Erin D. Grassl

Mechanisms of Stiffening and Strengthening in Media-Equivalents Fabricated Using Glycation

We have recently reported that glycation can be exploited to increase the circumferential tensile stiffness and ultimate tensile strength of media-equivalents (MEs) and increase their resistance to collagenolytic degradation, all without loss of cell viability (Girton et al., 1999). The glycated MEs were fabricated by entrapping high passage adult rat aorta SMCs in collagen gel made from pepsin-digested bovine dermal collagen, and incubated for up to 10 weeks in complete medium with 30 mM ribose added. We report here on experiments showing that ME compaction due to traction exerted by the SMCs with consequent alignment of collagen fibrils was necessary to realize the glycation-mediated stiffening and strengthening, but that synthesis of extracellular matrix constituents by these cells likely contributed little, even when 50 micrograms/ml ascorbate was added to the medium. These glycated MEs exhibited a compliance similar to arteries, but possessed less tensile strength and much less burst strength. MEs fabricated with low rather than high passage adult rat aorta SMCs possessed almost ten times greater tensile strength, suggesting that alternative SMCs sources and biopolymer gels may yield sufficient strength by compositional remodeling prior to implantation in addition to the structural remodeling (i.e., circumferential alignment) already obtained.

A Cryoinjury Model Using Engineered Tissue Equivalents for Cryosurgical Applications

Cryosurgery is emerging as a promising treatment modality for various cancers, but there are still challenges to be addressed to improve its efficacy. Two primary challenges are determining thermal injury thresholds for various types of cell/tissue, and understanding of the mechanisms of freezing induced cell/tissue injury within a cryolesion. To address these challenges, various model systems ranging from cell suspensions to three-dimensional in vivo tissues have been developed and used. However, these models are either oversimplifications of in vivo tissues or difficult to control and extract precise experimental conditions from. Therefore, a more readily controllable model system with tissue-like characteristics is needed. In this study, a cryoinjury model was developed using tissue engineering technology, and the capabilities of the model were demonstrated. Engineered tissue equivalents (TEs) were constructed by seeding and culturing cells in a type I collagen matrix. Two different cell lines were used in this study, AT-1 rat prostate tumor cells and LNCaP human prostate cancer cells. The constructed TEs underwent a freeze/thaw cycle imitating in vivo cryosurgery. Thermal conditions within TEs during freeze/thaw cycles were characterized, and the responses of TEs to these thermal conditions including freezing induced cellular injury and extracellular matrix damage were investigated at three different time points. The results illustrate the feasibility to establish thermal thresholds of cryoinjury for different cell/tissue types using the presently developed model, and its potential capabilities to study cell death mechanisms, cell proliferation or migration, and extracellular matrix structural damage after a freeze/thaw cycle.

CT Visualization and Histopathological Assessment of Cryoablation in Pulmonary Veins

Over 2 million adults in the United States are affected by atrial fibrillation (AF), a common cardiac arrhythmia that is associated with decreased survival, increased cardiovascular morbidities, and a decrease in quality of life. Atrial fibrillation can be initiated by ectopic beats originating in the myocardial sleeves surrounding the pulmonary veins [1]. Pulmonary vein (PV) isolation via radiofrequency ablation is the current gold standard for treating patients with drug-refractory AF [2]. However, cryoablation is emerging as a new minimally-invasive technique to achieve PV isolation. Cryoablation is fast gaining acceptance due to its minimal tissue disruption, decreased thrombogenicity, and reduced complications (RF can lead to low rate of pulmonary vein stenosis) [2]. One important question in regard to this technology is whether the PV lesion is transmural and circumferential and to what extent adjacent tissues are involved in the freezing process. As ice formation lends itself to image contrast in the body, we hypothesized that intraprocedural CT visualization of the iceball formation would allow us to predict the extent of the cryolesion and/or provide us with a measure of the adjacent tissue damage.Copyright