ESCA investigation of low-temperature ammonia plasma-treated polyethylene substrate for immobilization of protein

Effects of chemical composition and the addition of H2 in a N2 atmospheric pressure dielectric barrier discharge on polymer surface functionalization

We examined the effect of hydrogen content in various polymers in a N2/H2 discharge for surface amine functionalization. Three polymers (polyethylene (PE), polyvinylidene fluoride (PVDF), and poly(tetrafluoroethylene) (PTFE)) containing various amounts of hydrogen and fluorine were treated with an atmospheric pressure dielectric barrier discharge (DBD). While surface modification was observed on the PE and the PVDF in a pure N2 discharge, adding H2 in a N2 discharge was necessary to observe the fluorine etching on the surface of the PVDF and PTFE polymers. The presence of a slight amount of hydrogen in the gas mixture was also a prerequisite to the formation of amino groups on the surface of all three polymers (max NH2/C approximately 5%). Aging revealed that the modified polymer surfaces treated in a N2-H2 discharge were less prone to hydrophobic recovery than were surfaces treated in pure N2, due primarily to the presence of a higher density of polar groups on the surfaces. We demonstrated that H atoms in the discharge are necessary for the surface amine functionalization of polymers in a N2 atmospheric pressure DBD, regardless of polymer chemical composition. It is therefore possible to control the plasma functionalization process and to optimize the concentration and specificity of NH2 grafted onto polymer surfaces by varying the H2 concentration in a N2 atmospheric pressure DBD.

Photoactivation of alkyl C-H and silanization: a simple and general route to prepare high-density primary amines on inert polymer surfaces for protein immobilization

Surface modification through implanting functional groups has been demonstrated to be extremely important to biomedical applications. The usage of organic polymer phase is often required to achieve satisfactory results. However, organic surfaces usually have poor chemical reactivity toward other reactants and target biomolecules because these surfaces usually only consist of simple alkyl (C-H) and/or alkyl ether (ROR') structures. For the first time, we here report the potential to perform silanization techniques on alkyl polymer surface, which provide a simple, fast, inexpensive, and general method to decorate versatile functional groups at the molecular level. As an example, high-density primary amines could be obtained on a model polymer, polypropylene substrate, through the reaction between amine-capped silane, 3-aminopropyltriethoxysilane (APTES) and hydroxylated polypropylene surface. A model protein, immunoglobulin (IgG), could be effectively immobilized on the surface after transforming amines to aldehydes by the aldehyde-amine condensation reaction between glutaraldehyde (GA) and amines. The routes we report here could directly make use of the benefits from well-developed silane chemistry, and hereby are capable of grafting any functionalities on inert alkyl surfaces via changing the terminal groups in silanes, which should instantly stimulate the development of many realms such as microarrays, immunoassays, biosensors, filtrations, and microseparation.

Determination of amine and aldehyde surface densities: application to the study of aged plasma treated polyethylene films

The aim of this work was to test and to compare different methods reported in the literature to quantify amine and aldehyde functions on the surface of polyethylene (PE) films treated by ammonia plasma and to specify their stability against time. A low pressure ammonia plasma reactor was used to functionalize PE films with amine groups, which could be subsequently used for further immobilization of biomolecules. In order to determine the density of amine groups on the surface of treated films, various molecule probes and spectrophotometric analytical methods have been investigated. Two methods using (i) sulfosuccinimidyl 6-[3'-(2-pyridyldithio)-propionamido] hexanoate (sulfo-LC-SPDP) and (ii) 2-iminothiolane (ITL) associated with bicinchoninic acid (BCA) have been proved to be reliable and sensitive enough to estimate the surface concentration of primary amine functions. The amount of primary amino groups on the functionalized polyethylene films was found to be between 1.2 and 1.4 molecules/nm2. In a second step, the surface concentration of glutaraldehyde (GA), which is currently used as a spacer arm before immobilization of biomolecules, has been assessed: two methods were used to determine the surface density of available aldehyde functions, after the reaction of GA with the aminated polyethylene film. The concentration of GA was found to be in the same range as primary amine concentration. The influence of aging time on the density of available amino and aldehyde groups on the surfaces were evaluated under different storage conditions. The results showed that 50% of the initial density of primary amine functions remained available after storage during 6 days of the PE samples in PBS (pH 7.6) at 4 degrees C. In the case of aldehyde groups, the same percentage of the initial density (50%) remained active after storage in air at RT over a longer period, i.e., 15 days.

Attachment, growth, and activity of rat osteoblasts on polylactide membranes treated with various low-temperature radiofrequency plasmas

Nonporous and porous membranes from poly(L/DL-lactide) 80/20% were treated with low-temperature oxygen, ammonia, or sulphur dioxide-hydrogen plasmas and the late effects of plasma treatment on physicochemical characteristics of the membranes' surface were analyzed. The plasma treatment resulted in the permanent attachment of sulphur and nitrogen functionalities to the membrane's surface, and increased the surface concentration of oxygen, thereby increasing the surface wettability. To assess whether the plasma treatment affects the cellular response, primary rat osteoblasts were cultured on nontreated and plasma-treated nonporous and microporous membranes, and attachment, growth, and activity of cells were investigated. It was found that attachment and growth of osteoblasts on all the plasma-treated membranes were greater compared with nontreated controls. The treatment with ammonia plasma was most efficacious. The beneficial effects of plasma treatment on cells were most pronounced for microporous polylactide membranes irrespective of the plasma used. The results of the study suggest that the treatment of porous polylactide structures with plasma can be an effective means of enhancing their suitability for tissue engineering. Plasma exposure may also have an advantageous effect on bone healing when polylactide membranes are used to treat bone defects.

Covalent immobilization of proteins onto photoactivated polystyrene microtiter plates for enzyme-linked immunosorbent assay procedures

Enhancement of the speed and sensitivity of an ELISA technique was achieved by doing it on a polystyrene microtiter plate preactivated by a simple photochemical reaction. Immobilization of Epicoccum nigrum antigen (allergenic antigen) or goat anti-rabbit IgG onto the photoactivated plates was found to occur in only 45 min with higher binding than that obtained through adsorption during the same period onto the untreated surface. Nearly 1.5-2-folds higher readings were obtained when the ELISA was carried out with the solid phase prepared on the photoactivated surface rather than on the untreated surface. Moreover, solid phases prepared on the activated surface could detect IgE (E. nigrum antibody) even at 1/50 (v/v) dilutions, whereas a solid phase prepared on the untreated surface failed to do so. Around three times higher ELISA values were obtained in the activated plate than the untreated plate when IgE was diluted to 1/5 (v/v). Such photoactivated surface could be of great importance in diagnostic tests involving the ELISA technique particularly to confirm false negative cases and for other immunoassays such as radioimmunoassay procedures.

Introduction of functional groups onto polypropylene and polyethylene surfaces for immobilization of enzymes

Polypropylene and polyethylene surfaces are activated by introducing an active functional group through 1-fluoro-2 nitro-4-azidobenzene by UV irradiation. Horseradish peroxidase and glucose oxidase are immobilized onto the activated surfaces, simply by incubating the enzymes at 37 degrees C. When untreated surfaces are used, insignificant immobilization of the enzymes is observed.

Surface characterization and biological properties study of silicone rubber membrane grafted with phospholipid as biomaterial via plasma induced graft copolymerization

Poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) was grafted onto the surface of a silicon rubber (SR) membrane (pMPC-SR) by plasma induced grafted copolymerization (PIP). Argon plasma was used to activate the SR surfaces. Determination was also made of the influences of grafted copolymerization reaction time, reaction temperature, and monomer concentration on polymerization yield. The surface properties of SR were characterized by ATR-FTIR, ESCA, and SEM. In those analyses the ATR-FTIR spectra indicated that the pMPC grafted onto the SR surface at 1720 and 3300 cm(-1). The elemental composition and different carbon bindings on the surface of the SR were examined by ESCA. An increasing P1s/C1s value g was obtained in the grafted polymerization yield with a concentration of 0.05-0.5M of MPC in the isolated ethanol solution. The surface morphologies of pMPC-SR differed more than those of control and Ar plasma treated surfaces. The difference could have been caused by the homogeneous graft polymerization of pMPC onto the SR membrane. In the biological analyses, protein adsorption on pMPC-SR surfaces was reduced. The reduced level increased with an increase in the pMPC grafted amount. The epithelial cell attachment and growth onto these samples were suppressed. The blood compatibility for a series of pMPC-SR surfaces was examined by platelet adhesion. Blood platelet morphologies in contact with the high ratio of pMPC-SR surfaces were maintained, meaning that in this case the release reaction for platelets never occurred. Consequently, the high amount of pMPC-SR surface had excellent blood compatibility, further suggesting that prevention of adhesion, activation of platelets, and adsorption of blood protein could be achieved.

Heterobifunctional membranes by plasma induced graft polymerization as an artificial organ for penetration keratoprosthesis

Highly biocompatible polymer membrane was developed for an artificial cornea in this surface modification study. Heterobifunctional silicone rubber membranes (hetero-SR) were prepared by grafting different functional polymers on each side of a silicone rubber membrane (SR). A novel type of bifunctional membrane was developed with the upper-side favoring cell attachment and growth, and the lower-side suppressing cell adhesion. The preparation of heterobifunctional membranes, characterization of polymer membrane surface properties such as ATR-FTIR and ESCA and contact angle, and biological analysis (in vitro and in vivo studies) were investigated in this work. Based on the biological analysis, the heterobifunctional membrane displays promising potential for use as an artificial cornea.

Patterning of immobilized antibody layers via photolithography and oxygen plasma exposure

A novel technique for patterning immobilized antibody layers based upon photolithography and oxygen plasma exposure has been developed. Mouse monoclonal antibodies specific for thiabendazole (a post-harvest fungicide and veterinary anthelmintic) were covalently linked through free amine groups to aminosilanized silicon dioxide films using glutaraldehyde. Immobilized antibody layers were stabilized with sucrose, dehydrated, and stored refrigerated with desiccant. Photolithographic patterning was performed with a positive photoresist with modified bake temperatures and times, selective UV exposure with a contact mask, and aqueous alkaline solubilization of exposed resist. Exposed regions of immobilized antibody were then removed by exposure to a low power, radio frequency oxygen discharge. Residual resist was stripped with acetone. Successful patterning was demonstrated by challenging surfaces with goat anti-mouse antibody conjugated to tetramethylrhodamine isothiocyanate. Sucrose stabilization was necessary for antibody to undergo photoresist processing without loss of binding activity. Challenge with enzyme linked antigen of oxygen plasma exposed antibody layers demonstrated that plasma treatment completely neutralized antibody capture ability. Ellipsometry measurements of oxygen plasma exposed antibody layers indicated complete removal of immobilized antibodies. Fluorescent imaging demonstrated smallest line widths of 2-3 microns.

Plasma-induced grafted polymerization of acrylic acid and subsequent grafting of collagen onto polymer film as biomaterials

Polyacrylic acid (pAA) was introduced onto Ar-plasma treatment silicone rubber (SR) membrane surfaces by plasma-induced grafted polymerization. Collagen (type III) was also linked with the carboxylic group of pAA grafted onto the SR surface via a carbodiimine agent to obtain a secondary structure of SR. The SR surface properties were characterized by ATR-FTIR, ESCA, contact angle, and SEM. The biocompatibility of the SR surface was evaluated by a culture of cornea epithelial (CE) cells. Subsequently, 75-450 micrograms cm-2 of pAA were obtained on the SR surfaces under different reactive conditions; 3-12 micrograms cm-2 of collagen were linked on modified surfaces of SR. Moreover, ATR-FTIR and ESCA were utilized to confirm the proceedings of these reactions. The hydrophility of the modified SR was measured by a contact angle meter. The values of contact angle for SR grafted with pAA were approximately 45-50 degrees; a 50-55 degrees contact angle on pAA-g-SR to be further linked with collagen was subsequently obtained. Moreover, the influence of surface properties toward migration, growth and attachment of CE cells on the modified surfaces was also examined. Here, untreated SR was used as a control. Experimental results indicated that the number of CE cells attached onto the controlled SR was negligible. The attachment of cells onto pAA-grafted surfaces was clearly observed and peusopoda occurred; however, cell growth was depressed. This depression may have been caused by the acid environment of the pAA-grafted membrane. Nevertheless, both cell attachment and growth onto collagen-linked surfaces were significant. In addition, the morphology of the cells attached onto this surface was considered normal for primary cells. Collagen introduced on the SR surface was not denatured, i.e the natural properties of collagen were maintained. The results obtained in this study will hopefully lead to the successful development of modified SR for clinical applications.

Artificial cornea: surface modification of silicone rubber membrane by graft polymerization of pHEMA via glow discharge

A method for producing various surfaces of silicone rubber membrane (SR) was developed in this study by grafting various amounts of poly(2-hydroxy ethyl methacrylate) (pHEMA) onto SR by plasma-induced grafted polymerization (PIP) as a homobifunctional membrane. The elemental composition and different carbon bindings on the surface of SR were examined by electron spectroscopy for chemical analysis with the amount of O1s/C1s being approximately 0.7 at 1 min, 60 W, 200 mTorr of Ar-plasma treatment. The peroxide group introduced on SR was measured via 1,1-diphenyl-2-picrylhydrazyl (DPPH) and the amount of 6.85 x 10(-8) mol cm-2 reached optimum value at 1 min of Ar-plasma treatment. After Ar-plasma treated SR, the peroxide group (33D peak) was introduced on the surface of SR by negative spectra of secondary ion mass spectroscopy analysis, whereas ester groups (72D peak) were observed for pHEMA-grafted SR. For the in vitro test, the influence of various surfaces of SR on attachment and growth of rabbit corneal epithelial cells (CEC) was studied by cell culture assay. These results indicated that 56-150 micrograms cm-2 of pHEMA grafted onto SR were suitable values for attachment and growth of CEC. On the contrary, the large grafted amounts (500-1650 micrograms cm-2) of pHEMA on SR were insufficient for attachment and growth of CEC. For the in vivo test, the migration of CEC from host cornea to implant was investigated by slit lamp microscopy. The experimental results indicated that SRs grafted with pHEMA were completely covered with CEC 3 weeks after implantation of the membranes into the host cornea. These results provide a valuable reference for developing an artificial cornea.

Platelet adhesion and cellular interaction with poly(ethylene oxide) immobilized onto silicone rubber membrane surfaces

Cellular interaction and platelet adsorption were investigated on poly(ethylene oxide) (PEO) immobilized silicone rubber membrane (SR) which has polyacrylic acid grafts on the surfaces. Polyacrylic acid (PAA) had been introduced to the SR surface after Ar plasma treatment of SR surfaces to introduce peroxide groups. Surface characterizations were made using ATR-FTIR, ESCA, SEM, and contact angle measurements. Experimental results obtained by ESCA high resolution curve fitting spectra indicated that the amount of bisamino PEO of different molecular weights immobilized onto SR surfaces were similar, which showed that the influence of the length of molecular chains (-C-C-O-) on the reactivity of terminal amino group is negligible. The wettability of modified SR surfaces increased with an increase in PEO molecular weight. Biological studies such as corneal epithelial cell culture and blood platelet adhesion were performed to understand the biocompatibility of modified SR surfaces. Biological studies using corneal epithelial cells showed that cell migration, attachment and proliferation onto PEO-20000 immobilized SR surface were suppressed, whereas these biological activities on PEO-600 were enhanced. Another study on platelet adhesion revealed that many platelets attached to PEO-600 immobilized SR, while platelet deposition was rarely observed on SR grafted with PEO-3350. The effects of different PEO molecular chains on biological response were discussed.

Introduction of functional groups onto the surface of polyethylene for protein immobilization

Amino and carboxyl groups could be introduced onto the surface of high-density polyethylene film by utilizing graft polymerization of acrylamide and the subsequent Hofmann degradation and alkaline hydrolysis of grafted polyacrylamide. Graft polymerization was carried out by immersing an argon-plasma treated film in an aqueous solution of the monomer, followed by heating after degassing the monomer/film mixture. The surface density of these functional groups could be increased up to 10(-7) mol/cm2. The surfaces having amino and carboxyl groups exhibited positive and negative zeta potentials, respectively, when contacted with KCl aqueous solution. Both of the functional groups introduced onto the polyethylene surface were found to be utilizable for covalent immobilization of protein using carbodiimide for the carboxylic group or mediators such as glutaraldehyde and ethylene glycol diglycidyl ether for the amino group.