Page 38 - ASME_NEMB_2016_Program

Technical Program TRACK 3

na-Champaign, Urbana, IL, United States na-Champaign, Urbana, IL, United States, Sanjay Misra, Mayo
Clinic, Rochester, MN, United States, Steven Zimmerman, Hyun-
4:00pm On The Intrinsic Stress Fiber Contractile Forces In joon Kong, University of Illinois At Urbana-Champaign, Urbana, IL,
Semilunar Heart Valve Interstitial Cells United States

Technical Presentation. NEMB2016-6139 Inflammatory, leaky blood vessels are one of the primary characteristics of
vascular diseases, which remain a leading cause of disability and morbidity
Michael Sacks, Yusuke Sakamoto, University of Texas at Austin, worldwide. Early detection of pathologic vasculature leads to better ther-
apeutic outcomes, which has stimulated efforts to locate vascular defects
Austin, TX, United States using non-invasive imaging modalities such as magnetic resonance imaging
(MRI). However, the ability to locate leaky vasculature remains elusive, due
Heart valve interstitial cells (VICs) play a critical role in the maintenance and in part to the low sensitivity of MRI to imaging probes that could potentially
pathophysiology of heart valve tissues. Normally quiescent in the adult, VICs highlight such areas. This study demonstrates that superparamagnetic iron
can become activated in periods of growth and disease. When activated, oxide nanoparticle (SPION) clusters assembled to present an MR relaxivity
VICs exhibit increased levels of cytokines and extracellular matrix (ECM) approaching their theoretical maximal possible value can localize in the ex-
synthesis, and upregulated expression and strong contraction of α-smooth travascular space of leaky vessels and mark the region of interest in an MRI
muscle actin (α-SMA) fibers. However, it remains unknown how expression scan, even at doses 5-10 fold lower than those typically used in preclinical
and contraction of the f-actin augmented α-SMA fibers, which vary among studies. Such SPION clusters were prepared by packaging nanoparticles
different VIC types, contribute to the VIC mechanical function, including the with a hyperbranched, amphiphilic polyglycerol inspired by glycogen. We
nucleus and other cytoskeleton contributions. Moreover, our current under- suggest that the results of this study will greatly serve to expedite current
standing of VIC intracellular biophysical behavior results mainly from whole efforts to detect vascular diseases during early stages of their progression
cell imaging and whole-cell biomechanical studies. and ultimately improve quality of patient care.

To being to address these limitations, we recently developed a novel com- 4:50pm Enhancing Bone Augmentation by Mimicking the Hu-
putational model for VIC biomechanical behavior that incorporated 1) the
underlying 3D cytoskeletal network, 2) the oriented α-SMA stress fibers with man Osteogenic Niche
passive elastic and active contractile responses, 3) a finite deformable elas-
tic nucleus. We examined the respective mechanical responses of aortic and Technical Presentation. NEMB2016-6045
pulmonary VICs, which are known to have different levels of α-SMA expres-
sion levels and contractile behaviors. To calibrate the model, we simulated Silvia Minardi, Department of NanoMedicine, Houston Methodist
the combined mechanical responses of VICs in both micropipette aspiration Research Institute, Houston, TX, USA, Houston, TX, United States,
(MA) and atomic force microscopy (AFM) experiments. These two states Francesca Taraballi, Houston Methodist Research Institute, Hous-
were chosen as the VICs were under significantly different mechanical load- ton, TX, United States, Bruna Corradetti, Universita’ Politecnica
ing conditions and activation states, with the α-SMA fibers inactivated in the delle Marche, Ancona, Ancona, Italy, Jeffrey Van Eps, Fernando
MA studies while fully activated in the AFM studies. Our model predicted
that the substantial differences found in stiffening of the AVIC compared to Cabrera, Xin Wang, Bradley K. Weiner, Ennio Tasciotti, Houston
the PVICs was due to a 9 to 16 times stronger intrinsic AVIC α-SMA stress Methodist Research Institute, Houston, TX, United States
fiber contractile force.
Regenerative osteogenesis represents a major clinical need, as hundreds
In the present study, we extended this model to explore how the expression of thousands of patients are left with insufficient healing of bony defects
levels of F-actin and α-SMA change, and how the quantified 3D structure of related to multiple insults, as congenital abnormalities, traumatic injury or
the stress fibers and their contractile behaviors change and are influenced surgically-induced deficits. The limitations of the current devices and thera-
by the expression levels of F-actin and α-SMAs. Bulk cell mechanical re- peutic strategies, dictated the development of a plethora of synthetic graft-
sponses were obtained using a 5-micron diameter micro-indenter system. ing materials. The main advantages of off-the-shelf synthetic materials in-
An improved stress fiber contraction model with length-tension relationship clude: lower cost, biocompatibility, and biosafety, lower risk of rejection and
to study how the amount of these proteins within the cell can affect the simplification of the procedure to a single operation. A synthetic material
contractile behavior of stress fibers, using activation states controlled by that closely mimics the composition and structure of the human osteogenic
KCl concentration and TGF-b. We also explored the hypothesis that the niche represents great potential to successfully address this high demand.
total contraction strength linearly depends on the expression levels of co- Our approach to achieve these goals is biomimicry.
localized F-actin and α-SMA. Model results were verified with traction force In this study, we describe a material obtained through a biologically inspired
microscopy results and with the application of CytoD as a control to remove process, recapitulating bio-mineralization. The resulting magnesium-doped
the stress-fiber contractile function. Our complete VIC computational model hydroxyapatite/type I collagen scaffold was fully characterized by XRD, FTIR,
revealed treatment of TGF-b and KCl activates the VICs, increasing F-actin ICP and TGA, as well as its micro- and nano-structure and nano-mechani-
and α-SMA expression. Overall, activated VICs become stiffer due to: 1) cal properties, by AFM. We demonstrated mimicking of both the chemical,
greater expression of the stiffer F-actin stress fiber phase, 2) stronger net physical and morphological cues of human bone. The apatite phase nucle-
contractility of stress fibers, and 3) the addition of α-SMA fibers. The mag- ated on the collagen fibers presented the same composition and level of
nitude of traction in the TFM data was very similar to the cell contraction crystallinity of that of human trabecular bone. Human bone marrow-derived
strength estimated in this study. We are currently extending the model to mesenchymal stem cells were used to test the in vitro capability of the scaf-
account for observed loading rate dependence, which suggest the stress fold to promote osteogenic differentiation. Cells promptly adhered onto the
fibers are viscoelastic, which is critical to the high strain environment that the material, and were found completely reorganized few days after seeding.
VICs reside in the functioning heart valve. After 3 weeks of culture, a significant increase in the expression of osteo-
blastogenesis-associated markers (Spp1 and Bglap) was found. Finally, to
4:30pm Diagnostic Imaging of Vascular Defects Using assess its in vivo osteoinductive potential, the scaffold was implanted in an
Nanoclusters with Maximum Theoretical Magnetic Resonance ectopic model in rabbit, where most osteogenic stimuli, such as cytokines,
Relaxivity bone cells and mechanotransduction are lacking (or significantly reduced).
Remarkably, a striking mass of trabecular bone formed on the volume of
the implanted scaffold (approximately 2 cm x 1 cm x 1 cm). This result was
Technical Presentation. NEMB2016-6106 achieved in only 2 weeks, which is a third of the time usually necessary for
38 scaffolds to produce bone-like tissue. Furthermore, we showed that the
Cartney Smith, Kala Pharmaceuticals, Waltham, MA, United States, remodeling and maturation of this new bone mass initiated as early as 6
Dawn Ernenwein, Nicholas Clay, University of Illinois At Urba- weeks after implantation.