A Bioreactor to Apply Multimodal Physical Stimuli to Cultured Cells

Consecutive-Day Ventricular and Atrial Cardiomyocyte Isolations from the Same Heart: Shifting the Cost-Benefit Balance of Cardiac Primary Cell Research

Freshly isolated primary cardiomyocytes (CM) are indispensable for cardiac research. Experimental CM research is generally incompatible with life of the donor animal, while human heart samples are usually small and scarce. CM isolation from animal hearts, traditionally performed by coronary artery perfusion of enzymes, liberates millions of cells from the heart. However, due to progressive cell remodeling following isolation, freshly isolated primary CM need to be used within 4-8 h post-isolation for most functional assays, meaning that the majority of cells is essentially wasted. In addition, coronary perfusion-based isolation cannot easily be applied to human tissue biopsies, and it does not straightforwardly allow for assessment of regional differences in CM function within the same heart. Here, we provide a method of multi-day CM isolation from one animal heart, yielding calcium-tolerant ventricular and atrial CM. This is based on cell isolation from cardiac tissue slices following repeated (usually overnight) storage of the tissue under conditions that prolong CM viability beyond the day of organ excision by two additional days. The maintenance of cells in their near-native microenvironment slows the otherwise rapid structural and functional decline seen in isolated CM during attempts for prolonged storage or culture. Multi-day slice-based CM isolation increases the amount of useful information gained per animal heart, improving reproducibility and reducing the number of experimental animals required in basic cardiac research. It also opens the doors to novel experimental designs, including exploring same-heart regional differences.

Electrophysiological Stimulation of Whole Heart Constructs in an 8-Pole Electrical Field

Today 2D and 3D electrophysiological stimulation represents a well established concept to enhance myocardial development and maturation in tissue-engineered constructs. However, electrical field stimulation has never been adapted to complex whole heart constructs (WHC). This study demonstrates the impact of three-dimensional electrophysiological stimulation of tissue-engineered WHC in a custom made eight-pole electrical field stimulation system by short model cultivations with neonatal rat cardiomyocytes (CM). Therefore, WHC were generated by repopulation of decellularized rat hearts with neonatal CM and subjected to perfusion based cultivation with or without additional biophysicalstimulation for 96 h. Spontaneous electrophysiological (EP) activity of the processed WHC was analyzed by qualitative evaluation of multielectrode assay (MEA) signal sequences, descriptive comparative spike sorting, and direct contrasting assessment in simple numerical quantities complemented by impulse response tests after phasing out spontaneous EP activity. As strong reduction of voltage signals by the decellularized extracellular matrix (ECM) component of WHC was observed, the active principle was determined and used to estimate the spectrum of source signals to recorded values by calculative elimination. Western blotting of key myocardial markers was employed to substantiate the functional EP evaluation by classical biochemical analysis. We observed stable spontaneous EP activity showing clear R and S, but predominantly rS patterns, for both stimulated WHC and non-stimulated controls. By the impact of stimulation, mean voltage amplitudes and beating frequencies could be significantly increased. The active principle of signal reduction in decellularized ECM could be shown to follow a nonlinear damping function with remarkable accuracy, illustrating that recorded signals of moderate voltage amplitudes can also represent far-field measurements of strong signals that are emitted in distant depths of the ECM while small amplitudes are limited to actually represent also rather weak source-signals. After phasing out spontaneous activity, both stimulated WHC and non-stimulated controls could be excited again to emit immediate impulse responses. The observed beneficial impact of 8-pole field stimulation on functional EP activity could finally be validated on the biochemical level by showing increased ratios for myosin heavy chain, cardiac tropnin T, desmin, and connexin 43 for stimulated WHC by Western blot analysis. In conclusion, we found that although electrophysiological stimulation has been incorporated into the whole heart tissue-engineered concept from the very beginning, this study presents for the first time a concept for the transfer of electrical field stimulation to the whole heart tissue-engineered approach. Furthermore to the best knowledge of the authors, this is the first control-based study showing a comparative investigation of electrophysiological stimulation of whole heart constructs.

Real-Time Bioluminescence Imaging of Cell Distribution, Growth, and Differentiation in a Three-Dimensional Scaffold Under Interstitial Perfusion for Tissue Engineering

Bioreactor systems allow safe and reproducible production of tissue constructs and functional analysis of cell behavior in biomaterials. However, current procedures for the analysis of tissue generated in biomaterials are destructive. We describe a transparent perfusion system that allows real-time bioluminescence imaging of luciferase expressing cells seeded in scaffolds for the study of cell-biomaterial interactions and bioreactor performance. A prototype provided with a poly(lactic) acid scaffold was used for "proof of principle" studies to monitor cell survival in the scaffold (up to 22 days). Moreover, using cells expressing a luciferase reporter under the control of inducible tissue-specific promoters, it was possible to monitor changes in gene expression resulting from hypoxic state and endothelial cell differentiation. This system should be useful in numerous tissue engineering applications, the optimization of bioreactor operation conditions, and the analysis of cell behavior in three-dimensional scaffolds.