Co-evolving with Nature: The Recent Trends on the Mussel-inspired Polymers in Medical Adhesion

Mussel-Inspired, Underwater Self-Healing Ionoelastomers Based on α-Lipoic Acid for Iontronics

Weak adhesion and lack of underwater self-healability hinder advancing soft iontronics particularly in wet environments like sweaty skin and biological fluids. Mussel-inspired, liquid-free ionoelastomers are reported based on seminal thermal ring-opening polymerization of a biomass molecule of α-lipoic acid (LA), followed by sequentially incorporating dopamine methacrylamide as a chain extender, N,N'-bis(acryloyl) cystamine, and lithium bis(trifluoromethanesulphonyl) imide (LiTFSI). The ionoelastomers exhibit universal adhesion to 12 substrates in both dry and wet states, superfast self-healing underwater, sensing capability for monitoring human motion, and flame retardancy. The underwater self-repairabilitiy prolongs over three months without deterioration, and sustains even when mechanical properties greatly increase. The unprecedented underwater self-mendability benefits synergistically from the maximized availability of dynamic disulfide bonds and diverse reversible noncovalent interactions endowed by carboxylic groups, catechols, and LiTFSI, along with the prevented depolymerization by LiTFSI and tunability in mechanical strength. The ionic conductivity reaches 1.4 × 10^-6 -2.7 × 10^-5 S m^-1 because of partial dissociation of LiTFSI. The design rationale offers a new route for creating a wide range of LA- and sulfur-derived supramolecular (bio)polymers with superior adhesion, healability, and other functionalities, and thus has technological implications for coatings, adhesives, binders and sealants, biomedical engineering and drug delivery, wearable and flexible electronics, and human-machine interfaces.

Adhesion and Cohesion Differences between Catechol- and Pyrogallol-Functionalized Chitosan

Marine-inspired phenolic compounds that exhibit underwater adhesion are used as biomedical adhesives under wet conditions. While these applications mainly use catechol and pyrogallol moieties that contain different numbers of hydroxyl groups on their benzene rings, how this difference affects adhesion and cohesion is not well understood. Herein, the chitosan backbone is functionalized with catechol and pyrogallol at similar modification rates (to give chitosan-catechol (CS-CA) and chitosan-pyrogallol (CS-GA), respectively) and their interaction energies are compared by using a surface forces apparatus (SFA). The phenolic moieties decrease the rigidity of the chitosan chain and increase solubility; consequently, CS-CA and CS-GA are more cohesive and adhesive than chitosan at pH 7.4. Moreover, the additional hydroxyl group of GA provides a further interacting chance; hence, CS-GA is more cohesive and adhesive than CS-CA. This study provides in-depth insight into interactions involving chitosan derivatives bearing introduced phenolic moieties that will help to develop biomedical adhesives.

Controllable performance of a dopamine-modified silk fibroin-based bio-adhesive by doping metal ions

Bio-adhesives are essential for wound healing because of their convenience and safety. Although widely used as biomaterials, silk fibroin's (SF's) further application as bio-adhesive is hindered due to its weak stickiness with tissue and slow gelation speed. Here, a dopamine-modified SF-based bio-adhesive is fabricated by using genipin as the chemical cross-linking agent. Furthermore, metal ions have been used to adjust the adhesion property of the bio-adhesive. The experimental results shows that the dopamine-modified SF-based composite holds a better stickiness except slow gelation speed. The doping of Cu²⁺and Fe³⁺can accelerate the gelation of the bio-adhesive. Compared with Cu²⁺, Fe³⁺has a stronger effect on the gelation speed of the bio-adhesive, which is positive correlative to the concentration of Fe³⁺. The adhesive has injectability and degradability. In addition, the SF-based adhesive has good biocompatibility and good improvement for cell migrationin vitro. The SF-based bio-adhesive holds potential application in the field of rapid fixation of wounds.