Marine adhesive proteins and some biotechnological applications

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.

Direct surface modification of metallic biomaterials via tyrosine oxidation aiming to accelerate the re-endothelialization of vascular stents

Rapid in-situ re-endothelialization of coronary stents is one of the most effective approaches to inhibit late thrombosis and restenosis. Strut surfaces allowing excellent adhesion and migration of endothelial cells and endothelial progenitor cells may accelerate in-situ re-endothelialization. Here, a well-known endothelial cell adhesive peptide, Arg-Glu-Asp-Val (REDV), was directly immobilized onto metallic surfaces by means of single-step tyrosine oxidation with copper chloride (II) and hydrogen peroxide, which we recently reported as a new biomaterial modification technique. REDV immobilization on a 316L stainless steel plate improved endothelial cell adhesion and effectively suppressed platelet adhesion in vitro. In addition, a Co-Cr stent immobilized with Ac-Tyr-Gly-Gly-Gly-Arg-Glu-Asp-Val (Y-REDV) was implanted into a rabbit abdominal aorta. On 7 days postimplantation, 80% of the strut surface of the Y-REDV-immobilized stent was covered by a thin neointimal layer and was similar in appearance to native endothelium. Restenosis and late thrombosis were not observed in the Y-REDV-immobilized stent for 42 days. These findings suggest that direct immobilization of Y-REDV peptide onto metallic biomaterials by tyrosine oxidation is effective for promoting in-situ re-endothelialization in vascular stents. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 491-499, 2018.

Recovery property of double-network hydrogel containing mussel-inspired adhesive moiety and nano-silicate

Altough double network (DN) hydrogels are extremly tough, they are irreversibly softened during large strain deformation. We incorporated mussel-inspired adhesive moiety, catechol, and a synthetic nano-silicate, Laponite, into DN to examine the effect of strong, reversible crosslinks on the DN's ability to recover its mechanical properties during successive loading cycles. The introduction of catechol and Laponite drastically increased the compressive strength and toughness of DN without compromising the compliance of the hydrogel. After 2 hours of recovery at room temperature, the nanocomposite DN hydrogel recovered over 95 and 82 % of its strain energy and hysteresis, respectively, during successive compressive loading to a strain of 0.5. Both equilibrium swelling and oscillatory rheometry data confirmed that there were minimal changes to the network crosslinking density and stiffness after large strain compressive deformation, indicating that mechanical loading did not result in irreversible structural damage. Strong catechol-Laponite interactions can be repeatedly broken and reform to dissipate fracture energy and enable the recovery of DN hydrogel.

pH Responsive and Oxidation Resistant Wet Adhesive based on Reversible Catechol-Boronate Complexation

A smart adhesive capable of binding to a wetted surface was prepared by copolymerizing dopamine methacrylamide (DMA) and 3-acrylamido phenylboronic acid (AAPBA). pH was used to control the oxidation state and the adhesive property of the catechol side chain of DMA and to trigger the catechol-boronate complexation. FTIR spectroscopy confirmed the formation of the complex at pH 9, which was not present at pH 3. The formation of the catechol-boronate complex increased the cross-linking density of the adhesive network. Most notably, the loss modulus values of the adhesive were more than an order of magnitude higher for adhesive incubated at pH 9 when compared to those measured at pH 3. This drastic increase in the viscous dissipation property is attributed to the introduction of reversible complexation into the adhesive network. Based on the Johnson Kendall Roberts (JKR) contact mechanics test, adhesive containing both DMA and AAPBA demonstrated strong interfacial binding properties (work of adhesion (W_adh) = 2000 mJ/m²) to borosilicate glass wetted with an acidic solution (pH 3). When the pH was increased to 9, W_adh values (180 mJ/m²) decreased by more than an order of magnitude. During successive contact cycles, the adhesive demonstrated the capability to transition reversibly between its adhesive and nonadhesive states with changing pH. Adhesive containing only DMA responded slowly to repeated changes in pH and became progressively oxidized without the protection of boronic acid. Although adhesive containing only AAPBA also demonstrated strong wet adhesion (W_adh ∼ 500 mJ/m²), its adhesive properties were not pH responsive. Both DMA and AAPBA are required to fabricate a smart adhesive with tunable and reversible adhesive properties.

Nitro-Group Functionalization of Dopamine and its Contribution to the Viscoelastic Properties of Catechol-Containing Nanocomposite Hydrogels

Linear polyacrylamide (PAAm) is modified with dopamine or nitrodopamine (PAAm-D and PAAm-ND, respectively) to evaluate the effect of nitro-group modification on the interfacial binding properties of polymer-bound catechol. Nanocomposite hydrogels are prepared by mixing PAAm-based polymers with Laponite and the viscoelastic properties of these materials are determined using oscillatory rheometry. The incorporation of a small amount of catechol (≈0.1 wt% in swollen hydrogel) drastically increases the shear moduli by 1-2 orders of magnitude over those of the catechol-free control. Additionally, PAAm-ND exhibits higher shear moduli values than PAAm-D across the whole pH range tested (pH 3.0-9.0). Based on the calculated effective crosslinking density, effective functionality, and molecular weight between crosslinks, nitro-group functionalization of dopamine results in a polymer network with increased crosslinking density and crosslinking points with higher functionality. Nitro-functionalization enhances the interfacial binding property of dopamine and increases its resistant to oxidation, which results in nanocomposite hydrogels with enhanced stiffness and a viscous dissipation property.

Catechol-based biomimetic functional materials

Catechols are found in nature taking part in a remarkably broad scope of biochemical processes and functions. Though not exclusively, such versatility may be traced back to several properties uniquely found together in the o-dihydroxyaryl chemical function; namely, its ability to establish reversible equilibria at moderate redox potentials and pHs and to irreversibly cross-link through complex oxidation mechanisms; its excellent chelating properties, greatly exemplified by, but by no means exclusive, to the binding of Fe(3+); and the diverse modes of interaction of the vicinal hydroxyl groups with all kinds of surfaces of remarkably different chemical and physical nature. Thanks to this diversity, catechols can be found either as simple molecular systems, forming part of supramolacular structures, coordinated to different metal ions or as macromolecules mostly arising from polymerization mechanisms through covalent bonds. Such versatility has allowed catechols to participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of some transition metal ions. As a result of such an astonishing range of functionalities, catechol-based systems have in recent years been subject to intense research, aimed at mimicking these natural systems in order to develop new functional materials and coatings. A comprehensive review of these studies is discussed in this paper.

Biomechanical properties of Achilles tendon repair augmented with a bioadhesive-coated scaffold

The Achilles tendon is the most frequently ruptured tendon. Both acute and chronic (neglected) tendon ruptures can dramatically affect a patient's quality of life, and require a prolonged period of recovery before return to pre-injury activity levels. This paper describes the use of an adhesive-coated biologic scaffold to augment primary suture repair of transected Achilles tendons. The adhesive portion consisted of a synthetic mimic of mussel adhesive proteins that can adhere to various surfaces in a wet environment, including biologic tissues. When combined with biologic scaffolds such as bovine pericardium or porcine dermal tissues, these adhesive constructs demonstrated lap shear adhesive strengths significantly greater than that of fibrin glue, while reaching up to 60% of the strength of a cyanoacrylate-based adhesive. These adhesive constructs were wrapped around transected cadaveric porcine Achilles tendons repaired with a combination of parallel and three-loop suture patterns. Tensile mechanical testing of the augmented repairs exhibited significantly higher stiffness (22-34%), failure load (24-44%), and energy to failure (27-63%) when compared to control tendons with suture repair alone. Potential clinical implications of this novel adhesive biomaterial are discussed.

Adhesive performance of biomimetic adhesive-coated biologic scaffolds

Surgical repair of a discontinuity in traumatized or degenerated soft tissues is traditionally accomplished using sutures. A current trend is to reinforce this primary repair with surgical grafts, meshes, or patches secured with perforating mechanical devices (i.e., sutures, staples, or tacks). These fixation methods frequently lead to chronic pain and mesh detachment. We developed a series of biodegradable adhesive polymers that are synthetic mimics of mussel adhesive proteins (MAPs), composed of 3,4-dihydroxyphenylalanine (DOPA)-derivatives, polyethylene glycol (PEG), and polycaprolactone (PCL). These polymers can be cast into films, and their mechanical properties, extent of swelling, and degradation rate can be tailored through the composition of the polymers as well as blending with additives. When coated onto a biologic mesh used for hernia repair, these adhesive constructs demonstrated adhesive strengths significantly higher than fibrin glue. With further development, a precoated bioadhesive mesh may represent a new surgical option for soft tissue repair.

Synthesis of 3,4-dihydroxyphenylalanine (DOPA) containing monomers and their co-polymerization with PEG-diacrylate to form hydrogels

L-3,4-Dihydroxyphenylalanine (DOPA) is an unusual amino acid found in mussel adhesive proteins (MAPs) that is believed to lend adhesive characteristics to these proteins. Most previous efforts to incorporate DOPA into hydrogels have utilized oxidative cross-linking, which is hypothesized to reduce the adhesive properties of DOPA and requires reagents that are harmful to biological tissues. In this paper, we describe the synthesis of N-methacrylated DOPA monomers and their copolymerization with poly(ethylene glycol) diacrylate (PEG-DA) using either ultraviolet (UV) or visible light. The effect of DOPA containing monomers on gelation time, gel conversion and elastic modulus of the photocured hydrogels was investigated. Despite a retarding effect of DOPA on photopolymerization, DOPA was successfully incorporated into hydrogels with elastic moduli suitable for many biomedical applications. The incorporation of DOPA into hydrogels by photopolymerization may lead to new adhesive hydrogels for medical applications.

Synthesis of novel biomaterials in plants

Metabolic engineering of plants allows the possibility of using crops for the synthesis of novel polymers having useful material properties. Strong and flexible protein-based polymers, which are based on the structure of silk and elastin have been synthesized in transgenic plants. A wide range of polyhydroxyalkanoates having properties ranging from stiff plastics to soft elastomers and glues have been synthesized in various compartments of plants, such as the cytoplasm, plastid and peroxisome. These plant biomaterials could replace, in part, the synthetic plastics, fibers and elastomers produced from petroleum, thus offering the advantage of renewability, sustainability and biodegradability.

Mussel adhesive protein mimetic polymers for the preparation of nonfouling surfaces

A new biomimetic strategy for modification of biomaterial surfaces with poly(ethylene glycol) (PEG) was developed. The strategy exploits the adhesive characteristics of 3,4-dihydroxyphenylalanine (DOPA), an important component of mussel adhesive proteins, to anchor PEG onto surfaces, rendering the surfaces resistant to cell attachment. Linear monomethoxy-terminated PEGs were conjugated either to a single DOPA residue (mPEG-DOPA) or to the N-terminus of Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp-Thr-DOPA-Lys (mPEG-MAPD), a decapeptide analogue of a protein found in Mytilus edulis adhesive plaques. Gold and titanium surfaces were modified by adsorption of mPEG-DOPA and mPEG-MAPD from solution, after which surface analysis by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy confirmed the presence of immobilized PEG on the surface. The ability of modified surfaces to resist cell attachment was examined by culturing 3T3 fibroblasts on the surfaces for up to 14 days. Quantitative image analysis revealed that cell adhesion to mPEG-DOPA and mPEG-MAPD modified surfaces decreased by as much as 98% compared to control surfaces. Modified Ti surfaces exhibited low cell adhesion for up to 2 weeks in culture, indicating that the nonfouling properties of mPEG-DOPA and mPEG-MAPD treated surfaces persist for extended periods of time. This strategy paradoxically exploits the strong fouling characteristics of MAP analogues for antifouling purposes and may be broadly applied to medical implants and diagnostics, as well as numerous nonmedical applications in which the minimization of surface fouling is desired.

Synthesis and gelation of DOPA-modified poly(ethylene glycol) hydrogels

3,4-Dihydroxyphenylalanine (DOPA) residues are known for their ability to impart adhesive and curing properties to mussel adhesive proteins. In this paper, we report the preparation of linear and branched DOPA-modified poly(ethylene glycol)s (PEG-DOPAs) containing one to four DOPA endgroups. Gel permeation chromatography-multiple-angle laser light scattering analysis of methoxy-PEG-DOPA in the presence of oxidizing reagents (sodium periodate, horseradish peroxidase, and mushroom tyrosinase) revealed the formation of oligomers of methoxy-PEG-DOPA, presumably resulting from oxidative polymerization of DOPA endgroups. In the case of PEG-DOPAs containing two or more DOPA endgroups, oxidative polymerization resulted in polymer network formation and rapid gelation. The amount of time required for gelation of aqueous PEG-DOPA solutions was found to be as little as 1 min and was dependent on the polymer architecture as well as the type and concentration of oxidizing reagent used. Analysis of reaction mixtures by UV-vis spectroscopy allowed the identification of reaction intermediates and the elucidation of reaction pathways. On the basis of the observed reaction intermediates, oxidation of the catechol side chain of DOPA resulted in the formation of highly reactive DOPA-quinone, which further reacted to form cross-linked products via one of several pathways, depending on the presence or absence of N-terminal protecting groups on the PEG-DOPA. N-Boc protected PEG-DOPA cross-linked via phenol coupling and quinone methide tanning pathways, whereas PEG-DOPA containing a free amino group cross-linked via a pathway that resembled melanogenesis. Similar differences were observed for the rate of gel formation as well as the molecular weight between cross-links ((-)M(c)), calculated using equilibrium swelling and the Flory-Rehner equation.

Synthesis and characterization of self-assembling block copolymers containing bioadhesive end groups

3,4-Dihydroxyphenyl-L-alanine (DOPA) is an unusual amino acid found in mussel adhesive proteins (MAPs) that is believed to lend adhesive characteristics to these proteins. In this paper, we describe a route for the conjugation of DOPA moieties to poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers. Hydroxyl end groups of PEO-PPO-PEO block copolymers were activated by N,N'-disuccinimidyl carbonate and then reacted with DOPA or its methyl ester with high coupling efficiencies from both aqueous and organic solvents. DOPA-modified PEO-PPO-PEO block copolymers were freely soluble in cold water, and dye partitioning and differential scanning calorimetry analysis of these solutions revealed that the copolymers aggregated into micelles at a characteristic temperature that was dependent on block copolymer composition and concentration in solution. Oscillatory rheometry demonstrated that above a block copolymer concentration of approximately 20 wt %, solutions of DOPA-modified PEO-PPO-PEO block copolymers exhibited sol-gel transitions upon heating. The gelation temperature could be tailored between approximately 23 and 46 degrees C by changing the composition, concentration, and molecular weight of the block copolymer. Rheological measurement of the bioadhesive interaction between DOPA-modified Pluronic and bovine submaxillary mucin indicated that DOPA-modified Pluronic was significantly more bioadhesive than unmodified Pluronic.