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Almost 30 years have passed since the term ‘tissue engineering’ was created to represent a new concept that focuses on the regeneration of neotissues from cells with the support of biomaterials and growth factors. This interdisciplinary engineering has attracted much attention as a new therapeutic means that may overcome the drawbacks involved in the current artificial organs and organ transplantation that have also been aiming at replacing lost or severely damaged tissues or organs. However, the tissues regenerated by tissue engineering and widely applied to patients are still minimal, including skin, bone, cartilage, capillary, and periodontal tissues. What are the reasons for such slow advances in clinical applications of tissue engineering? This article gives a brief overview of the current state of tissue engineering, covering the fundamentals and applications. The fundamentals of tissue engineering involve cell sources, scaffolds for cell expansion and differentiation, as well as carriers for growth factors. Animal and human trials are a major part of the applications. Based on these results, some critical problems to be resolved for the advances of tissue engineering are addressed from the engineering point of view, emphasizing the close collaboration between medical doctors and biomaterials scientists.

This letter introduces two new OTA-C universal Current mode biquads which offer almost all of the desirable features (expected from a good universal biquad) simultaneously, without any trade-offs. With first OTA removed and the input current source replaced by an input voltage source, both the new circuits can also realise trans-admittance-type universal biquad filters. Circ. Sign. Processing, vol. 19, pp. 241-254, 1999. [10] T. Tsukutani, Y. Sumi, M. Higashimura, and Y. Fukui, "Current-mode biquad using OTAs and CF," Electron. Lett., vol. 39, no. 3, pp. 262-263, Feb. 2003. [11] R. Senani, "A simple approach of deriving single-input-multiple-output current-mode biquad filters, " Frequenz, vol. 50, no. 5-6, pp. 124-127, May-June 1996. [12] A. Toker, O. Cicekoglu, S. Ozcan, and H. Kuntman, "High-output impedance trans-admittance type continuous-time multifunction filter with minimum active elements," Int.