Aarash Sofla’s research while affiliated with University of Toronto and other places

We describe here a bioreactor capable of applying electrical field stimulation in conjunction with static strain and on-line force of contraction measurements. It consisted of a polydimethylsiloxane (PDMS) tissue chamber and a pneumatically driven stretch platform. The chamber contained eight tissue microwells (8.05 mm in length and 2.5 mm in width) with a pair of posts (2.78 mm in height and 0.8 mm in diameter) in each well to serve as fixation points and for measurements of contraction force. Carbon rods, stimulating electrodes, were placed into the PDMS chamber such that one pair stimulated four microwells. For feasibility studies, neonatal rat cardiomyocytes were seeded in collagen gels into the microwells. Following 3 days of gel compaction, electrical field stimulation at 3-4 V cm(-1) and 1 Hz, mechanical stimulation of 5% static strain or electromechanical stimulation (field stimulation at 3-4 V cm(-1), 1 Hz and 5% static strain) were applied for 3 days. Cardiac microtissues subjected to electromechanical stimulation exhibited elevated amplitude of contraction and improved sarcomere structure as evidenced by sarcomeric α-actinin, actin and troponin T staining compared to microtissues subjected to electrical or mechanical stimulation alone or non-stimulated controls. The expression of atrial natriuretic factor and brain natriuretic peptide was also elevated in the electromechanically stimulated group.

A novel method for fabrication of branched, tubular, perfusable microvessels for use in vascular tissue engineering is reported. A tubular, elastomeric, biodegradable scaffold is first fabricated via a new, double fusible injection molding technique that uses a ternary alloy with a low melting temperature, Field's metal, and paraffin as sacrificial components. A cylindrical core metal of 500 μm or lower dia-meter with the target branching scaffold geometry is first constructed, then the metal structure is coated with paraffin and, finally, the metal-paraffin construct is embedded in polydimethylsiloxane (PDMS). The paraffin layer is then removed by heating and replaced by a biodegradable elastomeric pre-polymer that is subsequently UV-cured inside the PDMS. Next, the metal core is melted away and the PDMS is removed to attain the branched tubular elastomeric biodegradable scaffold. Finally, it is also demonstrated that human umbilical vein endothelial cells (HUVEC) were able to spread on the surface of the scaffold and form a confluent monolayer, confirming the potential of this new technique for making engineered blood vessels.

The majority of available cardiomyocyte markers are intercellular proteins, limiting our ability to enrich live cardiomyocytes from heterogeneous cell preparations in the absence of genetic labeling. Here, we describe enrichment of live cardiomyocytes from the hearts of adult mice in a label-free microfluidic approach. The separation device consisted of a vertical column (15 mm long, 700 μm diameter), placed between permanent magnets resulting in a field strength of 1.23 T. To concentrate the field at the column wall, the column was wrapped with 69 μm diameter nickel wire. Before passing the cells through the column, the cardiomyocytes in the cell suspension had been rendered paramagnetic by treatment of the adult mouse heart cell preparation with sodium nitrite (2.5 mM) for 20 min on ice. The cell suspension was loaded into the vertical column from the top and upon settling, the non-myocytes were removed by the upward flow from the column. The cardiomyocytes were then collected from the column by applying a higher flow rate (144 μl/min). We found that by applying a separation flow rate of 4.2 μl/min in the first step, we can enrich live adult cardiomyocytes to 93% ± 2% in a label-free manner. The cardiomyocytes maintained viability immediately after separation and upon 24 h in culture.

High-gradient magnetic separation (HGMS) has attracted considerable attention in recent time, both experimentally and theoretically. It has established itself as a powerful technique for the manipulation of particles with magnetic properties. In the present study, analytical and numerical analysis of magnetic separation of cardiomyocytes (CMs) is presented. These enriched cells can be used for therapeutic or tissue engineering applications where no ?labeling? method is accepted. Calculation of applied magnetic force for these particles that can be rendered as paramagnetic inside column was performed in order to clarify the effect of magnetic field gradient on the accumulation possibility of these particles. Numerical solutions of 2D fluid-structure finite element methods are compared with semi-analytical results for combination of magnetic field strength and average flow.