Designing Bio-Inspired Wet Adhesives through Tunable Molecular Interactions

Hydrogel adhesives for tissue recovery

Hydrogel adhesives (HAs) are promising and rewarding tools for improving tissue therapy management. Such HAs had excellent properties and potential applications in biological tissues, such as suture replacement, long-term administration, and hemostatic sealing. In this review, the common designs and the latest progress of HAs based on various methodologies are systematically concluded. Thereafter, how to deal with interfacial water to form a robust wet adhesion and how to balance the adhesion and non-adhesion are underlined. This review also provides a brief description of gelation strategies and raw materials. Finally, the potentials of wound healing, hemostatic sealing, controlled drug delivery, and the current applications in dermal, dental, ocular, cardiac, stomach, and bone tissues are discussed. The comprehensive insight in this review will inspire more novel and practical HAs in the future.

Mussel-Inspired Molecular Strategies for Fabricating Functional Materials With Underwater Adhesion and Self-Healing Properties

The exceptional underwater adhesion and self-healing capabilities of mussels have fascinated researchers for over two decades. Extensive studies have shown that these remarkable properties arise from a series of reversible and dynamic molecular interactions involving mussel foot proteins. Inspired by these molecular interaction strategies, numerous functional materials exhibiting strong underwater adhesion and self-healing performance have been successfully developed. This review systematically explores the nanomechanical mechanisms of mussel-inspired molecular interactions, mainly revealed by direct force measurement techniques such as surface forces apparatus and atomic force microscopy. The development of functional materials, including coacervates, coatings, and hydrogels, with underwater adhesion and self-healing properties, is then summarized. Furthermore, the macroscopic material performances are correlated with the underlying molecular mechanisms, providing valuable insights for the rational design of next-generation mussel-inspired functional materials with enhanced underwater adhesion and self-healing properties.

Sustainable, temperature-tolerant, dual network conductive pressure sensitive adhesive from cellulose and rosin for wearable sensing

Conductive pressure sensitive adhesives (PSA) used for wearable and smart electronic sensors have attracted a significant amount of attention recently. However, achieving multifunctional conductive PSA with the feature of temperature tolerance and sustainability via a convenient and environment-friendly approach still remains challenge. Herein, a novel cellulose-rosin based poly(esterimide) (PEI) was first prepared by esterification and imidization. Then, the cellulose-rosin based PEI was integrated with polymerizable deep eutectic solvents (PDES, 2-hydroxyethyl acrylate and triethanolamine as hydrogen bond donor, choline chloride as hydrogen bond receptor) and performed UV-induced polymerization for formation of the conductive PSA with dual network (DN). The DN structure and the existence of extensive hydrogen bonds endowed these cellulose-rosin based conductive PSA with excellent adhesion property (shear resistance more than 70 h, tack of 14.6 N and 180° peel strength of 148.1 N/m, are higher than that of some typical commercial PSA), exceptional UV-blocking, solvent-resistance (usable in low polar solvent) and temperature tolerance (perform well between -25 °C to 140 °C). Furthermore, these conductive PSA could be used as wearable sensor to monitor subtle movements and achieve real-time monitoring of interface adhesion states even under extreme environmental conditions. This work provides a green strategy for the next-generation of multifunctional PSA.

Biocompatible Hybrid Graphenic Thin Coatings on Flexible Substrates through Matrix-Assisted Pulsed Laser Evaporation (MAPLE)

This work reports the production of biocompatible thin layers for biomedical applications based on a graphene-like material (GL), a graphene-related material (GRM) obtained from carbon black. GL was combined in a hybrid fashion with polydopamine (pDA), a mussel-inspired water-resistant wet adhesive bonding obtained by the oxidative polymerization of dopamine (DA), and polyvinyl pyrrolidinone (PVP), a nontoxic synthetic polymer with intrinsic adhesion properties, to obtain a tighter adhesion of the thin layer to the substrate (silicone slices). Matrix-assisted pulsed laser evaporation (MAPLE) was used to coat PDMS slices with thin films of GL-pDA and GL-PVP directly from their frozen suspensions in water. The results indicate that the relevant chemical-physical characteristics of both thin films (evidenced by FTIR and AFM) were maintained after MAPLE deposition and that the films exhibit uniformity also at the nanometric level. After deposition, the GL-pDA and GL-PVP films underwent a biological survey toward murine fibroblasts (NIH3T3), human keratinocytes (HaCAT), and human cervical adenocarcinoma epithelial-like (HeLa) cells to assess the feasibility of this approach. Results indicate that both the GL-pDA and GL-PVP films did not perturb the biological parameters evaluated, including cytoskeleton alterations. Both hybrid films enhanced the effects of GL on cellular vitality across all cell lines. Specifically, the GL-pDA film exhibited a more stable effect over time (up to 72 h), whereas the GL-PVP film behaved similarly to the GL film in NIH3T3 and HeLa cell lines after long-term exposure. These promising results make the GL-pDA and GL-PVP films potential candidates for the manufacture of coated flexible devices for biomedical applications.

Clay Sculpture-Inspired 3D Printed Microcage Module Using Bioadhesion Assembly for Specific-Shaped Tissue Vascularization and Regeneration

3D bioprinting techniques have enabled the fabrication of irregular large-sized tissue engineering scaffolds. However, complicated customized designs increase the medical burden. Meanwhile, the integrated printing process hinders the cellular uniform distribution and local angiogenesis. A novel approach is introduced to the construction of sizable tissue engineering grafts by employing hydrogel 3D printing for modular bioadhesion assembly, and a poly (ethylene glycol) diacrylate (PEGDA)-gelatin-dopamine (PGD) hydrogel, photosensitive and adhesive, enabling fine microcage module fabrication via DLP 3D printing is developed. The PGD hydrogel printed micocages are flexible, allowing various shapes and cell/tissue fillings for repairing diverse irregular tissue defects. In vivo experiments demonstrate robust vascularization and superior graft survival in nude mice. This assembly strategy based on scalable 3D printed hydrogel microcage module could simplify the construction of tissue with large volume and complex components, offering promise for diverse large tissue defect repairs.

All natural mussel-inspired bioadhesives from soy proteins and plant derived polyphenols with marked water-resistance and favourable antibacterial profile for wound treatment applications

HYPOTHESIS

Implementation of tissue adhesives from natural sources endowed with good mechanical properties and underwater resistance still represents a challenging research goal. Inspired by the extraordinary wet adhesion properties of mussel byssus proteins resulting from interaction of catechol and amino residues, hydrogels from soy protein isolate (SPI) and selected polyphenols i.e. caffeic acid (CA), chlorogenic acid (CGA) and gallic acid (GA) under mild aerial oxidative conditions were prepared.

EXPERIMENTS

The hydrogels were subjected to chemical assays, ATR FT-IR and EPR spectroscopy, rheological and morphological SEM analysis. Mechanical tests were carried out on hydrogels prepared by inclusion of agarose. Biological tests included evaluation of the antibacterial and wound healing activity, and hemocompatibility.

FINDINGS

The decrease of free NH2 and SH groups of SPI, the EPR features, the good cohesive strength and excellent underwater resistance (15 days for SPI/GA) under conditions relevant to their use as surgical glues indicated an efficient interaction of the polyphenols with the protein in the hydrogels. The polyphenols greatly also improved the mechanical properties of the SPI/ agarose/polyphenols hydrogels. These latter proved biocompatible, hemocompatible, not harmful to skin, displayed durable adhesiveness and good water-vapour permeability. Excellent antibacterial properties and in some cases (SPI/CGA) a favourable wound healing activity on dermal fibroblasts was obtained.