The Design of Sulfobetaine Polymers with Thermoresponsiveness under Physiological Salt Conditions

Adhesive Sulfabetaine Polymer Hydrogels for the Sandwich Cell Culture

Sandwich culture systems are techniques that cultivate cells by sandwiching them between the top and bottom substrates. Since the substrates can be separated, the system is expected to be applied to the construct layering of patterned cells and to the isolation of stacked cells. In this study, we prepared hydrogels composed of zwitterionic sulfabetaine polymers, poly[2-(2-(methacryloyloxyethyl)dimethylammonio)ethyl-1-sulfate] (PZBMA). The ZBMA homopolymers have been shown to form aggregates in aqueous solutions due to their intermolecular interactions. The water content of the PZBMA hydrogels in water was ∼70% regardless of N,N'-methylenebis(acrylamide), BIS, content as the cross-linker. The results indicated that the intermolecular interaction contributed more to the swelling behaviors than the chemical cross-linker. However, PZBMA hydrogels with 0.1 mol % BIS showed not only high elongation (∼850%) properties but also high adhesiveness and self-healing properties. When this PZBMA hydrogel was impregnated with collagen and subjected to sandwich culture using Madin-Darby canine kidney (MDCK) cells, a three-dimensional morphology of MDCK cell aggregates was constructed. Such a sulfabetaine hydrogel is expected to be developed for regenerative medicine.

Sulfobetaine polymers for effective permeability into multicellular tumor spheroids (MCTSs)

Multicellular tumor spheroids (MCTSs) are attractive for drug screening before animal tests because they emulate an in vivo microenvironment. The permeability of the MCTSs and tumor tissues towards the candidate drugs is not sufficient even though the drugs can penetrate monolayer cultured cells; therefore, nanocarriers are required to enhance permeability and deliver drugs. In this study, we prepared zwitterionic polymers of sulfobetaine methacrylates and (meth)acrylamides with or without hydroxy groups between the zwitterions to serve as highly permeable nanocarriers. In the sulfobetaine polymers, poly(2-hydroxy-3-((3-methacrylamidopropyl)dimethylammonio)propane-1-sulfonate), P(OH-MAAmSB), the hydroxy group containing methacrylamide polymer exhibited little cytotoxicity and membrane translocation ability against monolayer cultured cells. Moreover, the excellent permeability of the hepatocyte MCTS enabled P(OH-MAAmSB) to permeate it and reach the center region (∼325 μm in diameter) at approximately 150 s, although poly(trimethyl-2-methacroyloxyethylammonium), a cationic polymer, penetrated just 1 to 2 layers from the periphery. The superior permeability of P(OH-MAAmSB) might be due to its good solubility and side chain conformation. P(OH-MAAmSB) is a promising nanocarrier with membrane translocation and permeability.

Programmable Zwitterionic Droplets as Biomolecular Sorters and Model of Membraneless Organelles

Increasing evidence indicates that cells can regulate biochemical functions in time and space by generating membraneless compartments with well-defined mesoscopic properties. One important mechanism underlying this control is simple coacervation driven by associative disordered proteins that encode multivalent interactions. Inspired by these observations, programmable droplets based on simple coacervation of responsive synthetic polymers that mimic the "stickers-and-spacers" architecture of biological disordered proteins are developed. Zwitterionic polymers that undergo an enthalpy-driven liquid-liquid phase separation process and form liquid droplets that remarkably exclude most molecules are developed. Starting from this reference material, different functional groups in the zwitterionic polymer are progressively added to encode an increasing number of different intermolecular interactions. This strategy allowed the multiple emerging properties of the droplets to be controlled independently, such as stimulus-responsiveness, polarity, selective uptake of client molecules, fusion times, and miscibility. By exploiting this high programmability, a model of cellular compartmentalization is reproduced and droplets capable of confining different molecules in space without physical barriers are generated. Moreover, these biomolecular sorters are demonstrated to be able to localize, separate, and enable the detection of target molecules even within complex mixtures, opening attractive applications in bioseparation, and diagnostics.

Zwitterionic Ammonium Sulfonate Polymers: Synthesis and Properties in Fluids

Polymer zwitterions continue to emerge as useful materials for numerous applications, ranging from hydrophilic and antifouling coatings to electronic materials interfaces. While several polymer zwitterion compositions are now well established, interest in this field of soft materials science has grown rapidly in recent years due to the introduction of new structures that diversify their chemistry and architecture. Nonetheless, at present, the variation of the chemical composition of the anionic and cationic components of zwitterionic structures remains relatively limited to a few primary examples. In this article, we highlight the versatility of 4-vinylbenzyl sultone as a precursor to ammonium sulfonate zwitterionic monomers, which are then used in controlled free radical polymerization chemistry to afford "inverted sulfobetaine" polymer zwitterions. An evaluation of the solubility, interfacial activity, and solution configuration of the resultant polymers revealed the dependence of properties on the selection of tertiary amines used for nucleophilic ring-opening of the sultone precursor, as well as useful properties comparisons across different zwitterionic compositions. This article is protected by copyright. All rights reserved.

Synthesis of Temperature-Responsive Polymers Containing Piperidine Carboxamide and N,N-diethylcarbamoly Piperidine Moiety via RAFT Polymerization

In this study, poly(N-acryloyl-nipecotamide) (PNANAm), poly(N-acryloyl-isonipecotamide) (PNAiNAm), and poly(N-acryloyl-N,N-diethylnipecotamide) (PNADNAm) are synthesized as novel temperature-responsive polymers using reversible addition-fragmentation chain-transfer polymerization. Aqueous solutions of these three polymers are examined via temperature-dependent optical transmittance measurements. The PNANAm sample with a hydrophilic terminal group shows an upper critical solution temperature (UCST) in phosphate-buffered saline (PBS) when its molecular weight (M_n ) is 7600 or higher, whereas PNANAm (M_n < 7600) is soluble. The UCST is influenced by molecular weight and the polymer concentration. In contrast, PNANAm sample with nonionic terminal group shows UCST, when M_n is below 7600, suggesting that the terminal nonionic group possibly increases UCST of PNANAm. The urea addition experiment suggests that the driving force for expression of UCST of PNANAm is the formation of inter-and intramolecular hydrogen bonds among the polymer chains. PNAiNAm is soluble in PBS but exhibits an UCST in an appropriate concentration of ammonium sulfate. In contrast, PNADNAm exhibits a lower critical solution temperature. Comparing the chemical structure of these polymers and their phase transition behaviors suggests that the carboxamide group position in the piperidine ring could determine the UCST expression. These results could help design temperature-responsive polymers with a desired the cloud point temperature.

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.

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.

Internalization Mechanisms of Pyridinium Sulfobetaine Polymers Evaluated by Induced Protic Perturbations on Cell Surfaces

Understanding the interactions of soft nanomatters with cell membranes is particularly important for research into nanocarrier-based drug delivery systems, cell engineering, and subcellular imaging. Most nanoparticles, vesicles, micelles, and polymeric aggregates are internalized into endosomes and, eventually, lysosomes in the cytosol because of energy-dependent endocytic processes. Endocytic uptake substantially limits the access to the cytoplasm where a cargo agent acts. Bypassing the endocytic pathways by direct penetration into plasma membrane barriers would enhance the efficacy of nanomedicines. Some zwitterionic polymer nanoaggregates have been shown to permeate into the cell interior in an energy-independent manner. We have elucidated this phenomenon by observing changes in the biomembrane barrier functions against protons as the smallest indicator and have used these results to further design and develop poly(betaines). In this work, we investigated the translocation mechanisms for a series of zwitterionic poly(methacrylamide) and poly(methacrylate) species bearing a pyridinium propane sulfonate moiety in the monomers. Minor differences in the monomer structures and functional groups were observed to have dramatic effects on the interaction with plasma membranes during translocation. The ability to cross the plasma membrane involves a balance among the betaine dipole-dipole interaction, NH-π interaction, π-π interaction, cation-π interaction, and amide hydrogen bonding. We found that the cell-penetrating polysulfobetaines had limited or no detrimental effect on cell proliferation. Our findings enhance the opportunity to design and synthesize soft nanomatters for cell manipulations by passing across biomembrane partitions.