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IGERT Profiles
Krystyn J. Van Vliet is presently the Thomas Lord Assistant
Professor of Materials Science and Engineering at MIT, with a joint appointment
in Bioengineering. Van Vliet earned her Sc.B. and Ph.D. in Materials Science
and Engineering at Brown University (1998) MIT (2002), respectively, then completed
postdoctoral studies in the Vascular Biology Program at Children's Hospital
Boston. Van Vliet's thesis and postdoctoral work focused on nanoscale mechanics
of defect nucleation in metallic crystals and in vascular tissues, respectively.
Though disparate in chemical complexity, crystalline and biopolymeric materials
undergo phase transitions that can be induced and studied under nanoscale forces
and displacements. Her current group, the Laboratory for Material Chemomechanics,
focuses on multiscale measurement and computational prediction of the fundamental
mechanisms of coupling between chemical and mechanical states of materials
ranging from synthetic crystals to biological organisms. One application of
this approach is directed modulation of tissue and microbial cell functions,
through physical and mechanical cues rather than solely through chemical stimuli.
Van Vliet directs the Nanomechanical Technology Laboratory, a shared experimental
facility in the MIT Department of Materials Science and Engineering.
Abstract: Chemomechanics of Cell-Material
Interactions
Krystyn Van Vliet, Ph.D.
It is increasingly appreciated that both the chemical and mechanical states
of cells and molecules are strongly coupled. For example, we and others have
shown that the stiffness of the substrata underlying adherent cells is correlative
with the efficiency of adhesion, proliferation, and differentiation potential
of tissue cells. Although the mechanisms are incompletely understood, this
chemomechanical coupling is generally considered to involve force transmission
from the extracellular matrix materials through cell surface receptors associated
with the internal cytoskeleton. Here, we discuss our recent experimental and
multiscale computational work in the use of nanoscale contact to map the chemomechanical
response of amorphous polymers that serve as cell substrata, of living biological
cell surfaces, and of individual molecular ligand-receptor complexes. Together,
these results indicate that kinetics of reversible adhesion between the cell
and polymeric substrata depend directly on the thickness and stiffness of that
substratum. We have applied these results to predict, control, and model the
function of tissue cells adhered to chemomechanically defined materials; and
to demonstrate why prokaryotic cells such as bacteria also exhibit mechanoselective
adhesion.
Mariah Hahn graduate from UT Austin in Chemical Engineering in 1998. Her
PhD research with Robert Langer focused on tissue engineering strategies for
vocal fold regeneration. Her postdoctoral research with Dr. Jennifer
West at Rice University expanded her research focus to include bioreactor based-vascular
tissue engineering and control over scaffold properties at the microscale.
She joined Texas A&M's department of Chemical Engineering in 2005. Her
research focuses on systematic examination of the impact of material properties
and mechanical cues on internal cellular signaling toward rational scaffold
design.
Abstract: Toward Rational Scaffold Design
for Tissue Engineering Vascular Graft Applications
Mariah Hahn
A fundamental understanding of the cell responses invoked by specific scaffold
material properties is critical for the rational design and selection of tissue
engineering scaffolds. Systematic investigation of cell-material interactions
requires the ability to control scaffold properties at the microscale as well
as insight into the impact of material property alterations on internal cell
signaling. Results for our laboratory’s efforts at rational scaffold
design will be discussed in the context of tissue engineered vascular grafts.
Specifically, scaffold property modulation of the serum response factor pathway,
a signaling pathway critical to vascular smooth muscle cell differentiation
will be explored.
Abstract: Optical Spectroscopy and Imaging in Early Cancer Detection
James W. Tunnell
Histopathologic analysis, requiring tissue excision and processing, is the
current gold standard in the clinical diagnosis of precancerous and cancerous
tissue. This process is inherently invasive, time-consuming and subject to
inter-observer agreement. Therefore, there is an increasing interest in quantitative
optical sensing and imaging strategies to determine tissue morphology and function in
vivo (i.e. without the need for tissue removal). This presentation focuses
on recent developments of in vivo optical techniques for both spectroscopic
sensing and imaging of precancerous changes in tissue. These techniques include
fiber-based optical spectroscopy, contrast enhancement using nanoparticles,
and hyper-spectral imaging.
Dr. Laura Niklason is an Associate Professor of
Anesthesia and Biomedical Engineering at Yale. She received her Bachelors
degrees in Physics and Biophysics from the University of Illinois, and
went on to the University of Chicago for her PhD in Biophysics in 1988. Dr.
Niklason subsequently received her MD from the University of Michigan,
where she did her internship. She then went on to the Massachusetts General
Hospital for residency in Anesthesia, followed by fellowship training
in Critical Care Medicine. During her time in Boston, Dr. Niklason
was also a post-doctoral researcher at MIT with Dr. Robert Langer, where she
developed techniques for the tissue engineering of autologous arteries. Dr.
Niklason joined the faculty at Duke University in 1998, where she continued
her work in cardiovascular tissue engineering, and founded a biotechnology
company designed to bring tissue engineered cardiovascular products to the
clinic. Dr. Niklason has received
national and international recognition for her work in this field, receiving
the Discover Magazine award for Technological Innovation in 2000, and
being named a Hunt Scholar in the Duke School of Engineering in 2001. In
January of 2006, Niklason moved to Yale University, where she is expanding
her research program in tissue engineering and in understanding the basic
aspects of cellular aging.
Currrently, Dr. Niklason’s research program has several areas of focus. With
regard to engineered arteries, Niklason is engaged in preclinical studies in
large animals to validate the method for generating engineered tissues that
are available “off the shelf”. Large animal studies on vascular
grafts are centered on immune/inflammatory response minimization to these off-the-shelf
tissues, and on the long-term function of the grafts in the arterial circulation. In
addition, Niklason is developing tissue engineering approaches to generating
vascularized cardiac muscle, as well as vascularized lung tissue. In
addition, Niklason has active research interests in vascular remodeling
that is associated with various disease states, including atherosclerosis and
arterial vasospasm.
Prospects for Human Vascular Tissue Engineering?
Laura Niklason, M.D., Ph.D.
Regenerative medicine strategies often rely on cells to repair or replace
damaged tissues. But the capacity of differentiated cells to regenerate
functional tissues is adversely affected by aging. Indeed, a high proportion
of tissue engineering applications that have been clinically successful – i.e.
venous reconstruction, bladder replacement – have been applied in children,
using cells derived from these youthful subjects. However, the vast majority
of patients who need tissue replacements are elderly. Many investigators
have developed tissue engineering technologies using cells that are derived
from young animals, with the hopes of being able to extend these technologies
to cells from elderly humans. Our initial work in arterial regeneration exploited
cells derived from young animals, which we have shown could be used to “grow” new
arteries that are functional in these same animals. However, our initial
attempts to translate these strategies to cells derived from elderly humans
have met with important stumbling blocks. Specifically, we have shown
that limitations in cellular replicative lifespan are an important limitation
for tissue engineering in the elderly, but that this roadblock can be partially
overcome by gene therapies to increase telomere length. However, increases
in cell lifespan do not de facto reverse all of the consequences of cellular
aging. If autologous cells are to be used to re-grow tissues, it is likely
that, in many cases, a “younger” cell source will have to be identified. This
has led our group to investigate the functional utility of adult stem cells
for vascular reconstruction. While preliminary results are promising,
we have yet to understand whether adult stem cells are immune to the
adverse effects of human aging.
Kinetic and Spatial Analysis of Intracellular Signal Transduction Networks
Jason Haugh, Department of Chemical and Biomolecular Engineering
North Carolina State University
An ongoing challenge in mammalian cell biology is to bridge the gaps in our understanding of processes at the molecular, cellular, and tissue levels. Central to the hierarchy of biological complexity is the field of signal transduction, which deals with the biochemical mechanisms and pathways by which cells respond to external stimuli, such as soluble growth factors/cytokines, immobilized ligands such as those found in extracellular matrix or the surfaces of other cells, and mechanical forces. Intracellular signaling processes control the growth, survival, and migration of cells in normal physiological contexts, and defects in signaling form the molecular basis for cancer, immune system disorders, and other diseases. Using a quantitative approach that combines biochemical measurements, live-cell fluorescence microscopy, and mathematical modeling, we seek to characterize signal transduction networks through analysis of their kinetics and spatial patterns in cells. Based on analysis of experimental data and informed where appropriate by knowledge of protein domain structure, mechanistic models are developed that may be embedded (in coarse-grained form) in mathematical representations of cell population dynamics, with the goal of evaluating hypotheses regarding the concerted responses of cells in tissues.
As an example of this approach, our efforts to characterize signal transduction mediated by cell surface receptors for platelet-derived growth factor (PDGF), a soluble factor that accelerates dermal wound healing by directing the migration and proliferation of dermal fibroblasts, will be described in two parts. In the first part of the talk, I will describe spatial modeling and subcellular characterization of the signaling mechanism by which fibroblasts sense PDGF gradients, which in turn has led us to analyze tissue-scale models of wound invasion driven by such gradients. The second part of the talk will cover the elucidation and kinetic characterization of the so-called crosstalk interactions between two canonical signaling pathways strongly activated by PDGF receptors (Ras/Erk and PI 3-kinase), which has moved us towards predictive modeling at the level of signal transduction networks.
Histotripsy: Controlled Mechanical Sub-Division of Soft Tissues by High Intensity Pulsed Ultrasound
Charles A. Cain
Department of Biomedical Engineering, University of Michigan, Ann Arbor, USA
Our primary research goal is to develop a non-invasive image-guided ultrasound procedure for precise and effective tissue ablation for the treatment of many malignant and nonmalignant tumors. Current thermally based local ablation techniques have inherent limitations: (1) lack of reliable imaging feedback for targeting and lesion detection; (2) lack of precision often resulting in damage to the intervening and surrounding tissue; and (3) extensive treatment times for tumors larger than 3cm. We have developed a new local ablation technique that addresses these limitations. This technique, which we call histotripsy, produces mechanical tissue fractionation using successive high intensity ultrasound pulses. These pulses form mircobubbles and the energetic microbubble activity (acoustic cavitation) that fragments and subdivides tissue structures. Our data show that histotripsy results in complete cellular disruption of treated volumes while preserving adjacent tissues, often leaving intact cells within microns of completely disrupted (fractionated) tissue. The level of tissue ablation depends on the histotripsy acoustic parameters (e.g., pulse intensity, pulse repetition frequency, and the number of pulses). Ultrasound imaging of histotripsy generated bubbles was used successfully for targeting and real-time monitoring of the treatment progress, and histotripsy generated lesions were clearly mapped using ultrasound and magnetic resonance imaging (MRI). Moreover, the imaging information promises to give reliable information on clinical outcome immediately after (or possibly during) treatment informing a clinician when a volume has been sufficiently treated.
Polymeric Micelles for Combination Drug Delivery
Glen S. Kwon, Pharmaceutical Sciences Division
School of Pharmacy, University of Wisconsin
Amphiphilic block copolymer (ABC) micelles have been widely studied as nanoscopic vehicles for potent yet poorly water-soluble drugs in pre-clinical and clinical settings for life-threatening diseases, such as systemic fungal disease and cancer. Poly(ethylene glycol)-block-poly(-hydroxy acid)s and poly(ethylene glycol)-b-poly(-amino acid)s are two major classes of ABC micelles in the field of drug delivery. Poly(ethylene glycol)-b-poly(-hydroxy acid) micelles solubilize paclitaxel, rapamycin, and 17-allyl-amino-17-demethoxygeldanamycin, very poorly water-soluble drugs, requiring drug solubilization. Poly(ethylene glycol)-b-poly(-amino acid) micelles have pH-sensitive linkages for poorly water-soluble drugs, aiming for tumor-selective drug release. Both classes of ABC micelles permit a combination of poorly water-soluble drugs in the same aqueous vehicle for concurrent intravenous infusion, aiming for synergistic drug effects. In the latter case, mixed ABC micelles have been prepared from a conventional chemotherapeutic drug and a signal transduction inhibitor, aiming for a synergistic effect that might be enhanced an identical pharmacokinetic profile, identical tumor uptake, and identical or sequential pattern of drug release. Polymeric micelles offer exciting flexibility for combination drug delivery for poorly water-soluble compounds used to combat life-threatening diseases.
Correlation Between Extracellular Matrix Stiffness, Intracellular Viscoelastic Properties, and Invasive Ability of Cancer Cells
Erin L. Baker, Muhammad H. Zaman, and Roger T. Bonnecaze
Tumors exhibit elevated stiffness compared to normal tissue, and some aspects of tumor cell invasive ability are in part governed by extracellular matrix (ECM) stiffness. Yet neither the relationship between ECM stiffness and intracellular mechanical properties, nor that between intracellular mechanical properties and invasive ability, is well understood. In order to establish these relationships quantitatively, we employ particle-tracking microrheology to investigate the intracellular viscoelastic properties of single cancer cells that are attached to two-dimensional (2D) substrates, as well as those that are embedded within three-dimensional (3D) matrices. While particle-tracking rheological protocols have been established, these techniques have yet to be applied in linking the cytoplasmic mechanical environment of cancer cells to their invasive ability. Specifically, the intracellular mechanical properties of elasticity, viscosity, and compliance of human prostate cancer (PC-3) cells and transformed human breast cancer (MCF-10A) cells of varying invasive ability are extracted from Brownian motions of individual 1.0μm polystyrene spheres that are ballistically delivered to their cytoplasm. Results indicate that the cytoplasmic mechanical environment of PC-3 cells attached to a 2D substrate is non-homogenous, independent of matrix stiffness. Furthermore, the heterogeneously varying intracellular viscoelastic properties show a strong correlation with matrix chemistry and mechanical architecture. These viscoelastic properties are also shown to correlate with the invasiveness of the cancer cells.
Metal-Polymer Composites as Externally-Controlled Intelligent Therapeutic Systems
Martin Gran
Delivery of therapeutics via externally-triggered intelligent nanocarriers can increase the quality of life of patients by controlling the time and location of delivery, thereby lowering systemic doses and related side effects. The metal-polymer nanocomposites composed of a metal core and a surrounding temperature-sensitive polymer layer can be triggered to release encapsulated therapeutics upon exposure to an external light source. Metal nanoparticle or nanoshell cores can be tuned to absorb light at wavelengths ranging from visible to near-infrared. Absorbed light is converted to heat, inducing a size transition in the polymer layer causing encapsulated agents to be released.
Gold nanoparticles have been incorporated within an interpenetrating polymer network (IPN) composed of poly(acrylic acid) and poly(acrylamide). The nanocomposites are synthesized using a two-step water in oil emulsion polymerization with a cyclohexane continuous phase, where two aqueous premixes are added and reacted separately, the first premix containing acrylamide, and the second acrylic acid. Gold nanoparticles are added with the first aqueous premix and incorporated in the aqueous droplet phase. Additional temperature responsive polymers continue to be investigated for use in the system and future work includes the addition of targeting ligands and studies of the biocompatibility of the nanocomposite systems.
Photodissociation Mass Spectrometry of Biological Molecules
Jennifer S. Brodbelt, Department of Chemistry and Biochemistry
The University of Texas at Austin
As our understanding of genomics, proteomics, and glycomics continues to evolve, the ability to address increasingly difficult biological questions depends on the identification of biological molecules in complex mixtures with high sensitivity and minimal sample consumption. In this context, the tremendous growth in the application of tandem mass spectrometry for detection, quantification and characterization of biological molecules has spurred the exploration of new ion activation/dissociation methods for structural characterization of biological molecules. Although collisionally activated dissociation remains the gold standard, it has several shortcomings (e.g. insufficient energy deposition, limited applicability for pinpointing post-translational modifications in peptides, etc.) that have stimulated the search for other activation methods, such as electron capture dissociation and photodissociation. Photoactivation entails using a laser to irradiate gas-phase ions with photons, thus increasing their internal energy and promoting diagnostic cleavages that allow identification of biological molecules whose sequences and structures are unknown. The ability to vary energy deposition based on variation of irradiation time or photon flux makes PD a "tunable" activation method. This presentation will describe the use of both infrared and UV lasers for mass spectrometric characterization of biological molecules, along with novel chemical derivatization methods to add chemical selectivity or enhance absorptivities of molecules.
Eduardo J. Juan received a BSEE degree from the University of Puerto Rico – Mayagüez (UPRM), in 1997, and a Ph.D. degree in electrical and computer engineering from Purdue University in 2001. Currently, he is an Associate Professor of Electrical and Computer Engineering at the University of Puerto Rico – Mayagüez, where he teaches courses in control systems and biomedical engineering. His research interests include medical instrumentation, biomedical acoustics, and biosensors. Dr. Juan is the director of the Medical Devices Research Group (MDRG) at UPRM, and is co-founder and scientific advisor of SonarMed Inc., a medical device start-up company recently established in the state of Indiana.
Acoustical Guidance of Indwelling Tubes and Catheters
Eduardo J. Juan, PhD, PE, Associate Professor of Electrical and Computer Engineering
University of Puerto Rico - Mayagüez
For many centuries, tubes and catheters have been used in medicine to deliver medications, for drainage, to maintain patency of biological conduits, for imaging body structures, and for the deployment of therapeutic devices. In many instances, knowing the position and patency of these tubes and catheters is of significant clinical relevance. Preferred positioning methods include the use of x-rays and ultrasound, which provide excellent resolution, but have limitations if continuous monitoring of tubes and catheters is desired. Time-domain acoustic reflectometry is presented as an alternative method to guide, position, and continuously monitor tubes and catheters used in either air or liquid filled biological conduits.
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