Fatigue-resistant adhesion of hydrogels

Abstract

The adhesion of soft connective tissues (tendons, ligaments, and cartilages) on bones in many animals can maintain high toughness (∽800 J m−2) over millions of cycles of mechanical loads. Such fatigue-resistant adhesion has not been achieved between synthetic hydrogels and engineering materials, but is highly desirable for diverse applications such as artificial cartilages and tendons, robust antifouling coatings, and hydrogel robots. Inspired by the nanostructured interfaces between tendons/ligaments/cartilages and bones, we report that bonding ordered nanocrystalline domains of synthetic hydrogels on engineering materials can give a fatigue-resistant adhesion with an interfacial fatigue threshold of 800 J m−2, because the fatigue-crack propagation at the interface requires a higher energy to fracture the ordered nanostructures than amorphous polymer chains. Our method enables fatigue-resistant hydrogel coatings on diverse engineering materials with complex geometries. We further demonstrate that the fatigue-resistant hydrogel coatings exhibit low friction and low wear against natural cartilages.

Graphene fatigue through van der Waals interactions

“…The fatigue crack growth behavior in Regime B has commonly been described by the Paris’ law, which states that d a /d N scales with the stress intensity factor range (∆ K ) by the power law relationship , where c and m are fitting parameters, and with Δσ representing the applied stress range, and a is the half crack length. Interfacial fatigue of various contacts has also been investigated through multiple approaches, including, but not limited to, cyclic pullout tests, lap-shear tests, and peeling tests, with the main damage behavior identified as sliding and delamination at the interfaces ( 15 – 17 ). However, interfacial fatigue behavior of the vdW contacts between graphene and its substrates remains largely unexplored.…”

Structured Interfaces for Improving the Tensile Strength and Toughness of Stiff/Highly Stretchable Polymer Hybrids

“…[ 32 ] Recently, fatigue‐resistant adhesion of hydrogel to elastomer substrate was achieved through the anchorage of ordered nanocrystalline domains on the substrate with hydrogen bonds. [ 33 ] Besides, the enhancement of elastomeric adhesion with stainless steel, [ 34 ] glass sphere, [ 35 ] and biological tissues [ 36 ] also have been achieved by using chemical modifications. The major limitation of the chemical‐based interface enhancement is its restriction on specific material systems and modification reagents, which sometimes could be difficult to implement in conventional materials or fabrication techniques.…”

Injectable hydrogels for tendon and ligament tissue engineering

“…Although hydrogels have many advantages, traditional hydrogels generally have disadvantages such as poor mechanical properties and weakness after being stressed, which greatly limits their application in T/L tissue (Mohammadinejad et al, 2020). During the mechanical load cycle of many animals, the adhesion of soft connective tissues (such as T/L) on bones of many animals can maintain high toughness (≈800 J m −2 ; Liu et al, 2020). Controlling the biomechanical properties of hydrogels is critical.…”

“…By combining ordered nanostructures in hydrogels on engineering materials, researchers have developed a simple and versatile strategy for the antifatigue bonding of hydrogels on various engineering materials. The adhesion between these hydrogels and solids can reach an interface fatigue threshold of 800 J m −2 , and a durable hydrogel coating can be used on devices with various characteristic sizes, curvatures, and substrate materials (Liu et al, 2020). The introduction of energy dissipation mechanisms in hydrogels is conducive to enhancing their mechanical properties.…”