Nonthrombogenic Hydrogel Coatings with Carbene-Cross-Linking Bioadhesives

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

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.

An in situ grown ultrathin and robust protein nanocoating for mitigating thromboembolic issues associated with cardiovascular medical devices

Thromboembolism, arising from the utilization of cardiovascular medical devices, remains a prevalent issue entailing substantial morbidity and mortality. Despite the proposal of various surface modification strategies, each approach possesses inherent limitations and drawbacks. Herein, we propose a novel approach for the in situ growth of nanocoatings on various material surfaces through the cooperative assembly of silk fibroin (SF) and lysozyme. The intrinsic in situ growth characteristic enables the nanocoatings to achieve stable and uniform adherence to diverse substrate surfaces, including the inner surface of intravascular catheters, to redefine the surface properties of the material. The features of the hydrophilic and negatively charged nanocoating contribute to its antithrombotic properties, as evidenced by the reduced likelihood of platelet adhesion upon modification of the ultrathin and mechanically robust coating. In vitro assessment confirms a significant reduction in blood clot formation along with the promotion of anticoagulation. Such a SF/Ly nanocoating holds substantial promise as a surface modification strategy to enhance the hemocompatibility of medical devices and other materials that come into contact with blood, particularly in situations where medical-grade materials are temporarily unavailable, thus providing a feasible alternative.

Building Surfaces with Controlled Site-Density of Anchored Human Serum Albumin

Stable and uniform layers of protein molecules at the surface are important to build passive devices as well as active constructs for smart biointerfaces for a large number of biomedical applications. In this context, a strategy to build-up surfaces able to anchor protein molecules on specific and controlled surface sites has been developed. Human serum albumin (HSA) has been chosen as a model protein due to its important antithrombogenic properties and its features in cell response highly valuable for in vivo devices. Uniform self-assembled monolayers of 2,2':6'2″-terpyridines (SAM), whose sites were further employed to chelate copper and iron ions, forming SAM-Cu(II) and SAM-Fe(II) complexes, have been developed. The effect of two metal cations on the physicochemical features of SAM, including thickness, Young's modulus, and tip-monolayer adhesion factors, has been investigated. Protein adsorption at different concentrations showed that the copper ion-templated surfaces exhibit highly specific mass uptake, kinetic behavior, and recognition and anchoring of HSA molecules owing to the coordination sphere of the different cations. The results pave the way to the development of a more general strategy to obtain ordered and density-tuned arrays of specific metal cations, which in turn would drive the anchoring of precise proteins for different biological functions.

Thermoresponsive shear-thinning hydrogel (T-STH) hemostats for minimally invasive treatment of external hemorrhages

Hemorrhage is the leading cause of death following battlefield injuries. Although several hemostats are commercially available, they do not meet all the necessary requirements to stop bleeding in combat injuries. Here, we engineer thermoresponsive shear-thinning hydrogels (T-STH) composed of a thermoresponsive polymer, poly(N-isopropyl acrylamide) (p(NIPAM)), and hemostatic silicate nanodisks, LAPONITE®, as minimally invasive injectable hemostatic agents. Our T-STH is a physiologically stable hydrogel that can be easily injected through a syringe and needle and exhibits rapid mechanical recovery. Additionally, it demonstrates temperature-dependent blood coagulation owing to the phase transition of p(NIPAM). It decreases in vitro blood clotting times over 50% at physiological temperatures compared to room temperature. Furthermore, it significantly prevents blood loss in an ex vivo bleeding model at different blood flow rates (1 mL min^-1 and 5 mL min^-1) by forming a wound plug. More importantly, our T-STH is comparable to a commercially available hemostat, Floseal, in terms of blood loss and blood clotting time in an in vivo rat liver bleeding model. Furthermore, once the hemorrhage is stabilized, our T-STH can be easily removed using a cold saline wash without any rebleeding or leaving any residues. Taken together, our T-STH can be used as a first aid hemostat to treat external hemorrhages in emergency situations.

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.

Fibrillated bacterial cellulose liquid carbene bioadhesives for mimicking and bonding oral cavity surfaces

Topical treatments for oral wounds and infections exhibit weak adhesion to wet surfaces which results in short retention duration (6-8 hours), frequent dosing requirement and patient incompatibility. To address these limitations, aqueous composites made of fibrillated bacterial cellulose and photoactive bioadhesives are designed for soft epithelial surfaces. The aqueous composites crosslink upon photocuring within a minute and exhibit a transition from viscous to elastic adhesive hydrogels. The light-cured composites have shear moduli mimicking oral mucosa and other soft tissues. The tunable adhesion strength ranges from 3 to 35 kPa on hydrated tissue-mimicking surfaces (collagen film). The results support the application of bacterial cellulose hydrogel systems for potential treatment of mucosal wounds.

Hydrogel Adhesive Formed via Multiple Chemical Interactions: From Persistent Wet Adhesion to Rapid Hemostasis

Thus far, robust and durable adhesion capability of hydrogel adhesive in wet environment remains a huge challenge. Here, a chemically-physically double-network cross-linked hydrogel matrix was prepared by first mixing acrylic...

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.

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.

Minimally invasive electroceutical catheter for endoluminal defect sealing

Surgical repair of lumen defects is associated with periprocedural morbidity and mortality. Endovascular repair with tissue adhesives may reduce host tissue damage, but current bioadhesive designs do not support minimally invasive deployment. Voltage-activated tissue adhesives offer a new strategy for endoluminal repair. To facilitate the clinical translation of voltage-activated adhesives, an electroceutical patch (ePATCH) paired with a minimally invasive catheter with retractable electrodes (CATRE) is challenged against the repair of in vivo and ex vivo lumen defects. The ePATCH/CATRE platform demonstrates the sealing of lumen defects up to 2 millimeters in diameter on wet tissue substrates. Water-tight seals are flexible and resilient, withstanding over 20,000 physiological relevant stress/strain cycles. No disruption to electrical signals was observed when the ePATCH was electrically activated on the beating heart. The ePATCH/CATRE platform has diverse potential applications ranging from endovascular treatment of pseudo-aneurysms/fistulas to bioelectrodes toward electrophysiological mapping.

Bioadhesives in neurosurgery: a review

OBJECTIVE

Neurosurgery presents unique surgical challenges arising from delicate neural structures, limited accessibility, and the risk of CSF leakage that can lead to CNS infections. Sutures and staples may have limited applicability in the complex anatomical constraints of cranial and spinal surgeries, especially in trauma settings when time is of the essence. Surgical bioadhesives are emerging as attractive alternatives because they avoid traumatic application methods, provide a stress-distributed fixation, and provide good cosmesis and outcomes. This article presents the history of the development of surgical bioadhesives, and is also a review of current applications of commercial surgical bioadhesives within neurosurgical procedures and the unmet clinical needs that should be addressed in bioadhesives technologies.

METHODS

A PubMed literature search was performed using the terms "(glue OR bioadhesive OR fibrin OR tisseel OR evicel OR tachosil OR cyanoacrylate OR duraseal OR bioglue) AND (neurosurgery OR spine OR spinal OR dural OR microvascular decompression OR transsphenoidal OR endovascular)." Of 2433 records screened, 168 studies were identified that described the use of bioadhesives in neurosurgical procedures.

RESULTS

The greatest number of studies describing the use of bioadhesives in neurosurgery were identified for endovascular embolization, followed by dural closure and transsphenoidal surgeries. Other common areas of application were for microvascular decompression, skin closure, peripheral nerve repair, and other novel uses. Numerous case reports were also identified describing complications associated with bioadhesive use.

CONCLUSIONS

Despite the paucity of approved indications, surgical bioadhesive use in neurosurgical procedures is prevalent. However, current bioadhesives still each have their own limitations and research is intense in the development of novel solutions.

Photocurable platelet rich plasma bioadhesives

Closure of wounds with tissue adhesives has many advantages over sutures, but existing synthetic adhesives are toxic and have poor workability. Blood-derived adhesives display complete resorption but have adhesion too weak for reliable wound dressings. We propose a semi-synthetic design that combines the positive attributes of synthetic and blood-derived tissue adhesives. PAMAM-g-diazirine (PDz) is a rapidly gelling bioadhesive miscible in both aqueous and organic solvents. PDz blended with platelet-rich plasma (PRP) forms PDz/PRP composite, a semi-synthetic formulation that combines PDz's wet tissue adhesion with PRP's potent wound healing properties. Light-activated PDz/PRP bioadhesive composite has similar elasticity to soft tissues and behaves as an induced hemostat-an unmet clinical need for rapid wound dressings. PDz/PRP composite applied to in-vivo full-thickness wounds observed a 25% reduction in inflammation, as assessed by the host-cell response.

Ultrathin and Robust Hydrogel Coatings on Cardiovascular Medical Devices to Mitigate Thromboembolic and Infectious Complications

Thromboembolic and infectious complications stemming from the use of cardiovascular medical devices are still common and result in significant morbidity and mortality. There is no strategy to date that effectively addresses both challenges at the same time. Various surface modification strategies (e.g., silver, heparin, and liquid-impregnated surfaces) are proposed yet each has several limitations and shortcomings. Here, it is shown that the incorporation of an ultrathin and mechanically robust hydrogel layer reduces bacterial adhesion to medical-grade tubing by 95%. It is additionally demonstrated, through a combination of in vitro and in vivo tests, that the hydrogel layer significantly reduces the formation and adhesion of blood clots to the tubing without affecting the blood's intrinsic clotting ability. The adhesion of clots to the tubing walls is reduced by over 90% (in vitro model), which results in an ≈60% increase in the device occlusion time (time before closure due to clot formation) in an in vivo porcine model. The advantageous properties of this passive coating make it a promising surface material candidate for medical devices interfacing with blood.

CaproGlu: Multifunctional tissue adhesive platform

Driven by the clinical need for a strong tissue adhesive with elastomeric material properties, a departure from legacy crosslinking chemistries was sought as a multipurpose platform for tissue mending. A fresh approach to bonding wet substrates has yielded a synthetic biomaterial that overcomes the drawbacks of free-radical and nature-inspired bioadhesives. A food-grade liquid polycaprolactone grafted with carbene precursors yields CaproGlu. The first-of-its-kind low-viscosity prepolymer is VOC-free and requires no photoinitiators. Grafted diazirine end-groups form carbene diradicals upon low energy UVA (365 nm) activation that immediately crosslink tissue surfaces; no pre-heating or animal-derived components are required. The hydrophobic polymeric environment enables metastable functional groups not possible in formulations requiring solvents or water. Activated diazirine within CaproGlu is uniquely capable of crosslinking all amino acids, even on wet tissue substrates. CaproGlu undergoes rapid liquid-to-biorubber transition within seconds of UVA exposure-features not found in any other bioadhesive. The exceptional shelf stability of CaproGlu allows gamma sterilization with no change in material properties. CaproGlu wet adhesiveness is challenged against current unmet clinical needs: anastomosis of spliced blood vessels, anesthetic muscle patches, and human platelet-mediating coatings. The versatility of CaproGlu enables both organic and inorganic composites for future bioadhesive platforms.

A self-adhesive microneedle patch with drug loading capability through swelling effect

Microneedles (MNs) offer a rapid method of transdermal drug delivery through penetration of the stratum corneum. However, commercial translation has been limited by fabrication techniques unique to each drug. Herein, a broadly applicable platform is explored by drug-loading via swelling effect of a hydrogel MN patch. A range of small molecule hydrophilic, hydrophobic, and biomacromolecule therapeutics demonstrate successful loading and burst release from hydrogel MNs fabricated from methacrylated hyaluronic acid (MeHA). The post-fabrication drug loading process allows MeHA MN patches with drug loadings of 10 μg cm-2. Additional post-fabrication processes are explored with dendrimer bioadhesives that increase work of adhesion, ensuring stable fixation on skin, and allow for additional drug loading strategies.

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.

Non-aqueous, tissue compliant carbene-crosslinking bioadhesives

Surgical adhesives are an attractive alternative to traditional mechanical tissue fixation methods of sutures and staples. Ease of application, biocompatibility, enhanced functionality (drug delivery) are known advantages but weak adhesion strength in the wet environment and lack of tissue compliant behavior still pose a challenge. In order to address these issues, non-aqueous bioadhesive based on blends of polyamidoamine (PAMAM) dendrimer, conjugated with 4-[3-(trifluoromethyl)-3H-diazirin-3-yl] benzyl bromide (PAMAM-g-diazirine) and liquid polyethylene glycol (PEG 400) has been developed. PEG 400 biocompatible solvent reduces the viscosity of PAMAM-g-diazirine dendrimer without incorporating aqueous solvents or plasticizers, allowing application by syringe or spray. Upon UV activation, diazirine-generated reactive intermediates lead to intermolecular dendrimer crosslinking. The properties of the crosslinked matrix are tissue compliant, with anisotropic material properties dependent on the PEG 400 wt%, UV dose, pressure and uncured adhesive thickness. The hygroscopic PAMAM-g-diazirine/PEG 400 blend was hypothesized to absorb water at the tissue interface, leading to high interfacial adhesion, however porous matrices led to cohesive failure. The hydrophilic nature of the polyether backbone (PEG 400) shielded cationic PAMAM dendrimers with cured bioadhesive film displaying significantly less platelet activation than neat PAMAM-g-diazirine or PLGA thin films.

Self curing and voltage activated catechol adhesives

Catechol adhesives are designed for curing with a low voltage signal—no oxidants or metal chelators are required.

Voltaglue Bioadhesives Energized with Interdigitated 3D-Graphene Electrodes

Soft tissue fixation of implant and bioelectrodes relies on mechanical means (e.g., sutures, staples, and screws), with associated complications of tissue perforation, scarring, and interfacial stress concentrations. Adhesive bioelectrodes address these shortcomings with voltage cured carbene-based bioadhesives, locally energized through graphene interdigitated electrodes. Electrorheometry and adhesion structure activity relationships are explored with respect to voltage and electrolyte on bioelectrodes synthesized from graphene 3D-printed onto resorbable polyester substrates. Adhesive leachates effects on in vitro metabolism and human-derived platelet-rich plasma response serves to qualitatively assess biological response. The voltage activated bioadhesives are found to have gelation times of 60 s or less with maximum shear storage modulus (G') of 3 kPa. Shear modulus mimics reported values for human soft tissues (0.1-10 kPa). The maximum adhesion strength achieved for the ≈50 mg bioelectrode films is 170 g cm^-2 (17 kPa), which exceeds the force required for tethering of electrodes on dynamic soft tissues. The method provides the groundwork for implantable bio/electrodes that may be permanently incorporated into soft tissues, vis-à-vis graphene backscattering wireless electronics since all components are bioresorbable.

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.