CaproGlu: Multifunctional tissue adhesive platform

Carbene-mediated gelatin and hyaluronic acid hydrogel paints with ultra adhesive ability for arthroscopic cartilage repair

In articular cartilage defect, particularly in arthroscopy, regenerative hydrogels are urgently needed. It should be able to firmly adhere to the cartilage tissue and maintain sufficient mechanical strength to withstand approximately 10 kPa of arthroscopic hydraulic flushing. In this study, we report a carbene-mediated ultra adhesive hybrid hydrogel paints for arthroscopic cartilage repair, which combined the photo initiation of double crosslinking system with the addition of diatomite, as a further reinforcing agent and biological inorganic substances. The double network consisting of ultraviolet initiated polymerization of hyaluronic acid methacrylate (HAMA) and carbene insertion chemistry of diazirine-grafted gelatin (GelDA) formed an ultra-strong adhesive hydrogel paint (H2G5DE). Diatomite helped the H2G5DE hydrogel paint firmly adhere to the cartilage defect, withstanding nearly 100 kPa of hydraulic pressure, almost 10 times that in clinical arthroscopy. Furthermore, the H2G5DE hydrogel supported cell growth, proliferation, and migration, thus successfully repairing cartilage defects. Overall, this study demonstrates a proof-of-concept of ultra-adhesive polysaccharide hydrogel paints, which can firmly adhere to the articular cartilage defects, can resist continuous hydraulic pressure, can promote effective cartilage regeneration, and is very suitable for minimally invasive arthroscopy.

Tougher Bioadhesives through Dual Stimulation Strategies

Carbene-based bioadhesives have favourable attributes for tissue adhesion, including non-specific bonding to wet and dry tissues, but suffer from relatively weak fracture strength after photocuring. Light irradiation of carbene-precursor (diazirine) also creates inert side products that are absent under thermal activation. Herein, a dual activation method combines light irradiation at elevated temperatures for the evaluation of diazirine depletion and effects on cohesive properties. A customized photo/thermal-rheometer evaluates viscoelastic properties, correlated to the kinetics of carbene:diazoalkane ratios via 19F NMR). The latter exploits the sensitive -CF3 functional group to determine joule-based light/temperature kinetics on trifluoroaryl diazirine consumption. The combination of heat and photoactivation produced bioadhesives that are 3× tougher compared to control. Dual thermal/light irradiation may be a strategy to improve viscoelastic dissipation and toughness of photo-activated adhesive resins.

Color changing bioadhesive barrier for peripherally inserted central catheters

Bacteria migration at catheter insertion sites presents a serious complication (bacteraemia) with high mortality rates. One strategy to mediate bacteraemia is a physical barrier at the skin-catheter interface. Herein a colorimetric biosensor adhesive (CathoGlu) is designed and evaluated for both colorimetric detection of bacterial infection and application as a bacteria barrier. The design intent combines viscous, hydrophobic bioadhesive with an organic pH indicator (bromothymol blue). Visual observation can then distinguish healthy skin at pH = ∼5 from an infected catheter insertion site at pH = ∼8. The liquid-to-biorubber transition of CathoGlu formulation occurs via a brief exposure to UVA penlight, providing an elastic barrier to the skin flora. Leachates from CathoGlu demonstrate no genotoxic and skin sensitization effect, assessed by OECD-recommended in vitro and in chemico assays. The CathoGlu formulation was found non-inferior against clinically approved 2-octyl-cyanoacrylate (Dermabond™), and adhesive tape (Micropore™) within an in vivo porcine model. CathoGlu skin adhesive provides new opportunities to prevent sepsis in challenging clinical situations.

A controlled light-induced gas-foaming porous hydrogel with adhesion property for infected wound healing

Porous hydrogels as scaffolds have great potential in tissue engineering. However, there are still challenges in preparing porous hydrogels with tunable pore size and controlled porosity. Here, we successfully established a photoinduced gas-foaming method of porous hydrogels with controlled macro-micro-nano multiscale. A diazirine (DZ)-modified gelatin (GelDZ) biomaterial was prepared by introducing photocrosslinked DZ group into gelatin. Upon exposure to 365 nm UV light, DZ could be converted to the active group carbene, which could randomly insert into OH, NH, or CH bonds to form covalent crosslinks. GelDZ generated N2 by photodegradation and formed gas-induced porous hydrogels by intermolecular crosslinking without initiator. The loose porous structure of the hydrogel can promote the infiltration of host cells and blood vessels, which was conducive to tissue repair. The interfacial crosslinking of photoactivated GelDZ with tissue proteins imparted adhesion properties to the hydrogel. GelDZ also possessed photoreduction ability, which can reduce silver ions from metal precursors to silver nanoparticles (Ag NPs) in situ, and showed great antibacterial activity due to the sustained release of Ag NPs. GelDZ-Ag NPs prepared by in situ photoreaction can effectively inhibit wound infection and promote skin wound healing, providing a new strategy for designing porous hydrogel in tissue engineering.

Bacterial cellulose adhesive patches designed for soft mucosal interfaces

The wet environment in the oral cavity is challenging for topical disease management approaches. The compromised material properties leading to weak adhesion and short retention (<8 h) in such environment result in frequent reapplication of the therapeutics. Composites of bacterial cellulose (BC) and carbene-based bioadhesives attempt to address these shortcomings. Previous designs comprised of aqueous formulations. The current design, for the first time, presents dry, shelf-stable cellulose patches for convenient ready-to-use application. The dry patches simultaneously remove tissue surface hydration while retaining carbene-based photocuring and offers on-demand adhesion. The dry patch prototypes are optimized by controlling BC/adhesive mole ratios and dehydration technique. The adhesion strength is higher than commercial denture adhesives on soft mucosal tissues. The structural integrity is maintained for a minimum of 7 days in aqueous environment. The patches act as selective nanoporous barrier against bacteria while allowing permeation of proteins. The results support the application of BC-based adhesive patches as a flexible platform for wound dressings, drug depots, or combination thereof.

Poly(lactic acid)-hyperbranched polyglycerol nanoparticles enhance bioadhesive treatment of esophageal disease and reduce systemic drug exposure

The effective treatment of esophageal disease represents a significant unmet clinical need, as existing treatments often lead to unnecessary systemic drug exposure and suboptimal concentrations at the disease site. Here, surface-modified bioadhesive poly(lactic acid)-hyperbranched polyglycerol nanoparticles (BNPs), with an average 100-200 nm diameter, were developed for local and sustained esophageal drug delivery. BNPs showed significantly higher adhesion and permeation into ex vivo human and rat esophageal tissue than non-adhesive nanoparticles (NNPs) and had longer residence times within the rat esophagus in vivo. Incubation with human esophagus (Het-1A) cells confirmed BNPs' biocompatibility at clinically relevant concentrations. In a rat model of achalasia, nifedipine-loaded BNPs significantly enhanced esophageal drug exposure, increased therapeutic efficacy, and reduced systemic drug exposure compared to NNPs and free drug. The safety of BNPs was demonstrated by an absence of intestinal, hepatic, and splenic toxicity following administration. This study is the first to demonstrate the efficacy of BNPs for esophageal drug delivery and highlight their potential for improving the lives of patients suffering with esophageal conditions.

Electronically optimized diazirine-based polymer crosslinkers

Electronically optimized bis-diazirine crosslinkers allow aliphatic polymers to be crosslinked with up to 10-fold improved efficacy, relative to earlier designs. Activation is achieved using modest temperatures or through UV or visible light.

Hydrophobic Bioadhesive Composites for Human Motion Detection

Conductive hydrogels are rapidly rising as sensing materials for bioelectronics applications, but lack mechanical and adhesion strength due to their excess water content. We propose a diazirine-grafted polycaprolactone adhesive (CaproGlu)/carbon nanotubes (CNTs) composite that can provide wet adhesion and strong mechanical properties at the tissue-machine interface. The introduced CNTs not only reinforced the CaproGlu, but also formed electrically conducting pathways. The CaproGlu composites exhibited conductivity of 0.1 S m^-1 and a charge storage capacity of 5 μC cm^-2. The resulting composites are biocompatible and can be used as strain sensors to detect mechanical deformations.

Bacterial cellulose adhesive composites for oral cavity applications

Topical approaches to oral diseases require frequent dosing due to limited retention time. A mucoadhesive drug delivery platform with extended soft tissue adhesion capability of up to 7 days is proposed for on-site management of oral wound. Bacterial cellulose (BC) and photoactivated carbene-based bioadhesives (PDz) are combined to yield flexible film platform for interfacing soft tissues in dynamic, wet environments. Structure-activity relationships evaluate UV dose and hydration state with respect to adhesive strength on soft tissue mimics. The bioadhesive composite has an adhesion strength ranging from 7 to 17 kPa and duration exceeding 48 h in wet conditions under sustained shear forces, while other mucoadhesives based on hydrophilic macromolecules exhibit adhesion strength of 0.5-5 kPa and last only a few hours. The work highlights the first evaluation of BC composites for mucoadhesive treatments in the buccal cavity.

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.

Emerging bioadhesives: from traditional bioactive and bioinert to a new biomimetic protein-based approach

Bioadhesives have reached significant milestones over the past two decades. Research has shown not only to produce adhesives capable of adhering to dry tissue but recently wet tissue as well. However, most bioadhesives developed have exhibited high adhesion strength yet lack other properties required for versatility in application, such as elasticity, biocompatibility and biodegradability. Adapting from limitations met from early bioadhesives and meeting the current demand allows novel bioadhesives to reach new milestones for the future. In this review, we overview the progression and variations of bioadhesives, current trends, characterisation techniques and conclude with future perspectives for bioadhesives for tissue engineering applications.

Liquid Copolymers as Biodegradable Surgical Sealant

Surgical sealants are widely used to prevent seepage of fluids and liquids, promote hemostasis, and close incisions. Despite the remarkable progress the field of biomaterials has undergone, the clinical uses of surgical sealants are limited because of their short persistence time in vivo, toxicity, and high production costs. Here, the development of two complementary neat (solvent-free) prepolymers, PEG₄ -PLGA-NHS and PEG₄ -NH₂ , that harden upon mixing to yield an elastic biodegradable sealant is presented. The mechanical and rheological properties and cross-linking rate can be controlled by varying the ratio between the two prepolymers. The tested sealants show a longer persistence time compared with fibrin glue, minimal cytotoxicity in vitro, and excellent biocompatibility in vivo. The neat, multiarmed approach demonstrated here improves the mechanical and biocompatibility properties and provides a promising tissue sealant solution for wound closure in future surgical procedures.

Fixation of Transparent Bone Pins with Photocuring Biocomposites

Bone fractures are in need of rapid fixation methods, but the current strategies are limited to metal pins and screws, which necessitate secondary surgeries upon removal. New techniques are sought to avoid surgical revisions, while maintaining or improving the fixation speed. Herein, a method of bone fixation is proposed with transparent biopolymers anchored in place via light-activated biocomposites based on expanding CaproGlu bioadhesives. The transparent biopolymers serve as a UV light guide for the activation of CaproGlu biocomposites, which results in evolution of molecular nitrogen (from diazirine photolysis), simultaneously expanding the covalently cross-linked matrix. Osseointegration additives of hydroxyapatite or Bioglass 45S5 yield a biocomposite matrix with increased stiffness and pullout strength. The structure-property relationships of UV joules dose, pin diameter, and biocomposite additives are assessed with respect to the apparent viscosity, shear modulus, spatiotemporal pin curing, and lap-shear adhesion. Finally, a model system is proposed based on ex vivo investigation with bone tissue for the exploration and optimization of UV-active transparent biopolymer fixation.

Rapid Activation of Diazirine Biomaterials with the Blue Light Photocatalyst

Carbene-based macromolecules are an emerging new stimuli-sensitive class of biomaterials that avoid the impediments of free radical polymerization but maintain a rapid liquid-to-biorubber transition. Activation of diazirine-grafted polycaprolactone polyol (CaproGlu) is limited to UVA wavelengths that have tissue exposure constraints and limited light intensities. For the first time, UVA is circumvented with visible light-emitting diodes at 445 nm (blue) to rapidly activate diazirine-to-carbene covalent cross-linking. Iridium photocatalysts serve to initiate diazirine, despite having little to no absorption at 445 nm. CaproGlu's liquid organic matrix dissolves the photocatalyst with no solvents required, creating a light transparent matrix. Considerable differences in cross-linking chemistry are observed in UVA vs visible/photocatalyst formulations. Empirical analysis and theoretical calculations reveal a more efficient conversion of diazirine directly to carbene with no diazoalkane intermediate detected. Photorheometry results demonstrate a correlation between shear moduli, joules light dose, and the lower limits of photocatalyst concentration required for the liquid-to-biorubber transition. Adhesion strength on ex vivo hydrated tissues exceeds that of cyanoacrylates, with a fixation strength of up to 20 kg·f·cm². Preliminary toxicity assessment on leachates and materials directly in contact with mammalian fibroblast cells displays no signs of fibroblast cytotoxicity.

Sunlight activated film forming adhesive polymers

Stimuli-sensitive biomaterials that are activated by light are in need of formulations that are stable under indoor lighting yet can be activated under direct sunlight. Carbene-based bioadhesives are a new generation of film-forming polymers that are stable under indoor lighting yet are rapidly activated with low-energy UVA light, but have never been evaluated under sunlight exposure. Previous investigations have evolved two flexible carbene-based platforms, where aryl-diazirine is grafted on to polyamidoamine dendrimers (PAMAM-NH₂; generation-5) or hydrophobic liquid polycaprolactone tetrol to yield G5-Dz_x and CaproGlu, respectively. For the first time the activation of G5-Dz_x and CaproGlu is investigated by natural sunlight with intensities up to 10 mW·cm^-2. Structure-property relationships of bioadhesion are investigated by: (1) joules dose of sunlight; (2) bioadhesive polymer structure; and (3) optical concentrators of magnifying glass and Fresnel lens. Using only natural sunlight, adhesion strength could be tuned from 20 to 150 kPa with crosslinking achieved in under 1 min. The results show that carbene-based polymers are a class of stimuli-sensitive biomaterials that are stable to indoor lighting, yet can be rapidly activated under direct sunlight, which may be useful for topical film forming polymers or as active ingredients in sunscreen formulations.

Ex Vivo Comparison of a UV-Polymerizable Methacrylate Adhesive versus an Inverting Pattern as the Second Layer of a Two-Layer Hand-Sewn Jejunal Anastomosis in Horses: A Pilot Study

Resection and anastomosis of small intestine during colic can lead to adhesions and recurrent colic. Several methods are available to reduce the rate of adhesions in the postoperative period, such as the use of serosal barriers. Surgical glues form a smooth surface, are fast to apply, and could reduce surgery time when performing anastomosis. A recently developed UV-polymerizable methacrylate adhesive (UV-PMA) is designed to anchor into the biological tissues' top surface offering sealant and a smooth cover over the anastomosis site. This adhesive was used ex vivo on fifteen samples of equine jejunum as the second layer of a two-layer anastomosis (1L-UV-PMA group) and compared to a two-layer anastomosis (simple continuous pattern covered with a Cushing pattern; 2L-CT group), in terms of feasibility, bursting strength pressure (BSP), luminal diameter reduction (LDR), and time of construction. Data were analysed using a paired t-test or a chi²-test (P < 0.05). The results showed no statistical difference in BSP, LDR, or any mode of failure between the two anastomosis types. However, the glue anastomosis formed a tunnel-like anastomosis and shredded under pressure, before apparition of leakage, preventing its usage in clinical cases with this methodology. It was concluded that modification of the technique is warranted before testing in clinical cases. A preprint of a former version of the manuscript is available on researchsquare.com, which was not conducted to print and publication after peer reviewing. Since then, the manuscript has been modified to this current version.