A pH-Sensitive Stretchable Zwitterionic Hydrogel with Bipolar Thermoelectricity.

Amid growing interest in using body heat for electricity in wearables, creating stretchable devices poses a major challenge. Herein, a hydrogel composed of two core constituents, namely the negatively-charged 2-acrylamido-2-methylpropanesulfonic acid and the zwitterionic (ZI) sulfobetaine acrylamide, is engineered into a double-network hydrogel. This results in a significant enhancement in mechanical properties, with tensile stress and strain of up to 470.3 kPa and 106.6%, respectively. Moreover, the ZI nature of the polymer enables the fabrication of a device with polar thermoelectric properties by modulating the pH. Thus, the ionic Seebeck coefficient (Si ) of the ZI hydrogel ranges from -32.6 to 31.7 mV K-1 as the pH is varied from 1 to 14, giving substantial figure of merit (ZTi ) values of 3.8 and 3.6, respectively. Moreover, a prototype stretchable ionic thermoelectric supercapacitor incorporating the ZI hydrogel exhibits notable power densities of 1.8 and 0.9 mW m-2 at pH 1 and 14, respectively. Thus, the present work paves the way for the utilization of pH-sensitive, stretchable ZI hydrogels for thermoelectric applications, with a specific focus on harvesting low-grade waste heat within the temperature range of 25-40 °C.

Bio-inspired zwitterionic polymeric chelating assembly for treatment of copper-induced cytotoxicity and hemolysis.

We developed a hemocompatible, bio-inspired, multivalent, polymeric-chelating assembly based on the poly(2-methacryloyloxyethyl phosphorylcholine)-b-poly(serinyl acrylate) (PMPC-b-PserA) zwitterionic diblock copolymer. Functional PMPC-b-PserA was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization to catch and encapsulate free copper ions (Cu2+) in a solution. PMPC with an identical polar group to phospholipids exhibits high hydrophilicity and fouling resistance against non-specific adsorption, and inertness to the metal ions. On the other hand, PserA with pendant groups of amino acids possesses a strong capability to react with Cu2+ by coordination interaction. Therefore, when PMPC-b-PserA was brought into contact with Cu2+, a hydrophobic core with multiple coordination "bridges" between polymers and Cu2+ was formed, leading to self-assembly of core-shell polymer-metal nanoparticles. As a result, free Cu2+ ions can be removed from the solution to prevent damage to cells and tissues. The synthesis and chemical structure of PMPC-b-PserA were characterized, and the formation of self-assembled polymer-Cu2+ nanoparticles and colloidal stability were analyzed. More importantly, the detoxification of PMPC-b-PserA in presence of Cu2+ with fibroblast cells was demonstrated by increased cell viability >80%. In addition, the hemolysis, which occurred due to disruption of RBC membranes by free Cu2+, was effectively suppressed by adding PMPC-b-PserA. The bio-inspired and biocompatible chelating agent of PMPC-b-PserA provides a new treatment approach to encapsulate and detoxify heavy metals in complex media for chelation therapy.

Complete zwitterionic double network hydrogels with great toughness and resistance against foreign body reaction and thrombus.

Conventional tough hydrogels offer enhanced mechanical properties for load-bearing implants; however, their application is still hindered by a lack of biocompatibility. In this study, we demonstrate a new methodology for developing biocompatible double network (DN) hydrogels by using a responsive amphoteric polymer as a first framework. Tough DN hydrogels were formed by penetrating zwitterionic poly(sulfobetaine acrylamide) (PSBAA) into a swollen poly(lysine acrylamide) (PLysAA) network in an acidic or alkaline solution, and polymerizing under UV irradiation. The DN hydrogels were able to become zwitterionic entirely under physiological conditions, and possess excellent mechanical strength, comparable to conventional DN hydrogels with permanently charged polyelectrolyte frameworks. Additionally, in vitro studies including biofouling, cytotoxicity and hemolysis were conducted to show the superior biocompatibility of the complete zwitterionic DN hydrogels. After the circulation of human blood in tubular DN hydrogels, the zwitterionic DN gels displayed negligible thrombus formation. Furthermore, PLysAA/PSBAA hydrogels were implanted subcutaneously, showing excellent resistance against inflammatory response and long-term capsule formation. This work has presented a new strategy for synthesizing a biocompatible tough DN hydrogel to effectively mitigate the foreign body reaction to render great benefit for the development of biomedical implants.

Polyelectrolyte and Antipolyelectrolyte Effects for Dual Salt-Responsive Interpenetrating Network Hydrogels.

This work presents a salt-responsive interpenetrating network (IPN) hydrogel with effective antimicrobial properties and surface regeneration. The hydrogels were engineered using the double network strategy to form loosely cross-linked zwitterionic poly(sulfobetaine vinylimidazole) (pSBVI) networks into the highly cross-linked cationic poly((trimethylamino)ethyl methacrylate chloride) (pTMAEMA) framework via photopolymerization. The pTMAEMA/pSBVI hydrogel has strong mechanical properties, with a fracture stress 120× higher than single network pTMAEMA hydrogel. In addition, there is inverse correlation between elastic modulus and elastic strain of pTMAEMA/pSBVI hydrogels as a function of ionic strength. The cationic pTMAEMA and zwitterionic pSBVI show opposite swelling behaviors in salt solutions due to the polyelectrolyte effect and antipolyelectrolyte effect. Therefore, the pTMAEMA/pSBVI hydrogel elicits a significant interfacial transition in solutions with different ionic strengths. The IPN hydrogels have switchable lubrication and optical transmittance between deionized water and 1.0 M NaCl solution. The protein adsorption tests further confirmed the switchable interface of salt-responsive IPN hydrogels. In addition, bacterial attachment test on pTMAEMA/pSBVI hydrogels with Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli) show bacterial killing rates of the IPN hydrogel over 80% for S. epidermidis and 90% for E. coli after incubating the hydrogels in the bacterial solutions for 24 h. The bacterial release rate from the IPN hydrogel reached 96% after washing with 1.0 M NaCl solution. Furthermore, the excellent reusability of the pTMAEMA/pSBVI hydrogels was demonstrated by the high bacterial killing and bacterial release rates after five kill/release cycles. The work presents a new stimuli-responsive IPN hydrogel with structural modulation, tunable antimicrobial properties, and surface regeneration by ionic strength. Integrating two salt-responsive polymers with mutually independent actions into a single material provides a new direction for smart materials with potential medical and industrial applications.

Non-sticky and antimicrobial zwitterionic nanocomposite dressings for infected chronic wounds.

Zwitterionic poly(sulfobetaine acrylamide) (pSBAA)-based nanocomposite hydrogels impregnated with germicidal silver nanoparticles (AgNPs) were synthesized and implemented for the treatment of infected chronic wounds. The zwitterionic hydrogels exhibited excellent non-sticky properties and had reinforced mechanical properties by the addition of hectorite nanoclay and poly(ethylene glycol)dimethacrylate as physical and chemical crosslinkers, respectively. In addition, AgNPs were grown within the intercalated clay/polymer structure by in situ free radical reduction, as confirmed by UV-vis spectroscopy and transmission electron microscopy (TEM). The silver-containing pSBAA nanocomposite hydrogels (pSBAA/Ag) exhibited germicidal properties against Gram-positive S. epidermidis and Gram-negative P. aeruginosa. The zwitterionic hydrogels show higher water content than 2-hydroxyethyl methacrylate (pHEMA) hydrogels, owing to the strong hydration via ionic solvation. The negligible cytotoxicity of pSBAA/Ag hydrogels was assessed with human fibroblasts by the MTT assay. Moreover, the zwitterionic hydrogels demonstrated excellent resistance to the adsorption of bovine serum albumin (BSA). To evaluate the feasibility of the hydrogels for clinical application as wound dressings, we created infected diabetic rat models and compared with commercial wound dressings. The results show that pSBAA/Ag hydrogels did not adhere to the newly formed tissue, and were readily removed from the wounds after treatment for 3 days. Moreover, the healing recovery was evaluated by visual observation of infected dorsal wounds on rats with induction of diabetes by streptozotocin. The finding indicates complete healing with the pSBAA/Ag hydrogels after 15 days, faster than other dressings. A histological examination also proved that the zwitterionic hydrogels facilitated epithelialization and collagen distribution in the infected diabetic wounds. Consequently, these novel non-sticky and antimicrobial zwitterionic nanocomposite hydrogels can have high potential for the treatment of infected chronic wounds.

Zwitterionic nanocomposite hydrogels as effective wound dressings.

In this study, zwitterionic poly(sulfobetaine acrylamide) (pSBAA) nanocomposite hydrogels were synthesized and implemented as effective chronic wound dressings. The hydrogels exhibited reinforced mechanical properties from added hectorite nanoclay as a physical crosslinker in the polymer chains. Due to the strong interaction with water molecules via ionic solvation, the hydration of the zwitterionic nanocomposite hydrogels was superior to the non-ionic 2-hydroxyethyl methacrylate (pHEMA) hydrogels, which interacts with water molecules via hydrogen bonding. The pSBAA nanocomposite hydrogels cytotoxicity was accessed with NIH-3T3 fibroblast by the MTT assay, the results indicated negligible cytotoxicity after incubation for three days. In addition, the zwitterionic hydrogels displayed evident resistance to adsorption of bovine serum albumin (BSA), NIH-3T3 fibroblast, and bacteria of gram positive S. epidermidis and gram negative P. aeruginosa. The need for antifouling properties in a wound dressing is because commercial dressings removal typically damaging newly formed tissues and colonization of microorganisms occurs on the dressings. For clinical applications as wound dressings, we created normal and diabetic wounds on mice and compared newly developed pSBAA nanocomposite hydrogels with commercial available products. We demonstrated that non-adhesive pSBAA nanocomposite hydrogels enabled ready wound surface removal. Moreover, the wound recovery was conducted with normal and diabetic wounds on rat dorsal by visual observation and showed a complete heal after 10 and 12 days, respectively. Moreover, the histological examination of mice skin confirmed that the zwitterionic hydrogels exhibited thorough re-epithelialization and total formation of new connective tissues in the normal and diabetic wounds after 10 and 12 days, respectively, which was faster than commercial dressings. Consequently, we demonstrated that the pSBAA nanocomposite can serve as an effective dressing for wound management.

Surface Modification for Superhydrophilicity and Underwater Superoleophobicity: Applications in Antifog, Underwater Self-Cleaning, and Oil-Water Separation.

A facile yet effective surface modification strategy for superhydrophilicity and underwater superoleophobicity was developed by silanization of zwitterionic sulfobetaine silane (SBSi) on oxidized surfaces. The coatings exhibit excellent wetting properties, as indicated by static contact angles of <5°, and long-term stability under exposure to heat and UV irradiation. The SBSi-modified surfaces were employed for applications in antifog, self-cleaning, and oil-water separation. The SBSi glasses retained their optical transmittance because of the rapid formation of coalesced water thin films on surfaces in contact with water vapor and moisture. In addition, the underwater-oil contact-angle measurements verified the underwater superoleophobicity of the zwitterionic SBSi coatings. The oil spills on the SBSi coating could be readily removed in contact with water to realize the self-cleaning property. Besides, we modified stainless steel wire meshes with SBSi for oil-water separation. The optimal oil recovery rate for the oil-water mixtures reached >99.5% when using the SBSi-coated meshes with a pore size of 17 µm. More importantly, the water flux with modified meshes achieved 6.5 × 10(7) L/m(2)·h·bar, enabling gravity-driven and energy-saving separation. Consequently, we demonstrated the superhydrophilicity and underwater superoleophobicity of SBSi, offering promise in solving technological problems of interfacial fog, oil spills, and oil-water separation and thereby showing great potential in large-scale commercial applications.