Unlike braided fabrics, knitted scaffolds have been proven to favor deposition of collagenous connective tissue matrix, which is crucial for tendon/ligament reconstruction. But cell seeding of such scaffolds often requires a gel system, which is unstable in a dynamic situation, especially in the knee joint. This study developed a novel, biodegradable nano-microfibrous polymer scaffold by electrospinning PLGA nanofibers onto a knitted PLGA scaffold in order to provide a large biomimetic surface for cell attachment. Porcine bone marrow stromal cells were seeded onto either the novel scaffolds by pipetting a cell suspension (Group I) or the knitted PLGA scaffolds by immobilizing in fibrin gel (Group II). Cell attachment at 36 hours, cell proliferation and extracellular matrix synthesis at 1 week, and mechanical properties over 2 weeks were investigated. Cell attachment was comparable and cell proliferation was faster in Group I. Moreover, cellular function was more actively exhibited in Group I, as evident by the higher expression of collagen I, decorin, and biglycan genes. Thus, this novel scaffold, facilitating cell seeding and promoting cell proliferation, function, and differentiation, could be applied with promise in tissue engineering of tendon/ligament.

Delamination is a major failure mode in laminated composites and has received much research attention. A huge amount of literature has been published on this subject, resulting in considerable improvement in our understanding of delamination behavior. A rather comprehensive review paper was published by Garg in 1988. That paper contains 136 references from 1971 to 1988, a period spanning roughly two decades. A more recent survey by Pagano and Schoeppner contains critical reviews of many selected papers, especially the pioneering works on delamination research. An overview of Russian and Soviet literature on this subject is also given by Bolotin. The present paper aims to review major developments in the analysis and characterization of buckling driven delamination from 1990 to the present. Its abridged version was presented in a plenary lecture at the 13th International Conference on Composite Materials, Beijing. Particular emphasis is placed on the application of fracture mechanics methods in the analysis of delamination. The question of the extent of fracture mechanics’ success in characterizing delamination, both in laboratory-based specimens and in more realistic structural composite components, is discussed. Some recent numerical formulations for efficient computational modeling and analysis of delaminations are also reviewed. This review lists 270 major works covering a period of about a decade, indicating that there is still considerable research interest and activity in this field.

Recent developments in the aircraft industry towards substantially improving fuel economy and extending flight range have accelerated interest in the use of advanced composites as primary structural materials. The airframes of next-generation airliners will have substantial parts made of light-weight composites. This means that the engineering demands on the performance of fiber-reinforced composites will become greater. There is therefore a need to better understand and predict the multiple complex failure mechanisms in composite structures, and to devise more reliable failure theories and damage progression models. There is a large body of literature on progressive damage analysis in composites, much of which employs damage mechanics and material stiffness degradation methods. This article reviews some of the more recent work in this area and describes the issues pertinent to application in composite structures. The authors' ongoing research efforts in modeling and prediction of progressive damage through the relatively novel element-failure method (EFM), which has been coded into a user-defined UEL code in Abaqus, are discussed. In particular, results for notched composite laminates and pin-loaded (PL) analyses are shown and compared to experimental data. Although EFM is the computational platform on which the damage is advanced in the structure, the results are dependent on the choice of the failure criterion. Various failure criteria are used throughout the cases discussed herein, from the more traditional Tsai—Wu (TW) criterion to the very recently proposed micromechanics-based failure (MMF) criterion. The EFM may also be used with cohesive elements, with the former intended for modeling in-plane damage progression, while the latter for delamination onset and propagation. This hybrid EFM-cohesive element approach is illustrated with an analysis of double-notched composite laminate. The computational models are relatively robust up to and including ultimate load, and enable the mapping of extensive damage patterns in composite structures. They represent a suite of computational tools that extend the capability to model damage and failure propagation beyond initial failure prediction.