On-demand and negative-thermo-swelling tissue adhesive based on highly branched ambivalent PEG-catechol copolymers

Mucoadhesive, antioxidant, and lubricant catechol-functionalized poly(phosphobetaine) as biomaterial nanotherapeutics for treating ocular dryness

Dry eye disease (DED) is associated with ocular hyperosmolarity and inflammation. The marketed topical eye drops for DED treatment often lack bioavailability and precorneal residence time. In this study, we investigated catechol-functionalized polyzwitterion p(MPC-co-DMA), composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and dopamine methacrylamide (DMA) monomers, as potential topical nanotherapeutics for DED. The copolymers were synthesized via random free-radical copolymerization, producing different proportions of catecholic functionalization. All as-prepared polymer compositions displayed good ocular biocompatibility. At a feeding ratio of 1:1, p(MPC1-co-DMA1) can facilitate a robust mucoadhesion via Michael addition and/or Schiff base reaction, thus prolonging ocular residence time after 4 days of topical instillation. The hydration lubrication of MPC and radical-scavenging DMA endow the nano-agent to ease tear-film hyperosmolarity and corneal inflammation. A single dose of p(MPC1-co-DMA1) (1 mg/mL) after 4 days post-instillation can protect the cornea against reactive oxygen species, inhibiting cell apoptosis and the over-expression of pro-inflammatory factors (IL-6 and TNF-α). In clinical assessment, DED-induced rabbit eyes receiving p(MPC1-co-DMA1) could increase lacrimal fluid secretion by 5-fold higher than cyclosporine A. The catechol-functionalized polyzwitterion with enhanced lubricity, mucoadhesion, and anti-oxidation/anti-inflammation properties has shown high promise as a bioactive eye drop formulation for treating DED.

(Controlled) Free radical (co)polymerization of multivinyl monomers: strategies, topological structures and biomedical applications

Free radical (co)polymerization (FRP/FRcP) of multivinyl monomers (MVMs) has emerged as a powerful strategy for the synthesis of chemically and topologically complex polymers due to its unique reaction kinetics, which enables the preparation of polymers with multiple functional groups and novel macromolecular structures. However, conventional FRP/FRcP of MVMs inevitably leads to insoluble crosslinked materials. Therefore, the development of advanced strategies for the controlled polymerization of MVMs is essential for the preparation of chemically and topologically complex polymers. In this review, we introduce the gelation mechanism of conventional FRP of MVMs and present the strategies of controlled polymerization of MVMs for the preparation of chemically and topologically complex polymers. We also discuss polymers with unique topologies synthesized by controlled polymerization of MVMs, such as crosslinked networks, (hyper)branched, star, cyclic, and single-chain cyclized/knotted structures. Finally, biomedical applications of various advanced polymeric materials prepared by controlled polymerization of MVMs are highlighted and the challenges is this field are discussed.

Composition, host responses and clinical applications of bioadhesives

Bioadhesives are medical devices used to join or seal tissues that have been injured or incised. They have been classified into tissue adhesives, sealants, and hemostatic agents. Bioadhesives such as FloSeal®, CoSeal®, BioGlue®, Evicel®, Tisseel®, Progel™ PALS, and TissuGlu® have been commercialized and used in clinical setting. They can be formulated with natural or synthetic components or a combination of both including albumin, glutaraldehyde, chitosan, cyanoacrylate, fibrin and thrombin, gelatin, polyethylene glycol (PEG), along with urethanes. Each formulation has intrinsic properties and has been developed and validated for a specific application. This review article briefs the mechanisms by which bioadhesives forms adhesion to tissues and highlights the correlation between bioadhesives composition and their potential host responses. Furthermore, clinical applications of bioadhesives and their application-driven requirements are outlined.

Bio-macromolecular design roadmap towards tough bioadhesives

Emerging sutureless wound-closure techniques have led to paradigm shifts in wound management. State-of-the-art biomaterials offer biocompatible and biodegradable platforms enabling high cohesion (toughness) and adhesion for rapid bleeding control as well as robust attachment of implantable devices. Tough bioadhesion stems from the synergistic contributions of cohesive and adhesive interactions. This Review provides a biomacromolecular design roadmap for the development of tough adhesive surgical sealants. We discuss a library of materials and methods to introduce toughness and adhesion to biomaterials. Intrinsically tough and elastic polymers are leveraged primarily by introducing strong but dynamic inter- and intramolecular interactions either through polymer chain design or using crosslink regulating additives. In addition, many efforts have been made to promote underwater adhesion via covalent/noncovalent bonds, or through micro/macro-interlock mechanisms at the tissue interfaces. The materials settings and functional additives for this purpose and the related characterization methods are reviewed. Measurements and reporting needs for fair comparisons of different materials and their properties are discussed. Finally, future directions and further research opportunities for developing tough bioadhesive surgical sealants are highlighted.

A double-network strategy for the tough tissue adhesion of hydrogels with long-term stability under physiological environment

Achieving tough and stable tissue adhesion under a physiological environment is of great significance for the clinical applications of hydrogel adhesives. The current tough hydrogel adhesives face challenges in the preservation of the maximal adhesion for a long time due to swelling. Here, we propose a double-network strategy for tough tissue adhesion by a hydrogel with long-term stability under a physiological environment. A double-network hydrogel consisting of a covalently crosslinked primary network with tunable hydrophilicity and a non-covalently crosslinked secondary network with functional groups is designed. The primary network exhibited hydrophobicity in the physiological environment, which could constrict the secondary network and limit the swelling of the entire hydrogel. The secondary network could form strong interlinks with tissue and provide large energy dissipation through the unzipping of its noncovalent crosslinks when separated by a force. The combination of the two networks resulted in a tough and stable tissue adhesion. A poly(N-isopropylacrylamide)/calcium alginate hydrogel synthesized based on this strategy realized an adhesion energy of 300-500 J m^-2 with porcine tissues, and the maximal adhesion could be maintained for over 1000 min after submerging in a PBS solution at 37 °C. The swelling behavior of the hydrogel and changes in mechanical properties under the physiological environment are studied, and its application in repairing the aorta wound is demonstrated.

Cellulose-Based Cryogel Microspheres with Nanoporous and Controllable Wrinkled Morphologies for Rapid Hemostasis

First-aid hemostatic agents for acute bleeding can save lives in emergency situations. However, rapid hemostasis remains challenging when uncontrolled hemorrhage occurs on lethal noncompressible and irregular wounds. Herein, cellulose-based cryogel microspheres with deliberately customized micromorphologies for ultrafast water transportation and diffusion, including the shark skin riblet-inspired wrinkled surface with low fluid drag and the hydrophilic nanoporous 3D networks, are developed to deal with the acute noncompressible bleeding within seconds. These cryogel microspheres can rapidly absorb a large amount of blood over 6 times their own weight in 10 s and form a robust barrier to seal a bleeding wound without applying pressure. Remarkably, massive bleeding from a cardiac penetrating hole is effectively stopped using the microspheres within 20 s and no blood leakage is observed after 30 min. Additionally, these microspheres could be readily removed without rebleeding and capillary thrombus, which is highly favorable to rapid hemostasis in emergency rescue.

Cohesion mechanisms for bioadhesives

Due to the nature of non-invasive wound closure, the ability to close different forms of leaks, and the potential to immobilize various devices, bioadhesives are altering clinical practices. As one of the vital factors, bioadhesives' strength is determined by adhesion and cohesion mechanisms. As well as being essential for adhesion strength, the cohesion mechanism also influences their bulk functions and the way the adhesives can be applied. Although there are many published reports on various adhesion mechanisms, cohesion mechanisms have rarely been addressed. In this review, we have summarized the most used cohesion mechanisms. Furthermore, the relationship of cohesion strategies and adhesion strategies has been discussed, including employing the same functional groups harnessed for adhesion, using combinational approaches, and exploiting different strategies for cohesion mechanism. By providing a comprehensive insight into cohesion strategies, the paper has been integrated to offer a roadmap to facilitate the commercialization of bioadhesives.

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Bioadhesive are altering clinical practices.

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Bioadhesives for medical applications needs different cohesion strategies.

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Better understanding of cohesion mechanism can design suitable bioadhesives.

Biodegradable polyaspartamide-g-C18 /DOPA/GLY-NEO nano-adhesives for wound closure/healing with antimicrobial activity

This study was focused on the development of biodegradable nano-adhesives with efficient sealing and antibiotic effects for wound healing. Biodegradable polyaspartamide (PASPAM) was grafted with several functional groups to implement diverse roles-octadecylamine (C₁₈ ) for nano-aggregate formation, dopamine (DOPA) for adhesive function, neomycin (NEO) for inhibition of bacterial infection. Specifically, NEO was conjugated to PASPAM with a pH-sensitive glycine (GLY) linker for targeted delivery on the acidic wound site. About 60% of the drug was ramteleased at pH 6.0, while about 22% was released at pH 7.4, showing the faster drug release pattern of nano-adhesives in the acidic environment. The C₁₈ /DOPA/GLY-NEO-g-PASPAM nano-adhesives showed the bacterial viability higher than 70% at pH 7.4, but about 40% at pH 6.0. The wound breaking strength of the polymer-treated skin was much higher than that of the bare skin. According to the in vivo wound healing test using a mouse model, C₁₈ /DOPA/GLY-NEO-g-PASPAM nano-adhesives showed much faster healing performance than sutures. From those results, C₁₈ /DOPA/GLY-NEO-g-PASPAM nano-adhesives are expected to be utilized as effective adhesives that promote the wound healing with inhibition of bacterial infection.

The tick and I: Parasite-host interactions between ticks and humans

Ticks, particularly hard ticks (Ixodidae), which are among the most important vectors of dangerous infectious agents, feed on their hosts for extended periods of time. With this lifestyle, numerous adaptations have evolved in ticks and their hosts, the pharmacological importance of which is increasingly being recognized. Many bioactive substances in tick saliva are being considered as the basis of new drugs. For example, components of tick cement can be developed into tissue adhesives or wound closures. Analgesic and antipruritic salivary components inhibit histamine or bradykinin, while other tick-derived molecules bind opioid or cannabinoid receptors. Tick saliva inhibits the extrinsic, intrinsic, or common pathway of blood coagulation with implications for the treatment of thromboembolic diseases. It contains vasodilating substances and affects wound healing. The broad spectrum of immunomodulatory and immunosuppressive effects of tick saliva, such as inhibition of chemokines or cellular immune responses, allows development of drugs against inflammation in autoimmune diseases and/or infections. Finally, modern vaccines against ticks can curb the spread of serious infections. The medical importance of the complex tick-host interactions is increasingly being recognized and translated into first clinical applications. Using selected examples, an overview of the mutual adaptations of ticks and hosts is given here, focusing on their significance to medical advance.

Cutting-Edge Progress in Stimuli-Responsive Bioadhesives: From Synthesis to Clinical Applications

With the advent of “intelligent” materials, the design of smart bioadhesives responding to chemical, physical, or biological stimuli has been widely developed in biomedical applications to minimize the risk of wounds reopening, chronic pain, and inflammation. Intelligent bioadhesives are free-flowing liquid solutions passing through a phase shift in the physiological environment due to stimuli such as light, temperature, pH, and electric field. They possess great merits, such as ease to access and the ability to sustained release as well as the spatial transfer of a biomolecule with reduced side effects. Tissue engineering, wound healing, drug delivery, regenerative biomedicine, cancer therapy, and other fields have benefited from smart bioadhesives. Recently, many disciplinary attempts have been performed to promote the functionality of smart bioadhesives and discover innovative compositions. However, according to our knowledge, the development of multifunctional bioadhesives for various biomedical applications has not been adequately explored. This review aims to summarize the most recent cutting-edge strategies (years 2015–2021) developed for stimuli-sensitive bioadhesives responding to external stimuli. We first focus on five primary categories of stimuli-responsive bioadhesive systems (pH, thermal, light, electric field, and biomolecules), their properties, and limitations. Following the introduction of principal criteria for smart bioadhesives, their performances are discussed, and certain smart polymeric materials employed in their creation in 2015 are studied. Finally, advantages, disadvantages, and future directions regarding smart bioadhesives for biomedical applications are surveyed.

Liquid Copolymers as Biodegradable Surgical Sealant

Surgical sealants are widely used to prevent seepage of fluids and liquids, promote hemostasis, and close incisions. Despite the remarkable progress the field of biomaterials has undergone, the clinical uses of surgical sealants are limited because of their short persistence time in vivo, toxicity, and high production costs. Here, the development of two complementary neat (solvent-free) prepolymers, PEG₄ -PLGA-NHS and PEG₄ -NH₂ , that harden upon mixing to yield an elastic biodegradable sealant is presented. The mechanical and rheological properties and cross-linking rate can be controlled by varying the ratio between the two prepolymers. The tested sealants show a longer persistence time compared with fibrin glue, minimal cytotoxicity in vitro, and excellent biocompatibility in vivo. The neat, multiarmed approach demonstrated here improves the mechanical and biocompatibility properties and provides a promising tissue sealant solution for wound closure in future surgical procedures.

Dopamine-Initiated Photopolymerization for a Versatile Catechol-Functionalized Hydrogel

Biomimetic catechol-functionalized hydrogels have attracted substantial attention due to their potential in a variety of biomedical applications, such as tissue repair and regeneration, drug delivery, and antimicrobial and antifouling applications. In this study, a one-pot strategy for fabrication of functional catecholic hydrogels using dopamine as a photoinitiator was developed. Under UV irradiation in an acidic solution, dopamine generates free radicals, likely semiquinone radicals, to trigger the addition polymerization, following pseudo-first-order kinetics. The dopamine-initiated photopolymerization provides a straightforward and facile approach and, in addition, prevents the undesirable oxidation to catecholic groups. Superhydrophilic sulfobetaine methacrylate (SBMA) was applied for developing biocompatible hydrogels. ¹H nuclear magnetic resonance, UV-vis spectroscopy, gel permeation chromatography, and rheological studies were conducted to explore the polymerization mechanism and optimal experimental conditions in terms of pH, UV doses, and the concentration of dopamine. The unique properties of the resultant catechol-functionalized pSBMA hydrogels were demonstrated by enhanced mechanical properties through metal-catechol complexation, self-healing and injectable capability, high adhesiveness, and fouling resistance. Consequently, the synthetic strategy to design catecholic hydrogels can leverage the use of dopamine in a variety of applications.

A platform for functionalization of cellulose, chitin/chitosan, alginate with polydopamine: A review on fundamentals and technical applications

Nature provides concepts and materials with interesting functionalities to be implemented in innovative and sustainable materials. In this review, it is illustrated how the combination of biological macromolecules, i.e. polydopamine and polysaccharides (cellulose, chitin/chitosan, alginate), enables to create functional materials with controlled properties. The mussel-adhesive properties rely on the secretion of proteins having 3,4-dihydroxyphenylalanine amino acid with catechol groups. Fundamental understanding on the biological functionality and interaction mechanisms of dopamine in the mussel foot plaque is presented in parallel with the development of synthetic analogues through extraction or chemical polymer synthesis. Subsequently, modification of cellulose, chitin/chitosan or alginate and their nanoscale structures with polydopamine is discussed for various technical applications, including bio- and nanocomposites, films, filtration or medical membranes, adhesives, aerogels, or hydrogels. The presence of polydopamine stretches far beyond surface adhesive properties, as it can be used as an intermediate to provide additional performance of hydrophobicity, self-healing, antimicrobial, photocatalytic, sensoric, adsorption, biocompatibility, conductivity, coloring or mechanical properties. The dopamine-based 'green' chemistry can be extended towards generalized catechol chemistry for modification of polysaccharides with tannic acid, caffeic acid or laccase-mediated catechol functionalization. Therefore, the modification of polysaccharides with polydopamine or catechol analogues provides a general platform for sustainable material functionalization.

Polymeric Tissue Adhesives

Polymeric tissue adhesives provide versatile materials for wound management and are widely used in a variety of medical settings ranging from minor to life-threatening tissue injuries. Compared to the traditional methods of wound closure (i.e., suturing and stapling), they are relatively easy to use, enable rapid application, and introduce minimal tissue damage. Furthermore, they can act as hemostats to control bleeding and provide a tissue-healing environment at the wound site. Despite their numerous current applications, tissue adhesives still face several limitations and unresolved challenges (e.g., weak adhesion strength and poor mechanical properties) that limit their use, leaving ample room for future improvements. Successful development of next-generation adhesives will likely require a holistic understanding of the chemical and physical properties of the tissue-adhesive interface, fundamental mechanisms of tissue adhesion, and requirements for specific clinical applications. In this review, we discuss a set of rational guidelines for design of adhesives, recent progress in the field along with examples of commercially available adhesives and those under development, tissue-specific considerations, and finally potential functions for future adhesives. Advances in tissue adhesives will open new avenues for wound care and potentially provide potent therapeutics for various medical applications.

β-Cyclodextrin/Triclosan Complex-Grafted Methacrylated Glycol Chitosan Hydorgel by Photocrosslinking via Visible Light Irradiation for a Tissue Bio-Adhesive

Accelerating wound healing with minimized bacterial infection has become a topic of interest in the development of the new generation of tissue bio-adhesives. In this study, we fabricated a hydrogel system (MGC-g-CD-ic-TCS) consisting of triclosan (TCS)-complexed beta-cyclodextrin (β-CD)-conjugated methacrylated glycol chitosan (MGC) as an antibacterial tissue adhesive. Proton nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC) results showed the inclusion complex formation between MGC-g-CD and TCS. The increase of storage modulus (G') of MGC-g-CD-ic-TCS after visible light irradiation for 200 s indicated its hydrogelation. The swollen hydrogel in aqueous solution resulted in two release behaviors of an initial burst and sustained release. Importantly, in vitro and in vivo results indicated that MGC-g-CD-ic-TCS inhibited bacterial infection and improved wound healing, suggesting its high potential application as an antibacterial tissue bio-adhesive.

Dopamine/Phosphorylcholine Copolymer as an Efficient Joint Lubricant and ROS Scavenger for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a chronic joint disease and its progression and pathogenesis are highly associated with the significant increase of joint friction and overproduction of reactive oxygen species (ROS) in inflammation. Combination of ROS elimination and lubrication enhancement may provide a novel strategy for the treatment of OA. In the present study, a pure biomaterial and nondrug system P(DMA-co-MPC), synthesized via free radical copolymerization, was designed and developed for the first time using 2-methacryloxyethyl phosphorylcholine (MPC) as a bioinspired lubricant and N-(3,4-dihydroxyphenethyl)methacrylamide (DMA) as an ROS scavenger. Our results showed that the P(DMA-co-MPC) aggregates could efficiently eliminate the ROS radicals and provide good lubrication property by adjusting the molar ratio of DMA and MPC in the copolymer. It is attributed to the antioxidant function of the hydroquinone moiety in DMA and the hydration lubrication effect of the zwitterionic phosphocholine group in MPC. Furthermore, the in vitro experiments demonstrated that the P(DMA-co-MPC) showed good biocompatibility with MC3T3-E1 cells and intracellular anti-inflammatory property by inhibiting the production of ROS and regulating the expression levels of pro-inflammatory cytokines, pain-related gene, anabolic genes, and catabolic genes. In conclusion, the drug-free P(DMA-co-MPC) aggregates developed herein can achieve dual functions of lubrication enhancement and anti-inflammatory effect and thus they may be representative as promising candidates for the treatment of OA.

Recent Advances in Mussel-Inspired Synthetic Polymers as Marine Antifouling Coatings

Synthetic oligomers and polymers inspired by the multifunctional tethering system (byssus) of the common mussel (genus Mytilus) have emerged since the 1980s as a very active research domain within the wider bioinspired and biomimetic materials arena. The unique combination of strong underwater adhesion, robust mechanical properties and self-healing capacity has been linked to a large extent to the presence of the unusual α-amino acid derivative l-DOPA (l-3,4-dihydroxyphenylalanine) as a building block of the mussel byssus proteins. This paper provides a short overview of marine biofouling, discussing the different marine biofouling species and natural defenses against these, as well as biomimicry as a concept investigated in the marine antifouling context. A detailed discussion of the literature on the Mytilus mussel family follows, covering elements of their biology, biochemistry and the specific measures adopted by these mussels to utilise their l-DOPA-rich protein sequences (and specifically the ortho-bisphenol (catechol) moiety) in their benefit. A comprehensive account is then given of the key catechol chemistries (covalent and non-covalent/intermolecular) relevant to adhesion, cohesion and self-healing, as well as of some of the most characteristic mussel protein synthetic mimics reported over the past 30 years and the related polymer functionalisation strategies with l-DOPA/catechol. Lastly, we review some of the most recent advances in such mussel-inspired synthetic oligomers and polymers, claimed as specifically aimed or intended for use in marine antifouling coatings and/or tested against marine biofouling species.

The recent progress of tissue adhesives in design strategies, adhesive mechanism and applications

Tissue adhesives have emerged as an effective method for wound closure and hemostasis in recent decades, due to their ability to bond tissues together, preventing separation from one tissue to another. However, existing tissue adhesives still have several limitations. Tremendous efforts have been invested into developing new tissue adhesives by improving upon existing adhesives through different strategies. Therefore, highlighting and analyzing these design strategies are essential for developing the next generation of advanced adhesives. To this end, we reviewed the available strategies for modifying traditional adhesives (including cyanoacrylate glues, fibrin sealants and BioGlue), as well as design of emerging adhesives (including gelatin sealants, methacrylated sealants and bioinspired adhesives), focusing on their structures, adhesive mechanisms, advantages, limitations, and current applications. The bioinspired adhesives have numerous advantages over traditional adhesives, which will be a wise direction for achieving tissue adhesives with superior properties.

Recent progress in synthesis and application of mussel-inspired adhesives

The rapid and robust adhesion of marine mussels to diverse solid surfaces in wet environments is mediated by the secreted mussel adhesive proteins which are abundant in a catecholic amino acid, l-3,4-dihydroxyphenylalanine (Dopa). Over the last two decades, enormous efforts have been devoted to the development of synthetic mussel-inspired adhesives with water-resistant adhesion and cohesion properties by modifying polymer systems with Dopa and its analogues. In the present review, an overview of the unique features of various mussel foot proteins is provided in combination with an up-to-date understanding of catechol chemistry, which contributes to the strong interfacial binding via balancing a variety of covalent and noncovalent interactions including oxidative cross-linking, electrostatic interaction, metal-catechol coordination, hydrogen bonding, hydrophobic interactions and π-π/cation-π interactions. The recent developments of novel Dopa-containing adhesives with on-demand mechanical properties and other functionalities are then summarized under four broad categories: viscous coacervated adhesives, soft adhesive hydrogels, smart adhesives, and stiff adhesive polyesters, where their emerging applications in engineering, biological and biomedical fields are discussed. Limitations of the developed adhesives are identified and future research perspectives in this field are proposed.

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.

Bioinspired by both mussel foot protein and bone sialoprotein: universal adhesive coatings for the promotion of mineralization and osteogenic differentiation

Natural protein bioinspired coatings are developed to promote the mineralization and osteogenic differentiation of MC3T3-E1 cells for implant material use.

A Facile Preparation of Mussel-Inspired Poly(dopamine phosphonate-co-PEGMA)s via a One-Pot Multicomponent Polymerization System

Mussel-inspired polymers attract much research interest due to their potential as effective adhesives. In this work, a new kind of mussel-inspired polymer, poly(dopamine phosphonate-co-PEGMA), is prepared via a one-pot multicomponent polymerization system. The multicomponent polymerization system refers to a combination of multicomponent Kabachnik-Fields (KF) reaction and reversible addition-fragmentation chain transfer (RAFT) polymerization system. Reactants are converted to dopamine phosphonate monomers in situ through the KF reaction and polymerized simultaneously along with poly(ethylene glycol methyl ether) methacrylate (PEGMA) co-monomers by the RAFT process in a one-pot operation. Target polymers with dopamine phosphonate as side groups and well-defined polymer structures are thus facilely and successfully prepared. Afterwards, a series of polymers with various ratios of dopamine phosphonates as well as the crosslinked polymer analogues are prepared. Benefiting from the dopamine phosphonate side groups, aqueous solutions of those polymers show potential as effective adhesives in both dry and wet conditions, and their adhesive strengths are highly related to ratios of dopamine phosphonates in the polymers. Those polymers are non-cytotoxic and show strong bonding affinities on various substrates including metals, polymers, and bovine bones, suggesting their potential as environmentally friendly general adhesives in broad areas.

Influence of Polymer Composition and Substrate on the Performance of Bioinspired Coatings with Antibacterial Activity

A series of methacrylic copolymers bearing thiazolium cationic groups and catechol moieties were evaluated as antibacterial coatings on a variety of materials including aluminum and plastics such as polycarbonate, poly(methyl methacrylate), and silicone rubber. The thermal properties of the copolymers were first studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The cationic copolymers were thermally stable up to 200 °C and presented glass transition temperatures values well above 100 °C; thus, an acceptable thermal behavior for typical biomedical applications. The cationic copolymers with variable content of the adhesive anchoring N-(3,4-dihydroxyphenethyl) methacrylamide (DOMA) units were coated onto the metal and polymeric substrates by drop casting and the adhesive properties of the obtained coatings were further evaluated as a function of DOMA content and substrate. Optical profilometry, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra, and antimicrobial studies reveal that the coatings adhere stronger to metal substrates than to the polymeric substrates. The copolymers with higher content of DOMA, 24 mol.%, resist solvent erosion treatment when coated onto all substrates and exhibit antimicrobial activity against Gram-positive S. aureus bacteria after this erosion treatment. In contrast, copolymers with low content, 9 mol.% of DOMA, only remain attached onto the aluminum metal substrate after solvent treatment, while on polymeric substrates the coatings are almost removed and do not show any efficacy against S. aureus bacteria.

Dual-Mode Cross-Linking Enhances Adhesion of Silk Fibroin Hydrogels to Intestinal Tissue

Compared to conventional wound closure methods like sutures and staples, polymer-based tissue adhesives afford some distinct advantages, such as greater ease of deployment in spatially constrained surgical sites. One way to achieve aqueous adhesion is by introducing catechol functional groups that form coordinate and covalent bonds with a variety of substrates. This approach, inspired by marine organisms, has been applied to biopolymers and synthetic polymers, but one key challenge is that compositions that are soluble in water are often susceptible to high swelling ratios that can result in undesired compression of neighboring tissues. This work sought to synthesize aqueous adhesive gels that are capable of two modes of association: (1) adhesion and covalent cross-linking reactions arising from catechol oxidation and (2) noncovalent cross-linking arising from self-assembly of polymer backbones within the gelled adhesive. The network's self-assembly after gelation was envisioned to afford control over swelling and reinforce its strength. Bombyx mori silk fibroin was selected as the backbone of the adhesive network because it can be processed into an aqueous solution yet later be rendered insoluble in water through the assembly of its hydrophobic protein core. Distinct from a previous approach to functionalize silk directly with catechol groups, this work investigated in situ generation of catechol on silk fibroin by enzymatically modifying phenolic side chains, where it was found that this enzymatic approach led to conjugates with higher degrees of catechol functionalization and aqueous solubility. Silk fibroin was functionalized with tyramine to enrich the protein's phenolic side chains, which were subsequently oxidized into catechol groups using mushroom tyrosinase (MT). The gelation of the silk conjugates with MT was monitored by rheology, and the gels exhibited low water uptake. Phenolic enrichment increased the rate of chemical cross-linking leading to gelation but did not interrupt assembly of silk's secondary structures. Adhesion of the tyramine-silk conjugates to porcine intestine was found to be superior to fibrin sealant, and induction of β sheet secondary structures was found to further enhance adhesive strength through a second mode of cross-linking. Neither the chemical functionalization nor phenol oxidation affected the ability of intestinal epithelial cells (Caco-2) to attach and proliferate. Phenolic functionalization and oxidative cross-linking of silk fibroin was found to afford a new route to water-soluble, catechol-functionalized polymers, which were found to display excellent adhesion to mucosal tissue and whose secondary structure provides an additional mode to control strength and swelling of adhesive gels.

A shear-thinning adhesive hydrogel reinforced by photo-initiated crosslinking as a fit-to-shape tissue sealant

A fit-to-shape sealant enhanced by photo-initiated crosslinking treated a wound with a nonplanar complex contour rapidly and effectively.

Mussel-inspired fabrication of pH-sensitive biomimetic hydrogels based on greenhouse gas carbon dioxide

Biomimetic hydrogels were prepared from carbon dioxide using a facile method. The PPC block and catechol groups contained in PPC-PU-LDA enable the hydrogel to have good cell compatibility and adhesion.

Bioadhesives for internal medical applications: A review

Bioadhesives such as tissue adhesives, hemostatic agents, and tissue sealants have gained increasing popularity in different areas of clinical operations during the last three decades. Bioadhesives can be categorized into internal and external ones according to their application conditions. External bioadhesives are generally applied in topical medications such as wound closure and epidermal grafting. Internal bioadhesives are mainly used in intracorporal conditions with direct contact to internal environment including tissues, organs and body fluids, such as chronic organ leak repair and bleeding complication reduction. This review focuses on internal bioadhesives that, in contrast with external bioadhesives, emphasize much more on biocompatibility and adhesive ability to wet surfaces rather than on gluing time and intensity. The crosslinking mechanisms of present internal bioadhesives can be generally classified as follows: 1) chemical conjugation between reactive groups; 2) free radical polymerization by light or redox initiation; 3) biological or biochemical coupling with specificity; and 4) biomimetic adhesion inspired from natural phenomena. In this review, bioadhesive products of each class are summarized and discussed by comparing their designs, features, and applications as well as their prospects for future development.

STATEMENT OF SIGNIFICANCE

Despite the emergence of numerous novel bioadhesive formulations in recent years, thus far, the classification of internal and external bioadhesives has not been well defined and universally acknowledged. Many of the formulations have been proposed for treatment of several diseases even though they are not applicable for such conditions. This is because of the lack of a systematic standard or evaluation protocol during the development of a new adhesive product. In this review, the definition of internal and external bioadhesives is given for the first time, and with a focus on internal bioadhesives, the criteria of an ideal internal bioadhesive are adequately discussed; this is followed by the review of recently developed internal bioadhesives based on different gluing mechanisms.

Tick attachment cement - reviewing the mysteries of a biological skin plug system

The majority of ticks in the family Ixodidae secrete a substance anchoring their mouthparts to the host skin. This substance is termed cement. It has adhesive properties and seals the lesion during feeding. The particular chemical composition and the curing process of the cement are unclear. This review summarizes the literature, starting with a historical overview, briefly introducing the different hypotheses on the origin of the adhesive and how the tick salivary glands have been identified as its source. Details on the sequence of cement deposition, the curing process and detachment are provided. Other possible functions of the cement, such as protection from the host immune system and antimicrobial properties, are presented. Histochemical and ultrastructural data of the intracellular granules in the salivary gland cells, as well as the secreted cement, suggest that proteins constitute the main material, with biochemical data revealing glycine to be the dominant amino acid. Applied methods and their restrictions are discussed. Tick cement is compared with adhesives of other animals such as barnacles, mussels and sea urchins. Finally, we address the potential of tick cement for the field of biomaterial research and in particular for medical applications in future.

All-in-one hyperbranched polypeptides for surgical adhesives and interventional embolization of tumors

A series of hyperbranched, thermo-responsive and mussel-inspired polypeptides were synthesized and used for surgical adhesion, hemostasis and interventional embolization.

Bioadhesive Nanoaggregates Based on Polyaspartamide-g-C18/DOPA for Wound Healing

Biocompatible adhesive nanoaggregates were synthesized based on polyaspartamide copolymers grafted with octadecylamine (C18) and 3,4-dihydroxyphenylalanine (DOPA), and their adhesive properties were investigated with regard to wound healing. The chemical structure and morphology of the synthesized polyaspartamide-g-C18/DOPA nanoaggregates were analyzed using ¹H-nuclear magnetic resonance spectroscopy (¹H NMR), dynamic light scattering (DLS), and transmission electron microscope (TEM). The in vitro adhesive energy was up to 31.04 J m^-2 for poly(dimethylacrylamide) gel substrates and 0.1209 MPa for mouse skin, and the in vivo wound breaking strength after 48 h was 1.8291 MPa for C57BL/6 mouse. The MTT assay demonstrated that the synthesized polymeric nanoaggregates were nontoxic. The polyaspartamide-g-C18/DOPA nanoaggregates were in vivo tested to mouse model and demonstrated successful skin adhesion, as the mouse skin was perfectly cured in their dermis within 6 d. As this material has biocompatibility and enough adhesive strength for wound closure, it is expected to be applied as a new type of bioadhesive agent in the human body.

Ultrasound-Mediated Self-Healing Hydrogels Based on Tunable Metal-Organic Bonding

Stimulus-responsive hydrogels make up an important class of programmable materials for a wide range of biomedical applications. Ultrasound (US) is a stimulus that offers utility because of its ability to permeate tissue and rapidly induce chemical alterations in aqueous media. Here we report on the synthesis and US-mediated disintegration of stimulus-responsive telechelic Dopa-modified polyethylene glycol-based hydrogels. Fe³⁺-[PEG-Dopa]₄ hydrogels are formed through Fe³⁺-induced cross-linking of four-arm polyethylene glycol-dopamine precursors to produce networks. The relative amounts of H-bonds, coordination bonds, and covalent bonds can be controlled by the [Fe³⁺]:[Dopa] molar ratio in precursor solutions. Networks formed from precursors with high [Fe³⁺]:[Dopa] ratios create mechanically robust networks (G' = 6880 ± 240 Pa) that are largely impervious to US-mediated disintegration at intensities of ≤43 W/cm². Conversely, lightly cross-linked networks formed through [Fe³⁺]:[Dopa] molar ratios of <0.73 are susceptible to rapid disintegration upon exposure to US. Pulsatile US exposure allows temporal control over hydrogel disintegration and programmable self-healing. Sustained US energy can also stabilize hydrogels through the formation of additional cross-links via free radical-mediated coupling of pendant catechols. Taken together, the diverse ranges of mechanical behavior, self-healing capability, and differential susceptibility to ultrasonic disintegration suggest that Fe³⁺-[PEG-Dopa]₄ hydrogels yield a class of application-specific stimulus-responsive polymers as smart materials for applications ranging from transient medical implants to matrices for smart drug delivery.

Click chemistry improved wet adhesion strength of mussel-inspired citrate-based antimicrobial bioadhesives

For the first time, a convenient copper-catalyzed azide-alkyne cycloaddition (CuAAC, click chemistry) was successfully introduced into injectable citrate-based mussel-inspired bioadhesives (iCMBAs, iCs) to improve both cohesive and wet adhesive strengths and elongate the degradation time, providing numerous advantages in surgical applications. The major challenge in developing such adhesives was the mutual inhibition effect between the oxidant used for crosslinking catechol groups and the Cu(II) reductant used for CuAAC, which was successfully minimized by adding a biocompatible buffering agent typically used in cell culture, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), as a copper chelating agent. Among the investigated formulations, the highest adhesion strength achieved (223.11 ± 15.94 kPa) was around 13 times higher than that of a commercially available fibrin glue (15.4 ± 2.8 kPa). In addition, dual-crosslinked (i.e. click crosslinking and mussel-inspired crosslinking) iCMBAs still preserved considerable antibacterial and antifungal capabilities that are beneficial for the bioadhesives used as hemostatic adhesives or sealants for wound management.

Mussel-inspired hydrogel tissue adhesives for wound closure

Tissue adhesives have been introduced as a promising alternative for the traditional wound closure method of suturing.

A hyperbranched dopamine-containing PEG-based polymer for the inhibition of α-synuclein fibrillation

Aggregation of α-synuclein is believed to play an important role in Parkinson's disease and in other neurodegenerative maladies. Small molecule inhibitors of this process are among the most promising drug candidates for neurodegenerative diseases. Dendrimers have also been studied for anti-fibrillation applications but they can be difficult and expensive to synthetize. Here we show that RAFT polymerization can be used to produce a hyperbranched polyethylene glycol structure via a one-pot reaction. This polymer included a dopamine moiety, a known inhibitor of α-synuclein fibril formation. Dopamine within the polymer structure was capable of aggregation inhibition, although not to the same degree as free dopamine. This result opens up new avenues for the use of controlled radical polymerizations as a means of preparing hyperbranched polymers for anti-fibrillation activity, but shows that the incorporation of functional groups from known small molecules within polymers may alter their biological activity.

Synthesis of acid-degradable hyperbranched polymers by chain-growth CuAAC polymerization of an AB3 monomer

The first synthesis of acid-degradable hyperbranched polymers using chain-growth CuAAC click polymerization of an AB₃ monomer.

The synthesis and tissue adhesiveness of temperature-sensitive hyperbranched poly(amino acid)s with functional side groups

The adhesive strength of poly(amino acid)s can be improved by clicking a cross-link, forming a disulfide bond and so on. In addition, the adhesion strength becomes better on grafting with different monomers at 37 °C.