Modified Polystyrene Surfaces Research Articles

Hyperosmotic Infusion and Oxidized Surfaces Are Essential for Biofilm Formation of Staphylococcus capitis From the Neonatal Intensive Care Unit.

Staphylococcus capitis is an opportunistic pathogen often implicated in bloodstream infections in the neonatal intensive care unit (NICU). This is assisted by its ability to form biofilms on indwelling central venous catheters (CVC), which are highly resistant to antibiotics and the immune system. We sought to understand the fundamentals of biofilm formation by S. capitis in the NICU, using seventeen clinical isolates including the endemic NRCS-A clone and assessing nine commercial and two modified polystyrene surfaces. S. capitis clinical isolates from the NICU initiated biofilm formation only in response to hyperosmotic conditions, followed by a developmental progression driven by icaADBC expression to establish mature biofilms, with polysaccharide being their major extracellular polymer substance (EPS) matrix component. Physicochemical features of the biomaterial surface, and in particular the level of the element oxygen present on the surface, significantly influenced biofilm development of S. capitis. A lack of highly oxidized carbon species on the surface prevented the immobilization of S. capitis EPS and the formation of mature biofilms. This information provides guidance in regard to the preparation of hyperosmolar total parenteral nutrition and the engineering of CVC surfaces that can minimize the risk of catheter-related bloodstream infections caused by S. capitis in the NICU.

Influence of Photocatalysis on Blood Cell Attachment over Protein-Immobilized Polystyrene Surfaces Modified with a Poly(styrene)-b-Poly(acrylic acid) Copolymer.

In the present study, thrombocytes, erythrocytes, and leukocytes were individually brought into contact with different immobilized blood proteins on the surface of polystyrene (PS), which was modified with a poly(styrene)-b-poly(acrylic acid) copolymer. When the concentration of fibronectin was greater than 5 μg mL-1, the attachment of erythrocytes increased, which indicated that the modified PS surface was less compatible with erythrocytes. In addition, vitronectin and laminin attached on the surface increased the adhesion of thrombocytes; higher adhesion was observed for leukocytes in the cases of fibrinogen, lysozyme, and laminin. Interestingly, adhesion properties of blood cells on the protein surface could be influenced by the addition of metal oxide- and carbon-based photocatalysts. After a photocatalytic treatment by metal oxide-based TiO2, the adhesion amounts of erythrocytes improved slightly, whereas the adhesion of leukocytes and thrombocytes decreased after treatment with a carbon-based g-C3N4 nanosheet. Our results suggested that the surface modification of the substrate through photocatalysis using various photocatalysts along with the grafting of the poly(styrene)-b-poly(acrylic acid) copolymer could be a promising approach to alternatively control the blood compatibility on the protein surface.

Precipitant induced porosity augmentation of polystyrene preserves the chondrogenicity of human chondrocytes.

Cells constantly sense and receive chemical and physical signals from neighboring cells, interstitial fluid, and extracellular matrix, which they integrate and translate into intracellular responses. Thus, the nature of the surface on which cells are cultured in vitro plays an important role for cell adhesion, proliferation, and differentiation. Autologs chondrocyte implantation is considered the treatment of choice for larger cartilage defects in the knee. To obtain a sufficient number of chondrocytes for implantation multiple passaging is often needed, which raises concerns about the changes in the chondrogenic phenotype. In the present study, we analyzed the effect at cellular and molecular level of precipitant induced porosity augmentation (PIPA) of polystyrene surfaces on proliferation and differentiation of human chondrocytes. Human chondrocytes were isolated from healthy patients undergoing anterior cruciate ligament reconstruction and cultured on PIPA modified polystyrene surfaces. Microscopical analysis revealed topographically arranged porosity with micron pores and nanometer pits. Chondrocytes cultured on PIPA surfaces revealed no difference in cell viability and proliferation, but gene- and protein expressions of collagen type II were pronounced in the first passage of chondrocytes when compared to chondrocytes cultured on control surfaces. Additionally, an analysis of 40 kinases revealed that chondrocytes expanded on PIPA caused upregulated PI3K/mTOR pathway activation and inhibition of mTORC1 resulted in reduced sGAG synthesis. These findings indicate that PIPA modified polystyrene preserved the chondrogenicity of expanded human chondrocytes at gene and protein levels, which clinically may be attractive for the next generation of cell-culture surfaces for ex vivo cell growth. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3073-3081, 2016.

Vacuum UV photo-oxidation of polystyrene

Polystyrene (PS) was treated with vacuum UV (VUV) (λ = 104.8 and 106.7 nm) photo-oxidation and X-ray photoelectron spectroscopy detected a controlled increase in the atomic percentage of oxygen up to a saturation level of ca. 20 at% O. Initially, C–O and carbonyl groups are observed due to the formation of alcohols, ethers, esters, and ketones. Water contact angle measurements showed ca. 25% increase in hydrophilicity of the surface with oxidation. Atomic Force Microscopy observed little changes in surface roughness with treatment time. The super water absorbent polymer poly(acrylic acid) was thinly grafted to the modified PS surface.

Surface characterization of polystyrene treated with ozone and grafted with poly(acrylic acid)

Polystyrene (PS) is one of the most widely used thermoplastic polymers and is often not recycled because of its light weight and low scrap value. The discarded PS in landfill sites has limited capacity for water absorption, and physical and chemical properties that make it relatively inert. To increase wettability and introduce oxygen-containing functional groups, PS was treated at room temperature with ozone in the absence of the UV radiation which was used to make the ozone from the photodissociation of oxygen. X-ray photoelectron spectroscopy detected the increase of oxygen content on the PS surface and the formation of functional groups with reaction time. Advancing contact angle measurements showed an increase of hydrophilicity with treatment time. The superabsorbent polymer poly(acrylic acid) was partially and/or thinly grafted onto the modified PS surface.

Investigating the effect of surface topography on hydrophobicity and bacterial attachment on polystyrene

In this paper, we present an investigation into the effects of surface topography (roughness) and hydrophobicity (contact angle measurement) on bacteria adhesion for polystyrene materials. The surfaces of polystyrene substrates were patterned using UV-laser radiation with a wavelength of 193 nm under different conditions. Various surface topographies were fabricated and were measured by an optical surface profiler and contact angle measurements were recorded. For the bacterial adhesion experiments, an assay of Escherichia coli (E. coli) was developed and used for measurements on both as-received and modified polystyrene surfaces. The method is based on the staining of attached bacterial cells with the nucleic acid-binding, green fluorescent DAPI (4′, 6-diamidino-2-phenylindole) stain. The preliminary results show that laser-assisted modification induced by laser ablation can make polystyrene substrates either more hydrophilic (with oxygen) or more hydrophobic (with air). The contact angle can be varied from 37° to 108°. The results on bacterial attachment show that the polystyrene substrates as received have no bacteria attached, indicating a good anti-bacterial performance. The treated substrates show some bacterial attachment and, in particular, the surfaces with a high contact angle have much higher numbers of bacterial cells attached. This indicates that such a laser-assisted process with air can make polystyrene surfaces more attractive to E. coli bacteria.

Nanostructured polystyrene films engineered by plasma processes: Surface characterization and stem cell interaction

ABSTRACTIn this work we showed the promising perspectives offered by the radiofrequency plasma processes on polymeric substrates. Polystyrene (PS) films with micropatterned grooves and nanostructured roughness were developed by Oxygen plasma treatment coupled with mask, and t process parameters, as power supply and treatment time were modulated. Then, hydrogenated amorphous carbon (a‐C:H) coatings (∼30 nm thickness) were deposited by methane radiofrequency plasma enhanced chemical vapor deposition (rf‐PECVD) on the polymer surface. Oxygen modified PS surface showed improved wettability, roughness and etching rate by increasing the power supply and the treatment time. Uniform and patterned bi‐layer films show a regular surface morphology, uniform chemical properties, with a contact angle to water of 77°, a surface energy of 51.15 mN m−1 and good stability in physiological conditions. Nanoindentation measurements revealed a decrease of the bi‐layer friction coefficient from 0.76 of PS to 0.17, highlighting the improvement of the nanomechanical properties of the novel developed system. Interaction with human bone‐marrow mesenchymal stem cells demonstrates that uniform and patterned PS based films are biocompatible surfaces and remarkable, that groove patterned substrates induce stem cell alignment and elongation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40427.

Synthesis and characterization of chemically modified polystyrene as processable carbon fiber precursors

In this study, the chemically modified polystyrene was studied for improvement of polystyrene which had low carbon yield, as a carbon fiber precursor. The polystyrene was synthesized with divinylbenzene which was used as a cross-linking agent by the solution polymerization method. Then the synthesized polystyrene was nitrated with sulfuric and nitric acids solution (H2SO4/HNO3) followed by reduction to form nitrogen-functional groups. The surface properties of the modified polystyrene were investigated by Fourier transfer infrared spectroscopy to confirm the introduction of functional groups on the modified polystyrene surfaces. The thermal properties of the modified polystyrene were measured by thermogravimetric analysis and differential scanning calorimetry. The morphologies of the electrospun polystyrene fibers by a chemical modification were observed by scanning electron microscopy. From the results, the nitrogen-functional groups were introduced on the modified polystyrene surfaces which affected the quantity of functional groups. Also, the chemical treatment affected the carbon yield of the polystyrene owing to the introduction of nitrogen-functional groups on polystyrene surfaces. Consequently, it was concluded that the chemical treatment of polystyrene fibers enables it to be used as a possible carbon fiber precursor.

SYNTHESIS AND APPLICATIONS OF NOVEL FLUOROALKYL END-CAPPED OLIGOMERS CONTAINING 3,5-DIMETHYL-4-HYDROXYBENZYL AND 3-(2H-BENZOTRIAZOL-2-yl)-4-HYDROXYPHENYL SEGMENTS

New fluoroalkyl end-capped co-oligomers containing 3,5-dimethyl-4-hydroxybenzyl segments [RF‒(DMHB)x‒(DMAA)y–RF] were prepared by the reactions of fluoroalkanoyl peroxides with N-(3,5-dimethyl-4-hydroxybenzyl)methacrylamide [DMHB] and N,N-dimethylacrylamide (DMAA). Similarly, fluoroalkyl end-capped homo- and co-oligomers containing 3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl segments [RF–(BTRI)x–(Co–M)y–RF] were prepared by the reactions of fluoroalkanoyl peroxides with 2-[3–(2H‒benzotriazol–2–yl)–4–hydroxyphenyl]ethyl methacrylate [BTRI] and co-monomers [Co–M] such as acrylic acid (ACA), DMAA, and acryloylmorpholine (ACMO). The fluoroalkyl end-capped DMHB and BTRI co-oligomers thus obtained were soluble not only in water but also in common organic solvents. In addition, these fluorinated co-oligomers were able to reduce the surface tension of 0.1 N NaOH solutions quite effectively to around 20 mN/mlevels, although the corresponding non-fluorinated co-oligomers were not effective in reducing the surface tension of 0.1 N NaOH solutions. A modified polystyrene film surface treated with these fluoroalkyl end-capped DMHB and BTRI co-oligomers was found to exhibit a good oleophobicity imparted by fluorine with an excellent hydrophilicity. XPS analyses showed that end-capped fluoroalkyl groups in RF-(BTRI)n-RF homo-oligomer were arranged regularly above the modified polystyrene surface. Of particular interest, it was demonstrated that the self-assembled molecular aggregates formed by RF-(DMHB)x-(DMAA)y-RF co-oligomers could interact strongly with 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a guest molecule to form a host–guest intermolecular complex, though such a host–guest interaction was not observed in the corresponding non-fluorinated DMHB co-oligomer.

Improved cellular adhesion to acetone plasma modified polystyrene surfaces

The plasma polymerization of acetone has been used to modify polystyrene substrates for the controlled growth of human fibroblast cells. The surface modified polystyrene was studied by X-ray photoelectron spectroscopy, water contact angle and atomic force microscopy. This showed the surface oxygen levels and wettability to increase rapidly with exposure to the acetone plasma. High-resolution XPS allowed the determination of the relative amounts of surface hydroxyl, carbonyl and carboxyl groups. This showed that there was little incorporation of carboxyl groups in the deposited films. AFM measurements revealed the films to be conformal with a surface roughness equivalent to that of the underlying polystyrene substrate with film growth rates of approximately 0.5 nm min(-1). High edge-definition patterns were produced with a simple masking procedure and allowed the confinement of cells to selected areas of the substrate. These chemically patterned surfaces allowed the study of cells confined to particular regions of the substrate as a function of incubation time.

Solubilization of phthalocyanines into methanol with fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)‐ and N,N‐dimethyl‐acrylamide oligomers

AbstractSelf‐assembled molecular aggregates of fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)‐ and N,N‐dimethyl‐acrylamide oligomers in methanol were found to interact with phthalocyanines as guest molecules to exhibit good solubility. On the other hand, the corresponding nonfluorinated oligomers were not effective in solubilizing phthalocyanines under similar conditions. In these oligomers, fluorinated N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomers were more effective in solubilizing phthalocyanines in methanol. Self‐assemblies formed by fluorinated oligomer‐phthalocyanine complexes are applied to the surface modifications of polystyrene (PS), and the modified PS surface exhibited not only a strong oleophobicity imparted by fluorine but also good hydrophilicity. Thus, these fluorinated molecular aggregate‐phthalocyanine systems are suggested to have high potential for new fluorinated functional materials through their excellent properties imparted by fluorine and phthalocyanines. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 521–525, 2004

Synthesis and surface properties of novel fluoroalkyl end-capped amphiphilic fullerene cooligomers

New fluoroalkyl end-capped fullerene cooligomers were prepared by the reactions of fluoroalkanoyl peroxides with fullerene and comonomers such as acryloylmorpholine, N, N-dimethylacrylamide and acrylic acid. These fluorinated fullerene cooligomers were easily soluble in water and common organic solvents, and were able to reduce the surface tensions of both water and benzene, quite effectively. Additionally, these fullerene cooligomers were found to form a stable monomolecular film at the air–water interface, and the modified polystyrene surface treated with these cooligomers was shown to have a strong hydrophilicity with good oil repellency.

Effects of Serum on the Kinetics of CHO Attachment to Ultraviolet–Ozone Modified Polystyrene Surfaces

Attachment kinetics of Chinese hamster ovarian (CHO) cells were investigated on ultraviolet-ozone oxidized polystyrene (UVO-PS) dishes in the presence and absence of serum. The surface chemistry of UVO-PS has been extensively characterized. Although cells attached rapidly to the oxidized dishes with serum present it was found that serum actually inhibits the rate of attachment. Spreading of attached cells was favored by the presence of serum. It is suggested that the increased quantity of hydrophilic carboxyl groups on longer exposed UVO-PS leads to a change in the protein layer adsorbed from serum and also a higher affinity of the surface for extracellular proteins secreted by the attached cells. The UVO-PS surfaces present a new way of producing tissue culture grade polystyrene (TCPS) in a highly controllable method, which would ensure greater consistency in TCPS surfaces.

Adhesion, growth and detachment of cells on modified polystyrene surface.

By adsorbing poly(N-isopropylacrylamide) (PNIPAAm) from an aqueous solution onto oxidised polystyrene without the need for grafting the polymer to the surface, we showed here that cells(CHO-K1) adhere and grow well at 37 degrees C and are detached by lowering the temperature to 10 degrees C without any other deleterious treatment. Both bacterial culture grade polystyrene Petri dishes and polystyrene beads (120 to 250mum diameters) commercially available used in static conditions of growth were tested with similar results. The contact angle of modified Petri dishes with a water droplet increases from 36 to 58 degrees when the temperature is raised from 25 to 37 degrees C indicating change in hydrophilicity of the surface as a function of temperature.

The effects of surface chemistry and adsorbed proteins on monocyte/macrophage adhesion to chemically modified polystyrene surfaces.

Monocytes and macrophages play critical roles in inflammatory responses to implanted biomaterials. Monocyte adhesion may lead to macrophage activation and the foreign body response. We report that surface chemistry, preadsorbed proteins, and adhesion time all play important roles during monocyte adhesion in vitro. The surface chemistry of tissue culture polystyrene (TCPS), polystyrene, Primaria, and ultra low attachment (ULA) used for adhesion studies was characterized by electron spectroscopy for chemical analysis. Fibrinogen adsorption measured by (125)I-labeled fibrinogen was the lowest on ULA, higher on TCPS, and the highest on polystyrene or Primaria. Monocyte adhesion on protein preadsorbed surfaces for 2 h or 1 day was measured with a lactate-dehydrogenase method. Monocyte adhesion decreased over time. The ability of preadsorbed proteins to modulate monocyte adhesion was surface dependent. Adhesion was the lowest on ULA, higher and similar on TCPS or polystyrene, and the highest on Primaria. Monocyte adhesion on plasma or fibrinogen adsorbed surfaces correlated positively and linearly to the amount of adsorbed fibrinogen. Preadsorbed fibronectin, immunoglobulin G, plasma, or serum also promoted adhesion compared with albumin preadsorbed or uncoated surfaces. Overall, biomaterial surface chemistry, the type and amount of adsorbed proteins, and adhesion time all affected monocyte adhesion in vitro.

A Distinctive Surface for Phospholipid Assays

Solid-phase immunoassay is a commonly used immunological technique in many clinical and research laboratories. It is known that proteins will adsorb to a solid surface such as polystyrene. Many studies have also indicated that surface modifications such as the introduction of different functional groups onto the polystyrene surface will enhance the overall protein-binding properties of the plastic polymer (1). Nevertheless, the increased binding also means increased nonspecific binding, producing higher background signals. The currently available polystyrene surfaces work well for most protein antigens. However, these polystyrene surfaces are not adequate for the measurement of all antigenic substances. Certain antigenic lipids are not easily detected and measured using these surfaces (2). A commonly used diagnostic test for anti-phospholipid antibodies (aPLs) is an ELISA using cardiolipin, an anionic phospholipid, as the antigen in the solid-phase immunoassay (3). aPLs are antibodies associated with the clinical syndrome of thrombosis and recurrent midtrimester fetal death and other, less common manifestations, termed antiphospholipid syndrome (4). aPLs are also detected in patients with systemic lupus erythematosus and related autoimmune disorders (5)(6)(7). There are numerous critical variables for anticardiolipin assays. Critical factors that can influence ELISA results include the amount of phospholipids coated on the surface, the solvent for the phospholipids, choice of blocking agents and serum diluent, incubation temperature, and the type of microwell plates (8)(9)(10). To develop a solid-phase immunoassay optimized for phospholipids, we examined various modified polystyrene surfaces for the ability to bind protein and phospholipids, including cardiolipin. The following reagents were obtained from Sigma: cardiolipin (diphosphatidylglycerol), sodium salt from beef heart, 4.8 g/L in ethanol; o -phenylenediamine dihydrochloride (OPD), 30-mg tablets; p -nitrophenyl phosphate, disodium; and diethanolamine, ACS reagent grade. Nitrobenzoxadizole (NBD)-labeled 1-palmitoyl-2-[6-(7-nitro-2-1,3-benzoxadiazol-4-y)]- sn -glycerol 3-phosphoserine (sodium salt), M r 796.81, 1 g/L in …

Self-Assembled Peptides Exposing Epitopes Recognizable by Human Lymphoma Cells

A bifunctional N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer containing nitrilotriacetic acid (NTA) and benzophenone (BP) groups was synthesized by free-radical copolymerization of HPMA, 2-methacrylamidobutyl nitrilotriacetic acid (MABNTA), and 4-methacrylamido benzophenone (MABP) using 2, 2'-azobisisobutyronitrile (AIBN) as initiator. A His-tagged coiled coil stem loop peptide containing a tridecapeptide (TDP) epitope (GFLGEDPGFFNVE) in the loop region (CCSL-TDP) was designed and synthesized genetically by expressing an artificial gene in Escherichia coli BL21 (DE3). The peptide was characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), size-exclusion chromatography (SEC), and circular dichroism (CD) spectroscopy. Surfaces containing self-assembled CCSL-TDP peptide were prepared by first covalently grafting poly(HPMA-co-MABNTA-co-MABP) onto polystyrene (PS) surface by UV irradiation, then charging the surface with nickel through NTA groups, and finally attaching the CCSL-TDP peptide through Ni-histidine chelation. The modified PS surfaces with and without self-assembled CCSL-TDP peptide were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Cell attachment studies with human Burkitt's lymphoma Raji B cells showed that the cells selectively bound to the self-assembled CCSL-TDP peptide surfaces, but not to the surfaces of PS, PS with grafted copolymer, and PS with grafted copolymer and self-assembled coiled coil peptide with similar structure but without the epitope. This indicates that the cell attachment was mediated by the CCSL-TDP peptide, most probably by the TDP epitope region. The CCSL peptide self-assembly presented here may represent a feasible model of exposing epitopes for biorecognition studies.

Cellular Attachment to Ultraviolet Ozone Modified Polystyrene Surfaces

The surfaces of standard untreated polystyrene cell culture dishes have been oxidatively modified for up to 8 min exposure time using an ultraviolet ozone treater in order to promote cell adhesion. Surface oxygen chemisorption and topographical modification has been characterized using monochromatic X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The oxidation process is shown to proceed at low exposure times ( 60 s is in the form of loosely bound low molecular weight oxidized material (LMWOM) which is produced by oxidative scission of the PS backbone. Water washing leads to a reduction in surface oxygen content mainly by the removal of ROCO and R2CO functiona...

Fluid shear induced endothelial cell detachment from modified polystyrene substrata

In this study, human umbilical vein endothelial cells were seeded for 3 and 24 h on polystyrene (PS), tissue culture polystyrene (TCPS) and polystyrene modified by oxygen plasma treatment (PtPS) in order to investigate their detachment behaviour during exposure to fluid shear. All three materials have smooth surfaces at the submicron level. Equilibrium water contact angles were higher on PS (88°) than on TCPS (78°) and PtPS (79°). Furthermore, contact angle hysteresis, i.e. the difference between advancing and receding angles, was much larger on TCPS (39°) and PtPS (41°) than on PS (14°), indicating either a large surface heterogeneity or a possible reorientation of functional groups on TCPS and PtPS. X-ray photoelectron spectroscopy data revealed that both TCPS and PtPS had oxygen incorporated at their surfaces (18.6% and 9.9%, respectively), whereas only TCPS had a small amount of nitrogen (0.9%) at its surface. Cells seeded on these materials were exposed to various shear stresses in the range 88–352 dyn cm −2 in order to gain more insight into the influence of the specific physico-chemical surface properties of these polystyrene surfaces on cell retention, cell morphology and migration. The retention of cells having adhered during 24 h on TCPS and PtPS was not different from the retention of cells having adhered during 3 h, but retention on TCPS and PtPS was higher than on PS. At shear stresses of 88 and 176 dyn cm −2, however, differences in the morphology of cells adhered to TCPS during 3 and 24 h were observed, indicating that between 3 and 24 h changes in cell-substratum interactions occurred. Migration on TCPS and PtPS was accompanied by the presence of fibrillike structures left behind on the surface. Summarizing, this study shows that cell retention is higher on modified polystyrenes than on polystyrene, the only major difference between the polystyrenes being the higher contact angle hysteresis and oxygen content of the modified polystyrene surfaces.

Immobilization of protein to surface-grafted PEO/PPO block copolymers

Adsorption and covalent immobilization of Ig G to a grafted tetrabranched PEO/PPO block copolymer have been studied and related to the temperature-dependent properties of the grafted polymer. The investigation was performed by means of in situ ellipsometry, as well as by ESCA and ELISA measurements. The results show that the copolymer grafted to polystyrene (PS) surface contracts substantially upon increasing the temperature. A close interrelation was found between the properties of the grafted layer and the amount of protein (Ig G) that could be either adsorbed or covalently immobilized to the modified PS surface. By utilizing the reversed temperature phase behavior exhibited by these copolymers a relatively high loading of protein was obtained at temperatures close to the cloud point. By lowering the temperature after immobilization, the grafted layer regains its hydrophilicity and protein-rejecting properties. Thus, problems associated with interaction between bound protein and the underlying solid surface are minimized.