Hydrogel-Tissue Adhesion Using Blood Coagulation Induced by Silica Nanoparticle Coatings

Hydrogel-tissue adhesion by particle bridging: sensitivity to interfacial wetting and tissue composition

Solid particles placed at the interface between hydrogels and biological tissues can create an adhesive joint through the adsorption of macromolecules onto their surfaces. Here, we investigated how this adhesion by particle bridging depends on the wetting of tissue surfaces and on the heterogeneities in tissue composition. Ex vivo peeling experiments were performed using poly(ethylene glycol) films coated with aggregates of silica nanoparticles deposited on the internal tissues of porcine liver. We show that the adhesion produced by particle bridging is altered by the presence of fluid wetting the tissue-hydrogel interface. For both uncoated and coated films, a transition from lubricated to adhesive contact was observed when all the interfacial fluid was drained. The presence of a silica nanoparticle coating shifted the transition towards more hydrated conditions and significantly enhanced adhesion in the adhesive regime. After 5 min of contact, the adhesion energy achieved on liver parenchyma with the coated films (7.7 ± 1.9 J m-2) was more than twice that of the uncoated films (3.2 ± 0.3 J m-2) or with a surgical cyanoacrylate glue (2.9 ± 1.9 J m-2). Microscopic observations during and after peeling revealed different detachment processes through either particle detachment or cohesive fracture in the tissue. These mechanisms could be directly related to the microanatomy of the liver parenchyma. The effects of both interfacial wetting and tissue composition on adhesion may provide guidelines to tailor the design of tissue adhesives using particle bridging.

Chain-like One-Dimensional Assembly of Mesoporous Silica Nanoparticles: An Approach To Improve Hydrogel Adhesion

Mesoporous silica nanoparticles (MSNPs) are well known for their adhesive properties with hydrogels and living tissues. However, achieving direct contact between the silica nanoparticle surface and the adherend necessitates the removal of capping agents, which can lead to severe aggregation when exposed to wet surfaces. This aggregation is ineffective for simultaneously bridging the two adherends, resulting in a reduced adhesive strength. In this study, we designed and synthesized mesoporous silica nanochains (MSNCs) to enhance the interactions with hydrogels by promoting the formation of coarser structures with increased nanopore exposure. Chain-like one-dimensional assemblies in the MSNCs were generated by depleting the capping ligand, cetyltrimethylammonium bromide, from the surface of the MSNPs. To quantify the porous areas of the MSNCs, we analyzed scanning electron microscopy (SEM) images using an in-house SEM image analysis algorithm. Additionally, we conducted a comparative assessment of the adhesion energies of MSNCs and MSNPs on a poly(dimethylacrylamide) hydrogel using a universal testing machine. The MSNCs exhibited a maximum adhesion energy of 13.7 ± 0.7 J/m2 at 3 wt %, surpassing that of MSNPs (10.9 ± 0.3 J/m2) at 2 wt %. Moreover, the unique stacking structure of the MSNCs enabled them to maintain an adhesion energy of 13.4 ± 1.0 J/m2 at a high concentration of 9 wt %, whereas the adhesion energy of MSNPs decreased to 8.2 ± 0.4 J/m2. This underscores their potential as superior hydrogel adhesives in challenging wet tissue-like environments.

Advanced Functional Polymers for Unmet Medical Challenges

A significant part of medicine relies on biomaterials, which are designed to interact with biological tissues for therapeutic or diagnostic purposes. A number of major trends can be distinguished in the multidisciplinary field of biomaterials science, including the precise synthesis of biomaterial building blocks, elucidation of biomaterial processing-structure-property correlations, as well as clarification of the interactions between living tissues and biomaterials. Moreover, advances in biofabrication facilitate the development of tailored implants with improved functionality, whereas recent achievements in medical imaging allow for a detailed evaluation of the performance and spatiotemporal behavior of medical devices and nanomedicine formulations.

Designing nanohesives for rapid, universal, and robust hydrogel adhesion

Nanoparticles-based glues have recently been shown with substantial potential for hydrogel adhesion. Nevertheless, the transformative advance in hydrogel-based application places great challenges on the rapidity, robustness, and universality of achieving hydrogel adhesion, which are rarely accommodated by existing nanoparticles-based glues. Herein, we design a type of nanohesives based on the modulation of hydrogel mechanics and the surface chemical activation of nanoparticles. The nanohesives can form robust hydrogel adhesion in seconds, to the surface of arbitrary engineering solids and biological tissues without any surface pre-treatments. A representative application of hydrogel machine demonstrates the tough and compliant adhesion between dynamic tissues and sensors via nanohesives, guaranteeing accurate and stable blood flow monitoring in vivo. Combined with their biocompatibility and inherent antimicrobial properties, the nanohesives provide a promising strategy in the field of hydrogel based engineering.

Silk composite interfacial layer eliminates rebleeding with chitosan-based hemostats

Chitosan foams are among the approved hemostats for pre-hospital hemorrhagic control but suffer from drawbacks related to mucoadhesiveness and rebleeding. Herein, we have developed a designer bilayered hemostatic foam consisting of a bioactive layer composed of silica particles (≈300 nm) and silk fibroin to serve as the tissue interfacing component on a chitosan foam. The foam composition was optimized based on the in vitro clotting behavior and cytocompatibility of individual components. In vivo analysis in a rat model demonstrated that the developed hemostat could achieve rapid clotting (31 ± 4 s), similar to a chitosan-based hemostat, but the former had significantly lower blood loss. Notably, removal of the bilayered hemostat prevented rebleeding, unlike the chitosan foam, which was associated with markedly higher incidences of rebleeding (50 %) and left behind material residue. Thus, the designer bilayered foam presented here is a potent inducer of blood clotting whilst affording easy removal with minimal rebleeding.

Coatings of hydroxyapatite-bioactive glass microparticles for adhesion to biological tissues

Adsorption of particles across interfaces has been proposed as a way to create adhesion between hydrogels and biological tissues. Here, we explore how this particle bridging approach can be applied to attach a soft polymer substrate to biological tissues, using bioresorbable and nanostructured hydroxyapatite-bioactive glass microparticles. For this, microparticles of aggregated flower-like hydroxyapatite and bioactive glass (HA-BG) were synthesized via a bioinspired route. A deposition technique using suspension spreading was developed to tune the coverage of HA-BG coatings at the surface of weakly cross-linked poly(beta-thioester) films. By varying the concentration of the deposited suspensions, we produced coatings having surface coverages ranging from 4% to 100% and coating densities ranging from 0.02 to 1.0 mg cm-2. The progressive dissolution of these coatings within 21 days in phosphate-buffered saline was followed by SEM. Ex vivo peeling experiments on pig liver capsules demonstrated that HA-BG coatings produce an up-to-two-fold increase in adhesion energy (9.8 ± 1.5 J m-2) as compared to the uncoated film (4.6 ± 0.8 J m-2). Adhesion energy was found to increase with increasing coating density until a maximum at 0.2 mg cm-2, well below full surface coverage, and then it decreased for larger coating densities. Using microscopy observations during and after peeling, we show that this maximum in adhesion corresponds to the appearance of particle stacks, which are easily separated and transferred onto the tissue. Such bioresorbable HA-BG coatings give the possibility of combining particle bridging with the storage and release of active compounds, therefore offering opportunities to design functional bioadhesive surfaces.

Poly(N-vinyl imidazole) Cross-Linked β-Cyclodextrin Hydrogel for Rapid Hemostasis in Severe Renal Arterial Hemorrhagic Model

A unique facile process has been adopted for fast assembly of a poly(N-vinyl imidazole) cross-linked β-cyclodextrin hydrogel through microwave-assisted free radical polymerization, using N,N'-methylenebis(acrylamide) cross-linker. The copolymer possesses positive surface charge, one of the characteristic properties of an ideal hemostatic hydrogel. The functionalized imidazole-based hydrogel demonstrates rapid, superior blood coagulation kinetics under in vitro and in vivo conditions. On application to a major renal arterial hemorrhagic model, this hydrogel shows better blood clotting kinetics, leading to complete hemostasis in as few as ∼144 ± 7 s. Additionally, 350 μL of whole blood was clotted instantly, in ∼35 s, and therefore, reinforcing its hemostatic potential. The hydrogel demonstrates excellent biocompatibility, when seeded with human dermal fibroblast cells, retaining the native property of its predecessor. In addition, the hydrogel presents excellent hemocompatibility when tested with whole blood with the highest hemolytic ratio of 1.07 ± 0.05%. Moreover, it also demonstrates potential as a carrier for sustained release of an anesthetic drug, lidocaine hydrochloride monohydrate (∼83% in 24 h). The rapid hemostatic behavior of the hydrogel is coupled with its cytocompatibility and hemocompatibilty properties along with controlled drug release characteristics. These behaviors evidently demonstrate it to be an excellent alternative for a superior hemostatic material for severe hemorrhagic conditions.

A review of the properties and applications of bioadhesive hydrogels

Due to their outstanding properties, bioadhesive hydrogels have been extensively studied by researchers in recent years.