Intermolecular Interaction of Polymer Brushes Containing Phosphorylcholine and Inverse-Phosphorylcholine

Honeycomb-Shaped Supermacroporous Adsorbent Integrating Size-Exclusion and Selective Chemisorption Enables High-Efficiency Extraction and Analysis of Exosomes from Plasma

As cell secretions, exosomes play an important role in disease diagnosis, but the extraction of high-purity exosomes from body fluids faces great challenges. To address this issue, this work creates an excellently selective adsorbent by modifying the zwitterionic polymer carrying choline phosphate on the surface of honeycomb-shaped supermacroporous silica, which integrates chemisorption and size-exclusion principles. The results indicate that the supermacropore with a thin pore wall allows exosomes to enter and thereby be adsorbed by the polymer via specific multivalent interaction and, meanwhile, excludes large cell debris and microvesicles. Moreover, the amphiphilic polymer can inhibit the adsorption of coexisting proteins. Taking advantage of these properties, the adsorbent can extract higher purity exosomes in a simpler way over "gold standard" ultracentrifugation and normal adsorbents. Furthermore, the in situ lysis of adsorbed exosomes simplifies the subsequent analysis and enhances the sensitivity. Consequently, 422 proteins are identified in the exosomes extracted from healthy human plasma, which is higher than that obtained by ultracentrifugation. For plasma from colorectal cancer patients, 62 upregulated and 165 downregulated proteins are identified and can be used as potential biomarkers. In conclusion, the adsorbent can serve as a platform for the high-efficiency extraction of exosomes in clinical diagnostic research.

Synthesis of Arsenocholine-Type Polycation Brush and Its Hydration Structure in Aqueous Solution

Arsenocholine-containing methacrylate (MTAsB) inspired by marine organisms was synthesized by the reaction of 2-bromoethyl methacrylate and trimethylarsine to investigate its polymerization behavior and the fundamental properties of the resulting polymer. Controlled radical polymerization of MTAsB proceeded in the presence of a copper catalyst and imidazolium chloride at 60 °C for 8 h to give a water-soluble polycation with a 94% yield. The smaller amount of nonfreezing water and intermediate water of poly(MTAsB) was observed compared with that of the ammonium-containing polycations. A poly(MTAsB) brush was also prepared on a silicon substrate to investigate its swelling structure in aqueous salt solution by scanning probe microscopy and neutron reflectivity measurements. The brush chains adopted a relatively extended conformation in pure water because of the Coulombic repulsion among the arsenic cation groups of the polyelectrolyte, while the brush formed a collapsed structure in aqueous solutions of Hofmeister series anions as a result of the screening effect by salt ions. In particular, thiocyanate ions induced a significant reduction in the swollen thickness of the brush, probably caused by the attractive interaction between arsenic cations and chaotropic thiocyanate ions. The salt concentration dependency of the poly(MTAsB) brush was similar to that of the ammonium-cation-type polyelectrolyte brushes.

Experimental and computational techniques to investigate the protein resistance of zwitterionic polymers

Most surfaces undergo non-specific protein adsorption upon direct contact with protein-containing environments, resulting in the formation of a protein corona, and the nature and composition of the corona affect the properties of the material. Zwitterionic polymers have oppositely charged groups in their repeating units, which facilitate the formation of a hydration layer on the surface through electrostatic interactions. The hydration layer possesses a strong water-binding ability and can prevent protein adsorption. Therefore, the hydration effect of zwitterionic polymers has become a research focus, and many researchers have investigated this mechanism using experimental and computational methods. This paper reviews the experimental techniques and simulation methods to study the hydration effect of zwitterionic polymers and the advantages and disadvantages of different techniques are discussed.

Reversible zwitterionic coordination enables rapid, high-yield, and high-purity isolation of extracellular vesicles from biofluids

Extracellular vesicles (EVs) hold great clinical value as promising diagnostic biomarkers and therapeutic agents. This field, however, is hindered by technical challenges in the isolation of EVs from biofluids for downstream purposes. We here report a rapid (<30 min) isolation method for EV extraction from diverse biofluids with yield and purity exceeding 90%. These high performances are ascribed to the reversible zwitterionic coordination between the phosphatidylcholine (PC) on EV membranes and the "PC-inverse" choline phosphate (CP) decorated on magnetic beads. By coupling this isolation method with proteomics, a set of differentially expressed proteins on the EVs were identified as potential colon cancer biomarkers. Last, we demonstrated that the EVs in various clinically relevant biofluids, such as blood serum, urine, and saliva, can also be isolated efficiently, outperforming the conventional approaches in terms of simplicity, speed, yield, and purity.

Trojan Horse Delivery of Spherical Nucleic Acid Probes into the Cytoplasm for High-Fidelity Imaging of MicroRNAs

We report a Trojan horse strategy to efficiently deliver the spherical nucleic acid probes (namely, nanoflares) into the cytoplasm for microRNA (miRNA) imaging with high fidelity, breaking through the cytoplasmic transport dilemma of RNA probes in living cells. The nanoflare is encapsulated into a "Trojan horse" consisting of zwitterionic choline phosphates (CPs) and acid-degradable crosslinkers; the former effectively promotes cell uptake and the latter triggers instantaneous liberation of the nanoflare probes from the lysosome to the cytoplasm. The exposed nanoflares in the cytoplasm can be lightened up by the target miRNAs specifically. Compared with the conventional nanoflares as well as the improved ones in previous reports, the "Trojan horse" nanoflares avoid nuclease degradation and thiol displacement during the delivery process, providing unprecedentedly high accuracy for intracellular miRNA imaging.

Characterization of Hydration Water Bound to Choline Phosphate-Containing Polymers

Zwitterionic methacrylate polymers with either choline phosphate (CP) (poly(MCP)) or phosphorylcholine (PC) (poly(MPC)) side groups were analyzed to characterize the bound hydration water molecules as nonfreezing water (NFW), intermediate water (IW), or free water (FW). This characterization was carried out by differential scanning calorimetry (DSC) of polymer/water systems, and the enthalpy changes of cold crystallization and melting were determined. The electron pair orientation of CP is opposite to that of PC, and the former binds the alkyl terminal groups at the phosphate esters. The numbers of NFW and IW molecules per monomer unit of poly(MCP) with an isopropyl terminal group were estimated to be 10.7 and 11.3 mol/mol, respectively, which were slightly greater than those of the poly(MCP) bearing an ethyl terminal group. More NFW and IW molecules hydrated the phosphobetaine polyzwitterions, poly(MCP) and poly(MPC), compared with carboxybetaine and sulfobetaine polymers. Moreover, the hydration states of polyelectrolytes were compared with the zwitterionic polymers. Finally, we discuss the relationship between the amount of hydration water and bio-inert properties.

Functional Polymer Zwitterions as Reactive Surfactants for Nanoparticle Capture

We describe the synthesis of sulfothetin (ST)-containing polymer zwitterions and their use as polymer surfactants for stabilizing emulsion droplets and for capturing and transporting nanoparticles (NPs) through a flowing aqueous fluid. In contrast to conventional zwitterions, which are chemically inert, the multifunctional ST-containing copolymers we describe both participate in droplet stabilization and embed reactive functionality directly into the zwitterionic framework. Advantageously including these ST zwitterions in phosphorylcholine (PC)-containing copolymers proved particularly useful for producing surfactants that contributed characteristics of droplet stabilization and interfacial reactivity. This was demonstrated by NP pickup, or "capture", experiments that were performed by circulating ST-coated emulsion droplets across a substrate, in a flow cell, containing amine-functionalized silica NPs. The resultant NP adherence to the fluid-fluid interface of the droplets hinged on the available reactivity of both the electrophilic (from ST) and nucleophilic (from the NPs) components as well as the solution pH and extent of amine functionality on the NPs.

Sulfobetaine Methacrylate Polymers of Unconventional Polyzwitterion Architecture and Their Antifouling Properties

Combining high hydrophilicity with charge neutrality, polyzwitterions are intensely explored for their high biocompatibility and low-fouling properties. Recent reports indicated that in addition to charge neutrality, the zwitterion's segmental dipole orientation is an important factor for interacting with the environment. Accordingly, a series of polysulfobetaines with a novel architecture was designed, in which the cationic and anionic groups of the zwitterionic moiety are placed at equal distances from the backbone. They were investigated by in vitro biofouling assays, covering proteins of different charges and model marine organisms. All polyzwitterion coatings reduced the fouling effectively compared to model polymer surfaces of poly(butyl methacrylate), with a nearly equally good performance as the reference polybetaine poly(3-(N-(2-(methacryloyloxy)ethyl)-N,N-dimethylammonio)propanesulfonate). The specific fouling resistance depended on the detailed chemical structure of the polyzwitterions. Still, while clearly affecting the performance, the precise dipole orientation of the sulfobetaine group in the polyzwitterions seems overall to be only of secondary importance for their antifouling behavior.

Effect of Dipole Orientation in Mixed, Charge-Equilibrated Self-assembled Monolayers on Protein Adsorption and Marine Biofouling

While zwitterionic interfaces are known for their excellent low-fouling properties, the underlying molecular principles are still under debate. In particular, the role of the zwitterion orientation at the interface has been discussed recently. For elucidation of the effect of this parameter, self-assembled monolayers (SAMs) on gold were prepared from stoichiometric mixtures of oppositely charged alkyl thiols bearing either a quaternary ammonium or a carboxylate moiety. The alkyl chain length of the cationic component (11-mercaptoundecyl)-N,N,N-trimethylammonium, which controls the distance of the positively charged end group from the substrate's surface, was kept constant. In contrast, the anionic component and, correspondingly, the distance of the negatively charged carboxylate groups from the surface was varied by changing the alkyl chain length in the thiol molecules from 7 (8-mercaptooctanoic acid) to 11 (12-mercaptododecanoic acid) to 15 (16-mercaptohexadecanoic acid). In this way, the charge neutrality of the coating was maintained, but the charged groups exposed at the interface to water were varied, and thus, the orientation of the dipoles in the SAMs was altered. In model biofouling studies, protein adsorption, diatom accumulation, and the settlement of zoospores were all affected by the altered charge distribution. This demonstrates the importance of the dipole orientation in mixed-charged SAMs for their inertness to nonspecific protein adsorption and the accumulation of marine organisms. Overall, biofouling was lowest when both the anionic and the cationic groups were placed at the same distance from the substrate's surface.

Hydration State Variation of Polyzwitterion Brushes through Interplay with Ions

Polyzwitterions have emerged as a new class of antifouling materials alternating poly(ethylene glycol). The exemplary biopassivation and lubrication behaviors are often attributed to the particular chemical structure of zwitterions, which involve a large dipole moment of the charged groups and a neutral net charge, while the hydration state and dynamics also associate with these characteristics. Polymer brushes composed of surface-tethered polyzwitterion chains produced by surface-initiated controlled radical polymerization have been developed as thin films which exhibit excellent antifouling and lubrication properties. In past decades, numerous studies have been devoted to examining the structure and dynamics of polyzwitterion brush chains in aqueous solutions. This feature article provides an overview of recent studies exploring the hydration state of polyzwitterion brushes with specular neutron reflectivity, highlights some newly published work on the nonuniform equilibrium structure, ion concentration dependence, ion specificity, and the effects of charge spacer length in the zwitterions, and discusses future perspective in this field.

Synthesis of a conductive polymer thin film having a choline phosphate side group and its bioadhesive properties

A conductive polymer thin film having choline phosphate as the side group was prepared. The polymer thin film can prevent bovine serum albumin binding while present nice fibroblast cell adhesion.

Engineering Antifouling Conducting Polymers for Modern Biomedical Applications

Conducting polymers are considered to be favorable electrode materials for implanted biosensors and bioelectronics, because their mechanical properties are similar to those of biological tissues such as nerve and brain tissues. However, one of the primary challenges for implanted devices is to prevent the unwanted protein adhesion or cell binding within biological fluids. The nonspecific adsorption generally causes the malfunction of implanted devices, which is problematic for long-term applications. When responding to the requirements of solving the problems caused by nonspecific adsorption, an increasing number of studies on antifouling conducting polymers has been recently published. In this review, synthetic strategies for preparing antifouling conducting polymers, including direct synthesis of functional monomers and post-functionalization, are introduced. The applications of antifouling conducting polymers in modern biomedical applications are particularly highlighted. This paper presents focuses on the features of antifouling conducting polymers and the challenges of modern biomedical applications.