Istituto di Fisiologia Clinica     
Tirella A., Vozzi F., Vozzi G., Ahluwalia A. PAM2: a new Rapid Prototyping Technique for bio-fabrication of cell incorporated scaffolds. In: Tissue Engineering, vol. 1 pp. 1 - 10. Mary Ann Liebert, Inc, 2010.
Tissue engineering may be defined as the science and engineering of functional tissues and organs for the replacement of diseased body parts (Sun & Lal, Recent development on computer aided tissue engineering- a review, 2002). Traditionally, this has been realized by cell seeding onto a suitable scaffold material to create three-dimensional constructs. The classical tissue engineering approach involves the use of solid, rigid scaffolds made of polymers (polyglycolic acid, PGA, polylactide acid, PLA, or polycaprolactone, PCL) and isolated cells (Langer & Vacanti, 1993). However there are a number of drawbacks for this technique. Firstly preformed, rigid scaffolds are not suitable for engineering soft tissues, and there is a variable degree of cellular colonization that does not proceed uniformly through the scaffold. Moreover, organs consist of different cell types in specific locations, and this is hard to replicate with the traditional tissue engineering approach. Adapting manufacture approaches of micro-electromechanical device to tissue engineering is a genuine challenge. Since the first application of fused deposition modeling for tissue engineering scaffolds (Hutmacher, 2000), considerable effort has been focused on printing synthetic biodegradable scaffolds (Yang, Leong, Du, & Chua, 2002). Concurrently, a variety of Rapid Prototyping (RP) techniques have been developed to define macroscopically the shapes of deposited biomaterials, including photolithography (Vozzi, Flaim, Ahluwalia, & Bhatia, 2003), syringe-based gel deposition (Landers, Hubner, Schmelzeisen, & Mulhaupt, 2002) and solid freeform fabrication (Sachlos & Czemuszka, 2003). These approaches have not yet led to the construction of harmonically organized complex tissues may be due to the difficulty of embedding different cell types within the intricate designs. Recently, we developed a tissue engineering approach combines RP procedures with microencapsulation (Wilson & Boland, 2003) to print viable well-defined structures with a new piston syringe method, named as PAM2. In brief, PAM2 system incorporates a controlled stepper motor to a three-dimensional micro-positioner. Using a specially designed CAD software it is possible to control and define a desired topology, while with the stepper motor we are able to control material (hydrogel solutions) outflow during the scaffold fabrication. A commercial syringe is used as a reservoir in which include the cell suspension into alginate solution. The desired topology of scaffold is printed and a single bi-dimensional is realized; although, it is possible to obtain three-dimensional structure with a layer by layer process. After a characterization of the spatial resolution, as a function of the controlling parameters for the fabrication process, we set-up a convenient protocol for the realization of well- defined hydrogel scaffolds. We have printed hexagonal scaffold with hepatic cells in order to reproduce the hepatic lobule. Moreover, a Finite Element Model of the extrusion method is performed for the evaluation of the shear stress influence on the cell membrane during the RP process. Furthermore, different tests are carried out to evaluate cell viability and analyze hepatic.
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