Ambivalent Adhesives: Combining Biomimetic Cross-Linking With Antiadhesive Oligo(ethylene glycol)

Poly(2-isopropenyl-2-oxazoline) as a Versatile Functional Polymer for Biomedical Applications

Functional polymers play an important role in various biomedical applications. From many choices, poly(2-isopropenyl-2-oxazoline) (PIPOx) represents a promising reactive polymer with great potential in various biomedical applications. PIPOx, with pendant reactive 2-oxazoline groups, can be readily prepared in a controllable manner via several controlled/living polymerization methods, such as living anionic polymerization, atom transfer radical polymerization (ATRP), reversible addition-fragmentation transfer (RAFT) or rare earth metal-mediated group transfer polymerization. The reactivity of pendant 2-oxazoline allows selective reactions with thiol and carboxylic group-containing compounds without the presence of any catalyst. Moreover, PIPOx has been demonstrated to be a non-cytotoxic polymer with immunomodulative properties. Post-polymerization functionalization of PIPOx has been used for the preparation of thermosensitive or cationic polymers, drug conjugates, hydrogels, brush-like materials, and polymer coatings available for drug and gene delivery, tissue engineering, blood-like materials, antimicrobial materials, and many others. This mini-review covers new achievements in PIPOx synthesis, reactivity, and use in biomedical applications.

Development of Biocompatible Mussel-Inspired Cellulose-Based Underwater Adhesives

Conventional adhesives have poor underwater adhesion and harm to human health and the environment during their use, which largely limits their practical applications. Herein, we synthesized cellulose-based adhesives with underwater adhesion and biocompatibility by grafting N-(3,4-dihydroxyphenethyl)methacrylamide into the cellulose chain via atom transfer radical polymerization (ATRP). FTIR, 1H NMR, and XPS analyses ensured the successful preparation of the cellulose-based adhesive polymers. The different properties of the prepared adhesives, including swelling ratio, adhesion strength, and biocompatibility are examined. Results found that the lap shear strength is enhanced by increasing the catechol content. When catechol content is 27.2 mol %, cellulose-based adhesive with the addition of Fe3+ possesses a strong lap shear strength of 2.13 MPa in a dry environment, 0.10 MPa underwater, and 0.16 MPa under seawater for iron substrate, respectively. In addition, the cell culture test demonstrated that the prepared adhesives have outstanding biocompatibility. The cellulose-based adhesives with underwater adhesion and biocompatibility have potential applications in biomedicine, electronic engineering, and construction fields.

Forced Gradient Copolymer for Rational Design of Mussel-Inspired Adhesives and Dispersants

In recent years, there has been considerable research into functional materials inspired by living things. Much attention has been paid to the development of adhesive materials that mimic the adhesive proteins secreted by a mussel's foot. These mussel-inspired materials have superior adhesiveness to various adherents owing to the non-covalent interactions of their polyphenolic moieties, e.g., hydrogen bonding, electrostatic interactions, and even hydrophobic interactions. Various factors significantly affect the adhesiveness of mussel-inspired polymers, such as the molecular weight, cross-linking density, and composition ratio of the components, as well as the chemical structure of the polyphenolic adhesive moieties, such as l-3,4-dihydroxyphenylalanine (l-Dopa). However, the contributions of the position and distribution of the adhesive moiety in mussel-inspired polymers are often underestimated. In the present study, we prepared a series of mussel-inspired alkyl methacrylate copolymers by controlling the position and distribution of the adhesive moiety, which are known as "forced gradient copolymers". We used a newly designed gallic-acid-bearing methacrylate (GMA) as the polyphenolic adhesive moiety and copolymerized it with 2-ethylhexyl methacrylate (EHMA). The resulting forced gradient adhesive copolymer of GMA and EHMA (poly(GMA-co-EHMA), Poly1) was subjected to adhesion and dispersion tests with an aluminum substrate and a BaTiO₃ nanoparticle in organic solvents, respectively. In particular, this study aims to clarify how the monomer position and distribution of the adhesive moiety in the mussel-inspired polymer affect its adhesion and dispersion behavior on a flat metal oxide surface and spherical inorganic oxide surfaces of several tens of nanometers in diameter, respectively. Here, forced gradient copolymer Poly1 consisted of a homopolymer moiety of EHMA (Poly3) and a random copolymer moiety of EHMA and GMA (Poly4). The composition ratio of GMA and the molecular weight were kept constant among the Poly1 series. Simultaneous control of the molecular lengths of Poly3 and Poly4 allowed us to discuss the effects on the distribution of GMA in Poly1. Poly1 exhibited apparent distribution dependency with regard to the adhesiveness and the dispersibility of BaTiO₃. Poly1 showed the highest adhesion strength when the composition ratio of GMA was approximately 9 mol% in the portion of the Poly4 segment. In contrast, the block copolymer consisting of the Poly3 segment and Poly4 segment with only adhesive moiety 1 showed the lowest viscosity for dispersion of BaTiO₃ nanoparticles. These results indicate that copolymers with mussel-inspired adhesive motifs require the proper design of the monomer position and distribution in Poly1 according to the shape and characteristics of the adherend to maximize their functionality. This research will facilitate the rational design of bio-inspired adhesive materials derived from plants that outperform natural materials, and it will eventually contribute to a sustainable circular economy.

Strong and bioactive bioinspired biomaterials, next generation of bone adhesives

The bone adhesive is a clinical requirement for complicated bone fractures always articulated by surgeons. Applying glue is a quick and easy way to fix broken bones. Adhesives, unlike conventional fixation methods such as wires and sutures, improve healing conditions and reduce postoperative pain by creating a complete connection at the fractured joint. Despite many efforts in the field of bone adhesives, the creation of a successful adhesive with robust adhesion and appropriate bioactivity for the treatment of bone fractures is still in its infancy. Because of the resemblance of the body's humid environment to the underwater environment, in the latest decades, researchers have pursued inspiration from nature to develop strong bioactive adhesives for bone tissue. The aim of this review article is to discuss the recent state of the art in bone adhesives with a specific focus on biomimetic adhesives, their action mechanisms, and upcoming perspective. Firstly, the adhesive biomaterials with specific affinity to bone tissue are introduced and their rational design is studied. Consequently, various types of synthetic and natural bioadhesives for bone tissue are comprehensively overviewed. Then, bioinspired-adhesives are described, highlighting relevant structures and examples of biomimetic adhesives mainly made of DOPA and the complex coacervates inspired by proteins secreted in mussel and sandcastle worms, respectively. Finally, this article overviews the challenges of the current bioadhesives and the future research for the improvement of the properties of biomimetic adhesives for use as bone adhesives.

Dopamine based adhesive nano-coatings on extracellular matrix (ECM) based grafts for enhanced host-graft interfacing affinity

Interfacing affinity between grafts and host tissues is an urgent issue that needs to be addressed for the clinical translation of tissue engineered extracellular matrix (ECM) based grafts. Dopamine is known as a universal adhesive, the catechol groups on which could form chelating bonds with metal ions. Herein we developed an adhesive nano-coating on ECM based grafts which could crosslink in situ with ferric ions for fixation with surrounding tissues after implantation without affecting the porous structures of the grafts. Therefore, decellularized living hyaline cartilage graft (dLhCG), a model ECM-based graft, with dopamine based natural biological material adhesive coatings was manufactured to address the interfacing affinity issue between ECM-based grafts and cartilage. A macromolecule backbone was needed for the coating material to avoid the formation of a rigid crosslinking system and adverse effects caused by small molecules of dopamine. Chondroitin sulfate (CS), a cartilage derived sulfated GAG, was chosen as the backbone to fabricate dopamine modified CS (CSD) with no impurities introduced to the joint. Dopamine modified serum albumin (BCD) was also chosen for the favorable biocompatibility of albumin. Both dLhCG coated with CSD and dLhCG coated with BCD showed enhanced adhesive strength with cartilage after chelating with ferric ions in situ compared to dLhCG and further potential in improving the interfacing affinity of dLhCG with cartilage.

A Novel Surface Modification Strategy via Photopolymerized Poly-Sulfobetaine Methacrylate Coating to Prevent Bacterial Adhesion on Titanium Surfaces

Recent investigations on the anti-adhesive properties of polysulfobetaine methacrylate (pSBMA) coatings had shown promising potential as antifouling surfaces and have given the impetus for the present paper, where a pSBMA coating is applied via photopolymerization on a macro-roughened, sandblasted, and acid-etched titanium implant surface in order to assess its antifouling properties. Current emphasis is placed on how the coating is efficient against the adhesion of Enterococcus faecalis by quantitative assessment of colony forming units and qualitative investigation of fluorescence imaging and scanning electron microscopy. pSBMA coatings via photopolymerization of titanium surfaces seems to be a promising antiadhesion strategy, which should bring substantial benefits once certain aspects such as biodegradation and osseointegration were addressed. Additionally, commercial SAL-titanium substrates may be coated with the super-hydrophilic coating, appearing resistant to physiological salt concentrations and most importantly lowering E. faecalis colonization significantly, compared to titanium substrates in the as-received state. It is very likely that pSBMA coatings may also prevent the adhesion of other germs.

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.

Mussel-Inspired Alternating Copolymer as a High-Performance Adhesive Material Both at Dry and Under-Seawater Conditions

Marine mussels have the ability to cling to various surfaces at wet or underwater conditions, which inspires the research of catechol-functionalized polymers (CFPs) to develop high-performance adhesive materials. However, these polymeric adhesives generally face the problems of complex synthetic route, and it is still high challenging to prepare CFPs with excellent adhesive performance both at dry and underwater conditions. Herein, a mussel-inspired alternating copolymer, poly(dopamine-alt-2,2-bis(4-glycidyloxyphenyl)propane) (P(DA-a-BGOP)), is synthesized in one step by using commercially available monomers through epoxy-amino click chemistry. The incorporation of polar groups and rigid bisphenol A structures into the polymer backbone enhances the cohesion energy of polymer matrix. The alternating polymer structure endows the polymers with high catechol content and controlled polymer sequence. As a result, P(DA-a-BGOP) exhibits a strong bonding strength as high as 16.39 ± 2.13 MPa on stainless steel substrates after a hot pressing procedure and displays a bonding strength of 1.05 ± 0.05 MPa on glass substrates at an under-seawater condition, which surpasses most commercial adhesives.

Facile Fabrication of Bio- and Dual-Functional Poly(2-oxazoline) Bottle-Brush Brush Surfaces

Poly(2-oxazoline)s (POx) bottle-brush brushes have excellent biocompatible and lubricious properties, which are promising for the functionalization of surfaces for biomedical devices. Herein, a facile synthesis of POx is reported which is based bottle-brush brushes (BBBs) on solid substrates. Initially, backbone brushes of poly(2-isopropenyl-2-oxazoline) (PIPOx) were fabricated via surface initiated Cu0 plate-mediated controlled radical polymerization (SI-Cu0 CRP). Poly(2-methyl-2-oxazoline) (PMeOx) side chains were subsequently grafted from the PIPOx backbone via living cationic ring opening polymerization (LCROP), which result in ≈100 % increase in brush thickness (from 58 to 110 nm). The resultant BBBs shows tunable thickness up to 300 nm and high grafting density (σ) with 0.42 chains nm-2 . The synthetic procedure of POx BBBs can be further simplified by using SI-Cu0 CRP with POx molecular brush as macromonomer (Mn =536 g mol-1 , PDI=1.10), which results in BBBs surface up to 60 nm with well-defined molecular structure. Both procedures are significantly superior to the state-of-art approaches for the synthesis of POx BBBs, which are promising to design bio-functional surfaces.

Bioinspired Adhesion Polymers: Wear Resistance of Adsorption Layers

Mussel adhesive polymers owe their ability to strongly bind to a large variety of surfaces under water to their high content of 3,4-dihydroxy-l-phenylalanine (DOPA) groups and high positive charge. In this work, we use a set of statistical copolymers that contain medium-length poly(ethylene oxide) side chains that are anchored to the surface in three different ways: by means of (i) electrostatic forces, (ii) catechol groups (as in DOPA), and (iii) the combination of electrostatic forces and catechol groups. A nanotribological scanning probe method was utilized to evaluate the wear resistance of the formed layers as a function of normal load. It was found that the combined measurement of surface topography and stiffness provided an accurate assessment of the wear resistance of such thin layers. In particular, surface stiffness maps allowed us to identify the initiation of wear before a clear topographical wear scar was developed. Our data demonstrate that the molecular and abrasive wear resistance on silica surfaces depends on the anchoring mode and follows the order catechol groups combined with electrostatic forces > catechol groups alone > electrostatic forces alone. The devised methodology should be generally applicable for evaluating wear resistance or "robustness" of thin adsorbed layers on a variety of surfaces.

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.

Rational design of a biomimetic glue with tunable strength and ductility

A biomimetic design has been explored to achieve high-performance polymer glue with tuneable strength and ductility, which is suitable for a wide-range of substrates under both similar and dissimilar bonding.

Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein

Marine mussels secret protein-based adhesives, which enable them to anchor to various surfaces in a saline, intertidal zone. Mussel foot proteins (Mfps) contain a large abundance of a unique, catecholic amino acid, Dopa, in their protein sequences. Catechol offers robust and durable adhesion to various substrate surfaces and contributes to the curing of the adhesive plaques. In this article, we review the unique features and the key functionalities of Mfps, catechol chemistry, and strategies for preparing catechol-functionalized polymers. Specifically, we reviewed recent findings on the contributions of various features of Mfps on interfacial binding, which include coacervate formation, surface drying properties, control of the oxidation state of catechol, among other features. We also summarized recent developments in designing advanced biomimetic materials including coacervate-forming adhesives, mechanically improved nano- and micro-composite adhesive hydrogels, as well as smart and self-healing materials. Finally, we review the applications of catechol-functionalized materials for the use as biomedical adhesives, therapeutic applications, and antifouling coatings. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 9-33.

Rheology of nitrile rubber with hybrid crosslinked network composed of covalent bonding and hydrogen bonding

A hybrid crosslinked network composed of covalent bonding and non-covalent bonding was constructed in nitrile rubber (NBR) by using a compound crosslinking agents dicumyl peroxide (DCP) and N,N-methylenebis acrylamide (MBA).

Antifouling Zwitterionic Coating via Electrochemically Mediated Atom Transfer Radical Polymerization on Enzyme-Based Glucose Sensors for Long-Time Stability in 37 °C Serum

In this study, a versatile fabrication method for coating enzyme-based biosensors with ultrathin antifouling zwitterionic polymer films to meet the challenge of the long-time stability of sensors in vivo was developed. Electrochemically mediated atom transfer radical polymerization (eATRP) was applied to polymerize zwitterionic sulfobetaine methacrylate monomers on the rough enzyme-absorbed electrode surfaces; meanwhile, a refined overall bromination was developed to improve the coverage of polymers on the biosensor surfaces and to maintain the enzyme activity simultaneously for the first time. X-ray photoelectron spectroscopy and atomic force microscopy were used to characterize the properties of the polymer layers. The antifouling performance and long-time stability in 37 °C undiluted bovine serum in vitro were evaluated. The results showed that the polymer brush coatings diminished over 99% nonspecific protein adsorption and that the sensitivity of the evaluated sensor was maintained at 94% after 15 days. The overall sensitivity deviation of 7% was nearly 50% lower than that of the polyurethane-coated ones and also much smaller than the current commercially available glucose biosensors. The results suggested that this highly controllable electrodeposition procedure could be a promising method to develop implantable biosensors with long-time stability.

Hydrolytically degradable hyperbranched PEG-polyester adhesive with low swelling and robust mechanical properties

Photocrosslinkable and water soluble hyperbranched PEG-polyester polymers (HPEGDA) have been developed as robust degradable adhesives. The HPEGDA polymers have been synthesized from controlled homopolymerization of poly(ethylene glycol) diacrylate (PEGDA700 ) via in situ deactivation enhanced atom transfer radical polymerization (DE-ATRP). By introducing a high initiator-to-monomer ratio, the obtained HPEGDA polymer is composed of extremely short carbon-carbon backbones interconnected together by the long PEG chains as well as pendent photocrosslinkable acrylate moieties. Due to the extremely short C-C backbone, the long PEG chains can therefore be seen as the main chain, thus, HPEGDA polymers behave more like polyester which is a category of polymers that contain the ester functional group in their main chain. Photo-cured HPEGDA can be readily adhered to tissue forming a patch with robust mechanical and adhesive strengths. The degradation profile by hydrolysis of polyester blocks as well as a significantly low swelling ratio of HPEGDA gels in an aqueous environment allow them to have great potential for sealing and repair of internal tissue. Furthermore, HPEGDA gels appear to have minor significant cytotoxicity in vitro. These unique properties indicate that the reported HPEGDA polymers are well poised for the development of adhesive tissue engineering matrixes, wound dressings, and sealants.

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

A series of well-designed highly branched PEG-catechol based thermo-responsive copolymers were synthesized via a one-pot RAFT polymerization. A varying degree of photocrosslinkable (meth)acrylate moieties were incorporated within the 3D structure to allow on-demand photocuring (strong cohesion, unlike conventional PEG adhesives). At the same time, multitudes of free catechol groups inspired from adhesive proteins of marine mussels were also introduced in the hyperbranched structure, giving rise to adherence to skin and cardiac tissue. The resulting ambivalent PEG-catechol based copolymers were systematically studied to investigate the effects of polymer composition on tissue bioadhesive and swelling properties, comparing acrylates to methacrylates and PEG to 2-hydroxyethyl acrylamide (HEAA). It was proved that DOPA played a major role in the adhesion performance as it significantly enhanced the adhesion performances on varied substrates. The highly branched PEG-catechol copolymers demonstrate the great potential in the design of novel surgical glues, sealants or drug delivery vectors.

Mussel-inspired protein-repelling ambivalent block copolymers: controlled synthesis and characterization

This paper describes the reversible addition–fragmentation chain transfer (RAFT) polymerization of mussel-inspired acetonide-protected dopamine (meth)acrylamide monomers (ADA and ADMA) and its implementation to the synthesis of innovative ambivalent block copolymers.

Robust, self-healing hydrogels synthesised from catechol rich polymers

Catechol rich polymers yield robust, self-healing hydrogels.

Enzymatically crosslinked alginate hydrogels with improved adhesion properties

Alginate–dopamine (Alg–DA) conjugate, a polymer with catechol side groups instead of phenol groups, gels in situ in the presence of HRP and H₂O₂. The resulting hydrogels exhibit significantly improved adhesion properties.

Bioinspired materials: from low to high dimensional structure

The surprising properties of biomaterials are the results of billions of years of evolution. Generally, biomaterials are assembled under mild conditions with very limited supply of constituents available for living organism, and their amazing properties largely result from the sophisticated hierarchical structures. Following the biomimetic principles to prepare manmade materials has drawn great research interests in materials science and engineering. In this review, we summarize the recent progress in fabricating bioinspired materials with the emphasis on mimicking the structure from one to three dimensions. Selected examples are described with a focus on the relationship between the structural characters and the corresponding functions. For one-dimensional materials, spider fibers, polar bear hair, multichannel plant roots and so on have been involved. Natural structure color and color shifting surfaces, and the antifouling, antireflective coatings of biomaterials are chosen as the typical examples of the two-dimensional biomimicking. The outstanding protection performance, and the stimuli responsive and self-healing functions of biomaterials based on the sophisticated hierarchical bulk structures are the emphases of the three-dimensional mimicking. Finally, a summary and outlook are given.

Metals & polymers in the mix: fine-tuning the mechanical properties & color of self-healing mussel-inspired hydrogels

Ways to orchestrate the mechanical properties and colors of mussel-inspired metal cross-linked hydrogels based on DOPA functionalized cationic polymers are demonstrated. This is achieved by systematically varying the hardness of the coordinating metal and/or the cationic polymer.

Novel L-DOPA-derived poly(ester amide)s: monomers, polymers, and the first L-DOPA-functionalized biobased adhesive tape

The synthesis, characterization, and testing of a range of novel bio-inspired L-DOPA-derived poly(ester amide)s is presented, using a widely applicable, straightforward chemistry. A model system is used to study and establish the monomer and polymer synthetic protocols, and to provide a set of optimum reaction conditions. It is further shown that fully biobased L-DOPA-containing adhesive tapes can be fabricated, which are positively evaluated in terms of their adhesive properties. The newly developed synthetic protocol constitutes a versatile platform for accessing and tailoring a plethora of relevant structures, including a variety of potentially biocompatible poly(ethylene glycol)-based materials.

Molecular weight effects upon the adhesive bonding of a mussel mimetic polymer

Characterization of marine biological adhesives are teaching us how nature makes materials and providing new ideas for synthetic systems. One of the most widely studied adhering animals is the marine mussel. This mollusk bonds to wet rocks by producing an adhesive from cross-linked proteins. Several laboratories are now making synthetic mimics of mussel adhesive proteins, with 3,4-dihydroxyphenylalanine (DOPA) or similar molecules pendant from polymer chains. In select cases, appreciable bulk bonding results, with strengths as high as commercial glues. Polymer molecular weight is amongst several parameters that need to be examined in order to both understand biomimetic adhesion as well as to maximize performance. Experiments presented here explore how the bulk adhesion of a mussel mimetic polymer varies as a function of molecular weight. Systematic structure-function studies were carried out both with and without the presence of an oxidative cross-linker. Without cross-linking, higher molecular weights generally afforded higher adhesion. When a [N(C4H9)4](IO4) cross-linker was added, adhesion peaked at molecular weights of ~50,000-65,000 g/mol. These data help to illustrate how changes to the balance of cohesion versus adhesion influence bulk bonding. Mussel adhesive plaques achieve this balance by incorporating several proteins with molecular weights ranging from 6000 to 110,000 g/mol. To mimic these varied proteins we made a blend of polymers containing a range of molecular weights. Interestingly, this blend adhered more strongly than any of the individual polymers when cross-linked with [N(C4H9)4](IO4). These results are helping us to both understand the origins of biological materials as well as design high performance polymers.