Synthesis of Highly Stretchable, Mechanically Tough, Zwitterionic Sulfobetaine Nanocomposite Gels with Controlled Thermosensitivities

Enhanced Diabetic Rat Wound Healing by Platelet-Rich Plasma Adhesion Zwitterionic Hydrogel

BACKGROUND

The skin is the largest organ in the human body and serves as a barrier for protective, immune, and sensory functions. Continuous and permanent exposure to the external environment results in different levels of skin and extracellular matrix damage. During skin wound healing, the use of good dressings and addition of growth factors to the wound site can effectively modulate the rate of wound healing. A dressing containing bioactive substances can absorb wound exudates and reduce adhesion between the wound and dressing, whereas growth factors, cytokines, and signaling factors can promote cell motility and proliferation.

AIM AND OBJECTIVES

We prepared a functional wound dressing by combining platelet-rich plasma (PRP) and zwitterionic hydrogels. Functional wound dressings are rich in various naturally occurring growth factors that can effectively promote the healing process in various types of tissues and absorb wound exudates to reduce adhesion between wounds and dressings. Furthermore, PRP-incorporated zwitterionic hydrogels have been used to repair full-thickness wounds in Sprague-Dawley rats with diabetes (DM SD).

MATERIALS AND METHODS

Fibroblasts and keratinocytes were cultured with PRP, zwitterionic hydrogels, and PRP-incorporated zwitterionic hydrogels to assess cell proliferation and specific gene expression. Furthermore, PRP-incorporated zwitterionic hydrogels were used to repair full-thickness skin defects in DM SD rats.

RESULTS

The swelling ratio of hydrogel, hydrogel + PRP1000 (108 platelets/mL), and hydrogel + PRP1000 (109 platelets/mL) groups were similar (~07.71% ± 1.396%, 700.17% ± 1.901%, 687.48% ± 4.661%, respectively) at 144 hours. The tensile strength and Young modulus of the hydrogel and hydrogel + PRP10000 groups were not significantly different. High concentrations of PRP (approximately 108 and 109 platelets/mL) effectively promoted the proliferation of fibroblasts and keratinocytes. The zwitterionic hydrogels were not cytotoxic to any cell type. High PRP concentration-incorporated zwitterionic hydrogels increased the rate of cell proliferation and significantly increased the expression of characteristic genes such as collagen, fibronectin, involucrin, and keratin. Subsequently, zwitterionic hydrogels with high PRP concentrations were used to repair full-thickness skin defects in DM SD rats, and a wound healing rate of more than 90% was recorded on day 12.

CONCLUSIONS

PRP contains high concentrations of growth factors that promote cell viability, enhance specific gene expression, and have a high medical value in cell therapy. Zwitterionic hydrogels have a 3-dimensional interconnected microporous structure and can resist cell adhesion without causing cytotoxicity. Platelet-rich plasma-incorporated zwitterionic hydrogels further enhance the cellular properties and provide an effective therapeutic option for wound healing.

Effect of Hydrophobicity and Salt on the Temperature Responsiveness of Polymeric Micelles Consisting of Hydrophobic and Sulfobetaine Chains

The effect of the hydrophobicity of the core part and salt on the temperature responsiveness of polymeric micelles composed of sulfobetaine and hydrophobic blocks was investigated. Poly(sulfopropyl dimethylammonium propylacrylamide) (PSPP) was used as the sulfobetaine; poly(2-ethylhexyl acrylate) (PEHA), poly(n-butyl acrylate) (PnBA), poly(ethyl acrylate) (PEA), or poly(n-hexyl acrylate) (PnHA) was used as the hydrophobic polymer. Measurement of the transmittance revealed that the transition temperature of the sulfobetaine homopolymer could be controlled by adjusting the concentration, the degree of polymerization (DP), and the concentration of the added salt. The effect of the anionic species of the added salt due to the chemical structural properties of the sulfobetaine chain was consistent with the order of ionic species with strong structural destruction in the Hofmeister series. The temperature response and micelle formation behavior of the polymeric micelles according to the hydrophobicity of the core part and the preparation method were examined by static light scattering (SLS), fluorescence measurement with pyrene, dynamic light scattering (DLS), transmittance, and atomic force microscopy (AFM). Micelles that had EHA (solubility in water was 0.01 g/100 mL) as the core and did not show temperature responsiveness expressed temperature responsiveness at a lower hydrophobicity (solubility of nBA in water was 0.14 g/100 mL). nBA-b-SPP did not show temperature responsiveness due to the block ratio. However, when micelles were prepared by dialysis, smaller and more stable micelles could be formed in an equilibrium state, and temperature responsiveness was observed. Their transition temperature can be controlled by adjusting the ratio of the sulfobetaine blocks, the hydrophobicity of the core part, the concentration of the polymer aqueous solution, and the concentration of the added salt. Furthermore, like the sulfobetaine homopolymer, the effect depended on the anionic species of the added salt.

Tethering zwitterionic polymer coatings to mediated glucose biosensor enzyme electrodes can decrease sensor foreign body response yet retain sensor sensitivity to glucose

Foreign body response (FBR) is a major challenge that affects implantable biosensors and medical devices, including glucose biosensors, leading to a deterioration in device response over time. Polymer shields are often used to mitigate this issue. Zwitterionic polymers (ZPs) are a promising class of materials that reduce biofouling of implanted devices. A series of ZPs each containing tetherable epoxide functional groups was synthesised for application as a polymer shield for eventual application as implantable glucose biosensors. The polymer shields were initially tested for the ability to resist fibrinogen adsorption and fibroblast adhesion. All synthesised ZPs showed comparable behaviour to a commercial Lipidure ZP in resisting fibrinogen adsorption. Nafion, a common anionic shield used against electrochemical interferents, showed higher protein adsorption and comparable cell adhesion resistance as uncoated control surfaces. However, a poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) (MPC)-type ZP showed similar behaviour to Lipidure, with approximately 50% reduced fibrinogen adsorption and 80% decrease in fibroblast adhesion compared to uncoated controls. An MPC-coated amperometric glucose biosensor showed comparable current density and a 1.5-fold increase in sensitivity over an uncoated control biosensor, whereas all other polymer shields tested, including Lipidure, Nafion and a poly(ethyleneglycol) polymer, resulted in lower sensitivity and current density. Collectively, these characteristics make MPC-polymer shield coatings an appealing possibility for use in implantable glucose sensors and other implanted devices with the aim of reducing FBR while maintaining sensor performance.

Microgel reinforced zwitterionic hydrogel coating for blood-contacting biomedical devices

Zwitterionic hydrogels exhibit eminent nonfouling and hemocompatibility. Several key challenges hinder their application as coating materials for blood-contacting biomedical devices, including weak mechanical strength and low adhesion to the substrate. Here, we report a poly(carboxybetaine) microgel reinforced poly(sulfobetaine) (pCBM/pSB) pure zwitterionic hydrogel with excellent mechanical robustness and anti-swelling properties. The pCBM/pSB hydrogel coating was bonded to the PVC substrate via the entanglement network between the pSB and PVC chain. Moreover, the pCBM/pSB hydrogel coating can maintain favorable stability even after 21 d PBS shearing, 0.5 h strong water flushing, 1000 underwater bends, and 100 sandpaper abrasions. Notably, the pCBM/pSB hydrogel coated PVC tubing can not only mitigate the foreign body response but also prevent thrombus formation ex vivo in rats and rabbits blood circulation without anticoagulants. This work provides new insights to guide the design of pure zwitterionic hydrogel coatings for biomedical devices.

Double Lock Label Based on Thermosensitive Polymer Hydrogels for Information Camouflage and Multilevel Encryption

Developing extra safety encryption technologies to prevent information leakage and combat fakes is in high demand but is challenging. Herein, we propose a "double lock" strategy based on both lower critical solution temperature (LCST) and upper critical solution temperature (UCST) polymer hydrogels for information camouflage and multilevel encryption. Two types of hydrogels were synthesized by the method of random copolymerization. The number of -CO-NH₂ groups in the network structure of the hydrogels changed the enthalpic or entropic thermo-responsive hydrogels, and ultimately precisely controlled their phase transition temperature. The crosslink density of the polymer hydrogels governs the diffusion kinetics, resulting in a difference in the time for their color change. The combination of multiple LCST and UCST hydrogels in one label realized information encryption and dynamic information identification in the dimensions of both time and temperature. This work is highly interesting for the fields of information encryption, anti-counterfeiting, and smart responsive materials.

Experimental Study on Physicochemical Properties of a Shear Thixotropic Polymer Gel for Lost Circulation Control

Polymer gel lost circulation control technology is a common and effective technique to control fractured lost circulation. The performance of a lost circulation control agent is the key to the success of lost circulation control techniques. In this study, rheological tests were used to study the physical and chemical properties of a shear thixotropic polymer gel system, such as anti-dilution, high temperature resistance and high salt resistance. The results showed that the shear thixotropic polymer gel system had the ability of anti-dilution, and the gel could be formed under a mixture of 3 times volume of heavy salt water and 3/7 volume white oil, and could keep the structure and morphology stable. Secondly, the gel formation time of shear thixotropic polymer gel system could be controlled and had good injection performance under the condition of 140 °C and different initiator concentrations. Meanwhile, the shear thixotropic polymer gel system had the ability of high temperature and high salt resistance, and the gel formation effect was good in salt water. When the scanning frequency was 4 Hz and the temperature was 140 °C, the storage modulus (G′) of the gel was 4700 Pa. The gel was dominated by elasticity and had excellent mechanical properties. By scanning electron microscope observation, it was found that the shear thixotropic polymer gel system had a stable three-dimensional reticular space skeleton under the condition of high salt, indicating that it had excellent ability to tolerate high salt. Therefore, the shear thixotropic polymer gel had high temperature and high salt resistance, dilution resistance and good shear responsiveness. It is believed that the results presented in this work are of importance for extending real-life applications of shear thixotropic polymer gel systems.

Skin-Adaptable, Long-Lasting Moisture, and Temperature-Tolerant Hydrogel Dressings for Accelerating Burn Wound Healing without Secondary Damage

Developing multifunctional wound dressings, possessing not only skin-like mechanical properties and adaptability, long-lasting moisture, and temperature tolerance that maximally mimics the human skin but also on-demand adhesion without unnecessary bleeding and secondary damage upon peeling, is necessary but remains a challenge. Herein, a novel dual cross-linked and multifunctional hydrogel, termed PSNC hydrogel for polymerized sulfobetaine methacrylate (SBMA), N-(2-amino-2-oxyethyl)acrylamide (NAGA), and 1-carboxy-N-methyl-N-di(2-methacryloyloxy-ethyl)methanaminium inner salt (CBMAX), was fabricated as a wound dressing for burn injuries via one-pot radical polymerization in glycerine (GLY)/H₂O solvent. The dual cross-linked network of the PSNC hydrogel combined the double hydrogen bonding of N-(2-amino-2-oxyethyl)acrylamide (NAGA) with a covalently cross-linked zwitterionic network, endowing the hydrogel with skin-like mechanical properties with a high stretchability of 1613.8 ± 79.8%, a tensile strength of 77.5 ± 1.8 kPa, and a tensile modulus of 1.9 ± 0.1 kPa. Moreover, the hydrogel with well-developed adaptability can withstand skin deformation without breaking or debonding attributed to its good tissue adhesiveness and self-healing ability. Further, the utilization of the GLY/H₂O binary solvent effectively prevented the crystallization and evaporation of free water, endowing the hydrogel with not only long-lasting moisture but also excellent temperature tolerance in a wide range from -20 to 60 °C. More importantly, the PSNC hydrogel could effectively accelerate wound healing of burn injuries and could be easily removed on-demand with saline without causing secondary damage due to intense hydration. Such a novel PSNC zwitterionic hydrogel could be a promising candidate for the treatment of burn wounds and tissue regeneration.

Complex Formation in the Sulfobetaine-Containing Entirely Ionic Block Copolymer/Ionic Homopolymer System and Their Temperature Responsivity

The behavior of micelle formation in the sulfobetaine-containing entirely ionic block copolymer/ionic homopolymer system and its functional expression (temperature responsivity) were investigated. Poly(sulfopropyl dimethylammonium propylacrylamide) was used as the sulfobetaine, poly[3-(methacrylamido)propyl trimethylammonium chloride] was used as the cationic polymer, and poly(p-styrenesulfonic acid sodium salt) was used as the anionic polymer. The changes in transition temperature with the concentration and the behavior of micelle formation in the block-/cationic homopolymer and block-/anionic homopolymer system were compared and examined by transmittance, dynamic light scattering, atomic force microscopy, and ¹H nuclear magnetic resonance. Only block-/cationic homopolymer systems with a core-shell (polyion complex-sulfobetaine) structure showed temperature responsivity of upper critical solution temperature type, and the responsiveness was dependent on the concentration. On the other hand, the block-/anionic homopolymer system had a core-shell structure at a concentration of 0.05 wt %, but temperature responsiveness was not observed at this concentration. At higher concentrations, electrostatic attraction caused the anionic homopolymer and block copolymer to interact as a whole, resulting in a loss of responsiveness. When the ionic homopolymer had a higher degree of polymerization than the sulfobetaine, it could not form a core-shell structure by interacting with the sulfobetaine and ionic polymer moieties of the block copolymer, thus resulting in the loss of responsiveness. The block-/ionic homopolymer system prepared by the reforming method through dialysis formed uniform and small micelles but lost responsiveness due to morphological stability and electrostatic interaction between the block copolymer and ionic homopolymer.

A Zwitterionic-Aromatic Motif-Based ionic skin for highly biocompatible and Glucose-Responsive sensor

Electronic skins that can sense external stimuli have been of great significance in artificial intelligence and smart wearable devices in recent years. However, most of current skin materials are unable to achieve high biocompatibility and anti-bacterial activity, which are particularly critical to wearable sensors for neonatal/premature monitoring or tissue-interfaced biosensors (such as electronic wound dressing and smart contact lens). Herein, a zwitterionic-aromatic motif-based conductive hydrogel with electrostatic and π-π interactions is designed for the development of ionic skin sensors. The hydrogel possesses high biocompatibility, anti-bacterial activity, especially glucose-responsive property which has not been achieved by previous ionic skins. Due to its unique molecular design, the zwitterionic-aromatic skin sensor exhibits excellent mechanical properties (robust elasticity and large stretchability) and high-sensitive pressure detection (including a gentle finger touch, small water droplets, and vocal cord vibration). More importantly, aromatic motives in phenylboronic acid segments endow the skin with glucose-responsive property. This skin sensor not only shows great potential in wearable e-skins, but also possesses a promising property for the tissue-interfaced and implantable continuous-glucose-monitor biosensors such as smart wound dressing with a high demand of biocompatibility.

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.

Clay-based nanocomposite hydrogel with attractive mechanical properties and sustained bioactive ion release for bone defect repair

Although clay-based nanocomposite hydrogels have been widely explored, their instability in hot water and saline solution inhibits their applications in biomedical engineering, and the exploration of clay-based nanocomposite hydrogels in bone defect repair is even less. In this work, we developed a stable clay-based nanocomposite hydrogel using 4-acryloylmorpholine as the monomer. After UV light illumination, the obtained poly(4-acryloylmorpholine) clay-based nanocomposite hydrogel (poly(4-acry)-clay nanocomposite hydrogel) exhibits excellent mechanical properties due to the hydrogen bond interactions between the poly(4-acryloylmorpholine) chains and the physical crosslinking effect of the nanoclay. Besides good biocompatibility, the sustainable release of intrinsic Mg2+ and Si4+ from the poly(4-acry)-clay nanocomposite hydrogel endows the system with excellent ability to promote the osteogenic differentiation of primary rat osteoblasts (ROBs) and can promote new bone formation effectively after implantation. We anticipate that these kinds of clay-based nanocomposite hydrogels with sustained release of bioactive ions will open a new avenue for the development of novel biomaterials for bone regeneration.

Cationic Cellulose Nanocrystals-Based Nanocomposite Hydrogels: Achieving 3D Printable Capacitive Sensors with High Transparency and Mechanical Strength

Hydrogel ionotronics are intriguing soft materials that have been applied in wearable electronics and artificial muscles. These applications often require the hydrogels to be tough, transparent, and 3D printable. Renewable materials like cellulose nanocrystals (CNCs) with tunable surface chemistry provide a means to prepare tough nanocomposite hydrogels. Here, we designed ink for 3D printable sensors with cationic cellulose nanocrystals (CCNCs) and zwitterionic hydrogels. CCNCs were first dispersed in an aqueous solution of monomers to prepare the ink with a reversible physical network. Subsequent photopolymerization and the introduction of Al3+ ion led to strong hydrogels with multiple physical cross-links. When compared to the hydrogels using conventional CNCs, CCNCs formed a stronger physical network in water that greatly reduced the concentration of nanocrystals needed for reinforcing and 3D printing. In addition, the low concentration of nanofillers enhanced the transparency of the hydrogels for wearable electronics. We then assembled the CCNC-reinforced nanocomposite hydrogels with stretchable dielectrics into capacitive sensors for the monitoring of various human activities. 3D printing further enabled a facile design of tactile sensors with enhanced sensitivity. By harnessing the surface chemistry of the nanocrystals, our nanocomposite hydrogels simultaneously achieved good mechanical strength, high transparency, and 3D printability.

Collapse Behavior of Polyion Complex (PIC) Micelles upon Salt Addition and Reforming Behavior by Dialysis and Its Temperature Responsivity

Temperature-responsive polyion complex (PIC) micelles were prepared by using two diblock copolymers composed of a sulfobetaine chain (poly(sulfopropyldimethylammonium propylacrylamide), PSPP) and ionic chains (poly(sodium styrenesulfonate), PSSNa, or poly(3-(methacrylamido)propyltrimethylammonium chloride), PMAPTAC). Because the core is PIC and the shell is sulfobetaine with UCST-type temperature response, the corona expands and contracts in response to temperature. To control the size and uniformity of the PIC micelles, the collapse of PIC micelles by salt addition and the reforming behavior by dialysis were investigated by transmittance, DLS, TEM, AFM, and ¹H NMR measurements. Investigation of the ionic species dependence of the added salt in the collapse behavior of PIC micelles revealed that it was dependent on the anionic species, although no dependence on the cationic species was observed. Its effectiveness was in the order of I^- > Br^- > Cl^- > F^-, which is in agreement with the order of ionic species with strong structural destruction in the Hofmeister series. Heterogeneous and large PIC micelles were formed by the simple mixing method. They collapsed by salt addition and were reformed by the dialysis method to form uniform and smaller PIC micelles. This is considered to be because a uniform and smaller micelle is formed to reform in equilibrium state by dialysis. The temperature response of PIC micelles formed by the simple mixing method and PIC micelles reformed by dialysis showed nearly the same temperature-transmittance curves. These results indicate that the temperature response of PIC micelles is affected by the concentration rather than the hydrodynamic radius. Furthermore, the stability of PIC micelles was found to be affected by the concentration temperature (the temperature at the time of concentration).

Bioinspired Self-Healing Human-Machine Interactive Touch Pad with Pressure-Sensitive Adhesiveness on Targeted Substrates

There is an increasing interest to develop a next generation of touch pads that require stretchability and biocompatibility to allow their integration with a human body, and even to mimic the self-healing behavior with fast functionality recovery upon damage. However, most touch pads are developed based on stiff and brittle electrodes with the lack of the important nature of self-healing. Polyzwitterion-clay nanocomposite hydrogels as a soft, stretchable, and transparent ionic conductor with transmittance of 98.8% and fracture strain beyond 1500% are developed, which can be used as a self-healing human-machine interactive touch pad with pressure-sensitive adhesiveness on target substrates. A surface-capacitive touch system is adopted to sense a touched position. Finger positions are perceived during both point-by-point touch and continuous moving. Hydrogel touch pads are adhered to curved or flat insulators, with the high-resolution and self-healable input functions demonstrated by drawing, writing, and playing electronic games.

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.

A pH and UCST thermo-responsive tri-block copolymer (PAA-b-PDMA-b-P(AM-co-AN)) with micellization and gelatinization in aqueous media for drug release

A brand new pH and thermo-responsive amphiphilic ABC triblock copolymer of poly(acrylic acid)-block-poly(N,N-dimethyl acrylamide)-block-poly(acrylamide-co-acrylonitrile) (PAA-b-PDMA-b-P(AM-co-AN)) was applied as drug carrier systems.

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

A new methodology for developing biocompatible double network hydrogels by using a responsive amphoteric polymer as a first framework.

Surface-Initiated ARGET ATRP of Antifouling Zwitterionic Brushes Using Versatile and Uniform Initiator Film

In this study, we developed a uniform initiator layer that can be formed on various surfaces, and formed site-selectively, for the subsequent antifouling polymer brush formation. Initially, metal-organic films composed of tannic acid (TA) and Fe^III ions (TA-Fe^III) were formed on various surfaces, followed by functionalization with an aryl azide-based initiator (ABI) under photoreaction. In particular, combination with a photolithographic technique enabled the presentation of initiators only on the intended region within a single-surface platform. A resultant initiator film (TF-ABI) was formed under mild reaction conditions and meets the uniformity and transparency requirements concurrently. Subsequently, we showed that TF-ABI can be further utilized to form a polymer brush by proceeding with surface-initiated polymerization using a zwitterionic monomer, namely, sulfobetaine acrylamide (SBAA). Instead of applying a classical, yet air-sensitive atom transfer radical polymerization (ATRP) technique, we utilized an activator regenerated by electron transfer (ARGET) ATRP under air conditions without a cumbersome deoxygenation step. Overall, our initiator layer allowed the antifouling poly(SBAA) brush to be used on various surfaces, and enabled their pattern generation.

NIR-Triggered "OFF/ON" Photodynamic Therapy through a Upper Critical Solution Temperature Block Copolymer

Activatable photodynamic therapy (A-PDT) has attracted great attention in precision medicine, which can be activated by endogenous or exogenous stimuli to selectively produce reactive oxygen species (ROS) at the disease site. Thermal responsive polymers with a lower critical solution temperature (LCST) have normally been utilized for constructing A-PDT system. Herein, we fabricated a photothermal activatable photosensitizer (A-PS) by the combination of thermal responsive porphyrin-containing P(AAm-co-AN-co-TPP)-b-POEGMA amphiphilic block copolymer with an upper critical solution temperature (UCST) of 42 °C and a cyanine dye of IR780. The photoactivity of porphyrin units could be severely inhibited by IR780 due to the fluorescence resonance energy transfer (FRET) from TPP to IR780 during blood circulation process ("OFF" state). After an uptake by A549 cells and then irradiated with 808 nm laser, A-PS nanoparticles were subsequently dissociated owing to the increased local temperature above the UCST of the polymer chains by excellent photothermal conversion of IR780, resulting in the enhanced photoactivity of TPP ("ON" state) and the remarkable antitumor effect. Therefore, the UCST-based A-PS extended the biological application of thermal responsive polymers, which may provide a new insight into the design of smart cancer therapeutic systems.

Systematic Comparison of Zwitterionic and Non-Zwitterionic Antifouling Polymer Brushes on a Bead-Based Platform

Nonspecific adsorption of biomolecules to solid surfaces, a process called biofouling, is a major concern in many biomedical applications. Great effort has been made in the development of antifouling polymer coatings that are capable of repelling the nonspecific adsorption of proteins, cells, and micro-organisms. In this respect, we herein contribute to understanding the factors that determine which polymer brush results in the best antifouling coating. To this end, we compared five different monomers: two sulfobetaines, a carboxybetaine, a phosphocholine, and a hydroxyl acrylamide. The antifouling coatings were analyzed using our previously described bead-based method with flow cytometry as the read-out system. This method allows for the quick and automated analysis of thousands of beads per second, enabling fast analysis and good statistics. We report the first direct comparison made between a sulfobetaine with opposite charges separated by two and three methylene groups and a carboxybetaine bearing two separating methylene groups. It was concluded that both the distance between opposite charges and the nature of the anionic groups have a distinct effect on the antifouling performance. Phosphocholines and simple hydroxyl acrylamides are not often compared with the betaines. However, here we found that they perform equally well or even better, yielding the following overall antifouling ranking: HPMAA ≥ PCMA-2 ≈ CBMAA-2 > SBMAA-2 > SBMAA-3 ≫ nonmodified beads (HPMAA being the best).

Sulfobetaines Meet Carboxybetaines: Modulation of Thermo- and Ion-Responsivity, Water Structure, Mechanical Properties, and Cell Adhesion

A procedure for the preparation of copolymers bearing sulfobetaine and carboxybetaine methacrylic-based monomers by free-radical polymerization is described and discussed. A combination of monomers affects the upper critical solution temperature (UCST) in water and in the presence of a simple NaCl electrolyte while retaining the zwitterionic character. In addition, hydrogel samples were prepared and showed tunable water structure and mechanical properties. The total nonfreezable water content decreases with the amount of carboxybetaine segment in the hydrogel feed and the compression moduli were in a range of 0.7-1.6 MPa. Responses to external conditions such as temperature and ion strength were investigated and a potential application such as modulated thermal detection is proposed. The presence of the carboxylate group in the carboxybetaine segment enables a small fluorescence probe and peptide bearing RDG motif to be attached to polymer and hydrogel samples, respectively. The hydrogel samples functionalized with the RGD motif exhibit controlled cell adhesion. Such synthetic strategy based on combination of different zwitterionic segments offers a simple pathway for the development of zwitterionic materials with programmable properties.

Tough, Adhesive, Self-Healable, and Transparent Ionically Conductive Zwitterionic Nanocomposite Hydrogels as Skin Strain Sensors

It is desired to create skin strain sensors composed of multifunctional conductive hydrogels with excellent toughness and adhesion properties to sustain cyclic loadings during use and facilitate the electrical signal transmission. Herein, we prepared transparent, compliant, and adhesive zwitterionic nanocomposite hydrogels with excellent mechanical properties. The incorporated zwitterionic polymers can form interchain dipole-dipole associations to offer additional physical cross-linking of the network. The hydrogels show a high fracture elongation up to 2000%, a fracture strength up to 0.27 MPa, and a fracture toughness up to 2.45 MJ/m³. Moreover, the reversible physical interaction imparts the hydrogels with rapid self-healing ability without any stimuli. The hydrogels are adhesive to many surfaces including polyelectrolyte hydrogels, skin, glasses, silicone rubbers, and nitrile rubbers. The presence of abundant zwitterionic groups facilitates ionic conductivity in the hydrogels. The combination of these properties enables the hydrogels to act as strain sensors with high sensitivity (gauge factor = 1.8). The strategy to design the tough, adhesive, self-healable, and conductive hydrogels as skin strain sensors by the zwitterionic nanocomposite hydrogels is promising for practical applications.

Nonfouling textiles with tunable antimicrobial activity based on a zwitterionic polyamine finish

Depending on the degree of substitution DS, the antiadhesive (high DS) or antimicrobial (lower DS) character of the coating will be dominant.

Self-healing zwitterionic sulfobetaine nanocomposite hydrogels with good mechanical properties

The development of zwitterionic hydrogels possessing both excellent self-healing and mechanical properties is of great significance. Herein, a class of zwitterionic sulfobetaine nanocomposite hydrogels was prepared by UV-initiated copolymerisation of zwitterionic sulfobetaine monomer N,N-dimethyl-N-(3-methacrylamidopropyl)-N-(3-sulfopropyl) ammonium betaine (DMAPMAPS) and 2-hydroxyethyl methacrylate (HEMA) in the presence of exfoliated clay platelets uniformly dispersed in an aqueous medium. The effects of the hydrogel compositions, including the DMAPMAPS/HEMA mass ratio and the amount of clay, on the self-healing behaviors and mechanical properties of the nanocomposite hydrogels were investigated. The results indicate that the fabricated zwitterionic sulfobetaine nanocomposite hydrogels can autonomously repair incisions or cracks at ambient temperature without the need for any stimulus and possess excellent mechanical properties.

The prepared zwitterionic sulfobetaine nanocomposite hydrogels can autonomously repair incisions or cracks at ambient temperature without the need for any stimulus and possess excellent mechanical properties.

Recent advances of on-demand dissolution of hydrogel dressings

Wound management is a major global challenge and a big financial burden to the healthcare system due to the rapid growth of chronic diseases including the diabetes, obesity, and aging population. Modern solutions to wound management include hydrogels that dissolve on demand, and the development of such hydrogels is of keen research interest. The formation and subsequent on-demand dissolution of hydrogels is of keen interest to scientists and clinicians. These hydrogels have excellent properties such as tissue adhesion, swelling, and water absorption. In addition, these hydrogels have a distinctive capacity to form in situ and dissolve on-demand via physical or chemical reactions. Some of these hydrogels have been successfully used as a dressing to reduce bleeding in hepatic and aortal models, and the hydrogels remove easily afterwards. However, there is an extremely wide array of different ways to synthesize these hydrogels. Therefore, we summarize here the recent advances of hydrogels that dissolve on demand, covering both chemical cross-linking cases and physical cross-linking cases. We believe that continuous exploration of dissolution strategies will uncover new mechanisms of dissolution and extend the range of applications for hydrogel dressings.

Fouling-Resistant Hydrogels Prepared by the Swelling-Assisted Infusion and Polymerization of Dopamine

Biofilm-associated infections stemming from medical devices are increasingly challenging to treat due to the spread of antibiotic resistance. In this study, we present a simple strategy that significantly enhances the antifouling performance of covalently crosslinked poly(ethylene glycol) (PEG) and physically crosslinked agar hydrogels by incorporation of the fouling-resistant polymer zwitterion, poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC). Dopamine polymerization was initiated during swelling of the hydrogels, which provided dopamine and pMPC an osmotic driving force into the hydrogel interior. Both PEG and agar hydrogels were synthesized over a broad range of storage moduli (1.7,1300 kPa), which remained statistically equivalent after being functionalized with pMPC and polydopamine (PDA). When challenged with fibrinogen, a model blood-clotting protein, the pMPC/PDA-functionalized PEG and agar hydrogels displayed a >90% reduction in protein adsorption compared to hydrogel controls. Further, greater than an order-of-magnitude reduction in Escherichia coli and Staphylococcus aureus adherence was observed. This study demonstrates a versatile materials platform to enhance the fouling resistance of hydrogels through a pMPC/PDA incorporation strategy that is independent of the chemical composition and network structure of the original hydrogel.

Engineering Polyzwitterion and Polydopamine Decorated Doxorubicin-Loaded Mesoporous Silica Nanoparticles as a pH-Sensitive Drug Delivery

Multifunctional drug carriers have great applications in biomedical field. In this study, we introduced both polydopamine (PDA) and zwitterionic polymer of poly(3-(3-methacrylamidopropyl-(dimethyl)-ammonio)propane-1-sulfonate) (PSPP) onto the surface of mesoporous silica nanoparticles (MSNs) to develop a novel nanoparticle (MSNs@PDA-PSPP), which was employed as a new kind of drug carrier for the delivery of doxorubicin (DOX). The PDA coating, as a gatekeeper, could endow the drug carrier with pH-sensitive drug release performance. The outermost PSPP layer would make the drug carrier possess protein resistance performance. The chemical structure and properties were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS) and thermogravimetric analysis (TGA). MSNs@PDA-PSPP could keep good colloidal stability within 72 h in phosphate buffered saline (PBS) and protein solutions. Meanwhile, MSNs@PDA-PSPP exhibited a high drug loading for DOX. In vitro drug release experiments suggested MSNs-DOX@PDA-PSPP exhibited pH-dependent drug release behaviors. Besides, MSNs@PDA-PSPP had no cytotoxicity to human hepatocellular carcinoma cells (HepG2 cells) even at a concentration of 125 µg/mL. More importantly, cellular uptake and in vitro anticancer activity tests suggested that MSNs-DOX@PDA-PSPP could be taken up by HepG2 cells and DOX could be successfully released and delivered into the cell nuclei. Taken together, MSNs@PDA-PSPP have great potential in the biomedical field.

Highly Specific Binding on Antifouling Zwitterionic Polymer-Coated Microbeads as Measured by Flow Cytometry

Micron- and nano-sized particles are extensively used in various biomedical applications. However, their performance is often drastically hampered by the nonspecific adsorption of biomolecules, a process called biofouling, which can cause false-positive and false-negative outcomes in diagnostic tests. Although antifouling coatings have been extensively studied on flat surfaces, their use on micro- and nanoparticles remains largely unexplored, despite the widespread experimental (specifically, clinical) uncertainties that arise because of biofouling. Here, we describe the preparation of magnetic micron-sized beads coated with zwitterionic sulfobetaine polymer brushes that display strong antifouling characteristics. These coated beads can then be equipped with recognition elements of choice, to enable the specific binding of target molecules. First, we present a proof of principle with biotin-functionalized beads that are able to specifically bind fluorescently labeled streptavidin from a complex mixture of serum proteins. Moreover, we show the versatility of the method by demonstrating that it is also possible to functionalize the beads with mannose moieties to specifically bind the carbohydrate-binding protein concanavalin A. Flow cytometry was used to show that thus-modified beads only bind specifically targeted proteins, with minimal/near-zero nonspecific protein adsorption from other proteins that are present. These antifouling zwitterionic polymer-coated beads, therefore, provide a significant advancement for the many bead-based diagnostic and other biosensing applications that require stringent antifouling conditions.

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

Zwitterionic poly(sulfobetaine acrylamide) (pSBAA)-based nanocomposite hydrogels can have high potential for the treatment of infected chronic wounds.