Fabrication, Characterization, and Biocompatibility of Single-Walled Carbon Nanotube-Reinforced Alginate Composite Scaffolds Manufactured Using Freeform Fabrication Technique Eda D. Yildirim, Xi Yin, Kalyani Nair, Wei Sun Laboratory for Computer-Aided Tissue Engineering, Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, Pennsylvania 19104 Received 5 March 2007; revised 21 October 2007; accepted 13 December 2008 Published online 27 May 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.31118 Abstract: Composite polymeric scaffolds from alginate and single-walled carbon nanotube (SWCNT) were produced using a freeform fabrication technique. The scaffolds were characterized for their structural, mechanical, and biological properties by scanning electron microscopy, Raman spectroscopy, tensile testing, and cell–scaffold interaction study. Three- dimensional hybrid alginate/SWCNT tissue scaffolds were fabricated in a multinozzle biopolymer deposition system, which makes possible to disperse and align SWCNTs in the alginate matrix. The structure of the resultant scaffolds was significantly altered due to SWCNT reinforcement, which was confirmed by Raman spectroscopy. Microtensile testing presented a reinforcement effect of SWCNT to the mechanical strength of the alginate struts. Ogden constitutive modeling was utilized to predict the stress–strain relationship of the alginate scaffold, which compared well with the experimental data. Cellular study by rat heart endothelial cell showed that the SWCNT incorporated in the alginate structure improved cell adhesion and proliferation. Our study suggests that hybrid alginate/SWCNT scaffolds are a promising biomaterial for tissue engineering applications. ' 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 87B: 406–414, 2008 Keywords: tissue scaffold; tissue engineering; alginate; single-walled carbon nanotube (SWCNT); freeform fabrication INTRODUCTION Tissue engineering works on the principle of replacement of dead or diseased tissue with living tissues. It is an inter- disciplinary field, which applies the principles of engineer- ing and the life sciences toward the development of biological substitutes that restore, maintain, or improve tis- sue function. 1 Tissue engineering processes involve devel- opment of cell adhesion-specific material and fabrication of artificial three-dimensional (3D) matrices (scaffolds) to pro- vide the structural integrity similar to the natural extracellu- lar matrix (ECM). The scaffolds are then seeded with tissue-specific cells or stem cells from a patient’s normal tissue or donor. The biochemical signals or mechanical sig- nals or both are then provided for the differentiation of the cells into tissues. Ideally, the tissue will form and the scaf- folds will degrade leaving behind the regenerated tissue. 2 Various approaches are currently under investigation for exploring new biomaterials for better tissue regeneration. 3–16 It is necessary to build the scaffolds that mimic the mechani- cal and geometrical properties of the native tissue. The nanoscale biomaterials are the major candidate scaffold ma- terial, as they mimic properties of biological tissue in syn- thetic formulations. 17 The cells seeded on the nanoscale biomaterial surfaces tend to attach, migrate, proliferate, and differentiate better than conventional ones. 6,12,13,15,18–21 To match the biological and mechanical properties of natural tissue, researchers have looked into the possibility of using a composite material consisting of an appropriate polymer and a nanomaterial. One such nanoscale material with extensive application is the carbon nanotube. 22–32 Synthetic polymers like polylactic acid, polyglycolic acid, poly-lactic-co-glycolic acid, and polycaprolactone are used for the fabrication of tissue scaffolds. However, natu- ral materials are of considerable interest due generally to both their structural properties and superior biocompatibil- ity. In view of its eminent structural formability, good bio- compatibility with many living tissues, 33 and numerous applications in conventional scaffold fabrication, alginate, one typical hydrogel material, was selected as the scaffold Correspondence to: W. Sun (e-mail: sunwei@drexel.edu) Contract grant sponsor: NSF; contract grant numbers: 0427216, 0219176 ' 2008 Wiley Periodicals, Inc. 406