Catechol-Functionalized Chitosan/Pluronic Hydrogels for Tissue Adhesives and Hemostatic Materials

Mussel-inspired hydrogels for biomedical and environmental applications

This mini-review highlights the recent development of mussel-inspired hydrogels in biomedical and environmental fields.

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.

Sticky tubes and magnetic hydrogels co-assembled by a short peptide and melanin-like nanoparticles

The co-assembly of peptide monomers and polydopamine-based nanoparticles leads to the formation of either tubular structures decorated with adhesive particles or magnetic hydrogel.

Tissue repair strength using chitosan adhesives with different physical-chemical characteristics

A range of chitosan-based biomaterials have recently been used to perform sutureless, laser-activated tissue repair. Laser-activation has the advantage of bonding to tissue through a non-contact, aseptic mechanism. Chitosan adhesive films have also been shown to adhere to sheep intestine strongly without any chemical modification to chitosan. In this study, we continue to investigate chitosan adhesive films and explore the impact on the tissue repair strength and tensile strength characteristics of four types of adhesive film based on chitosan with different molecular weight and degree of deacetylation. Results showed that adhesives based on chitosan with medium molecular weight achieved the highest bonding strength, tensile strength and E-modulus when compared to the other adhesives.

Polydopamine-coated electrospun poly(vinyl alcohol)/poly(acrylic acid) membranes as efficient dye adsorbent with good recyclability

Free-standing poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) membranes with polydopamine (PDA) coating were prepared based on the combination of electrospinning and self-polymerization of dopamine. This is a facile, mild, controllable, and low-energy consumption process without any rigorous restriction to reactive conditions. Benefiting from the high specific surface area of electrospun membranes and the abundant "adhesive" functional groups of polydopamine, the as-prepared membranes exhibit efficient adsorption performance towards methyl blue with the adsorption capacity reaching up to 1147.6 mg g(-1). Moreover, compared to other nanoparticle adsorbents, the as-prepared self-standing membrane is highly flexible, easy to operate and retrieve, and most importantly, easy to elute, and regenerate, which enable its potential applications in wastewater treatment.

Endotoxins affect diverse biological activity of chitosans in matters of hemocompatibility and cytocompatibility

Chitosan is used in several pharmaceutical and medical applications, owing to its good cytocompatibility and hemocompatibility. However, there are conflicting reports regarding the biological activities of chitosan with some studies reporting anti-inflammatory properties while others report pro-inflammatory properties. In this regards we analyzed the endotoxin content in five different chitosans and examined these chitosans with their different deacetylation degrees for their hemocompatibility and cytocompatibility. Therefore, we incubated primary human endothelial cells or whole blood with different chitosan concentrations and studied the protein and mRNA expression of different inflammatory markers or cytokines. Our data indicate a correlation of the endotoxin content and cytokine up-regulation in whole blood for Poly-Morpho-Nuclear (PMN)-Elastase, soluble terminal complement complex SC5b-9, complement component C5/C5a, granulocyte colony-stimulating factor, Interleukin-8 (IL), IL-10, IL-13, IL-17E, Il-32α and monocyte chemotactic protein-1. In contrast, the incubation of low endotoxin containing chitosans with primary endothelial cells resulted in increased expression of E-selectin, intercellular adhesion molecule-1, vascular cell adhesion protein-1, IL-1β, IL-6 and IL-8 in endothelial cells. We suggest that the endotoxin content in chitosan plays a major role in the biological activity of chitosan. Therefore, we strongly recommend analysis of the endotoxin concentration in chitosan, before further determining if it has pro- or anti-inflammatory properties or if it is applicable for pharmaceutical and medical fields.

Facile preparation of mussel-inspired polyurethane hydrogel and its rapid curing behavior

A facile method was found to incorporate a mussel-inspired adhesive moiety into synthetic polymers, and mussel mimetic polyurethanes were developed as adhesive hydrogels. In these polymers, a urethane backbone was substituted for the polyamide chain of mussel adhesive proteins, and dopamine was appended to mimic the adhesive moiety of adhesive proteins. A series of mussel mimetic polyurethanes were created through a step-growth polymerization based on hexamethylene diisocyanate as a hard segment, PEG having different molecular weights as a soft segment, and lysine-dopamine as a chain extender. Upon a treatment with Fe(3+), the aqueous mussel mimetic polyurethane solutions can be triggered by pH adjustment to form adhesive hydrogels instantaneously; these materials can be used as injectable adhesive hydrogels. Upon a treatment with NaIO4, the mussel mimetic polyurethane solutions can be cured in a controllable period of time. The successful combination of the unique mussel-inspired adhesive moiety with a tunable polyurethane structure can result in a new kind of mussel-inspired adhesive polymers.

Airflow-directed in situ electrospinning of a medical glue of cyanoacrylate for rapid hemostasis in liver resection

Rapid hemostasis of solitary organs is still a big challenge in surgical procedures or after major trauma in both civilians and on the battlefield. Here, we report the first use of an airflow-directed in situ electrospinning method to precisely and homogeneously deposit a medical glue of n-octyl-2-cyanoacrylate (OCA) ultrathin fibers onto a wound surface to realize rapid hemostasis in dozens of seconds. In vivo and in vitro experiments on pig liver resection demonstrate that the self-assembled electrospun OCA membrane with high strength, good flexibility and integrity is very compact and no fluid seeping is observed even under a pressure of 147 mm Hg. A similar effect has been achieved in an in vivo experiment on pig lung resection. The results provide a very promising alternative for rapid hemostasis of solitary organs as well as other traumas, providing evidence that the postoperative drainage tube may not be always necessary for surgery in the near future.

Mussel-mimetic protein-based adhesive hydrogel

Hydrogel systems based on cross-linked polymeric materials which could provide both adhesion and cohesion in wet environment have been considered as a promising formulation of tissue adhesives. Inspired by marine mussel adhesion, many researchers have tried to exploit the 3,4-dihydroxyphenylalanine (DOPA) molecule as a cross-linking mediator of synthetic polymer-based hydrogels which is known to be able to achieve cohesive hardening as well as adhesive bonding with diverse surfaces. Beside DOPA residue, composition of other amino acid residues and structure of mussel adhesive proteins (MAPs) have also been considered important elements for mussel adhesion. Herein, we represent a novel protein-based hydrogel system using DOPA-containing recombinant MAP. Gelation can be achieved using both oxdiation-induced DOPA quinone-mediated covalent and Fe(3+)-mediated coordinative noncovalent cross-linking. Fe(3+)-mediated hydrogels show deformable and self-healing viscoelastic behavior in rheological analysis, which is also well-reflected in bulk adhesion strength measurement. Quinone-mediated hydrogel has higher cohesive strength and can provide sufficient gelation time for easier handling. Collectively, our newly developed MAP hydrogel can potentially be used as tissue adhesive and sealant for future applications.

Smart functional polymers – a new route towards creating a sustainable environment

Smart functional polymers have gained a huge amount of interest in recent times due to their innumerable applications in areas including sensors, actuators, switchable wettability, bio-medical and environmental applications.

In situ functionalization of highly porous polymer microspheres with silver nanoparticles via bio-inspired chemistry

Organic–inorganic hybrid porous microparticles.

Chitosan-g-hematin: enzyme-mimicking polymeric catalyst for adhesive hydrogels

Phenol derivative-containing adhesive hydrogels has been widely recognized as having potential for biomedical applications, but their conventional production methods, utilizing a moderate/strong base, alkaline buffers, the addition of oxidizing agents or the use of enzymes, require alternative approaches to improve their biocompatibility. In this study, we report a polymeric, enzyme-mimetic biocatalyst, hematin-grafted chitosan (chitosan-g-hem), which results in effective gelation without the use of alkaline buffers or enzymes. Furthermore, gelation occurs under mild physiological conditions. Chitosan-g-hem biocatalyst (0.01%, w/v) has excellent catalytic properties, forming chitosan-catechol hydrogels rapidly (within 5 min). In vivo adhesive force measurement demonstrated that the hydrogel formed by the chitosan-g-hem activity showed an increase in adhesion force (33.6 ± 5.9 kPa) compared with the same hydrogel formed by pH-induced catechol oxidation (20.6 ± 5.5 kPa) in mouse subcutaneous tissue. Using the chitosan-g-hem biocatalyst, other catechol-functionalized polymers (hyaluronic acid-catechol and poly(vinyl alcohol)-catechol) also formed hydrogels, indicating that chitosan-g-hem can be used as a general polymeric catalyst for preparing catechol-containing hydrogels.

Preparation of sticky Escherichia coli through surface display of an adhesive catecholamine moiety

Mussels attach to virtually all types of inorganic and organic surfaces in aqueous environments, and catecholamines composed of 3,4-dihydroxy-l-phenylalanine (DOPA), lysine, and histidine in mussel adhesive proteins play a key role in the robust adhesion. DOPA is an unusual catecholic amino acid, and its side chain is called catechol. In this study, we displayed the adhesive moiety of DOPA-histidine on Escherichia coli surfaces using outer membrane protein W as an anchoring motif for the first time. Localization of catecholamines on the cell surface was confirmed by Western blot and immunofluorescence microscopy. Furthermore, cell-to-cell cohesion (i.e., cellular aggregation) induced by the displayed catecholamine and synthesis of gold nanoparticles on the cell surface support functional display of adhesive catecholamines. The engineered E. coli exhibited significant adhesion onto various material surfaces, including silica and glass microparticles, gold, titanium, silicon, poly(ethylene terephthalate), poly(urethane), and poly(dimethylsiloxane). The uniqueness of this approach utilizing the engineered sticky E. coli is that no chemistry for cell attachment are necessary, and the ability of spontaneous E. coli attachment allows one to immobilize the cells on challenging material surfaces such as synthetic polymers. Therefore, we envision that mussel-inspired catecholamine yielded sticky E. coli that can be used as a new type of engineered microbe for various emerging fields, such as whole living cell attachment on versatile material surfaces, cell-to-cell communication systems, and many others.

Catalyst-mediated yet catalyst-free hydrogels formed by interfacial chemical activation

Catalyst-mediated yet catalyst-free catechol-containing adhesive hydrogels.

Hemostatic polymers: the concept, state of the art and perspectives

This article presents a critical overview of the most significant developments in the use of polymers as hemostatic agents.

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.

Hemostatic strategies for traumatic and surgical bleeding

Wide interest in new hemostatic approaches has stemmed from unmet needs in the hospital and on the battlefield. Many current commercial hemostatic agents fail to fulfill the design requirements of safety, efficacy, cost, and storage. Academic focus has led to the improvement of existing strategies as well as new developments. This review will identify and discuss the three major classes of hemostatic approaches: biologically derived materials, synthetically derived materials, and intravenously administered hemostatic agents. The general class is first discussed, then specific approaches discussed in detail, including the hemostatic mechanisms and the advancement of the method. As hemostatic strategies evolve and synthetic-biologic interactions are more fully understood, current clinical methodologies will be replaced.

Thermosensitive hydrogels of poly(methyl vinyl ether-co-maleic anhydride) - Pluronic(®) F127 copolymers for controlled protein release

Thermosensitive hydrogels are of a great interest due to their many biomedical and pharmaceutical applications. In this study, we synthesized a new series of random poly (methyl vinyl ether-co-maleic anhydride) (Gantrez(®) AN, GZ) and Pluronic(®) F127 (PF127) copolymers (GZ-PF127), that formed thermosensitive hydrogels whose gelation temperature and mechanical properties could be controlled by the molar ratio of GZ and PF127 polymers and the copolymer concentration in water. Gelation temperatures tended to decrease when the GZm/PF127 ratio increased. Thus, at a fixed GZm/PF127 value, sol-gel temperatures decreased at higher copolymer concentrations. Moreover, these hydrogels controlled the release of proteins such as bovine serum albumin (BSA) and recombinant recombinant kinetoplastid membrane protein of Leishmania (rKMP-11) more than the PF127 system. Toxicity studies carried out in J774.2 macrophages showed that cell viability was higher than 80%. Finally, histopathological analysis revealed that subcutaneous administration of low volumes of these hydrogels elicited a tolerable inflammatory response that could be useful to induce immune responses against the protein cargo in the development of vaccine adjuvants.

Laser-activated adhesive films for sutureless median nerve anastomosis

A novel chitosan adhesive film that incorporates the dye 'Rose Bengal' (RB) was used in conjunction with a green laser to repair transected rat median nerves in vivo. Histology and electrophysiological recording assessed the impact of the laser-adhesive technique on nerves. One week post-operatively, the sham-control group (laser-adhesive technique applied on un-transected nerves) conserved the average number and size of myelinated fibres in comparison to its contralateral side and electrophysiological recordings demonstrated no significant difference with un-operated nerves. Twelve weeks after the laser-adhesive anastomoses, nerves were in continuity with regenerated axons that crossed the anastomotic site.

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.

Cross-linked iron oxide nanoparticles for therapeutic engineering and in vivo monitoring of mesenchymal stem cells in cerebral ischemia model

Poly(ethylene glycol)-coated cross-linked iron oxide nanoparticles (PCIONs) are developed for therapeutic engineering of mesenchymal stem cells (MSCs) and their monitoring via magnetic resonance (MR) imaging at a time. PCIONs successfully combine with plasmid DNA (pDNA) via ionic interaction. Accordingly, PCION/pDNA complexes mediate superior translocations of vascular endothelial growth factor (VEGF) pDNA into intracellular regions of MSCs under external magnetic field, which significantly elevate production of VEGF from MSCs. Genetically engineered MSCs are also clearly visualized via MR imaging after administration to rat cerebrovascular ischemia models, which enable tracking of MSCs migration from injected sites to injured ischemic area.

Injectable biodegradable hydrogels: progress and challenges

Over the past decades, injectable hydrogels have emerged as promising biomaterials because of their biocompatibility, excellent permeability, minimal invasion, and easy integration into surgical procedures. These systems provide an effective and convenient way to administer a wide variety of bioactive agents such as proteins, genes, and even living cells. Additionally, they can be designed to be degradable and eventually cleared from the body after completing their missions. Given their unique characteristics, injectable biodegradable hydrogels have been actively explored as drug reservoir systems for sustained release of bioactive agents and temporary extracellular matrices for tissue engineering. This review provides an overview of state-of-the-art strategies towards constructing a rational design of injectable biodegradable hydrogels for protein drug delivery and tissue engineering. We also discuss the use of injectable hydrogels for gene delivery systems and biomedical adhesives.

PDMS bonding to a bio-friendly photoresist via self-polymerized poly(dopamine) adhesive for complex protein micropatterning inside microfluidic channels

Protein micropatterned surfaces integrated with microfluidics are useful in numerous bioanalytical and biological applications. In this study, we demonstrated the fabrication of complex protein micropatterned surfaces within poly(dimethylsiloxane) (PDMS) microfluidic channels by attaching the PDMS channels to bio-friendly photoresist films and subsequently performing microscope projection photolithography (MPP). A muscle-inspired poly(dopamine) (PDA) coating was employed to mediate the bonding between the PDMS and the bio-friendly photoresist poly(2,2-dimethoxy nitrobenzyl methacrylate-r-methyl methacrylate-r-poly(ethylene glycol) methacrylate) (PDMP). By adjusting the dip-coating time for the PDA coating, we could successfully introduce sufficient amounts of functional groups on the PDMP surfaces to mediate strong bonding between the PDMS channels and the PDA-coated PDMP thin films with minimal alteration of the surface properties of the PDMP thin films that are critical for protein micropatterning. Using this novel bonding strategy, we successfully fabricated multiple protein micropatterns and gradient micropatterns of proteins within microfluidic channels. The technique developed in this study will be useful for the fabrication of complex biochips for multiplex bioassays and fundamental cell biological studies.

Bioinspired templating synthesis of metal-polymer hybrid nanostructures within 3D electrospun nanofibers

Novel metal nanostructures immobilized within three-dimensional (3D) porous polymeric scaffolds have been utilized for catalysts and biosensors. However, efficient, robust immobilization of the nanostructures both outside and inside of the 3D scaffolds is a challenging task. To address the challenge, we synthesized a redox-active polymer, catechol-grafted poly(vinyl alcohol), PVA-g-ct. The grafted catechol is inspired by the adhesion mechanism of marine mussels, which facilitates binding and reduction of noble metal ions. Electrospinning the PVA-g-ct polymer results in highly open porous, 3D nanostructures, on which catechol mediates the spontaneous reduction of silver ions to solid silver nanocubes at an ambient temperature. Yet, gold and platinum ions are partially reduced and complexed with the nanofiber template, requiring an additional thermal treatment for complete reduction into solid metal nanostructures. Furthermore, silver-gold and silver-platinum hybrid nanostructures are generated by sequential treatments with metal ion precursor solutions of each. This study suggests that catechol-grafted polymer nanofibers are an attractive reactive template for the facile synthesis and immobilization of noble metal nanostructures within a 3D porous matrix for the potential applications to sensors, catalysis, and tissue engineering.

Mechanically robust, negative-swelling, mussel-inspired tissue adhesives

Most synthetic polymer hydrogel tissue adhesives and sealants swell considerably in physiologic conditions, which can result in mechanical weakening and adverse medical complications. This paper describes the synthesis and characterization of mechanically tough zero- or negative-swelling mussel-inspired surgical adhesives based on catechol-modified amphiphilic poly(propylene oxide)-poly(ethylene oxide) block copolymers. The formation, swelling, bulk mechanical, and tissue adhesive properties of the resulting thermosensitive gels were characterized. Catechol oxidation at or below room temperature rapidly resulted in a chemically cross-linked network, with subsequent warming to physiological temperature inducing a thermal hydrophobic transition in the PPO domains and providing a mechanism for volumetric reduction and mechanical toughening. The described approach can be easily adapted for other thermally sensitive block copolymers and cross-linking strategies, representing a general approach that can be employed to control swelling and enhance mechanical properties of polymer hydrogels used in a medical context.

Rapidly in situ forming chitosan/ε-polylysine hydrogels for adhesive sealants and hemostatic materials

A novel in situ forming polysaccharides/polypeptide hydrogel composed of naturally derived materials for applications as adhesive sealant and hemostatic material was developed via Michael addition crosslinking, taking advantage of its mild condition. Thiol-modified chitosan (CSS) was fast in situ crosslinked by an efficient polypeptide crosslinker (EPLM) which was prepared by introducing maleimide groups onto ε-polylysine. Gelation can happen swiftly within 15-215s depending on the CSS concentration, the degree of substitution (DS) of maleimide groups, and the molar ratio of maleimide group to thiol group. Results indicated that storage modulus of the hydrogel increased dramatically with the increase of CSS concentration and DS of maleimide. The obtained adhesive hydrogel had an adhesion strength 4 times higher than that of the commercial fibrin glue. Notably, it is non-toxic to L929 cells and exhibits excellent prompt hemostatic property. Polysaccharides/polypeptide structure designed here facilitates to improve both the biocompatibility and the adhesive property.