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

Transforming Natural Eggshell and Diatomite into Bioactive Calcium Silicate Material for Bone Regeneration

Calcium silicate (CS), a new and important bioceramic bone graft material, is prepared by using eggshells, which have a porous structure and are rich in calcium ions. Furthermore, the preparation of new CS materials using eggshells and diatomaceous earth minimizes their negative impact on the environment. In this study, we prepared CS materials using a high-temperature calcination method. The composition of the material was demonstrated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. Scanning electron microscopy (SEM) analysis confirmed the porous structure of the CS material. We also introduced ZnO to prepare ZnO-CS with antibacterial properties and showed that ZnO-CS exhibits excellent antibacterial effects through in vitro antibacterial experiments. Subsequent in vitro mineralization experiments demonstrated that ZnO-CS promoted the formation of a hydroxyapatite layer. Furthermore, in vitro cytotoxicity experiments demonstrated that ZnO-CS had very good biosafety and promoted cell proliferation. These findings were confirmed through subsequent cell proliferation experiments. Our results indicate that the novel ZnO-CS is a promising candidate for bone tissue engineering.

Silk fibroin hydrogel adhesive enables sealed-tight reconstruction of meniscus tears

Despite orientationally variant tears of the meniscus, suture repair is the current clinical gold treatment. However, inaccessible tears in company with re-tears susceptibility remain unresolved. To extend meniscal repair tools from the perspective of adhesion and regeneration, we design a dual functional biologic-released bioadhesive (S-PIL10) comprised of methacrylated silk fibroin crosslinked with phenylboronic acid-ionic liquid loading with growth factor TGF-β1, which integrates chemo-mechanical restoration with inner meniscal regeneration. Supramolecular interactions of β-sheets and hydrogen bonds richened by phenylboronic acid-ionic liquid (PIL) result in enhanced wet adhesion, swelling resistance, and anti-fatigue capabilities, compared to neat silk fibroin gel. Besides, elimination of reactive oxygen species (ROS) by S-PIL10 further fortifies localized meniscus tear repair by affecting inflammatory microenvironment with dynamic borate ester bonds, and S-PIL10 continuously releases TGF-β1 for cell recruitment and bridging of defect edge. In vivo rabbit models functionally evidence the seamless and dense reconstruction of torn meniscus, verifying that the concept of meniscus adhesive is feasible and providing a promising revolutionary strategy for preclinical research to repair meniscus tears.

Bio-inspired switchable soft adhesion for the boost of adhesive surfaces and robotics applications: A brief review

In nature, millions of creatures, such as geckos, tree frogs, octopuses, etc., have evolved fantastic switchable adhesion capabilities to climb swiftly on vertical even inverted surfaces or hunt for prey easily, adapting to harsh and unpredictable environments. Notably, these fascinating adhesive behaviors depend on interfacial forces (friction, van der Waals force, capillary force, vacuum suction, etc.), which primarily originate from the interactions between the soft micro/nanostructures evolved in the natural creatures and objects. Over the past few decades, these biological switchable adhesives have inspired scientists to explore and engineer desirable artificial adhesives. In this review, we summarized the state-of-the-art research on the ultra-fast adhesive motion of three types of biological organisms (gecko, tree frog, and octopus). Firstly, the basic adhesion principles in the three representative organisms, including micro/nanostructures, interfacial forces, and fundamental adhesion models, are reviewed. Then, we discussed the adhesion mechanisms of the prominent organisms from the perspective of soft contacts between micro/nanostructures and the substrates. Later, the mechanics-guided design principles of artificial adhesive surfaces, as well as the smart adhesion strategies, are summarized. The applications of these bio-inspired switchable adhesives are demonstrated, including wearable electronic devices, soft grippers, and climbing robots. The challenges and opportunities in this fast-growing field are also discussed.

Multifunctional Bioinspired Bredigite-Modified Adhesive for Bone Fracture Healing

Despite recent advances in bone adhesives applied for full median sternotomy, the regeneration of bone defects has remained challenging since the healing process is hampered by poor adhesiveness, limited bioactivity, and lack of antibacterial functions. Bioinspired adhesives by marine organisms provide a novel concept to circumvent these problems. Herein, a dual cross-link strategy is employed in designing a multifaceted bioinspired adhesive consisting of a catechol amine-functionalized hyperbranched polymer (polydopamine-co-acrylate, PDA), bredigite (BR) nanoparticles, and Fe³⁺ ions. The hybrid adhesives exhibit strong adhesion to various substrates such as poly(methyl methacrylate), glass, bone, and skin tissues through synergy between irreversible covalent and reversible noncovalent cross-linking, depending on the BR content. Noticeably, the adhesion strength of hybrid adhesives containing 2 wt % BR nanoparticles to bone tissues is 2.3 ± 0.8 MPa, which is about 3 times higher than that of pure PDA adhesives. We also demonstrate that these hybrid adhesives not only are bioactive and accelerate in vitro bone-like apatite formation but also exhibit antibacterial properties against Staphylococcus aureus, depending on the BR concentration. Furthermore, the superior cellular responses in contact with hybrid adhesives, including improved human osteosarcoma MG63 cell spreading and osteogenic differentiation, are achieved owing to the appropriate ion release and flexibility of the cross-linked double-network adhesive. In summary, multifunctional hybrid PDA/BR adhesives with appreciable osteoconductive, mechanical, and antibacterial properties represent the potential applications for median sternotomy surgery as a bone tissue adhesive.

Biodegradable and Biocompatible Adhesives for the Effective Stabilisation, Repair and Regeneration of Bone

Bone defects and complex fractures present significant challenges for orthopaedic surgeons. Current surgical procedures involve the reconstruction and mechanical stabilisation of complex fractures using metal hardware (i.e., wires, plates and screws). However, these procedures often result in poor healing. An injectable, biocompatible, biodegradable bone adhesive that could glue bone fragments back together would present a highly attractive solution. A bone adhesive that meets the many clinical requirements for such an application has yet to be developed. While synthetic and biological polymer-based adhesives (e.g., cyanoacrylates, PMMA, fibrin, etc.) have been used effectively as bone void fillers, these materials lack biomechanical integrity and demonstrate poor injectability, which limits the clinical effectiveness and potential for minimally invasive delivery. This systematic review summarises conventional approaches and recent developments in the area of bone adhesives for orthopaedic applications. The required properties for successful bone repair adhesives, which include suitable injectability, setting characteristics, mechanical properties, biocompatibility and an ability to promote new bone formation, are highlighted. Finally, the potential to achieve repair of challenging bone voids and fractures as well as the potential of new bioinspired adhesives and the future directions relating to their clinical development are discussed.

Polyelectrolyte Gels: Fundamentals, Fabrication and Applications

Polyelectrolyte gels are an important class of polymer gels and a versatile platform with charged polymer networks with ionisable groups. They have drawn significant recent attention as a class of smart material and have demonstrated potential for a variety of applications. This review begins with the fundamentals of polyelectrolyte gels, which encompass various classifications (i.e., origin, charge, shape) and crucial aspects (ionic conductivity and stimuli responsiveness). It further centralises recent developments of polyelectrolyte gels, emphasising their synthesis, structure-property relationships and responsive properties. Sequentially, this review demonstrates how polyelectrolyte gels' flourishing properties create attractiveness to a range of applications including tissue engineering, drug delivery, actuators and bioelectronics. Finally, the review outlines the indisputable appeal, further improvements and emerging trends in polyelectrolyte gels.