Tunable blood compatibility of polysulfobetaine from controllable molecular-weight dependence of zwitterionic nonfouling nature in aqueous solution

Sulfobetaine-Siloxanes: A Class of Self-Destructive Surfactants

The hydrolytic susceptibility of sulfobetaine-siloxane surfactants is investigated by comparison of a homologous series in this subclass of surfactants (R-(CH2)3N+(Me)2(CH2)3SO3-; R = (Me3SiO)3Si-, (Me3SiO)2Si(Me)-, (Me2SiO)3-Si(Me)-) with an analogue series of oxyethylene-siloxane surfactants (R-(CH2)3(OCH2CH2)10.2OH; R = (Me3SiO)3Si-, (Me3SiO)2Si(Me)-, (Me2SiO)3-Si(Me)-). Nuclear magnetic resonance (NMR) monitoring of these surfactants in an aqueous solution shows that the presence of the sulfobetaine head structure greatly enhances the hydrolysis rate of the siloxane tail as compared with oxyethylene-siloxane analogue control experiments. This sulfobetaine effect is confirmed by adding a model compound, (Me)3N+(CH2)3SO3-, to the oxyethylene-siloxane surfactants and observing the large hydrolysis enhancement. Measurements of pH indicate the sulfobetaine presence greatly enhances acidity, but rigorous analysis could discover no source of acid other than the presence of the sulfobetaine structure. Titration measurements confirmed the presence of a tightly bound hydration layer of 4-7 water molecules per sulfobetaine group. It is speculated that the source of acidity may originate from an aqueous exclusion zone nucleated by the hydrated sulfobetaine at the interface of a sulfobetaine-siloxane surfactant bilayer aggregate. Hydrolysis prevention is investigated by addition of a pH 7 phosphate buffer, of an alkyl polyglycoside cosurfactant, and of a combination of both, with a finding of very significant but not complete suppression of the hydrolysis.

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.

Determination of non-freezing water in different nonfouling materials by differential scanning calorimetry

Nonfouling materials have attracted increasing interest for their excellent biocompatibility and low immunogenicity. Strong hydration is believed to be the key reason for their resisting capability to nonspecific protein adsorption. However, little attention has been paid to quantifying their strong water binding capacity. In this study, we synthesized four zwitterionic polymers, including poly(sulfobetaine methacrylate) (pSBMA), poly(carboxybetaine methacrylate) (pCBMA), poly(carboxybetaine acrylamide) (pCBAA) and poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC), and compared non-freezing water of these zwitterionic polymers with typical antifouling polymer poly(ethylene glycol) (PEG) using differential scanning calorimetry (DSC). Non-freezing water of their monomers was also investigated. The non-freezing water of the polymers (per unit) is pMPC (10.7 ± 1.4) ≈ pCBAA (10.8 ± 1.5) > pCBMA (9.0 ± 0.6) > pSBMA (6.6 ± 0.4) > PEG20000 (0.60 ± 0.04). Similar trend is observed for their monomers. For all studied zwitterionic materials, they showed higher binding capacity than PEG. We attribute the stronger hydration of zwitterionic polymers to their strong electrostatic interactions.

In-vitro and in-vivo biocompatibility of dECM-alginate as a promising candidate in cell delivery for kidney regeneration

In this study, kidney decellularized extracellular matrix (dECM) and alginate (ALG) hybrid injectable hydrogel, with the purpose of delivering progenitor cells for tissue engineering, were prepared by using a physical crosslinking method in a CaCl₂ solution with high porosity for the exchange of nutrition and waste. In addition, the physical appearance and surface morphology of the hydrogel were investigated using optical and scanning electron microscopy, respectively. The functional groups of the dECM/ALG xerogels was examined via Fourier transform infrared spectroscopy. The biocompatibility of dECM/ALG xerogels was examined in-vitro using renal progenitor cells obtained from adult rat kidney. Enhanced biocompatibility and significant hemostatic behavior was noticed. Furthermore, the in-vivo biocompatibility of dECM/ALG hydrogel with progenitor cells was determined in the deep renal cortex for 7 and 21 days, in order to assess the foreign body reaction and inflammatory response. Early-stage glomerulus-like structure and dense linear cell network-like phenomenon were noticed. Loading of progenitor cells together with hydrogel enhances the cell density obviously due to cell migration from host and form a pattern. The desired early stage in-vivo response to progenitor cell-laden dECM/ALG hydrogel plays a potential role in kidney regeneration long term.

Recent advances of zwitterionic based topological polymers for biomedical applications

Zwitterionic polymers, comprising hydrophilic anionic and cationic groups with the same total number of positive and negative charges on the same monomer residue, have received increasing attention due to their...

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.%.

Enhanced tumour penetration and prolonged circulation in blood of polyzwitterion-drug conjugates with cell-membrane affinity

Effective anticancer nanomedicines need to exhibit prolonged circulation in blood, to extravasate and accumulate in tumours, and to be taken up by tumour cells. These contrasting criteria for persistent circulation and cell-membrane affinity have often led to complex nanoparticle designs with hampered clinical translatability. Here, we show that conjugates of small-molecule anticancer drugs with the polyzwitterion poly(2-(N-oxide-N,N-diethylamino)ethyl methacrylate) have long blood-circulation half-lives and bind reversibly to cell membranes, owing to the negligible interaction of the polyzwitterion with proteins and its weak interaction with phospholipids. Adsorption of the polyzwitterion-drug conjugates to tumour endothelial cells and then to cancer cells favoured their transcytosis-mediated extravasation into tumour interstitium and infiltration into tumours, and led to the eradication of large tumours and patient-derived tumour xenografts in mice. The simplicity and potency of the polyzwitterion-drug conjugates should facilitate the design of translational anticancer nanomedicines.

Constrained thermoresponsive polymers - new insights into fundamentals and applications

In the last decades, numerous stimuli-responsive polymers have been developed and investigated regarding their switching properties. In particular, thermoresponsive polymers, which form a miscibility gap with the ambient solvent with a lower or upper critical demixing point depending on the temperature, have been intensively studied in solution. For the application of such polymers in novel sensors, drug delivery systems or as multifunctional coatings, they typically have to be transferred into specific arrangements, such as micelles, polymer films or grafted nanoparticles. However, it turns out that the thermodynamic concept for the phase transition of free polymer chains fails, when thermoresponsive polymers are assembled into such sterically confined architectures. Whereas many published studies focus on synthetic aspects as well as individual applications of thermoresponsive polymers, the underlying structure-property relationships governing the thermoresponse of sterically constrained assemblies, are still poorly understood. Furthermore, the clear majority of publications deals with polymers that exhibit a lower critical solution temperature (LCST) behavior, with PNIPAAM as their main representative. In contrast, for polymer arrangements with an upper critical solution temperature (UCST), there is only limited knowledge about preparation, application and precise physical understanding of the phase transition. This review article provides an overview about the current knowledge of thermoresponsive polymers with limited mobility focusing on UCST behavior and the possibilities for influencing their thermoresponsive switching characteristics. It comprises star polymers, micelles as well as polymer chains grafted to flat substrates and particulate inorganic surfaces. The elaboration of the physicochemical interplay between the architecture of the polymer assembly and the resulting thermoresponsive switching behavior will be in the foreground of this consideration.

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.

Thermally Stable Bioinert Zwitterionic Sulfobetaine Interfaces Tolerated in the Medical Sterilization Process

This work introduces a thermally stable zwitterionic structure able to withstand steam sterilization as a general antifouling medical device interface. The sulfobetaine methacrylate (SBMA) monomer and its polymer form are among the most widely used zwitterionic materials. They are easy to synthesize and have good antifouling properties. However, they partially lose their properties after steam sterilization, a common procedure used to sterilize biomedical interfaces. In this study, ultrahigh-performance liquid chromatography/mass spectrometry (UHPLC-MS) was used to analyze and discuss the molecular structure of SBMA before and after a steam sterilization procedure, and a strategy to address the thermal stability issue proposed, using sulfobetaine methacrylamide (SBAA) instead of SBMA. Interestingly, it was found that the chemical structure of SBAA material can withstand the medical sterilization process at 121 °C while maintaining good antifouling properties, tested with proteins (fibrinogen), bacteria (Escherichia coli), and whole blood. On the other hand, SBMA gels failed at maintaining their excellent antifouling properties after sterilization. This study suggests that the SBAA structure can be used to replace SBMA in the bioinert interface of sterilizable medical devices, such as rayon fiber membranes used for disease control.

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.

Complex Formation of Sulfobetaine Surfactant and Ionic Polymers and Their Stimuli Responsivity

We investigated the kinds of complexes sulfobetaine surfactant and ionic polymer formed using lauramidopropyl hydroxysultane (LAPHS) as a sulfobetaine surfactant, poly(sodium styrenesulfonate) (PSSNa) as the anionic polymer and poly[3-(methacrylamido)propyl trimethylammonium chloride] (PMAPTAC) as the cationic polymer. The fundamental properties of LAPHS at various salt concentrations were estimated by various measurements, and it was confirmed that the LAPHS micelles alone did not show temperature responsiveness. The presence of large aggregates in addition to LAPHS micelles was confirmed in the aggregates prepared by adding PSSNa to LAPHS at a charge ratio of 1:0.5, 1:1, and 1:2. However, the aggregates could not be formed when the salt concentration was high or when a monomer was added instead of the polymer. This revealed that the cation part of sulfobetaine, which is the shell of LAPHS micelles, and the anion part of PSSNa electrostatically interacted with each other to form a large aggregate. On the other hand, unlike the case of LAPHS micelles alone and the aggregate consisting of LAPHS micelles and PSSNa, the aggregate of LAPHS micelles and PMAPTAC showed an unprecedented phenomenon of "clear → opaque → clear" with increasing concentration in the concentration range above CMC. The change in the transition temperature due to the change of concentration was a factor. Additionally, we confirmed that the transition temperature was lowered when the concentration was higher than CMC or the salt concentration was increased, and the transition temperature was increased when the PMAPTAC with a high degree of polymerization was added. These results suggested that the LAPHS micelles and the ionic polymer form an aggregate, and the temperature responsivity can be expressed by the interaction with the cationic polymer.

Temperature-triggered attachment and detachment of general human bio-foulants on zwitterionic polydimethylsiloxane

Biofouling has long been a problem for biomaterials, so being able to control the fouling on the surface of a biomaterial would be ideal. In this study a copolymer system was designed comprising three moieties: an epoxy containing group, glycidyl methacrylate (GMA); a thermoresponsive segment, N-isopropylacrylamide (NIPAAm); and an antifouling zwitterionic unit, sulfobetaine methacrylate (SBMA). The copolymers (pGSN), synthesized via free radical polymerization with these 3 moieties, were then grafted onto polydimethylsiloxane (PDMS). The presence of a critical temperature for both the copolymers and the coated PDMS was evidenced by particle size and contact angle measurements. The coated PDMS exhibited controllable temperature-dependent antifouling behaviors and stimuli-responsive phase characteristics in the presence of salts. The interactions of the coated PDMS with biomolecules were tested via attachment of fibrinogen protein, platelets, human whole blood, and tumor cells (HT1080). The attachment and detachment of these biomolecules were studied at different temperatures. Exposed hydrophobic domains of thermoresponsive NIPAAm-rich pGSN containing NIPAAm at 56 mol% generally allows molecular and cellular attachment on the PDMS surface at 37 °C. On the other hand, the coated PDMS with a relatively high content of SBMA (>41 mol%) in the copolymer started to exhibit fouling resistance and lower the thermoresponsive properties. Interestingly, the incorporation of zwitterionic SBMA units into the copolymers was found to accelerate the hydration of the PDMS surfaces and resulted in biomolecular and cellular detachment at 25 °C, which is comparable to the detachment at 4 °C. This modified surface behavior is found to be consistent through all biofouling tests.

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.

Formation of Sulfobetaine-Containing Entirely Ionic PIC (Polyion Complex) Micelles and Their Temperature Responsivity

Sulfobetaine, a type of zwitterionic polymer, is highly biocompatible with temperature responsiveness of the upper critical solution temperature (UCST) type. The objective of this research was to construct polyion complex (PIC) micelles in the shell of sulfobetaine that had these properties. We used poly(sulfopropyl dimethylammonium propylacrylamide) (PSPP) as sulfobetaine, poly(sodium styrenesulfonate) (PSSNa) as the anionic polymer, and poly[3-(methacrylamido)propyl trimethylammonium chloride] (PMAPTAC) as the cationic polymer. The fundamental properties of the sulfobetaine-containing polymer and the complex were investigated to construct micelles in which the corona expands and contracts in response to temperature changes. Changes in the cloud point were observed from the transmittance for sulfobetaine homopolymers with different degrees of polymerization and concentration and aqueous solution of temperature-responsive diblock copolymers with different concentrations. The concentration and degree of polymerization dependencies on temperature responsivity were determined. Then we mixed two diblock copolymer aqueous solutions that did not have temperature responsivity so that the charge number of anions and cations became equal, and the temperature responsivity and the formation of micelles were confirmed from ¹H NMR, DLS, and transmittance. This confirmed the formation of PIC micelles with temperature responsivity. The diblock copolymer did not have temperature responsivity due to the influence of the block ratio by introduction of the ionic chain. However, it is considered to have temperature responsivity because the ionic chain becomes the core when PIC micelles are formed. Furthermore, the PIC micelles with temperature responsivity also had a degree of polymerization and concentration dependencies.

Novel zwitterionic vectors: Multi-functional delivery systems for therapeutic genes and drugs

Zwitterions consist of equal molar cationic and anionic moieties and thus exhibit overall electroneutrality. Zwitterionic materials include phosphorylcholine, sulfobetaine, carboxybetaine, zwitterionic amino acids/peptides, and other mix-charged zwitterions that could form dense and stable hydration shells through the strong ion-dipole interaction among water molecules and zwitterions. As a result of their remarkable hydration capability and low interfacial energy, zwitterionic materials have become ideal choices for designing therapeutic vectors to prevent undesired biosorption especially nonspecific biomacromolecules during circulation, which was termed antifouling capability. And along with their great biocompatibility, low cytotoxicity, negligible immunogenicity, systematic stability and long circulation time, zwitterionic materials have been widely utilized for the delivery of drugs and therapeutic genes. In this review, we first summarized the possible antifouling mechanism of zwitterions briefly, and separately introduced the features and advantages of each type of zwitterionic materials. Then we highlighted their applications in stimuli-responsive "intelligent" drug delivery systems as well as tumor-targeting carriers and stressed the multifunctional role they played in therapeutic gene delivery.

Amphiphilic poly(caprolactone-b-N-hydroxyethyl acrylamide) micelles for controlled drug delivery

To increase the bioavailability and water solubility of hydrophobic medicine, an amphiphilic block copolymer, polycaprolactone-block-polyhydroxyethyl acrylamide (PCL-b-PHEAA), was synthesized.

Synthesis of star-shaped polyzwitterions with adjustable UCST and fast responsiveness by a facile RAFT polymerization

We describe crosslinking of polyzwitterions for the formation of novel star-shaped polymers with low polydispersities and dual-responsiveness using RAFT polymerization.

Protein-Stabilizing Effect of Amphiphilic Block Copolymers with a Tertiary Sulfonium-Containing Zwitterionic Segment

Tertiary sulfonium-containing zwitterionic block copolymers consisting of N-acryloyl-l-methionine methyl sulfonium salt (A-Met(S+)-OH) and n-butyl acrylate (BA) were newly synthesized to develop a novel protein stabilizer. The zwitterionic block copolymers were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization of BA using a hydrophilic macro-chain-transfer agent (CTA) obtained from N-acryloyl-l-methionine (A-Met-OH) and subsequent postmodification. RAFT polymerization of A-Met-OH using poly(BA) macro-CTA, followed by postmodification, also afforded the target poly(A-Met(S+)-OH)-b-poly(BA). The block copolymers stabilized horseradish peroxidase (HRP) during storage at 37 °C for 5 days, and the protein-stabilizing effect was enhanced with increase in the A-Met(S+)-OH content. In particular, the block copolymer with ∼85% A-Met(S+)-OH content showed a significant protein-stabilizing effect at a temperature (37 °C) higher than the room temperature, which is highly desirable for practical and industrial applications. The addition of sucrose into the block copolymer-protein solution led to a considerable increase in the HRP activity under the same conditions. Excellent alkaline phosphatase stabilization at 37 °C for 12 days was also achieved using the block copolymers. The zwitterionic block copolymers with the optimal hydrophilic/hydrophobic balance were found to serve as efficient protein-stabilizing agents, in comparison with the corresponding homopolymer and random copolymers. Dynamic light scattering, zeta potential, transmission electron microscopy, and circular dichroism measurements revealed that the zwitterionic block copolymer stabilizes an enzyme by wrapping with a slight change in the size, whereas the secondary and ordered structures of the enzyme are maintained.

Dimethyl Sulfoxide-Free Cryopreservation of Chondrocytes Based on Zwitterionic Molecule and Polymers

Cartilage tissue engineering highly relies on the ability to store and transport chondrocytes in order to be clinically successful. Cryopreservation is a most reliable technology for chondrocyte storage, but it suffers from the intrinsic toxicity of current state-of-the-art cryoprotectant, dimethyl sulfoxide (DMSO). In this work, we used the first fully zwitterionic compound-based approach for effective chondrocyte cryopreservation. A zwitterionic molecule combined with zwitterionic polymers could balance intra/extracellular osmotic stress and prevent ice formation, which were the keys of successful cryopreservation. Moreover, this zwitterionic combination showed noncytotoxicity due to its high biocompatibility, superior to cytotoxic DMSO. On the basis of these performances, chondrocytes could be well cryopreserved (∼90% post-thaw survival efficiency) for a long time without any addition of DMSO, and the recovered cells could maintain their normal functionalities. In view of the association between polymer molecular weight and cryopreservation efficacy, further mechanism of cryoprotection provided by zwitterionic molecule/polymer was proposed. This work opens a new window of opportunity for DMSO-free cryopreservation using biocompatible zwitterionic materials.

Ex Vivo and In Vivo Biocompatibility Assessment (Blood and Tissue) of Three-Dimensional Bacterial Nanocellulose Biomaterials for Soft Tissue Implants

Bacterial nanocellulose (BNC) is a promising biomedical material. However, the haemocompatibility (haemolysis and thrombogenicity) and acute and sub-chronic immune responses to three-dimensional (3D) BNC biomaterials have not been evaluated. Accordingly, this manuscript focused on the effect of 3D microporosity on BNC haemocompatibility and a comparison with 2D BNC architecture, followed by the evaluation of the immune response to 3D BNC. Blood ex vivo studies indicated that compared with other 2D and 3D BNC architectures, never-dried 2D BNC presented antihemolytic and antithrombogenic effects. Nevertheless, in vivo studies indicated that 3D BNC did not interfere with wound haemostasis and elicited a mild acute inflammatory response, not a foreign body or chronic inflammatory response. Moreover, compared with the polyethylene controls, the implant design with micropores ca. 60 µm in diameter showed a high level of collagen, neovascularization and low fibrosis. Cell/tissue infiltration increased to 91% after 12 weeks and was characterized by fibroblastic, capillary and extracellular matrix infiltration. Accordingly, 3D BNC biomaterials can be considered a potential implantable biomaterial for soft tissue augmentation or replacement.

Toward Antibiofouling PVDF Membranes

Membranes for biologically and biomedically related applications must be bioinert, that is, resist biofouling by proteins, human cells, bacteria, algae, etc. Hydrophobic materials such as polysulfone, polypropylene, or poly(vinylidene fluoride) (PVDF) are often chosen as matrix materials but their hydrophobicity make them prone to biofouling, which in turn limits their application in biological/biomedical fields. Here, we designed PVDF-based membranes by precipitation from the vapor phase and zwitterionized them in situ to reduce their propensity to biofouling. To achieve this goal, we used a copolymer containing phosphorylcholine groups. An in-depth physicochemical characterization revealed not only the controlled presence of the copolymer in the membrane but also that bicontinuous membranes could be formed. Membrane hydrophilicity was greatly improved, resulting in the mitigation of a variety of biofoulants: the attachment of Stenotrophomonas maltophilia, Streptococcus mutans, and platelets was reduced by 99.9, 99.9, and 98.9%, respectively. Besides, despite incubation in a plasma platelet-poor medium, rich in plasma proteins, a flux recovery ratio of 75% could be measured while it was only 40% with a hydrophilic commercial membrane of similar structure and physical properties. Similarly, the zwitterionic membrane severely mitigated biofouling by microalgae during their harvesting. All in all, the material/process combination presented in this work leads to antibiofouling porous membranes with a large span of potential biomedically and biologically related applications.

Solution Properties of Amphoteric Random Copolymers Bearing Pendant Sulfonate and Quaternary Ammonium Groups with Controlled Structures

Amphoteric random copolymers P(AMPS/APTAC50) _x, where x = 41, 89, and 117, composed of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) and 3-acrylamidopropyltrimethylammonium chloride (APTAC) were prepared via reversible addition-fragmentation chain transfer radical polymerization. P(AMPS/APTAC50) _x can dissolve in pure water to form small interpolymer aggregates. In aqueous solutions of NaCl, P(AMPS/APTAC50) _x can dissolve in the unimer state. Amphoteric random copolymer P(AMPS/APTAC50)_c with high molecular weight was prepared via conventional free-radical polymerization. Although P(AMPS/APTAC50)_c cannot dissolve in pure water, it can dissolve in aqueous solutions of NaCl. In amphoteric random copolymers with high molecular weight, the possibility of continuous sequences of monomers with the same charge may increase, which may cause strong interactions between polymer chains. When fetal bovine serum (FBS) and polyelectrolytes were mixed in phosphate-buffered saline, the hydrodynamic radius and light-scattering intensity increased. There was no interaction between P(AMPS/APTAC50) _x and FBS because corresponding increases could not be observed.

Designs of Zwitterionic Interfaces and Membranes

Zwitterionic materials are the latest generation of materials for nonfouling interfaces and membranes. They outperform poly(ethylene glycol) derivatives because they form tighter bonds with water molecules and can trap more water molecules. This feature article summarizes our laboratory's fundamental developments related to the functionalization of interfaces and membranes using zwitterionic materials. Our molecular designs of zwitterionic polymers and copolymers, sulfobetaine-based, carboxybetaine-based, or phosphobetaine-based, are first reviewed. Then, the strategies used to functionalize surfaces/membranes by coating, grafting onto, grafting from, or in situ modification are examined and discussed, and the third part of this article shifts the focus to key applications of zwitterionic materials. Finally, some potential future directions for molecular designs, functionalization processes, and applications are presented.

One-Pot Synthesis of a Zwitterionic Small Molecule Bearing Disulfide Moiety for Antibiofouling Macro- and Nanoscale Gold Surfaces

The goal of this study is to develop a simple one-pot method for the synthesis of a zwitterionic small molecule bearing disulfide moiety, which can effectively inhibit nonspecific protein adsorption on macroscopic and nanoscopic gold surfaces. To this end, the optimal molecular structure of a pyridine disulfide derivative was explored and a zwitterionic small molecule was successfully synthesized from the tertiary amine residue on the pyridine ring through a one-pot method. The coating conditions of the synthesized zwitterionic molecules on the gold surface were optimized through contact angle measurements, and the strong interactions between the gold surface and the disulfide moiety of the zwitterion small molecule were confirmed by surface plasmon resonance (SPR) analysis and X-ray photoelectron spectroscopy. The antibiofouling properties of the coated gold surface were analyzed by fluorescence microscopic observations after contacting with FITC-labeled bovine serum albumin (BSA) and SPR sensor as contacting with BSA solution. In addition, the effect of zwitterion-coating on the salt stability of and protein adsorption on nanoscopic gold surfaces were examined through a NaCl stability test and BSA adsorption test, respectively. From the obtained results, it was confirmed that the simply synthesized zwitterionic small molecule was effective in inhibiting nonspecific protein adsorption on macroscopic and nanoscopic gold surfaces; further, it enhanced the salt stability of gold nanoparticle surfaces.

Study of the Interactions of Zwitterions and Carbon Nanotubes by Nonlinear Rheology in an Aqueous Environment

Aqueous nanocomposite solutions of P(NIPAM) and P(NIPAM- co- N-(3-Sulfopropyl)- N-(methacryloxyethyl)- N,N-dimethylammonium betaine), a zwitterionic monomer with carbon nanotubes (CNT) as filler, were synthesized and characterized rheologically. While the influence of P(NIPAM) content and CNT content can be considered to be relatively minor, the introduction of a zwitterionic monomer (Zw) into the polymer leads to clear rheological traces of strong interactions between zwitterionic moieties and surface moieties on the CNTs, namely, a significantly lower nonlinearity limit and a lower modulus at high Zw contents and a higher modulus at intermediate contents due to adsorption of zwitterionic moieties on the CNT surface as well as a significantly lengthened time for the sample to adjust itself to the applied deformation, suggesting that the adsorbed polymer chains need to reorganize themselves significantly to accommodate to the applied strain γ₀.

Chemical Tuning of Zwitterionic Ionic Liquids for Variable Thermophysical Behaviours, Nanostructured Aggregates and Dual-Stimuli Responsiveness

The design and synthesis of a series of zwitterionic ionic liquids (ZILs) to understand the structure-property relationship towards an increase of the thermal stability, a variation of the glass transition temperature, the shape-tuning of nanostructured aggregates and the tuning of the stimuli responsiveness are demonstrated. The substitution reaction of imidazole with various aliphatic and aromatic bromides followed by the reaction of the corresponding substituted imidazoles with bromoalkyl carboxylic acids of varying spacer length produces the ZILs. In aqueous solution, a ZIL molecule either exist in its ionic liquid (substituted imidazolium bromide) form or its zwitterionic (substituted imidazolium alkyl carboxylate) form with an isoelectric point (pI) depending on the pH value of the solution. Upon changing the pH to near or above the pI, the aqueous ZIL solution undergoes transition from a transparent to a turbid phase due to the formation of insoluble hierarchical nanostructured aggregates of various morphologies, such as spheres, tripods, tetrapods, fern-like, flower-like, dendrites etc. depending on the pH of the solution and the nature of the alkyl/vinyl/aryl substituents. Upon heating the solution a phase transition occurs from turbid to transparent, exhibiting a distinct reversible upper critical solution temperature (UCST)-type cloud point (T_cp ). It is observed that the cloud point varies with the nature of the substituent, an increase of the concentration of the ZIL as well as with changes of the pH of the solution.

Heparin mimetics with anticoagulant activity

Heparin, a sulfated polysaccharide belonging to the glycosaminoglycan family, has been widely used as an anticoagulant drug for decades and remains the most commonly used parenteral anticoagulant in adults and children. However, heparin has important clinical limitations and is derived from animal sources which pose significant safety and supply problems. The ever growing shortage of the raw material for heparin manufacturing may become a very significant issue in the future. These global limitations have prompted much research, especially following the recent well-publicized contamination scandal, into the development of alternative anticoagulants derived from non-animal and/or totally synthetic sources that mimic the structural features and properties of heparin. Such compounds, termed heparin mimetics, are also needed as anticoagulant materials for use in biomedical applications (e.g., stents, grafts, implants etc.). This review encompasses the development of heparin mimetics of various structural classes, including synthetic polymers and non-carbohydrate small molecules as well as sulfated oligo- and polysaccharides, and fondaparinux derivatives and conjugates, with a focus on developments in the past 10 years.

Introduction of Nature's Complexity in Engineered Blood-compatible Biomaterials

Biomaterials with excellent blood-compatibility are needed for applications in vascular replacement therapies, such as vascular grafts, heart valves and stents, and in extracorporeal devices such as hemodialysis machines and blood-storage bags. The modification of materials that are being used for blood-contacting devices has advanced from passive surface modifications to the design of more complex, smart biomaterials that respond to relevant stimuli from blood to counteract coagulation. Logically, the main source of inspiration for the design of new biomaterials has been the endogenous endothelium. Endothelial regulation of hemostasis is complex and involves a delicate interplay of structural components and feedback mechanisms. Thus, challenges to develop new strategies for blood-compatible biomaterials now lie in incorporating true feedback controlled mechanisms that can regulate blood compatibility in a dynamic way. Here, supramolecular material systems are highlighted as they provide a promising platform to introduce dynamic reciprocity, due to their inherent dynamic nature.

Low-fouling PES membranes fabricated via in situ copolymerization mediated surface zwitterionicalization

PEGylated and zwitterionic PES membranes were fabricated during membrane formation, showing superior antifouling and anticoagulant properties.

Dual Thermoresponsive Aggregation of Schizophrenic PDMAEMA-b-PSBMA Copolymer with an Unrepeatable pH Response and a Recycled CO2/N2 Response

A dual thermoresponsive block copolymer of poly[2-(dimethylamino)ethyl methacrylate]-block-poly(sulfobetaine methacrylate) (PDMAEMA-b-PSBMA) exhibited reversible schizophrenic aggregation behavior in water because of the upper critical solution temperature (UCST) of the PSBMA block and the lower critical solution temperature (LCST) of the PDMAEMA block. Both the UCST and LCST shifted to lower values with increasing DMAEMA/SBMA block ratios, which was ascribed to the hydrophobic/hydrophilic balance of both blocks. Because of the salt-sensitive PSBMA and pH-responsive PDMAEMA, the UCST and LCST values of PDMAEMA-b-PSBMA were codetermined by varying the salt concentrations and pH. Specifically, increasing the salt concentration resulted in a notable decrease in the UCST and a slight increase in the LCST due to the salt-induced screening of the electrostatic attractions of the PSBMA and salt-enhanced solubility of the PSBMA blocks, respectively. The LCST decreased with increasing pH because of the deprotonation of PDMAEMA, and the UCST first increased and then decreased with increasing pH. Besides, the copolymer with larger PDMAEMA content was more sensitive to pH. For the repetitive adjustment to thermoresponsive aggregation, repeated addition of acids and bases induced salt accumulation and diminished the switchability of pH, whereas repeated switching cycles were achieved by CO₂/N₂ bubbling without introducing salt enrichment. The difference in HCl/NaOH titration and CO₂/N₂ bubbling also existed in the switching cycles when PDMAEMA-b-PSBMA served as a stimulus-responsive emulsifier.

A Zwitterionic-Shielded Carrier with pH-Modulated Reversible Self-Assembly for Gene Transfection

Cationic vectors are ideal candidates for gene delivery thanks to their capability to carry large gene inserts and their scalable production. However, their cationic density gives rise to high cytotoxicity. We present the proper designed core-shell polyplexes made of either poly(ethylene imine) (PEI) or poly(2-dimethylamino ethyl methacrylate) (PDMAEMA) as the core and zwitterionic poly(acrylic acid)-block-poly(sulfobetaine methacrylate) (PAA-b-PSBMA) diblock copolymer as the shell. Gel retardation and ethidium bromide displacement assays were used to determine the PEI/DNA or PDMAEMA/DNA complexation. At neutral pH, the copolymer serves as a protective shell of the complex. As PSBMA is a nonfouling block, the shell reduced the cytotoxicity and enhanced the hemocompatibility (lower hemolysis activity, longer plasma clotting time) of the gene carriers. PAA segments in the copolymer impart pH sensitivity by allowing deshielding of the core in acidic solution. Therefore, the transfection efficiency of polyplexes at pH 6.5 was better than at pH 7.0, from β-galactosidase assay, and for all PAA-b-PSBMA tested. These results were supported by more favorable physicochemical properties in acidic solution (zeta potential, particle size, and interactions between the polymer and DNA). Thus, the results of this study offer a potential route to the development of efficient and nontoxic pH-sensitive gene carriers.

Biomimetic Principles to Develop Blood Compatible Surfaces

Functionalized biomaterial surface patterns capable of resisting nonspecific adsorption while retaining their bioactivity are crucial in the advancement of biomedical technologies, but currently available biomaterials intended for use in whole blood frequently suffer from nonspecific adsorption of proteins and cells, leading to a loss of activity over time. In this review, we address two concepts for the design and modification of blood compatible biomaterial surfaces, zwitterionic modification and surface functionalization with glycans – both of which are inspired by the membrane structure of mammalian cells – and discuss their potential for biomedical applications.