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

An efficient photothermal-chemotherapy platform based on polyacrylamide/phytic acid/polydopamine hydrogel

In this work, the polyacrylamide/phytic acid/polydopamine (termed as, PAAM/PA/PDA) hydrogel is used as drug loading matrix and photothermal conversion reagent, which is prepared by copolymerization of dopamine with acrylamide through...

Protein-mediated bioadhesion in marine organisms: A review

Protein-mediated bioadhesion is one of the crucial physiological processes in marine organisms, by which they can firmly adhere to underwater substrates. Most marine adhesive organisms are biofoulers, causing negative effects on marine ecosystems and huge economic losses to aquaculture and maritime industries. Furthermore, adhesive proteins in these organisms are promising bionic candidates for high-performance artificial materials with great application value. In-depth understanding of the bioadhesion in marine ecosystems is of dual significance for resolving biofouling issue and developing marine bionic products. Here, we review the research progress of protein-mediated bioadhesion in marine organisms. The adhesion processes such as protein biosynthesis and secretion are similar among organisms, but the detailed features such as compositions, structures, and molecular functions of adhesive proteins are distinct. Hydroxylation, glycosylation, and phosphorylation are important post-translational modifications during the processes of adhesion. The contents of some amino acids such as glycine, tyrosine and cysteine involved in underwater adhesion are significantly higher, which is a sequence feature of barnacle cement and mussel foot proteins. The amyloid structures and conserved domains/motifs such as EGF and vWFA distributed in adhesive proteins are involved in the underwater adhesion. In addition, the oxidative cross-linking also plays an important role in marine bioadhesion. Overall, the unique and common features identified for the protein-mediated bioadhesion in diverse marine organisms here provide background information and essential reference for characterizing marine adhesive proteins and associated functional domains, formulating antifouling strategies, and developing novel biomimetic adhesives.

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.

The useful agent to have an ideal biological scaffold

Tissue engineering which is applied in regenerative medicine has three basic components: cells, scaffolds and growth factors. This multidisciplinary field can regulate cell behaviors in different conditions using scaffolds and growth factors. Scaffolds perform this regulation with their structural, mechanical, functional and bioinductive properties and growth factors by attaching to and activating their receptors in cells. There are various types of biological extracellular matrix (ECM) and polymeric scaffolds in tissue engineering. Recently, many researchers have turned to using biological ECM rather than polymeric scaffolds because of its safety and growth factors. Therefore, selection the right scaffold with the best properties tailored to clinical use is an ideal way to regulate cell behaviors in order to repair or improve damaged tissue functions in regenerative medicine. In this review we first divided properties of biological scaffold into intrinsic and extrinsic elements and then explain the components of each element. Finally, the types of scaffold storage methods and their advantages and disadvantages are examined.

Bioadhesives for musculoskeletal tissue regeneration

Natural or synthetic materials designed to adhere to biological components, bioadhesives, have received significant attention in clinics and surgeries. As a result, there are several commercially available, FDA-approved bioadhesives used for skin wound closure, hemostasis, and sealing tissue gaps or cracks in soft tissues. Recently, the application of bioadhesives has been expanded to various areas including musculoskeletal tissue engineering and regenerative medicine. The instant establishment of a strong adhesion force on tissue surfaces has shown potential to augment repair of connective tissues. Bioadhesives have also been applied to secure tissue grafts to host bodies and to fill or seal gaps in musculoskeletal tissues caused by injuries or degenerative diseases. In addition, the injectability equipped with the instant adhesion formation may provide the great potential of bioadhesives as vehicles for localized delivery of cells, growth factors, and small molecules to facilitate tissue healing and regeneration. This review covers recent research progress in bioadhesives as focused on their applications in musculoskeletal tissue repair and regeneration. We also discuss the advantages and outstanding challenges of bioadhesives, as well as the future perspective toward regeneration of connective tissues with high mechanical demand.

Exploiting the role of nanoparticle shape in enhancing hydrogel adhesive and mechanical properties

The ability to control nanostructure shape and dimensions presents opportunities to design materials in which their macroscopic properties are dependent upon the nature of the nanoparticle. Although particle morphology has been recognized as a crucial parameter, the exploitation of the potential shape-dependent properties has, to date, been limited. Herein, we demonstrate that nanoparticle shape is a critical consideration in the determination of nanocomposite hydrogel properties. Using translationally relevant calcium-alginate hydrogels, we show that the use of poly(L-lactide)-based nanoparticles with platelet morphology as an adhesive results in a significant enhancement of adhesion over nanoparticle glues comprised of spherical or cylindrical micelles. Furthermore, gel nanocomposites containing platelets showed an enhanced resistance to breaking under strain compared to their spherical and cylindrical counterparts. This study opens the doors to a change in direction in the field of gel nanocomposites, where nanoparticle shape plays an important role in tuning mechanical properties.

The ability to control nanostructure shape and dimensions presents opportunities to design materials in which their macroscopic properties are dependent upon the nature of the nanoparticle. Here the authors show nanoparticle shape is a critical consideration in the determination of nanocomposite hydrogel properties.

Mussel-inspired bioadhesives in healthcare: design parameters, current trends, and future perspectives

Mussels are well-known for their extraordinary capacity to adhere onto different surfaces in various hydrophillic conditions. Their unique adhesion ability under water or in wet conditions has generated considerable interest towards developing mussel inspired polymeric systems that can mimic the chemical mechanisms used by mussels for their adhesive properties. Catechols like 3,4-dihydroxy phenylalanine (DOPA) and their biochemical interactions have been largely implicated in mussels' strong adhesion to various substrates and have been the centerpoint of research and development efforts towards creating superior tissue adhesives for surgical and tissue engineering applications. In this article, we review bioadhesion and adhesives from an engineering standpoint, specifically the requirements of a good tissue glue, the relevance that DOPA and other catechols have in tissue adhesion, current trends in mussel-inspired bioadhesives, strategies to develop mussel-inspired tissue glues, and perspectives for future development of these materials.

Multifunctional Biomedical Adhesives

Currently available biomedical adhesives are mainly engineered to have one function (i.e., providing mechanical support for the repaired tissue). To improve the performance of existing bioadhesives and broaden their applications in medicine, numerous multifunctional bioadhesives are reported in the literature. These adhesives can be categorized as passive or active by design. Passive multifunctional bioadhesives contain inherent compositions and structural designs that can carry out additional functions without added external influences. These adhesives exhibit new functionalities such as antimicrobial properties, self-healing abilities, the ability to promote cellular ingrowth, and the ability to be reshaped. Conversely, active multifunctional bioadhesives respond to environmental changes (e.g., pH, temperature, electricity, light, and biomolecule concentration), which initiate a change in the adhesive to release encapsulated drugs or to activate or deactivate the bioadhesive for interfacial binding. This review article highlights recent advances in multifunctional bioadhesives.

Recent Developments in Tough Hydrogels for Biomedical Applications

A hydrogel is a three-dimensional polymer network with high water content and has been attractive for many biomedical applications due to its excellent biocompatibility. However, classic hydrogels are mechanically weak and unsuitable for most physiological load-bearing situations. Thus, the development of tough hydrogels used in the biomedical field becomes critical. This work reviews various strategies to fabricate tough hydrogels with the introduction of non-covalent bonds and the construction of stretchable polymer networks and interpenetrated networks, such as the so-called double-network hydrogel. Additionally, the design of tough hydrogels for tissue adhesive, tissue engineering, and soft actuators is reviewed.

Three-Dimensional Bio-Printed Scaffold Sleeves With Mesenchymal Stem Cells for Enhancement of Tendon-to-Bone Healing in Anterior Cruciate Ligament Reconstruction Using Soft-Tissue Tendon Graft

PURPOSE

To investigate the efficacy of the insertion of 3-dimensional (3D) bio-printed scaffold sleeves seeded with mesenchymal stem cells (MSCs) to enhance osteointegration between the tendon and tunnel bone in anterior cruciate ligament (ACL) reconstruction in a rabbit model.

METHODS

Scaffold sleeves were fabricated by 3D bio-printing. Before ACL reconstruction, MSCs were seeded into the scaffold sleeves. ACL reconstruction with hamstring tendon was performed on both legs of 15 adult rabbits (aged 12 weeks). We implanted 15 bone tunnels with scaffold sleeves with MSCs and implanted another 15 bone tunnels with scaffold sleeves without MSCs before passing the graft. The specimens were harvested at 4, 8, and 12 weeks. H&E staining, immunohistochemical staining of type II collagen, and micro-computed tomography of the tunnel cross-sectional area were evaluated. Histologic assessment was conducted with a histologic scoring system.

RESULTS

In the histologic assessment, a smooth bone-to-tendon transition through broad fibrocartilage formation was identified in the treatment group, and the interface zone showed abundant type II collagen production on immunohistochemical staining. Bone-tendon healing histologic scores were significantly higher in the treatment group than in the control group at all time points. Micro-computed tomography at 12 weeks showed smaller tibial (control, 9.4 ± 0.9 mm²; treatment, 5.8 ± 2.9 mm²; P = .044) and femoral (control, 9.6 ± 2.9 mm²; treatment, 6.0 ± 1.0 mm²; P = .03) bone-tunnel areas in the treated group than in the control group.

CONCLUSIONS

The 3D bio-printed scaffold sleeve with MSCs exhibited excellent results in osteointegration enhancement between the tendon and tunnel bone in ACL reconstruction in a rabbit model.

CLINICAL RELEVANCE

If secure biological healing between the tendon graft and tunnel bone can be induced in the early postoperative period, earlier, more successful rehabilitation may be facilitated. Three-dimensional bio-printed scaffold sleeves with MSCs have the potential to accelerate bone-tendon healing in ACL reconstruction.

Self-assembled adhesive biomaterials formed by a genetically designed fusion protein

A spider with mussel: a supramolecular fiber formed by a spider dragline protein was tuned to have underwater adhesion property by genetic fusion of a mussel foot protein.

A Moldable Nanocomposite Hydrogel Composed of a Mussel-Inspired Polymer and a Nanosilicate as a Fit-to-Shape Tissue Sealant

The engineering of bioadhesives to bind and conform to the complex contour of tissue surfaces remains a challenge. We have developed a novel moldable nanocomposite hydrogel by combining dopamine-modified poly(ethylene glycol) and the nanosilicate Laponite, without the use of cytotoxic oxidants. The hydrogel transitioned from a reversibly cross-linked network formed by dopamine-Laponite interfacial interactions to a covalently cross-linked network through the slow autoxidation and cross-linking of catechol moieties. Initially, the hydrogel could be remolded to different shapes, could recover from large strain deformation, and could be injected through a syringe to adhere to the convex contour of a tissue surface. With time, the hydrogel solidified to adopt the new shape and sealed defects on the tissue. This fit-to-shape sealant has potential in sealing tissues with non-flat geometries, such as a sutured anastomosis.

Model polymer system for investigating the generation of hydrogen peroxide and its biological responses during the crosslinking of mussel adhesive moiety

Mussel adhesive moiety, catechol, has been utilized to design a wide variety of biomaterials. However, the biocompatibility and biological responses associated with the byproducts generated during the curing process of catechol has never been characterized. An in situ curable polymer model system, 4-armed polyethylene glycol polymer end-capped with dopamine (PEG-D4), was used to characterize the production of hydrogen peroxide (H2O2) during the oxidative crosslinking of catechol. Although PEG-D4 cured rapidly (under 30s), catechol continues to polymerize over several hours to form a more densely crosslinked network over time. PEG-D4 hydrogels were examined at two different time points; 5min and 16h after initiation of crosslinking. Catechol in the 5min-cured PEG-D4 retained the ability to continue to crosslink and generated an order of magnitude higher H2O2 (40μM) over 6h when compared to 16h-cured samples that ceased to crosslink. H2O2 generated during catechol crosslinking exhibited localized cytotoxicity in culture and upregulated the expression of an antioxidant enzyme, peroxiredoxin 2, in primary dermal and tendon fibroblasts. Subcutaneous implantation study indicated that H2O2 released during oxidative crosslinking of PEG-D4 hydrogel promoted superoxide generation, macrophage recruitment, and M2 macrophage polarization in tissues surrounding the implant. Given the multitude of biological responses associated with H2O2, it is important to monitor and tailor the production of H2O2 generated from catechol-containing biomaterials for a given application.

STATEMENT OF SIGNIFICANCE

Remarkable underwater adhesion strategy employed by mussels has been utilized to design a wide variety of biomaterials ranging from tissue adhesives to drug carrier and tissue engineering scaffolds. Catechol is the main adhesive moiety that is widely incorporated to create an injectable biomaterials and bioadhesives. However, the biocompatibility and biological responses associated with the byproducts generated during the curing process of catechol has never been characterized. In this manuscript, we design a model system to systemically characterize the release of hydrogen peroxide (H2O2) during the crosslinking of catechol. Given the multitude of biological responses associated with H2O2 (i.e., wound healing, antimicrobial, chronic inflammation), its release from catechol-containing biomaterials need to be carefully monitored and controlled for a desired application.

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.

Monitoring the Long-Term Degradation Behavior of Biomimetic Bioadhesive Using Wireless Magnetoelastic Sensor

The degradation behavior of a tissue adhesive is critical to its ability to repair a wound while minimizing prolonged inflammatory response. Traditional degradation tests can be expensive to perform, as they require large numbers of samples. The potential for using magnetoelastic resonant sensors to track bioadhesive degradation behavior was investigated. Specifically, biomimetic poly (ethylene glycol)- (PEG-) based adhesive was coated onto magnetoelastic (ME) sensor strips. Adhesive-coated samples were submerged in solutions buffered at multiple pH levels (5.7, 7.4 and 10.0) at body temperature (37 °C) and the degradation behavior of the adhesive was tracked wirelessly by monitoring the changes in the resonant amplitude of the sensors for over 80 days. Adhesive incubated at pH 7.4 degraded over 75 days, which matched previously published data for bulk degradation behavior of the adhesive while utilizing significantly less material (∼10(3) times lower). Adhesive incubated at pH 10.0 degraded within 25 days while samples incubated at pH 5.7 did not completely degrade even after 80 days of incubation. As expected, the rate of degradation increased with increasing pH as the rate of ester bond hydrolysis is higher under basic conditions. As a result of requiring a significantly lower amount of samples compared to traditional methods, the ME sensing technology is highly attractive for fully characterizing the degradation behavior of tissue adhesives in a wide range of physiological conditions.

Biomedical and Clinical Importance of Mussel-Inspired Polymers and Materials

The substance secreted by mussels, also known as nature's glue, is a type of liquid protein that hardens rapidly into a solid water-resistant adhesive material. While in seawater or saline conditions, mussels can adhere to all types of surfaces, sustaining its bonds via mussel adhesive proteins (MAPs), a group of proteins containing 3,4-dihydroxyphenylalanine (DOPA) and catecholic amino acid. Several aspects of this adhesion process have inspired the development of various types of synthetic materials for biomedical applications. Further, there is an urgent need to utilize biologically inspired strategies to develop new biocompatible materials for medical applications. Consequently, many researchers have recently reported bio-inspired techniques and materials that show results similar to or better than those shown by MAPs for a range of medical applications. However, the susceptibility to oxidation of 3,4-dihydroxyphenylalanine poses major challenges with regard to the practical translation of mussel adhesion. In this review, various strategies are discussed to provide an option for DOPA/metal ion chelation and to compensate for the limitations imposed by facile 3,4-dihydroxyphenylalanine autoxidation. We discuss the anti-proliferative, anti-inflammatory, anti-microbial activity, and adhesive behaviors of mussel bio-products and mussel-inspired materials (MIMs) that make them attractive for synthetic adaptation. The development of biologically inspired adhesive interfaces, bioactive mussel products, MIMs, and arising areas of research leading to biomedical applications are considered in this review.

Hydrogen peroxide generation and biocompatibility of hydrogel-bound mussel adhesive moiety

To decouple the extracellular oxidative toxicity of catechol adhesive moiety from its intracellular non-oxidative toxicity, dopamine was chemically bound to a non-degradable polyacrylamide hydrogel through photo-initiated polymerization of dopamine methacrylamide (DMA) with acrylamide monomers. Network-bound dopamine released cytotoxic levels of H2O2 when its catechol side chain oxidized to quinone. Introduction of catalase at a concentration as low as 7.5 U/mL counteracted the cytotoxic effect of H2O2 and enhanced the viability and proliferation rate of fibroblasts. These results indicated that H2O2 generation is one of the main contributors to the cytotoxicity of dopamine in culture. Additionally, catalase is a potentially useful supplement to suppress the elevated oxidative stress found in typical culture conditions and can more accurately evaluate the biocompatibility of mussel-mimetic biomaterials. The release of H2O2 also induced a higher foreign body reaction to catechol-modified hydrogel when it was implanted subcutaneously in rat. Given that H2O2 has a multitude of biological effects, both beneficiary and deleterious, regulation of H2O2 production from catechol-containing biomaterials is necessary to optimize the performance of these materials for a desired application.

Wireless magnetoelastic sensors for tracking degradation profiles of nitrodopamine-modified poly(ethylene glycol)

A critical property for tissue adhesives is a controllable degradation rate so that these adhesives do not act as barriers to wound healing. Typical degradation tests require large amount of samples, which can be tedious and expensive to perform. Additionally, current degradation tests are carried out in vitro under simulated physiological conditions and may not accurately reflect the complex environment that an adhesive would experience in vivo. As a means to develop a simple technique for testing tissue adhesive, a rapidly degrading adhesive hydrogel that mimics mussel adhesive proteins was coated onto magnetoelastic (ME) sensor strips to track the degradation of the adhesive remotely and in real time. Adhesive-coated ME sensors were submerged in phosphate buffer saline solution (pH 7.4) at body temperature (37 °C). Based on the change in the resonant amplitude, the degradation time was determined to be 22 min, which was in agreement with qualitative monitoring of the bulk adhesive hydrogel. Additionally, when the adhesive-coated ME sensor was incubated in a slightly acidic medium (pH 5.7), the degradation rate was drastically lengthened (3 hrs) as the hydrolysis of ester bonds is faster under basic conditions. Oscillatory rheological testing confirmed the formation and degradation of the adhesive. However, rheological test results did not accurately reflect the degradation rate of the adhesive hydrogel, potentially due to a slow exchange of acidic degradation products with the surrounding medium. ME sensor was demonstrated as a potential useful tool for evaluating the degradation rate of bioadhesives.

Effect of Nitro-Functionalization on the Cross-Linking and Bioadhesion of Biomimetic Adhesive Moiety

Dopamine mimics the exceptional moisture-resistant adhesive properties of the amino acid, DOPA, found in adhesive proteins secreted by marine mussels. The catechol side chain of dopamine was functionalized with a nitro-group, and the effect of the electron withdrawing group modification on the cross-linking chemistry and bioadhesive properties of the adhesive moiety was evaluated. Both nitrodopamine and dopamine were covalently attached as a terminal group onto an inert, 4-armed poly(ethylene glygol) (PEG-ND and PEG-D, respectively). PEG-ND and PEG-D exhibited different dependence on the concentration of NaIO₄ and pH, which affected the curing rate, mechanical properties, and adhesive performance of these biomimetic adhesives differently. PEG-ND cured instantly and its bioadhesive properties were minimally affected by the change in pH (5.7–8) within the physiological range. Under mildly acidic conditions (pH 5.7 and 6.7), PEG-ND outperformed PEG-D in lap shear adhesion testing using wetted pericardium tissues. However, nitrodopamine only formed dimers, which resulted in the formation of loosely cross-linked network and adhesive with reduced cohesive properties. UV–vis spectroscopy further confirmed nitrodopamine’s ability for rapid dimer formation. The ability for nitrodopamine to rapidly cure and adhere to biological substrates in an acidic pH make it suitable for designing adhesive biomaterials targeted at tissues that are more acidic (i.e., subcutaneous, dysoxic, or tumor tissues).

Injectable dopamine-modified poly(ethylene glycol) nanocomposite hydrogel with enhanced adhesive property and bioactivity

A synthetic mimic of mussel adhesive protein, dopamine-modified four-armed poly(ethylene glycol) (PEG-D4), was combined with a synthetic nanosilicate, Laponite (Na(0.7+)(Mg5.5Li0.3Si8)O20(OH)4)(0.7-)), to form an injectable naoncomposite tissue adhesive hydrogel. Incorporation of up to 2 wt % Laponite significantly reduced the cure time while enhancing the bulk mechanical and adhesive properties of the adhesive due to strong interfacial binding between dopamine and Laponite. The addition of Laponite did not alter the degradation rate and cytocompatibility of PEG-D4 adhesive. On the basis of subcutaneous implantation in rat, PEG-D4 nanocomposite hydrogels elicited minimal inflammatory response and exhibited an enhanced level of cellular infiltration as compared to Laponite-free samples. The addition of Laponite is potentially a simple and effective method for promoting bioactivity in a bioinert, synthetic PEG-based adhesive while simultaneously enhancing its mechanical and adhesive properties.

Effect of pH on the rate of curing and bioadhesive properties of dopamine functionalized poly(ethylene glycol) hydrogels

The remarkable underwater adhesion strategy employed by mussels has inspired bioadhesives that have demonstrated promise in connective tissue repair, wound closure, and local delivery of therapeutic cells and drugs. While the pH of oxygenated blood and internal tissues is typically around 7.4, skin and tumor tissues are significantly more acidic. Additionally, blood loss during surgery and ischemia can lead to dysoxia, which lowers pH levels of internal tissues and organs. Using 4-armed PEG end-capped with dopamine (PEG-D) as a model adhesive polymer, the effect of pH on the rate of intermolecular cross-linking and adhesion to biological substrates of catechol-containing adhesives was determined. Adhesive formulated at an acidic pH (pH 5.7-6.7) demonstrated reduced curing rate, mechanical properties, and adhesive performance to pericardium tissues. Although a faster curing rate was observed at pH 8, these adhesives also demonstrated reduced mechanical and bioadhesive properties when compared to adhesives buffered at pH 7.4. Adhesives formulated at pH 7.4 demonstrated a good balance of fast curing rate, elevated mechanical properties and interfacial binding ability. UV-vis spectroscopy evaluation revealed that the stability of the transient oxidation intermediate of dopamine was increased under acidic conditions, which likely reduced the rate of intermolecular cross-linking and bulk cohesive properties for hydrogels formulated at these pH levels. At pH 8, competing cross-linking reaction mechanisms and reduced concentration of dopamine catechol due to auto-oxidation likely reduced the degree of dopamine polymerization and adhesive strength for these hydrogels. pH plays an important role in the adhesive performance of mussel-inspired bioadhesives and the pH of the adhesive formulation needs to be adjusted for the intended application.

Novel hydrogel actuator inspired by reversible mussel adhesive protein chemistry

A novel hydrogel actuator that combines ionoprinting techniques with reversible catechol-metal ion coordination chemistry found in mussel adhesive proteins is developed. Deposited metal ions increase the local crosslinking density, which induces sharp bending of the hydrogel. Reversibly bound metal ions can be removed and reintroduced in a different pattern so that the hydrogel can be reprogrammed to transform into a different 3-dimentional shape.

A novel repair method for the treatment of acute Achilles tendon rupture with minimally invasive approach using button implant: a biomechanical study

BACKGROUND

Minimally invasive Q3 repair has been proposed for acute Achilles tendon rupture with low rate of complications. However there are still controversies about optimal technique. In this study we aimed to describe Endobutton-assisted modified Bunnell configuration as a new Achilles tendon repair technique and evaluate its biomechanical properties comparing with native tendon and Krackow technique.

METHODS

27 ovine Achilles tendons were obtained and randomly placed into 3 groups with 9 specimens ineach. The Achilles tendons were repaired with Endobutton-assisted modified Bunnell technique in group 1, Krackow suture technique in group 2 and group 3 was defined as the control group including native tendons. Unidirectional tensile loading to failure was performed at 25mm/min. Biomechanicalproperties such as peak force to failure (N), stress at peak (MPa), elongation at failure, and Young'smodulus (GPa) was measured for each group. All groups were compared with each other using one-wayANOVA followed by the Tukey HSD multiple comparison test (a=0.05).

RESULTS

The average peak force (N) to failure of group 1 and group 2 and control group was 415.6±57.6, 268.1±65.2 and 704.5±85.8, respectively. There was no statistically significant difference between native tendon and group 1 for the amount elongation at failure (p>0.05).

CONCLUSIONS

Regarding the results, we concluded that Endobutton-assisted modified Bunnell technique provides stronger fixation than conventional techniques. It may allow early range of motion and can be easily applied in minimally invasive and percutaneous methods particularly for cases with poor quality tendon at the distal part of rupture.

LEVEL OF EVIDENCE

Level II, Biomechanical research study.

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.

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

Oligo(ethylene glycol) (OEG) and poly(ethylene glycol) (PEG) exhibit several desirable properties including biocompatibility and resistance to fouling by protein adsorption. Still needed are surgical glues and orthopedic cements, among several other materials, that display similar traits. However the very lack of interactions with other molecules that prevents toxicity and fouling also makes adhesion elusive. In work described here the cross-linking chemistry of marine mussel adhesive is combined with OEG to make a family of terpolymers. The effect of polymer composition upon bulk adhesion was examined. High strength bonding was found with a subset of the polymers containing appreciable OEG content. These structure-property insights may help the design of new materials for which the properties of OEG and high strength adhesion are both being sought.

Augmentation of tendon healing with butyric acid-impregnated sutures: biomechanical evaluation in a rabbit model

BACKGROUND

Butyric acid (BA) has been shown to be angiogenic and to enhance transcriptional activity in tissue. These properties of BA have the potential to augment biological healing of a repaired tendon.

PURPOSE

To evaluate this possibility both biomechanically and histologically in an animal tendon repair model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A rabbit Achilles tendon healing model was used to evaluate the biomechanical strength and histological properties at 6 and 12 weeks after repair. Unilateral tendon defects were created in the middle bundle of the Achilles tendon of each rabbit, which were repaired equivalently with either Ultrabraid BA-impregnated sutures or control Ultrabraid sutures.

RESULTS

After 6 weeks, BA-impregnated suture repairs had a significantly increased (P < .0001) Young's modulus and ultimate tensile strength relative to the control suture repairs. At 12 weeks, no statistical difference was observed between these measures. The histological data at 6 weeks demonstrated significantly increased (P < .005) vessel density within 0.25 mm of the repair suture in the BA-impregnated group. There was also an associated 42% increase in the local number of myofibroblasts in the BA samples relative to the controls at this time. By 12 weeks, these differences were not observed.

CONCLUSION

Tendons repaired with BA-impregnated sutures demonstrated improved biomechanical properties at 6 weeks relative to control sutures, suggesting a neoangiogenic mechanism of enhanced healing through an increased myofibroblast presence.

CLINICAL RELEVANCE

These findings demonstrate that a relatively simple alteration of suture material may augment early tendon healing to create a stronger repair construct during this time.

Polymer composition and substrate influences on the adhesive bonding of a biomimetic, cross-linking polymer

Hierarchical biological materials such as bone, sea shells, and marine bioadhesives are providing inspiration for the assembly of synthetic molecules into complex structures. The adhesive system of marine mussels has been the focus of much attention in recent years. Several catechol-containing polymers are being developed to mimic the cross-linking of proteins containing 3,4-dihydroxyphenylalanine (DOPA) used by shellfish for sticking to rocks. Many of these biomimetic polymer systems have been shown to form surface coatings or hydrogels; however, bulk adhesion is demonstrated less often. Developing adhesives requires addressing design issues including finding a good balance between cohesive and adhesive bonding interactions. Despite the growing number of mussel-mimicking polymers, there has been little effort to generate structure-property relations and gain insights on what chemical traits give rise to the best glues. In this report, we examine the simplest of these biomimetic polymers, poly[(3,4-dihydroxystyrene)-co-styrene]. Pendant catechol groups (i.e., 3,4-dihydroxystyrene) are distributed throughout a polystyrene backbone. Several polymer derivatives were prepared, each with a different 3,4-dihyroxystyrene content. Bulk adhesion testing showed where the optimal middle ground of cohesive and adhesive bonding resides. Adhesive performance was benchmarked against commercial glues as well as the genuine material produced by live mussels. In the best case, bonding was similar to that obtained with cyanoacrylate "Krazy Glue". Performance was also examined using low- (e.g., plastics) and high-energy (e.g., metals, wood) surfaces. The adhesive bonding of poly[(3,4-dihydroxystyrene)-co-styrene] may be the strongest of reported mussel protein mimics. These insights should help us to design future biomimetic systems, thereby bringing us closer to development of bone cements, dental composites, and surgical glues.