Conductive polymers, such as polypyrrole, have recently been studied as potential surfaces/matrices for cell- and tissue-culture applications. We have investigated the adhesion and proliferation properties of H9c2 cardiac myoblasts on a conductive polyaniline substrate. Both the non-conductive emeraldine base (PANi) and its conductive salt (E-PANi) forms of polyaniline were found to be biocompatible, viz., allowing for cell attachment and proliferation and, in the case of E-PANi, maintaining electrical conductivity. By comparison to tissue-culture-treated polystyrene (TCP), the initial adhesion of H9c2 cells to both PANi and E-PANi was slightly reduced by 7% (P < 0.05, n = 18). By contrast, the overall rate of cell proliferation on the conductive surfaces, although initially decreased, was similar to control TCP surfaces. After 6 days in culture on the different surfaces, the cells formed confluent monolayers which were morphologically indistinguishable. Furthermore, we observed that E-PANi, when maintained in an aqueous physiologic environment, retained a significant level of electrical conductivity for at least 100 h, even though this conductivity gradually decreased by about 3 orders of magnitude over time. These results demonstrate the potential for using polyaniline as an electroactive polymer in the culture of excitable cells and open the possibility of using this material as an electroactive scaffold for cardiac and/or neuronal tissue engineering applications that require biocompatibility of conductive polymers.

4Although the application of bioengineered 3D in-vitro tissue models in pharma ceutical research is in its infancy, the interdisciplinary approach and the achievements described in this chapter provide an encouraging fi rst step towards the accelerated development of such models for drug discovery.

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Cardiovascular diseases account for more deaths than any other illness. Cardiac tissue engineering has turned to embryonic stem cells as a renewable source of myocytes for use in tissue replacement. Existing methods for stem cell differentiation toward the cardiac lineage are relatively non-specific, yielding low numbers of myocytes with varying contraction frequencies and strengths. Here we describe novel experimental approaches, utilizing an electrical stimulation regimen, aimed at increasing the efficiency of cardiac differentiation from mouse embryonic stem (mES) cells. These methods generate cardiac myocytes with functional characteristics that more closely resemble native tissues. The amplitude, duration, and frequency of the electrical stimulus as well as the timing of its onset are some of the critical experimental parameters that determine the enhancement of cardiac differentiation.In order to form embryoid bodies, an optimum differentiation regime was followed incorporating the hanging drop method followed by suspension culture and subsequent post-plating on conductive slides with electrical stimulation. Approximately three times more stimulated mES cells exhibited evidence of cardiac differentiation than their non-stimulated counterparts, as determined by the expression of ventricular marker myosin light chain-2v. Spontaneous contractions of the stimulated cell populations began up to 1 day earlier and had an average beat frequency close to that of the stimulus applied during differentiation. The spontaneously contracting regions had larger areas of contraction, which beat more rhythmically, as determined by real-time digital imaging analysis.Our results suggest that appropriate electrical stimulation generates greater numbers of more robust cardiac myocytes, which in turn may be better suited for repairing or regenerating an ailing heart and for use as 3D model systems for drug discovery.