Complete prevention of blood loss with self-sealing haemostatic needles

Supramolecular Cross-Links in Mussel-Inspired Tissue Adhesives

Here we introduce a tissue-adhesive patch with orthogonal cohesive and adhesive chemistries; supramolecular ureido-4-pyrimidinone (UPy) cross-links provide cohesive strength, and catechols provide mussel-inspired tissue adhesion. In the development of tissue-adhesive biomaterials, prior research has focused on forming strong adhesive interfaces in wet conditions, leaving the use of supramolecular cross-links for cohesive strength underexplored. In developing this adhesive patch, the influence of the comonomers' composition and amphiphilicity on adhesion was investigated by lap shear adhesion to wet tissue. We determined failed lap joints' failure mechanism using catechol-specific Arnow's stain and identified formulations with improved cohesive strength. The adhesive materials were cytocompatible in mammalian cell conditioned media viability studies. We found that using orthogonal motifs to independently control adhesives' cohesive and adhesive strengths resulted in stronger tissue adhesion. The design principles presented here advance the development of wet tissue adhesives and could allow for the future design of biomaterials with desirable stimuli-responsive properties.

Chitosan-polydopamine hydrogel complex: a novel green adhesion agent for reversibly bonding thermoplastic microdevice and its application for cell-friendly microfluidic 3D cell culture

Owing to biocompatible characteristics and supporting cell growth capability, hydrogels have been widely used for scaffold fabrication and surface coating for cell culture. To employ the advantages of hydrogels, in the present study, we introduce a biocompatible chitosan (CS)-polydopamine (pDA) hydrogel complex as a green adhesion agent for the reversible bonding of thermoplastics assisted by UV irradiation. Poly(methyl methacrylate) (PMMA) substrates were bonded due to the covalent bond network formed between the amine groups of either CS or pDA in the hydrogel complex and the aldehyde groups of the oxidized PMMA surface via the Schiff-base reaction during the UV irradiation. Furthermore, the introduced method allowed for reversible bonding, which is highly appropriate for the fabrication of microdevices for cell-related applications. Surface characterizations such as water contact angle measurement, scanning electron microscopy analysis (SEM), atomic force microscopy analysis (AFM), and Fourier-transform infrared microscopy analysis (FTIR) were performed to confirm the successful coating of the hydrogel complex on the PMMA surface. Moreover, the bonding between two PMMAs or PMMA with other thermoplastics was successfully investigated with high bond strengths ranging from 0.4 to 0.7 MPa. The potential for reversible bonding of this method was verified by repeating the bonding/debonding cycle of the bonded PMMAs for three times, which maintained the bond strength at approximately 0.5 MPa. The compatibility of the bonding method in biological applications was examined by culturing mesenchymal stem cells (MSCs) inside a microchannel where multiple uniform-sized MSC spheroids were successfully formed. Then, spheroids were harvested for off-chip experiments enabled by the reversibility of the introduced bonding strategy. The bonding strategy employing a green hydrogel complex as a cell-friendly and eco-friendly adhesion agent could have a high impact on the fabrication of microdevices suitable for advanced organ-on-a-chip studies.

Antiswelling and Durable Adhesion Biodegradable Hydrogels for Tissue Repairs and Strain Sensors

Adhesive hydrogels have gained great interest for biomedical applications, because of their great adhesion, tunable structure, high water content, and biocompatibility. However, it is still challenging to engineer hydrogel materials combining tissue repairs and strain sensors. In this work, poly(thioctic acid) (PTA) is used as a skeleton structure and mixed with polydopamine (PDA), resulting in hydrogels with excellent stretchability, resilience, and adhesion, which can adhere to various organic (porcine skin) and inorganic materials (ceramic, wood, glass, etc.) in both dry and wet environments. The hydrogels also exhibit antiswelling behavior, self-healing, and repeatable adhesion capacity (seven times), which are meaningful for bioapplications and show satisfactory biocompatibility, biodegradation, cell affinity, and ability to limit apoptosis in both in vitro and in vivo experiments. In the full-thickness skin defect model, the hydrogels can accelerate the wound healing process. The introduction of Fe³⁺ can significantly enhance the conductivity of the hydrogels, making it possible for the hydrogels to be used as strain sensors. This functional hydrogel may find an appealing application as an antiswelling and durability adhesive for strain sensors.

Polydopamine and Its Derivative Surface Chemistry in Material Science: A Focused Review for Studies at KAIST

Polydopamine coating, the first material-independent surface chemistry, and its related methods significantly influence virtually all areas of material science and engineering. Functionalized surfaces of metal oxides, synthetic polymers, noble metals, and carbon materials by polydopamine and its related derivatives exhibit a variety of properties for cell culture, microfluidics, energy storage devices, superwettability, artificial photosynthesis, encapsulation, drug delivery, and numerous others. Unlike other articles, this review particularly focuses on the development of material science utilizing polydopamine and its derivatives coatings at the Korea Advanced Institute of Science and Technology for a decade. Herein, it is demonstrated how material-independent coating methods provide solutions for challenging problems existed in many interdisciplinary areas in bio-, energy-, and nanomaterial science by collaborations and independent research.

Multifunctional Tissue-Adhesive Cryogel Wound Dressing for Rapid Nonpressing Surface Hemorrhage and Wound Repair

Cryogels with tissue adhesion have great potential as wound dressings for rapid hemostasis for uncontrollable nonpressing surface hemorrhage and wound healing, but their use has not been reported previously. Herein, we designed a series of antibacterial and antioxidant tissue-adhesive cryogels based on quaternized chitosan (QCS) and polydopamine (PDA). These cryogels had good blood cell and platelet adhesion, enrichment, and activation properties for rapid nonpressing surface hemostasis and wound healing. The cryogels exhibited outstanding mechanical strength and easy removability, antioxidant activity, and NIR photothermal-enhanced antibacterial performance. The cryogels showed much better hemostasis than gauze and gelatin sponge in a standardized strip rat liver injury model, a standardized circular rabbit liver section model, and a pig skin laceration model. Furthermore, the excellent hemostatic performance of the QCS/PDA2.0 cryogel (containing 20 mg/mL QCS and 2.0 mg/mL PDA) for coagulopathic hemorrhages was confirmed in a standardized coagulation disorder rabbit circular liver section model. In addition, the QCS/PDA2.0 cryogel promoted rapid hemostasis in a deep noncompressible wound and a much better wound healing effect than a chitosan sponge and Tegaderm film in a full-thickness skin defect model. Overall, these multifunctional tissue-adhesive cryogels with excellent hemostatic performance and enhanced wound healing properties are suitable candidates for tissue-adhesive hemostat and wound healing dressings.

Molecular design principles of Lysine-DOPA wet adhesion

The mussel byssus has long been a source of inspiration for the adhesion community. Recently, adhesive synergy between flanking lysine (Lys, K) and 3,4-Dihydroxyphenylalanine (DOPA, Y) residues in the mussel foot proteins (Mfps) has been highlighted. However, the complex topological relationship of DOPA and Lys as well as the interfacial adhesive roles of other amino acids have been understudied. Herein, we study adhesion of Lys and DOPA-containing peptides to organic and inorganic substrates using single-molecule force spectroscopy (SMFS). We show that a modest increase in peptide length, from KY to (KY)3, increases adhesion strength to TiO2. Surprisingly, further increase in peptide length offers no additional benefit. Additionally, comparison of adhesion of dipeptides containing Lys and either DOPA (KY) or phenylalanine (KF) shows that DOPA is stronger and more versatile. We furthermore demonstrate that incorporating a nonadhesive spacer between (KY) repeats can mimic the hidden length in the Mfp and act as an effective strategy to dissipate energy.

Catechol modified quaternized chitosan enhanced wet adhesive and antibacterial properties of injectable thermo-sensitive hydrogel for wound healing

Wound dressings based on injectable thermo-sensitive hydrogel possess several advantages over preformed conventional dressings such as rapid reversible sol-gel transition behavior and the capacity of filling the irregular wound defect. Nevertheless, its clinical application is hindered by the weak tissue adhesiveness. Therefore, in this study, the catechol modified quaternized chitosan (QCS-C) was fabricated and incorporated into poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PLEL) hydrogel to develop an injectable hydrogel with the properties of thermo-sensitive, antibacterial and tissue adhesive. QCS-C could lower the LCST of hydrogel for easy gelation at physiological temperature, and significantly enhanced the tissue adhesion. For wound generation, nano-scaled bioactive glass (nBG：80 SiO₂, 16 CaO and 4 P₂O₅; mol%) was loaded into hydrogel to promote angiogenesis. The mice partial laceration experiment showed that PLEL-nBG-QCS-C hydrogel could effectively seal the ruptured skin and significantly accelerate wound healing. Thus, our findings established a new type of clinical treatment technology for complicated wounds.

Diatom Frustule Silica Exhibits Superhydrophilicity and Superhemophilicity

Special surface wettability attracts significant attention. In this study, dramatic differences in wettability are demonstrated for microparticles with the same chemical composition, SiO₂. One is natural silica prepared from the diatom, Melosira nummuloides, and the other is synthetic silica. We found that surface properties of synthetic silica are hydro- and hemophobic. However, diatom frustule silica exhibits superhydrophilicity and even superhemophilicity. Interestingly, such superhydrophilicity of natural silica is not solely originated from nanoporous structures of diatoms but from the synergy of high-density silanol anions and the nanoarchitecture. Furthermore, the observation of superhemophilicity of natural silica is also an interesting finding, because not all superhydrophilic surfaces show superhemophilicity. We demonstrate that superhemowettability is a fundamental principle for developing micropowder-based hemostatic materials despite existing hemorrhaging studies using diatoms.

Anti-Infective and Pro-Coagulant Chitosan-Based Hydrogel Tissue Adhesive for Sutureless Wound Closure

Multifunctional tissue adhesives with excellent adhesion, antibleeding, anti-infection, and wound healing properties are desperately needed in clinical surgery. However, the successful development of multifunctional tissue adhesives that simultaneously possess all these properties remains a challenge. We have prepared a novel chitosan-based hydrogel adhesive by integration of hydrocaffeic acid-modified chitosan (CS-HA) with hydrophobically modified chitosan lactate (hmCS lactate) and characterized its gelation time, mechanical properties, and microstructure. Tissue adhesion properties were evaluated using both pigskin and intestine models. In situ antibleeding efficacy was demonstrated via the rat hemorrhaging liver and full-thickness wound closure models. Good antibacterial activity and anti-infection capability toward S. aureus and P. aeruginosa were confirmed using in vitro contact-killing assays and an infected pigskin model. The result of coculturing with 3T3 fibroblast cells indicated that the hydrogels have no significant cytotoxicity. Most importantly, the biocompatible and biodegradable CS-HA/hmCS lactate hydrogel was able to close the wound in a sutureless way and promote wound healing. Our results demonstrate that this hydrogel has great promise for sutureless closure of surgical incisions.

Activated Platelet-Derived Vesicles for Efficient Hemostatic Activity

In this study, activated platelet-derived vesicles (Act-VEs) are developed as a novel hemostatic biomaterial. Spherical Act-VEs (114.40 ± 11.69 nm in size) with surface charges of -24.73 ± 1.32 mV are successfully prepared from thrombin-activated murine platelets with high surface expression of active glycoprotein IIb/IIIa (GP IIb/IIIa, also known as αIIbβ3) and P-selectin. Although nanosized vesicles from resting platelets (VEs) and Act-VEs showed similar sizes and surface charges, Act-VEs formed much larger aggregates in the presence of thrombin and CaCl₂ , compared to VEs. After incubation with fibrinogen, Act-VEs formed much denser fibrin networks compared to platelets or VEs, probably due to active αIIbβ3 on the surfaces of the Act-VEs. After intravenous injection of the Act-VEs, tail bleeding time and the blood loss are greatly reduced by Act-VEs in vivo. In addition, Act-VEs showed approximately sevenfold lower release of pro-inflammatory interleukin-1β (IL-1β) during incubation for 4 days, compared to platelets. Taken together, the formulated Act-VEs can serve as a promising hemostatic biomaterial for the efficient formation of fibrin clots without releasing pro-inflammatory cytokine.

Combination of Polypropylene Mesh and in Situ Injectable Mussel-Inspired Hydrogel in Laparoscopic Hernia Repair for Preventing Post-Surgical Adhesions in the Piglet Model

Polypropylene (PP) mesh has been used successfully for a long time in clinical practice as an impressive prosthesis for ventral hernia repair. To utilize a physical barrier for separating mesh from viscera is a general approach for preventing adhesions in clinical practice. However, a serious abdominal adhesion between the mesh and viscera can possibly occur post-hernia, especially with the small intestine; this can lead to a series of complications, such as chronic pain, intestinal obstruction, and fistula. Thus, determining how to prevent abdominal adhesions between the mesh and viscera is still an urgent clinical problem. In this study, a dopamine-functionalized polysaccharide derivative (oxidized-carboxymethylcellulose-g-dopamine, OCMC-DA) was synthesized; this was blended with carboxymethylchitosan (CMCS) to form a hydrogel (OCMC-DA/CMCS) in situ at the appropriate time. The physical and chemical properties of the hydrogel were characterized successfully, and its excellent biocompatibility was presented by the in vitro cell test. The combination of this hydrogel and PP mesh was used in laparoscopic surgery for repairing the abdominal wall defect, where the hydrogel could become fixed in situ on the PP mesh to form an anti-adhesion gel-mesh. The results showed that the gel-mesh could prevent abdominal adhesions effectively in the piglet model. Moreover, the histology and immunohistochemical staining proved that the gel-mesh could effectively alleviate the inflammation reaction and deposition of collagen around the mesh, and it did not disturb the integration between mesh and abdominal wall. Thus, the gel-mesh has superior tissue compatibility.

Adaptive control in lubrication, adhesion, and hemostasis by Chitosan-Catechol-pNIPAM

Bio-inspired wet adhesives attract considerable attention in the biomedical field. However, achieving reversible and controllable wet adhesion still remains a challenging issue. In this study, we report a new thermo-responsive polysaccharide wet adhesive conjugate named Chitosan-Catechol-poly(N-isopropyl acrylamide) (Chitosan-Catechol-pNIPAM), where catechol, the wet adhesive moiety, and pNIPAM, the thermal responsive group, are chemically tethered to a chitosan backbone. The as-synthesized Chitosan-Catechol-pNIPAM presents a reversible sol-gel transition behavior when the temperature is cycled below and above the lower critical solution temperature (LCST, 35 °C), along with dynamic switching between lubrication and wet adhesion on various materials. Based on these excellent features, Chitosan-Catechol-pNIPAM can realize controllable attachment/detachment behavior over the skin through heating/cooling processes. Due to its good biocompatibility, the Chitosan-Catechol-pNIPAM coated syringe needles exhibit instant hemostasis after removing the needles from the punctured sites of mouse veins. Overall, the as-synthesized Chitosan-Catechol-pNIPAM is expected to be used as a new intelligent adhesive in various biomedical settings.

A Biodegradable Antibacterial Nanocomposite Based on Oxidized Bacterial Nanocellulose for Rapid Hemostasis and Wound Healing

The development of biodegradable and antibacterial hemostatic materials with high blood absorption to halt the internal hemorrhage of deep noncompressible wounds remains a challenge. In this study, a novel hemostatic nanocomposite (OBC/COL/CS) was fabricated by coupling oxidized bacterial cellulose (OBC) and chitosan (CS) with collagen (COL), that is, during the electrostatic self-assembly of OBC with CS (OBC/CS), COL was ingeniously attached as a functional component by the electrostatic attraction of cationic CS and anionic OBC. The introduction of collagen was anticipated to provide functional properties such as enhanced hemostasis and promotion of wound healing so as to achieve a new functional composite. This study is the first to evaluate the performance of OBC, OBC/CS, and the OBC/COL/CS composite for rapid internal hemostasis using a rat liver injury model. To our knowledge, this is also the first study to report that OBC has a faster biodegradability in vivo than commercial hemostatic oxidized regenerated plant cellulose (ORC). The OBC/COL/CS nanocomposite exhibited appropriate mechanical strength, broad spectrum antimicrobial properties, and excellent biodegradation in vivo. Furthermore, excellent hemostatic efficacy of the composite was confirmed in vivo. OBC/COL/CS exhibited greater procoagulant properties and blood-clotting capability, higher adhesion of erythrocytes and platelets with concomitant lower blood loss, in addition to ultrafast cessation of bleeding, superior to the commercial hemostatic ORC product Surgicel gauze. The results suggest that the OBC/COL/CS is a fast and efficient procoagulant agent with good antibacterial properties and great potential for use as an absorbable hemostat for control of internal bleeding.

Catechol-functionalized hydrogels: biomimetic design, adhesion mechanism, and biomedical applications

Hydrogels are a unique class of polymeric materials that possess an interconnected porous network across various length scales from nano- to macroscopic dimensions and exhibit remarkable structure-derived properties, including high surface area, an accommodating matrix, inherent flexibility, controllable mechanical strength, and excellent biocompatibility. Strong and robust adhesion between hydrogels and substrates is highly desirable for their integration into and subsequent performance in biomedical devices and systems. However, the adhesive behavior of hydrogels is severely weakened by the large amount of water that interacts with the adhesive groups reducing the interfacial interactions. The challenges of developing tough hydrogel-solid interfaces and robust bonding in wet conditions are analogous to the adhesion problems solved by marine organisms. Inspired by mussel adhesion, a variety of catechol-functionalized adhesive hydrogels have been developed, opening a door for the design of multi-functional platforms. This review is structured to give a comprehensive overview of adhesive hydrogels starting with the fundamental challenges of underwater adhesion, followed by synthetic approaches and fabrication techniques, as well as characterization methods, and finally their practical applications in tissue repair and regeneration, antifouling and antimicrobial applications, drug delivery, and cell encapsulation and delivery. Insights on these topics will provide rational guidelines for using nature's blueprints to develop hydrogel materials with advanced functionalities and uncompromised adhesive properties.

Fabrication of Mixed-Charge Polypeptide Coating for Enhanced Hemocompatibility and Anti-Infective Effect

Medical catheters are prone to fouling by protein adsorption and platelet adhesion/activation due to their hydrophobic surface, resulting in bacterial adhesion/biofilm formation, associated infection, and thrombosis. Hence, an ultralow-fouling and exceptional infection-resistant coating on devices is urgently needed. Herein, we synthesized mussel-inspired cationic polypeptide (cPep) and mixed-charge polypeptide (mPep) via an N-carboxyanhydride ring opening polymerization method. In the view of the chemical structure, in addition to the catechol group of levodopa, the cationic group of l-lysine (K), and the hydrophobic group of l-phenylalanine (F), the mPep, comparing with cPep, contains the anionic group of l-glutamic acid (E) since the negatively charge amino acid sequence is newly introduced, so as to guarantee its bactericidal ability, low toxicity, and surface self-deposition. Both cPep and mPep coatings are conveniently obtained by a dopamine-assisted codeposition technique. Compared with the cPep coating, the mPep coating has a similar antibacterial activity level (>99%) against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. Meanwhile, it is demonstrated that the mPep coating has most effective antibiofilm activity (>3 days) and protein/platelet-resistant ability in vitro, as well as improving hemocompatibility. Furthermore, the mPep-coated silicone catheter induces no inflammatory response and significantly lowers the bacterial cell number with 6 log reduction in a mouse model of infection. Consequently, the rationally designed mPep with a simple coating technique has great potential in combating against medical catheter-related clinical infections.

A facile strategy to construct silk fibroin based GTR membranes with appropriate mechanical performance and enhanced osteogenic capacity

A facile method to modify electrospun silk fibroin nanofibrous membranes for enhanced mechanical properties and osteogenic function via polyphenol chemistry.

A novel injectable starch-based tissue adhesive for hemostasis

The starch which is modified by catechol can form hydrogel in situ so that seal the wound and reduce bleeding.

Absorbable nanocomposites composed of mesoporous bioglass nanoparticles and polyelectrolyte complexes for surgical hemorrhage control

Absorbable polyelectrolyte complexes-based hemostats are promising for controlling hemorrhage in iatrogenic injuries during surgery, whereas their hemostatic efficacy and other performances require further improvement for clinical application. Herein, spherical mesoporous bioglass nanoparticles (mBGN) were fabricated, and mBGN-polyelectrolyte complexes (composed of carboxymethyl starch and chitosan oligosaccharide) nanocomposites (BGN/PEC) with different mBGN contents were prepared via in situ coprecipitation followed by lyophilization. The effect of various mBGN content (10 and 20 wt%) on morphology, zeta potential, water absorption, degradation behavior and ion release were systematically evaluated. The in vitro degradability was dramatically promoted and a more neutral environment was achieved with the incorporation of mBGN, which is preferable for surgical applications. The in vitro coagulation test with whole blood demonstrated that the incorporation of mBGN facilitated blood clotting process. The plasma coagulation evaluation indicated that BGN/PEC had increased capability to accelerate coagulation cascade via the intrinsic pathway than that of the PEC, while have inapparent influence on the extrinsic and common pathway. The in vivo hemostatic evaluation in a rabbit hepatic hemorrhage model revealed that BGN/PEC with 10 wt% mBGN (10BGN/PEC) treatment group had the lowest blood loss, although its hemostatic time is close to that of 20BGN/PEC treatment group. The cytocompatibility evaluation with MC3T3-L1 fibroblasts indicated that 10BGN/PEC induced a ~25% increase of cell viability compared to the PEC at days 4 and 7, indicating improved biocompatibility. These findings support the promising application of absorbable BGN/PEC with optimized mBGN content as internal hemostats and present a platform for further development of PEC-based hemostats.

Catechol-Functionalized Chitosan: Optimized Preparation Method and Its Interaction with Mucin

Chitosan is one of the most popular biopolymers used for biomedical applications with its unique properties of blood clotting and adhesion to tissues. Catechol-functionalized chitosan (CatChit) has shown a significant improvement of those properties of chitosan as biomaterials. However, some well-cited methods of CatChit preparation in existing literature, repeatedly followed by numerous research groups in the past decades, have not stressed the importance of the vulnerability of catechol to oxidation, which resulted in many priceless in vivo studies that used wrong materials, i.e., partially oxidized forms of CatChit. Since some key synthesis parameters were erroneous in those previous reports, it is a challenge to reproduce the published results. To avoid the loss of critical details with these repeated citations, it is essential that we re-establish the critical parameters in these methods. In this study, we examined the accuracy of existing protocols, and optimized one of the protocols to synthesize CatChit. We have confirmed that a notable degree of catechol oxidation is inevitable with the inaccurate synthetic protocols and the maintenance of pH < 5 throughout the preparation of CatChit is essential. We have also re-evaluated interaction between CatChit and mucin, which is widely present in the gastrointestinal (GI) tract, at different pH values using CatChit prepared via our optimized synthetic protocol. Turbidimetric titrations suggested that regardless of the reaction pH, the association between CatChit and mucin increased with increasing concentration of polymer with respect to mucin. The decrease in the average size of the aggregated particles observed by Dynamic Light Scattering (DLS) studies was attributed to the formation of a large number of aggregations with increasing polymer to mucin ratio. ζ potential (ZP) measurements suggested that at acidic reaction pH, the average particle size was dictated by electrostatic interactions, while at a physiological pH, consolidation of covalent and charge-based interactions contributed to the overall surface charge.

In vitro and in vivo evaluation of 3D bioprinted small-diameter vasculature with smooth muscle and endothelium

The ability to fabricate perfusable, small-diameter vasculature is a foundational step toward generating human tissues/organs for clinical applications. Currently, it is highly challenging to generate vasculature integrated with smooth muscle and endothelium that replicates the complexity and functionality of natural vessels. Here, a novel method for directly printing self-standing, small-diameter vasculature with smooth muscle and endothelium is presented through combining tailored mussel-inspired bioink and unique 'fugitive-migration' tactics, and its effectiveness and advantages over other methods (i.e. traditional alginate/calcium hydrogel, post-perfusion of endothelial cells) are demonstrated. The biologically inspired, catechol-functionalized, gelatin methacrylate (GelMA/C) undergoes rapid oxidative crosslinking in situ to form an elastic hydrogel, which can be engineered with controllable mechanical strength, high cell/tissue adhesion, and excellent bio-functionalization. The results demonstrate the bioprinted vascular construct possessed numerous favorable, biomimetic characteristics such as proper biomechanics, higher tissue affinity, vascularized tissue manufacturing ability, beneficial perfusability and permeability, excellent vasculoactivity, and in vivo autonomous connection (∼2 weeks) as well as vascular remodeling (∼6 weeks). The advanced achievements in creating biomimetic, functional vasculature illustrate significant potential toward generating a complicated vascularized tissue/organ for clinical transplantation.

Supramolecular design and applications of polyphenol-based architecture: A review

Polyphenol-based materials are of wide-spread interest because of the unique properties of the polyphenol itself. Tannic acid, contains high level of galloyl groups, could be coordinated to a range of metal ions to generate robust mental ion-TA films on substrate or even forming hollow capsules. These films or capsules can be used in the field of sensing, separation and catalysis, most importantly in drug/nutraceutical delivery, allowing for the high loading efficiency, high mechanical and thermal stability, pH-responsive disassembly and fluorescence behavior. Additionally, such coating could also provide protection of the sensitive molecules and cells. With the numerous carbonyl and phenolic functional groups, TA has also been demonstrated to form strong hydrogen bonded multilayers with various non-ionic polymers. The properties of the hydrogen-bonded system were highly influenced by the chemical structure of the polymers, which will change the behavior of pH-, temperature- or ionic strength-responsive release of the loading molecules. Additionally, the ionization of galloyl phenol group was attributed to the interaction between TA and other ionic polymers by electrostatic interaction. The electrostatic interaction/hydrogen bonding derived TA/polyme$$%r complexes could deposit on glass slides, microcores or even forming hollow capsules, promising in their applicability to nutraceutical encapsulation, delivery and depot. Notably, polyphenols self-polymerizing could also deposit coatings on different substrates without any exogenous additives, while the comprehensive undertanding about the self-polymerizing mechenism remains unclear. This review provides a promising prospect for utilizing polyphenol-based materials to design versatile architecture in different system, used in the field of chemistry and materials science.

Bioinspired Adhesive Architectures: From Skin Patch to Integrated Bioelectronics

The attachment phenomena of various hierarchical architectures found in nature have extensively drawn attention for developing highly biocompatible adhesive on skin or wet inner organs without any chemical glue. Structural adhesive systems have become important to address the issues of human-machine interactions by smart outer/inner organ-attachable devices for diagnosis and therapy. Here, advances in designs of biologically inspired adhesive architectures are reviewed in terms of distinct structural properties, attachment mechanisms to biosurfaces by physical interactions, and noteworthy fabrication methods. Recent demonstrations of bioinspired adhesive architectures as adhesive layers for medical applications from skin patches to multifunctional bioelectronics are presented. To conclude, current challenges and prospects on potential applications are also briefly discussed.

Pro- and Anti-oxidant Properties of Redox-Active Catechol-Chitosan Films

Catechols are abundant in nature and are believed to perform diverse biological functions that include photoprotection (e.g., melanins), molecular signaling (e.g., catecholamine neurotransmitters), and mechanical adhesion (e.g., mussel glue). Currently, the structure-property-function relationships for catechols remain poorly resolved, and this is especially true for redox-based properties (e.g., antioxidant, pro-oxidant, and radical scavenging activities). Importantly, there are few characterization methods available to probe the redox properties of materials. In this review, we focus on recent studies with redox-active catechol-chitosan films. First, we describe film fabrication methods to oxidatively-graft catechols to chitosan through chemical, enzymatic, or electrochemical methods. Second, we discuss a new experimental characterization method to probe the redox properties of catechol-functionalized materials. This mediated electrochemical probing (MEP) method probes the redox-activities of catechol-chitosan films by: (i) employing diffusible mediators to shuttle electrons between the electrode and grafted catechols; (ii) imposing tailored sequences of input voltages to “tune” redox probing; and (iii) analyzing the output current response characteristics to infer properties. Finally, we demonstrate that the redox properties of catechol-chitosan films enable them to perform antioxidant radical scavenging functions, as well as a pro-oxidant (reactive oxygen-generation) antimicrobial functions. In summary, our increasing knowledge of catechol-chitosan films is enabling us to better-understand the functions of catechols in biology as well as enhancing our capabilities to create advanced functional materials.

Toxicity-Attenuated Glycol Chitosan Adhesive Inspired by Mussel Adhesion Mechanisms

Chitosan-catechol, inspired from mussel-adhesive-proteins, is characterized by the formation of an adhesive membrane complex through instant bonding with serum proteins not found in chitosan. Using this intrinsic property, chitosan-catechol is widely applied for hemostatic needles, general hemostatic materials, nanoparticle composites, and 3D printing. Despite its versatility, the practical use of chitosan-catechol in the clinic is limited due to its undesired immune responses. Herein, a catechol-conjugated glycol chitosan is proposed as an alternative hemostatic hydrogel with negligible immune responses enabling the replacement of chitosan-catechol. Comparative cellular toxicity and in vivo skin irritation between chitosan-catechol and glycol chitosan-catechol are evaluated. Their immune responses are also assessed using histological analysis after subcutaneous implantation into mice. The results show that glycol chitosan-catechol significantly attenuates the immune response compared with chitosan-catechol; this finding is likely due to the antibiofouling effect of ethylene glycol groups and the reduced adhesion of immune cells. Finally, the tissue adhesion and hemostatic ability of glycol chitosan-catechol hydrogels reveal that these ethylene glycol groups do not dramatically modify the adhesiveness and hemostatic ability compared with nonglycol chitosan-catechol. This study suggests that glycol chitosan-catechol can be a promising alternative to chitosan-catechol in various biomedical fields such as hemostatic agents.

Marine-Inspired Polymers in Medical Adhesion

Medical adhesives that are strong, easy to apply and biocompatible are promising alternatives to sutures and staples in a large variety of surgical and clinical procedures. Despite progress in the development and regulatory approval of adhesives for use in the clinic, adhesion to wet tissue remains challenging. Marine organisms have evolved a diverse set of highly effective wet adhesive approaches that have inspired the design of new medical adhesives. Here we provide an overview of selected marine animals and their chemical and physical adhesion strategies, the state of clinical translation of adhesives inspired by these organisms, and target applications where marine-inspired adhesives can have a significant impact. We will focus on medical adhesive polymers inspired by mussels, sandcastle worms, and cephalopods, emphasize the history of bioinspired medical adhesives from the peer reviewed and patent literature, and explore future directions including overlooked sources of bioinspiration and materials that exploit multiple bioinspired strategies.

Light-Triggered In Situ Gelation to Enable Robust Photodynamic-Immunotherapy by Repeated Stimulations

Photodynamic therapy (PDT) has shown the potential of triggering systemic antitumor immune responses. However, while the oxygen-deficient hypoxic tumor microenvironment is a factor that limits the PDT efficacy, the immune responses after conventional PDT usually are not strong enough to eliminate metastatic tumors. Herein, a light-triggered in situ gelation system containing photosensitizer-modified catalase together with poly(ethylene glycol) double acrylate (PEGDA) as the polymeric matrix is designed. Immune adjuvant nanoparticles are further introduced into this system to trigger robust antitumor immune responses after PDT. Following local injection of the mixed precursor solution into tumors and the subsequent light exposure, polymerization of PEGDA can be initiated to induce in situ gelation. Such hybrid hydrogel with long-term tumor retention of various agents and the ability to enable persistent tumor hypoxia relief can enable multiple rounds of PDT, which results in significantly enhanced immune responses by multiround stimulation. Further combination of such gel-based multiround PDT with anticytotoxic T-lymphocyte antigen-4 checkpoint blockade offers not only the abscopal effect to inhibit growth of distant tumors but also effective long-term immune memory protection from rechallenged tumors. Therefore, such a light-triggered in situ gelation system by a single-dose injection can enable greatly enhanced photoimmunotherapy by means of repeated stimulations.

In situ synthesis of poly (γ- glutamic acid)/alginate/AgNP composite microspheres with antibacterial and hemostatic properties

In the present work, a poly(γ-glutamic acid)/alginate/silver nanoparticle (PGA/Alg/AgNP) composite microsphere with excellent antibacterial and hemostatic properties was prepared by the in situ UV reduction and emulsion internal gelation method, and its potential application for antibacterial hemostatic dressing was explored. Well dispersed AgNPs were in situ synthesized by a UV reduction method with alginate as stabilizer and reductant. The AgNPs showed excellent antibacterial activities against both gram-negative and gram-positive bacteria. Additionally, the AgNPs prepared by the in-situ UV reduction exhibited better biocompatibility and antibacterial effects than those prepared by the conventional chemical reduction method. PGA/Alg/AgNP composite microspheres were then prepared with the AgNPs by an emulsion internal gelation method. Such microspheres were found to be a porous and hollow network with pH-sensitive swelling properties and excellent hemostatic performance, indicating its application potentials as an advanced antibacterial hemostatic material.

Chitosan-bound carboxymethylated cotton fabric and its application as wound dressing

Cotton fabric (CF) is commonly used in wound treatment, however, its hemostatic efficiency is far from sufficient. In this study, modified cotton fabric (MCF-0.39) was obtained by a carboxymethylation process, which endowed MCF-0.39 with good swelling ability and water absorption capacity. Chitosan (CHI) was bound to MCF-0.39 by the binder sodium carboxymethyl cellulose (NaCMC) via flat-screen printing technique to prepare the hybrid hemostatic material (CHI-MCF-0.39). The blood clotting index (BCI) of CHI-MCF-0.39 was 3.15-fold lower than that of CF, demonstrating the good clotting ability of the material. In rat liver injury and femoral artery animal model, the groups using CHI-MCF-0.39 had less hemostasis time and blood loss compared with those groups using CF. All the above results indicate that the prepared CHI-MCF-0.39 has promising future applications as effective hemostatic material in trauma treatment.

4-(3-Aminopropyl)-benzene-1,2-diol: An Improved Material-Independent Surface-Coating Reagent Compared to Dopamine

Dopamine surface chemistry has been of great interest because of its universal coating property and ability to transform nonadhesive molecules into adhesive molecules. Catechol oxidation and intramolecular cyclization underlie the unique property of dopamine (DA) surface chemistry and provide clues for developing new surface modification reagents such as norepinephrine, 5-pyrogallol-2-aminoethane, and perfluorinated DA derivatives. Based on these inspiring properties, a fast and universal surface chemistry technique using 4-(3-aminopropyl)-benzene-1,2-diol (3-catecholpropanamine, CPA) is reported herein. A single carbon insertion in the aliphatic chain of DA gives rise to the significantly accelerated intermolecular assembly and surface coating of CPA. The effect of CPA conjugation on an anticoagulant polysaccharide coating is also investigated. The use of CPA instead of DA to make polysaccharide coating materials improves the coating rate, while maintaining excellent antiplatelet performance on the coated surface.

A strongly adhesive hemostatic hydrogel for the repair of arterial and heart bleeds

Uncontrollable bleeding is a major problem in surgical procedures and after major trauma. Existing hemostatic agents poorly control hemorrhaging from traumatic arterial and cardiac wounds because of their weak adhesion to wet and mobile tissues. Here we design a photo-reactive adhesive that mimics the extracellular matrix (ECM) composition. This biomacromolecule-based matrix hydrogel can undergo rapid gelling and fixation to adhere and seal bleeding arteries and cardiac walls after UV light irradiation. These repairs can withstand up to 290 mm Hg blood pressure, significantly higher than blood pressures in most clinical settings (systolic BP 60–160 mm Hg). Most importantly, the hydrogel can stop high-pressure bleeding from pig carotid arteries with 4~ 5 mm-long incision wounds and from pig hearts with 6 mm diameter cardiac penetration holes. Treated pigs survived after hemostatic treatments with this hydrogel, which is well-tolerated and appears to offer significant clinical advantage as a traumatic wound sealant.

Uncontrollable bleeding is a major problem in surgery and after trauma. Here the authors design a photo-reactive adhesive that mimics the composition of connective tissue and is able to stop high pressure bleeding within half a minute.

N-alkylated chitosan/graphene oxide porous sponge for rapid and effective hemostasis in emergency situations

N-alkylated chitosan (AC) sponges and graphene oxide (GO) sponges are promising candidates for emergency hemostat. However, AC sponges have weak mechanical strength and GO sponges may induce toxicity. To overcome these problems, a series of AC/GO composite spongs (ACGS) were prepared with various ratios (GO/AC, 0%, 5%, 10%, and 20%) using a dilute solution freeze phase separation and drying process. The sponges exhibit excellent absorption capacity, mechanical stability, and biocompatibility. In serial in vitro clotting tests, the higher the ratio of GO, the better the coagulation efficiency. ACGS with 20% ratio of GO (ACGS20) has shorter hemostatic time than Celox in a rabbit femoral injury test. Moreover, ACGS20 can accelerate erythrocyte and platelet adhesion. CD62p and intracellular Ca²⁺ measurements show that ACGS20 can promote the release of intracellular Ca²⁺ and stimulate platelet activation. These results suggest that ACGS20 is a good candidate composition for a safe and efficacious hemostatic dressing.

Coassembly of Short Peptide and Polyoxometalate into Complex Coacervate Adapted for pH and Metal Ion-Triggered Underwater Adhesion

The fabrication of peptide assemblies to mimic the functions of natural proteins represents an intriguing aim in the fields of soft materials. Herein, we present a kind of novel peptide-based adhesive coacervate for the exploration of the environment-responsive underwater adhesion. Adhesive coacervates are designed and synthesized by self-assembled condensation of a tripeptide and polyoxometalates in aqueous solution. Rheological measurements demonstrate that the adhesive coacervates exhibit shear thinning behavior, which allows them to be conveniently delivered for interfacial spreading through a narrow gauge syringe without high pressure. The complex coacervates are susceptible to pH and metal ions, resulting in the occurrence of a phase transition from the fluid phase to the gel state. Scanning electron microscopy demonstrates that the microscale structures of the gel-like phases are composed of interconnected three-dimensional porous networks. The rheological study reveals that the gel-like assemblies exhibited mechanical stiffness and self-healing properties. Interestingly, the gel-like samples show the capacity to adhere to various wet solid substrates under the waterline. The adhesion strength of the peptide-based gel is quantified by lap shear mechanical analysis. The fluid coacervate is further exploited in the preparation of "on-site" injectable underwater adhesives triggered by environmental factors. This finding is exciting and serves to expand our capability for the fabrication of peptide-based underwater adhesives in a controllable way.

A Self-Pumping Dressing for Draining Excessive Biofluid around Wounds

Excessive biofluid around wounds often causes infection and hinders wound healing. However, the intrinsic hydrophilicity of the conventional dressing inevitably retains excessive biofluid at the interface between the dressing and the wound. Herein, a self-pumping dressing is reported, by electrospinning a hydrophobic nanofiber array onto a hydrophilic microfiber network, which can unidirectionally drain excessive biofluid away from wounds and finally accelerate the wound healing process. The hydrophilic microfiber network offers a draining force to pump excessive biofluid through the hydrophobic nanofiber array, which can further keep those pumped biofluids from rewetting the wounds. In the proof of concept, the self-pumping dressing unidirectionally drains the biofluid from murine dorsum wounds, thereby resulting in faster wound healing than conventional dressings. This unique self-pumping dressing has enormous potential to be a next-generation dressing for healing wounds clinically.

Platelet-derived nanovesicles for hemostasis without release of pro-inflammatory cytokines

In this study, natural platelet-derived nanovesicles with a vacant core were prepared by hypotonic sonication. The nanovesicles efficiently formed platelet-like aggregates without a notable release of pro-inflammatory cytokines. These natural and biocompatible platelet-derived nanovesicles have great potential as biomaterials for inflammation-free injectable hemostasis.

Well-ordered mesoporous silica and bioactive glasses: promise for improved hemostasis

Mesoporous silica and bioactive glasses with unique textural properties are new generations of inorganic hemostats with efficient hemostatic ability.

Mussel-inspired copolymer-coated polypropylene mesh with anti-adhesion efficiency for abdominal wall defect repair

Construction of anti-adhesive polypropylene meshes through the in situ copolymerization grafting of poly(ethylene glycol) methacrylate and dopamine methacrylamide.