DOTAGEL: a hydrogen and amide bonded, gelatin based, tunable, antibacterial, and high strength adhesive synthesized in an unoxidized environment

The development of bioadhesives that concurrently exhibit high adhesion strength, biocompatibility, and tunable properties and involve simple fabrication processes continues to be a significant challenge. In this study, a novel bioadhesive named DOTAGEL is synthesized by crosslinking gelatin (GA), dopamine (DA), and tannic acid (TA) in an unoxidized environment due to the advantage of controlling the degree of protonation in GA and TA, as well as controlling the degree of intermolecular amide and hydrogen bonding in the acidic medium. DOTAGEL (DA + TA + GA) shows superior adhesion strengths of 104.6 ± 46 kPa on dry skin and 35.6 ± 4.5 kPa on wet skin, up to 13 attachment-detachment cycles, retains adhesion strength under water for up to 10 days and is capable of joining two cut parts of internal organs of mice. Moreover, DOTAGEL shows strong antibacterial properties, self-healing, and biocompatibility since it contains TA, a natural and antibacterial cross-linker with abundant hydroxyl groups and the capability of forming non-covalent bonds in an unoxidized environment, and dopamine hydrochloride, a mussel inspired biomaterial containing both the amine and catechol groups for amide bonding and hydrogen bonding with TA and GA. The cross-linking among 20% (w/v) GA, 0.2% (w/v) DA, and 20% (w/v) TA is done by the centrifugation process at room temperature. Two different acids, hydrochloric acid and acetic acid, were used for tuning the pH of the medium, which led to two different samples named DOTAGEL/AA and DOTAGEL/HCL. The degree of cross-linking and mechanical and biochemical properties, like adhesion strength, degradation rate, antibacterial properties, stickiness, etc., are tuned by adjusting the pH of the medium. DOTAGEL/HCL showed 6.5 times faster degradation in 10 days, a faster release rate in the antibacterial study, 2 times adhesion strength in a dry medium, and more stickiness. The novelty lies not only in increased adhesion strength but also in the single-step fabrication process of the adhesive in the acidic medium. This research proposes the formation of a tunable antibacterial adhesive that is capable of working on wet surfaces within the body and that has the potential to become a successful tissue adhesive with a wide range of possibilities in controlled drug delivery at wound sites and other biomedical applications.

Electrospun Polymeric Fiber Systems Inoculated with Cyanoacrylate Tissue Adhesive: A Novel Hemostatic Alternative during Open Surgery

Natural-based and synthetic tissue adhesives have attracted extensive attention in the last two decades for their ability to stabilize uncontrolled bleeding instances. However; these materials present several drawbacks during use that scientists have tried to minimize in order to optimize their usage. This study comprises the development of a novel wound dressing, combining the excellent properties of polylactic acid (PLA) non-woven textile, as substrate, obtained through electrospinning, and a cyanoacrylate-based (CA) tissue adhesive, for rapid hemostatic action. Thus, the fabrication of electrospun PLA membranes at three different PLA concentrations, the design and manufacturing of the support system and the production of surgical patches were carried out. SEM and FT-IR methods were employed for analyzing the morphology as well as the indicative markers for the shelf life evolution of the obtained patches. PLA fibers with well-defined structures and a mean diameter varying between 4.6 and 7.24 μm were obtained with the increase of the concentration of the PLA solutions. In vivo tests on a rat model as well as peeling tests for good patch adhesion on liver fragments harvested from the test animals, with a limit for the strength of the liver tissue of 1.5 N, were carried out. The devices exhibited excellent adhesion to the parenchymal tissue and a long enough shelf life to be used with success in surgical procedures, also facilitating prompt hemostatic action.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

In situ generated hemostatic adhesives: From mechanisms of action to recent advances and applications

Conventional surgical closure techniques, such as sutures, clips, or skin closure strips, may not always provide optimal wound closure and may require invasive procedures, which can result in potential post-surgical complications. As result, there is a growing demand for innovative solutions to achieve superior wound closure and improve patient outcomes. To overcome the abovementioned issues, in situ generated hemostatic adhesives/sealants have emerged as a promising alternative, offering a targeted, controllable, and minimally invasive procedure for a wide variety of medical applications. The aim of this review is to provide a comprehensive overview of the mechanisms of action and recent advances of in situ generated hemostatic adhesives, particularly protein-based, thermoresponsive, bioinspired, and photocrosslinkable formulations, as well as the design challenges that must be addressed. Overall, this review aims to enhance a comprehensive understanding of the latest advancements of in situ generated hemostatic adhesives and their mechanisms of action, with the objective of promoting further research in this field.

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

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

Encapsulation of β-NGF in injectable microrods for localized delivery accelerates endochondral fracture repair

Introduction: Currently, there are no non-surgical FDA-approved biological approaches to accelerate fracture repair. Injectable therapies designed to stimulate bone healing represent an exciting alternative to surgically implanted biologics, however, the translation of effective osteoinductive therapies remains challenging due to the need for safe and effective drug delivery. Hydrogel-based microparticle platforms may be a clinically relevant solution to create controlled and localized drug delivery to treat bone fractures. Here, we describe poly (ethylene glycol) dimethacrylate (PEGDMA)-based microparticles, in the shape of microrods, loaded with beta nerve growth factor (β-NGF) for the purpose of promoting fracture repair. Methods: Herein, PEGDMA microrods were fabricated through photolithography. PEGDMA microrods were loaded with β-NGF and in vitro release was examined. Subsequently, bioactivity assays were evaluated in vitro using the TF-1 tyrosine receptor kinase A (Trk-A) expressing cell line. Finally, in vivo studies using our well-established murine tibia fracture model were performed and a single injection of the β-NGF loaded PEGDMA microrods, non-loaded PEGDMA microrods, or soluble β-NGF was administered to assess the extent of fracture healing using Micro-computed tomography (µCT) and histomorphometry. Results: In vitro release studies showed there is significant retention of protein within the polymer matrix over 168 hours through physiochemical interactions. Bioactivity of protein post-loading was confirmed with the TF-1 cell line. In vivo studies using our murine tibia fracture model show that PEGDMA microrods injected at the site of fracture remained adjacent to the callus for over 7 days. Importantly, a single injection of β-NGF loaded PEGDMA microrods resulted in improved fracture healing as indicated by a significant increase in the percent bone in the fracture callus, trabecular connective density, and bone mineral density relative to soluble β-NGF control indicating improved drug retention within the tissue. The concomitant decrease in cartilage fraction supports our prior work showing that β-NGF promotes endochondral conversion of cartilage to bone to accelerate healing. Discussion: We demonstrate a novel and translational method wherein β-NGF can be encapsulated within PEGDMA microrods for local delivery and that β-NGF bioactivity is maintained resulting in improved bone fracture repair.

Bone adhesive materials: From bench to bedside

Biodegradable bone adhesives represent a highly sought-after type of biomaterial which would enable replacement of traditional metallic devices for fixation of bone. However, these biomaterials should fulfil an extremely large number of requirements. As a consequence, bone-adhesive biomaterials which meet all of these requirements are not yet commercially available. Therefore, this comprehensive review provides an extensive overview of the development of bone adhesives from a translational perspective. First, the definition, classification, and chemistry of various types of bone adhesives are highlighted to provide a detailed overview of this emerging class of biomaterials. In this review we particularly focused studies which describe the use of materials that are capable of gluing two pieces of bone together within a time frame of minutes to days. Second, this review critically reflects on i) the experimental conditions of commonly employed adhesion tests to assess bone adhesion and ii) the current state-of-the-art regarding their preclinical and clinical applicability.

Bridging wounds: tissue adhesives' essential mechanisms, synthesis and characterization, bioinspired adhesives and future perspectives

Bioadhesives act as a bridge in wound closure by forming an effective interface to protect against liquid and gas leakage and aid the stoppage of bleeding. To their credit, tissue adhesives have made an indelible impact on almost all wound-related surgeries. Their unique properties include minimal damage to tissues, low chance of infection, ease of use and short wound-closure time. In contrast, classic closures, like suturing and stapling, exhibit potential additional complications with long operation times and undesirable inflammatory responses. Although tremendous progress has been made in the development of tissue adhesives, they are not yet ideal. Therefore, highlighting and summarizing existing adhesive designs and synthesis, and comparing the different products will contribute to future development. This review first provides a summary of current commercial traditional tissue adhesives. Then, based on adhesion interaction mechanisms, the tissue adhesives are categorized into three main types: adhesive patches that bind molecularly with tissue, tissue-stitching adhesives based on pre-polymer or precursor solutions, and bioinspired or biomimetic tissue adhesives. Their specific adhesion mechanisms, properties and related applications are discussed. The adhesion mechanisms of commercial traditional adhesives as well as their limitations and shortcomings are also reviewed. Finally, we also discuss the future perspectives of tissue adhesives.

Medical Adhesives and Their Role in Laparoscopic Surgery—A Review of Literature

Laparoscopic surgery is undergoing rapid development. Replacing the traditional method of joining cut tissues with sutures or staples could greatly simplify and speed up laparoscopic procedures. This alternative could undoubtedly be adhesives. For decades, scientists have been working on a material to bond tissues together to create the best possible conditions for tissue regeneration. The results of research on tissue adhesives achieved over the past years show comparable treatment effects to traditional methods. Tissue adhesives are a good alternative to surgical sutures in wound closure. This article is a review of the most important groups of tissue adhesives including their properties and possible applications. Recent reports on the development of biological adhesives are also discussed.

On the Development of Ultradurable Extremely Water-Repellent and Oleophobic Soot-Based Fabrics with Direct Relevance to Sperm Cryopreservation

Nowadays, the tremendous progress of nanotechnologies and materials science facilitates the fabrication of universal and multifunctional superhydrophobic surfaces on a large scale. Yet, integrating icephobic and anti-bioadhesive properties in an individual water-repellent functional coating, for addressing the difficulties faced by cryobiologists, aircraft, and seacraft manufacturers, is quite tricky but feasible if using nonpolar soot nanoparticles, whose fragility, however, impedes their industrial applicability. Here, we advance the current state-of-the-art to an extent, permitting the introduction of economically affordable and ultradurable non-wettable soot-based coatings. The deposition of rapeseed oil soot, cyanoacrylate glue and fluorine compounds onto different fabrics confers the latter with superior tolerance to harsh mechanical and thermal interventions [e.g., scratching, blade scraping, liquid nitrogen immersion (T ∼ -196 °C), torsion and water jetting], while in the meantime retaining water repellency and oleophobicity. The as-prepared soot fabrics can stick continuously to the selected host surface and favor the recovery of ∼60% of the initial motility of human spermatozoa subjected to cryopreservation or being detached and utilized as standalone non-wettable membranes. Our invention may be considered as the first fundamental stage of safely (without any health concerns) transferring the soot in reproductive medicine and developing enhanced cryogenic and antibacterial medical devices.

Novel Application of Photo-Crosslinked Urocanic-Acid-Modified Chitosan in Corneal Wounds

In the last few years, the use of tissue adhesives in corneal perforation has gained immense popularity in clinical practices. The present study aimed to devise a new application of urocanic-acid-modified chitosan (CS) with methylene blue (MB) as a photosensitizer for the development of a photo-crosslinked tissue adhesive. In particular, the curing time was controlled with the aid of a 650 nm red diode. Under the same irradiation condition, the mechanical properties were tuned using the photosensitizer at different concentrations. In vitro tests revealed that the gel was ductile and biocompatible. The application of the gel to a perforated cornea model stopped the leakage of aqueous humor, immediately after the gel was photo-crosslinked. The blue appearance of the gel provided high precision when applied to corneal wounds. Importantly, the crosslinked gel became transparent within 24 h, owing to the dissipation of MB from tears, and the gel spontaneously sloughed off without artificial removal. Altogether, the study reported the development of a novel photo-crosslinkable urocanic-acid-modified CS gel that exhibited significant potential to be utilized in the healing of corneal perforation.

Rapid fabrication of bionic pyrogallol-based self-adhesive hydrogel with mechanically tunable, self-healing, antibacterial, wound healing, and hemostatic properties

Hydrogels are functional materials that are similar to human skin and have received much attention in recent years for biomedical applications. However, the preparation of nontoxic, highly adhesive, and antimicrobial hydrogels in an efficient way remains a great challenge. Inspired by adhesive mussel foot proteins (mfps) which consist of abundant catecholic amino acids and lysine (Lys) residues, gallic acid-modified ε-poly-L-lysine (EPL/GA) was synthesized, and an active functional monomer (AA-EPL/GA) was then created through a reaction with acrylic acid (AA). The polymerization of AA-EPL/GA occurred rapidly (30-160 s) under blue light (λ = 405 nm) irradiation to produce a biomimetic PAA-EPL/GA hydrogel under mild conditions. The biomimetic pyrogallol-Lys distribution endowed the PAA-EPL/GA hydrogels with superior adhesion in humid environments (with an adhesive strength of 50.02 kPa toward wet porcine skin) and tunable mechanical and self-healing properties. Additionally, the PAA-EPL/GA hydrogels exhibited outstanding antibacterial ability due to the inherent characteristics of GA and EPL. In a mouse model, PAA-EPL/GA adhered firmly around the wound tissues. Photographs of the wound and the histological results demonstrated the ability of the hydrogel to promote wound healing, control wound infection, and suppress scar formation. Moreover, the hydrogel had a good hemostatic effect on liver bleeding. Our results highlighted the promising application potential of GA-based hydrogels, which were easily, harmlessly, and efficiently fabricated by blue light irradiation.

Correlating Rheological Properties of a Gellan Gum-Based Bioink: A Study of the Impact of Cell Density

Here, for the production of a bioink-based gellan gum, an amino derivative of this polysaccharide was mixed with a mono-functionalized aldehyde polyethyleneglycol in order to improve viscoelastic macroscopic properties and the potential processability by means of bioprinting techniques as confirmed by the printing tests. The dynamic Schiff base linkage between amino and aldehyde groups temporally modulates the rheological properties and allows a reduction of the applied pressure during extrusion followed by the recovery of gellan gum strength. Rheological properties, often related to printing resolution, were extensively investigated confirming pseudoplastic behavior and thermotropic and ionotropic responses. The success of bioprinting is related to different parameters. Among them, cell density must be carefully selected, and in order to quantify their role on printability, murine preostoblastic cells (MC3T3-E1) and human colon tumor cells (HCT-116) were chosen as cell line models. Here, we investigated the effect of their density on the bioink’s rheological properties, showing a more significant difference between cell densities for MC3T3-E1 compared to HCT-116. The results suggest the necessity of not neglecting this aspect and carrying out preliminary studies to choose the best cell densities to have the maximum viability and consequently to set the printing parameters.

Crosslink bio-adhesives for bronchoscopic lung volume reduction: current status and future direction

Several bronchoscopic lung volume reduction (BLVR) treatments have been developed to reduce hyperinflation in emphysema patients. Lung bio-adhesives are among the most promising new BLVR treatment options, as they potentially provide a permanent solution for emphysematous patients after only a single application. To date, bio-adhesives have mainly been used as haemostats and tissue sealants, while their application in permanently contracting and sealing hyperinflated lung tissue has recently been identified as a novel and enticing opportunity. However, a major drawback of the current adhesive technology is the induction of severe inflammatory responses and adverse events upon administration. In our review, we distinguish between and discuss various natural, semi-synthetic and synthetic tissue haemostats and sealants that have been used for pulmonary applications such as sealing air/fluid leaks. Furthermore, we present an overview of the different materials including AeriSeal and autologous blood that have been used to achieve lung volume reduction and discuss their respective advantages and drawbacks. In conclusion, we describe the key biological (therapeutic benefit and biocompatibility) and biomechanical (degradability, adhesive strength, stiffness, viscoelasticity, tunability and self-healing capacity) characteristics that are essential for an ideal lung bio-adhesive material with the potential to overcome the concerns related to current adhesives.

Gluing Living Bone Using a Biomimetic Bioadhesive: From Initial Cut to Final Healing

Osteoporotic fractures are a growing issue due to the increasing incidence of osteoporosis worldwide. High reoperation rates in osteoporotic fractures call for investigation into new methods in improving fixation of osteoporotic bones. In the present study, the strength of a recently developed bone bioadhesive, OsStic^tm, was evaluated in vivo using a novel bone core assay in a murine animal model at 0, 3, 7, 14, 28, and 42 days. Histology and micro-CT were obtained at all time points, and the mean peak pull-out force was assessed on days 0–28. The adhesive provided immediate fixation to the bone core. The mean peak bone core pull-out force gradually decreased from 6.09 N (σ 1.77 N) at day 0 to a minimum of 3.09 N (σ 1.08 N) at day 7, recovering to 6.37 N (σ 4.18 N) by day 28. The corresponding fibrin (Tisseel) control mean peak bone core pull-out characteristic was 0.27 N (σ 0.27 N) at day 0, with an abrupt increase from 0.37 N (σ 0.28) at day 3, 6.39 N (σ 5.09 N) at day 7, and continuing to increase to 11.34 N (σ 6.5 N) by day 28. The bone cores failed either through core pull-out or by the cancellous part of the core fracturing. Overall, the adhesive does not interrupt healing with pathological changes or rapid resorption. Initially, the adhesive bonded the bone core to the femur, and over time, the adhesive was replaced by a vascularised bone of equivalent quality and quantity to the original bone. At the 42 day time point, 70% of the adhesive in the cancellous compartment and 50% in the cortical compartment had been replaced. The adhesive outwith the bone shell was metabolized by cells that are only removing the material excess with no ectopic bone formation. It is concluded that the adhesive is not a physical and biochemical barrier as the bone heals through the adhesive and is replaced by a normal bone tissue. This adhesive composition meets many of the clinical unmet needs expressed in the literature, and may, after further preclinical assessments, have potential in the repair of bone and osteochondral fragments.

Design principles for creating synthetic underwater adhesives

Water and adhesives have a conflicting relationship as demonstrated by the failure of most man-made adhesives in underwater environments. However, living creatures routinely adhere to substrates underwater. For example, sandcastle worms create protective reefs underwater by secreting a cocktail of protein glue that binds mineral particles together, and mussels attach themselves to rocks near tide-swept sea shores using byssal threads formed from their extracellular secretions. Over the past few decades, the physicochemical examination of biological underwater adhesives has begun to decipher the mysteries behind underwater adhesion. These naturally occurring adhesives have inspired the creation of several synthetic materials that can stick underwater - a task that was once thought to be "impossible". This review provides a comprehensive overview of the progress in the science of underwater adhesion over the past few decades. In this review, we introduce the basic thermodynamics processes and kinetic parameters involved in adhesion. Second, we describe the challenges brought by water when adhering underwater. Third, we explore the adhesive mechanisms showcased by mussels and sandcastle worms to overcome the challenges brought by water. We then present a detailed review of synthetic underwater adhesives that have been reported to date. Finally, we discuss some potential applications of underwater adhesives and the current challenges in the field by using a tandem analysis of the reported chemical structures and their adhesive strength. This review is aimed to inspire and facilitate the design of novel synthetic underwater adhesives, that will, in turn expand our understanding of the physical and chemical parameters that influence underwater adhesion.

Electrospinning of cyanoacrylate tissue adhesives for human dural repair in endonasal surgery

Cerebral spinal fluid (CSF) leakage is a major postoperative complication requiring surgical intervention, resulting in prolonged healing and higher costs. Biocompatible polymers, such as cyanoacrylates, are currently used as tissue adhesives for closing surgical defects and incisions. Coupling these polymers with nanofiber technology shows promising results for generating nanofibers used in wound care, tissue engineering, and drug delivery. Fiber membranes formed by electrospinning of n-octyl-2-cyanoacrylate (NOCA) are investigated for in situ dural closures after neurosurgery to improve the quality of the closure and prevent post-surgical CSF leaks. Electrospun NOCA fiber membranes showed significantly higher sealing capabilities of defects in human dura, with an average burst pressure of 149 mmHg, compared with that of an FDA-approved common dural sealant that had an average burst pressure of 37 mmHg. In this study, microfabrication of NOCA fibers demonstrates a promising technique for dural repairs.

Chemically Modified Biopolymers for the Formation of Biomedical Hydrogels

Biopolymers are natural polymers sourced from plants and animals, which include a variety of polysaccharides and polypeptides. The inclusion of biopolymers into biomedical hydrogels is of great interest because of their inherent biochemical and biophysical properties, such as cellular adhesion, degradation, and viscoelasticity. The objective of this Review is to provide a detailed overview of the design and development of biopolymer hydrogels for biomedical applications, with an emphasis on biopolymer chemical modifications and cross-linking methods. First, the fundamentals of biopolymers and chemical conjugation methods to introduce cross-linking groups are described. Cross-linking methods to form biopolymer networks are then discussed in detail, including (i) covalent cross-linking (e.g., free radical chain polymerization, click cross-linking, cross-linking due to oxidation of phenolic groups), (ii) dynamic covalent cross-linking (e.g., Schiff base formation, disulfide formation, reversible Diels-Alder reactions), and (iii) physical cross-linking (e.g., guest-host interactions, hydrogen bonding, metal-ligand coordination, grafted biopolymers). Finally, recent advances in the use of chemically modified biopolymer hydrogels for the biofabrication of tissue scaffolds, therapeutic delivery, tissue adhesives and sealants, as well as the formation of interpenetrating network biopolymer hydrogels, are highlighted.

Soft Electronic Materials with Combinatorial Properties Generated via Mussel-Inspired Chemistry and Halloysite Nanotube Reinforcement

Soft and electrically active materials are currently being utilized for intelligent systems, including electronic skin, cybernetics, soft robotics, and wearable devices. However, fabricating materials that fulfill the complex requirements of such advanced applications remains a challenge. These attributes include electronic, adhesive, self-healing, flexible, moldable, printable, and strong mechanical properties. Inspired by the recent interest in transforming monofunctional materials into multifunctional ones through nanoreinforcement and mussel-inspired chemistry, we have designed a simple two-step methodology based on halloysite nanotube (HNT) and polydopamine (PDA) to address the grand challenges in the field. In brief, HNTs were coated with PDA and embedded within a poly(vinyl alcohol) (PVA)-based polymeric matrix in combination with ferric ions (Fe³⁺). The final composite displayed a 3-fold increase in electrical conductivity, a 20-fold increase in mechanical stiffness, and a 7-fold increase in energy dissipation in comparison to their nonfunctional counterparts, which arose from a combination of nanotube alignment and mussel-inspired chemistry. Moreover, the developed composite could elongate up to 30000% of its original length, maintain its electrical properties after 600% strain, self-heal within seconds (both electrically and mechanically), and display strain-sensitivity. Finally, it was 3D-printable and thus amenable for engineering of customized wearable electronics.

Bioinspired self-degradable hydrogels towards wound sealing

Inspired by the autolysis of shaggy mane, we developed a self-degradable hydrogel as a medical adhesive for skin wounds. The rapid gelation and self-degradation of the hydrogel were achieved via the Michael addition and subsequent hydrolysis of the addition product. In vivo experiments further showed that the hydrogel adhesive was efficiently applied for skin wound repair.

Enzyme Catalyzed Hydrogel as Versatile Bioadhesive for Tissue Wound Hemostasis, Bonding, and Continuous Repair

Developing a versatile bioadhesive which is biocompatible, adhesive, hemostatic, and therapeutic is of great significance to promote wound sealing and healing. Herein, an adhesive (GTT-3 hydrogel) is fabricated by catalysis of tannic acid modified gelatin (Gel-TA) with transglutaminase (TG). The hydrogen bonding, imine linking, and acyl-transfer reaction between GTT-3 hydrogel and tissue enable efficient hydrogel integration and adhesion to tissue instantly, so as to seal the wound and stop bleeding. Moreover, the intrinsic wound healing ability of gelatin and the antibacterial properties of TA provide favorable conditions for wound healing after adhesion. In vitro mechanical property testing and cell experimental results determine the elasticity, adhesion, and biocompatibility of the GTT-3 hydrogel. The wound operation in mouse models and pathological sectioning results indicate that GTT-3 adhesive obviously accelerates hemostasis, wound bonding, and healing. With the special property of instant adhesion and excellent hemostatic and therapeutic repair effects, GTT-3 hydrogel may provide a new option for surgical operation.

Polymeric Tissue Adhesives

Polymeric tissue adhesives provide versatile materials for wound management and are widely used in a variety of medical settings ranging from minor to life-threatening tissue injuries. Compared to the traditional methods of wound closure (i.e., suturing and stapling), they are relatively easy to use, enable rapid application, and introduce minimal tissue damage. Furthermore, they can act as hemostats to control bleeding and provide a tissue-healing environment at the wound site. Despite their numerous current applications, tissue adhesives still face several limitations and unresolved challenges (e.g., weak adhesion strength and poor mechanical properties) that limit their use, leaving ample room for future improvements. Successful development of next-generation adhesives will likely require a holistic understanding of the chemical and physical properties of the tissue-adhesive interface, fundamental mechanisms of tissue adhesion, and requirements for specific clinical applications. In this review, we discuss a set of rational guidelines for design of adhesives, recent progress in the field along with examples of commercially available adhesives and those under development, tissue-specific considerations, and finally potential functions for future adhesives. Advances in tissue adhesives will open new avenues for wound care and potentially provide potent therapeutics for various medical applications.

Injectable, self-healing and pH responsive stem cell factor loaded collagen hydrogel as a dynamic bioadhesive dressing for diabetic wound repair

As one of the serious complications of diabetes, diabetic ulcers induce several clinical problems. Although a variety of wound dressings are commonly employed, their role is too simple to integrate wound adaptation, therapeutics and effectiveness. To meet this comprehensive need, an injectable hydrogel (Col/APG) consisting of collagen and polyethylene glycol was prepared and loaded with umbilical cord stem cell factor (SCF) for the treatment of diabetic wounds. The physico-chemical properties of the Col/APG hydrogel, including rheology, self-shaping and self-healing, were demonstrated to adapt to the wound. After loading with the SCF, the adhesion strength of the resulting Col/APG + SCF hydrogel was enhanced to 17 kPa and it also showed favorable biocompatibility. A rapid cellular response, sufficient collagen deposition and marked neovascularization were observed in the whole cortex defect model of a diabetic rat after the Col/APG + SCF hydrogel was applied. Additionally, the skew toward M2 macrophages, credited with providing the anti-inflammatory function, also existed in both hydrogel groups. These findings suggested that the Col/APG hydrogel is a desirable scaffold and the Col/APG hydrogel loaded stem cell factor as a dressing is a promising treatment for diabetic tissue regeneration.

Single-Molecule Force Spectroscopy Reveals Adhesion-by-Demand in Statherin at the Protein-Hydroxyapatite Interface

Achieving strong adhesion in wet environments remains a technological challenge in biomedical applications demanding biocompatibility. Attention for adhesive motifs meeting such demands has largely been focused on marine organisms. However, bioadhesion to inorganic surfaces is also present in the human body, in the hard tissues of teeth and bones, and is mediated through serines (S). The specific amino acid sequence DpSpSEEKC has been previously suggested to be responsible for the strong binding abilities of the protein statherin to hydroxyapatite, where pS denotes phosphorylated serine. Notably, similar sequences are present in the non-collagenous bone protein osteopontin (OPN) and the mussel foot protein 5 (Mefp5). OPN has previously been shown to promote fracture toughness and physiological damage formation. Here, we investigated the adhesion strength of the motif D(pS)(pS)EEKC on substrates of hydroxyapatite, TiO₂, and mica using atomic force microscopy (AFM) single-molecule force spectroscopy (SMFS). Specifically, we investigated the dependence of adhesion force on phosphorylation of serines by comparing findings with the unphosphorylated variant DSSEEKC. Our results show that high adhesion forces of over 1 nN on hydroxyapatite and on TiO₂ are only present for the phosphorylated variant D(pS)(pS)EEKC. This warrants further exploitation of this motif or similar residues in technological applications. Further, the dependence of adhesion force on phosphorylation suggests that biological systems potentially employ an adhesion-by-demand mechanism via expression of enzymes that up- or down-regulate phosphorylation, to increase or decrease adhesion forces, respectively.

Rational Design and Bulk Synthesis of Water-Containing Supramolecular Polymers

The utilization of structural water in chemical self-assembly has not only effectively eliminated the negative influences of solvents from solutions or gels but has also provided new insight into the fabrication of new materials in bulk. However, up to now, supramolecular polymerization triggered by structural water has been dominated more by serendipity than rational design. After carefully analyzing the chemical structures of artificial monomers and gaining a deep understanding of the water-triggered assembly process, we report herein the bulk formation of polymeric materials from water and low-molecular weight monomers by rational design instead of serendipity.

Advances in Photoreactive Tissue Adhesives Derived from Natural Polymers

To stop blood loss and accelerate wound healing, conventional wound closure techniques such as sutures and staples are currently used in the clinic. These tissue-piercing wound closure techniques have several disadvantages such as the potential for causing inflammation, infections, and scar formation. Surgical sealants and tissue adhesives can address some of the disadvantages of current sutures and staples. An ideal tissue adhesive will demonstrate strong interfacial adhesion and cohesive strength to wet tissue surfaces. Most reported studies rely on the liquid-to-solid transition of organic molecules by taking advantage of polymerization and crosslinking reactions for improving the cohesive strength of the adhesives. Crosslinking reactions triggered using light are commonly used for increasing tissue adhesive strength since the reactions can be controlled spatially and temporally, providing the on-demand curing of the adhesives with minimum misplacements. In this review, we describe the recent advances in the field of naturally derived tissue adhesives and sealants in which the adhesive and cohesive strengths are modulated using photochemical reactions.

Hybrid Complex Coacervate

Underwater adhesion represents a huge technological challenge as the presence of water compromises the performance of most commercially available adhesives. Inspired by natural organisms, we have designed an adhesive based on complex coacervation, a liquid-liquid phase separation phenomenon. A complex coacervate adhesive is formed by mixing oppositely charged polyelectrolytes bearing pendant thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) chains. The material fully sets underwater due to a change in the environmental conditions, namely temperature and ionic strength. In this work, we incorporate silica nanoparticles forming a hybrid complex coacervate and investigate the resulting mechanical properties. An enhancement of the mechanical properties is observed below the PNIPAM lower critical solution temperature (LCST): this is due to the formation of PNIPAM-silica junctions, which, after setting, contribute to a moderate increase in the moduli and in the adhesive properties only when applying an ionic strength gradient. By contrast, when raising the temperature above the LCST, the mechanical properties are dominated by the association of PNIPAM chains and the nanofiller incorporation leads to an increased heterogeneity with the formation of fracture planes at the interface between areas of different concentrations of nanoparticles, promoting earlier failure of the network-an unexpected and noteworthy consequence of this hybrid system.

The Importance of Poly(ethylene glycol) Alternatives for Overcoming PEG Immunogenicity in Drug Delivery and Bioconjugation

Poly(ethylene glycol) (PEG) is widely used as a gold standard in bioconjugation and nanomedicine to prolong blood circulation time and improve drug efficacy. The conjugation of PEG to proteins, peptides, oligonucleotides (DNA, small interfering RNA (siRNA), microRNA (miRNA)) and nanoparticles is a well-established technique known as PEGylation, with PEGylated products have been using in clinics for the last few decades. However, it is increasingly recognized that treating patients with PEGylated drugs can lead to the formation of antibodies that specifically recognize and bind to PEG (i.e., anti-PEG antibodies). Anti-PEG antibodies are also found in patients who have never been treated with PEGylated drugs but have consumed products containing PEG. Consequently, treating patients who have acquired anti-PEG antibodies with PEGylated drugs results in accelerated blood clearance, low drug efficacy, hypersensitivity, and, in some cases, life-threatening side effects. In this succinct review, we collate recent literature to draw the attention of polymer chemists to the issue of PEG immunogenicity in drug delivery and bioconjugation, thereby highlighting the importance of developing alternative polymers to replace PEG. Several promising yet imperfect alternatives to PEG are also discussed. To achieve asatisfactory alternative, further joint efforts of polymer chemists and scientists in related fields are urgently needed to design, synthesize and evaluate new alternatives to PEG.

A natural polymer based bioadhesive with self-healing behavior and improved antibacterial properties

Bioadhesives are of great interest for tissue/wound closure to reduce surgical time, minimize treatment invasiveness, and prevent body fluid leakage.

A dopamine-functionalized aqueous-based silk protein hydrogel bioadhesive for biomedical wound closure

The functionalization of a PEGylated silk protein hydrogel with dopamine significantly improved its wet adhesive strength.

Light-Activated, Bioadhesive, Poly(2-hydroxyethyl methacrylate) Brush Coatings

Rapid adhesion between tissue and synthetic materials is relevant to accelerate wound healing and to facilitate the integration of implantable medical devices. Most frequently, tissue adhesives are applied as a gel or a liquid formulation. This manuscript presents an alternative approach to mediate adhesion between synthetic surfaces and tissue. The strategy presented here is based on the modification of the surface of interest with a thin polymer film that can be transformed on-demand, using UV-light as a trigger, from a nonadhesive into a reactive and tissue adhesive state. As a first proof-of-concept, the feasibility of two photoreactive, thin polymer film platforms has been explored. Both of these films, colloquially referred to as polymer brushes, have been prepared using surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-hydroxyethyl methacrylate (HEMA). In the first part of this study, it is shown that direct UV-light irradiation of PHEMA brushes generates tissue-reactive aldehyde groups and facilitates adhesion to meniscus tissue. While this strategy is very straightforward from an experimental point of view, a main drawback is that the generation of the tissue reactive aldehyde groups uses the 250 nm wavelength region of the UV spectrum, which simultaneously leads to extensive photodegradation of the polymer brush. The second part of this report outlines the synthesis of PHEMA brushes that are modified with 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzoic acid (TFMDA) moieties. UV-irradiation of the TFMDA containing brushes transforms the diazirine moieties into reactive carbenes that can insert into C-H, N-H, and O-H bonds and mediate the formation of covalent bonds between the brush surface and meniscus tissue. The advantage of the TFMDA-modified polymer brushes is that these can be activated with 365 nm wavelength UV light, which does not cause photodegradation of the polymer films. While the work presented in this manuscript has used silicon wafers and fused silica substrates as a first proof-of-concept, the versatility of SI-ATRP should enable the application of this strategy to a broad range of biomedically relevant surfaces.

Design and Evaluation of a Poly(Lactide-co-Glycolide)-Based In Situ Film-Forming System for Topical Delivery of Trolamine Salicylate

Trolamine salicylate (TS) is a topical anti-inflammatory analgesic used to treat small joint pain. The topical route is preferred over the oral one owing to gastrointestinal side effects. In this study, a poly(lactide-co-glycolide) (PLGA)-based in situ bio-adhesive film-forming system for the transdermal delivery of TS was designed and evaluated. Therefore, varying amounts (0%, 5%, 10%, 20%, and 25% (w/w)) of PLGA (EXPANSORB® DLG 50-2A, 50-5A, 50-8A, and 75-5A), ethyl 2-cyanoacrylate, poly (ethylene glycol) 400, and 1% of TS were dissolved together in acetone to form the bio-adhesive polymeric solution. In vitro drug permeation studies were performed on a vertical Franz diffusion cell and dermatomed porcine ear skin to evaluate the distinct formulations. The bio-adhesive polymeric solutions were prepared successfully and formed a thin film upon application in situ. A significantly higher amount of TS was delivered from a formulation containing 20% PLGA (45 ± 4 µg/cm2) and compared to PLGA-free counterpart (0.6 ± 0.2 µg/cm2). Furthermore, the addition of PLGA to the polymer film facilitated an early onset of TS delivery across dermatomed porcine skin. The optimized formulation also enhanced the delivery of TS into and across the skin.

Adhesive Cements That Bond Soft Tissue Ex Vivo

The aim of the present study was to evaluate the soft tissue bond strength of a newly developed, monomeric, biomimetic, tissue adhesive called phosphoserine modified cement (PMC). Two types of PMCs were evaluated using lap shear strength (LSS) testing, on porcine skin: a calcium metasilicate (CS1), and alpha tricalcium phosphate (αTCP) PMC. CS1 PCM bonded strongly to skin, reaching a peak LSS of 84, 132, and 154 KPa after curing for 0.5, 1.5, and 4 h, respectively. Cyanoacrylate and fibrin glues reached an LSS of 207 kPa and 33 kPa, respectively. αTCP PMCs reached a final LSS of ≈110 kPa. In soft tissues, stronger bond strengths were obtained with αTCP PMCs containing large amounts of amino acid (70-90 mol%), in contrast to prior studies in calcified tissues (30-50 mol%). When αTCP particle size was reduced by wet milling, and for CS1 PMCs, the strongest bonding was obtained with mole ratios of 30-50% phosphoserine. While PM-CPCs behave like stiff ceramics after setting, they bond to soft tissues, and warrant further investigation as tissue adhesives, particularly at the interface between hard and soft tissues.

Light-Activated Tissue-Integrating Sutures as Surgical Nanodevices

Sutures are typically the primary means of soft tissue repair in surgery and trauma. Despite their widespread use, sutures do not result in immediate sealing of approximated tissues, which can result in bacterial infection and leakage. Nonabsorbable sutures and staples can be traumatic to tissue, and the trauma can be exacerbated by their subsequent removal. Use of cyanoacrylate glues is limited because of their brittleness and toxicity. In this work, laser-activated tissue-integrating sutures (LATIS) are described as novel nanodevices for soft tissue approximation and repair. Incorporation of gold nanorods within fibers generated from collagen result in LATIS fibers which demonstrate robust photothermal responses following irradiation with near infrared laser light. Compared to conventional sutures, LATIS fibers result in greater biomechanical recovery of incised skin in a mouse model of skin closure after spine surgeries. Histopathology analyses show improved repair of the epidermal gap in skin, which indicate faster tissue recovery using LATIS. The studies indicate that LATIS-facilitated approximation of skin in live mice synergizes the benefits of conventional suturing and laser-activated tissue integration, resulting in new approaches for faster sealing, tissue repair, and healing.

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.

Preserving the adhesion of catechol-conjugated hydrogels by thiourea-quinone coupling

Mussel adhesion has inspired the development of catechol-based adhesive polymers. However, conventional strategies require basic pH conditions and lead to the loss of adhesion. To solve the problem, we report the first attempt to use thiourea-functionalized polymers for preserving hydrogel adhesion. We believe that this simple thiourea-quinone coupling chemistry is instrumental to synthetic adhesive materials.

Multifunctional Smart Skin Adhesive Patches for Advanced Health Care

A skin adhesive patch is the most fundamental and widely used medical device for diverse health-care purposes. Conventional skin adhesive patches have been mainly utilized for routine medical purposes such as wound management, fixation of medical devices, and simple drug release. In contrast to traditional skin adhesive patches, recently developed patches incorporate multiple key functions of bulky medical devices into a thin, flexible patch based on emerging nanomaterials and flexible electronic technologies. Consequently, the meaning of the term "skin adhesive patch" becomes broader and smarter compared to the traditional term. This review summarizes recent efforts undertaken in the development of multifunctional advanced skin adhesive patches, and briefly describes future directions and challenges toward the next generation of smart skin adhesive patches for ubiquitous personalized health care.

Bioadhesives for internal medical applications: A review

Bioadhesives such as tissue adhesives, hemostatic agents, and tissue sealants have gained increasing popularity in different areas of clinical operations during the last three decades. Bioadhesives can be categorized into internal and external ones according to their application conditions. External bioadhesives are generally applied in topical medications such as wound closure and epidermal grafting. Internal bioadhesives are mainly used in intracorporal conditions with direct contact to internal environment including tissues, organs and body fluids, such as chronic organ leak repair and bleeding complication reduction. This review focuses on internal bioadhesives that, in contrast with external bioadhesives, emphasize much more on biocompatibility and adhesive ability to wet surfaces rather than on gluing time and intensity. The crosslinking mechanisms of present internal bioadhesives can be generally classified as follows: 1) chemical conjugation between reactive groups; 2) free radical polymerization by light or redox initiation; 3) biological or biochemical coupling with specificity; and 4) biomimetic adhesion inspired from natural phenomena. In this review, bioadhesive products of each class are summarized and discussed by comparing their designs, features, and applications as well as their prospects for future development.

STATEMENT OF SIGNIFICANCE

Despite the emergence of numerous novel bioadhesive formulations in recent years, thus far, the classification of internal and external bioadhesives has not been well defined and universally acknowledged. Many of the formulations have been proposed for treatment of several diseases even though they are not applicable for such conditions. This is because of the lack of a systematic standard or evaluation protocol during the development of a new adhesive product. In this review, the definition of internal and external bioadhesives is given for the first time, and with a focus on internal bioadhesives, the criteria of an ideal internal bioadhesive are adequately discussed; this is followed by the review of recently developed internal bioadhesives based on different gluing mechanisms.

On-Demand Bioadhesive Dendrimers with Reduced Cytotoxicity

Tissue adhesives based on polyamidoamine (PAMAM) dendrimer, grafted with UV-sensitive aryldiazirine (PAMAM-g-diazirine) are promising new candidates for light active adhesion on soft tissues. Diazirine carbene precursors form interfacial and intermolecular covalent crosslinks with tissues after UV light activation that requires no premixing or inclusion of free radical initiators. However, primary amines on the PAMAM dendrimer surface present a potential risk due to their cytotoxic and immunological effects. PAMAM-g-diazirine formulations with cationic pendant amines converted into neutral amide groups were evaluated. In vitro toxicity is reduced by an order of magnitude upon amine capping while retaining bioadhesive properties. The in vivo immunological response to PAMAM-g-diazirine formulations was found to be optimal in comparison to standard poly(lactic-co-glycolic acid) (PLGA) thin films.

Polydopamine and Polydopamine-Silane Hybrid Surface Treatments in Structural Adhesive Applications

Numerous studies have focused on the remarkable adhesive properties of polydopamine, which can bind to substrates with a wide range of surface energies, even under aqueous conditions. This behavior suggests that polydopamine may be an attractive option as a surface treatment in structural bonding applications, where good bond durability is required. Here, we assessed polydopamine as a surface treatment for bonding aluminum plates with an epoxy resin. A model epoxy adhesive consisting of diglycidyl ether of bisphenol A (DGEBA) and Jeffamine D230 polyetheramine was employed, and lap shear measurements (ASTM D1002 10) were made (i) under dry conditions to examine initial bond strength and (ii) after exposure to hot/wet (63 °C in water for 14 days) conditions to assess bond durability. Surprisingly, our results showed that polydopamine alone as a surface treatment provided no benefit beyond that obtained by exposing the substrates to an alkaline solution of tris buffer used for the deposition of polydopamine. This implies that polydopamine has a potential Achilles' heel, namely, the formation of a weak boundary layer that was identified using X-ray photoelectron spectroscopy (XPS) of the fractured surfaces. In fact, for longer deposition times (2.5 and 18 h), the tris buffer-treated surface outperformed the polydopamine surface treatments, suggesting that tris buffer plays a unique role in improving adhesive performance even in the absence of polydopamine. We further showed that the use of polydopamine-3-aminopropyltriethoxysilane (APTES) hybrid surface treatments provided significant improvements in bond durability at extended deposition times relative to both polydopamine and an untreated control.

Biocompatible alkyl cyanoacrylates and their derivatives as bio-adhesives

Cyanoacrylate adhesives and their homologues have elicited interest over the past few decades owing to their applications in the biomedical sector, extending from tissue adhesives to scaffolds to implants to dental material and adhesives, because of their inherent biocompatibility and ability to polymerize solely with moisture, thanks to which they adhere to any substrate containing moisture such as the skin.

Mechanically Reinforced Catechol-Containing Hydrogels with Improved Tissue Gluing Performance

In situ forming hydrogels with catechol groups as tissue reactive functionalities are interesting bioinspired materials for tissue adhesion. Poly(ethylene glycol) (PEG)⁻catechol tissue glues have been intensively investigated for this purpose. Different cross-linking mechanisms (oxidative or metal complexation) and cross-linking conditions (pH, oxidant concentration, etc.) have been studied in order to optimize the curing kinetics and final cross-linking degree of the system. However, reported systems still show limited mechanical stability, as expected from a PEG network, and this fact limits their potential application to load bearing tissues. Here, we describe mechanically reinforced PEG⁻catechol adhesives showing excellent and tunable cohesive properties and adhesive performance to tissue in the presence of blood. We used collagen/PEG mixtures, eventually filled with hydroxyapatite nanoparticles. The composite hydrogels show far better mechanical performance than the individual components. It is noteworthy that the adhesion strength measured on skin covered with blood was >40 kPa, largely surpassing (>6 fold) the performance of cyanoacrylate, fibrin, and PEG⁻catechol systems. Moreover, the mechanical and interfacial properties could be easily tuned by slight changes in the composition of the glue to adapt them to the particular properties of the tissue. The reported adhesive compositions can tune and improve cohesive and adhesive properties of PEG⁻catechol-based tissue glues for load-bearing surgery applications.