Investigation of the interaction between poly(ethylene glycol) and protein molecules using low field nuclear magnetic resonance

Ultra-high-performance liquid chromatography with tandem mass spectrometry method for cellular toxicity and pharmacokinetic study of PEG1K polymers

Polyethylene glycol (PEG) is one of the most commonly used polymers in drug delivery systems. The investigation of the pharmacokinetic behavior of PEG is important for revealing the toxicity and efficiency of PEG-related Nano-drug delivery systems. A high through-put and selective ultra-high-performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) method coupled with collision-induced dissociation (CID) in source technique was developed and validated to determine PEG1K polymers in cellular samples in this study. The countless precursor ions of PEG1K are dissociated in the source to generate numerous product ions which have different numbers of subunits. The transition of [M+H]+ precursor ions → product ions at m/z 177.1 (four subunits)→89.1 (two subunits) was selected to determine PEG1K due to its high sensitivity. The UHPLC-MS/MS method coupled with CID in the source showed good linearity over the range of 0.1-10 μg/mL. Intra-day and inter-day accuracies and precisions of the assay were all within ± 12.39%. The assay was successfully applied to a cellular pharmacokinetic study of PEG1K in human breast cancer cells. The cytotoxicity of PEG1K polymers was also studied and the results indicated that the cytotoxicity of PEG1K was not significant in the range of 5-1200 μg/mL.

Multiscale Spectral Analysis on Lysozyme Aqueous Solutions in the Presence of PolyEthyleneGlycol

Infrared spectroscopy measurements were performed on Lysozyme aqueous solutions also in the presence of PolyEthylene Glycol (PEG 400) as a function of an increasing temperature from T = 27 °C to 90 °C, and, successively in sequence, by decreasing temperatures from T = 90 °C to 27 °C. Data were analyzed by evaluating the spectral difference with respect to the initial spectrum collected at 27 °C. This procedure allows to quantitatively evaluate the thermal restraint related to the thermal scan from T = 27 °C to 90 °C, as well as to introduce a spectral resilience concerning the entire increasing and decreasing thermal paths which allow to highlight the bioprotectant effectiveness of low molecular weight PEG. In particular, the main purpose of the present work is to highlight the effects of a thermal treatment on a mixture of Lysozyme/water and of Lysozyme/water/PEG 400 during an increasing temperature scan, and then after a successive decreasing temperature scan, in order to highlight the bioprotectant role of PEG 400. On that score, an evaluation of the spectral distances of the registered spectra as a function of increasing and decreasing temperatures has been performed and analyzed.

Quantification of Polyethylene Glycol 400 Excreted in the Urine by MALDI-TOF Mass Spectrometry

Polyethylene glycol 400 (PEG 400) was used as a permeability probe to examine the gastrointestinal tract which can be involved in the pathogenesis of some inflammatory and autoimmune diseases. A novel methodology was developed and validated for the quantitation of PEG 400 excreted in human urine after oral administration using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The excretion ratios were determined for the most intense ions corresponding to nine PEG 400 oligomers. The relative error of accuracy was between –6.0% and 8.5%, and the relative standard deviation (RSD) of the precision was below 15%. Our method was successfully applied in a large-scale experimental study involving nearly two hundred volunteers. Due to the large number of measurements, detailed and reliable statistical analysis was performed. No significant difference was found between the male and female group of volunteers at 0.05 significance level, except the two largest PEG oligomers. However, the average excretion ratios of the male volunteers are greater than that of the women for all the nine PEG oligomers, suggesting a difference in the intestinal permeability between men and women.

Accurate Correction of the "Bulk Response" in Surface Plasmon Resonance Sensing Provides New Insights on Interactions Involving Lysozyme and Poly(ethylene glycol)

Surface plasmon resonance is a very well-established surface sensitive technique for label-free analysis of biomolecular interactions, generating thousands of publications each year. An inconvenient effect that complicates interpretation of SPR results is the “bulk response” from molecules in solution, which generate signals without really binding to the surface. Here we present a physical model for determining the bulk response contribution and verify its accuracy. Our method does not require a reference channel or a separate surface region. We show that proper subtraction of the bulk response reveals an interaction between poly(ethylene glycol) brushes and the protein lysozyme at physiological conditions. Importantly, we also show that the bulk response correction method implemented in commercial instruments is not generally accurate. Using our method, the equilibrium affinity between polymer and protein is determined to be K_D = 200 μM. One reason for the weak affinity is that the interaction is relatively short-lived (1/k_off < 30 s). Furthermore, we show that the bulk response correction also reveals the dynamics of self-interactions between lysozyme molecules on surfaces. Besides providing new insights on important biomolecular interactions, our method can be widely applied to improve the accuracy of SPR data generated by instruments worldwide.

Recent Advances in Zwitterionic Hydrogels: Preparation, Property, and Biomedical Application

Nonspecific protein adsorption impedes the sustainability of materials in biologically related applications. Such adsorption activates the immune system by quick identification of allogeneic materials and triggers a rejection, resulting in the rapid failure of implant materials and drugs. Antifouling materials have been rapidly developed in the past 20 years, from natural polysaccharides (such as dextran) to synthetic polymers (such as polyethylene glycol, PEG). However, recent studies have shown that traditional antifouling materials, including PEG, still fail to overcome the challenges of a complex human environment. Zwitterionic materials are a class of materials that contain both cationic and anionic groups, with their overall charge being neutral. Compared with PEG materials, zwitterionic materials have much stronger hydration, which is considered the most important factor for antifouling. Among zwitterionic materials, zwitterionic hydrogels have excellent structural stability and controllable regulation capabilities for various biomedical scenarios. Here, we first describe the mechanism and structure of zwitterionic materials. Following the preparation and property of zwitterionic hydrogels, recent advances in zwitterionic hydrogels in various biomedical applications are reviewed.

Protein folding and assembly in confined environments: Implications for protein aggregation in hydrogels and tissues

In the biological milieu of a cell, soluble crowding molecules and rigid confined environments strongly influence whether the protein is properly folded, intrinsically disordered proteins assemble into distinct phases, or a denatured or aggregated protein species is favored. Such crowding and confinement factors act to exclude solvent volume from the protein molecules, resulting in an increased local protein concentration and decreased protein entropy. A protein's structure is inherently tied to its function. Examples of processes where crowding and confinement may strongly influence protein function include transmembrane protein dimerization, enzymatic activity, assembly of supramolecular structures (e.g., microtubules), nuclear condensates containing transcriptional machinery, protein aggregation in the contexts of disease and protein therapeutics. Historically, most protein structures have been determined from pure, dilute protein solutions or pure crystals. However, these are not the environments in which these proteins function. Thus, there has been an increased emphasis on analyzing protein structure and dynamics in more "in vivo-like" environments. Complex in vitro models using hydrogel scaffolds to study proteins may better mimic features of the in vivo environment. Therefore, analytical techniques need to be optimized for real-time analysis of proteins within hydrogel scaffolds.

pH-Dependent Nitrotyrosine Formation in Ribonuclease A is Enhanced in the Presence of Polyethylene Glycol (PEG)

Protein nitration can occur as a result of peroxynitrite-mediated oxidative stress. Excess production of peroxynitrite (PN) within the cellular medium can cause oxidative damage to biomolecules. The in vitro nitration of Ribonuclease A (RNase A) results in nitrotyrosine (NT) formation with a strong dependence on the pH of the medium. In order to mimic the cellular environment in this study, PN-mediated RNase A nitration has been carried out in a crowded medium. The degree of nitration is higher at pH 7.4 (physiological pH) compared to pH 6.0 (tumor cell pH). The extent of nitration increases significantly when PN is added to RNase A in the presence of crowding agents PEG 400 and PEG 6000. PEG has been found to stabilize PN over a prolonged period, thereby increasing the degree of nitration. NT formation in RNase A also results in a significant loss in enzymatic activity.

Impact of soft protein interactions on the excretion, extent of receptor occupancy and tumor accumulation of ultrasmall metal nanoparticles: a compartmental model simulation

Ultrasmall metal nanoparticles (NPs) are next-generation nano-based platforms for in vivo disease diagnosis and treatment. Due to their small size below the kidney filtration threshold and marked resistance to nonspecific serum protein adsorption, ultrasmall NPs can be rapidly excreted through the kidneys and escape liver uptake. However, although ultrasmall particles may be deemed highly resistant to protein adsorption, the real extent of this resistance is not known. Here, a simple compartmental model simulation was therefore implemented to understand how NP behavior in vivo could be modulated by soft, transient NP-plasma protein interactions characterized by dissociation constants in the millimolar range. In Model 1, ultrasmall NPs functionalized with a targeting probe, plasma proteins and target receptors were assumed to co-exist within a single compartment. Simulations were performed to understand the synergistic effect of soft interactions, systemic clearance and NP size on receptor occupancy in the single compartment. The results revealed the existence of a narrow range of ultraweak affinities and optimal particle sizes leading to greater target occupancy. In Model 2, simulations were performed to understand the impact of soft interactions on NP accumulation into a peripheral (tumor) compartment. The results revealed that soft interactions - but not active targeting - enhanced tumor uptake levels when tumor accumulation was limited by 'fast' plasma clearance and 'slow' vascular extravasation. The simple model presented here provides a basic framework to quantitatively understand the blood and tumor pharmacokinetics of ultrasmall NPs under the influence of transient protein interactions.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

Chaperone-like activity of the N-terminal region of a human small heat shock protein and chaperone-functionalized nanoparticles

Small heat shock proteins (sHsps) are molecular chaperones employed to interact with a diverse range of substrates as the first line of defense against cellular protein aggregation. The N-terminal region (NTR) is implicated in defining features of sHsps; notably in their ability to form dynamic and polydisperse oligomers, and chaperone activity. The physiological relevance of oligomerization and chemical-scale mode(s) of chaperone function remain undefined. We present novel chemical tools to investigate chaperone activity and substrate specificity of human HspB1 (B1NTR), through isolation of B1NTR and development of peptide-conjugated gold nanoparticles (AuNPs). We demonstrate that B1NTR exhibits chaperone capacity for some substrates, determined by anti-aggregation assays and size-exclusion chromatography. The importance of protein dynamics and multivalency on chaperone capacity was investigated using B1NTR-conjugated AuNPs, which exhibit concentration-dependent chaperone activity for some substrates. Our results implicate sHsp NTRs in chaperone activity, and demonstrate the therapeutic potential of sHsp-AuNPs in rescuing aberrant protein aggregation.

Computational studies of micellar and nanoparticle nanomedicines

The review highlights recent computational modeling of micellar and nanoparticle nanomedicines, which elucidates their functional roles in atomistic details.

PEG and mPEG-anthracene conjugate with trypsin and trypsin inhibitor: hydrophobic and hydrophilic contacts

The conjugation of trypsin (try) and trypsin inhibitor (tryi) with poly(ethylene glycol) (PEG) and methoxypoly(ethylene glycol) anthracene (mPEG-anthracene) was investigated in aqueous solution, using multiple spectroscopic methods, thermodynamic analysis, and molecular modeling. Thermodynamic parameters ΔS, ΔH, and ΔG showed protein-PEG bindings occur via H-bonding and van der Waals contacts with trypsin inhibitor forming more stable conjugate than trypsin. As polymer size increased more stable PEG-protein conjugate formed, while hydrophobic mPEG-anthracene forms less stable protein complexes. Modeling showed the presence of several H-bonding contacts between polymer and amino acids that stabilize protein-polymer conjugation. Polymer complexation induces more perturbations of trypsin inhibitor structure than trypsin with reduction of protein alpha-helix and major increase in random structures, indicating protein structural destabilization.

A bis-corannulene based molecular tweezer with highly sensitive and selective complexation of C70 over C60

A corannulene-based tweezer-like receptor was conveniently synthesized, which showed highly sensitive and selective complexation of C₇₀ over C₆₀.

Protein diffusion characteristics in the hydrogels of poly(ethylene glycol) and zwitterionic poly(sulfobetaine methacrylate) (pSBMA)

Nonfouling materials such as neutral poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) (pSBMA) are ideal biocompatible materials for drug, especially protein drug delivery. The interaction behavior of protein between the nonfouling materials could cause great impact on their future applications, such as controlled release drug delivery systems. In this work, we investigated the diffusion behavior of the fluorescence-labeled model proteins (bovine serum albumin (BSA) and lysozyme (LYZ)) in nonfouling PEG, pSBMA and mixed PEG-SBMA hydrogels (SBMA:PEG 4:1, SBMA:PEG 1:4). It was observed that these four hydrogels showed varied diffusion behavior for either negatively charged BSA or positively charged LYZ due to protein-polymer interaction and the free water content in hydrogel matrix. The relatively stronger interaction between protein-PEG than protein-pSBMA could increase protein loading efficiency and control release rate by changing ratio of PEG to SBMA in the hybrid hydrogel. Moreover, it is further demonstrated the free water (freezable water) content in low cross-linked hydrogel, not the equilibrium water content (EWC), is a more accurate parameter to reflect the diffusion behavior of protein molecules. Thus, these results together provide new insights of the interactions between protein molecules and nonfouling polymers as well as the bio applications of the nonfouling polymeric hydrogels.

STATEMENT OF SIGNIFICANCE

This work shows that the relative stronger interaction between protein-PEG than protein-pSBMA could increase protein loading efficiency and control release rate by the change ratio of PEG to SBMA in the hydrogel, while the free water (freezable water) content in low cross-linked hydrogel, not the equilibrium water content (EWC), is a more accurate parameter to reflect the diffusion behavior of protein molecules. The impact of this work (i) gains some new insights of the interactions between protein molecules and nonfouling polymer matrixes for protein drug delivery; (ii) prompts to apply the weak PEG-protein interactions to protein drug loading and release; (iii) provides a new fundamental understanding of free water in hydrogel for protein diffusion.

Development of Long-Circulating Zwitterionic Cross-Linked Micelles for Active-Targeted Drug Delivery

Blood stability, active targeting, and controlled drug release are the most important features to design desirable drug carriers. Here, we demonstrate a zwitterionic biodegradable cross-linked micelle based on a penta-block copolymer, which utilizes poly(carboxybetaine methacrylate) as hydrophilic segment, poly(ε-caprolactone) as biodegradable hydrophobic segment, poly(S-2-hydroxyethyl-O-ethyl dithiocarbonate methacrylate) (PSODMA) block as thiol protecting segment for cross-linking, and cyclic Arg-Gly-Asp-d-Tyr-Lys [c(RGDyK)] as targeting ligand. As a result, this micelle possessed excellent colloidal stability at high dilution and in 50% fetal bovine serum. In vitro drug release experiment showed no burst release under physiological conditions but accelerated drug release in mimicking tumor tissue environment. In vivo tests showed that the drug-loaded micelles had prolonged half-life in bloodstream, enhanced therapeutic efficiency, and reduced cardiac toxicity and biotoxicity compared with free drug formulation. Taken together, the reported c(RGDyK)-modified zwitterionic interfacially cross-linked micelle has emerged as an appealing platform for cancer therapy.

Characterization of water state and distribution in fibre materials by low-field nuclear magnetic resonance

The states of absorbed water in the cotton and PET fibres materials characterized by LF-NMR method.

Stabilization of Chromobacterium viscosum Lipase (CVL) Against Ultrasound Inactivation by the Pretreatment with Polyethylene Glycol (PEG)

Although ultrasound has been used to accelerate many enzymatic reactions, the low stability of enzymes in such a system still remains a critical issue, limiting its industrial application. Here, we have reported that polyethylene glycol (PEG) pretreatment stabilized Chromobacterium viscosum lipase (CVL) in ultrasound-assisted water-isooctane emulsion. PEGs of different molecular weights and concentrations were used to pretreat CVL, and the pretreated lipase activities for olive oil hydrolysis were investigated at different ultrasonic powers. The best result was attained with PEG400 at 100 mg/ml for a lipase concentration of 0.02 mg/ml and an ultrasonic power of 106 W. The half-life time of PEG400-treated lipase at 106 W was 54 min, a 27-fold higher than that attained using untreated lipase. Circular dichroism (CD) spectra suggested that PEG increased the rigidity of CVL structure, which favored the lipase stability against ultrasound inactivation. These results have important implications for the exploitation of ultrasound in biocatalytic process.

Probing the Surface Hydration of Nonfouling Zwitterionic and PEG Materials in Contact with Proteins

Zwitterionic polymers and poly(ethylene glycol) (PEG) have been reported as promising nonfouling materials, and strong surface hydration has been proposed as a significant contributor to the nonfouling mechanism. Better understanding of the similarity and difference between these two types of materials in terms of hydration and protein interaction will benefit the design of new and effective nonfouling materials. In this study, sum frequency generation (SFG) vibrational spectroscopy was applied for in situ and real-time assessment of the surface hydration of the sulfobetaine methacrylate (SBMA) and oligo(ethylene glycol) methacrylate (OEGMA) polymer brushes, denoted as pSBMA and pOEGMA, in contact with proteins. Whereas a majority of strongly hydrogen-bonded water was observed at both pSBMA and pOEGMA surfaces, upon contact with proteins, the surface hydration of pSBMA remained unaffected, but the water ordering at the pOEGMA surface was disturbed. The effects of free sulfobetaine, free PEG chains with two different molecular weights, and PEG coated gold nanoparticles on the surface hydration of proteins were investigated. The results indicated that free sulfobetaine could strengthen the protein hydration layer, but free PEG chains greatly disrupt the protein hydration layer and likely directly interact with the protein molecules. In contrast to free PEG, the PEG chains anchored on the nanoparticles behave similarly to the pOEGMA surface and could induce strong hydrogen bonding of the water molecules at the protein surfaces.

Effect of mucoadhesive polymers on the in vitro performance of insulin-loaded silica nanoparticles: Interactions with mucin and biomembrane models

The present paper focuses on the development and characterization of silica nanoparticles (SiNP) coated with hydrophilic polymers as mucoadhesive carriers for oral administration of insulin. SiNP were prepared by sol-gel technology under mild conditions and coated with different hydrophilic polymers, namely, chitosan, sodium alginate or poly(ethylene glycol) (PEG) with low and high molecular weight (PEG 6000 and PEG 20000) to increase the residence time at intestinal mucosa. The mean size and size distribution, association efficiency, insulin structure and insulin thermal denaturation have been determined. The mean nanoparticle diameter ranged from 289 nm to 625 nm with a PI between 0.251 and 0.580. The insulin association efficiency in SiNP was recorded above 70%. After coating, the association efficiency of insulin increased up to 90%, showing the high affinity of the protein to the hydrophilic polymer chains. Circular dichroism (CD) indicated that no conformation changes of insulin structure occurred after loading the peptide into SiNP. Nano-differential scanning calorimetry (nDSC) showed that SiNP shifted the insulin endothermic peak to higher temperatures. The influence of coating on the interaction of nanoparticles with dipalmitoylphosphatidylcholine (DPPC) biomembrane models was also evaluated by nDSC. The increase of ΔH values suggested a strong association of non-coated SiNP and those PEGylated nanoparticles coated with DPPC polar heads by forming hydrogen bonds and/or by electrostatic interaction. The mucoadhesive properties of nanoparticles were examined by studying the interaction with mucin in aqueous solution. SiNP coated with alginate or chitosan showed high contact with mucin. On the other hand, non-coated SiNP and PEGylated SiNP showed lower interaction with mucin, indicating that these nanoparticles can interdiffuse across mucus network. The results of the present work provide valuable data in assessing the in vitro performance of insulin-loaded SiNP coated with mucoadhesive polymers.

Effects of synthetic biomacromolecule addition on the flow behavior of concentrated mesenchymal cell suspensions

In the fields of tissue engineering and regenerative medicine, many researchers and companies alike are investigating the utility of concentrated mesenchymal stem cell suspensions as therapeutic injectables, with the hope of regenerating the damaged tissue site. These cells are seldom used alone, being instead combined with synthetic biomacromolecules, such as branched poly(ethylene glycol) (PEG) polymers, in order to form cross-linked hydrogels postinjection. In this article, we present the results of a detailed experimental and analytical investigation into the impacts of a range of eight-arm PEG polymers, each presenting functional end groups, on the rheological properties of concentrated living cells of mesenchymal origin. Using two-photon confocal microscopy, we confirmed that the aggregates formed by the cells are fractal structures, the dimension of which changed with PEG polymer type addition. From these results and the observed substantial variation in rheological footprint with increasing volume fraction and different PEG polymer type, we propose a number of mechanisms driving such structural changes. Lastly, we derived a modified Krieger-Dougherty model to produce a master curve for the relative viscosity as a function of volume fraction over the range of conditions investigated (including shear stress and PEG polymer type), from which we extract the adhesion force between individual cells within these concentrated suspensions. The outcomes of this study provide new insights into the complex interactions occurring in concentrated mesenchymal cell suspensions when combined with synthetic biomacromolecules commonly used as precursors in tissue engineering hydrogels, highlighting their substantial impacts on the resultant rheological footprint.

Biocompatible long-circulating star carboxybetaine polymers

Polyethylene glycol (PEG) is considered to be the most effective material to prolong the circulation time of nanoparticles by reducing non-specific protein adsorption in blood. However, it is recognized that PEG decomposes in most physiological solutions, and an anti-PEG antibody has been detected in some normal blood donors as a response to injection with PEGylated polymer particles. Zwitterionic polymers are potential alternatives to PEG for biomedical applications because of their super resistance to non-specific protein adsorption. Thus, finding one polymer with a long circulation time and resistance to the immune response is of significant importance. Here, we prepared four star carboxybetaine polymers of different molecular weights via atom transfer radical polymerization (ATRP) from a β-cyclodextrin (β-CD) initiator for investigating the biocompatibility of carboxybetaine polymer, a typical zwitterionic polymer. The circulation half-life of the largest star polymer (123 kDa) in mice was prolonged to 40 h in vivo, with no appreciable damage or inflammation observed in the major organ tissues. Furthermore, the circulation time of repeat injections showed similar results to the first injection, with no obvious increase in the amount of antibody in blood. The internalization of the star carboxybetaine polymers by macrophage cells was a relatively slow process. The high cell viability in the presence of star carboxybetaine polymers up to 2 mg mL^-1 was maintained. The hemolytic activity of the star carboxybetaine polymers at 5 mg mL^-1 was almost undetectable. In vitro results prove a key prediction of excellent biocompatibility in vivo. All the results suggest that the carboxybetaine polymer, perhaps even most of the zwitterionic ones, might be a good alternative to PEG in the development of a drug delivery system.

Binding characteristics between polyethylene glycol (PEG) and proteins in aqueous solution

Polymer-protein interactions are crucial for determining the activity of both polymer and protein for many bio-related applications. Poly(ethylene glycol) (PEG) as a well-known antifouling material is often coated on surfaces to form highly solvated brushes, which exhibit excellent protein-repellent properties. However, unlike surface-induced antifouling effects, little is known about the intrinsic PEG-protein interactions in aqueous solution, which is an important yet neglected problem. Here, we investigate the interactions between PEG and proteins in aqueous solution using fluorescence spectroscopy, atomic force microscopy (AFM), and nuclear magnetic resonance (NMR). Two important characteristics, molecular weight of PEG and mass ratio of PEG : protein, are examined to determine the effect of each on PEG-protein interactions as well as binding characteristics between PEG and proteins. In contrast to too long and too short PEG chains, collective results have shown that PEG with optimal molecular weight (MW) is more capable of interacting with proteins, which induces the conformational change of proteins through more stable binding sites and stronger interactions with long chain PEG. Enhanced PEG-protein interactions are likely due to the change of hydrophilicity to amphiphilicity of PEG with increasing MW_PEG. In contrast to almost none or weak interactions of PEG surfaces with proteins, this work provides new evidence to demonstrate the existence of interactions between PEG and proteins in aqueous solution, which is important not only for better understanding of the structure-activity relationship of PEG both in solution and on surfaces, but also for the rational design of new PEG-based materials for specific applications.

Probing the weak interaction of proteins with neutral and zwitterionic antifouling polymers

Protein-polymer interactions are of great interest in a wide range of scientific and technological applications. Neutral poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) (pSBMA) are two well-known nonfouling materials that exhibit strong surface resistance to proteins. However, it still remains unclear or unexplored how PEG and pSBMA interact with proteins in solution. In this work, we examine the interactions between two model proteins (bovine serum albumin and lysozyme) and two typical antifouling polymers of PEG and pSBMA in aqueous solution using fluorescence spectroscopy, atomic force microscopy and nuclear magnetic resonance. The effect of protein:polymer mass ratios on the interactions is also examined. Collective data clearly demonstrate the existence of weak hydrophobic interactions between PEG and proteins, while there are no detectable interactions between pSBMA and proteins. The elimination of protein interaction with pSBMA could be due to an enhanced surface hydration of zwitterionic groups in pSBMA. New evidence is given to demonstrate the interactions between PEG and proteins, which are often neglected in the literature because the PEG-protein interactions are weak and reversible, as well as the structural change caused by hydrophobic interaction. This work provides a better fundamental understanding of the intrinsic structure-activity relationship of polymers underlying polymer-protein interactions, which are important for designing new biomaterials for biosensor, medical diagnostics and drug delivery applications.

Development of nonfouling polypeptides with uniform alternating charges by polycondensation of the covalently bonded dimer of glutamic acid and lysine

In this work, nonfouling polypeptides with homogenous alternating charges were synthesized by polycondensation of the covalently bonded dimer of glutamic acid (E) and lysine (K) (EK dimer) with benzyloxycarbonyl (Z)-protected side chains. This facile method successfully solved the uniformity problem of nonfouling peptides caused by the copolymerization of two different monomers and enabled the incorporation of various terminal functional groups for future applications. The molecular weights (MWs) of the nonfouling peptides can be easily controlled by the ratio of the terminal group, lipoic acid, to the EK dimer. The nonfouling peptides can form self-assembling monolayers (SAMs) on a gold surface through two terminal thiol groups, which were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and ellipsometry (ELL). The resistance to nonspecific protein adsorption, cell attachment and bacterial adhesion of these nonfouling peptide SAMs and the in vitro cytotoxicity and haemolytic activity of these peptides were also evaluated. The results show that the lowest relative protein adsorptions of antibody (anti-IgG) and fibrinogen (Fg) on the SAMs are 5.1 ± 1.6% and 7.3 ± 1.8%, respectively, determined by enzyme-linked immunosorbent assay (ELISA), where the protein adsorption on a tissue culture polystyrene (TCPS) surface was set to 100%. Almost no obvious cell attachment and bacterial adhesion were observed, and no cytotoxicity and no haemolytic activity in vitro were detected. With the advantages of biocompatibility, biodegradability and the abundance of moieties for ligand immobilization, these nonfouling peptides developed by the facile method can be used in a wide range of biomedical applications.