Design Characteristics of a Neoteric, Superhydrophilic, Mechanically Robust Hydrogel Engineered To Limit Fouling in the Ocular Environment

Current challenges with ocular drug delivery and the chronic nature of many ocular ailments render the use of traditional ocular devices for additional drug delivery purposes very attractive. To achieve this feat, there is the need to develop biomaterials that are biocompatible, mechanically robust for ocular applications, highly transparent (depending on the targeted ocular device), and with ultralow protein adhesion potential (the primary step in processes that lead to fouling and potential device failure). Herein is reported the facile synthesis of a novel, highly transparent, mechanically robust, nontoxic, bulk functionalized hydrogel with characteristics suited to scalable fabrication of ocular implantable and nonimplantable devices. Synergistic superhydrophilicity between methacrylated poly(vinyl alcohol) (PVAGMA) and zwitterionic sulfobetaine methacrylate was exploited to obtain a superhydrophilic polymer conjugate through facile photoinitiated cross-linking polymerization. Proton nuclear magnetic resonance (1H NMR), attenuated total reflectance-Fourier transform infrared spectroscopy (ATF-FTIR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) were used to confirm the synthesis and establish the physicochemical parameters for both the starting materials, the conjugated polymer, and the hydrogels. Cytotoxicity and cell adhesion potential evaluated in primary human retinal epithelial cells showed no toxicity or adhesion of the ocular cells. Biofilm adhesion studies in Escherichia coli and Staphylococcus aureus showed over 85% reduction in biofilm adhesion for the best-modified polymer compared to the unconjugated PVAGMA, highlighting its antifouling potential.

A comprehensive review on the inherent and enhanced antifouling mechanisms of hydrogels and their applications

Biofouling remains a persistent challenge within the domains of biomedicine, tissue engineering, marine industry, and membrane separation processes. Multifunctional hydrogels have garnered substantial attention due to their complex three-dimensional architecture, hydrophilicity, biocompatibility, and flexibility. These hydrogels have shown notable advances across various engineering disciplines. The antifouling efficacy of hydrogels typically covers a range of strategies to mitigate or inhibit the adhesion of particulate matter, biological entities, or extraneous pollutants onto their external or internal surfaces. This review provides a comprehensive review of the antifouling properties and applications of hydrogels. We first focus on elucidating the fundamental principles for the inherent resistance of hydrogels to fouling. This is followed by a comprehensive investigation of the methods employed to enhance the antifouling properties enabled by the hydrogels' composition, network structure, conductivity, photothermal properties, release of reactive oxygen species (ROS), and incorporation of silicon and fluorine compounds. Additionally, we explore the emerging prospects of antifouling hydrogels to alleviate the severe challenges posed by surface contamination, membrane separation and wound dressings. The inclusion of detailed mechanistic insights and the judicious selection of antifouling hydrogels are geared toward identifying extant gaps that must be bridged to meet practical requisites while concurrently addressing long-term antifouling applications.

Antifouling Zwitterionic Nanofibrous Wound Dressing for Long-Lasting Antibacterial Photodynamic Therapy

Nanofibrous mats as a wound dressing have received great attention in recent year. The development of biocompatible dressings with antibiofouling capability and long-lasting antibacterial properties is important but challenging. Antibacterial photodynamic therapy (aPDT) effectively eliminates pathogens via a photodynamic process that can circumvent the emergence of antibiotic-resistant pathogens. In this study, we integrated the zwitterionic materials (2-methacryloyloxyethyl phosphorylcholine (MPC) moiety) and aPDT photosensitizer, methylene blue (MB), to fabricate a long-lasting antibacterial nanofibrous mat using electrospinning technology. The prepared nanofibers possessed an appropriate water absorption and retention ability, superior cytocompatibility, and antibiofouling ability against both proteins and L929 cell adhesion. MB-loaded nanofibrous mats have exhibited superior aPDT against Gram-positive Staphylococcus aureus compared to Gram-negative Escherichia coli under moderate irradiation (100 W m-2) due to the presence of an extra outer membrane of Gram-negative bacteria serving as a protective barrier. In vitro release study demonstrated that the nanofibrous mat had a long-lasting drug release profile, which can efficiently suppress bacterial growth via aPDT. The antibacterial ability of the MB-loaded nanofibrous mat was commensurate or slightly inferior to antibiotics such as tetracycline and kanamycin, suggesting that it has the potential to be used as an antibiotic alternative. Overall, this zwitterionic nanofibrous mat with long-lasting aPDT function and nonadherent properties has potential as a promising antibacterial wound dressing.

Synthesis and characterisation of a novel poly(2-hydroxyethylmethacrylate)-chitosan hydrogels loaded cerium oxide nanocomposites dressing on cutaneous wound healing on nursing care of chronic wound

This study was designed to establish the composition of wound dressing based on poly(2-hydroxyethylmethacrylate)-chitosan (PHEM-CS) hydrogels-loaded cerium oxide nanoparticle (CeONPs) composites for cutaneous wound healing on nursing care of the chronic wound. The as-synthesised PHEM-CS/CeONPs hydrogels nanocomposites were characterised by using UV-visible spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermo gravimetric analysis. The influence of PHEM-CS/CeONPs hydrogels nanocomposites on the gelation time, swelling ratio, in vitro degradation, and mechanical properties was investigated. The as-prepared PHEM-CS/CeONPs hydrogels nanocomposites dressing shows high antimicrobial activity against Staphylococcus aureus and Escherichia coli. Similar trends were observed for the treatment of biofilms where PHEM-CS/CeONPs hydrogels nanocomposites displayed better efficiency. Furthermore, the biological properties of PHEM-CS/CeONPs hydrogels nanocomposites had non-toxic in cell viability and excellent cell adhesion behaviour. After 2 weeks, the wounds treated with the PHEM-CS/CeONPs hydrogels nanocomposite wound dressing achieved a significant closure to 98.5 ± 4.95% compared with the PHEM-CS hydrogels with nearly 71 ± 3.55% of wound closure. Hence, this study strongly supports the possibility of using this novel PHEM-CS/CeONPs hydrogels nanocomposites wound dressing for efficient cutaneous wound healing on chronic wound infection and nursing care.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Developments on the Smart Hydrogel-Based Drug Delivery System for Oral Tumor Therapy

At present, an oral tumor is usually treated by surgery combined with preoperative or postoperative radiotherapies and chemotherapies. However, traditional chemotherapies frequently result in substantial toxic side effects, including bone marrow suppression, malfunction of the liver and kidneys, and neurotoxicity. As a new local drug delivery system, the smart drug delivery system based on hydrogel can control drug release in time and space, and effectively alleviate or avoid these problems. Environmentally responsive hydrogels for smart drug delivery could be triggered by temperature, photoelectricity, enzyme, and pH. An overview of the most recent research on smart hydrogels and their controlled-release drug delivery systems for the treatment of oral cancer is given in this review. It is anticipated that the local drug release method and environment-responsive benefits of smart hydrogels will offer a novel technique for the low-toxicity and highly effective treatment of oral malignancy.

Photopolymerized Zwitterionic Hydrogels with a Sustained Delivery of Cerium Oxide Nanoparticle-miR146a Conjugate Accelerate Diabetic Wound Healing

In the United States, $87 billion per year is spent on the care of diabetic ulcers alone. Although the pathophysiology of diabetic wound healing is multifaceted, high systemic levels of inflammation and increased reactive oxygen species are often implicated in the wound healing impairment. Zwitterionic materials have been demonstrated to reduce inflammation and increase extracellular matrix deposition in wound beds, and here, we demonstrate a fabrication method for photopolymerized zwitterionic hydrogels that also enables sustained drug delivery over time. A therapeutic molecule of interest that is examined in this work is cerium oxide nanoparticle tagged with microRNA-146a (CNP-miR146a) to combat both oxidative stress and inflammation. The hydrogels are composed of zwitterionic and nonzwitterionic monomers, and the hydrogel formation occurs in the absence of a crosslinker. The hydrogels exhibit a wide range of stiffness and mechanical properties depending on their monomer content. Additionally, these hydrogels exhibit sustained release of nanoparticles and proteins. Finally, when employed in an in vivo diabetic mouse wound healing model, the zwitterionic hydrogels alone and laden with the CNP-miR146a conjugate significantly improved the rate of diabetic wound healing. Overall, these materials have excellent potential to be used as a topical treatment for chronic diabetic wounds.

Antibacterial thyme oil-loaded zwitterionic emulsion hydrogels

Emulsion hydrogels are structurally composite materials combining the advantages of emulsions and hydrogels with the ability to accommodate hydrophobic and hydrophilic components in one system. It is a promising strategy for the excellent encapsulation and delivery of many bioactive ingredients. In this work, the thyme oil-loaded zwitterionic emulsion hydrogels are constructed by the cellulose acetoacetate-horseradish peroxidase-hydrogen peroxide-initiated (CAA-HRP-H₂O₂-initiated) ternary enzyme-mediated polymerization of the thyme oil-in-water (O/W) emulsions stabilized by cellulose acetoacetate (CAA). CAA is the key component in the system, acting as the emulsifier and the polymerization mediator simultaneously. The formed zwitterionic poly(sulfobetaine methacrylate) (PSBMA) hydrogel network provides emulsion hydrogels with good hydration capacity and potential anti-fouling performance. The thyme oil-loaded zwitterionic emulsion hydrogels exhibit interconnected, uniform, and adjustable porous structures with tunable mechanical properties, antifouling performance, good biocompatibility, and excellent antibacterial activity against S. aureus and E. coli. These results all demonstrate that the ternary enzyme-mediated polymerization of zwitterionic monomers in the continuous phase of O/W emulsion templates is a facile and efficient strategy to encapsulate hydrophobic bioactive ingredients.

Diverse nanocomposites as a potential dressing for diabetic wound healing

Wound healing is a programmed process of continuous events which is impaired in the case of diabetic patients. This impaired process of healing in diabetics leads to amputation, longer hospitalisation, immobilisation, low self-esteem, and mortality in some patients. This problem has paved the way for several innovative strategies like the use of nanotechnology for the treatment of wounds in diabetic patients. The use of biomaterials, nanomaterials have advanced approaches in tissue engineering by designing multi-functional nanocomposite scaffolds. Stimuli-responsive scaffolds that interact with the wound microenvironment and controlled release of bioactive molecules have helped in overcoming barriers in healing. The use of different types of nanocomposite scaffolds for faster healing of diabetic wounds is constantly being studied. Nanocomposites have helped in addressing specific issues with respect to healing and improving angiogenesis. Method: A literature search was followed to retrieve the articles on strategies for wound healing in diabetes across several databases like PubMed, EMBASE, Scopus and Cochrane database. The search was performed in May 2022 by two researchers independently. They keywords used were "diabetic wounds, nanotechnology, nanocomposites, nanoparticles, chronic diabetic wounds, diabetic foot ulcer, hydrogel". Exclusion criteria included insulin resistance, burn wound, dressing material.

A review on the features, performance and potential applications of hydrogel-based wearable strain/pressure sensors

Over the past few years, development of wearable devices has gained increasing momentum. Notably, the demand for stretchable strain sensors has significantly increased due to many potential and emerging applications such as human motion monitoring, prosthetics, robotic systems, and touch panels. Recently, hydrogels have been developed to overcome the drawbacks of the elastomer-based wearable strain sensors, caused by insufficient biocompatibility, brittle mechanical properties, complicated fabrication process, as the hydrogels can provide a combination of various exciting properties such as intrinsic electrical conductivity, suitable mechanical properties, and biocompatibility. There are numerous research works reported in the literature which consider various aspects as preparation approaches, design strategies, properties control, and applications of hydrogel-based strain sensors. This article aims to present a review on this exciting topic with a new insight on the hydrogel-based wearable strain sensors in terms of their features, strain sensory performance, and prospective applications. In this respect, we first briefly review recent advances related to designing the materials and the methods for promoting hydrogels' intrinsic features. Then, strain (both tensile and pressure) sensing performance of prepared hydrogels is critically studied, and alternative approaches for their high-performance sensing are proposed. Subsequently, this review provides several promising applications of hydrogel-based strain sensors, including bioapplications and human-machine interface devices. Finally, challenges and future outlooks of conductive and stretchable hydrogels employed in the wearable strain sensors are discussed.

Switchable Photonic Bio-Adhesive Materials

A soft photonic bio-adhesive material is designed with real-time colorimetrical monitoring of switchable adhesion by integrating a responsive bio-photonic matrix with mobile hydrogen-binding networking. Synergetic materials sequencing creates a unique iridescent appearance directly coupled with both adhesive ability and shearing strength, in a highly reversible manner. The responsive photonic materials, having a physically hydrogen-bonded chiral nematic organization, vary their adhesion strength due to a transition in cohesive and interfacial failure mechanism in humid surroundings. The bright color appearance shifts from blue to red to transparent and back due to a change in pitch length of the chiral helicoidal organization that also triggers coupled changes in both mechanical strength and interfacial adhesion. Such reversible strength-adhesion-iridescence triple-coupling phenomenon is further explored for design of super-strong switchable bio-adhesives for synthetic/biological surfaces with quick remotely triggered sticky-to-nonsticky transitions, removable conformal soft stickers, and wound dressings with visual monitoring of the healing process, to colorimetric stickers for contaminated respiratory masks.

Biomimetic Mineralization of Tannic Acid-Supplemented HEMA/SBMA Nanocomposite Hydrogels

This study developed a tannic acid (TA)-supplemented 2-hydroxyethyl methacrylate-co-sulfobetaine methacrylate (HEMA-co-SBMA) nanocomposite hydrogel with mineralization and antibacterial functions. Initially, hybrid hydrogels were synthesized by incorporating SBMA into the HEMA network and the influence of SBMA on the chemical structure, water content, mechanical properties, and antibacterial characteristics of the hybrid HEMA/SBMA hydrogels was examined. Then, nanoclay (Laponite XLG) was introduced into the hybrid HEMA/SBMA hydrogels and the effects evaluated of the nanoclay on the chemical structure, water content, and mechanical properties of these supplemented hydrogels. The 50/50 hybrid HEMA/SBMA hydrogel with 30 mg/mL nanoclay showed outstanding mechanical properties (3 MPa) and water content (60%) compared to pure polyHEMA hydrogels. TA then went on to be incorporated into these hybrid nanocomposite hydrogels and its effects investigated on biomimetic mineralization. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) showed that bone-like spheroidal precipitates with a Ca/P ratio of 1.67% were observed after 28 days within these mineralized hydrogels. These mineralized hydrogels demonstrated an almost 1.5-fold increase in compressive moduli compared to the hydrogels without mineralization. These multifunctional hydrogels display good mechanical and biomimetic properties and may have applications in bone regeneration therapies.

Near-Infrared Light-, Magneto-, and pH-Responsive GO-Fe3O4/Poly(N-isopropylacrylamide)/alginate Nanocomposite Hydrogel Microcapsules for Controlled Drug Release

Responsive hydrogels have found widespread applications in biomedical science and engineering fields, especially for drug delivery. Despite the superior performance of responsive hydrogels, challenges still exist in drug-delivery efficiency when environmental stimuli are weak. Recently, the demand in the design of hydrogel-based drug delivery systems has stimulated considerable interest in the search for new strategies, for instance, the application of nanocomposite hydrogels for reinforcing the versatility and flexibility in controlled drug delivery. In this study, a novel and effective nanocomposite hydrogel microcapsule drug delivery system, which is composed of poly(N-isopropylacrylamide) (PNIPAM) and alginate interpenetrating polymer and GO-Fe₃O₄ nanomaterials, is developed to achieve NIR light-, magneto-, and pH-responsive drug release. The GO-Fe₃O₄ nanomaterials embedded in the interpenetrating polymer enable the PNIPAM hydrogel deswelling by raising temperature above the lower critical solution temperature under NIR light and alternating magnetic field, thus accelerating the release of doxorubicin. In addition, the introduction of alginate into PNIPAM hydrogels endows nanocomposite hydrogels (NCHs) with quick gelation property, enhanced mechanical property, and pH-responsive performance. The in vitro cytotoxicity assay confirmed that the NCH platform can effectively kill the cancer cells. This novel multiresponsive drug delivery system holds great promise for the treatment of diseases.

Highly antifouling, biocompatible and tough double network hydrogel based on carboxybetaine-type zwitterionic polymer and alginate

Because of resistance to bio-macromolecular adhesion, antifouling hydrogels have attracted great attention in biomedical field. But traditional antifouling hydrogels made by hydrophilic polymers are always poor of mechanical properties. Herein, a new hybrid ionic-covalent cross-linked double network (DN) hydrogel was prepared by a simple one-pot method based on sodium alginate and the zwitterionic material carboxybetaine acrylamide (CBAA). The DN hydrogel has good mechanical properties, including high elastic modulus (0.28 MPa), high tensile strength (0.69 MPa), as well as good self-recovery capability. More importantly, the DN hydrogel is highly resistance to the adsorption of non-specific protein, cells, bacteria and algae, exhibiting an outstanding antifouling property. The in vitro and in vivo experiments prove that the DN hydrogel is highly biocompatible. This study provides a new strategy for the preparation of antifouling DN hydrogels with good mechanical properties for different needs, such as tissue scaffolds, wound dressings, implantable devices, and other fields.

Development of a Mechanically Strong Nondegradable Protein Hydrogel with a Sponge-Like Morphology

Protein-based hydrogels are important functional materials with many potential applications. However, the relatively small pore size and poor mechanical properties substantially limit their application. Here a superporous bovine serum albumin (BSA) hydrogel is prepared with high porosity and interconnectivity by using BSA and 1,2,7,8-diepoxyoctane (DEO). The equilibrium water contents of hydrogels can reach 76.5%. Moreover, the BSA hydrogels show excellent mechanical properties and excellent deformation recoverability, with a maximum compression modulus of 50 MPa at 75% strain and no residual strain generated after 500 cyclic compression tests. The resulting BSA hydrogel has excellent biocompatibility for cell adherence and is nonbiodegradable for 40 weeks. More importantly, the BSA hydrogel exhibits excellent hemostatic ability, with hemostatic times in a rabbit ear artery and rabbit liver of 33 and 28 s, respectively. Therefore, BSA hydrogels have potential applications as painless nonadherent wound dressings and implant materials for plastic surgery.

Antifouling Antioxidant Zwitterionic Dextran Hydrogels as Wound Dressing Materials with Excellent Healing Activities

Hydrogels as wound dressings have received great attention in recent years. It is highly important yet challenging to develop hydrogel dressings that are biocompatible and that can promote wound healing by lowering the risk of inflammatory responses. In this work, we designed and prepared zwitterionic dextran-based hydrogels using carboxybetaine dextran (CB-Dex) and sulfobetaine dextran (SB-Dex) as raw materials, respectively. The efficacy of CB-Dex and SB-Dex hydrogels in promoting wound recovery was evaluated using a mouse skin wound model. Results suggested that the zwitterionic dextran wound dressings showed a faster healing rate than natural dextran hydrogel and a commercial wound dressing (Duoderm film) due to their excellent protein resistance and capacity to scavenge free hydroxyl radicals. In addition, both CB-Dex and SB-Dex hydrogel wound dressings showed excellent cytocompatibility with NIH3T3 and L929 cells, as well as antibacterial adhesion against Staphylococcus aureus and Escherichia coli. Furthermore, both zwitterionic hydrogels demonstrated self-healing properties and can be stretched to adapt to irregular full-thickness wound beds. More importantly, they can be removed from the wound site painlessly by washing with normal saline. Overall, this work provided a new pathway to fabricate multifunctional polysaccharide hydrogels for wound treatment and pain relief when changing wound dressings.

Zwitterionic Hydrogel with High Transparency, Ultrastretchability, and Remarkable Freezing Resistance for Wearable Strain Sensors

Multifunctional hydrogel with outstanding conductivity and mechanical flexibility has received enormous attention as wearable electronic devices. However, fabricating transparent, ultrastretchable, and biocompatible hydrogel with low-temperature stability still remains a tremendous challenge. In this study, an ultrastretchable, highly transparent, and antifreezing zwitterionic-based electronic sensor is developed by introducing zwitterionic proline (ZP) into gellan gum/polyacrylamide (GG/PAAm) double network (DN) hydrogel. The existence of ZP endows the hydrogel with remarkable frost resistance. The toughness and transparency of zwitterionic Ca-GG/PAAm-ZP DN hydrogel can be maintained down to -40 °C. Also, the zwitterionic hydrogel shows good biocompatibility and protein adsorption resistance. The zwitterionic Ca-GG/PAAm-ZP DN hydrogel-based strain sensor can accurately monitor human motions (such as speaking and various joint bendings) under a broad temperature range from -40 to 25 °C. The zwitterionic Ca-GG/PAAm-ZP DN hydrogel-based strain sensor will be of immense value in the field of wearable electronic devices, especially for extreme environment applications.

Zwitterionized Nanofibrous Poly(vinylidene fluoride) Membranes for Improving the Healing of Diabetic Wounds

This work presents nanofibrous membranes made of poly(vinylidene fluoride) (PVDF) and poly(2-methacryloyloxyethyl phosphorylcholine-co-methacryloyloxyethyl butylurethane) (PMBU) for promoting the healing of acute and chronic wounds. Membranes were prepared by an electrospinning process, which led to matrixes with a pore size mimicking the extracellular matrix. PMBU greatly improves the hydration of membranes, resulting in very low biofouling by protein or bacteria and enhanced blood compatibility while the cell viability remains close to 100%. This set of properties exhibited by the suitable combination of physical structure and material composition led to applying the zwitterionic nanofibrous membranes as wound-dressing materials for acute and chronic wounds. The results demonstrated that the zwitterionic membrane could compete with commercial dressings in terms of wound-healing kinetics and could outperform them with regard to the quality of new tissue. Histological analyses suggested that inflammation was reduced while proliferative and maturation phases were accelerated, leading to homogeneous re-epithelialization. This study unveils another potential biomedical application of antifouling zwitterionic membranes.

Peritoneal adhesions: Occurrence, prevention and experimental models

Peritoneal adhesions (PA) are a postoperative syndrome with high incidence rate, which can cause chronic abdominal pain, intestinal obstruction, and female infertility. Previous studies have identified that PA are caused by a disordered feedback of blood coagulation, inflammation, and fibrinolysis. Monocytes, macrophages, fibroblasts, and mesothelial cells are involved in this process, and secreted signaling molecules, such as tumor necrosis factor alpha (TNF-α), interleukin-10 (IL-10), tissue plasminogen activator (tPA), and type 1 plasminogen activator inhibitor (PAI-1), play a key role in PA development. There have been many attempts to prevent PA formation by anti-PA drugs, barriers, and other therapeutic methods, but their effectiveness has not been widely accepted. Treatment by biomaterial-based barriers is believed to be the most promising method to prevent PA formation in recent years. In this review, the pathogenesis, treatment approaches, and animal models of PA are summarized and discussed to understand the challenges faced in the biomaterial-based anti-PA treatments.

Cysteine-Capped Hydrogels Incorporating Copper as Effective Antimicrobial Materials against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (S. aureus) (MRSA) has become an alarming threat to public health, and infected soft tissue. Antibiotics are commonly used to treat skin infection with MRSA, but the inappropriate use of antibiotics runs a considerable risk of generating resistant S. aureus. In this study, we created a cysteine-capped hydrogel able to absorb and release copper, an ion with the capability of suppressing the growth of USA300, a community-acquired MRSA. The results of analysis of Fourier transform infrared spectroscopy (FTIR) revealed the binding of copper to a cysteine-capped hydrogel. The topical application of a cysteine-capped hydrogel binding with copper on USA300-infected skin wounds in the dorsal skin of Institute of Cancer Research (ICR) mice significantly enhanced wound healing, hindered the growth of USA300, and reduced the production of pro-inflammatory macrophage inflammatory protein 2-alpha (MIP-2) cytokine. Our work demonstrates a newly designed hydrogel that conjugates a cysteine molecule for copper binding. The cysteine-capped hydrogel can potentially chelate various antimicrobial metals as a novel wound dressing.

Injectable, self-healable zwitterionic cryogels with sustained microRNA - cerium oxide nanoparticle release promote accelerated wound healing

Diabetics are prone to chronic wounds that have slower healing, and methods of accelerating the wound closure and to ensure protection from infections are critically needed. MicroRNA-146a gets dysregulated in diabetic wounds and injection of this microRNA combined with reactive oxygen species-scavenging cerium oxide nanoparticles (CNPs) can reduce inflammation and improve wound healing; however, a better delivery method than intradermal injections is needed. Here we demonstrate a biomaterial system of zwitterionic cryogels (gels formed below freezing temperatures) laden with CNP-miR146a that are topically applicable, injectable, self-healable, and provide sustained release of the therapeutic molecules. These cryogels are comprised of CBMA or SBMA and HEMA, and do not contain chemical crosslinkers. Properties of the gels can be manipulated by changing monomer type and ratio. These materials have demonstrated efficacy and viability in vivo with a diabetic mouse wound healing model. Overall, these materials have a high potential for application in wound treatments due to their ease of production, antifouling characteristics, durability, topical application, and sustained release mechanics. STATEMENT OF SIGNIFICANCE: This work presents the development of zwitterionic cryogels with unique physical properties including injectability and self-healing, that also offer highly sustained release of nanoparticles over time to improve wound healing in a diabetic mouse model. The nanoparticles are made of cerium oxide, which is known to scavenge reactive oxygen species and reduce oxidative stress, and these particles have been further tagged with a microRNA146a that has been shown to reduce inflammation. Zwitterionic materials are known for their superior antifouling properties and good biocompatibility and ability to incorporate bioactive factors. Given these properties, the use of these materials as wound healing dressings would be exciting, yet to date it has been difficult to prolong the release of bioactive factors from them due to their hydrophilicity. Previously we developed zwitterionic cyrogels with very sustained protein release over time, but those materials were quite brittle and difficult to handle. Here, we demonstrate for the first time that by removing the crosslinker molecule from our reaction and polymerizing gels under cryo-conditions, we are able to form zwitterionic cryogels that are injectable, self-healing, and with sustained release profiles. The sustained release of miRNA146a-tagged cerium oxide nanoparticles from these gels is demonstrated to speed up diabetic wound healing time and significantly reduce inflammation.

3D-printable zwitterionic nano-composite hydrogel system for biomedical applications

Herein, the cytotoxicity of a novel zwitterionic sulfobetaine hydrogel system with a nano-clay crosslinker has been investigated. We demonstrate that careful selection of the composition of the system (monomer to Laponite content) allows the material to be formed into controlled shapes using an extrusion based additive manufacturing technique with the ability to tune the mechanical properties of the product. Moreover, the printed structures can support their own weight without requiring curing during printing which enables the use of a printing-then-curing approach. Cell culture experiments were conducted to evaluate the neural cytotoxicity of the developed hydrogel system. Cytotoxicity evaluations were conducted on three different conditions; a control condition, an indirect condition (where the culture medium used had been in contact with the hydrogel to investigate leaching) and a direct condition (cells growing directly on the hydrogel). The result showed no significant difference in cell viability between the different conditions and cells were also found to be growing on the hydrogel surface with extended neurites present.

Bi-Layered Polymer Carriers with Surface Modification by Electrospinning for Potential Wound Care Applications

Polymeric wound dressings with advanced properties are highly preferred formulations to promote the tissue healing process in wound care. In this study, a combinational technique was investigated for the fabrication of bi-layered carriers from a blend of polyvinyl alcohol (PVA) and sodium alginate (SA). The bi-layered carriers were prepared by solvent casting in combination with two surface modification approaches: electrospinning or three-dimensional (3D) printing. The bi-layered carriers were characterized and evaluated in terms of physical, physicochemical, adhesive properties and for the safety and biological cell behavior. In addition, an initial inkjet printing trial for the incorporation of bioactive substances for drug delivery purposes was performed. The solvent cast (SC) film served as a robust base layer. The bi-layered carriers with electrospun nanofibers (NFs) as the surface layer showed improved physical durability and decreased adhesiveness compared to the SC film and bi-layered carriers with patterned 3D printed layer. Thus, these bi-layered carriers presented favorable properties for dermal use with minimal tissue damage. In addition, electrospun NFs on SC films (bi-layered SC/NF carrier) provided the best physical structure for the cell adhesion and proliferation as the highest cell viability was measured compared to the SC film and the carrier with patterned 3D printed layer (bi-layered SC/3D carrier). The surface properties of the bi-layered carriers with electrospun NFs showed great potential to be utilized in advanced technical approach with inkjet printing for the fabrication of bioactive wound dressings.

Tough Polyelectrolyte Hydrogels with Antimicrobial Property via Incorporation of Natural Multivalent Phytic Acid

Tough and antimicrobial dual-crosslinked poly((trimethylamino)ethyl methacrylate chloride)-phytic acid hydrogel (pTMAEMA-PA) has been synthesized by adding a chemical crosslinker and docking a physical crosslinker of multivalent phytic acid into a cationic polyelectrolyte network. By increasing the loading concentration of PA, the tough hydrogel exhibits compressive stress of >1 MPa, along with high elasticity and fatigue-resistant properties. The enhanced mechanical properties of pTMAEMA-PA stem from the multivalent ion effect of PA via the formation of ion bridges within polyelectrolytes. In addition, a comparative study for a series of pTMAEMA-counterion complexes was conducted to elaborate the relationship between swelling ratio and mechanical strength. The study also revealed secondary factors, such as ion valency, ion specificity and hydrogen bond formation, holding crucial roles in tuning mechanical properties of the polyelectrolyte hydrogel. Furthermore, in bacteria attachment and disk diffusion tests, pTMAEMA-PA exhibits superior fouling resistance and antibacterial capability. The results reflect the fact that PA enables chelating strongly with divalent metal ions, hence, disrupting the outer membrane of bacteria, as well as dysfunction of organelles, DNA and protein. Overall, the work demonstrated a novel strategy for preparation of tough polyelectrolyte with antibacterial capability via docking PA to open up the potential use of PA in medical application.

Zwitterionic Hydrogel Incorporated Graphene Oxide Nanosheets with Improved Strength and Lubricity

Graphene oxide (GO) has been evaluated as a multifunctional cross-linker or reinforcement agent in composite hydrogels. In this study, a nanocomposite hydrogel consisting of GO nanosheets and zwitterionic poly(sulfobetaine methacrylate) (PSBMA) was synthesized in an aqueous system via chemical and physical cross-linking effects. GO nanosheets were well dispersed in the hydrogels and effectively cross-linked into the sulfobetaine methacrylate (SBMA) polymer chains through the electrostatic interactions. The PSBMA hydrogel exhibited a significant enhancement in the compressive stress (close to a 5-fold increase) and a remarkable reduction in the coefficient of friction (COF) (corresponding to a decline of 52-76%) after the embedding of GO nanosheets. These improvements indicate the existence of synergetic interaction and good compatibility between GO nanosheets and the PSBMA hydrogel matrix, which results in an intertwined network structure with higher load-bearing capacity and better lubrication properties. This study provides potential in the development of new graphene-polymer composites, which is beneficial for cartilage replacement with high mechanical properties and excellent lubrication characteristics.

Thermosensitive double network of zwitterionic polymers for controlled mechanical strength of hydrogels

Zwitterionic hydrogels have promising potential as a result of their anti-fouling and biocompatible properties, but they have recently also gained further attention due to their controllable stimuli responses. We successfully synthesized two zwitterionic polymers, poly(2-methacryloyloxyethyl phosphorylcholine) (poly-MPC) and poly(2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide) (poly-DMAPS), which have complementary ionic sequences in their respective zwitterionic side groups and likely form an interpenetrating double network to improve their mechanical strength. The synthesized poly-MPC was blended in a poly-DMAPS matrix (MD gel) and showed high viscosity, while poly-DMAPS was blended in a poly-MPC hydrogel (DM gel) and revealed UCST behavior as the temperature increased. In addition, cross-section images of the MD hydrogel exhibited its compact and uniform structure, while the DM gel was found to exhibit a porous micro-structure with clear boundaries. The results explained the low viscosity of the DM gel, which was also confirmed via 3D Raman mapping. To sum up, the preliminary data demonstrated that binary zwitterionic hydrogels have thermosensitive mechanical properties, promoting further bio-applications in the future, such as in wound healing.

Zwitterionic hydrogels have promising anti-fouling properties but weak mechanical strength. Here, we synthesized two polyzwitterions, formulated them as double network hydrogels for improving strength and for controlled by temperature stimuli.

Engineering Antifouling Conducting Polymers for Modern Biomedical Applications

Conducting polymers are considered to be favorable electrode materials for implanted biosensors and bioelectronics, because their mechanical properties are similar to those of biological tissues such as nerve and brain tissues. However, one of the primary challenges for implanted devices is to prevent the unwanted protein adhesion or cell binding within biological fluids. The nonspecific adsorption generally causes the malfunction of implanted devices, which is problematic for long-term applications. When responding to the requirements of solving the problems caused by nonspecific adsorption, an increasing number of studies on antifouling conducting polymers has been recently published. In this review, synthetic strategies for preparing antifouling conducting polymers, including direct synthesis of functional monomers and post-functionalization, are introduced. The applications of antifouling conducting polymers in modern biomedical applications are particularly highlighted. This paper presents focuses on the features of antifouling conducting polymers and the challenges of modern biomedical applications.

2D Nanoclay for Biomedical Applications: Regenerative Medicine, Therapeutic Delivery, and Additive Manufacturing

Clay nanomaterials are an emerging class of 2D biomaterials of interest due to their atomically thin layered structure, charged characteristics, and well-defined composition. Synthetic nanoclays are plate-like polyions composed of simple or complex salts of silicic acids with a heterogeneous charge distribution and patchy interactions. Due to their biocompatible characteristics, unique shape, high surface-to-volume ratio, and charge, nanoclays are investigated for various biomedical applications. Here, a critical overview of the physical, chemical, and physiological interactions of nanoclay with biological moieties, including cells, proteins, and polymers, is provided. The state-of-the-art biomedical applications of 2D nanoclay in regenerative medicine, therapeutic delivery, and additive manufacturing are reviewed. In addition, recent developments that are shaping this emerging field are discussed and promising new research directions for 2D nanoclay-based biomaterials are identified.

Atomistic Study of Zwitterionic Peptoid Antifouling Brushes

Using molecular dynamics (MD) simulations, we study the molecular behavior and hydration properties of a set of zwitterionic "peptoid" brushes, grafted on a rutile surface, that has been previously reported to exhibit excellent resistance against protein adsorption and cell attachment. Peptoids are novel poly( N-substituted glycine) peptide mimics with the side chains attached to amide nitrogens. They constitute a unique model polymer system because hundreds of side chains have been demonstrated, and the exact chain length and sequence order of the residues/monomers may be specified in experiments. In this report, we vary the brush grafting density as well as the side chain/polymer molecular volume. We include in our study polysarcosine as an uncharged comparison with a small polymer chain cross-section. Sarcosine is the simplest peptoid residue with only a nominally hydrophobic methyl group as side chain, but is also reported to exhibit high antifouling performance. Overall, we show in detail how molecular volume and hydration effects are intertwined in a zwitterionic polymer brush. For example, the zwitterionic design significantly promotes extended chain conformations and could actually lower the overall electrostatic potential. Some properties promoted by the balanced charges, such as chain flexibility and hydration, increase more prominently at "low" to "intermediate" chain densities. These and other observations should provide insight on the molecular behavior of peptoids and inform the design of zwitterionic antifouling polymer brushes.

Development of Antimicrobial and Antifouling Universal Coating via Rapid Deposition of Polydopamine and Zwitterionization

Biomaterials-associated infections (BAIs) are related to bacterial colonization on medical devices, which lead to a serious medical burden, such as increased healthcare cost, prolonged hospital stays, and high mortality and morbidity. To reduce the risk of infections, in this work, a new approach which makes use of a bioinspired coating with dual antimicrobial and antifouling functions was developed through rapid deposition of functional polydopamine (pDA) and antimicrobial copper ions, and subsequent conjugation of zwitterionic antifouling sulfobetaine (SB) moieties by the aza-Michael addition reaction. pDA permits surface-independent versatile functionalization on a variety of substrates, such as TiO₂, SiO₂, gold, plastics, and Nitinol alloy. The characterizations for chemical elemental compositions and hydrophilicity by X-ray photoelectron spectroscopy and contact angle goniometer, respectively, indicating the successful grafting of SB moieties and the presence of copper ions in the pDA adlayers. Ellipsometric thicknesses of the thin films were followed to monitor the formation of pDA films and the changes after the post conjugation. UV-vis spectroscopy and inductively coupled plasma-mass spectrometry revealed the coordination structure of catechol-Cu, and release profile of Cu²⁺ from the constructed functional coatings. The superhydrophilic and charge-balanced SB interface allowed effective resistance of bacterial adsorption. Intriguingly, we scrutinized that the release of bactericidal copper ions enables killing the residual amount of adsorbed bacteria. Moreover, viability tests for fibroblast cells indicate the excellent biocompatibility of the developed medical coatings. For real-world implementation, the antifouling and antimicrobial coatings were applied on commercially available silicone-based urinary catheters, and the existence of bacteria was evaluated by using the plate-counting assay. The results showed an undetectable level of living bacteria. Consequently, the dual functional medical coating offers a promising approach to eliminate BAIs for practical applications.

Simple Thermal Pretreatment Strategy to Tune Mechanical and Antifouling Properties of Zwitterionic Hydrogels

Zwitterionic hydrogels are promising biomaterials because of their high water content, three-dimensional network structure, and antifouling property. However, it still remains unclear about how mechanical properties of zwitterionic hydrogels affect their antifouling property. In this work, we propose a simple, thermal-pretreatment method to fabricate poly(sulfobetaine methacrylate) (pSBMA) hydrogels with varied mechanical properties that can be readily tuned by thermal pretreatment time and cross-linker density, as well as to correlate their mechanical property with antifouling property. The resulting thermal-treated pSBMA hydrogels show significantly enhanced mechanical properties with tunable compressive modulus and elastic modulus as compared to the untreated hydrogels. A combination of ELISA investigations and short-term cell adhesion assays also confirm that pSBMA hydrogels exhibit superior antifouling properties to resist protein adsorption and cell adhesion. Further analysis shows a linear inversion correlation between elastic modulus and protein adsorption of pSBMA hydrogels, i.e., the hydrogel with the higher elastic modulus exhibits the lower protein adsorption (the better antifouling property). This work not only provides a simple thermal-pretreatment strategy for fabricating pSBMA hydrogels, but also demonstrates multifunctional properties of the pSBMA hydrogels, which possess a great potential to fulfill some biomedical applications.

Self-assembled proteinaceous wound dressings attenuate secondary trauma and improve wound healing in vivo

Stimuli-responsive gauze coated with a phase-transitioned lysozyme nanofilm (PTLF@gauze) has been developed, which exhibits great potential for clinical applications by reducing secondary trauma and relieving the pain of patients.

One-step synthesis of an antibacterial and pro-healing wound dressing that can treat wound infections

Preventing bacterial contamination, treating wound infections and promoting wound healing have been major challenges in wound care management. In this work, a novel wound dressing based on a zwitterionic polycarboxybetaine (PCB) hydrogel and antibacterial silver nanoparticles (AgNPs) was developed via a one-step method for the efficient treatment of infected wounds. The PCB-AgNP hydrogel exhibits effective antibacterial ability against both Gram positive bacteria (Saphylococcus aureus) and Gram negative bacteria (Escherichia coli). Furthermore, in a murine model, the PCB-AgNP hydrogel is found to efficiently treat S. aureus infection and accelerate cutaneous wound healing. After a two-week healing process, histological tests indicate that it can promote the reconstruction of intact epidermis, which is much faster than those treated with a commercial wound dressing (Duoderm® film). This new bifunctional wound dressing provides new opportunities for highly efficient skin wound care and management.

Accelerated Healing of Diabetic Wounds Treated with L-Glutamic acid Loaded Hydrogels Through Enhanced Collagen Deposition and Angiogenesis: An In Vivo Study

We have developed L-glutamic acid (LG) loaded chitosan (CS) hydrogels to treat diabetic wounds. Although literature reports wound healing effects of poly(glutamic acid)-based materials, there are no studies on the potential of L-glutamic acid in treating diabetic wounds. As LG is a direct precursor for proline synthesis, which is crucial for collagen synthesis, we have prepared CS + LG hydrogels to accelerate diabetic wound healing. Physiochemical properties of the CS + LG hydrogels showed good swelling, thermal stability, smooth surface morphology, and controlled biodegradation. The addition of LG to CS hydrogels did not alter their biocompatibility significantly. CS + LG hydrogel treatment showed rapid wound contraction compared to control and chitosan hydrogel. Period of epithelialization is significantly reduced in CS + LG hydrogel treated wounds (16 days) compared to CS hydrogel (20 days), and control (26 days). Collagen synthesis and crosslinking are also significantly improved in CS + LG hydrogel treated diabetic rats. Histopathology and immunohistochemistry results revealed that the CS + LG hydrogel dressing accelerated vascularization and macrophage recruitment to enhance diabetic wound healing. These results demonstrate that incorporation of LG can improve collagen deposition, and vascularization, and aid in faster tissue regeneration. Therefore, CS + LG hydrogels could be an effective wound dressing used to treat diabetic wounds.

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.