Integral geometry analysis of fluorescence micrographs for quantitative relative comparison of protein adsorption onto polymer surfaces

Temperature-responsive properties of pH-sensitive poly(methacrylic acid)-grafted brush coatings with controlled wettability for cell culture

Poly(methacrylic acid) (PMAA) is a well-known pH-responsive polymer with under-explored temperature-responsive properties. This study investigated the temperature-responsive properties of PMAA-grafted brush coatings, synthesized via the SI-ATRP polymerization of sodium methacrylate (NaMAA) and methacrylic acid (MAA) on glass surfaces. Distinct water contact angles were observed for PMAA brush coatings fabricated from NaMAA (38 deg) and MAA (60 deg) solutions. The reduced wettability of PMAA brushes from MAA indicates a reduced exposure of the hydrophilic moieties acquired during synthesis, which is postulated to occur with a lower grafting density. PMAA brush coatings showed a lower critical solution temperature (LCST), characterized by changes in wettability and thickness; however, this transition was not observed after immersion in various pH buffer solutions. Although inhibited growth of cells cultured on PMAA brushes was previously reported, we observed that the increased hydrophobicity of PMAA coatings from MAA resulted in excellent biocompatibility, demonstrated by growth and viability of dermal fibroblast cultures, making them prospective for biomedical applications. However, the LCST transition of these coatings did not induce temperature-controlled changes in protein (BSA) adsorption and cell (fibroblast) morphology.

Protein Orientation and Polymer Phase Separation Induced by Poly(methyl methacrylate) Tacticity

Stereochemistry may affect the physicochemical and biological properties of polymer films that are important for their applications, including substrates for the fabrication of protein microarrays. In this study, we investigated the effect of poly(methyl methacrylate) (PMMA) tacticity on the interaction of polymer thin films with proteins and on the phase separation process in blends with poly(tert-butyl methacrylate) (PtBMA). Thin films of isotactic, atactic, and syndiotactic PMMA were studied for topography, surface chemistry, and protein adsorption. Secondary ion mass spectrometry and contact angle measurements revealed a lower surface exposure of polar ester functional groups for iso-PMMA, resulting in the reduced adsorption of albumin and fibrinogen proteins. We also showed that changes in surface chemistry alter the orientation of proteins adsorbed on iso-PMMA through hydrophobic and electrostatic interactions. In addition, blends composed of PMMA and PtBMA, both of different tacticities, were investigated in terms of protein microarray fabrication. The two-dimensional domain structure was obtained by a phase separation process for at-PtBMA blends prepared on silicon substrates modified with amino-silane. Finally, for an isotropic and regular polymer pattern of iso-PMMA/at-PtBMA, the possibility of protein microarray formation on this blend was demonstrated, showing selective adsorption to PtBMA domains and perfect mirroring of the polymer patterns.

Detecting normal and cancer skin cells via glycosylation and adhesion signatures: A path to enhanced microfluidic phenotyping

Recruiting circulating cells based on interactions between surface receptors and corresponding ligands holds promise for capturing cells with specific adhesive properties. Our study investigates the adhesion of skin cells to specific lectins, particularly focusing on advancements in lectin-based biosensors with diagnostic potential. We explore whether we can successfully capture normal skin (melanocytes and keratinocytes) and melanoma (WM35, WM115, WM266-4) cells in a low-shear flow environment by coating surfaces with lectins. Specifically, we coated surfaces with Dolichos biflorus (DBA) and Maackia Amurensis (MAL) lectins, which were used to detect and capture specific skin cells from the flow of cell mixture. Alterations in glycan expression (confirmed by fluorescent microscopy) demonstrated that DBA binds predominantly to normal skin cells, while MAL interacts strongly with melanoma cells. Assessing adhesion under static and dynamic low-shear stress conditions (up to 30 mPa) underscores the reliability of DBA and MAL as markers for discriminating specific cell type. Melanocytes and keratinocytes adhere to DBA-coated surfaces, while melanoma cells prefer MAL-coated surfaces. A comprehensive analysis encompassing cell shape, cytoskeleton, and focal adhesions shows the independence of our approach from the inherent characteristics of cells, thus demonstrating its robustness. Our results carry practical implications for lectin-biosensor designs, emphasizing the significance of glycan-based discrimination of pathologically altered cells. Combined with microfluidics, it demonstrates the value of cell adhesion as a discriminant of cancer-related changes, with potential applications spanning diagnostics, therapeutic interventions, and advanced biomedical technologies.

Plasma Treatment of PDMS for Microcontact Printing (μCP) of Lectins Decreases Silicone Transfer and Increases the Adhesion of Bladder Cancer Cells

The present study investigates silicone transfer occurring during microcontact printing (μCP) of lectins with polydimethylsiloxane (PDMS) stamps and its impact on the adhesion of cells. Static adhesion assays and single-cell force spectroscopy (SCFS) are used to compare adhesion of nonmalignant (HCV29) and cancer (HT1376) bladder cells, respectively, to high-affinity lectin layers (PHA-L and WGA, respectively) prepared by physical adsorption and μCP. The chemical composition of the μCP lectin patterns was monitored by time-of-flight secondary ion mass spectrometry (ToF-SIMS). We show that the amount of transferred silicone in the μCP process depends on the preprocessing of the PDMS stamps. It is revealed that silicone contamination within the patterned lectin layers inhibits the adhesion of bladder cells, and the work of adhesion is lower for μCP lectins than for drop-cast lectins. The binding capacity of microcontact printed lectins was larger when the PDMS stamps were treated with UV ozone plasma as compared to sonication in ethanol and deionized water. ToF-SIMS data show that ozone-based treatment of PDMS stamps used for μCP of lectin reduces the silicone contamination in the imprinting protocol regardless of stamp geometry (flat vs microstructured). The role of other possible contributors, such as the lectin conformation and organization of lectin layers, is also discussed.

Effect of poly(tert-butyl methacrylate) stereoregularity on polymer film interactions with peptides, proteins, and bacteria

The impact of polymer stereoregularity on its interactions with peptides, proteins and bacteria strains was studied for three stereoregular forms of poly(tert-butyl methacrylate) (PtBMA): isotactic (iso), atactic (at) and syndiotactic (syn) PtBMA. Principal component analysis of the time-of-flight secondary ion mass spectrometry data recorded for thin polymer films indicated a different orientation of ester groups, which in the case of iso-PtBMA are exposed away from the surface whereas for at-PtBMA and syn-PtBMA these are located deeper within the film. This arrangement of chemical groups modified the interactions of iso-PtBMA with biomolecules when compared to at-PtBMA and syn-PtBMA. For peptides, the affected interactions were explained by the preferential hydrogen bonding and electrostatic interaction between the exposed polar ester groups of iso-PtBMA and positively charged peptides. In turn, for protein adsorption no impact on the amount of adsorbed proteins was observed. However, the polymer stereoregularity influenced the orientation of immunoglobulin G and induced conformational changes in bovine serum albumin structure. Moreover, the impact of polymer stereoregularity occurred equally for their interactions with Gram-positive bacteria (S. aureus), which absorbed preferentially onto iso-PtBMA films as compared to two other stereoregularities.

Temperature-Controlled Orientation of Proteins on Temperature-Responsive Grafted Polymer Brushes: Poly(butyl methacrylate) vs Poly(butyl acrylate): Morphology, Wetting, and Protein Adsorption

Poly( n-butyl methacrylate) (PBMA) or poly( n-butyl acrylate) (PBA)-grafted brush coatings attached to glass were successfully prepared using atom-transfer radical polymerization "from the surface". The thicknesses and composition of the PBMA and PBA coatings were examined using ellipsometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. For PBMA, the glass-transition temperature constitutes a range close to the physiological limit, which is in contrast to PBA, where the glass-transition temperature is around -55 °C. Atomic force microscopy studies at different temperatures suggest a strong morphological transformation for PBMA coatings, in contrast to PBA, where such essential changes in the surface morphology are absent. Besides, for PBMA coatings, protein adsorption depicts a strong temperature dependence. The combination of bovine serum albumin and anti-IgG structure analysis with the principal component analysis of ToF-SIMS spectra revealed a different orientation of proteins adsorbed to PBMA coatings at different temperatures. In addition, the biological activity of anti-IgG molecules adsorbed at different temperatures was evaluated through tracing the specific binding with goat IgG.

Temperature-Controlled Three-Stage Switching of Wetting, Morphology, and Protein Adsorption

The novel polymeric coatings of oligoperoxide-graft-poly(4-vinylpyridine-co-oligo(ethylene glycol)ethyl ether methacrylate246) [oligoperoxide-graft-P(4VP-co-OEGMA246)] attached to glass were successfully fabricated. The composition, thickness, morphology, and wettability of resulting coatings were analyzed using X-ray photoelectron spectroscopy, ellipsometry, atomic force microscopy, and contact angle measurements, respectively. In addition, adsorption of the bovine serum albumin was examined with fluorescence microscopy. The thermal response of wettability and morphology of the coatings followed by that of protein adsorption revealed two distinct transitions at 10 and 23 °C. For the first time, three stage switching was observed not only for surface wetting but also for morphology and protein adsorption. Moreover, the influence of the pH on thermo-sensitivity of modified surfaces was shown.

Chain mobility and film softness mediated protein antifouling at the solid–liquid interface

Polymer chain mobility and film softness have been demonstrated to determine protein adsorption at the solid–liquid interface, and even overwhelm the hydrophilic effect under certain conditions. Polymers with high chain mobility and softness provide superior protein antifouling properties as a result of the high entropy barrier from film surfaces.

Temperature-responsive properties of poly(4-vinylpyridine) coatings: influence of temperature on the wettability, morphology, and protein adsorption

Poly(4-vinylpyridine)-grafted brushes demonstrate a thermal response of their wettability (stronger than that for spin-coated films), surface morphology, and protein adsorption.

Temperature-responsive peptide-mimetic coating based on poly(N-methacryloyl-l-leucine): properties, protein adsorption and cell growth

Poly(N-methacryloyl-l-leucine) (PNML) coatings were successfully fabricated via polymerization from peroxide initiator grafted to premodified glass substrate. Chemical composition and thickness of PNML coatings were determined using time of flight-secondary ion mass spectrometry (TOF- SIMS) and ellipsometry, respectively. PNML coatings exhibit thermal response of the wettability, between 4 and 28°C, which indicates a transition between hydrated loose coils and hydrophobic collapsed chains. Morphology of the PNML coating was observed with the AFM, transforming with increasing temperature from initially relatively smooth surface to rough and more structured surface. Protein adsorption observed by fluorescence microscopy for model proteins (bovine serum albumin and lentil lectin labeled with fluorescein isothiocyanate) at transition from 5 to 25°C, showed high affinity of PNML coating to proteins at all investigated temperatures and pH. Thus, PNML coating have significant potential for medical and biotechnological applications as protein capture agents or functional replacements of antibodies ("plastic antibodies"). The high proliferation growth of the human embryonic kidney cell (HEK 293) onto PNML coating was demonstrated, indicating its excellent cytocompatibility.

Temperature and pH dual-responsive POEGMA-based coatings for protein adsorption

Poly(oligo(ethylene glycol)ethyl ether methacrylate (POEGMA246) coatings were successfully fabricated using novel approach via polymerization from oligoperoxide grafted to premodified glass substrate. Wettability, content and composition of coatings fabricated with different polymerization times were determined using contact angle measurements, ellipsometry and Time of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS). Thermo- and pH-responsive properties of POEGMA246 coatings were found to depend significantly on concentration of the grafted POEGMA246. Coatings fabricated with polymerization time 30 h exhibit not only temperature- but also pH-dependence of wettability. Thermal response of wettability, measured between 20 and 32°C, was prominent at pH 9 and 7 and diminished or was absent at pH 5 and 3, indicating a transition between hydrated loose coils and hydrophobic collapsed chains, blocked at low pH. Protein adsorption, observed by fluorescence microscopy and analyzed semi-quantitatively using integral geometry approach, decreased dramatically for model protein (lentil lectin labeled with fluorescein isothiocyanate) at transition from pH 5 to pH 9, showing only very weak thermal-dependence. Strong protein adsorption response to pH and very weak one to temperature was confirmed by TOF-SIMS and Principal Component Analysis.

Zwitterionic phenyl layers: finally, stable, anti-biofouling coatings that do not passivate electrodes

Organic coatings on electrodes that limit biofouling by proteins but are of sufficiently low impedance to still allow Faradaic electrochemistry to proceed at the underlying electrode are described for the first time. These organic coatings formed using simple aryl diazonium salts present a zwitterionic surface and exhibit good electrochemical stability. The layers represent a low impedance alternative to the oligo (ethylene glycol) (OEG)-based anti-biofouling coatings and are expected to find applications in electrochemical biosensors and implantable electrodes. Two different zwitterionic layers grafted to glassy carbon surfaces are presented and compared to a number of better-known surfaces, including OEG-based phenyl-layer-grafted glassy carbon surfaces and OEG alkanethiol SAMs coated on gold, to allow the performance of these new layers to be compared to the body of work on other anti-biofouling surfaces. The results suggest that phenyl-based zwitterionic coatings are as effective as the OEG SAMs at resisting the nonspecific adsorption of bovine serum albumin and cytochrome c, as representative anionic and cationic proteins at physiological pH, whereas the impedance of the zwitterionic phenyl layers are two orders of magnitude lower than OEG SAMs.

Chemical-vapor-deposition-based polymer substrates for spatially resolved analysis of protein binding by imaging ellipsometry

Biomolecular interactions between proteins and synthetic surfaces impact diverse biomedical fields. Simple, quantitative, label-free technologies for the analysis of protein adsorption and binding of biomolecules are thus needed. Here, we report the use of a novel type of substrate, poly-p-xylylene coatings prepared by chemical vapor deposition (CVD) polymerization, for surface plasmon resonance enhanced ellipsometry (SPREE) studies and assess the reactive coatings as spatially resolved biomolecular sensing arrays. Prior to use in binding studies, reactive coatings were fully characterized by Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, and ellipsometry. As a result, the chemical structure, thickness, and homogeneous coverage of the substrate surface were confirmed for a series of CVD-coated samples. Subsequent SPREE imaging and fluorescence microscopy indicated that the synthetic substrates supported detectable binding of a cascade of biomolecules. Moreover, analysis revealed a useful thickness range for CVD films in the assessment of protein and/or antigen-antibody binding via SPREE imaging. With a variety of functionalized end groups available for biomolecule immobilization and ease of patterning, CVD thin films are useful substrates for spatially resolved, quantitative binding arrays.

An X-ray spectromicroscopy study of protein adsorption to polystyrene-poly(ethylene oxide) blends

Synchrotron-based X-ray photoemission electron microscopy (X-PEEM) and atomic force microscopy (AFM) were used to characterize the composition and surface morphology of thin films of a polystyrene-poly(ethylene oxide) blend (PS-PEO), spun cast from dichloromethane at various mass ratios and polymer concentrations. X-PEEM reveals incomplete segregation with ∼30% of PS in the PEO region and vice versa. Protein (human serum albumin) adsorption studies show that this partial phase separation leads to greater protein repellency in the PS region, whereas more protein is detected in the PEO region compared to control samples.