Changing polymer catechol content to generate adhesives for high versus low energy surfaces

Biocompatibility of mussel-inspired water-soluble tissue adhesives

Wound closure in surgeries is traditionally achieved using invasive methods such as sutures and staples. Adhesion-based wound closure methods such as tissue adhesives, sealants, and hemostats are slowly replacing these methods due to their ease of application. Although several chemistries have been developed and used commercially for wound closure, there is still a need for better tissue adhesives from the point of view of toxicity, wet-adhesion strength, and long-term bonding. Catechol chemistry has shown great promise in developing wet-set adhesives that meet these criteria. Herein, we have studied the biocompatibility of a catechol-based copolymer adhesive, poly([dopamine methacrylamide]-co-[methyl methacrylate]-co-[poly(ethylene glycol) methyl ether methacrylate]) or poly(catechol-MMA-OEG), which is soluble in water. The adhesive was injected subcutaneously in a mouse model on its own and in combination with a sodium periodate crosslinker. After 72 h, 4 weeks, and 12 weeks, the mice were euthanized and subjected to histopathological analysis. Both adhesives were present and still palpable at the end of 12 weeks. The moderate inflammation observed for the poly(catechol-MMA-OEG) cohort at 72 h had reduced to mild inflammation at the end of 12 weeks. However, the moderate inflammatory response observed for the poly(catechol-MMA-OEG) + crosslinker cohort at 72 h had not subsided at 12 weeks.

Effects of catechol grafting on chitosan-based coacervation and adhesion

In this study, we investigated detailedly the contribution of catechol in tuning the formation and adhesive properties of coacervates. We have constructed a series of catechol-grafted Chitosan (Chitosan-C), and investigated their coacervation with gum arabic (GA) and the corresponding adhesion. We demonstrate that, increasing catechol grafting ratio from 0 %-44 % impacted the coacervation moderately, while enhanced the adhesion of the coacervate up to 438 % when the catechol faction was 37 %. Further increasing the grafting ratio to 55 % led to precipitated coacervates associated with a declined adhesion. Our findings identify the optimal grafting threshold for coacervation and adhesion, providing insights into the underlying mechanism of coacervate binding. Moreover, the catechol enhancement on adhesion of coacervates tolerates different substrates and diverse polyelectrolyte pairs. The revealed principles shall be helpful for designing adhesive coacervates and boosting their applications in various industrial and biomedical areas.

Enhancing Adhesion Properties of Commodity Polymers through Thiol-Catechol Connectivities: A Case Study on Polymerizing Polystyrene-Telechelics via Thiol-Quinone Michael-Polyaddition

Segmented block copolymers with adhesive functionality bridges in between are synthesized through the combination of controlled radical polymerization (CRP) and thiol-quinone Michael-polyaddition. CRP provides a set of α,ω-dithiol polystyrenes (PS), which react as telechelics with a low molecular weight bisquinone, resulting in thiol-catechol connectivities (TCCs). By introducing as little as 3 mol % of TCC functionalities, the bonding of the polymer on dry and wet aluminum surfaces is significantly improved while keeping the integrity of the PS segments undisturbed to constitute favorable bulk properties. This improvement is evidenced by reaching up to 3.8 MPa adhesive strength, representing a 600% increase compared to nonfunctional PS.

Positive Charge Influences on the Surface Interactions and Cohesive Bonding of a Catechol-Containing Polymer

Achieving robust underwater adhesion remains challenging. Through generations of evolution, marine mussels have developed an adhesive system that allows them to anchor onto wet surfaces. Scientists have taken varied approaches to developing mussel-inspired adhesives. Mussel foot proteins are rich in lysine residues, which may play a role in the removal of salts from surfaces. Displacement of water and ions on substrates could then enable molecular contact with surfaces. The necessity of cations for underwater adhesion is still in debate. Here, we examined the performance of a methacrylate polymer containing quaternary ammonium and catechol groups. Varying amounts of charge in the polymers were studied. As opposed to protonated amines such as lysine, quaternary ammonium groups offer a nonreactive cation for isolating effects from only charge. Results shown for dry bonding demonstrated that cations tended to decrease bulk cohesion while increasing surface interactions. Stronger interactions at surfaces, along with weaker bulk bonding, indicate that cations decreased the cohesive forces. When under salt water, overall bulk adhesion also dropped with higher cation loadings. Surface attachment under salt water also dropped, indicating that the polymer cations could not displace surface waters or sodium ions. Salt did, however, appear to shield bulk cation-cation repulsions. These studies help to distinguish influences upon bulk cohesion from attachment at surfaces. The roles of cations in adhesion are complex, with both cohesive and surface bonding being relevant in different ways, sometimes even working in opposite directions.

Chemical Modification of Oxidized Polyethylene Enables Access to Functional Polyethylenes with Greater Reuse

Polyethylene is a commodity material that is widely used because of its low cost and valuable properties. However, the lack of functional groups in polyethylene limits its use in applications that include adhesives, gas barriers, and plastic blends. The inertness of polyethylene makes it difficult to install groups that would enhance its properties and enable programmed chemical decomposition. To overcome these deficiencies, the installation of pendent functional groups that imbue polyethylene with enhanced properties is an attractive strategy to overcome its inherent limitations. Here, we describe strategies to derivatize oxidized polyethylene that contains both ketones and alcohols to monofunctional variants with bulk properties superior to those of unmodified polyethylene. Iridium-catalyzed transfer dehydrogenation with acetone furnished polyethylenes with only ketones, and ruthenium-catalyzed hydrogenation with hydrogen furnished polyethylenes with only alcohols. We demonstrate that the ratio of these functional groups can be controlled by reduction with stoichiometric hydride-containing reagents. The ketones and alcohols serve as sites to introduce esters and oximes onto the polymer, thereby improving surface and bulk properties over those of polyethylene. These esters and oximes were removed by hydrolysis to regenerate the original oxygenated polyethylenes, showing how functionalization can lead to materials with circularity. Waste polyethylenes were equally amenable to oxidative functionalization and derivatization of the oxidized material, showing that this low- or negative-value feedstock can be used to prepare materials of higher value. Finally, the derivatized polymers with distinct solubilities were separated from mechanically mixed plastic blends by selective dissolution, demonstrating that functionalization can lead to novel approaches for distinguishing and separating polymers from a mixture.

Dopamine-Based Copolymer Bottlebrushes for Functional Adhesives: Synthesis, Characterization, and Applications in Surface Engineering of Antifouling Polyethylene

Nonpolar materials like polyolefins are notoriously challenging substrates for surface modification. However, this challenge is not observed in nature. Barnacle shells and mussels, for example, utilize catechol-based chemistry to fasten themselves onto all kinds of materials, such as boat hulls or plastic waste. Here, a design is proposed, synthesized, and demonstrated for a class of catechol-containing copolymers (terpolymers) for surface functionalization of polyolefins. Dopamine methacrylamide (DOMA), a catechol-containing monomer, is incorporated into a polymer chain together with methyl methacrylate (MMA) and 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM). DOMA serves as adhesion points, BIEM provides functional sites for subsequent "grafting from" reactions, and MMA provides the possibility for concentration and conformation adjustment. First, the adhesive capabilities of DOMA are demonstrated by varying its content in the copolymer. Then, terpolymers are spin-coated on model Si substrates. Subsequently, the atom transfer initiator (ATRP) initiating group is used to graft a poly(methyl methacrylate) (PMMA) layer from the copolymers, with 40% DOMA content providing a coherent PMMA film. To demonstrate functionalization on a polyolefin substrate, the copolymer is spin-coated on high-density polyethylene (HDPE) substrates. A POEGMA layer is grafted from the ATRP initiator sites on the terpolymer chain on the HDPE films to provide antifouling characteristics. Static contact angle values and Fourier transform infrared (FTIR) spectra confirm the presence of POEGMA on the HDPE substrate. Finally, the anticipated antifouling functionality of grafted POEGMA is demonstrated by observing the inhibition of nonspecific adsorption of the fluorescein-modified bovine serum albumin (BSA) protein. The poly(oligoethylene glycol methacrylate) POEGMA layers grafted on 30% DOMA-containing copolymers on HDPE show optimal antifouling performance exhibiting a 95% reduction of BSA fluorescence compared to nonfunctionalized and surface-fouled polyethylene. These results demonstrate the successful utilization of catechol-based materials for functionalizing polyolefin surfaces.

Underwater Bonding with a Biobased Adhesive from Tannic Acid and Zein Protein

Herein are presented several adhesive formulations made from zein protein and tannic acid that can bind to a wide range of surfaces underwater. Higher performance comes from more tannic acid than zein, whereas dry bonding required the opposite case of more zein than tannic acid. Each adhesive works best in the environment that it was designed and optimized for. We show underwater adhesion experiments done on different substrates and in different waters (sea water, saline solution, tap water, deionized water). Surprisingly, the water type does not influence the performance to a great deal but the substrate type does. An additional unexpected result was bond strength increasing over time when exposed to water, contradicting general experiments of working with glues. Initial adhesion underwater was stronger compared to benchtop adhesion, suggesting that water helps to make the glue stick. Temperature effects were determined, indicating maximum bonding at about 30 °C and then another increase at higher temperatures. Once the adhesive was placed underwater, a protective skin formed on the surface, keeping water from entering the rest of the material immediately. The shape of the adhesive could be manipulated easily and, once in place, the skin could be broken to induce faster bond formation. Data indicated that underwater adhesion was predominantly induced by tannic acid, cross-linking within the bulk for adhesion and to the substrate surfaces. The zein protein provided a less polar matrix that helped to keep the tannic acid molecules in place. These studies provide new plant-based adhesives for working underwater and for creating a more sustainable environment.

A bioinspired Janus polyurethane membrane for potential periodontal tissue regeneration

Guided tissue regeneration (GTR) is the main therapeutic method for periodontal tissue regeneration. The key to the GTR strategy is the membrane which can assist the reconstruction of bone tissue in the periodontal defect and prevent the migration of epithelium and fibroblasts to the defect. However, the existing periodontal membrane cannot effectively promote periodontal tissue regeneration due to the limited bioactivity and physicochemical function. Here, we developed a bioinspired degradable polyurethane membrane with Janus surface morphology by integrating bioactive dopamine (DA) and an antibacterial Gemini quaternary ammonium salt (QAS). The Janus surface of the membrane is fabricated through spontaneous microphase separation, resulting from the different migration of functional segments between the air-contact upper surface with enriched antibacterial QAS and the substrate-contact bottom with enriched bioactive DA. The smooth surface of the upper membrane used to face the soft tissues can reduce cell adhesion to suppress the migration of fibroblasts, while the rough surface with a topological micro-pit structure of the bottom side facing the bone has excellent function of autonomic mineralization and cell adhesion to promote bone tissue reconstruction. In addition, the membrane containing the antibacterial QAS shows excellent antibacterial effect on common oral pathogens, such as S. aureus and S. mutans. Moreover, the specific dopamine group also endows the membrane with excellent antioxidant efficiency. In vivo research shows that this Janus polyurethane membrane can effectively promote periodontal tissue regeneration in a rat periodontal defect model. Combined with its excellent mechanical properties and biocompatibility, the polyurethane membrane is a promising material for potential periodontal tissue regeneration.