Increased Fracture Toughness of Graphite-Epoxy Composites through Intermittent Interlaminar Bonding
The objective of this study has been to increase the fracture toughness of multi-layer continuous-filament graphite-epoxy composites. The method used is intermittent interlaminar bonding, which can lead to a large in crease in the fracture surface area. In this study we achieved intermittent bonding through introduction of thin perforated Mylar between the layers of the composite. For the best optimum condition included in this study, fracture toughness was increased from about 100 kJ/m2 for untreated specimens to an average of about 500 kJ/m2, while tensile strength dropped from 500 MPa to 400 MPa, and elastic modulus remained the same at about 75 GPa. An approximate analysis is presented to explain the observed improvement in toughness.
Improvement of transverse fracture toughness with interface control
Publisher Summary 
This chapter focuses on the role of the interface and its effects on the overall performance of composites. It presents the novel methods to improve the transverse fracture toughness of composites by means of controlled interfaces. It deals with the development of techniques to improve the fracture toughness of brittle fiber-brittle matrix composites in the transverse direction without impairing mechanical properties. These techniques can be classified into two major approaches: one relies on the improvement of the intrinsic properties of the composite constituents, the reinforcement or the matrix phase; and the other depends on the control of interface and/or interlaminar properties. The chapter summarizes the effectiveness of these toughening methods on transverse fracture toughness and strength in relation to the controls. It reviews the fiber coating techniques that have been developed specifically for brittle polymer-matrix composites (PMCs). The fiber coating technique, either fully or intermittently along the fiber, has been proven to be the most effective method for achieving both high strength and high fracture toughness of fiber composites when appropriate coating materials are selected.
In Vivo Comparison of Synthetic Macroporous Filamentous and Sponge-like Skin Substitute Matrices Reveals Morphometric Features of the Foreign Body Reaction According to 3D Biomaterial Designs
Synthetic macroporous biomaterials are widely used in the field of skin tissue engineering to mimic membrane functions of the native dermis. Biomaterial designs can be subclassified with respect to their shape in fibrous designs, namely fibers, meshes or fleeces, respectively, and porous designs, such as sponges and foams. However, synthetic matrices often have limitations regarding unfavorable foreign body responses (FBRs). Severe FBRs can result in unfavorable disintegration and rejection of an implant, whereas mild FBRs can lead to an acceptable integration of a biomaterial. In this context, comparative in vivo studies of different three-dimensional (3D) matrix designs are rare. Especially, the differences regarding FBRs between synthetically derived filamentous fleeces and sponge-like constructs are unknown. In the present study, the FBRs on two 3D matrix designs were explored after 25 days of subcutaneous implantation in a porcine model. Cellular reactions were quantified histopathologically to investigate in which way the FBR is influenced by the biomaterial architecture. Our results show that FBR metrics (polymorph-nucleated cells and fibrotic reactions) were significantly affected according to the matrix designs. Our findings contribute to a better understanding of the 3D matrix tissue interactions and can be useful for future developments of synthetically derived skin substitute biomaterials.