In this work, we show the strong resistance of zwitterionic phosphorylcholine (PC) self-assembled monolayers (SAMs) to protein adsorption and examine key factors leading to their nonfouling behavior using both experimental and molecular simulation techniques. Zwitterions with a balanced charge and minimized dipole are excellent candidates as nonfouling materials due to their strong hydration capacity via electrostatic interactions.
This study examined six different polymer and self-assembled monolayer (SAM) surface modifications for their interactions with human serum and plasma. It was demonstrated that zwitterionic polymer surfaces are viable alternatives to more traditional surfaces based on poly(ethylene glycol) (PEG) as nonfouling surfaces. All polymer surfaces were formed using atom transfer radical polymerization (ATRP) and they showed an increased resistance to nonspecific protein adsorption compared to SAMs. This improvement is due to an increase in the surface packing density of nonfouling groups on the surface, as well as a steric repulsion from the flexible polymer brush surfaces. The zwitterionic polymer surface based on carboxybetaine methacrylate (CBMA) also incorporates functional groups for protein immobilization in the nonfouling background, making it a strong candidate for many applications such as in diagnostics and drug delivery.
This work describes the superlow fouling properties of glass slides grafted with zwitterionic polymers to highly resist the adsorption of proteins and the adhesion of mammalian cells. Glass slides were first silanized using 2-bromo-2-methyl-N-3-[(triethoxysilyl)propyl]propanamide (BrTMOS). Two zwitterionic polymers, poly(sulfobetaine methacrylate) (polySBMA) and poly(carboxybetaine methacrylate) (polyCBMA), were then grafted from the silanized glass substrates using the atom-transfer radical polymerization (ATRP) method. X-ray photoelectron spectroscopy (XPS) was used to analyze the surfaces of the silanized glass substrates and the substrates grafted with the polymers. An enzyme-linked immonosobrbent assay (ELISA) using polyclonal antibodies was used to measure fibrinogen adsorption on these surfaces. The surfaces with polySBMA or polyCBMA layers were shown to reduce fibrinogen adsorption to a level comparable with that of adsorption on poly(ethylene glycol)-like films. Bovine aortic endothelial cells (BAECs) were seeded on these surfaces. The attachment and spreading of the cells were observed only on unpolymerized glass surfaces. This work further demonstrates that zwitterionic polymers highly resist nonspecific protein adsorption and cell adhesion and provides an effective method to modify glass slides or other oxide surfaces to achieve superlow fouling.
In this work, we report a study of long-chain zwitterionic poly(sulfobetaine methacrylate) (pSBMA) surfaces grafted via atom transfer radical polymerization (ATRP) for their resistance to bacterial adhesion and biofilm formation. Previously, we demonstrated that p(SBMA) is highly resistant to nonspecific protein adsorption. Poly(oligo(ethylene glycol) methyl ether methacrylate) (pOEGMA) grafted surfaces were also studied for comparison. Furthermore, we quantify how surface grafting methods will affect the long-term biological performance of the surface coatings. Thus, self-assembled monolayers (SAMs) of alkanethiols with shorter-chain oligo(ethylene glycol) (OEG) and mixed SO 3 − /N + (CH 3 ) 3 terminated groups were prepared on gold surfaces. The short-term adhesion (3 h) and the long-term accumulation (24 h or 48 h) of two bacterial species (Gram-positive Staphylococcus epidermidis and Gram-negative Pseudomonas aeruginosa) on these surfaces were studied using a laminar flow chamber. Methyl (CH 3 ) SAM on gold and a bare glass were chosen as references. p(SBMA) reduced short-term adhesion of S. epidermidis and P. aeruginosa relative to glass by 92% and 96%, respectively. For long-term biofilm formation, qualitative images showed that p(SBMA) dramatically reduced biofilm formation of S. epidermidis and P. aeruginosa as compared to glass.
The emergence of Turing structures is of fundamental importance, and designing these structures and developing their applications have practical effects in chemistry and biology. We use a facile route based on interfacial polymerization to generate Turing-type polyamide membranes for water purification. Manipulation of shapes by control of reaction conditions enabled the creation of membranes with bubble or tube structures. These membranes exhibit excellent water-salt separation performance that surpasses the upper-bound line of traditional desalination membranes. Furthermore, we show the existence of high water permeability sites in the Turing structures, where water transport through the membranes is enhanced.
One of the sulfobetaine methacrylate (SBMA) monomers, N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine, was polymerized onto initiator-covered gold surfaces using atom transfer radical polymerization (ATRP) to form uniform polymer brushes. Self-assembled monolayers (SAMs) with ATRP initiators were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The thickness of grafted poly(SBMA) films was measured by ellipsometry. Fibrinogen adsorption on poly(SBMA) grafted surfaces was measured with a surface plasmon resonance (SPR) sensor. Two approaches were compared to graft ATRP initiators onto gold surfaces for surface polymerization and subsequent protein adsorption on these polymer grafted surfaces. The first was to prepare a SAM from omega-mercaptoundecyl bromoisobutyrate onto a gold surface. Superlow fouling surfaces with well-controlled poly(SBMA) brushes were achieved using this approach (e.g., fibrinogen adsorption <0.3 ng/cm2). The second approach was to react bromoisobutyryl bromide with a hydroxyl-terminated SAM on a gold surface. Although protein adsorption decreased as the density of surface initiators increased, the surface prepared using the second approach was not able to achieve as low protein adsorption as the first approach. Key parameters to achieve superlow fouling surfaces were studied and discussed.
A study of protein resistance of oligo(ethylene glycol) (OEG), HS(CH2)11(OCH2CH2)nOH (n = 2, 4, and 6), self-assembled monolayers (SAMs) on Au(111) surfaces is presented here. Hydroxyl-terminated OEG-SAMs are chosen to avoid the hydrophobic effect observed with methyl-terminated OEG-SAMs, particularly at high packing densities. The structure of the OEG-SAM surfaces is controlled by adjusting the assembly solvent. These SAMs were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Protein adsorption on these surfaces was investigated by surface plasmon resonance (SPR). OEG-SAMs assembled from mixed ethanol and water solutions show higher packing density on gold than those from pure ethanol solution. For EG2OH- and EG4OH-SAMs, proteins (i.e., fibrinogen and lysozyme) adsorb more on the densely packed SAMs prepared from mixed ethanol and water solutions, while EG6OH-SAMs generally resist protein adsorption regardless of the assembly solvent used.
In this work, we report a systematic study of zwitterionic poly(carboxybetaine methacrylate) (pCBMA) grafted from glass surfaces via atom transfer radical polymerization (ATRP) for their resistance to long-term bacterial biofilm formation. Results show that pCBMA-grafted surfaces are highly resistant to nonspecific protein adsorption (fibrinogen and undiluted blood plasma) at 25, 30 and 37 °C. Long-term (over 24 h) colonization of two bacterial strains (Pseudomonas aeruginosa PAO1 and Pseudomonas putida strain 239) on pCBMA surface was studied using a parallel flow cell at 25, 30 and 37 °C. Uncoated glass cover slips were chosen as the positive reference. Results show that pCBMA coatings reduced long-term biofilm formation of P. aeruginosa up to 240 h by 95% at 25 °C and for 64 h by 93% at 37 °C, and suppressed P. putida biofilm accumulation up to 192 h by 95% at 30 °C, with respect to the glass reference. The ability of pCBMA coatings to resist non-specific protein adsorption and significantly retard bacterial biofilm formation makes it a very promising material for biomedical and industrial applications.
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