Model polymer system for investigating the generation of hydrogen peroxide and its biological responses during the crosslinking of mussel adhesive moiety

A MnO2 nanosheets doping double crosslinked hydrogel for cartilage defect repair through alleviating inflammation and guiding chondrogenic differentiation

The inflammatory microenvironment and inferior chondrogenesis are major symptoms after cartilage defect. Although various modifications strategies associated with hydrogels exhibit remarkable capacity of pro-cartilage regeneration, the adverse effect by prolonging inflammation is still formidable to hamper potential biomedical applications of different hydrogel implants. Herein, inspired by the repair microenvironment of articular cartilage defects, an injectable, immunomodulatory, and chondrogenic L-MNS-CMDA hydrogel is prepared through grafting vinyl and catechol groups to chitosan macromolecules using amide reaction, then further loading MnO2 nanosheets (MNS). The double crosslinking of photopolymerization and catechol oxidative polymerization endows L-MNS-CMDA hydrogel with preferable mechanical property, affording a suitable mechanical support for cartilage defect repair. Additionally, the robust tissue adhesion capability stemming from catechol groups guarantees the long-term retention of the hydrogel in the defect site. Meanwhile, L-MNS-CMDA hydrogel decomposes exogenous and intracellular H2O2 into O2 and H2O, to effectively alleviate cellular oxidative stress caused by long-term hypoxia. Under the synergies of catechol groups and MNS, L-MNS-CMDA hydrogel not only inhibits macrophages polarizing into M1 phenotype, but encourages them turn into M2 phenotype, thereby, reconstructing an immunization friendly microenvironment to ultimately enhance cartilage regeneration. Predictably, the hydrogel markedly induces rat bone marrow mesenchymal stem cells differentiating into chondrocytes by expressing abundant glycosaminoglycan and type II collagen. A cartilage defect model of rat knee joint indicates that L-MNS-CMDA hydrogel visually regulate the early inflammatory response of post-implantation, and facilitate cartilage regeneration and recovery of joint function after 12 weeks of post-implantation. All in all, this multifunctional L-MNS-CMDA hydrogel exhibits superior immunomodulatory and chondrogenic properties, holding immense clinical potential in the treatment of cartilage defects.

Synergistic effect of ROS-generating polydopamine on drug-induced bone tissue regeneration

A PHD (prolyl hydroxylase) inhibitor, 1,4-dihydrophenonthrolin-4-one-3-carboxylic acid (1,4-DPCA), is a drug that can artificially promote tissue regeneration by enhancing metabolic activity through the upregulation of hypoxia inducible factor 1 subunit alpha (Hif-1α) under normoxic conditions. This study presents a novel design methodology for a drug delivery system to maximize the regenerative effect of 1,4-DPCA. Specifically, by encapsulating 1,4-DPCA in polydopamine (PDA) that generates reactive oxygen species (ROS), the combined effects of Hif-1α upregulation and the induction of cellular antioxidant defense mechanisms by localized ROS can significantly enhance tissue regeneration. The study confirmed that each material (PDA and 1,4-DPCA) triggers a positive synergistic effect on the regenerative mechanisms. As a result, the use of a PDA drug delivery system loaded with 1,4-DPCA showed approximately six times greater bone regeneration compared to the control (no treatment) in a mouse calvarial defect model.

Utilizing Rapid Hydrogen Peroxide Generation from 6-Hydroxycatechol to Design Moisture-Activated, Self-Disinfecting Coating

A coating that can be activated by moisture found in respiratory droplets could be a convenient and effective way to control the spread of airborne pathogens and reduce fomite transmission. Here, the ability of a novel 6-hydroxycatechol-containing polymer to function as a self-disinfecting coating on the surface of polypropylene (PP) fabric was explored. Catechol is the main adhesive molecule found in mussel adhesive proteins. Molecular oxygen found in an aqueous solution can oxidize catechol and generate a known disinfectant, hydrogen peroxide (H2O2), as a byproduct. However, given the limited amount of moisture found in respiratory droplets, there is a need to enhance the rate of catechol autoxidation to generate antipathogenic levels of H2O2. 6-Hydroxycatechol contains an electron donating hydroxyl group on the 6-position of the benzene ring, which makes catechol more susceptible to autoxidation. 6-Hydroxycatechol-coated PP generated over 3000 μM of H2O2 within 1 h when hydrated with a small amount of aqueous solution (100 μL of PBS). The generated H2O2 was three orders of magnitude higher when compared to the amount generated by unmodified catechol. 6-Hydroxycatechol-containing coating demonstrated a more effective antimicrobial effect against both Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria when compared to unmodified catechol. Similarly, the self-disinfecting coating reduced the infectivity of both bovine viral diarrhea virus and human coronavirus 229E by as much as a 2.5 log reduction value (a 99.7% reduction in viral load). Coatings containing unmodified catechol did not generate sufficient H2O2 to demonstrate significant virucidal effects. 6-Hydroxycatechol-containing coating can potentially function as a self-disinfecting coating that can be activated by the moisture present in respiratory droplets to generate H2O2 for disinfecting a broad range of pathogens.

Acrylate monomer polymerization triggered by iron oxide magnetic nanoparticles and catechol containing microgels

Phenol and its derivatives are the most used polymerization inhibitors for vinyl-based monomers. Here, we reported a novel catalytic system composed of mussel inspired adhesive moiety, catechol, in combination with iron oxide nanoparticles (IONPs) to generate hydroxyl radical (•OH) at pH 7.4. Catechol-containing microgel (DHM) was prepared by copolymerizing dopamine methacrylamide (DMA) and N-hydroxyethyl acrylamide (HEAA), which generated superoxide (•O2-) and hydrogen peroxide (H2O2) as a result of catechol oxidation. In the presence of IONPs, the generated reactive oxygen species were further converted to •OH, which initiated free radical polymerization of various water-soluble acrylate-based monomers including neutral (acrylamide, methyl acrylamide, etc.), anionic (2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt), cationic ([2-(methacryloyloxy)ethyl]trimethylammonium chloride), and zwitterionic (2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide) monomers. Compared with the typical free radical initiating systems, the reported system does not require the addition of extra initiators for polymerization. During the process of polymerization, a bilayer hydrogel was formed in situ and exhibited the ability to bend during the process of swelling. The incorporation of IONPs significantly enhanced magnetic property of the hydrogel and the combination of DHM and IONPs also improved the mechanical properties of these hydrogels.

Adhesive and self-healing materials for central nervous system repair

The central nervous system (CNS) has a limited ability to regenerate after a traumatic injury or a disease due to the low capacity of the neurons to re-grow and the inhibitory environment formed in situ. Current therapies include the use of drugs and rehabilitation, which do not fully restore the CNS functions and only delay the pathology progression. Tissue engineering offers a simple and versatile solution for this problem through the use of bioconstructs that promote nerve tissue repair by bridging cavity spaces. In this approach, the choice of biomaterial is crucial. Herein, we present recent advances in the design and development of adhesive and self-healing materials that support CNS healing. The adhesive materials have the advantage of promoting recovery without the use of needles or sewing, while the self-healing materials have the capacity to restore the tissue integrity without the need for external intervention. These materials can be used alone or in combination with cells and/or bioactive agents to control the inflammation, formation of free radicals, and proteases activity. We discuss the advantages and drawbacks of different systems. The remaining challenges that can bring these materials to clinical reality are also briefly presented.

Utilizing Robust Design to Optimize Composite Bioadhesive for Promoting Dermal Wound Repair

Catechol-modified bioadhesives generate hydrogen peroxide (H2O2) during the process of curing. A robust design experiment was utilized to tune the H2O2 release profile and adhesive performance of a catechol-modified polyethylene glycol (PEG) containing silica particles (SiP). An L9 orthogonal array was used to determine the relative contributions of four factors (the PEG architecture, PEG concentration, phosphate-buffered saline (PBS) concentration, and SiP concentration) at three factor levels to the performance of the composite adhesive. The PEG architecture and SiP wt% contributed the most to the variation in the results associated with the H2O2 release profile, as both factors affected the crosslinking of the adhesive matrix and SiP actively degraded the H2O2. The predicted values from this robust design experiment were used to select the adhesive formulations that released 40-80 µM of H2O2 and evaluate their ability to promote wound healing in a full-thickness murine dermal wound model. The treatment with the composite adhesive drastically increased the rate of the wound healing when compared to the untreated controls, while minimizing the epidermal hyperplasia. The release of H2O2 from the catechol and soluble silica from the SiP contributed to the recruitment of keratinocytes to the wound site and effectively promoted the wound healing.

A smart hydrogel patch with high transparency, adhesiveness and hemostasis for all-round treatment and glucose monitoring of diabetic foot ulcers

The treatment and management of diabetic foot ulcers (DFUs) is a pretty intractable problem for clinical nursing. Urgently, the "Black Box" status of the healing process prevents surgeons from providing timely analysis for more effective diagnosis and therapy of the wound. Herein, we designed a transparent monitoring system to treat and manage the DFUs with blood oozing and hard-healing, which resolved the problem of blind management for the other conductive patches. This system was prepared from a conductive hydrogel patch with ultra-high transparence (up to 93.6%), adhesiveness and hemostasis, which is engineered by assembling in situ formed poly(tannic acid) (PTA)-doped polypyrrole (PPy) nanofibrils in the poly(acrylamide-acrylated adenine) (P(AM-Aa)) polymer networks. Significantly, the high transparent conductive hydrogel patch can monitor the wound-healing status visually and effectively promote the healing of DFUs by accelerating hemostasis, improving communication between cells, preventing wound infection, facilitating collagen deposition, and promoting angiogenesis. In addition, the versatile hydrogel patch could realize indirect blood glucose monitoring by detecting the glucose levels on wounds, and further sense the movements with different magnitudes of human body timely. This research may provide a novel strategy in the design of chronic wound dressings for monitoring and treating the wounds synergistically.

Supramolecular Adhesive Hydrogels for Tissue Engineering Applications

Tissue engineering is a promising and revolutionary strategy to treat patients who suffer the loss or failure of an organ or tissue, with the aim to restore the dysfunctional tissues and enhance life expectancy. Supramolecular adhesive hydrogels are emerging as appealing materials for tissue engineering applications owing to their favorable attributes such as tailorable structure, inherent flexibility, excellent biocompatibility, near-physiological environment, dynamic mechanical strength, and particularly attractive self-adhesiveness. In this review, the key design principles and various supramolecular strategies to construct adhesive hydrogels are comprehensively summarized. Thereafter, the recent research progress regarding their tissue engineering applications, including primarily dermal tissue repair, muscle tissue repair, bone tissue repair, neural tissue repair, vascular tissue repair, oral tissue repair, corneal tissue repair, cardiac tissue repair, fetal membrane repair, hepatic tissue repair, and gastric tissue repair, is systematically highlighted. Finally, the scientific challenges and the remaining opportunities are underlined to show a full picture of the supramolecular adhesive hydrogels. This review is expected to offer comparative views and critical insights to inspire more advanced studies on supramolecular adhesive hydrogels and pave the way for different fields even beyond tissue engineering applications.

Engineering a naturally derived hemostatic sealant for sealing internal organs

Controlling bleeding from a raptured tissue, especially during the surgeries, is essentially important. Particularly for soft and dynamic internal organs where use of sutures, staples, or wires is limited, treatments with hemostatic adhesives have proven to be beneficial. However, major drawbacks with clinically used hemostats include lack of adhesion to wet tissue and poor mechanics. In view of these, herein, we engineered a double-crosslinked sealant which showed excellent hemostasis (comparable to existing commercial hemostat) without compromising its wet tissue adhesion. Mechanistically, the engineered hydrogel controlled the bleeding through its wound-sealing capability and inherent chemical activity. This mussel-inspired hemostatic adhesive hydrogel, named gelatin methacryloyl-catechol (GelMAC), contained covalently functionalized catechol and methacrylate moieties and showed excellent biocompatibility both in vitro and in vivo. Hemostatic property of GelMAC hydrogel was initially demonstrated with an in vitro blood clotting assay, which showed significantly reduced clotting time compared to the clinically used hemostat, Surgicel®. This was further assessed with an in vivo liver bleeding test in rats where GelMAC hydrogel closed the incision rapidly and initiated blood coagulation even faster than Surgicel®. The engineered GelMAC hydrogel-based seaalant with excellent hemostatic property and tissue adhesion can be utilized for controlling bleeding and sealing of soft internal organs.

Antibacterial Gel Coatings Inspired by the Cryptic Function of a Mussel Byssal Peptide

Although the adhesive and cohesive nature of mussel byssal proteins have long served to inspire the design of materials embodying these properties, their characteristic amino acid compositions suggest that they might also serve to inspire an unrelated material function not yet associated with this class of protein. Herein, it is demonstrated that a peptide derived from mussel foot protein-5, a key protein in mussel adhesion, displays antibacterial properties, a yet unreported activity. This cryptic function serves as inspiration for the design of a new class of peptide-based antibacterial adhesive hydrogels prepared via self-assembly, which are active against drug-resistant Gram-positive bacteria. The gels exert two mechanisms of action, surface-contact membrane disruption and oxidative killing affected by material-produced H₂ O₂ . Detailed studies relating amino acid composition and sequence to material mechanical adhesion/cohesion and antibacterial activity affords the MIKA2 adhesive gel, a material with a superior activity that is shown to inhibit colonization of titanium implants in mice.

Preventing post-surgical cardiac adhesions with a catechol-functionalized oxime hydrogel

Post-surgical cardiac adhesions represent a significant problem during routine cardiothoracic procedures. This fibrous tissue can impair heart function and inhibit surgical access in reoperation procedures. Here, we propose a hydrogel barrier composed of oxime crosslinked poly(ethylene glycol) (PEG) with the inclusion of a catechol (Cat) group to improve retention on the heart for pericardial adhesion prevention. This three component system is comprised of aldehyde (Ald), aminooxy (AO), and Cat functionalized PEG mixed to form the final gel (Ald-AO-Cat). Ald-AO-Cat has favorable mechanical properties, degradation kinetics, and minimal swelling, as well as superior tissue retention compared to an initial Ald-AO gel formulation. We show that the material is cytocompatible, resists cell adhesion, and led to a reduction in the severity of adhesions in an in vivo rat model. We further show feasibility in a pilot porcine study. The Ald-AO-Cat hydrogel barrier may therefore serve as a promising solution for preventing post-surgical cardiac adhesions.

Oxidation Chemistry of Catechol Utilized in Designing Stimuli-Responsive Adhesives and Antipathogenic Biomaterials

Mussel foot proteins (Mfps) contain a large amount of the catecholic amino acid, DOPA, allowing the marine organism to anchor themselves onto various surfaces in a turbulent and wet environment. Modification of polymers with catechol imparts these materials with a strong, wet adhesive property. The oxidation chemistry and oxidation state of catechol are critical to the design of synthetic adhesives and biomaterials. In this Mini-Review, the effect of catechol oxidation state on adhesion, oxidation-mediated catechol cross-linking, and the generation of reactive oxygen species (ROS) during catechol oxidation are reviewed. Finally, the tuning of catechol oxidation state in designing stimuli-responsive adhesives and the utilization of ROS byproducts for antimicrobial and antiviral applications are reviewed.

Nanocomposite adhesive hydrogels: from design to application

Hydrogels may exhibit strong adhesion upon embedding nanoparticles into them forming strong/weak bonds (via the multiple physical or chemical interactions).

Controlling the Release of Hydrogen Peroxide from Catechol-Based Adhesive Using Silica Nanoparticle

Catechol-based bioadhesives generate hydrogen peroxide (H₂O₂) as a byproduct during the curing process. H₂O₂ can have both beneficial and deleterious effects on biological systems depending on its concentration. To control the amount of H₂O₂ released from catechol-containing polyethylene glycol-based adhesive (PEG-DA), adhesive was formulated with silica nanoparticles (SiNP) prepared with increased porosity and acid treatment to increase Si-OH surface content. These SiNP demonstrated increased surface area, which promoted interaction with catechol and resulted in increased cure rate, bulk mechanical properties and adhesive properties of PEG-DA. Most importantly, SiNP demonstrated a 50% reduction in the released H₂O₂ while improving the cell viability and proliferation of three primary cell types, including rat dermal fibroblasts, human epidermal keratinocytes, and human tenocytes. Additionally, SiNP degraded into soluble Si, which also contributed to increased cell proliferation. Incorporation of porous and acid-treated SiNP can be a useful approach to simultaneously modulate the concentration of H₂O₂ while increasing the adhesive performance of catechol-based adhesives.

Iron Magnetic Nanoparticle-Induced ROS Generation from Catechol-Containing Microgel for Environmental and Biomedical Applications

Reactive oxygen species (ROS) can degrade organic compounds and function as a broad-spectrum disinfectant. Here, dopamine methacrylamide (DMA) was used to prepare catechol-containing microgels, which can release ROS via metal-catechol interaction. A combination of the microgel and iron magnetic nanoparticle (FeMNP) significantly reduced the concentration of four organic dyes (Alizarin Red S, Rhodamine B, Crystal Violet, and Malachite Green) and an antibiotic drug, ciprofloxacin, dissolved in solution. Degradation of dye occurred across a wide range of pH levels (pH 3-9). This simple combination was also antimicrobial against both Escherichia coli and Staphylococcus aureus. Electron paramagnetic resonance spectroscopy (EPR) results indicate that singlet oxygen was generated during the reaction between catechol and FeMNP at both pH 3 and 7.4, which was responsible for the degradation of organic compounds and bactericidal features of the microgel. Unlike autoxidation that only occurs at a neutral to basic pH, FeMNP-induced catechol oxidation generated singlet oxygen over a wide range of pH level. Additionally, catechol chelates heavy metal ions, resulting in their removal from solution and repurposed these metal ions for dye degradation. This multifunctional microgel can potentially be used for environmental applications for the removal of organic pollutants and heavy metal ions from wastewater, as well as reducing bacterial infection in biomedical applications.

Catechol-functionalized hydrogels: biomimetic design, adhesion mechanism, and biomedical applications

Hydrogels are a unique class of polymeric materials that possess an interconnected porous network across various length scales from nano- to macroscopic dimensions and exhibit remarkable structure-derived properties, including high surface area, an accommodating matrix, inherent flexibility, controllable mechanical strength, and excellent biocompatibility. Strong and robust adhesion between hydrogels and substrates is highly desirable for their integration into and subsequent performance in biomedical devices and systems. However, the adhesive behavior of hydrogels is severely weakened by the large amount of water that interacts with the adhesive groups reducing the interfacial interactions. The challenges of developing tough hydrogel-solid interfaces and robust bonding in wet conditions are analogous to the adhesion problems solved by marine organisms. Inspired by mussel adhesion, a variety of catechol-functionalized adhesive hydrogels have been developed, opening a door for the design of multi-functional platforms. This review is structured to give a comprehensive overview of adhesive hydrogels starting with the fundamental challenges of underwater adhesion, followed by synthetic approaches and fabrication techniques, as well as characterization methods, and finally their practical applications in tissue repair and regeneration, antifouling and antimicrobial applications, drug delivery, and cell encapsulation and delivery. Insights on these topics will provide rational guidelines for using nature's blueprints to develop hydrogel materials with advanced functionalities and uncompromised adhesive properties.

Antibacterial Properties of Mussel-Inspired Polydopamine Coatings Prepared by a Simple Two-Step Shaking-Assisted Method

A simple two-step, shaking-assisted polydopamine (PDA) coating technique was used to impart polypropylene (PP) mesh with antimicrobial properties. In this modified method, a relatively large concentration of dopamine (20 mg ml⁻¹) was first used to create a stable PDA primer layer, while the second step utilized a significantly lower concentration of dopamine (2 mg ml⁻¹) to promote the formation and deposition of large aggregates of PDA nanoparticles. Gentle shaking (70 rpm) was employed to increase the deposition of PDA nanoparticle aggregates and the formation of a thicker PDA coating with nano-scaled surface roughness (RMS = 110 nm and Ra = 82 nm). Cyclic voltammetry experiment confirmed that the PDA coating remained redox active, despite extensive oxidative cross-linking. When the PDA-coated mesh was hydrated in phosphate saline buffer (pH 7.4), it was activated to generate 200 μM hydrogen peroxide (H₂O₂) for over 48 h. The sustained release of low doses of H₂O₂ was antibacterial against both gram-positive (Staphylococcus epidermidis) and gram-negative (Escherichia coli) bacteria. PDA coating achieved 100% reduction (LRV ~3.15) when incubated against E. coli and 98.9% reduction (LRV ~1.97) against S. epi in 24 h.

Marine-Inspired Polymers in Medical Adhesion

Medical adhesives that are strong, easy to apply and biocompatible are promising alternatives to sutures and staples in a large variety of surgical and clinical procedures. Despite progress in the development and regulatory approval of adhesives for use in the clinic, adhesion to wet tissue remains challenging. Marine organisms have evolved a diverse set of highly effective wet adhesive approaches that have inspired the design of new medical adhesives. Here we provide an overview of selected marine animals and their chemical and physical adhesion strategies, the state of clinical translation of adhesives inspired by these organisms, and target applications where marine-inspired adhesives can have a significant impact. We will focus on medical adhesive polymers inspired by mussels, sandcastle worms, and cephalopods, emphasize the history of bioinspired medical adhesives from the peer reviewed and patent literature, and explore future directions including overlooked sources of bioinspiration and materials that exploit multiple bioinspired strategies.

Multifunctional Biomedical Adhesives

Currently available biomedical adhesives are mainly engineered to have one function (i.e., providing mechanical support for the repaired tissue). To improve the performance of existing bioadhesives and broaden their applications in medicine, numerous multifunctional bioadhesives are reported in the literature. These adhesives can be categorized as passive or active by design. Passive multifunctional bioadhesives contain inherent compositions and structural designs that can carry out additional functions without added external influences. These adhesives exhibit new functionalities such as antimicrobial properties, self-healing abilities, the ability to promote cellular ingrowth, and the ability to be reshaped. Conversely, active multifunctional bioadhesives respond to environmental changes (e.g., pH, temperature, electricity, light, and biomolecule concentration), which initiate a change in the adhesive to release encapsulated drugs or to activate or deactivate the bioadhesive for interfacial binding. This review article highlights recent advances in multifunctional bioadhesives.

Biomimetic recyclable microgels for on-demand generation of hydrogen peroxide and antipathogenic application

Microgels that can generate antipathogenic levels of hydrogen peroxide (H₂O₂) through simple rehydration in solutions with physiological pH are described herein. H₂O₂ is a widely used disinfectant but the oxidant is hazardous to store and transport. Catechol, an adhesive moiety found in mussel adhesive proteins, was incorporated into microgels, which generated 1-5 mM of H₂O₂ for up to four days as catechol autoxidized. The sustained release of low concentrations of H₂O₂ was antimicrobial against both gram-positive (Staphylococcus epidermidis) and gram-negative (Escherichia coli) bacteria and antiviral against both non-enveloped porcine parvovirus (PPV) and enveloped bovine viral diarrhea virus (BVDV). The amount of released H₂O₂ is several orders of magnitude lower than H₂O₂ concentration previously reported for antipathogenic activity. Most notably, these microgels reduced the infectivity of the more biocide resistant non-envelope virus by 3 log reduction value (99.9% reduction in infectivity). By controlling the oxidation state of catechol, microgels can be repeatedly activated and deactivated for H₂O₂ generation. These microgels do not contain a reservoir for storing the reactive H₂O₂ and can potentially function as a lightweight and portable dried powder source for the disinfectant for a wide range of applications. STATEMENT OF SIGNIFICANCE: Researchers have designed bioadhesives and coatings using the adhesive moiety catechol to mimic the strong adhesion capability of mussel adhesive proteins. During catechol autoxidation, hydrogen peroxide (H₂O₂) is generated as a byproduct. Here, catechol was incorporated into microgels, which can generate millimolar levels of H₂O₂ by simply hydrating the microgels in a solution with physiological pH. The sustained release of H₂O₂ was both antimicrobial and antiviral, inactivating even the more biocide resistant non-enveloped virus. These microgels can be repeatedly activated and deactivated for H₂O₂ generation by incubating them in solutions with different pH. This simplicity and recyclability will enable this biomaterial to function as a lightweight and portable source for the disinfectant for a wide range of applications.

Mussel adhesive Protein-conjugated Vitronectin (fp-151-VT) Induces Anti-inflammatory Activity on LPS-stimulated Macrophages and UVB-irradiated Keratinocytes

BACKGROUND

Skin inflammation and dermal injuries are a major clinical problem because current therapies are limited to treating established scars, and there is a poor understanding of healing mechanisms. Mussel adhesive proteins (MAPs) have great potential in many tissue engineering and biomedical applications. It has been successfully demonstrated that the redesigned hybrid type MAP (fp-151) can be utilized as a promising adhesive biomaterial. The aim of this study was to develop a novel recombinant protein using fp-151 and vitronectin (VT) and to elucidate the anti-inflammatory effects of this recombinant protein on macrophages and keratinocytes.

METHODS

Lipopolysaccharide (LPS) was used to stimulate macrophages and UVB was used to stimulate keratinocytes. Inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 were analyzed by Western Blot. Inflammatory cytokines and NO and ROS production were analyzed.

RESULT

In macrophages stimulated by LPS, expression of the inflammatory factors iNOS, COX-2, and NO production increased, while the r-fp-151-VT-treated groups had suppressed expression of iNOS, COX-2, and NO production in a dose-dependent manner. In addition, keratinocytes stimulated by UVB and treated with r-fp-151-VT had reduced expression of iNOS and COX-2. Interestingly, in UVB-irradiated keratinocytes, inflammatory cytokines, such as interleukin (IL)-1b, IL-6, and tumor necrosis factor (TNF)-a, were significantly reduced by r-fp-151-VT treatment.

CONCLUSIONS

These results suggest that the anti-inflammatory activity of r-fp-151-VT was more effective in keratinocytes, suggesting that it can be used as a therapeutic agent to treat skin inflammation.

Catechol-rich gelatin hydrogels in situ hybridizations with silver nanoparticle for enhanced antibacterial activity

Recently, the interest in antimicrobial hydrogels with impregnated antibacterial agents has significantly increased because of their ability to combat infection in biomedical applications, including wound management, tissue engineering, and biomaterial surface coating. Among these antibacterial reagents, silver nanoparticles (AgNP) show good antibacterial activity against both gram-negative and gram-positive bacteria, including highly multi-resistant strains. However, the entrapment of AgNP within a hydrogel matrix is often associated with toxicity issues because of the use of chemical reductants (e.g., commonly sodium borohydride), burst leaching, or unwanted agglomeration of AgNP in the absence of surfactants or stabilizers. In this study, we present catechol-rich gelatin hydrogels with in situ hybridization of AgNP for enhanced antimicrobial activities. AgNP were formed through a redox reaction between silver ions and the catechol moieties of a gelatin derivative polymer, without the addition of any chemical reductants. The AgNP with an average size of 20 nm were entrapped within hydrogel matrices and showed sustained release from the hydrogel matrix (8.7% for 14 days). The resulting hydrogels could kill both gram-negative and gram-positive bacteria, depending on the amount of AgNP released from the hydrogels and did not have a significant influence on mammalian cell viability. We believe that our catechol-rich hydrogels in situ hybridizations with AgNP have great potential for biomedical applications, such as wound management and surface coating, because of their excellent antibacterial activities and biocompatibility.

Effect of incorporating clustered silica nanoparticles on the performance and biocompatibility of catechol-containing PEG-based bioadhesive

A composite adhesive capable of inducing cellular infiltration was prepared by incorporating control clustered silica microparticle (MP) derived from the aggregation of silica nanoparticle (NP) into a catechol-terminated poly(ethylene glycol) bioadhesive (PEG-DA). Incorporation of MP into PEG-DA significantly improved the mechanical and adhesive properties of the bioadhesive. There was no statistical difference between the measured values for NP- and MP-incorporated adhesives, indicating that MP was equally as effective in enhancing the material properties of PEG-DA as NP. Most importantly, MP was significantly less cytotoxic when compared to NP when these particles were directly exposed to L929 fibroblast. When the adhesives were implanted subcutaneously in rats, MP-containing PEG-DA also exhibited reduced inflammatory responses, attracted elevated levels of regenerative M2 macrophage to its interface, and promoted cellular infiltration due to increased porosity within the adhesive network. Control clustered silica MP can be used to improve the performance and biocompatibility of PEG-based adhesive while minimizing undesirable cytotoxicity of silica NP.

Effect of Ionic Functional Groups on the Oxidation State and Interfacial Binding Property of Catechol-Based Adhesive

Adhesive hydrogels were prepared by copolymerizing dopamine methacrylamide with either acrylic acid (AAc) or N-(3-aminopropyl)methacrylamide hydrochloride (APMH). The effect of incorporating the anionic and cationic side chains on the oxidation state of catechol was characterized using the FOX assay to track the production of hydrogen peroxide byproduct generated during the autoxidation of catechol, and the interfacial binding property of the adhesive was determined by performing Johnson-Kendall-Roberts contact mechanics tests tested over a wide range of pH values (pH 3.0-9.0). The ionic species contributed to interfacial binding to surfaces with the opposite charge with measured work of adhesion values that were comparable to or in some cases higher than those of catechol. Addition of AAc minimized the oxidation of catechol even at a pH of 8.5 and correspondingly preserved the elevated adhesive property of catechol to both quartz and amine-functionalized surfaces. However, AAc lost its buffering capacity at pH 9.0, and catechol was oxidized at this pH. On the other hand, catechol formed a cohesive covalent bond with the network-bound amine side chain of APMH at basic pH, which interfered with the interfacial binding capability of APMH and the catechol.

Rough Adhesive Hydrogels (RAd gels) for Underwater Adhesion

In this work, underwater adhesion is achieved between biocompatible hydrogels and a suite of substrates. Surface roughness, which is typically detrimental for adhesion in air, is shown to be beneficial for underwater adhesion. Contact between the hydrogels with macroscopically flat substrates, and the resulting nonspecific chemical interaction, is facilitated by surface roughness, which enables drainage of the lubricating fluid layer. Hydrogel composition plays an important role in tuning the gel elasticity and interaction with the substrate. Hydrogels that are adhesive on two sides are synthesized for potential use as versatile adhesives in various applications.

A novel injectable tissue adhesive based on oxidized dextran and chitosan

A surgical adhesive that can be used in different surgical situations with or without sutures is a surgeons' dream and yet none has been able to fulfill many such demanding requirements. It was therefore a major challenge to develop an adhesive biomaterial that stops bleeding and bond tissues well, which at the same time is non-toxic, biocompatible and yet biodegradable, economically viable and appealing to the surgeon in terms of the simplicity of application in complex surgical situations. With this aim, we developed an in situ setting adhesive based on biopolymers such as chitosan and dextran. Dextran was oxidized using periodate to generate aldehyde functions on the biopolymer and then reacted with chitosan hydrochloride. Gelation occurred instantaneously upon mixing these components and the resulting gel showed good tissue adhesive properties with negligible cytotoxicity and minimal swelling in phosphate buffered saline (PBS). Rheology analysis confirmed the gelation process by demonstrating storage modulus having value higher than loss modulus. Adhesive strength was in the range 200-400gf/cm² which is about 4-5 times more than that of fibrin glue at comparable setting times. The adhesive showed burst strength in the range of 400-410mm of Hg which should make the same suitable as a sealant for controlling bleeding in many surgical situations even at high blood pressure. Efficacy of the adhesive as a hemostat was demonstrated in a rabbit liver injury model. Histological features after two weeks were comparable to that of commercially available BioGlue®. The adhesive also demonstrated its efficacy as a drug delivery vehicle. The present adhesive could function without the many toxicity and biocompatibility issues associated with such products.

STATEMENT OF SIGNIFICANCE

Though there are many tissue adhesives available in market, none are free of shortcomings. The newly developed surgical adhesive is a 2-component adhesive system based on time-tested, naturally occurring polysaccharides such as chitosan and dextran which are both biocompatible and biodegradable. Simple polymer modification has been carried out on both polysaccharides so that when aqueous solutions of both are mixed, the solutions gel in less than 10s and forms an adhesive that seals a variety of incisions. The strength of the adhesive is over 5-times the strength of commercially available Fibrin glue and is more tissue compliant than BioGlue®. This adhesive biomaterial showed excellent tissue bonding, was hemostatic, biocompatible and biodegradable. The significance of this work lies on the features of the developed tissue adhesive that it stops bleeding, bond the tissues well, can act as a drug delivery vehicle and would appeal to the surgeon in terms of the simplicity of application in complex surgical situations. There is no need for special delivery systems for application of this adhesive. The two-component adhesive can be applied one over the other using syringes. There is also no need for light curing with UV or visible light and the gelation between the two components spontaneously takes place on application leading to excellent tissue bonding.

A Moldable Nanocomposite Hydrogel Composed of a Mussel-Inspired Polymer and a Nanosilicate as a Fit-to-Shape Tissue Sealant

The engineering of bioadhesives to bind and conform to the complex contour of tissue surfaces remains a challenge. We have developed a novel moldable nanocomposite hydrogel by combining dopamine-modified poly(ethylene glycol) and the nanosilicate Laponite, without the use of cytotoxic oxidants. The hydrogel transitioned from a reversibly cross-linked network formed by dopamine-Laponite interfacial interactions to a covalently cross-linked network through the slow autoxidation and cross-linking of catechol moieties. Initially, the hydrogel could be remolded to different shapes, could recover from large strain deformation, and could be injected through a syringe to adhere to the convex contour of a tissue surface. With time, the hydrogel solidified to adopt the new shape and sealed defects on the tissue. This fit-to-shape sealant has potential in sealing tissues with non-flat geometries, such as a sutured anastomosis.