Cell biology
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Figure 1: Structure of polystyrene electrospun fibre mats as demonstrated using scanning electron microscopy. Fibres can be generated in a random (left) or aligned (right) orientation
Inert non-degradable scaffolds
Inert non-degradable scaffolds consist of pores or voids which are joined by interconnecting holes into which cells can grow. They are most often developed from synthetic polymers and their sim- plicity overcomes several of the limitations that other 3D substrates may experience. There are numerous methods of fabricating porous materials including emulsion templating17,18, leachable par- ticles19 and gas foaming technology20. Gas-in-liq- uid foam templating has been used as a method to create porous scaffolds for cell culture applica- tions21. In this process gas bubbles can coalesce leading to a broad range of scaffold porosities in which it is difficult to control the consistency of the material and consequently the reproducible growth of cells within the scaffold.
Electrospinning is technology that has been developed heavily in the textile industry. The prin- ciples behind electrospinning have been applied to produce mats of electrospun synthetic fibres designed to support 3D cell growth22. While the consistency and porosity of electrospun materials is a challenge to control, they have the potential advantage of orientating cell growth. Fibre mats can be spun either in a random fashion or in a manner where fibres are aligned in parallel pre- senting directional passage for guided cell growth (Figure 1). Electrospun materials can either be used to provide a physical 3D space in which cells grow (although the uniformity of such materials is diffi- cult to control) or they can be used to introduce topographical features upon which cells adhere. For example, Ultra-Web™ (Corning) was devel- oped as a commercial polyamide elecrospun
Drug Discovery World Spring 2011
nanofibre mat for cell culture. Cells grow as mono- layers on the roughen topography created by the nanoscale Ultra-Web™ fibre mat rather than with- in the physical lattice of the material. Fabrication technologies such as those described have been applied to the manufacture of porous polystyrene-based scaffolds. Polystyrene is chemi- cally inert, stable and is consistent and directly comparable to conventional 2D tissue culture plas- tic ware. These features make it an attractive medi- um as a scaffold to support 3D cell culture. The vast majority of in vitro cell culture experiments and resulting data have been conducted on poly- styrene surfaces in one form or another. The tran- sition from 2D to 3D cell culture is a major step change. However, the development of polystyrene- based scaffolds will ease the impact this has because the substrate remains the same and it is only the geometry of the polystyrene substrate which has changed from 2D to 3D. Polystyrene scaffolds are also beneficial given that they are designed as a consumable product with a long shelf life and they are generally simple and inexpensive to mass produce. These attributes make poly- styrene-based scaffolds well suited for routine 3D cell culture.
Emulsion templating has been developed as a method to manufacture porous polystyrene that can subsequently be tailored to support 3D cell cul- ture17,18. Alvetex™ (Reinnervate) is a new prod- uct that utilises this technology resulting in a poly- styrene-based scaffold that has a uniform structure (Figure 2). The scaffold has been engineered into a thin 200 micron membrane to address the issue of mass transfer, enabling cells to enter the material
11 Fisher, JP, Jo, S, Mikos, AG, Reddi, AH (2004). Thermoreversible hydrogel scaffolds for articular cartilage engineering. J Biomed Mater Res A, 71, 268-74. 12 Park, Y, Sugimoto, M, Watrin, A, Chiquet, M, Hunziker, EB (2005). BMP-2 induces the expression of chondrocyte-specific genes in bovine synovium-derived progenitor cells cultured in three-dimensional alginate hydrogel. Osteoarthritis Cartilage, 13, 527-36. 13 Dillon, GP, Yu, X, Sridharan, A, Ranieri, JP, Bellamkonda, RV (1998). The influence of physical structure and charge on neurite extension in a 3D hydrogel scaffold. J Biomater Sci Polym Ed, 9, 1049-69. 14 Arias, AE, Bendayan, M (1993). Differentiation of pancreatic acinar cells into duct-like cells in vitro. Lab Invest, 69, 518-530. 15 Mikos, AG, Sarakinos, G, Leite, SM, Vacanti, JP, Langer, R (1993). Laminated three- dimensional biodegradable foams for use in tissue engineering. Biomaterials, 14, 323-30. 16Temenoff, JS, Mikos, AG (2000). Injectable
biodegradable materials for orthopedic tissue engineering. Biomaterials, 21, 2405-2412. 17 Bokhari, M, Carnachan, R, Przyborski, SA, Cameron, NR (2007). Effect of synthesis parameters on emulsion- templated porous polymer formation and evaluation for 3D cell culture scaffolds. J Mat Chem, 17, 4088-4094. 18 Carnachan, RJ, Bokhari, M, Przyborski, SA, Cameron, NR (2006). Tailoring the morphology of emulsion- templated porous polymers. Soft Matter, 2, 608-616. 19 Aydin, HM, El Haj, AJ, Piskin, E, Yang, Y (2009). Improving pore interconnectivity in polymeric scaffolds for tissue engineering. J Tissue Eng Regen Med, 3, 470-476.
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