Adhesion Properties of Catechol-Based Biodegradable Amino Acid-Based Poly(ester urea) Copolymers Inspired from Mussel Proteins

Engineering proteins with catechol chemistry for biotechnological applications

Developing proteins with increased chemical space by expanding the amino acids alphabet has been an emerging technique to compete for the obstacle encountered by their need in various applications. 3,4-Dihydroxyphenylalanine (L-DOPA) catecholic unnatural amino acid is abundantly present in mussels foot proteins through post-translational modification of tyrosine to give a strong adhesion toward wet rocks. L-DOPA forms: bidentate coordination, H-bonding, metal-ligand complexes, long-ranged electrostatic, and van der Waals interactions via a pair of donor hydroxyl groups. Incorporating catechol in proteins through genetic code expansion paved the way for developing: protein-based bio-sensor, implant coating, bio-conjugation, adhesive bio-materials, biocatalyst, metal interaction and nano-biotechnological applications. The increased chemical spaces boost the protein properties by offering a new chemically active interaction ability to the protein. Here, we review the technique employed to develop a genetically expanded organism with catechol to provide novel properties and functionalities; and we highlight the importance of L-DOPA incorporated proteins in biomedical and industrial fields.

Silicone Bioadhesive with Shear-Stiffening Effect: Rate-Responsive Adhesion Behavior and Wound Dressing Application

Stimuli-responsive adhesives with on-demand adhesion capabilities are highly advantageous for facilitating wound healing. However, the triggering conditions of stimuli-responsive adhesives are cumbersome, even though some of them are detrimental to the adhesive and adjacent natural tissues. Herein, a novel stimuli-responsive adhesive called shear-stiffening adhesive (SSA) has been created by constructing a poly(diborosiloxane)-based silicone network for the first time, and SSA exhibits a rate-responsive adhesion behavior. Furthermore, we introduced bactericidal factors (PVP-I) into SSA and applied it as a wound dressing to promote the healing of infected wounds. Impressively, the wound dressing not only has excellent biocompatibility and long-term antibacterial properties but also performs well in accelerating wound healing. Therefore, this study provides a new strategy for the synthesis of intelligent adhesives with force rate response, which simplifies the triggering conditions by the force rate. Thus, SSA has great potential to be applied in wound management as an intelligent bioadhesive with on-demand adhesion performance.

Highly adhesive chitosan/poly(vinyl alcohol) hydrogels via the synergy of phytic acid and boric acid and their application as highly sensitive and widely linear strain sensors

In recent years, flexible strain sensors have attracted increasing interest, and accurate sensing and comfortable wearables are highly demanded. However, current flexible strain sensors fail to have wide linearity and high sensitivity simultaneously, and their adhesion is insufficient for convenient wear and precise motion monitoring. Herein, chitosan/poly(vinyl alcohol) hydrogels with phytic acid (PA) and boric acid (BA) as crosslinkers (CS/PVA-PA-BA hydrogels) were fabricated. The synergy of phytic acid and boric acid not only improved the mechanical properties of the obtained hydrogels (1070% of fracture strain and 0.83 MPa of fracture stress), but also provided them with outstandingly strong adhesion. Their adhesive strength was up to 527 kPa for a variety of materials, including glass, silica rubber, steel, polytetrafluoroethylene (PTFE), and skin. In addition, the hydrogel-based strain sensor demonstrated high sensitivity (gauge factor = 4.61), a wide linear strain range (up to 1000%, R2 = 0.996), fast response time (90 ms), and good stability. A flexible strain sensor with such high sensitivity and wide linear range simultaneously, to the best of our knowledge, has never been reported before. The development of CS/PVA-PA-BA hydrogels is expected to inspire a novel method for high-adhesive and high-sensing-performance wearable electronics.

Adhesive and Self-Healing Polyurethanes with Tunable Multifunctionality

Many polyurethanes (PUs) are blood-contacting materials due to their good mechanical properties, fatigue resistance, cytocompatibility, biosafety, and relatively good hemocompatibility. Further functionalization of the PUs using chemical synthetic methods is especially attractive for expanding their applications. Herein, a series of catechol functionalized PU (C-PU-PTMEG) elastomers containing variable molecular weight of polytetramethylene ether glycol (PTMEG) soft segment are reported by stepwise polymerization and further introduction of catechol. Tailoring the molecular weight of PTMEG fragment enables a regulable catechol content, mobility of the chain segment, hydrogen bond and microphase separation of the C-PU-PTMEG elastomers, thus offering tunability of mechanical strength (such as breaking strength from 1.3 MPa to 5.7 MPa), adhesion, self-healing efficiency (from 14.9% to 96.7% within 2 hours), anticoagulant, antioxidation, anti-inflammatory properties and cellular growth behavior. As cardiovascular stent coatings, the C-PU-PTMEGs demonstrate enough flexibility to withstand deformation during the balloon dilation procedure. Of special importance is that the C-PU-PTMEG-coated surfaces show the ability to rapidly scavenge free radicals to maintain normal growth of endothelial cells, inhibit smooth muscle cell proliferation, mediate inflammatory response, and reduce thrombus formation. With the universality of surface adhesion and tunable multifunctionality, these novel C-PU-PTMEG elastomers should find potential usage in artificial heart valves and surface engineering of stents.

Gelation of highly entangled hydrophobic macromolecular fluid for ultrastrong underwater in situ fast tissue adhesion

Although strong underwater bioadhesion is important for many biomedical applications, designing adhesives to perform in the presence of body fluids proves to be a challenge. To address this, we propose an underwater and in situ applicable hydrophobic adhesive (UIHA) composed of polydimethylsiloxane, entangled macromolecular silicone fluid, and a reactive silane. The hydrophobic fluid displaced the boundary water, formed an in situ gel, bonded to tissues, and achieved exceptional underwater adhesion strength. Its underwater lap shear adhesion on porcine skin was significantly higher than that of cyanoacrylate and fibrin glues, demonstrating excellent water resistance. The burst pressure of UIHA on porcine skin was 10 times higher than that of fibrin glue. The cytocompatible UIHA successfully sealed ruptured arteries, skin, and lungs in rats, pigs, rabbits, and dogs. Together, the gelation of highly entangled hydrophobic macromolecular fluid provided a means to prepare underwater bioadhesives with strong bonding to tissues and excellent water resistance.

Mussel Adhesive-Inspired Proteomimetic Polymer

Herein, a synthetic polymer proteomimetic is described that reconstitutes the key structural elements and function of mussel adhesive protein. The proteomimetic was prepared via graft-through ring-opening metathesis polymerization of a norbornenyl-peptide monomer. The peptide was derived from the natural underwater glue produced by marine mussels that is composed of a highly repetitive 10 amino acid tandem repeat sequence. The hypothesis was that recapitulation of the repeating unit in this manner would provide a facile route to a nature-inspired adhesive. To this end, the material, in which the arrangement of peptide units was as side chains on a brush polymer rather than in a linear fashion as in the natural protein, was examined and compared to the native protein. Mechanical measurements of adhesion forces between solid surfaces revealed improved adhesion properties over the natural protein, making this strategy attractive for diverse applications. One such application is demonstrated, using the polymers as a surface adhesive for the immobilization of live cells.

Effect of Cross-Linkers on Mussel- and Elastin-Inspired Adhesives on Physiological Substrates

Surgical adhesives can be useful in wound closure because they reduce the risk of infection and pain associated with sutures and staples. However, there are no commercially available surgical adhesives for soft tissue wound closure. To be effective, soft tissue adhesives must be soft and flexible, strongly cohesive and adhesive, biocompatible, and effective in a moist environment. To address these criteria, we draw inspiration from the elasticity and resilience of elastin proteins and the adhesive of marine mussels. We used an elastin-like polypeptide (ELP) for the backbone of our adhesive material due to its elasticity and biocompatibility. A mussel-inspired adhesive molecule, l-3,4-dihydroxyphenylalanine (DOPA), was incorporated into the adhesive to confer wet-setting adhesion. In this study, an ELP named YKV was designed to include tyrosine residues and lysine residues, which contain amine groups. A modified version of YKV, named mYKV, was created through enzymatic conversion of tyrosine residues into DOPA. The ELPs were combined with iron(III) nitrate, sodium periodate, and/or tris(hydroxymethyl)phosphine (THP) cross-linkers to investigate the effect of DOPA- and amine-based cross-linking on adhesion strength and cure time on porcine skin in a warm, humid environment. Incorporation of DOPA into the ELP increased adhesive strength by 2.5 times and reduced failure rates. Iron cross-linkers improved adhesion in the presence of DOPA. THP increased adhesion for all proteins tested even in the absence of DOPA. Using multiple cross-linkers in a single formulation did not significantly improve adhesion. The adhesives with the highest performance (iron nitrate mixed with mYKV and THP mixed with YKV or mYKV) on porcine skin had 10-18 times higher adhesion than a commercial sealant and reached appreciable adhesive strength within 10 min.

Bacterial cellulose adhesive composites for oral cavity applications

Topical approaches to oral diseases require frequent dosing due to limited retention time. A mucoadhesive drug delivery platform with extended soft tissue adhesion capability of up to 7 days is proposed for on-site management of oral wound. Bacterial cellulose (BC) and photoactivated carbene-based bioadhesives (PDz) are combined to yield flexible film platform for interfacing soft tissues in dynamic, wet environments. Structure-activity relationships evaluate UV dose and hydration state with respect to adhesive strength on soft tissue mimics. The bioadhesive composite has an adhesion strength ranging from 7 to 17 kPa and duration exceeding 48 h in wet conditions under sustained shear forces, while other mucoadhesives based on hydrophilic macromolecules exhibit adhesion strength of 0.5-5 kPa and last only a few hours. The work highlights the first evaluation of BC composites for mucoadhesive treatments in the buccal cavity.

Design principles for creating synthetic underwater adhesives

Water and adhesives have a conflicting relationship as demonstrated by the failure of most man-made adhesives in underwater environments. However, living creatures routinely adhere to substrates underwater. For example, sandcastle worms create protective reefs underwater by secreting a cocktail of protein glue that binds mineral particles together, and mussels attach themselves to rocks near tide-swept sea shores using byssal threads formed from their extracellular secretions. Over the past few decades, the physicochemical examination of biological underwater adhesives has begun to decipher the mysteries behind underwater adhesion. These naturally occurring adhesives have inspired the creation of several synthetic materials that can stick underwater - a task that was once thought to be "impossible". This review provides a comprehensive overview of the progress in the science of underwater adhesion over the past few decades. In this review, we introduce the basic thermodynamics processes and kinetic parameters involved in adhesion. Second, we describe the challenges brought by water when adhering underwater. Third, we explore the adhesive mechanisms showcased by mussels and sandcastle worms to overcome the challenges brought by water. We then present a detailed review of synthetic underwater adhesives that have been reported to date. Finally, we discuss some potential applications of underwater adhesives and the current challenges in the field by using a tandem analysis of the reported chemical structures and their adhesive strength. This review is aimed to inspire and facilitate the design of novel synthetic underwater adhesives, that will, in turn expand our understanding of the physical and chemical parameters that influence underwater adhesion.

Catechol functionalized ink system and thrombin-free fibrin gel for fabricating cellular constructs with mechanical support and inner micro channels

The development of 3D bio printing technology has contributed to protocols for the repair and regeneration of tissues in recent years. However, it is still a great challenge to fabricate structures that mimic the complexity of native tissue, including both the biomechanics and microscale internal structure. In this study, a catechol functionalized ink system was developed to produce tough and elastic scaffolds with built-in micro channels that simulate the vascular structure. And a skin model was designed to evaluate the cytocompatibility of the scaffolds. The mechanical support stemmed from the double network based on catechol-hyaluronic acid (HACA) and alginate, the micro channels were generated using sacrificial gelatin. HACA/alginate and gelatin were firstly printed using a 3D extrusion printer. Thrombin-free fibrinogen were then mixed with human dermal fibroblasts and introduced to the printed scaffolds to induce gelation. An immortal human keratinocyte cell line was introduced on top of the cellular construct to mimic the full thickness skin structure. The printed scaffolds demonstrated high elasticity and supported the formation of a double-layered cell-laden skin like structure. The results suggest the 3D printing platform developed here provides a platform for skin regeneration and could be explored further to engineer functional skin tissue by incorporation of other types of cells.

Reversible electroadhesion of hydrogels to animal tissues for suture-less repair of cuts or tears

Electroadhesion, i.e., adhesion induced by an electric field, occurs between non-sticky cationic and anionic hydrogels. Here, we demonstrate electroadhesion between cationic gels and animal (bovine) tissues. When gel and tissue are placed under an electric field (DC, 10 V) for 20 s, the pair strongly adhere, and the adhesion persists indefinitely thereafter. Applying the DC field with reversed polarity eliminates the adhesion. Electroadhesion works with the aorta, cornea, lung, and cartilage. We demonstrate the use of electroadhesion to seal cuts or tears in tissues or model anionic gels. Electroadhered gel-patches provide a robust seal over openings in bovine aorta, and a gel sleeve is able to rejoin pieces of a severed gel tube. These studies raise the possibility of using electroadhesion in surgery while obviating the need for sutures. Advantages include the ability to achieve adhesion on-command, and moreover the ability to reverse this adhesion in case of error.

The authors demonstrate strong adhesion of cationic hydrogels to bovine tissues under a DC electric field. Such electroadhesion can be reversed by switching the polarity of the field. This approach could enable simpler surgeries, where sutures are not needed.

An Engineered Protein Adhesive with Properties of Tissue Integration and Controlled Release for Efficient Cartilage Repair

Cartilage damage is a prevalent health concern among humans. The inertness of cartilage, the absence of self-healing properties, and the lack of appropriate repair materials that integrate into the tissue pose a significant challenge for cartilage repair. Thus, it is important to develop novel soft biomaterials with strong tissue adhesion and chondrogenic capabilities for cartilage repair. Herein, a new type of protein adhesive is reported that exhibits superior cartilage repair performance. The material is fabricated by the electrostatic combination of chondroitin sulfate (CS) and positively charged elastin-like protein, which is derived from natural components of the extracellular matrix (ECM). The adhesive showed robust adhesion properties on different tissue substrates, offering a favorable environment for cartilage tissue integration. Noncovalent bonding between CS molecules in the glue allows for its controlled release, which is required for efficient chondrogenic differentiation. When implanted into a rat model of cartilage defect, this protein adhesive exhibited beneficial healing effects, as evidenced by enhanced chondrogenesis, sufficient ECM production, and lateral integration. Therefore, this engineered protein complex is a promising candidate for translational application in the field of cartilage repair.

Fast-Curing Mussel-Inspired Adhesive Derived from Vegetable Oil

The development of functional materials based on renewable resources is of great significance in today's resource shortage. Here, we present an effective way to synthesize a mussel-inspired adhesive from acrylated epoxidized soybean oil (AESO), a renewable and commercially available small molecular material with a molecular weight around 1200 Da, by a one-step esterification reaction with the affordable 3,4-dihydroxybenzoic acid (DHA). By taking advantages of both the double bond and the catechol moiety presented in this small molecular adhesive, a short curing time was achieved with UV irradiation. An average bonding strength around 1.4 MPa at a curing time of only around 10 min on a glass substrate was observed, which reached 3.1 MPa (average 2.8 MPa) at a curing time of 2 h under ambient conditions. The curing time is much shorter, and the bonding strength is obviously stronger than the conditions where conventional oxidation agents such as IO₄^- or oxidation/coordination agents such as Fe³⁺ are used as the curing agent. Furthermore, the AESO-g-DHA can be used as an underwater adhesive, and an appreciable bonding strength up to 0.64 MPa was observed, which is superior than most of currently known commercialized glues. Given that the adhesive could be synthesized from low-cost renewable resources in one step, it might be a potential candidate for large-scale practical application.

Tissue Adhesives: From Research to Clinical Translation

Sutures, staples, clips and skin closure strips are used as the gold standard to close wounds after an injury. In spite of being the present standard of care, the utilization of these conventional methods is precarious amid complicated and sensitive surgeries such as vascular anastomosis, ocular surgeries, nerve repair, or due to the high-risk components included. Tissue adhesives function as an interface to connect the surfaces of wound edges and prevent them from separation. They are fluid or semi-fluid mixtures that can be easily used to seal any wound of any morphology - uniform or irregular. As such, they provide alternatives to new and novel platforms for wound closure methods. In this review, we offer a background on the improvement of distinctive tissue adhesives focusing on the chemistry of some of these products that have been a commercial success from the clinical application perspective. This review is aimed to provide a guide toward innovation of tissue bioadhesive materials and their associated biomedical applications.

Hydrophobic and Hydrophilic Effects in a Mussel-Inspired Citrate-Based Adhesive

The citrate-based tissue adhesive, synthesized by citric acid, diol, and dopamine, is a kind of mussel-inspired adhesive. The adhesion of mussel-inspired adhesive is not completely dependent on 3, 4-dihydroxyphenylalanine (Dopa) groups. The backbone structure of the adhesive also greatly affects the adhesion. In this study, to explore the effects of hydrophobicity and hydrophilicity of the backbone structure on adhesion, we prepared a series of citrate-based tissue adhesives (POEC-d) by changing the molar ratio of two diols, 1, 8-octanediol (O) and poly(ethylene oxide) (E), which formed hydrophobic segment units and hydrophilic segment units, respectively, in the molecule structure. The properties of cured adhesives showed that the adhesive with high E units had high swelling, rapid degradation, and low cohesion. In the adhesion strength measurement on the porcine skin, the adhesive with higher hydrophobicity was more likely to perform better. For the interfacial adhesion, hydrophilicity was conducive to the diffusion and penetration on the skin surface, but hydrophobic interaction showed a stronger effect to adhere with skin and hydrophobic association increased the adhesive concentration on the interface; for the bulk cohesion, hydrophobicity led to coacervation, promoting the Dopa-quinone coupling for cross-linking. In this amphipathic, citrate-based, soft-tissue adhesive system, when the feed ratio of hydrophilic segment was lower than 0.7, the coacervation could be formed through hydrophobic interaction, forming an efficient underwater adhesion system similar to that of mussels.

Mussel-inspired biocompatible polydopamine/carboxymethyl cellulose/polyacrylic acid adhesive hydrogels with UV-shielding capacity

Hydrogels are attractive due to their various applications in the fields of biomedical materials, cosmetics, and biosensors. To enhance UV protection and prevent skin penetration behaviors, inspired by the mussel adhesive proteins, the functional polydopamine (PDA) is employed herein to fabricate polydopamine/carboxymethyl cellulose/polyacrylic acid (PDA/CMC/PAA) adhesive hydrogels. To disperse PDA nanoparticles well in the PAA matrix, dopamine was self-polymerized in CMC solution to form PDA/CMC complex. Acrylic acid was polymerized in PDA/CMC complex solution and cross-linked to construct UV-resistant PDA/CMC/PAA hydrogel. The morphology, rheological behavior, mechanical properties and adhesion strength of PDA/CMC/PAA hydrogels were studied by scanning electron microscopy, rotational rheometer, universal test machine. Owing to the hydrogen bonding interaction between the PDA/CMC complex and PAA, the PDA/CMC/PAA hydrogels showed high resilience and compressive strength to withstand large deformation. The hydrogels exhibited strong adhesion to various substrate surfaces, such as stainless steel, aluminum, glass and porcine skin. The biocompatibility and UV-shielding properties were investigated through culture of cells and UV irradiation test. The adhesiveness of PDA promoted cell adhesion and provided the PDA/CMC/PAA hydrogels good biocompatibility with 96% of relative cell viability. The hydrogels possessed excellent UV-shielding ability to prevent collagen fibers from being destroyed during UV irradiation, which has promising potential in the practical applications for UV filtration membrane and skin care products.

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.

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.

A supramolecular copolymer based on small molecules, used for a multifunctional adhesive and rapid hemostasis

A multifunctional supramolecular adhesive synthesized using a natural small molecule monomer thioctic acid.

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.

An efficient one-pot synthesis of polyphenolic amino acids and evaluation of their radical-scavenging activity

A simple and efficient procedure for the synthesis of N-acyl 4-hydroxy, 4-hydroxy-3-methoxy and 3,4-dihydroxy phenylglycine amides by a strategy based on the multicomponent Ugi reaction is proposed. Hydroxybenzaldehyde derivatives were reacted with 4-methoxybenzylamine, cyclohexyl isocyanide and benzoic acid or 2-naphthylacetic acid to give Ugi adducts that were treated with trifluoroacetic acid yielding N-acyl hydroxyphenylglycine amides in good yields. The same procedure using as acid component protocatechuic acid or hydrocaffeic acid gave N-catechoyl 3,4-dihydroxyphenylglycine amides. The use of N-benzyloxycarbonylglycine as acid component allowed the preparation of a 3,4-dihydroxyphenylglycyl dipeptide derivative. Radical-scavenging activity studies of the polyphenolic amino acid derivatives showed a sharp increase in activity with the increase in number of hydroxyl or catechol groups present. Cyclic voltammetry experiments established a correlation between oxidation peak potentials and the radical-scavenging activity.

Investigation of surgical adhesives for vocal fold wound closure

OBJECTIVES

Surgical adhesives are increasingly used for vocal fold microsurgery to assist wound closure and reduce the risks of scar formation. Currently used vocal fold adhesives such as fibrin glue, however, have thus far not been found to promote wound closure or reduce scarring. The objectives of this study were to investigate the mechanical strength and the cytotoxicity of three commercially available adhesives (Glubran 2, GEM, Viareggio, Italy; BioGlue, CryoLife, Kennesaw, GA; and Tisseel, Baxter Healthcare, Deerfield, IL) for vocal fold wound closure.

METHODS

Shear and tension tests were performed on 150 porcine larynges. The cytotoxicity of the adhesives to immortalized human vocal fold fibroblasts was investigated using neutral red uptake assays.

RESULTS

The average shear adhesive strength for Tisseel, BioGlue, and Glubran 2 was 13.86 ± 5.03 kilopascal (kPa), 40.92 ± 17.94 kPa, and 68.79 ± 13.29 kPa, respectively. The tensile adhesive strength for Tisseel, BioGlue, and Glubran 2 was 10.70 ± 6.42 kPa, 34.27 ± 12.59 kPa, and 46.67 ± 12.13 kPa, respectively. The vocal fold cell viabilities in extracts of Tisseel, BioGlue, and Glubran 2 were 99.27%, 43.05%, and 1.79%, respectively.

CONCLUSION

There was a clear tradeoff between adhesive strength and toxicity. The maximum failure strength in shear or tension of the three surgical adhesives ranked from strongest to the weakest was: 1) Glubran 2, 2) BioGlue, and 3) Tisseel. Tisseel was found to be the least toxic of the three adhesives, whereas Glubran 2 was the most toxic.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:2139-2146, 2019.

Highly Cross-Linked Shape Memory Polymers with Tunable Oxidative and Hydrolytic Degradation Rates and Selected Products Based on Succinic Acid

Minimally invasive medical devices are of great interest, with shape memory polymers (SMPs) representing one such possibility for producing these devices. Previous work with low density, highly porous SMPs has demonstrated oxidative degradation, while attempts to incorporate hydrolytic degradation have resulted in rapidly decreasing glass transition temperature (T _g ), ultimately preventing strain fixity of the materials at clinically relevant temperatures. Through esterification of the amino alcohol triethanolamine, an alcohol containing network was synthesized and incorporated into SMPs. These ester networks were used to control the bulk morphology of the SMP, with the T _g remaining above 37 °C when 50% of the alcohol was contributed by the ester network. This methodology also yielded SMPs that could degrade through both hydrolysis and oxidation; by oxidation, the SMPs degrade at a similar rate as the control materials (0.2%/day mass) for the first 30 days, at which point the rate changes to 3.5%/day until the samples become too fragile to examine at 80 days. By comparison, control materials have lost approximately 30% of mass by 140 days, at a constant rate of degradation, demonstrating that the ester SMPs are a promising material system for producing more rapidly degradable, soft, porous biomaterials.

Cell-Adhesive Bioinspired and Catechol-Based Multilayer Freestanding Membranes for Bone Tissue Engineering

Mussels are marine organisms that have been mimicked due to their exceptional adhesive properties to all kind of surfaces, including rocks, under wet conditions. The proteins present on the mussel's foot contain 3,4-dihydroxy-l-alanine (DOPA), an amino acid from the catechol family that has been reported by their adhesive character. Therefore, we synthesized a mussel-inspired conjugated polymer, modifying the backbone of hyaluronic acid with dopamine by carbodiimide chemistry. Ultraviolet-visible (UV-vis) spectroscopy and nuclear magnetic resonance (NMR) techniques confirmed the success of this modification. Different techniques have been reported to produce two-dimensional (2D) or three-dimensional (3D) systems capable to support cells and tissue regeneration; among others, multilayer systems allow the construction of hierarchical structures from nano- to macroscales. In this study, the layer-by-layer (LbL) technique was used to produce freestanding multilayer membranes made uniquely of chitosan and dopamine-modified hyaluronic acid (HA-DN). The electrostatic interactions were found to be the main forces involved in the film construction. The surface morphology, chemistry, and mechanical properties of the freestanding membranes were characterized, confirming the enhancement of the adhesive properties in the presence of HA-DN. The MC3T3-E1 cell line was cultured on the surface of the membranes, demonstrating the potential of these freestanding multilayer systems to be used for bone tissue engineering.

Scarless Wound Closure by a Mussel-Inspired Poly(amidoamine) Tissue Adhesive with Tunable Degradability

Burn, trauma, and various medical conditions including bacterial infection, diabetes complication, and surgery could lead to an acute cutaneous wound and scar formation. Application of tissue glues instead of sutures could minimize the additional trauma and scar formation. Despite the countless efforts devoted to the development of high-strength tissue glues, little attention has been paid to their influence on the scar formation. Here, we report the development of a new tissue glue with excellent biocompatibility and tunable degradability for scarless wound closure. A series of catechol-containing poly(amidoamine) (CPAA) polymers were synthesized via the one-step Michael addition of dopamine and bisacrylamide. The tertiary amino group in the polymer backbone was used to introduce a zwitterionic sulfobetaine group by one-step ring-opening polymerization. The introduction of the zwitterionic sulfobetaine group could easily tune the hydrophilicity and the degradability of CPAA without influencing the density of the catechol group in the polymer. Lap-shear tests on the porcine skin demonstrated a high adhesion strength of 7 kPa at 1 h, rising to 24 kPa by 12 h. Addition of silica nanoparticles could further enhance the adhesion strength by 50%. In vivo studies further confirmed that the CPAA tissue glue could effectively accelerate the healing process of incisional wounds on the back of Sprague Dawley rats compared with suture and reduce the scar formation.

Mussel-Inspired Thermoresponsive Polypeptide-Pluronic Copolymers for Versatile Surgical Adhesives and Hemostasis

Inspired by marine mussel adhesive proteins, polymers with catechol side groups have been extensively explored in industrial and academic research. Here, Pluronic L-31 alcoholate ions were used as the initiator to prepare a series of polypeptide-Pluronic-polypeptide triblock copolymers via ring-opening polymerization of l-DOPA-N-carboxyanhydride (DOPA-NCA), l-arginine-NCA (Arg-NCA), l-cysteine-NCA (Cys-NCA), and ε-N-acryloyl lysine-NCA (Ac-Lys-NCA). These copolymers demonstrated good biodegradability, biocompatibility, and thermoresponsive properties. Adhesion tests using porcine skin and bone as adherends demonstrated lap-shear adhesion strengths up to 106 kPa and tensile adhesion strengths up to 675 kPa. The antibleeding activity and tissue adhesive ability were evaluated using a rat model. These polypeptide-Pluronic copolymer glues showed superior hemostatic properties and superior effects in wound healing and osteotomy gaps. Complete healing of skin incisions and remodeling of osteotomy gaps were observed in all rats after 14 and 60 days, respectively. These copolymers have potential uses as tissue adhesives, antibleeding, and tissue engineering materials.

Adhesive coatings based on melanin-like nanoparticles for surgical membranes

Adhesive coatings for implantable biomaterials can be designed to prevent material displacement from the site of implant. In this paper, a strategy based on the use of melanin-like nanoparticles (MNPs) for the development of adhesive coatings for polysaccharidic membranes was devised. MNPs were synthesized in vitro and characterized in terms of dimensions and surface potential, as a function of pH and ionic strength. The in vitro biocompatibility of MNPs was investigated on fibroblast cells, while the antimicrobial properties of MNPs in suspension were evaluated on E. coli and S. aureus cultures. The manufacturing of the adhesive coatings was carried out by spreading MNPs over the surface of polysaccharidic membranes; the adhesive properties of the nano-engineered coating to the target tissue (intestinal serosa) were studied in simulated physiological conditions. Overall, this study opens for novel approaches in the design of naturally inspired nanostructured adhesive systems.

Joining Two Natural Motifs: Catechol-Containing Poly(phosphoester)s

Numerous catechol-containing polymers, including biodegradable polymers, are currently heavily discussed for modern biomaterials. However, there is no report combining poly(phosphoester)s (PPEs) with catechols. Adhesive PPEs have been prepared via acyclic diene metathesis polymerization. A novel acetal-protected catechol phosphate monomer was homo- and copolymerized with phosphoester comonomers with molecular weights up to 42000 g/mol. Quantitative release of the catechols was achieved by careful hydrolysis of the acetal groups without backbone degradation. Degradation of the PPEs under basic conditions revealed complete and statistical degradation of the phosphotri- to phosphodiesters. In addition, a phosphodiester monomer with an adhesive P-OH group and no protective group chemistry was used to compare the binding to metal oxides with the multicatechol-PPEs. All PPEs can stabilize magnetite particles (NPs) in polar solvents, for example, methanol, due to the binding of the phosphoester groups in the backbone to the particles. ITC measurements reveal that multicatechol PPEs exhibit a higher binding affinity to magnetite NPs compared to PPEs bearing phosphodi- or phosphotriesters as repeating units. In addition, the catechol-containing PPEs were used to generate organo- and hydrogels by oxidative cross-linking, due to cohesive properties of catechol groups. This unique combination of two natural adhesive motives, catechols and phosphates, will allow the design of novel future gels for tissue engineering applications or novel degradable adhesives.

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.