of cell-biomaterial interaction, a low seeding density enabled us to observe the intrinsic surface-dependent differences in cell attachment capacity and morphogenesis, whereas extensive intercellular interactions at high seeding density masked differences between substrates and improved cell attachment on low-affinity substrates. During the later stage of cell-biomaterial interaction over 7-days of culture, the proliferation rate was found to be surface-dependent at low seeding density, whereas this surface-dependent difference was not apparent at high seeding density. It is recommended that low seeding density should be utilized for evaluating biomaterial applications where EC density is likely to be low, such as in situ endothelialization of blood-contacting devices.

Potential applications of natural origin polymer-based systems in soft tissue regeneration

Despite the many advances in tissue engineering approaches, scientists still face significant challenges in trying to repair and replace soft tissues. Nature-inspired routes involving the creation of polymer-based systems of natural origins constitute an interesting alternative route to produce novel materials. The interest in these materials comes from the possibility of constructing multi-component systems that can be manipulated by composition allowing one to mimic the tissue environment required for the cellular regeneration of soft tissues. For this purpose, factors such as the design, choice, and compatibility of the polymers are considered to be key factors for successful strategies in soft tissue regeneration. More recently, polysaccharide-protein based systems have being increasingly studied and proposed for the treatment of soft tissues. The characteristics, properties, and compatibility of the resulting materials investigated in the last 10 years, as well as commercially available matrices or those currently under investigation are the subject matter of this review.

Electrospinning of small diameter 3-D nanofibrous tubular scaffolds with controllable nanofiber orientations for vascular grafts

The control of nanofiber orientation in nanofibrous tubular scaffolds can benefit the cell responses along specific directions. For small diameter tubular scaffolds, however, it becomes difficult to engineer nanofiber orientation. This paper reports a novel electrospinning technique for the fabrication of 3-D nanofibrous tubular scaffolds with controllable nanofiber orientations. Synthetic absorbable poly-ε-caprolactone (PCL) was used as the model biomaterial to demonstrate this new electrospinning technique. Electrospun 3-D PCL nanofibrous tubular scaffolds of 4.5 mm in diameter with different nanofiber orientations (viz. circumferential, axial, and combinations of circumferential and axial directions) were successfully fabricated. The degree of nanofiber alignment in the electrospun 3-D tubular scaffolds was quantified by using the fast Fourier transform (FFT) analysis. The results indicated that excellent circumferential nanofiber alignment could be achieved in the 3-D nanofibrous PCL tubular scaffolds. The nanofibrous tubular scaffolds with oriented nanofibers had not only directional mechanical property but also could facilitate the orientation of the endothelial cell attachment on the fibers. Multiple layers of aligned nanofibers in different orientations can produce 3-D nanofibrous tubular scaffolds of different macroscopic properties.

Surface chemistry and polymer film thickness effects on endothelial cell adhesion and proliferation

Adherence and growth rates of human aortic endothelial cells (HAEC) on plasma polymerized poly(vinylacetic acid) films were measured as functions of the surface density of --COOH groups and plasma deposited film thickness. Pulsed plasma polymerization was employed to produce films containing 3.6 to 9% --COOH groups, expressed as a percent of total carbon content. Endothelial cells exhibited increased cell adherence and proliferation with increasing --COOH surface densities. Additionally, and unexpectedly, cell growth was also dependent on the film thicknesses, which ranged from 25 to 200 nm. The results indicate that optimization of the functional group surface density and film thickness could produce significant enhancements in initial adhesion and subsequent growth of the HAEC cells.

Cell Adhesion and Proliferation onto Chitosan-based Membranes Treated by Plasma Surface Modification

Surface properties play a vital role in the functioning of a biomaterial. Cellular adherence and growth onto biomaterials can be enhanced in biomaterial modifications of their surface. In this work, the cell behavior on chitosan membranes modified by argon and nitrogen-plasma treatments was investigated. Characterization of the membranes was performed using atomic force microscopy, contact angle measurements, and X-ray photoelectron spectroscopy. Cytotoxicity assessment and direct contact assay were carried out for untreated and treated chitosan membranes using L929 fibroblast-like cells. Cell morphology and cell viability were assessed to evaluate the cell attachment and proliferation. Changes in terms of roughness, surface chemistry, and hydrophilicity/hydrophobic balance of chitosan-modified membranes were observed. Regarding cell studies, the findings revealed that the extracts of all membranes do not induce cytotoxic effects. Moreover, the in vitro assays evidenced an improvement of the L929 adhesion and attachment when compared to untreated chitosan membranes. Overall, the data obtained clearly demonstrated that plasma treatments constitute an effective way of improving the biocompatibility of chitosan membranes towards to their use in biomedical applications.

Fabrication of arbitrary polymer patterns for cell study by two-photon polymerization process

Topographically patterned surfaces are known to be powerful tools for influencing cellular functions. Here we demonstrate a method for fabricating high aspect ratio ( approximately 10) patterns of varying height by using two-photon polymerization process to study contact guidance of cells. Ridge patterns of various heights and widths were fabricated through single laser scanning steps by low numerical aperture optics, hence at much higher processing throughput. Fibroblast cells were seeded on parallel line patterns of different height ( approximately 1.5-microm, approximately 0.8-microm, and approximately 0.5-microm) and orthogonal mesh patterns ( approximately 8-microm and approximately 4-microm height, approximately 5-microm and approximately 5.5-microm height, approximately 5-microm and approximately 6-microm height). Cells experienced different strength of contact guidance depending on the ridge height. Our results demonstrate that a height threshold of nearly 1 microm influences cell alignment on both parallel line and orthogonal mesh patterns. This fabrication technique may find wide application in the design of single cell traps for controlling cell behavior in microdevices and investigating signal transduction as influenced by surface topology.

A bilayered elastomeric scaffold for tissue engineering of small diameter vascular grafts

A major barrier to the development of a clinically useful small diameter tissue engineered vascular graft (TEVG) is the scaffold component. Scaffold requirements include matching the mechanical and structural properties with those of native vessels and optimizing the microenvironment to foster cell integration, adhesion and growth. We have developed a small diameter, bilayered, biodegradable, elastomeric scaffold based on a synthetic, biodegradable elastomer. The scaffold incorporates a highly porous inner layer, allowing cell integration and growth, and an external, fibrous reinforcing layer deposited by electrospinning. Scaffold morphology and mechanical properties were assessed, quantified and compared with those of native vessels. Scaffolds were then seeded with adult stem cells using a rotational vacuum seeding device to obtain a TEVG, cultured under dynamic conditions for 7 days and evaluated for cellularity. The scaffold showed firm integration of the two polymeric layers with no delamination. Mechanical properties were physiologically consistent, showing anisotropy, an elastic modulus (1.4 + or - 0.4 MPa) and an ultimate tensile stress (8.3 + or - 1.7 MPa) comparable with native vessels. The compliance and suture retention forces were 4.6 + or - 0.5 x 10(-4) mmHg(-1) and 3.4 + or - 0.3N, respectively. Seeding resulted in a rapid, uniform, bulk integration of cells, with a seeding efficiency of 92 + or - 1%. The scaffolds maintained a high level of cellular density throughout dynamic culture. This approach, combining artery-like mechanical properties and a rapid and efficient cellularization, might contribute to the future clinical translation of TEVGs.

Linker-free covalent attachment of the extracellular matrix protein tropoelastin to a polymer surface for directed cell spreading

Polymers are used for the fabrication of many prosthetic implants. It is desirable for these polymers to promote biological function by promoting the adhesion, differentiation and viability of cells. Here we have used plasma immersion ion implantation (PIII) treatment of polystyrene to modify the polymer surface, and so modulate the binding of the extracellular matrix protein tropoelastin. PIII treated, but not untreated polystyrene, bound tropoelastin in a sodium dodecyl sulfate (SDS)-resistant manner, consistent with previous enzyme-binding data that demonstrated the capability of these surfaces to covalently attach proteins without employing chemical linking molecules. Furthermore sulfo-NHS acetate (SNA) blocking of tropoelastin lysine side chains eliminated the SDS-resistant binding of tropoelastin to PIII-treated polystyrene. This implies tropoelastin is covalently attached to the PIII-treated surface via its lysine side chains. Cell spreading was only observed on tropoelastin coated, PIII-treated polystyrene surfaces, indicating that tropoelastin was more biologically active on the PIII-treated surface compared to the untreated surface. A contact mask was used to pattern the PIII treatment. Following tropoelastin attachment, cells spread preferentially on the PIII-treated sections of the polystyrene surface. This demonstrates that PIII treatment of polystyrene improves the polymer's tropoelastin binding properties, with advantages for tissue engineering and prosthetic design.

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

Improved attachment, adhesion and proliferation of the surrounding mature endothelial cells (ECs) and circulating endothelial progenitor cells (EPCs) is of primary importance to realize the in situ rapid re-endothelialization of cardiovascular stents. To achieve this, a combinatorial coating of synthesized mussel adhesive polypeptide mimics as well as anti-CD34 antibody was constructed onto the devices through a novel adsorption method in this study. To immobilize the polypeptide and target antibody effectively, polycaprolactone (PCL) was first spin-coated onto the substrate as intermediate. The immobilization of polypeptide and antibody was confirmed by the changes of water contact angles and the attachment, growth of ECs and EPCs on the substrates, respectively. The results showed that after adhesive polypeptide or/and antibody immobilization, the hydrophilicity of coated PCL substrate (PCLS) was obviously improved. The amount of the immobilized antibody, determined by enzymelinked immunoassay (ELISA) method, was enhanced with the increase of antibody concentrations in the range from 5 to 25 mug/ml. The coatings after BSA blocking prevented the unspecific protein adsorption as monitored by fluorescent microscopy. The results of in vitro cell culture showed that compared with the PCLS, polypeptide/anti-CD34 antibody coating could effectively enhance the attachment, growth and adhesion of ECs and EPCs, in particular EPCs. A platelet adhesion experiment revealed that the blood compatibility of the PCLS after polypeptide/anti-CD34 antibody coating was also obviously improved. The results showed that the surface modification with adhesive polypeptide and anti-CD34 antibody will be a promising coating technique for the surface modification of the intravascular prostheses for rapid re-endothelialization.

In vitro evaluation of electrospun nanofiber scaffolds for vascular graft application

Blood vessels are diverse in size, mechanical and biochemical properties, cellular content, and ultrastructural organization depending on their location and specific function. Therefore, it is required to control the fabrication of vascular grafts for obtaining desirable characteristics of blood vessel substitutes. In this study we have fabricated various scaffolds using the electrospinning technique with blends of collagen, elastin, and several biodegradable polymers. Biocompatibility, dimensional stability in vitro and mechanical properties were evaluated. Materials were blended at a relative concentration by weight of 45% collagen, 15% elastin, and 40% synthetic polymer to mimic the ratio of collagen and elastin in native blood vessels. The fabricated scaffolds are composed of randomly oriented fibers with diameters ranging from 477 to 765 nm. The electrospun scaffolds are nontoxic, dimensionally stable in an in vitro culture environment, easily fabricated, and possess controlled mechanical properties that simulate the ultrastructure of native blood vessels. The present study suggests that the introduction of synthetic biodegradable polymers enabled tailoring of mechanical properties of vascular substitutes and improving compliance matching for vascular tissue engineering.

Proliferation of aligned mammalian cells on laser-nanostructured polystyrene

Biomaterial surface chemistry and nanoscale topography are important for many potential applications in medicine and biotechnology as they strongly influence cell function, adhesion and proliferation. In this work, we present periodic surface structures generated by linearly polarized KrF laser light (248 nm) on polystyrene (PS) foils. These structures have a periodicity of 200-430 nm and a depth of 30-100 nm, depending on the angle of incidence of the laser beam. The changes in surface topography and chemistry were analysed by atomic force microscopy (AFM), advancing water contact-angle measurements, Fourier-transform infrared spectroscopy using an attenuated total reflection device (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). We show that the surface laser modification results in a significantly enhanced adhesion and proliferation of human embryonic kidney cells (HEK-293) compared to the unmodified polymer foil. Furthermore, we report on the alignment of HEK-293 cells, Chinese hamster ovary (CHO-K1) cells and skeletal myoblasts along the direction of the structures. The results indicate that the presence of nanostructures on the substrates can guide cell alignment along definite directions, and more importantly, in our opinion, that this alignment is only observed when the periodicity is above a critical periodicity value that is cell-type specific.

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.

Poly(styrenesulfonate)/poly(allylamine) multilayers: a route to favor endothelial cell growth on expanded poly(tetrafluoroethylene) vascular grafts

Small-diameter synthetic vascular grafts of expanded poly(tetrafluoroethylene) (ePTFE) polymer concern one of the most common alternatives for the replacement of diseased vessels. However, high failure rates arise especially due to the lack of endothelial cells (ECs). EC seeding was developed to build a monolayer on the luminal surface. Because ECs show little or no adhesion on synthetic prostheses, it is necessary to promote their retention. On ePTFE surfaces we successfully deposited polyelectrolyte multilayer films (PMFs) consisting of poly(ethylenimine) (PEI), poly(sodium 4-styrenesulfonate) (PSS), and poly(allylamine hydrochloride) (PAH) to obtain PEI-(PSS-PAH)3 films. EC adhesion and spreading on modified ePTFE were assessed by scanning electron and confocal microscopies. Cell viability was evaluated by Alamar Blue assay. After 7 days of culture, the ePTFE modified with PMF exhibited improvements of EC viability as compared to that of the controls (nonmodified ePTFE) or even ePTFE coated by a PAH monolayer (p < 0.05). Moreover, the spreading of ECs was largely enhanced compared to that of the same controls, resulting in a healthy confluent cell monolayer formation. Positive staining for the von Willebrand factor confirmed the EC phenotype. Promoting EC attachment and function on ePTFE modified with PMFs could become in the future a promising treatment for synthetic small-diameter vascular grafts.

Cytocompatibility of poly(acrylonitrile-co-N-vinyl-2-pyrrolidone) membranes with human endothelial cells and macrophages

Polyacrylonitrile modified with N-vinyl-2-pyrrolidone (NVP) shows good hemocompatibility. This work, which aims to evaluate the cytocompatibility of membranes fabricated from poly(acrylonitrile-co-N-vinyl-2-pyrrolidone) (PANCNVP), studied the adhesion of macrophages and endothelial cell (EC) cultures. It was found that PANCNVP membranes with higher NVP content decreased the adhesion of both macrophages and ECs. Compared with polyacrylonitrile and tissue culture polystyrene control, however, these PANCNVP membranes promoted the proliferation of ECs. Furthermore, the viability of ECs cultured on the PANCNVP membrane surfaces was also relatively competitive. Both static and dynamic water contact angle measurements were conducted to explain the nature of cell adhesion to the PANCNVP membranes. On the basis of these results and the phenomena of water swelling and water states reported previously, it was presumed that the coexistence of large amounts of bound water and free water induced by NVP moieties are responsible for the lower adhesion and better function of cells adhering to the PANCNVP membranes.

The effect of RGD fluorosurfactant polymer modification of ePTFE on endothelial cell adhesion, growth, and function

We have synthesized and characterized a novel peptide fluorosurfactant polymer (PFSP) modification that facilitates the adhesion and growth of endothelial cells on expanded polytetrafluoroetheylene (ePTFE) vascular graft material. This PFSP consists of a poly(vinyl amine) (PVAm) backbone with integrin binding Arg-Gly-Asp (RGD) peptides and perfluorocarbon pendant branches for adsorption and stable adhesion to underlying ePTFE. Aqueous PFSP solution was used to modify the surface of fluorocarbon substrates. Following subconfluent seeding, endothelial cell (EC) adhesion and growth on PFSP was assessed by determining cell population at different time points. Spectroscopic results indicated successful synthesis of PFSP. PFSP modification of ePTFE reduced the receding water contact angle measurement from 120 degrees to 6 degrees , indicating successful surface modification. Quantification of cell population demonstrated reduced EC attachment efficiency but increased growth rate on RGD PFSP compared with fibronectin (FN). Actin staining revealed a well-developed cytoskeleton for ECs on RGD PFSP indicative of stable adhesion. Uptake of acetylated low-density lipoprotein and positive staining for VE-Cadherin confirm EC phenotype for adherent cells. Production of prostacyclin, a potent antiplatelet agent, was equivalent between ECs on FN and RGD PFSP surfaces. Our results indicate successful synthesis and surface modification with PFSP; this is a simple, quantitative, and effective approach to modifying ePTFE to encourage endothelial cell attachment, growth, and function.

Mylar and Teflon-AF as cell culture substrates for studying endothelial cell adhesion

The textured and opaque nature of Dacron and ePTFE has prevented the use of these fabrics in conventional cell culture techniques normally employed to optimize cell attachment and retention. This lack of optimization has led, in part, to the poor performance of endothelialization strategies for improving vascular graft patency. Here we show that thin, transparent films of Mylar and Teflon-AF are viable in vitro cell culture mimics of Dacron and ePTFE vascular graft materials, particularly for the study of protein mediated endothelial cell (EC) attachment, spreading and adhesion. Glass substrates were used as controls. X-ray photoelectron spectroscopy (XPS) and contact angle analysis showed that Mylar and Teflon-AF have surface chemistries that closely match Dacron and ePTFE. (125)I radiolabeling was used to quantify fibronectin (FN) adsorption, and FN and biotinylated-BSA "dual ligand" co-adsorption onto glass, Mylar and Teflon-AF substrates. Native human umbilical vein endothelial cells (HUVEC) and streptavidin-incubated biotinylated-HUVEC (SA-b-HUVEC) spreading was measured using phase contrast microscopy. Cell retention and adhesion was determined using phase contrast microscopy under laminar flow. All surfaces lacking protein pre-treatment, regardless of surface type, showed the lowest degree of cell spreading and retention. Dual ligand treated Mylar films showed significantly greater SA-b-HUVEC spreading up to 2 h, but were similar to HUVEC on FN treated Mylar at longer times; whereas SA-b-HUVEC spreading on dual ligand treated Teflon-AF was never significantly different from HUVEC on FN treated Teflon-AF at any time point. SA-b-HUVEC retention was significantly greater on dual ligand treated Mylar compared to HUVEC on FN treated Mylar over the entire range of shear stresses tested (3.54-28.3 dynes/cm(2)); whereas SA-b-HUVEC retention to dual ligand and HUVEC retention to FN treated Teflon-AF gave similar results at each shear stress, with only the mid-range of stresses showing significant difference in cell retention to Teflon-AF.

Surface engineering of electrospun polyethylene terephthalate (PET) nanofibers towards development of a new material for blood vessel engineering

Non-woven polyethylene terephthalate nanofiber mats (PET NFM) were prepared by electrospinning technology and were surface modified to mimic the fibrous proteins in native extracellular matrix towards constructing a biocompatible surface for endothelial cells (ECs). The electrospun PET NFM was first treated in formaldehyde to yield hydroxyl groups on the surface, followed by the grafting polymerization of methacrylic acid (MAA) initiated by Ce(IV). Finally, the PMAA-grafted PET NFM was grafted with gelatin using water-soluble carbodiimide as coupling agent. Plane PET film was also surface modified and characterized for basic understanding of the surface modification process. The grafting of PMAA and gelatin on PET surface was confirmed by XPS spectroscopy and quantitatively analyzed by colorimetric methods. ECs were cultured on the original and gelatin-modified PET NFM and the cell morphology, proliferation and viability were studied. Three characteristic surface makers expressed by ECs were studied using immuno-florescent microscopy. The gelatin grafting method can obviously improve the spreading and proliferation of the ECs on the PET NFM, and moreover, can preserve the EC's phenotype.

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

An essential aspect of the treatment of patients with cardiovascular disease is the use of anticoagulant and antiplatelet agents for the prevention of further ischaemic events and vascular death resulting from thrombosis. Aspirin and heparin have been the standard therapy for the management of such conditions to date. Recently, numerous more potent platelet inhibitors together with anticoagulant agents have been developed and tested in randomized clinical trials. This article reviews the current state of the art of antiplatelet and anticoagulant therapy in light of its potential clinical efficacy. It then focuses on the usages of these agents in order to improve the performance of clinical devices such as balloon catheters, coronary stents, and femoropopliteal bypass grafting and extra corporeal circuits for cardiopulmonary bypass. The article then goes on to look at the usage of these agents more specifically heparin, heparan, hirudin, and coumarin in the development of more biocompatible scaffolds for tissue engineering.

In vitro study of cell-promoting multiple-armed peptides

The purpose of this study was to compare the effectiveness of several linear and branch cell-binding peptides to promote cell growth in prosthetic vascular grafts. In this in vitro study, the peptides were covalently immobilized onto expanded polytetrafluoroethylene (ePTFE) vascular grafts. Cell-growth properties were studied using primary human umbilical vein endothelial cells (HUVECs) and primary human umbilical artery smooth muscle cells (HUASMCs). Linear peptides (P15 and P15') and multiple-armed peptides (MAP4-I and MAP4-II) were covalently bonded onto ePTFE grafts by an atmospheric plasma coating method. X-ray photoelectron spectroscopy and amino acid analysis were used to analyze the surface characteristics of the peptide-coated samples. Cell adhesion, proliferation, and morphology were evaluated by culturing HUVECs and HUASMCs onto the surfaces of different samples: ePTFE control, chemically activated ePTFE, P15-coated ePTFE, and MAP4-coated ePTFE. The cell culture experiments were repeated several times to obtain statistically reliable cell-growth data. Cell-growth data were statistically analyzed by the two-way statistical analysis of variance. The study showed that multiple-armed MAP4 peptides were significantly more effective in promoting endothelial cells than the structurally similar linear P15 peptides. There were 800% more HUVECs proliferated on the MAP4-coated ePTFE samples compared with the ePTFE control. MAP4 peptides were 80% more effective for promoting HUVECs than P15 peptides. In contrast, MAP4 peptides were significantly less effective for promoting HUASMCs than HUVECs. There were only about 100% more HUASMCs proliferated on the MAP4-coated ePTFE samples compared with the ePTFE control. MAP4 and P15 peptides had similar cell-promoting characteristics for SMCs.