Summary of "Functional Tissue Engineered Valves from Cell-Remodeled Fibrin with Commissural Alignment of Cell-Produced Collagen "
Functional Tissue Engineered Valves from Cell-Remodeled Fibrin with Commissural Alignment of Cell-Produced Collagen
Paul S. Robinson, M.S., Sandra L. Johnson , B.S., Michael C. Evans, Ph.D., Victor H. Barocas, Ph.D., and Robert T. Tranquillo, Ph.D.
Tissue Engineer: Part A: Volume 14, Number 1, 2008
Summary:
The biomedical field has developed numerous devices to replace heart valves. These inert devices have their advantages, but scientists and engineers are trying to develop a heart valve replacement that will grow and adapt with an individual. This type of heart valve is especially important in pediatric patients whose hearts are still growing. This paper presents the work of a group of bioengineers at the University of Minnesota, Minneapolis, Minnesota, in their effort to develop a functional tissue-engineered heart valve replacement.
The paper first delineates the necessity for an adaptable heart valve replacement to supplant the present valve equivalents which are too inert to be effective in patients with growing hearts. To attend to this need, the bioengineers developed a method to tissue engineer a valve by using cells seeded into a gel in the form of a tubular mold. The device was designed to grow the cells so that the cells would align in such way that mimics the linearity of the cells in a real valve to maximize the effectiveness of the heart valve replacement. In past work, the group was unable to construct a valve equivalent that would withstand the stress experienced by a real heart valve due to a lack of supportive proteins in the extracellular matrix. In their present work, the group hoped to remedy this lack of strength by switching from collagen gels to fibrin gels.
The paper continues with a description of the group’s protocol. Human dermal fibroblasts were cultured in Dulbecco’s modified eagle medium in T-175 culture flasks. The cells were passaged when the cells were confluent. The cells were harvested at passage 9. The mold for the valve equivalent was made of polytetrafluoroethylene and had four parts; the plug, the upper and lower mandrels, and the outer housing. The size and shape of the mold was extracted from previous research. Cells mixed in with fibrin gel were then added to the mold and then cells were allowed to proliferate.
Figure 1. The mold for the valve equivalent.
The results of the procedure were successful. The team developed functional bi-leaflet and tri-leaflet valves. The cells in the leaflets of the valve equivalents were similarly aligned to the cells found in the leaflets of the native valve. Also, the valve equivalents were able to withstand stresses and pressures experienced by natural valves. However, problems did occur in the tri-leaflet valve after five weeks of culture. Due to excessive contraction, the valve failed at the root of the valve and thus could no longer function properly. As a result, the group’s results are focused on the bi-leaflet valve equivalent.
Significance:
This paper piqued my curiosity since I was searching for papers that used similar techniques we were learning in class. The protocol for the cell culture was different in that the team cultured hDF cells while we used 3T3 cells and Rex cells. The team also used eagle media instead of bovine growth media. Also, the cells were allowed to proliferate in a fibrin gel, but we proliferated our cells in agarose. In addition, when analyzing their data, the team used assays I was not aware of; the hydroxyproline assay of Stegeman and Stadler and a modified ninhydrin assay. I found the differences in the cell culture protocols enlightening as they showed me how different materials (different gels, cell types, and material surfaces) can lead to different physical properties (strength and doubling time) among cells.
Lastly, this research is significant because the development of functional tissue engineered valves brings the medical community one step closer towards their goal of a tissue-engineered heart.
2 comments:
The paper I reviewed also used fibrin gel for an injectable liver. In that paper the authors discussed the importance of the fibrin gel degrading while in vivo. The study you reviewed was in vitro, but did the authors mention the expected reaction to the fibrin gel in vivo or if there would be degradation of the gel? Also, you mentioned some interesting correlations between our work in the lab and the paper, for example the different cell type and the different gel, we found in our experiments that the 3T3's were not able to grow in the agarose gel, and in your paper they allowed the cells to proliferate in the fibrin gel. In relation to the previous question: could the cells grow to replace the fibrin gel in vivo and thus make an easy transition from a gel formation of a valve to a live valve, and did the authors mention possible issues with overgrowth of the cells?
Thanks Sydney for your comment. Here are my responses.
Did the authors mention the expected reaction to the fibrin gel in vivo or if there would be degradation of the gel?
The authors do mention an expected degradation of the gel. As cells grow in the fibrin gel, the cells produce collagen. This collagen ends up replacing the fibrin gel as the structural support for the cells. In terms of the expected reaction of the fibrin gel in vivo, to my understanding, the scientists have noted that the gel is expected to degrade while in vivo, however it is unclear to me whether the fibrin-based valve equivalents have been tested in vivo or if it is just speculation.
Could the cells grow to replace the fibrin gel in vivo and thus make an easy transition from a gel formation of a valve to a live valve, and did the authors mention possible issues with overgrowth of the cells?
In regards to whether the cells grow to replace the fibrin gel in vivo, the cells actually produce collagen to replace the fibrin gel. So the cells are not necessarily growing into the gel, but replacing the gel with the collagen they make. In terms of overgrowth of the cells, there was no mention of overgrowth in the article.
Thanks again for your comment, Sydney!
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