Contractile Three-Dimensional Bioengineered Heart Muscle for Myocardial Regeneration
Wiley Periodicas, Journal of Biomedical Materials Research (2006): 719-731
Yen-Chih Huang, Luda Khait, Ravi K. Birla
Department of Biomedical Engineering (Section of Cardiac Surgery), The University of Michigan, Ann Arbor, Michigan

Bioengineered heart muscle (BEHM) is being investigated as a method of treatment for early stage congestive heart failure. Various methods are currently under investigation including biodegradable gels/hydrogels and synthetic scaffolds. One of the biggest limitations of these methods is trying to provide a controllable mechanical environment for the engineered tissue that is a close match to the physiological environment of the native tissue; often the tissue constructs lack the necessary mechanical strength under physiological conditions.

This study investigated the use of a biodegradable fibrin gel as a novel method to engineer functional three-dimensional heart muscle. The fibrin gel functions as a support matrix to promote the formation of three-dimensional heart muscle, which forms from the self-organization of primary cardiac cells. The fibrin has the advantage that it has controllable degradation kinetics, so the rate of its degradation can be matched to the rate of tissue formation. This is important because it allows for the cardiac cells to organize into tissue and then allows for the gradual transfer of mechanical forces in the native environment from the matrix to the tissue.

Primary cardiac myocytes were isolated from newborn rats, and then two methods were used to form the BEHM: the layering method and the embedding method. With the layering approach, cells were plated on the surface of a tissue culture plate coated with PDMS, followed by thrombin and fibrin. In the second method, cells were suspended with thrombin and fibrin and then plated on PDMS tissue culture plates. Both approaches resulted in a three-dimensional tissue construct of cardiac tissue within seven days, and in both cases the monolayer of cardiac cells delaminated due to the spontaneous contraction of the cells.

Overall, the investigators found that the layering approach was better for myotube formation, which is necessary for the formation of cardiac tissue. The cardiac cells spread more, and the cell monolayer underwent spontaneous contractions with a consistent frequency that resembled the regular contractions of native myocardial tissue. The cells that were embedded in the fibrin gel didn’t spread as much, which is likely why only isolated patches of cells underwent contractions.

The investigators also looked at mechanical strength of the BEHMs generated via the two methods. The plating density didn’t affect the stimulated active force for the constructs produced via the embedded method, but the plating density did significantly affect the force for constructs that were produced via the layering method (the lower the density, the higher the forces). Additionally, the investigators found that by changing the media daily, they were able to maintain the stimulated active force for a period of two months. Unfortunately, these measured forces for the BEHMs was much lower compared to the specific force of native thin cardiac muscle.

Because my interests lie in tissue engineering, I found this paper interesting. In particular, it was exciting to me because it presents a rather new approach to generate engineered tissue; there has already been tremendous research investigating the use of synthetic scaffolds and hydrogels. Because this method is so novel there is a huge amount of research to be done, targeting some of the major problems (including the lower forces generated by BEHMs as compared to native cardiac tissue as mentioned earlier). Despite the limitations, this method is an exciting potential alternative to scaffolds and hydrogels in tissue engineering of cardiac muscle.