Cardiovascular

Curriculum Vitea

My lab at FIU, the “cardiovascular related disease and abnormalities engineering laboratory/ (the CARDAE lab)”, focuses on engineering approaches to and determining treatment strategies/solutions for medical conditions associated with the cardiovascular system. 

Specifically I am interested in:

1. In vitro tissue engineering strategies towards cardiovascular regenerative therapies and the study of tissue remodeling activity in vivo.
2. Biomechanical conditioning, including bioreactor design/development and the study of biochemical events that aid in engineered tissue formation.
3. Cellular magnetic resonance imaging (cMRI) techniques such as superparamagnetic iron oxide cellular labeling to assess cell fate in cell-based and regenerative medicine therapeutics.
4. Computational model development associated with moving cardiovascular boundaries to predict normal and altered stress fields in healthy and diseased tissue.

My immediate research interests focus on the development and application of methodologies that can be employed in the basic understanding and optimization of tissue engineered heart valves (TEHVs).  Specifically, I am focusing on the following themes (example research plans provided for 3) and 4) below):

1. Determining the best cell sources and scaffold materials for TEHV development.
   
   
2. The study of biomechanical and/or biochemical events that aid in engineered
   heart valve tissue formation.
   
   
3. The development/use of magnetic resonance imaging (MRI) and cellular MRI methods to provide noninvasive and nondestructive monitoring/assessment of engineered cardiovascular/musculoskeletal tissue and the cells from which they are derived, particularly when translating to in vivo models and clinical systems.
   
   
4. Computational fluid dynamic (CFD) models development to predict the effects of fluid-induced shear stresses on tissue formation.

EXAMPLE 1: I hypothesize that the importance of noninvasive and nondestructive monitoring of the cellular function within the developing valvular tissue is a critical aspect of implant success.  I thus propose an in-depth study on the longitudinal (temporal) position and migration patterns of cells during the tissue development process. This can be achieved through cMRI techniques such as with the labeling of cells with superparamagnetic iron oxide (SPIO) particles.  I wish to in particular conduct efficient, non-toxic, endosomal uptake studies of SPIO particles in bone marrow derived mesenchymal stem cells (BMSCs), human umbilical cord-derived progenitor cells (huc-dpcs), endothelial cells (ECs) and smooth muscle cells (SMCs) with a particular focus on extracellular matrix (ECM) production and differentiation capacity of these cell types after labeling.  The point to which these cell types, following SPIO labeling with appropriate concentrations of SPIO particles, remain viable and non-apoptotic, proliferate and if applicable differentiate to the preferred cell lineages, and produce ECM in comparison to unlabeled controls will be determined.  I have established previous experience in this area with respect to the SPIO-labeling of chondrocytes for cartilage tissue engineering applications as shown in Figs. 1 and 2 [1] below:

Figure 1: Abundant staining for proteoglycan (left) and collagen (right) derived from, SPIO-labeled chondrocytes in a nondegradable hydrogel scaffold [1].
 

Figure 2: 200 µm MRI slice (left) of SPIO-labeled chondrocytes (seen as dark spots) after 30 days of incubation, in correspondence to a 5 µm histological section (H&E stained) section taken from the same sample, at approximately same slice location [1].

The next step will involve longitudinal cMRI evaluation of cellular migration patterns of the cell types in vitro; first, at the scaffold level in static culture and subsequently dynamically under physiologically relevant flow conditions.  We will utilize a novel flow-stretch-flexure (FSF) bioreactor developed previously [2] to subject SPIO-labeled cell-seeded scaffolds to below normal, normal and above normal physiologically relevant flow fields and conduct intermittent longitudinal cMRI studies.  The exact scaffolds to be used will be determined from 1) above.  A modified MRI- compatible sample chamber of the FSF bioreactor will make it possible to conduct the cMRI experiments.

   Based on the in vitro studies, in vivo studies in either the porcine or ovine model can take place; this will involve TEHV implantation and longitudinal cMRI tracking of cell position and migration   In vivo longitudinal cellular distribution and tissue formation would be studied over the first 10 weeks following implantation, the duration in which most valve remodeling would occur. In this way, we would be able to noninvasively and nondestructively track and better understand changes in cell fate during in vivo tissue development.  In a similar manner, I am interested in performing studies with cMRI, focusing on cell populations involved in tissue engineered blood vessels as well.

EXAMPLE 2: I would like to develop CFD models to study the effects of the flow field on TEHV development.  Since part of the biomechanical conditioning event may cause samples to move through flexure and/or stretch states, I intend to use moving boundary methods to more accurately predict the flow field based on my previous experience in this area [3, 4].  Preliminary models I have performed in this work suggest that certain sample geometries and certain flow patterns such as oscillatory wall shear stress may be more conducive to tissue formation (see Fig. 2 [5]).  Moving boundary methods assume a priori knowledge of the sample motion and generally with TEHV leaflets, the sample motion can be quantified either by analytical approximations or empirically through high-speed image capture experiments.  These CFD models will provide insight into the precise nature of the flow field and how that changes with i) varying geometry ii) dynamic sample motion and iii) nature of the flow (pulsatile versus steady).  Accompanying experiments in the FSF bioreactor described in 2) coupled with the CFD results will help identify the specific nature of the fluid-induced stresses that optimizes tissue formation.  Subsequently a bioreactor system can be developed to maximize the occurrence of this specific flow environment so as to optimize TEHV formation.  Similarly I would also like to develop CFD models to study the effects of fluid-induced stresses on tissue engineered blood vessels.

Figure 4: CFD simulations showing high oscillatory shear effects on specimen inner wall under flexed states in rectangular strips of tissue engineering scaffolds [5].

References
1] Ramaswamy, S., et al., Tissue Engineering (Accepted, June 2009).
2] Ramaswamy S., et al., Flow-Stretch-Flexure Bioreactor (application #: 61119927),
US provisional patent, 12/04/2008.
3] Ramaswamy S., et al., Ann Biomed Eng. 2004 Dec;32(12):1628-41.
4] Ramaswamy S., et al., J Biomech Eng. 2006 Feb;128(1):40-8.
5] Ramaswamy S., et al., 8th World Biomaterials Congress: Crossing Frontiers in Biomaterials. and Regenerative Medicine, Amsterdam, The Netherlands, May 28th – June 1st 2008.