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Natural fiber-reinforced biocomposites with excellent mechanical and biological properties have attractive prospects for internal medical devices. However, poor interfacial adhesion between natural silk fiber and the polymer matrix has been a disturbing issue for such applications. Herein, rigid-flexible agents, such as polydopamine (PDA) and epoxy soybean oil (ESO), were introduced to enhance the interfacial adhesion between Antheraea pernyi (Ap) silk and a common medical polymer, polycaprolactone (PCL). We compared two strategies of depositing PDA first (Ap− PDA−ESO) and grafting ESO first (Ap−ESO−PDA). The rigidflexible interfacial agents introduced multiple molecular interactions at the silk−PCL interface. The "Ap−PDA−ESO" strategy exhibited a greater enhancement in interfacial adhesion, and interfacial toughening mechanisms were proposed. This work sheds light on engineering strong and tough silk fiber-based biocomposites for biomedical applications.

Carbon nanotubes (CNTs) are an economical and multi‐functional nanofiller that can further elevate the versatile performance of fiber‐reinforced polymer (FRP). The past two decades have seen significant progress in the design, fabrication, and characterization of CNTs modified FRPs (CNT‐FRPs). The introduction of CNTs has been proven to enhance the key mechanical properties of CNT‐FRPs and endow the composite with additional functional properties. In this review, the fabrication routes of CNT incorporation into FRPs are first discussed, and then the critical effects of CNTs on various mechanical properties of CNT‐FRPs are described. Next, as a complement to the experimental results, modeling studies on CNT‐FRPs are included to reveal the underlying structural effects, followed by a discussion on the reinforcement and toughening mechanisms of CNT‐FRPs. The intent of this review is to provide a comprehensive summary on CNT modified FRP composites, and to shed light on the future research and development of CNT modified composites.

Natural silk fibers achieve remarkable toughness by exploiting hierarchical structure organizations over many length scales. These hierarchical architectures are often decorated with defects that usually lead to catastrophic failure of artificial polymer materials. Silk fibers are self-tolerant of intrinsic/artificial defects to give surprising fracture toughness, but how they fulfill this function and the underlying mechanism remain elusive. Here, we unveil this puzzle by experimentally and theoretically investigating the tensile and facture behaviors of Antheraea pernyi (A. pernyi) silk monofilaments containing an artificial notch of controlled depth. The introduced transverse notch can be blunted effectively by ahead developed longitudinal crack through fibrillar separation. The notched silk fibers show ductile failure with tensile behavior dominated by the magnitude of longitudinal crack, which depends not only on the notch size but also on the interface interaction between nanofibrils. We propose that the highly oriented, disentangled nanofibrillar structure of A. pernyi silk offers it distinct tensile properties, path of crack propagation, and fracture mode in comparison with highly oriented synthetic fibers.