Microreactor optimisation for functional tissue engineering

Abstract

Many applications in tissue engineering aim at developing functional tissues from cells in combination with a suitable matrix to support and accelerate regenerative healing (Langer and Vacanti 1999; Vacanti and Langer 1999). Stem cells (Bianco and G 2001; Hori et al. 2002; Stanworth and Newland 2001; Xu and Reid 2001) as well as cells from adult tissues and organs (Vacanti et al. 1998) can generally be used for these projects. In a first step cells are isolated and expanded in culture to obtain a sufficient amount of cells. In the following step cells are seeded onto a three-dimensional scaffold to serve as a growth matrix which determines the threedimensional structure of the construct. That way the four basic tissue groups with their specific functional characteristics can be produced to regenerate loss of epithelium (Jahoda and Reynolds 2001; Nerem and Seliktar 2001), connective tissue injury (Erickson et al. 2002; Fisher et al. 2002; Kaps et al. 2002; Obradovic et al. 2001) as well as degeneration of muscle (Luyten et al. 2001; Shimizu et al. 2002) and neural tissue (Dillon et al. 1998; Woerly 2000). While the expansion of isolated cells in Petri-dishes poses no great difficulties, developing tissue constructs often show severe morphological, physiological and biochemical changes caused by dedifferentiation (Bhadriraju and Hansen 2000; Murphy and Sambanis 2001; Ziegelaar et al. 2002). It has been demonstrated in numerous studies that the quality of artificial tissue is highly dependant on the scaffold material (Doll et al. 2001; Hutmacher 2000; Kuberka et al. 2002; Ojeh et al. 2001), cellular attachment (Linhart et al. 2001; Ohgushi and Caplan 1999), intercellular communication (Boyan et al. 1996; Folch and Toner 2000; Francis and Palsson 1997) and the culture conditions (Feng et al. 1994; Korke et al. 2002; Yamato et al. 2002). All these factors have to complement one another in order to prevent the development of atypical characteristics by dedifferentiation. Characteristic examples are the expression of atypical collagen in tissue-engineered cartilage and bone constructs (Bradamante et al. 1991; Merker et al. 1978; Schmidt et al. 1986), the calcification of artificial heart valves (Korossis et al. 2000), the loss of their endothelial coating (Hoerstrup S.P. et al. 2000; Steinhoff et al. 2000) as well as the downregulation of specific cellular functions observed in liver (Kim and Vacanti 1999; Takezawa et al. 2000), pancreatic (Kaufmann et al. 1999; Papas et al. 1999; Tziampazis and Sambanis 1995), and kidney (Humes 2000; Humes et al. 1999) constructs. Many years of experiments have shown that the possibilities to generate fully functional tissue within the static environment of a culture dish are very limited. This can be attributed to the fact that tissue development in-vivo is governed by a multitude of cellular and extracellular influences which cannot be reproduced in a culture dish (Figure 1). Hence the need for a culture system that allows the simulation of individual environments for specific tissues in order to achieve a high degree of cellular differentiation in-vitro. To overcome the technical limitations of the culture dish different kinds of perfusion culture container have been constructed in the past (Jockenhoevel et al. 2002; Kremer et al. 2001; Minuth et al. 2000; Mizuno et al. 2001). (Figure presented). © 2005 Springer.