Chitin-based materials and their derivatives are receiving increased attention in tissue engineering because of their unique and appealing biological properties. In this review, we summarize the biomedical potential of chitin-based materials, specifically focusing on chitosan, in tissue engineering approaches for epithelial and soft tissues. Both types of tissues play an important role in supporting anatomical structures and physiological functions. Because of the attractive features of chitin-based materials, many characteristics beneficial to tissue regeneration including the preservation of cellular phenotype, binding and enhancement of bioactive factors, control of gene expression, and synthesis and deposition of tissue-specific extracellular matrix are well-regulated by chitin-based scaffolds. These scaffolds can be used in repairing body surface linings, reconstructing tissue structures, regenerating connective tissue, and supporting nerve and vascular growth and connection. The novel use of these scaffolds in promoting the regeneration of various tissues originating from the epithelium and soft tissue demonstrates that these chitin-based materials have versatile properties and functionality and serve as promising substrates for a great number of future applications.

Six critical issues relating to interfacial reactions arising from space confinement in 3-D integrated-circuit (3-D IC) packaging are presented in this paper. The first issue arises from the concern that intermetallics (IMCs) may occupy a large portion of the solder joint volume. It will be demonstrated that this concern is real even for Ni under bump metallurgy (UBM) or surface finish, which reacts very slowly with solders. The second issue relates to impingement and ripening of IMC grains. When IMCs occupy a large portion of a joint, the IMC grains growing from the opposite sides of a joint will eventually touch each other. The morphology evolution from this point on determines the final microstructure of a joint. Structural defects might form as a result of the impingement and ripening of IMC grains. The third issue is the rise of impurity concentration due to solder consumption. Many of the impurities in solders, such as those from electroplating, are not soluble in IMCs. As Sn reacts to form IMCs, these impurities are rejected from IMCs into the remaining solder. Consequently, the concentrations of these impurities increase with the progress of reaction. Eventually, these impurities are trapped between IMCs growing from the opposite directions. The impact of these trapped impurities on the properties of solder joints is an important issue. The fourth issue is similar to the third except that the role of impurities is replaced by inert alloy elements of solders. The most obvious element is Ag. The fifth issue arises from the fact that, as the size of a joint becomes smaller, the surface-area-to-volume ratio increases. This makes the impact of thin-film layers on UBM and surface finish become ever higher. One well-known element is Au. The so-called Au embrittlement issue may become relevant again. The last issue is the volume shrinkage from chemical reactions. Internal stress or structure defects may form because of this shrinkage. Experimental evidence will be used in this paper to illustrate these six issues, and the implications of these issues will be discussed.