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PubMed2006

Cell mimetic lateral stabilization of outer cell mimetic bilayer on polymer surfaces by peptide bonding and their blood compatibility.

The biological lipid bilayer membranes are stabilized laterally with the help of integral proteins. We have simulated this with an optimized ternary phospholipid/glycolipid/cholesterol system, and stabilized laterally on functionalized poly methyl methacrylate (PMMA) surfaces, using albumin, heparin, and polyethylene glycol as anchors. We have earlier demonstrated the differences due to orientation and packing of the ternary phospholipid monolayers in relation to blood compatibility (Kaladhar and Sharma, Langmuir 2004;20:11115-11122). The structure of albumin is changed here to expose its interior hydrophobic core by treating with organic solvent. The interaction between the hydrophobic core of the albumin molecule and the hydrophobic core of the lipid molecules is confirmed by incorporating the molecule into bilayer membranes. The secondary structure of the membrane incorporated albumin is studied by CD spectral analysis. The structure of the altered albumin molecule contains more beta-sheet as compared to the native albumin. This conformation is also retained in membranes. The partitioning of the different anchors based on its polarity and ionic interactions in the monolayer is studied from the pressure-area (pi-A) isotherm of the lipid monolayers at the air/water interface using Langmuir-Blodgett (LB) trough facility. Such two monolayers are deposited onto the functionalized PMMA surface using LB trough and crosslinked by carbodiimide chemistry. The structure of the deposited bilayer is studied by depth analysis using contact mode AFM in dry conditions. The stabilized bilayer shows stability up to 1 month by contact angle studies. Preliminary blood compatibility studies reveal that the calcification, protein adsorption, as well as blood-cell adhesion is significantly reduced after the surface modification. The reduced adsorption of ions, proteins, and cells to the modified surfaces may be due to the fluidity of the microenvironment along with the contribution of the mobile PEG groups at the surface and the phosphorylcholine groups of the phospholipids. The stability of the anchored bilayer under low shear stress conditions promises that the laterally stabilized supported bilayer system can be used for low shear applications like small diameter vascular graft and modification of biosensors, and so forth.

Animals↗

PubMed2005

Photochemically patterned poly(methyl methacrylate) surfaces used in the fabrication of microanalytical devices.

We report here the photochemical surface modification of poly(methyl methacrylate), PMMA, microfluidic devices by UV light to yield pendant carboxylic acid surface moieties. Patterns of carboxylic acid sites can be formed from the micrometer to millimeter scale by exposure of PMMA through a contact mask, and the chemical patterns allow for further functionalization of PMMA microdevice surfaces to yield arrays or other structured architectures. Demonstrated here is the relationship between UV exposure time and PMMA surface wettability, topography, surface functional group density, and electroosmotic flow (EOF) of aqueous buffer solutions in microchannels made of PMMA. It is found that the water contact angle on PMMA surfaces decreases from 70 degrees to 24 degrees after exposure to UV light as the result of the formation of carboxylic acid sites. However, upon rinsing with 2-propanol, the water contact angle increases to approximately 80 degrees , and this increase is attributed to changes in surface roughness resulting from removal of low molecular weight PMMA formed from scission events. In addition, the surface roughness and surface coverage of carboxylic acid groups exhibit a characteristic trend with UV exposure time. Electroosmotic flow (EOF) in PMMA microchannels increases upon UV modification and is pH dependent. The possible photolysis mechanism for formation of carboxylic acid groups on PMMA surfaces under the conditions outlined in this work is discussed.

Carboxylic Acids↗

PubMed2003

Engineering integrin-specific surfaces with a triple-helical collagen-mimetic peptide.

Integrin-mediated cell adhesion to extracellular matrix proteins anchors cells and triggers signals that direct cell function. The integrin alpha(2)beta(1) recognizes the glycine-phenylalanine-hydroxyproline-glycine-glutamate-arginine (GFOGER) motif in residues 502-507 of the alpha(1)(I) chain of type I collagen. Integrin recognition is entirely dependent on the triple-helical conformation of the ligand similar to that of native collagen. This study focuses on engineering alpha(2)beta(1)-specific bioadhesive surfaces by immobilizing a triple-helical collagen-mimetic peptide incorporating the GFOGER binding sequence onto model nonadhesive substrates. Circular dichroism spectroscopy verified that this peptide adopts a stable triple-helical conformation in solution. Passively adsorbed GFOGER-peptide exhibited dose-dependent HT1080 cell adhesion and spreading comparable to that observed on type I collagen. Subsequent antibody blocking conditions verified the involvement of integrin alpha(2)beta(1) in these adhesion events. Focal adhesion formation was observed by immunofluorescent staining for alpha(2)beta(1) and vinculin on MC3T3-E1 cells. Model functionalized surfaces then were engineered using three complementary peptide-tethering schemes. These peptide-functionalized substrates supported alpha(2)beta(1)-mediated cell adhesion and focal adhesion assembly. Our results suggest that this peptide is active in an immobilized conformation and may be applied as a surface modification agent to promote alpha(2)beta(1)-specific cell adhesion. Engineering surfaces that specifically target certain integrin-ligand interactions and signaling cascades provides a biomolecular strategy for optimizing cellular responses in biomaterials and tissue engineering applications.

3T3 Cells↗

PubMed2006

Patterned cell adhesion by self-assembled structures for use with a CMOS cell-based biosensor.

A strategy for patterned cell adhesion based on chemical surface modification is presented. To confine cell adhesion to specific locations, an engineered surface for high-contrast protein adsorption and, hence, cell attachment has been developed. Surface functionalization is based on selective molecular-assembly patterning (SMAP). An amine-terminated self-assembled monolayer is used to define areas of cell adhesion. A protein-repellent grafted copolymer, poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), is used to render the surrounding silicon dioxide resistant to protein adsorption. X-ray photoelectron spectroscopy, scanning ellipsometry and fluorescence microscopy techniques were used to monitor the individual steps of the patterning process. Successful guided growth using these layers is demonstrated with primary neonatal rat cardiomyocytes, up to 4 days in vitro, and with the HL-1 cardiomyocyte cell line, up to 7 days in vitro. The advantage of the presented method is that high-resolution engineered surfaces can be realized using a simple, cost-effective, dip-and-rinse process. The technique has been developed for application on a CMOS cell-based biosensor, which comprises an array of microelectrodes to extracellularly record electrical activity from cardiomyocytes.

Animals↗

PubMed2005

Improvement of in vitro titanium bioactivity by three different surface treatments.

OBJECTIVE: Dental implants are usually made from commercially pure titanium or titanium alloys. The aim of this investigation was to determine the influence of surface treatments of commercially pure titanium samples on in vitro bioactivity. METHODS: Commercially pure (cp) titanium (Ti) sheets were submitted to three different surface treatments, including, for all samples, etching with an HCl/H(2)SO(4) solution. Part of each etched sample was further submitted either to anodic oxidation by using an H(3)PO(4) solution or to thermal oxidation. Treated and non-treated samples were analyzed by using scanning electron microscopy (SEM), profilometry and photoelectron X-ray spectroscopy (XPS). The in vitro assessment was carried out through the immersion of samples in simulated body fluid (SBF). In vitro testing was carried out by SEM and by the determination of calcium (Ca) content in solution by atomic absorption spectrometry (AAS). The non-treated titanium samples were used as the control group. RESULTS: This study has shown that, after up to 7-day exposure, a calcium phosphate layer precipitated only on samples submitted to at least one of the three treatments used. This result, based on SEM images, is in good agreement with Ca content and XPS analysis, in which remarkable effects of surface modifications on Ti samples are highlighted. SIGNIFICANCE: These results suggest that suitable surface treatments, such as employed here, may improve in vitro titanium bioactivity in a SBF solution at 37 degrees C. This behavior suggests a possibility of a further favorable in vivo response.

Acid Etching, Dental↗

PubMed2001

Development of new urea-functionalized silica stationary phases. Characterization and chromatographic performance.

New urea-functionalized silica stationary phases were prepared by a single-step surface modification through reaction of LiChrosorb Si100 (5 microm particle size) with a homologous series of alkoxysilanes, synthesized in our laboratory, with the general formula (CH3CH2O)3Si(CH2)3NHC(O)NH(CH2)nCH3, where n=4, 6 and 11. The modified silicas were characterized by elemental analysis of carbon and nitrogen, solid-state 29Si- and 13C-cross polarization magic angle spinning nuclear magnetic resonance and nitrogen adsorption isotherms at 77 K. Chromatographic evaluation of the three urea-functionalized silicas in 150x3.9 mm I.D. HPLC columns was carried out by the separation of a test mixture composed of uracil, acetophenone, benzene, toluene and naphthalene, using acetonitrile-water as mobile phase. These new stationary phases, with embedded polar urea groups, are very promising when compared with amide phases prepared by the conventional two-step modification process. A single-step reaction process silica modification is better for obtaining a well-characterized and homogeneous modified surface.

Chromatography, High Pressure Liquid↗

PubMed1999

A novel textured surface for blood-contact.

Blood-contacting surface modifications aimed at reduction of thromboembolic complications have included the texturing of surfaces so as to promote the formation of a stable pseudo-neointima. A technique has been developed whereby a textured surface consisting of regularly spaced micro-fibres was produced on a smooth base plane. Polyurethane vascular patches with and without the textured luminal surface were fabricated and implanted bilaterally in ovine carotid arteries for 1- and 3-week implantation periods (n = 6 per period). One of 6 arteries with textured patches in the 1-week group was occluded. All other arteries were patent. At 1 week, all patent textured patches had adherent thrombus covering the entire patch surface. By 3 weeks, the thrombus had organised to form a stable pseudo-neointima. Non-textured patches at 1 week had only partial surface coverage of thrombus. At 3 weeks, 4 of 6 non-textured patches had significant red thrombus in the lumen. At 3 weeks, there was also evidence of cellular migration from artery onto both textured and non-textured patches. These findings suggest that the major role of the textured surface was as a promoter of a stabilised thrombus base onto which subsequent cellular migration and tissue healing occurred more rapidly than onto a smooth polyurethane surface.

Animals↗

PubMed2004

Scanning tunneling microscopy of self-assembled phenylene ethynylene oligomers on Au(111) substrates.

In this paper, we report the self-assembly, electrical characterization, and surface modification of dithiolated phenylene-ethynylene oligomer monolayers on a Au(111) surface. The self-assembly was accomplished by thiol bonding the molecules from solution to a Au(111) surface. We have confirmed the formation of self-assembled monolayers by scanning tunneling microscopy (STM) and optical ellipsometry, and have studied the kinetics of film growth. We suggest that self-assembled phenylene ethynylene oligomers on Au(111) surfaces grow as thiols rather than as thiolates. Using low-temperature STM, we collected local current-voltage spectra showing negative differential resistance at 6 K.

Journal Article↗

PubMed2004

Polymeric scaffolds for bone tissue engineering.

Bone tissue engineering is a rapidly developing area. Engineering bone typically uses an artificial extracellular matrix (scaffold), osteoblasts or cells that can become osteoblasts, and regulating factors that promote cell attachment, differentiation, and mineralized bone formation. Among them, highly porous scaffolds play a critical role in cell seeding, proliferation, and new 3D-tissue formation. A variety of biodegradable polymer materials and scaffolding fabrication techniques for bone tissue engineering have been investigated over the past decade. This article reviews the polymer materials, scaffold design, and fabrication methods for bone tissue engineering. Advantages and limitations of these materials and methods are analyzed. Various architectural parameters of scaffolds important for bone tissue engineering (e.g. porosity, pore size, interconnectivity, and pore-wall microstructures) are discussed. Surface modification of scaffolds is also discussed based on the significant effect of surface chemistry on cells adhesion and function.

Animals↗

PubMed2006

Removal kinetics and mechanism for crystal violet uptake by surfactant-modified alumina.

Sodium dodecyl sulfate (SDS), an anionic surfactant (AS) was used for the surface modification of neutral alumina. Micelle-like structures are formed on the surface of alumina, which was used for the removal of crystal violet (CV), a well-known cationic dye from aquatic environment. This process is called adsolubilization. The surfactant-modified alumina (SMA) was found to be very efficient showing >99% CV removal from a 200 ppm CV bearing solution with only 6 g/L of adsorbent dose. The kinetic studies showed that 60 minutes' shaking time was sufficient to achieve the equilibrium. The reaction kinetics data were analysed using four reaction kinetic models, viz., first-order reaction model, pseudo-first-order reaction model, second-order reaction model and pseudo-second-order reaction model, and it was found that the removal of CV followed the pseudo-second order reaction model. It was found that neither film diffusion nor pore diffusion was rate limiting for this process. Isotherm studies showed that Langmuir isotherm fitted more accurately compared to Freundlich isotherm. To test whether the removal of CV was possible from real water using SMA, the experiments were conducted using CV spiked distilled water and synthetic wastewater. It was interesting to note that the removal efficiency was better for wastewater as compared to that of distilled water.

Adsorption↗

PubMed2001

Development of novel dye-doped silica nanoparticles for biomarker application.

We report the development of novel luminescent nanoparticles composed of inorganic luminescent dye, Tris(2,2'-bipyridyl) dichlororuthenium (II) hexahydrate, doped inside a silica network. These dye doped silica (DDS) nanoparticles have been synthesized using a water-in-oil microemulsion technique in which controlled hydrolysis of the tetraethyl orthosilicate leads to the formation of monodispersed nanoparticles. They are prepared with a variety of sizes: small (5+/-1 nm), medium (63+/-4 nm), and large (400+/-10 nm), which shows the efficiency of the microemulsion technique for the synthesis of uniform nanoparticles. All these nanoparticles are suitable for biomarker application since they are much smaller than cellular dimension. These nanoparticles are highly photostable in comparison to most commonly used organic dyes. These nanoparticles have been characterized by various microscopic and spectroscopic techniques. The amount of dye content in these nanoparticles has been optimized to eliminate self-quenching. It has been observed that maximum luminescence intensity is achieved when the dye content is around 20 wt%. Silica surface of DDS nanoparticles is available for surface modification and bioconjunction. For demonstration as a biomarker, the DDS nanoparticle's surface has been biochemically modified to attach membrane-anchoring groups and applied successfully to stain human leukemia cells.

2,2'-Dipyridyl↗

PubMed1993

Enhanced attachment and growth of human endothelial cells derived from umbilical veins on ammonia plasma modified surfaces of PTFE and ePTFE synthetic vascular graft biomaterials.

Ammonia plasma generated by electrical discharge at low pressure was employed for the surface modification of PTFE and ePTFE. A new chemistry at the plasma treated surfaces is reported. X-ray photoelectron spectroscopy studies showed the incorporation of C-N, C-O, C = O etc functional groups on the plasma treated surfaces. Human endothelial cells derived from umbilical veins (HUEC) were used to seed the plasma treated PTFE and ePTFE surfaces to assess the attachment and growth. Enhanced attachment and growth of HUEC was observed on the plasma treated surfaces. In addition, the performance of these surfaces in this respect was found to be considerably superior to human collagen or human fibronectin or collagen-fibronectin coated PTFE. HUEC attachment and growth on these plasma treated surfaces was further enhanced by immobilizing collagen or fibronectin or collagen-fibronectin. Ammonia plasma treated and untreated ePTFE vascular graft samples were seeded with 3.6 X 10(4) cells/sample. At 24 hrs after seeding, HUEC cell attachment was studied. Although, HUEC attachment on collagen or fibronectin coated ePTFE was improved, but there was no significant difference between the number of cells attached to these surfaces when compared with those adhered to plasma treated ePTFE without collagen or fibronectin coating. Collagen or fibronectin coated plasma treated surfaces showed better performance over their respective controls.

Ammonia↗

PubMedDate not supplied

Generic bioaffinity silicone surfaces.

Synthetic polymer surfaces require surface modification to improve biocompatibility. A generic route to biocompatible silicone elastomers is described involving high yield surface functionalization of standard silicones with hydrosilanes, hydrosilylation using asymmetric, allyl-, NSC-terminated PEO of narrow molecular weight, and covalent modification in one step with amine-containing biological molecules including oligopeptides (YIGSR, RGDS), proteins (EGF, albumin, fibrinogen, mucin), and glycosaminoglycans (heparin). Efficient, high-density binding (e.g., 0.2 EGF molecules/nm2) was demonstrated using radiolabeling studies. The resulting surfaces were demonstrated to be biocompatible by further reaction with biomolecules, for example, thrombosis suppression on surfaces modified by heparin + ATIII, and the formation of confluent corneal epithelial cell layers on EGF, RGDS, or YIGSR surfaces.

Biocompatible Materials↗

PubMed1999

Effect of Charge and Hydrophobicity on Adsorption of Modified Starches on Polyester.

Polyester fabric (poly(ethylene terephthalate)) is a hydrophobic polymer. Its hydrophobic nature can be a disadvantage for certain applications like dyeing, finishing, detergency, etc. Physical or chemical modification of the polyester to make it more hydrophilic is therefore desirable for certain performance characteristics. Surface modification of polyester to make it hydrophilic can be achieved by adsorbing polymers on the polyester surface. Starch is a commonly available, hydrophilic polymer used in many textile applications that can be used to modify polyester. However, it needs to be chemically modified so that it can adsorb on the polyester fabric and physically modify the fabric characteristics. The polymers used in this study are two different modified starches-cationic and anionic starches and mixtures of the two. The adsorption kinetics on a polyester substrate was studied. The effect of charge and hydrophobicity on adsorption was investigated. Cationic starches were shown to readily adsorb on polyester and this was attributed to electrostatic interactions. Hydrophobic substituents on the cationic moiety resulted in increased adsorption. This was attributed to the weak hydrophobic interaction between the polymer chains which could result in a more coiled polymer conformation. It is hypothesized that more starch molecules are required for surface coverage of the polyester, resulting in an increase in adsorption. Anionic starch was adsorbed on the substrate but at a slower rate than the cationic starches. It is likely that there is a H bonding between acid groups on the starch and the ester groups of the polyester. However, the anionic starch is desorbed when the polyester is placed in an aqueous medium. When a blend of cationic starch and anionic starch was used, a low concentration of anionic starch was seen to increase adsorption, indicating that the polyelectrolyte complex itself may be adsorbing on the substrate. Further increases cause a decrease in adsorption as no sites may be available on the complex for adsorption. When hydrophobic substituents are present, addition of the anionic starch causes a decrease in adsorption at all concentrations. This was attributed to the "crosslinking" between the hydrophobically modified starch and the anionic polymer. Copyright 1999 Academic Press.

Journal Article↗

PubMed1995

Prevention of biofilm formation by polymer modification.

Bacterial biofilm formation on synthetic polymers plays an important role in industry and in modern medicine, leading, for example, to difficult-to-treat infections caused by colonized foreign bodies. Prevention of biofilm formation is a necessary step in the successful prophylaxis of such infections. One approach is to inhibit bacterial adherence by polymer surface modification. We have investigated polymer modification by glow discharge treatment in order to study the influence of the modified surface on bacterial adherence. Surface roughness, surface charge density and contact angles of the modified polymers were determined and related to the adherence of Staphylococcus epidermidis KH6. Although no influence of surface roughness and charge density on bacterial adherence was noticed, a correlation between the free enthalpy of adhesion (estimated from contact angle measurements) and adherence was observed. There seems to exist a certain minimum bacterial adherence, independent of the nature of the polymer surface. Modified polymers with negative surface charge allow for bacterial adherence close to the adherence minimum. These polymers could be improved further by the ionic bonding of silver ions to the surface. Such antimicrobial polymers are able to prevent bacterial colonization, which is a prerequisite for biofilm formation. It is suggested that modification of polymers and subsequent surface coupling of antimicrobials might be an effective approach for the prevention of bacterial biofilm formation.

Anti-Infective Agents, Local↗

PubMed1998

Effect of surface modifiers on the electrode reactions and conformation of cytochrome c3 adsorbed on a silver electrode.

Surface-enhanced resonance Raman scattering and electroreflectance voltammetry were used to investigate the effect of electrode surface modification on the structure and redox properties of cytochrome c3 immobilized on Ag surfaces. It is shown that the redox reactions of cytochrome c3 are more reversible at an 11-mercaptoundecanoic acid modified Ag electrode as compared to a bare metal surface. The heme of cytochrome c3 is in a mixed low and high spin state when adsorbed at the bare electrode, whereas only the low spin form is present on the 11-mercaptoundecanoic acid modified electrode, suggesting that the native conformation is maintained in the latter case. The reduction potential is close to that of the most positive macroscopic potential as determined by electroreflectance spectroscopy. In contrast, the reduction potential as determined by SERRS undergoes a large positive shift in the presence of 4,4'-bipyridine, the magnitude of which is dependent upon the concentration of 4,4'-bipyridine. These results indicate that the effect of the cytochrome c3 interaction with the 4,4'-bipyridine-modified surface is significantly different as compared to its interaction with the 11-mercaptoundecaodoic acid modified surface. Moreover, the results emphasize that electrode modifiers can have dramatically different effects on the redox properties of different proteins. It is well known that 4,4'-bipyridine acts as a redox promoter in the case of cytochrome c, whereas no electrochemical or electroreflectance response was observed in the case of cytochrome c3.

Adsorption↗

PubMed2003

Biocompatibility and hemocompatibility of surface-modified NiTi alloys.

Nickel titanium (NiTi) shape memory alloys have been investigated for several years with regard to biomedical applications. However, little is known about the influences of surface modifications on the biocompatibility of these alloys. The effects of a range of surface treatments were investigated. Cytotoxicity and cytocompatibility studies with both fibroblast and endothelial cells showed no differences in the biocompatibility of any of the NiTi surfaces. The cytotoxicity and cytocompatibility of all surfaces were favorable compared to the controls. The hemolysis caused by a range of NiTi surfaces was no different from that caused by polished 316L stainless steel or polished titanium surfaces. The spreading of platelets has been linked to the thrombogenicity of materials. Platelet studies here showed a significant increase in thrombogenicity on polished NiTi surfaces compared to 316L stainless steel and pure titanium surfaces. Heat treatment of NiTi was found to significantly reduce thrombogenicity, to the level of the control. The XPS results showed a significant decrease in the concentration of surface nickel with heat treatment and changes in the surface nickel itself from a metallic to an oxide state. This correlates with the observed reduction in thrombogenicity.

3T3 Cells↗

PubMed2006

Modified aminosilane substrates to evaluate osteoblast attachment, growth, and gene expression in vitro.

Bone cell-substrate interactions are important to understand in the design, selection, and surface modification of bone implants. To gain insight into such interactions, substrates designed with surface species approximating the physiological environment of bone matrix were studied. Osteoblasts (Ob) grown on three such surfaces were used to evaluate cell-substrate effects on attachment, growth, and gene expression as compared with controls. Initial surface preparation consisted of coating glass slides with aminopropyltriethoxy silane (APTES), after which the coated slides were modified with collagen-rich extracellular matrix components obtained from normally mineralizing avian tendon: the tripeptide arginine-glycine-aspartic acid (arg-gly-asp), or a precipitate formed from a metastable solution containing inorganic ions normally found in blood (simulated body fluid). Each of the modified substrates, as well as the nonmodified (APTES) control, provided distinctly different physical (evidenced by differences in rms roughness) and chemical surfaces for seeding primary osteoblasts obtained from 14-day-old normal embryonic chickens. Cell responses to each of the substrates were evaluated over a 21-day period in terms of Ob growth and growth rate, alkaline phosphatase (ALP) activity, and gene expression of type I collagen (COL I), osteopontin (OPN), osteocalcin (OC), and bone sialoprotein (BSP). From these preliminary experiments, indications are that cell attachment and growth in this study possibly are independent processes, an assumption that compels the need for further studies. Collagen-rich matrix-modified substrates had a distinct advantage over others when cell growth rate, ALP activity, and gene expression were considered; cells on these substrates exhibited increased ALP activity and enhanced expression of BSP, OPN, and OC when compared with those of cells on APTES controls or other modified substrates. These results indicate that matrix-modified substrates such as those used in this study provide favorable templates for tissue generation, suggesting their potential in the design of surfaces for bone implants.

Alkaline Phosphatase↗