Reconciling Low- and High-Salt Solution Behavior of Sulfobetaine Polyzwitterions

Dipole Theory of Polyzwitterion Microgels and Gels

The behavior of polyzwitterions, constituted by dipole-like zwitterionic monomers, is significantly different from that of uniformly charged polyelectrolytes. The origin of this difference lies in the intrinsic capacity of polyzwitterions to self-associate intramolecularly and associate with interpenetrating chains driven by dominant dipolar interactions. Earlier attempts to treat polyzwitterions implicitly assume that the dipoles of zwitterion monomers are randomly oriented. At ambient temperatures, the dipolar zwitterion monomers can readily align with each other generating quadrupoles and other multipoles and thus generating heterogeneous structures even in homogeneous solutions. Towards an attempt to understand the role of such dipolar associations, we present a mean field theory of solutions of polyzwitterions. Generally, we delineate a high-temperature regime where the zwitterion dipoles are randomly oriented from a low-temperature regime where quadrupole formation is significantly prevalent. We present closed-form formulas for: (1) Coil-globule transition in the low-temperature regime, the anti-polyelectrolyte effect of chain expansion upon addition of low molar mass salt, and chain relaxation times in dilute solutions. (2) Spontaneous formation of a mesomorphic state at the borderline between the high-temperature and low-temperature regimes and its characteristics. A universal law is presented for the radius of gyration of the microgel, as a proportionality to one-sixth power of the polymer concentration. (3) Swelling equilibrium of chemically cross-linked polyzwitterion gels in both the high temperature and low-temperature regimes. Addressing the hierarchical internal dynamics of polyzwitterion gels, we present a general stretched exponential law for the time-correlation function of gel displacement vector, that can be measured in dynamic light scattering experiments. The present theory is of direct experimental relevance and additional theoretical developments to all polyzwitterion systems, and generally to biological macromolecular systems such as intrinsically disordered proteins.

Short Zwitterionic Sulfobetaine-Modified Silica Nanoparticles: Is Neutrality Possible?

Zwitterionic coatings are an efficient strategy for preventing biomolecule adsorption and enhancing nanoparticle stability in solution. The properties of zwitterions and other antifouling materials, including suppression of nonspecific adsorption and improved colloidal stability of nanoparticles, are believed to derive from their electroneutral and highly hydrophilic nature. Among different zwitterions, short sulfobetaines have been demonstrated to be effective in preventing protein adsorption onto several nanoparticles and providing enhanced colloidal stability. Although zwitterionic sulfobetaine silane (ZS) is electrically neutral, the negatively charged zwitterionic sulfobetaine-functionalized silica nanoparticles (ZS@SiO2NPs) exhibit a similar ζ-potential to nonfunctionalized silica nanoparticles (SiO2NPs). In this work, we present a thorough comprehension of the surface properties of ZS@SiO2NPs, which encompasses the development of meticulous functionalization procedures, detailed characterization approaches, and cutting-edge modeling to address the questions that persist regarding the surface features of ZS@SiO2NPs. The negative charge of ZS@SiO2NPs is due to the stabilization of siloxide from residual surface silanols by the quaternary amine in the sulfobetaine structure. Consequently, we infer that zero-charge ZS@SiO2NPs are unlikely to be obtained since this stabilization increases the dissociation degree of surface silanols, increasing the overall structure negative charge. Additionally, colloidal stability was evaluated in different pH and ionic strength conditions, and it was found that ZS@SiO2NPs are more stable at higher ionic strengths. This suggests that the interaction between ZS and salt ions prevents the aggregation of ZS@SiO2NPs. Together, these results shed light on the nature of the ZS@SiO2NP negative charge and possible sources for the remarkable colloidal stability of zwitterionic nanoparticles in complex media.

The Effect of Block Ratio and Structure on the Thermosensitivity of Double and Triple Betaine Block Copolymers

AB-type and BAB-type betaine block copolymers composed of a carboxybetaine methacrylate and a sulfobetaine methacrylate, PGLBT-b-PSPE and PSPE-b-PGLBT-b-PSPE, respectively, were synthesized by one-pot RAFT polymerization. By optimizing the concentration of the monomer, initiator, and chain transfer agent, block extension with precise ratio control was enabled and a full conversion (~99%) of betaine monomers was achieved at each step. Two sets (total degree of polymerization: ~300 and ~600) of diblock copolymers having four different PGLBT:PSPE ratios were prepared to compare the influence of block ratio and molecular weight on the temperature-responsive behavior in aqueous solution. A turbidimetry and dynamic light scattering study revealed a shift to higher temperatures of the cloud point and micelle formation by increasing the ratio of PSPE, which exhibit upper critical solution temperature (UCST) behavior. PSPE-dominant diblocks created spherical micelles stabilized by PGLBT motifs, and the transition behavior diminished by decreasing the PSPE ratio. No particular change was found in the diblocks that had an identical AB ratio. This trend reappeared in the other set whose entire molecular weight approximately doubled, and each transition point was not recognizably impacted by the total molecular weight. For triblocks, the PSPE double ends provided a higher probability of interchain attractions and resulted in a more turbid solution at higher temperatures, compared to the diblocks which had similar block ratios and molecular weights. The intermediates assumed as network-like soft aggregates eventually rearranged to monodisperse flowerlike micelles. It is expected that the method for obtaining well-defined betaine block copolymers, as well as the relationship of the block ratio and the chain conformation to the temperature-responsive behavior, will be helpful for designing betaine-based polymeric applications.

Dual functional quaternary chitosans with thermoresponsive behavior: structure-activity relationships in antibacterial activity and biocompatibility

Cationically modified chitosan derivatives exhibit a range of appealing characteristics, with a particular emphasis on their antimicrobial potential across a broad spectrum of biomedical applications. This study aimed to delve deeper into quaternary chitosan (QC) derivatives. Through the synthesis of both homogeneously and heterogeneously dual-quaternized chitosan (DQC), utilizing AETMAC ([2-(acryloyloxy)ethyl]-trimethylammonium chloride) and GTMAC (glycidyl trimethylammonium chloride), a permanent charge was established, spanning a wide pH range. We assessed structural differences, the type of quaternary functional group, molecular weight (Mw), and charge density. Intriguingly, an upper critical solution temperature (UCST) behavior was observed in AETMAC-functionalized QC. To our knowledge, it is a novel discovery in cationically functionalized chitosan. These materials demonstrated excellent antimicrobial efficacy against model test organisms E. coli and P. syringae. Furthermore, we detected concentration-dependent cytotoxicity in NIH-3T3 fibroblasts. Striking a balance between antimicrobial activity and cytotoxicity becomes a crucial factor in application feasibility. AETMAC-functionalized chitosan emerges as the top performer in terms of overall antibacterial effectiveness, possibly owing to factors like molecular weight, charge characteristics, and variations in the quaternary linker. Quaternary chitosan derivatives, with their excellent antibacterial attributes, hold significant promise as antibacterial or sanitizing agents, as well as across a broad spectrum of biomedical and environmental contexts.

Correlation of Structure and Dynamics Behavior in Polyzwitterions: From Concentrated Solution to Gel-Like State

The dynamic behaviors of polyzwitterions, poly(4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulfonate) (PSBP), are investigated using dynamic light scattering, small angle X-ray scattering, and rheology.  The findings reveal two relaxation modes, including a fast and a slow mode, which  are observed in both solution state and gel-like state, with varying polyzwitterion concentration (CP ) and NaCl concentration (CNaCl ). As CP and CNaCl increasing, a slower slow mode and a faster fast mode are observed. The fast mode corresponds to the diffusion of chains, while the slow mode arises from chain aggregations. In solutions, the slow mode is dominated by the diffusion of chain aggregations. However, in the gel-like state, the "cage network" traps aggregations more densely, leading to their dynamic behavior being dominated by enhanced topological entanglements and ionic interactions. This difference highlights the unique nature of the slow relaxation mode between concentrated solution and gel-like state, arising from changes in the average distance between chain aggregations resulting from increased CP and CNaCl concentrations.

Molecular Dynamics Simulation of the Influence of Temperature and Salt on the Dynamic Hydration Layer in a Model Polyzwitterionic Polymer PAEDAPS

We investigate the hydration of poly(3-[2-(acrylamido) ethyldimethylammonio] propanesulfonate) over a range of temperatures in pure water and with the inclusion of 0.1 mol/L NaCl using atomistic molecular dynamics simulation. Drawing on concepts drawn from the field of glass-forming liquids, we use the Debye-Waller parameter () for describing the water mobility gradient around the polybetaine backbone extending to an overall distance ≈18 Å. The water mobility in this layer is defined through the mean-square water molecule displacement at a time on the order of water's β-relaxation time. The brushlike topology of polybetaines leads to two regions in the dynamic hydration layer. The inner region of ≈10.5 Å is explored by pendant group conformational motions, and the outer region of ≈7.5 Å represents an extended layer of reduced water mobility relative to bulk water. The dynamic hydration layer extends far beyond the static hydration layer, adjacent to the polymer.

Polyzwitterion fast and slow mode behavior are coupled to phase separation as observed by dynamic laser light scattering

A model zwitterionic polysulfobetaine, poly(3-(acrylamidopropyl-dimethyl-ammonium) propyl-1-sulfonate) (pAPAPS), phase separates upon cooling and exhibits an upper critical solution temperature (UCST) behavior with no added salt in deuterium oxide solutions. Dynamic light scattering measurements indicate the presence of distinct fast and slow diffusive modes, where the fast mode is interpreted as a collective diffusion coefficient and the slow mode is attributed to the diffusion of multi-chain dynamic clusters. The relative population of fast and slow modes varies systematically with temperature and concentration. A clustering temperature (T*) was assigned when the slow mode first appeared upon cooling. The slow mode then increases in relative scattering amplitude as the phase boundary is approached. The fast mode exhibits a concentration dependence above T* consistent with the virial expansion in the collective diffusion. The sign of the virial coefficient (kd) is negative, even in the good solvent region above the expected Flory temperature (Θ ≈ 39 °C), a behavior distinct from synthetic neutral polymers in organic solvents. The onset of multi-chain clustering at T < T* coincides with the poor solvent regime (T < Θ). Attractive dipolar interactions due to the zwitterionic sulfobetaine groups in pAPAPS are suggested as the origin of the multi-chain clusters with no salt. Upon the addition of 100 mM NaCl, the slow mode is suppressed, and the hydrodynamic radius is consistent with polyzwitterion chain dimensions in a dilute solution. We find that concentration dependent diffusion is highly linked to the theta temperature and the emergence of dynamic clusters as the polymer goes from good to poor solvent on approach to the UCST. The slow mode in the semidilute regime is reported along with preliminary small-angle neutron scattering data that show salt reduces clustering and leads to predominantly chain scattering.

Anti-polyelectrolyte and polyelectrolyte effects on conformations of polyzwitterionic chains in dilute aqueous solutions

Polyzwitterions (PZs) are considered as model synthetic analogs of intrinsically disordered proteins. Based on this analogy, PZs in dilute aqueous solutions are expected to attain either globular (i.e. molten, compact) or random coil conformations. Addition of salt is expected to open these conformations. To the best of our knowledge, these hypotheses about conformations of PZs have never been verified. In this study, we test these hypotheses by studying effects of added salt [potassium bromide (KBr)] on gyration and hydrodynamic radii of poly(sulfobetaine methacrylate) in dilute aqueous solutions using dynamic light scattering and small-angle X-ray scattering, respectively. Effects of zwitteration are revealed by direct comparisons of the PZs with the polymers of the same backbone but containing (1) no explicit charges on side groups such as poly(2-dimethylaminoethyl methacrylate)s and (2) explicit cationic side groups with tertiary amino bromide pendants. Zeta-potential measurements, transmission electron microscopy, and ab initio molecular dynamics simulations reveal that the PZs acquire net positive charge in near salt-free conditions due to protonation but retain coiled conformations. Added KBr leads to nonmonotonic changes exhibiting an increase followed by a decrease in radius of gyration (and hydrodynamic radius), which are called antipolyelectrolyte and polyelectrolyte effects, respectively. Charge regulation and screening of charge-charge interactions are discussed in relation to the antipolyelectrolyte and polyelectrolyte effects, respectively, which highlight the importance of salt in affecting net charge and conformations of PZs.

An electrochemically mediated ATRP synthesis of lignin-g-PDMAPS UCST-thermoresponsive polymer

It is a promising idea to graft zwitterionic polymers onto lignin and prepare lignin-grafted-poly [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (Lignin-g-PDMAPS) thermosensitive polymer with the upper critical solution temperature (UCST). In this paper, an electrochemically mediated atom transfer radical polymerization (eATRP) method was used to prepare Lignin-g-PDMAPS. The structure and property of the Lignin-g-PDMAPS polymer were characterized by the fourier transform infrared spectrum (FT-IR), nuclear magnetic resonance (NMR), X-ray electron spectroscopy (XPS), dynamic light scattering (DLS), differential scanning calorimeter (DSC). Furthermore, the effect of catalyst structure, applied potential, amount of Lignin-Br, Lignin-g-PDMAPS concentration, NaCl concentration on UCST of Lignin-g-PDMAPS were investigated. It was worth noting that polymerization was well controlled when the ligand was tris (2-aminoethyl) amine (Me₆TREN), applied potential was -0.38 V and the amount of Lignin-Br was 100 mg. And the UCST of the Lignin-g-PDMAPS aqueous solution (1 mg/ml) was 51.47 °C, the molecular weight was 8987 g/mol, and the particle size was 318 nm. It was also found that the UCST increased and the particle size decreased with the Lignin-g-PDMAPS polymer concentration increased, and the UCST decreased and the particle size increased with the NaCl concentration increases. This work investigated UCST-thermoresponsive polymer which possessed lignin main chain combining the zwitterionic side chain, and provided a new way for development of lignin based UCST-thermoresponsive materials and medical carrier materials, in addition to expand the scope of eATRP.

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.

Microporous Polyethersulfone Membranes Grafted with Zwitterionic Polymer Brushes Showing Microfiltration Permeance and Ultrafiltration Bacteriophage Removal

Virus removal from water using microfiltration (MF) membranes is of great interest but remains challenging owing to the membranes' mean pore sizes typically being significantly larger than most viruses. We present microporous membranes grafted with polyzwitterionic brushes (N-dimethylammonium betaine) that combine bacteriophage removal in the range of ultrafiltration (UF) membranes with the permeance of MF membranes. Brush structures were grafted in two steps: free-radical polymerization followed by atom transfer radical polymerization (ATRP). Attenuated total reflection Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) verified that grafting occurred at both sides of the membranes and that the grafting increased with increasing the zwitterion monomer concentration. The log reduction values (LRVs) of the pristine membrane increased from less than 0.5 LRV for T4 (∼100 nm) and NT1 (∼50 nm) bacteriophages to up to 4.5 LRV for the T4 and 3.1 LRV for the NT1 for the brush-grafted membranes with a permeance of about 1000 LMH/bar. The high permeance was attributed to a high-water fraction in the ultra-hydrophilic brush structure. The high measured LRVs of the brush-grafted membranes were attributed to enhanced bacteriophages exclusion from the membrane surface and entrapment of the ones that penetrated the pores due to the membranes' smaller mean pore-size and cross-section porosity than those of the pristine membrane, as seen by scanning electron microscopy (SEM) and measured using liquid-liquid porometry. Micro X-ray fluorescence (μ-XRF) spectrometry and nanoscale secondary ion mass spectrometry showed that 100 nm Si-coated gold nanospheres accumulated on the surface of the pristine membrane but not on the brush-coated membrane and that the nanospheres that penetrated the membranes were entrapped in the brush-grafted membrane but passed the pristine one. These results corroborate the LRVs obtained during filtration experiments and support the inference that the increased removal was due to a combined exclusion mechanism and entrapment. Overall, these microporous brush-grafted membranes show potential for use in advanced water treatment.

Influence of Ionic Strength and Specific Ion Effects on Polyelectrolyte Multilayer Films with pH-Responsive Behavior

Layer-by-layer assembled multilayer films have shown great potential for different applications owing to their responsive behavior. Herein, we systematically investigated the effects of composition, salt concentration, and ion specificity on the pH responsiveness of covalently crosslinked chitosan and alginate dialdehyde multilayer films. The changes in film swelling were measured using ellipsometry from low (0.01 mM) to high (3 M) salt (NaCl or NaSCN) concentrations at pH 3, 6, and 9. The swelling responses to increasing ionic strength matched the swelling responses observed for polyzwitterionic and weak monocomponent polyelectrolyte films and depended on the multilayer composition, pH, and ion specificity. Finally, we used the ellipsometric data to demonstrate that the pH responsiveness of such multilayer films, as measured using a quartz crystal microbalance with dissipation monitoring, strongly depends on the ionic condition under which the responses were measured. We thus show that erroneous conclusions about the pH responsiveness of polyelectrolyte multilayer films can be easily obtained if the ionic environment of the application does not closely resemble the ionic condition under which the pH responsiveness is tested.

LCST-UCST Transition Property of a Novel Retarding Swelling and Thermosensitive Particle Gel

Super absorbent resin particles used as profile control and water plugging agent remains a deficiency that the particles swells with high speed when absorbing water, resulting in low strength and limited depth of migration. To address this issue, we proposed a thermosensitive particle gel possessing the upper critical solution temperature (UCST), which was synthesized from hydrophobically modified poly(vinyl alcohol)s (PVA) with glutaraldehyde (GA) as a cross-linker. The structure of the hydrogel was characterized by Fourier transform infrared spectrophotometer (FTIR) and nuclear magnetic resonance (NMR). The thermosensitive-transparency measurement and swelling experiment show that the hydrophobic-modified PVA solutions and corresponding hydrogels exhibited thermosensitive phase transition behaviors with lower critical solution temperature (LCST) and UCST. The results indicated that the temperature-induced phase transition behavior of CHPVA hydrogels leads to their retarding swelling property and great potential as an efficient water plugging agent with excellent temperature and salt resistance.

Ion-Specific Antipolyelectrolyte Effect on the Swelling Behavior of Polyzwitterionic Layers

In this study, we systematically investigate the interactions between mobile ions generated from added salts and immobile charges within a sulfobetaine-based polyzwitterionic film in the presence of five salts (KCl, KBr, KSCN, LiCl, and CsCl). The sulfobetaine groups contain quaternary alkylammonium and sulfonate groups, giving the positive and negative charges. The swelling of the zwitterionic film in the presence of different salts is compared with the swelling behavior of a polycationic or polyanionic film containing the same charged groups. For such a comparative study, we design cross-linked terpolymer films with similar thicknesses, cross-link densities, and charge fractions, but with varying charged moieties. While the addition of salt in general leads to a collapse of both cationic and anionic films, the presence of specific types of mobile anions (Cl^-, Br^-, and SCN^-) considerably influences the swelling behavior of polycationic films. We attribute this observation to a different degree of ion-pair formations between the different types of anionic counterions and the immobile cationic quaternary alkylammonium groups in the films where highly polarizable counterions such as SCN^- lead to a high degree of ion pairing and less polarizable counterions, such as Cl^-, cause a low degree of ion pairing. Conversely, we do not observe any substantial effect of varying the type of cationic counterions (K⁺, Li⁺, and Cs⁺), which we assign to the lack of ion pairing between the weakly polarizable cations and the immobile anionic sulfonate groups in the films. In addition, we observe that the zwitterionic films swell with increasing ionic strength and the degree of swelling is anion dependent, which is in agreement with previous reports on the "antipolyelectrolyte effect". Herein, we explain this ion-specific swelling behavior with the different cation and anion abilities to form ion pairs with quaternary alkylammonium and sulfonate in the sulfobetaine groups.

Implantable biomedical materials for treatment of bone infection

The treatment of bone infections has always been difficult. The emergence of drug-resistant bacteria has led to a steady decline in the effectiveness of antibiotics. It is also especially important to fight bacterial infections while repairing bone defects and cleaning up dead bacteria to prevent biofilm formation. The development of biomedical materials has provided us with a research direction to address this issue. We aimed to review the current literature, and have summarized multifunctional antimicrobial materials that have long-lasting antimicrobial capabilities that promote angiogenesis, bone production, or "killing and releasing." This review provides a comprehensive summary of the use of biomedical materials in the treatment of bone infections and a reference thereof, as well as encouragement to perform further research in this field.

Dipole-driven interlude of mesomorphism in polyelectrolyte solutions

Uniformly charged polyelectrolyte molecules disperse uniformly in aqueous electrolyte solutions, due to electrostatic repulsion between them. In stark contrast to this well-established result of homogeneous polyelectrolyte solutions, we report a phenomenon where an aqueous solution of positively charged poly(L-lysine) (PLL) exhibits precipitation of similarly charged macromolecules at low ionic strength and a homogeneous solution at very high ionic strength, with a stable mesomorphic state of spherical aggregates as an interlude between these two limits. The precipitation at lower ionic strengths that is orthogonal to the standard polyelectrolyte behavior and the emergence of the mesomorphic state are triggered by the presence of a monovalent small organic anion, acrylate, in the electrolyte solution. Using light scattering, we find that the hydrodynamic radius R_h of isolated PLL chains shrinks upon a decrease in electrolyte (NaBr) concentration, exhibiting the "anti-polyelectrolyte effect." In addition, R_h of the aggregates in the mesomorphic state depends on PLL concentration c_p according to the scaling law, [Formula: see text]. Furthermore, at higher PLL concentration, the mesomorphic aggregates disassemble by a self-poisoning mechanism. We conjecture that all these findings can be attributed to both intra- and interchain dipolar interactions arising from the transformation of polycationic PLL into a physical polyzwitterionic PLL at higher concentrations of acrylate. The reported phenomenon of PLL exhibiting dipole-directed assembly of mesomorphic states and the anti-polyelectrolyte effect are of vital importance toward understanding more complex situations such as coacervation and formation of biomolecular condensates.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

Zwitterionic Polymers toward the Development of Orientation-Sensitive Bioprobes

Dynamics with an orientational degree of freedom are fundamental in biological events. Probes with polarized luminescence enable a determination of the orientation. Lanthanide-doped nanocrystals can provide more precise analysis than quantum dots due to the nonphotoblinking/bleaching nature and the multiple line-shaped emission. However, the intrinsic polarization property of the original nanocrystals often deteriorates in complex physiological environments because the colloidal stability easily breaks and the probes aggregate in the media with abundant salts and macromolecules. Engineering the surface chemistry of the probes is thus essential to be compatible with biosystems, which has remained a challenging task that should be exclusively addressed for each specific probe. Here, we demonstrate a facile and efficient surface functionalization of lanthanide-doped nanorods by zwitterionic block copolymers. Due to the steric interaction and the intrinsic zwitterionic nature of the polymers, high colloidal stability of the zwitterionic nanorod suspension is achieved over wide ranges of pH and concentration of salts, even giving rise to the lyotropic liquid crystalline behavior of the nanorods in physiological media. The shear-aligned ability is shown to be unaltered by the coated polymers, and thus, the strongly polarized emission of Eu³⁺ is preserved. Besides, biological experiments reveal good biocompatibility of the zwitterionic nanorods with negligible nonspecific binding. This study is a stepping stone for the use of the nanorods as orientation probes in biofluids and validates the strategy of coupling zwitterions to lanthanide-doped nanocrystals for various bioapplications.

Temperature dependent single-chain structure of poly[3-(acrylamidopropyl-dimethyl-ammonium) propyl-1-sulfonate] via small-angle neutron scattering

Responsive polyzwitterionic materials have become important for a range of applications such as environmental remediation and targeted drug delivery. Much is known about the macroscopic phase-behaviors of such materials, but how the smaller scale single-chain structures of polyzwitterions respond to external stimuli is not well understood, especially at temperatures close to their phase boundaries. Such chain conformation responses are important in directing larger-scale associative properties. Here, we study the temperature dependent single-chain structure of a model polysulfobetaine, poly[3-(acrylamidopropyl-dimethyl-ammonium) propyl-1-sulfonate], using small angle neutron scattering. In the absence of salt, we find that temperature has a large effect on solvent quality with a decreasing trend from good solvent conditions at 50 °C to poor solvent at 10 °C (a temperature just above the cloud point of 7.6 °C) and an estimated theta temperature of 39 °C. When 100 mM NaCl is present, the solvent quality is good with weak temperature dependence. Without salt present, the polymer chain appears to have a nearly Gaussian coil conformation and the backbone becomes slightly more rigid as the temperature is lowered to the cloud point as determined by the Debye-local rod model on a Kratky plot. The addition of salt has a notable effect on the intra-chain correlations where an increase in chain dimensions to a swollen coil conformation and an increase in chain rigidity is observed at 100 mM NaCl in D2O, however, with a negligible temperature dependence.

Designing the Surface Chemistry of Inorganic Nanocrystals for Cancer Imaging and Therapy

Inorganic nanocrystals, such as gold, iron oxide and semiconductor quantum dots, offer promising prospects for cancer diagnostics, imaging and therapy, due to their specific plasmonic, magnetic or fluorescent properties. The organic coating, or surface ligands, of these nanoparticles ensures their colloidal stability in complex biological fluids and enables their functionalization with targeting functions. It also controls the interactions of the nanoparticle with biomolecules in their environment. It therefore plays a crucial role in determining nanoparticle biodistribution and, ultimately, the imaging or therapeutic efficiency. This review summarizes the various strategies used to develop optimal surface chemistries for the in vivo preclinical and clinical application of inorganic nanocrystals. It discusses the current understanding of the influence of the nanoparticle surface chemistry on its colloidal stability, interaction with proteins, biodistribution and tumor uptake, and the requirements to develop an optimal surface chemistry.

Cell-membrane-inspired polymers for constructing biointerfaces with efficient molecular recognition

Fabrication of devices that accurately recognize, detect, and separate target molecules from mixtures is a crucial aspect of biotechnology for applications in medical, pharmaceutical, and food sciences. This technology has also been recently applied in solving environmental and energy-related problems. In molecular recognition, biomolecules are typically complexed with a substrate, and specific molecules from a mixture are recognized, captured, and reacted. To increase sensitivity and efficiency, the activity of the biomolecules used for capture should be maintained, and non-specific reactions on the surface should be prevented. This review summarizes polymeric materials that are used for constructing biointerfaces. Precise molecular recognition occurring at the surface of cell membranes is fundamental to sustaining life; therefore, materials that mimic the structure and properties of this particular surface are emphasized in this article. The requirements for biointerfaces to eliminate nonspecific interactions of biomolecules are described. In particular, the major issue of protein adsorption on biointerfaces is discussed by focusing on the structure of water near the interface from a thermodynamic viewpoint; moreover, the structure of polymer molecules that control the water structure is considered. Methodologies enabling stable formation of these interfaces on material surfaces are also presented.

Forces between mica and end-grafted statistical copolymers of sulfobetaine and oligoethylene glycol in aqueous electrolyte solutions

This study quantified the interfacial forces associated with end-grafted, statistical (AB) co-polymers of sulfobetaine methacrylate (SBMA) and oligoethylene glycol methacrylate (OEGMA) (poly(SBMA-co-OEGMA)). Surface force apparatus measurements compared forces between mica and end-grafted copolymers containing 0, 40, or 80 mol% SBMA. Studies compared forces measured at low grafting density (weakly overlapping chains) and at high density (brushes). At high density, the range of repulsive forces did not change significantly with increasing SBMA content. By contrast, at low density, both the range and the amplitude of the repulsion increased with the percentage of SBMA in the chains. The ionic strength dependence of the film thickness and repulsive forces increased similarly with SBMA content, reflecting the increasing influence of charged monomers and their interactions with ions in solution. The forces could be described by models of simple polymers in good solvent. However, the forces and fitted model parameters change continuously with the SBMA content. The latter behavior suggests that ethyene glycol and sulfobetaine behave as non-interacting, miscible monomers that contribute independently to the interfacial forces. The results suggest that molecular scale properties of statistical poly (SBMA-co-OEGMA) films can be readily tuned by simple variation of the monomer ratios.

Ionic strength dependent forces between end-grafted Poly(sulfobetaine) films and mica

The molecular surface properties of zwitterionic polymer coatings are central to their ultra-low fouling properties and effectiveness as steric stabilizers in concentrated salt solutions. Here, Surface Force Apparatus measurements quantified the molecular forces between end-grafted poly(sulfobetaine) methacrylate thin films and mica, as a function of the chain grafting density and ionic strength. These results demonstrate that, at the ionic strengths considered, end-grafted poly(sulfobetaine) films can be described by models for polymers in good solvent. Parameters determined from data fits to the Milner-Witten-Cates or Dolan and Edwards models for dense or dilute chains, respectively, varied with ionic strength, in ways that reflect poly(sulfobetaine) swelling and the increased excluded volume strength of chain segments. These force measurements provide new insight into how polymer coverage and salt cooperate to regulate repulsive poly(sulfobetaine) steric barriers. These findings have implications for the design of grafted poly(sulfobetaine) as colloidal stabilizers or nonfouling surface coatings.

Multiscale simulations of polyzwitterions in aqueous bulk solutions and brush array configurations

Zwitterionic polymers are very promising candidates for antifouling materials that exhibit high chemical stability as compared to polyethylene glycol-based systems. A number of simulation and experimental studies have emerged over recent years for the investigation of sulfobetaine-based zwitterionic polymers. Investigating the structural and thermodynamic properties of such polymers requires access to broad time and length regimes, thus necessitating the development of multiscale simulation strategies. The present article advocates a mesoscopic dissipative particle dynamics (DPD) model capable of addressing a wide range of time and length scales. The mesoscopic force field was developed hand-in-hand with atomistic simulations based on the OPLS force field through a bottom-up parameterization procedure that matches the atomistically calculated strand-length, strand-angle and pair distribution functions. The DPD model is validated against atomistic simulations conducted in this work, and against relevant atomistic simulation studies, theoretical predictions and experimental correlations from the literature. Properties examined include the conformations of SPE polymers in dilute bulk aqueous solution, the density profile and thickness of brush arrays as functions of the grafting density and chain length. In addition, we compute the potential of mean force of an approaching hydrophilic or hydrophobic foulant via umbrella sampling as a function of its position relative to the poly-zwitterion-covered surface. The aforementioned observables lead to important insights regarding the conformational tendencies of grafted polyzwitterions and their antifouling properties.

Dynamics of a single polyampholyte chain

Polymers that feature both positive and negative charges along chains, known as polyampholytes, represent a class of materials that hold promise for a new generation of energy storage devices, the design of which will require knowledge of the underlying structure and dynamics. Here, we develop a theory based on the Rouse model for the dynamic structure factor of a single polyampholyte chain in the weak coupling regime (negligible intramolecular electrostatics) or subjected to weak external electric fields (governed by linear response). Neglecting effects of small ions, we find deviations in scaling from the classic Rouse theory and make predictions for scattering experiments performed on polyampholytes. We find that, under weak coupling with arbitrarily strong fields, the dynamics are highly dependent on the charge distribution and consequently look at two representative examples-random charge densities and periodic charge densities-with different scaling properties. Under weak fields, the dynamics are largely independent of charge distribution. Finally, we investigate the influence of hydrodynamic effects and the implications of including inertial effects in the model.

Tandem Osmotic Engine Based on Hydrogel Particles with Antipolyelectrolyte and Polyelectrolyte Effect Fuelled by Both Salinity Gradient Modes

In this study, we propose a new approach to attain energy by salinity gradient engines with pistons based on hydrogels possessing polyelectrolyte and antipolyelectrolyte effects in a tandem arrangement, providing energy in each salinity gradient mode in a repeatable manner. The swelling of hydrogel with a polyelectrolyte effect and shrinking of hydrogel particles possessing an antipolyelectrolyte effect in desalinated water, and subsequent shrinking of hydrogel with polyelectrolyte and swelling of hydrogel antipolyelectrolyte effect in saline water, generate power in both increasing and decreasing salinity modes. To investigate the energy recovery, we scrutinized osmotic engine assemblies by a setup arrangement of pistons with hydrogel particles, with polyelectrolyte and antipolyelectrolyte effects, in tandem. The energy recovery from the tandem engine setup (calculated based on dry form for each polyelectrolyte polyacrylate-based hydrogel-SPA) and antipolyelectrolyte–sulfobetaine-based gel with methacrylate polymeric backbone-SBE) up to 581 J kg⁻¹ and a mean power of 0.16 W kg⁻¹ was obtained by the tandem setup of SPA and SBE hydrogel containing 3% crosslinking density and particle size of 500 microns with an external load of 3.0 kPa. Exchange of sulfobetaine with methacrylamide (SBAm), the main polymer backbone, revealed a positive increase in energy recovery of 670 J kg⁻¹ with a mean power of 0.19 W kg⁻¹ for the tandem system operating under the same parameters (SPA@SBAm). The energy recovery can be controlled, modulated and tuned by selecting both hydrogels with antipolyelectrolyte and polyelectrolyte effects and their performing parameters. This proof of concept provides blue energy harvesting by contributing both polyelectrolyte and antipolyelectrolyte effects in a single tandem setup; together with easy accessibility (diaper-based materials (SPA)) and known antibiofouling, these properties offer a robust alternative for energy harvesting.

Synthesis of Betaine Copolymer for Surface Modification of Cotton Fabric by Enhancing Temperature-Sensitive and Anti-Protein Specific Absorption Performance

The growth and reproduction of microorganisms on fabrics could not only affect the wearability of textiles but also cause harm to human health, and it is an important problem that should be solved to reduce the adsorption and growth of microorganisms on the surface of the fabric. A series of ω-vinyl betaine copolymers were synthesized by catalytic chain transfer polymerization (CCTP) and were modified by mercapto-vinyl click chemistry to synthesize silane-modified betaine copolymers, which were used to treat the cotton fabric. The hydrophilic–hydrophobic transition performance and anti-protein specific adhesion performance of cotton fabric with the betaine copolymer were systematically investigated. The copolymer was confirmed to be successfully finished on the cotton fabric via ¹H–NMR and FTIR. The cotton fabric, which was treated by the betaine copolymer, presented temperature response performance in the range of 30–55 °C and had excellent anti-protein adsorption performance. The treated fabric had the best temperature-sensitive and anti-protein specific absorption performance among all the specimens when the mass fraction of G06B in DMAPS was 6 wt.%.

Strong Surface Hydration and Salt Resistant Mechanism of a New Nonfouling Zwitterionic Polymer Based on Protein Stabilizer TMAO

Zwitterionic polymers exhibit excellent nonfouling performance due to their strong surface hydrations. However, salt molecules may severely reduce the surface hydrations of typical zwitterionic polymers, making the application of these polymers in real biological and marine environments challenging. Recently, a new zwitterionic polymer brush based on the protein stabilizer trimethylamine N-oxide (TMAO) was developed as an outstanding nonfouling material. Using surface-sensitive sum frequency generation (SFG) vibrational spectroscopy, we investigated the surface hydration of TMAO polymer brushes (pTMAO) and the effects of salts and proteins on such surface hydration. It was discovered that exposure to highly concentrated salt solutions such as seawater only moderately reduced surface hydration. This superior resistance to salt effects compared to other zwitterionic polymers is due to the shorter distance between the positively and negatively charged groups, thus a smaller dipole in pTMAO and strong hydration around TMAO zwitterion. This results in strong bonding interactions between the O^- in pTMAO and water, and weaker interaction between O^- and metal cations due to the strong repulsion from the N⁺ and hydration water. Computer simulations at quantum and atomistic scales were performed to support SFG analyses. In addition to the salt effect, it was discovered that exposure to proteins in seawater exerted minimal influence on the pTMAO surface hydration, indicating complete exclusion of protein attachment. The excellent nonfouling performance of pTMAO originates from its extremely strong surface hydration that exhibits effective resistance to disruptions induced by salts and proteins.

pH-Dependent complexation and polyelectrolyte chain conformation of polyzwitterion-polycation coacervates in salted water

The phase behavior and chain conformational structure of biphasic polyzwitterion-polyelectrolyte coacervates in salted aqueous solution are investigated with a model weak cationic polyelectrolyte, poly(2-vinylpyridine) (P2VP), whose charge fraction can be effectively tuned by pH. It is observed that increasing the pH leads to the increase of the yielding volume fraction and the water content of dense coacervates formed between net neutral polybetaine and cationic P2VP in contrast to the decrease of critical salt concentration for the onset of coacervation, where the P2VP charge fraction is reduced correspondingly. Surprisingly, a single-molecule fluorescence spectroscopic study suggests that P2VP chains upon coacervation seem to adopt a swollen or an even more expanded conformational structure at higher pH. As the hydrophobicity of P2VP chains is accompanied by a reduced charge fraction by increasing the pH, a strong pH-dependent phase and conformational behaviors suggest the shift of entropic and enthalpic contribution to the underlying thermodynamic energy landscape and chain structural dynamics of polyelectrolyte coacervation involving weak polyelectrolytes in aqueous solution.

Sulfobetaine-based polydisulfides with tunable upper critical solution temperature (UCST) in water alcohols mixture, depolymerization kinetics and surface wettability

HYPOTHESIS

Synthesis of a new family of polymers having a polydisulfide structure can be conducted from sulfobetaine-based derivative of natural (R)-lipoic acid. A polydisulfide backbone of polymer can be depolymerized by response to external stimuli and sulfobetaine pendant groups ensure the upper critical solution temperature (UCST) behaviour temperatures that can be modulated according to the nature of the solvent and concentration.

EXPERIMENTS

Sulfobetaine-bearing polydisulfides were synthesized from dithiolane derivatives and then characterized. UCST behavior of the polymers in water and in mixtures containing different alcohols (methanol, ethanol, isopropanol) was investigated. The regeneration of monomers from the polymers in response to external stimuli was examined using UV-vis and circular dichroism (CD) spectroscopy. Tunable surface wettability were shown on the grafted polymers.

FINDINGS

Decreasing polarity and/or increasing alcohol percentage in the water mixtures induced an increase in the cloud points of the polymers in the solutions. Thermoresponsive behaviour were repeatable and fully reversible with negligible hysteresis from aggregate to unimer state. The regeneration of monomers by depolymerization was tunable by temperature and sunlight. A thickness dependence on surface wettability was observed on wafers covalently modified with polydisulfides. This is the first report of sulfobetaine-based polydisulfides showing tunable UCST behavior and surface wettability.

Stimuli-responsive nanoparticles based on poly acrylic derivatives for tumor therapy

Serve side effects caused by discriminate damage of chemotherapeutic drugs to normal cell and cancer cells remain a main obstacle in clinic. Hence, continuous efforts have been made to find ways to effectively enhance drug delivery and reduce side effects. Recent decades have witnessed impressive progresses in fighting against cancer, with improved understanding of tumor microenvironment and rapid development in nanoscale drug delivery system (DDS). Nanocarriers based on biocompatible materials provide possibilities to improve antitumor efficiency and minimize off-target effects. Among all kinds of biocompatible materials applied in DDS, polymeric acrylic derivatives such as poly(acrylamide), poly(acrylic acid), poly(N-isopropylacrylamide) present inherent biocompatibility and stimuli-responsivity, and relatively easy to be functionalized. Furthermore, nanocarrier based on polymeric acrylic derivatives have demonstrated high drug encapsulation, improved uptake efficiency, prolonged circulation time and satisfactory therapeutic outcome in tumor. In this review, we aim to discuss recent progress in design and development of stimulus-responsive poly acrylic polymer based nanocarriers for tumor targeting drug delivery.

Design of an LCST-UCST-Like Thermoresponsive Zwitterionic Copolymer

Thermoresponsive polymers that possess both UCST- and LCST-like behaviors have generally been designed using diblock copolymers that are mostly composed of an LCST-like polymer and a UCST polymer. Herein, we prepared an LCST-UCST-type polymer composed of UCST-like thermoresponsive zwitterionic sulfabetaine methacrylate and nonthermoresponsive PEG methacrylate, ZB-PEG, by reversible addition-fragmentation chain transfer (RAFT) copolymerization. By adjusting the PEG composition, ZB-PEG formed a mesoglobule, a microglobule, and the dissociated states in phosphate-buffered saline (PBS). These states were found to be reversible via temperature control. Moreover, this behavior showed high reversibility and succeeded in stabilizing horseradish peroxidase (HRP) in the dilute condition. Such thermoresponsive ZB-PEG can be applied over a wide range of applications in biotechnology and other fields.

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.

Nanogels Capable of Triggered Release

This chapter provides an overview of soft and environmentally sensitive polymeric nanosystems, which are widely known as nanogels. These particles keep great promise to the area of drug delivery due to their high biocompatibility with body fluids and tissues, as well as due to their ability to encapsulate and release the loaded drugs in a controlled manner. For a long period of time, the controlled drug delivery systems were designed to provide long-termed or sustained release. However, some medical treatments such as cancer chemotherapy, protein and gene delivery do not require the prolonged release of the drug in the site of action. In contrast, the rapid increase of the drug concentration is needed for gaining the desired biological effect. Being very sensitive to surrounding media and different stimuli, nanogels can undergo physico-chemical transitions or chemical changes in their structure. Such changes can result in more rapid release of the drugs, which is usually referred to as triggered drug release. Herein we give the basic information on nanogel unique features, methods of sensitive nanogels preparation, as well as on main mechanisms of triggered release. Additionally, the triggered release of low-molecular drugs and biomacromolecules are discussed.

A crystallization driven thermoresponsive transition in a liquid crystalline polymer

A new thermoresponsive transition in a liquid crystalline polymer is found and the reason leading to the thermoresponse is discussed.

Effect of polyampholyte net charge on complex coacervation between polyampholytes and inorganic polyoxometalate giant anions

The effect of net charge of zwitterionic polymers on the phase behavior and viscoelastic properties of hybrid polyampholyte-polyoxometalate (POM) complexes in salted aqueous solutions is investigated with polyampholyte copolymers consisting of both positively and negatively charged monomers. Zwitterionic polyampholytes of varied net charge, abbreviated as PA_xM_y, are synthesized by varying the feeding molar ratio of negatively charged 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) to positively charged [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC) monomers in aqueous solution. The coacervate formation between PA_xM_y and inorganic anionic metatungstate POM ({W₁₂}) in LiCl added aqueous solutions can be enhanced by increasing the molar fraction of positively charged MAPTAC monomer and LiCl concentration. The salt-broadened coacervation, clearly distinct from the salt-suppressed one between oppositely charged polyelectrolytes, suggests the account of zwitterion-anion pairing for PA_xM_y-{W₁₂} coacervate formation due to stronger binding of multivalent {W₁₂} giant ions with PA_xM_y than simple ions. Importantly, as AMPS or MAPTAC monomer fraction in polyampholytes is varied by merely ±5% from the effective net neutral case, the viscoelasticity of PA_xM_y-{W₁₂} coacervates can be modified by 4-5 folds, suggesting a new tuning parameter to fine control the macroionic interactions and material properties of biomimetic complex coacervates.

Control of Mitochondrial Localization Using Thermoresponsive Sulfobetaine Polymer

Fast intracellular migration and controlled localization of molecules represent significant challenges for future applications of drug discovery and related fields. In this study, thermoresponsive sulfobetaine polymers with pyridinium cations are evaluated as biocompatible and mitochondria-localizing agents. Among the polymers, poly(3-(4-(2-methacrylamido)ethyl pyridinio-1-yl)propane-1-sulfonate), P(E-PySMAAm)14k (M_n  = 14 000 g mol^-1 ) exhibit thermoresponsiveness with an upper critical solution temperature like behavior in cell culture medium containing serum with minimal cytotoxicity. Upon the addition of P(E-PySMAAm)14k to HeLa cells at temperatures above the clearing point at 37 °C, effective localization is observed in mitochondria. However, increased intensity but nonspecific localization is observed below the clearing point at 4 °C. Doxorubicin is conjugated to the P(E-PySMAAm) and achieves effective mitochondrial delivery while maintaining drug efficacy. Such sulfobetaine polymers represent promising tools for intracellular delivery of molecules.