In vitro human tissue engineered human blood vessels (TEBV) that exhibit vasoactivity can be used to test human toxicity of pharmaceutical drug candidates prior to pre-clinical animal studies. TEBVs with 400–800 μM diameters were made by embedding human neonatal dermal fibroblasts or human bone marrow-derived mesenchymal stem cells in dense collagen gel. TEBVs were mechanically strong enough to allow endothelialization and perfusion at physiological shear stresses within 3 hours after fabrication. After 1 week of perfusion, TEBVs exhibited endothelial release of nitric oxide, phenylephrine-induced vasoconstriction, and acetylcholine-induced vasodilation, all of which were maintained up to 5 weeks in culture. Vasodilation was blocked with the addition of the nitric oxide synthase inhibitor L-NG-Nitroarginine methyl ester (L-NAME). TEBVs elicited reversible activation to acute inflammatory stimulation by TNF-α which had a transient effect upon acetylcholine-induced relaxation, and exhibited dose-dependent vasodilation in response to caffeine and theophylline. Treatment of TEBVs with 1 μM lovastatin for three days prior to addition of Tumor necrosis factor – α (TNF-α) blocked the injury response and maintained vasodilation. These results indicate the potential to develop a rapidly-producible, endothelialized TEBV for microphysiological systems capable of producing physiological responses to both pharmaceutical and immunological stimuli.

We developed a microfluidic flow-control system capable of dynamically generating various flow patterns on demand. The flow-control system is based on novel magnetoactive sponges embedded in microfluidic flow channels. Applying a non-uniform magnetic field compresses the magnetoactive sponge, significantly reducing porosity and hydraulic conductivity. Tuning the applied magnetic field can dynamically vary the flow rate in the microfluidic channel. Pulsatile and physiological flow patterns with frequency between 1 and 3 Hz, flow rates between 0.5 and 10 μL/min and duration over 3 weeks have been achieved. Smooth muscle cells in engineered blood vessels perfused for 7 days aligned perpendicular to the flow direction under pulsatile but not steady flow, similar to the in vivo orientation. Owing to its various advantages over traditional flow-control methods, the new system potentially has important applications in microfluidic-based microphysiological systems to simulate the physiological nature of blood flow.

Microphysiological tissue engineering models of human skeletal muscle (myobundles) provide a platform to investigate the mechanism of muscle diseases and to study the response to drugs and toxins in vitro. To examine the dynamic response to drugs, which often take several days to induce responses, we developed a system to monitor the contractile force of the same human skeletal muscle myobundles over time before and after treatment with drugs. Myobundles were formed in series with Ecoflex films (platinum-catalyzed silicones) with embedded microbeads. The displacement of the microbeads in Ecoflex exhibited a linear relation between muscle force production and Ecoflex film stretch. Forces measured with the microbeads embedded in Ecoflex agreed well with simultaneous measurements with a force transducer. Application of the Hill model for the myobundles showed that the Ecoflex affected the magnitude of the response, but not the kinetics. After continuous exposure to 100 nM cerivastatin, both active and passive forces were reduced relative to controls after 2-4 days. The decline in force was associated with a decline in the muscle myofiber organization. The inhibitory effect of cerivastatin was reduced when 0.1-1 mM mevalonate was added with cerivastatin. Although addition of co-enzyme Q10 with cerivastatin inhibited degradation of sarcomeric α-actinin (SAA) in myoblasts, the contractile force still declined, suggesting that statin-induced myopathy was related to mevalonate pathway but the addition of co-enzyme Q10 was insufficient to overcome the effect of statins on the mevalonate pathway. Thus, cerivastatin rapidly induces myopathy which can be reversds with mevalonate but not co-enzyme Q10.

During three-dimensional culture of skeletal muscle in vitro, electrical stimulation provides an important cue to enhance skeletal muscle mimicry of the in vivo structure and function. However, increased respiration can cause oxygen transport limitations in these avascular three-dimensional constructs, leading to a hypoxic, necrotic core, or nonuniform cell distributions in larger constructs. To enhance oxygen transport with convection, oxygen concentrations were measured using an optical sensor at the inlet and outlet of an 80 μl fluid volume microphysiological system (MPS) flow chamber containing three-dimensional human skeletal muscle myobundles. Finite element model simulations of convection around myobundles and oxygen metabolism by the myobundles in the 80 μl MPS flow chamber agreed well with the oxygen consumption rate (OCR) at different flow rates, suggesting that under basal conditions, mass transfer limitations were negligible for flow rates above 1.5 μl s−1. To accommodate electrodes for electrical stimulation, a modified 450 μl chamber was constructed. Electrical stimulation for 30 min increased the measured rate of oxygen consumption by the myobundles to slightly over 2 times the basal OCR. Model simulations indicate that mass transfer limitations were significant during electrical stimulation and, in the absence of mass transfer limitations, electrical stimulation induced about a 20-fold increase in the maximum rate of oxygen consumption. The results indicate that simulated exercise conditions increase respiration of skeletal muscle and mass transfer limitations reduce the measured levels of oxygen uptake, which may affect previous studies that model exercise with engineered muscle.