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PubMed1995

Phospholipid/alkanethiol bilayers for cell-surface receptor studies by surface plasmon resonance.

Supported hybrid bilayer membranes (HBM) composed of a monolayer of phospholipid and a monolayer of alkanethiol associated with a thin gold film on glass are useful as model lipid bilayer membranes for studying membrane receptor-ligand and cell-cell binding events by surface plasmon resonance (SPR). Measurements of specific binding of proteins and lipid vesicles to well-defined HBMs have been performed under conditions of continuous flow using a commercial SPR instrument (BIAcore). HBMs are shown to be stable in flow and to block nonspecific adsorption of proteins to the alkanethiol/gold surface. The use of such supported lipid bilayers in flow provides a means of conducting equilibrium and kinetic studies of models of ligand-cell and cell-cell interactions with receptors or ligands in a membrane environment. Compared to the extended dextran polymer layer that is currently used for surface modification of BIAcore "sensor chips," the described HBMs provide a well-defined surface that will permit less ambiguous modeling of these important biological interactions.

Biosensing Techniques↗

PubMed2006

Phenylaminopropyl silica monolithic column for pressure assisted capillary electrochromatography.

A novel stationary phase phenylaminopropyl silica (PhA-silica) monolith was successfully prepared for pressure assisted capillary electrochromatography (pCEC). The monolithic silica matrix from a sol-gel process was chemically modified by using [3-(phenylamino)propyl]trimethoxysilane as surface modification reagent to produce the phenylaminoporpyl function. The secondary amino groups on the surface of the monolithic stationary phase contributed to the generation of anodic electroosmotic flow (EOF) under acidic conditions. The phenyl group together with the spacer (-(CH(2))(3)-) in PhA-silica provides sufficient hydrophobic properties. To evaluate the column performance, effects of buffer pH and mobile phase composition on the mobile phase linear velocity and the retention factors of alkylbenzenes, phenols and anilines were investigated in pCEC mode. The monolithic stationary phases exhibit typical reversed-phase (RP) electrochromatographic behavior toward neutral solutes. Hydrophobic as well as electrophoretic migration process within the monoliths was observed for the separation of basic solutes such as anilines without peak tailing.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed1999

An investigation of the variables which may affect the bond between plastic teeth and denture base resin.

OBJECTIVES: The failure of the bond between acrylic resin denture base material and resin teeth remains a significant problem. This study evaluated the tensile bond strength of specimens produced by commonly employed tooth preparation and processing methods as used in dental laboratories. METHODS: Twenty-two experimental groups, each consisting of 36 specimens, were investigated by subjecting the tooth-resin bond to tensile loading. The groups were allocated to one of five experimental sets to investigate: (a) effect of resin dough time, (b) effect of tooth surface condition, (c) effect of processing variables, (d) effect of monomer cementing, and (e) effect of acrylic resin cement. The results were analysed statistically using a one factor ANOVA and a Student t test. RESULTS: A significantly stronger bond was obtained when the resin was packed late in the dough stage, and a superior bond, in all cases, when high-impact resin was used. Tooth surface modification by grinding or grooving made no significant difference when compared with unmodified surfaces. Wax-contaminated surfaces produced highly significant weaker bonds. Time of introduction and duration of water-bath processing had no significant effect on bond strength. Monomer cementing of the tooth surface, especially with high-impact monomer. significantly improved the bond strength. The application of resin cements was found to produce the most significant increase in denture tooth bond strength. CONCLUSIONS: The important steps in obtaining a consistently high value denture tooth bond are thorough dewaxing of the tooth surface followed by the application of a suitable resin cement.

Acrylic Resins↗

PubMed1997

Wear analysis of a retrieved hip implant with titanium nitride coating.

There is increasing interest in using surface modification technology to improve the wear properties of titanium alloy and limit articular surface wear of metal and polyethylene components. This report details the in vivo wear performance of titanium nitride coating on a retrieved hip implant obtained postmortem from a low demand patient 1 year after total hip arthroplasty. Analysis of the well-functioning implant revealed that wear debris can originate from a titanium nitride coated femoral head, as delaminated surface asperities, and manifest as adhesive wear on the articular surface. The wear observed on this implant indicates that rigorous testing and evaluation of titanium nitride coating technology should be conducted prior to widespread use on total joint implants.

Acetabulum↗

PubMedDate not supplied

Amine-reactive biodegradable diblock copolymers.

A new class of diblock copolymers was synthesized from biodegradable poly(lactic acid) and poly(ethylene glycol)minus signmonoamine. These polymers were activated by covalently attaching linkers such as disuccinimidyl tartrate or disuccinimidyl succinate to the hydrophilic polymer chain. The polymers were characterized by (1)H NMR spectroscopy, (13)C NMR spectroscopy and gel permeation chromatography (GPC). These investigations indicated that the polymers were obtained with the correct composition, in high purities, and the expected molecular weight. By using dyes containing primary amine groups such as 5-aminoeosin as model substrates, it was possible to show that the polymers are able to bind such compounds covalently. The diblock copolymers were developed to suppress unspecific protein adsorption and allow the binding of bioactive molecules by instant surface modification. The polymers are intended to be used for tissue engineering applications where surface immobilized cell adhesion peptides or growth factors are needed to control cell behavior.

Amines↗

PubMed2004

Polymer grafting via ATRP initiated from macroinitiator synthesized on surface.

Macromolecular anchoring layer approach was used for preparation of an effective macroinitiator for the synthesis of grafted polymer layers by atom transfer radical polymerization (ATRP) initiated from the surface. For the initial surface modification, a thin layer of poly(glycidyl methacrylate) (PGMA) was deposited on the surface of a silicon wafer. The ATRP macroinitiator was synthesized on the substrate surface by the reaction between epoxy groups of PGMA and carboxy functionality of bromoacetic acid (BAA). Variation of the time and temperature of the BAA deposition as well as PGMA layer thickness allowed control over the amount of BAA attached to the surface. The PGMA anchoring layer allowed the achievement of initiator surface density significantly higher than that reported for a self-assembled monolayer of ATRP initiators. Polymer brushes were synthesized on the PGMA/BAA-modified substrates by ATRP. Different surface concentrations of BAA were used in our grafting experiments to acquire knowledge about the relationship between the amount of initiator anchored to the surface through PGMA and the rate of the grafted layer formation. The increase in the surface density of the initiating moieties led to the increase in the grafting rate. However, a cutoff initiator concentration beyond which no increase of the thickness of the grafted layer was observed. From comparison between the surface densities of the initiator and the attached polymer it was determined that the efficiency of the initiation from the surface was on the level of 5-15%.

Journal Article↗

PubMed2005

Biomaterials functionalization using a novel peptide that selectively binds to a conducting polymer.

The goal in biomaterial surface modification is to retain a material's bulk properties while modifying only its surface to possess desired recognition and specificity. Here we develop a unique strategy for surface functionalization of an electrically conductive polymer, chlorine-doped polypyrrole (PPyCl), which has been widely researched for various electronic and biomedical applications. An M13 bacteriophage library was used to screen 10(9) different 12-mer peptide inserts against PPyCl. A binding phage (phiT59) was isolated, and its binding stability and specificity to PPyCl was assessed using fluorescence microscopy and titer count analysis. The relative binding strength and mechanism of the corresponding 12-mer peptide and its variants was studied using atomic force microscopy and fluorescamine assays. Further, the T59 peptide was joined to a cell adhesive sequence and used to promote cell attachment on PPyCl. This strategy can be extended to immobilize a variety of molecules to PPyCl for numerous applications. In addition, phage display can be applied to other polymers to develop bioactive materials without altering their bulk properties.

Adsorption↗

PubMed1996

Design of nonthrombogenic polymer surfaces for blood-contacting medical devices.

Although significant progress has been made in the design of blood-compatible polymers in the past decades, there is no ideal polymer surface which is comparable with a natural endothelial surface in preventing surface-induced thrombosis and maintaining hemostasis. This is due to the complex pattern of protein and cellular interactions with foreign surfaces, which still demands defining a proven hypothesis to develop non-thrombogenic surfaces. Synthesis of new polymers with optimal mechanical properties and the in vitro and in vivo characterization of these surfaces will require many more years of work. In this article, the surface modification of existing medical polymers for the improvement of blood compatibility is introduced. Surface immobilizing of heparin onto polyurethane, coatings of a polyurethane-poly(ethylene oxide)-heparin graft copolymer, and a coating of thermosensitive polymers on polyurethane will be discussed. All modified surfaces demonstrated superior blood compatibility both in vitro and in vivo. The biological response of these designed systems in vitro, ex vivo and in vivo should provide state-of-the-art materials for the specific application of controlling thrombosis and solving biocompatibility problems.

Anticoagulants↗

PubMed1999

Modification of Kaolinite Surfaces through Intercalation with Potassium Acetate, II.

The modification of kaolinite hydroxyl surfaces of both ordered and disordered kaolinites has been studied under a range of conditions and intercalating agents. This has been achieved by the study of the kaolinite hydroxyl deformation vibrations by the application of diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy. Kaolinites showed resolved bands at 940 and 915 cm-1 with an additional band at 923 cm-1. The bands at 940 and 923 cm-1 are assigned to the hydroxyl deformation modes of the inner surface hydroxyl groups, and the 915 cm-1 band is assigned to that of the inner hydroxyl group. When the kaolinite is intercalated with potassium acetate additional bands were found at 909 and 897 cm-1 for the ordered kaolinites. An additional band at 877 cm-1 is observed for the disordered kaolinite and is attributed to the hydroxyl deformation mode of non-hydrogen-bonded hydroxyl groups. The bands at 909 and 897 cm-1 range are attributed to inner surface hydroxyl groups hydrogen bonded to water or acetate groups. The intensity of these bands reflects the degree of disorder introduced into the kaolinite through intercalation. The intensities of the kaolinite hydroxyl deformation modes are a function of the starting kaolinite order and the method of preparation. Copyright 1999 Academic Press.

Journal Article↗

PubMed2005

Phospholipid polymer surfaces reduce bacteria and leukocyte adhesion under dynamic flow conditions.

Persistence of infection can occur when the host immune response is compromised because of the presence of a foreign implant. Surface modification of biomaterials with phospholipid polymers may enhance biocompatibility and reduce incidence of infection by impeding bacterial and leukocyte adhesion. A rotating disk model, which generates shear stress from 0 to 18 dynes/cm(2), was used to characterize adhesion of neutrophils, monocytes, and bacteria in phosphate-buffered saline (PBS) or 25% human serum on polyethylene terephthalate surfaces coated with a phospholipid polymer, poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate (BMA)]. The material designated PMB30 contains a methylene chain length, (CH(2))(n), of n = 2, whereas PMHB30 contains a chain length of n = 6. In PBS, bacterial adhesion was shear stress dependent with the lowest bacterial density observed on PMB30. However, the presence of serum proteins eliminated shear stress and surface chemistry effects in addition to bacterial adhesion reduced to <10% of adhesion in PBS. Trends for leukocyte adhesion in serum demonstrated shear dependence with PMB30 exhibiting the lowest cell density throughout the range of shear stresses. In conclusion, modification of the polyethylene terephthalate surfaces with phospholipid polymers resulted in reduced bacterial and leukocyte adhesion. Furthermore, shortening the methylene chain length of the MAPC copolymer most effectively reduced adhesion.

Bacterial Adhesion↗

PubMed2000

Surfactant polymers designed to suppress bacterial (Staphylococcus epidermidis) adhesion on biomaterials.

We describe a series of surfactant polymers designed as surface-modifying agents for the suppression of bacterial adhesion on biomaterials. The surfactant polymers consist of a poly(vinyl amine) backbone with hydrophilic poly(ethylene oxide) (PEO) and hydrophobic hexanal (Hex) side chains (PVAm/PEO:Hex). Surface modification is accomplished by simple dip coating from aqueous solution, from which surfactant polymers undergo spontaneous surface-induced assembly on hydrophobic biomaterials. The stability of PVAm/PEO:Hex on pyrolytic graphite (HOPG) and polyethylene (PE) was demonstrated by the absence of detectable desorption under flow conditions of pure water over a 24-h period. PEO surfactant polymers with four different PEO:Hex ratios (1:1.4, 1:2.5, 1:4.6, and 1:10.7) and a dextran surfactant polymer were compared with respect to S. epidermidis adhesion under dynamic flow conditions. Suppression of S. epidermidis adhesion was achieved for all modified surfaces over the shear range 0-15 dyn/cm(2). The effectiveness depended on the surfactant polymer composition such that S. epidermidis adhesion to modified surfaces decreased significantly with increasing PEO packing density. Modified HOPG was more effective in reducing bacterial adhesion compared with the corresponding modification on PE, which we attribute to the presence of defects in surfactant polymer assembly on PE. Our results are discussed from the perspective of critical factors, such as optimal PEO packing density and hydration thickness, that contribute to the effectiveness of surfactant polymers to shield a biomaterial from adhesive bacterial interactions.

Bacterial Adhesion↗

PubMed2004

Endothelium regeneration on luminal surface of polyurethane vascular scaffold modified with diamine and covalently grafted with gelatin.

Using the recently developed surface modification technique, free amino groups have been introduced onto polyester-type polyurethane (PU) scaffolds. The introduction of these free amino groups increases the surface energy and provides a convenient way to further immobilize bioactive species such as gelatin, collagen or chitosan, etc. on the scaffold surface by employing glutaraldehyde as a coupling agent. These modifications are advantageous to enhance cell-material interaction. The culture of human umbilical vein endothelial cells (HUVECs) in vitro proved that the cell proliferation ratio of both the aminolyzed and the biomacromolecules-immobilized PU membranes was improved greatly comparing with the control PU. Scanning electron microscopy and confocal laser scanning microscopy observations displayed that the gelatin-immobilized PU vascular scaffold had formed a monolayer of endothelial intima on its luminal surface after HUVECs were cultured for 6 d. Therefore, the aminolysis and the following biomacromolecule immobilization is a promising way to enhance the cell-PU interaction that can accelerate the endothelium regeneration, which is crucial for blood vessel tissue engineering.

Biocompatible Materials↗

PubMed1997

A simple, fluorescent method to internally label platelets suitable for physiological measurements.

Current methods for studying platelet survival in vivo are limited by the use of radioisotopes, with their inherent safety and regulatory concerns, systemic drug administrations that produce biochemical modifications of platelet functions, or external labeling techniques, which may produce artifacts due to surface modifications. For these reasons, we sought to develop a simple, nonisotopic method for labeling platelets internally, thereby producing platelets more likely to have in vivo properties equivalent to native cells. Murine platelets in protein-free buffer were fluorescently labeled internally by incubation with 2.5 microM 5-chloromethyl fluorescein diacetate (CMFDA), and without washing, were injected into mice for platelet survival studies. CMFDA-labeled platelets were unactivated, as shown by minimal P-selectin expression. When tested in vitro for function by aggregometry, the response of CMFDA-labeled platelets to collagen and thrombin was identical to that of unlabeled platelets. Flow cytometric analysis demonstrated that CMFDA platelets were an intensely stained, unimodal population that was completely separated from unlabeled platelets. The mean half-life of labeled platelets in the murine circulation was 37.5 +/- 4.5 hr (+/-1 SD), and the mean survival time was 3.1-3.3 days (n = 24), similar to results reported using 51Cr and (111)In. No evidence of in vivo transfer of dye from labeled platelets to unlabeled cells was observed. CMFDA produces a population of platelets that are nonradioactively, internally labeled with a highly fluorescent, stable product. The labeled platelets function equivalently to native platelets, as demonstrated by immunocytometry and aggregometry, and importantly, in vivo, by normal platelet survival.

Animals↗

PubMed1989

Stainless steel mesh supports high density cell growth and production of recombinant müllerian inhibiting substances.

Stainless steel mesh supported the high density growth of anchorage dependent CHO fibroblasts without the use of a special culture system. CHO cells, designated B-9, containing an amplified genomic construct of the human gene for Müllerian Inhibiting Substance (MIS), grew to a high confluent density on stainless steel meshwork while producing substantial amounts of human recombinant MIS over a long period of time. The mesh could be easily coated with various extracellular matrix proteins, such as Laminin, Fibronectin, Collagen or Matrigel, which permitted the testing of the effects of surface modifications on cell yield and recombinant protein production. Since the amount of medium per surface area required for optimal cell growth is lower than for some large volume cell culture methods, media costs can be reduced using mesh. In addition, no special cell culture equipment or complex manipulations are required. Thus, the use of meshwork for anchorage-dependent cells can increase the efficiency of growth and decrease the cost of recombinant protein production.

Animals↗

PubMed2006

Sodium dodecyl sulfate-modified carbon paste electrodes for selective determination of dopamine in the presence of ascorbic acid.

A carbon paste electrode (CPE) modified by a monolayer film of sodium dodecyl sulfate (SDS) was used for detection of dopamine (DA). Cyclic voltammetry demonstrated improved response of the DA sensor. This suggests the effectivity of surface modification of CPE by SDS. Impedance spectroscopy was used for the characterization of CPE surface properties. The effect of SDS concentration on the electrode quality also reveals that SDS formed a monolayer on CPE surface with a high density of negative-charged end directed outside the electrode. As a result, the carbon paste electrode modified with SDS (SDS/CPE) exerted discrimination against ascorbic acid in physiological circumstance. Thus, it can selectively determine dopamine even in the presence of 220-fold AA combined with differential pulse stripping voltammetry. In pH 7.40 phosphate buffer solution, the oxidation peak current on differential pulse voltammograms increases linearly with the concentration of DA in the range of 5.0 x 10(-7) to 8.0 x 10(-4) mol . L(-1) with a detection limit of 5.0 x 10(-8) mol . L(-1). Satisfying results are achieved when detecting the DA in injection and simulated biology sample.

Ascorbic Acid↗

PubMed2004

Poly(ethylene glycol) interfaces: an approach for enhanced performance of microfluidic systems.

Microfluidic systems are extensively used platform for analytical and therapeutic applications. One of the major problems encountered in these systems is the loss of material due to non-specific surface interactions. When biological solutions are flowed through microchannels, they tend to adsorb on the surface due to the negative charge of the surface. This results in a reduced efficiency of the system which can be critical in sensitive biological analysis. Poly(ethylene glycol) (PEG) is known to form non-fouling interfaces on silicon and glass which are common materials used in microfluidic systems. The most common approach for modifying silicon/glass with PEG involves a solution phase protocol. Since the micro/nanofluidic systems have channel sizes ranging from hundreds of microns to submicron with variety of complicated network, this surface modification approach is not sufficient in forming uniform, conformal, and ultrathin films on the surface. Due to the enclosed features in these systems, the properties of liquids such as viscosity and surface tension play an important role in the clogging and eventually biofouling of these microchannels. Hence, we have developed a solvent-free vapor deposition protocol for modifying silicon/glass surfaces with PEG. Various concentrations of protein solutions were flowed through unmodified and PEG-modified glass microcapillaries of different lengths at different flow rates. PEG surfaces formed on silicon have shown 80% reduction in protein adsorption in static conditions.

Boranes↗

PubMed2006

Preparation and evaluation of a hydrolytically stable amide-embedded stationary phase.

We have developed a new hydrolytically stable amide-embedded stationary phase via a simple and effective synthetic method. The preparation of the new phase involves the synthesis of multifunctional silane ligands and the surface modification of porous silica particles via multiple attachments of these ligands to the silica surface. A hydrolytically stable coating was produced as a result of multiple covalent linkages formed between silane ligands and the silica surface, and cross-linking between adjacent ligands. The resulting amide-embedded stationary phase showed excellent hydrolytic stability over a wide pH range. Like other existing amide-embedded columns, this new stationary phase exhibits higher retention for polar compounds and different selectivity as compared to conventional C18 columns. The new phase is compatible with 100% aqueous mobile phases, and also provides high column efficiency and good peak shapes for both acidic and basic compounds.

Amides↗

PubMed2006

Chemical force titrations of antigen- and antibody-modified poly(methylmethacrylate).

Poly(methylmethacrylate) (PMMA) is a versatile polymer that displays desirable properties for development of cheap and disposable microfluidic devices for sensing biomolecular interactions. Atomic force microscopy (AFM) and chemical force titrations were used to determine the efficacy of surface modifications made to accommodate protein-substrate linkage. AFM images show the effects on surface morphology of carboxylated-, amine-, hCG antigen- and anti-hCG antibody-modified PMMA substrates. Confocal microscopy was used to determine the fluorescent intensity of labeled antibody species on the PMMA substrate, confirming the success of surface antigen/antibody immobilization. Surface pK(1/2) value for carboxylic acid and amine species grafted on PMMA were determined. When carboxylic acid or amine-terminated tips were titrated against PMMA samples terminated with the hCG antigen and anti-hCG antibody, peaks appeared in the force titration curve consistent with the pI range of the antigen or antibody species. Strong adhesive forces were present at pH values above 7.0 when the antigen was present on the PMMA substrate, and these were attributed to hydrophobic interactions between the antigen and the alkane "linker" chain attaching the amine or carboxylate group to the AFM tip. Such hydrophobic interactions were not observed with the carboxylic acid or amine/antibody combinations suggesting that the surface-linked antibody was more resistant to denaturation under higher pH. The results demonstrated the feasibility of using AFM approaches for interrogating protein grafting strategies in the fabrication of PMMA-based microsystems.

Antibodies↗