Freezing-induced deformation of biomaterials in cryomedicine

Cryomedicine utilizes low temperature treatments of biological proteins, cells and tissues for cryopreservation, materials processing and cryotherapy. Lack of proper understanding of cryodamage that occurs during these applications remains to be the primary bottleneck for development of successful tissue cryopreservation and cryosurgery procedures. An engineering approach based on a view of biological systems as functional biomaterials can help identify, predict and control the primary cryodamage mechanisms by developing an understanding of underlying freezing-induced biophysical processes. In particular, freezing constitutes the main structural/mechanical origin of cryodamage and results in significant deformation of biomaterials at multiple length scales. Understanding of these freezing-induced deformation processes and their effects on post-thaw biomaterial functionality is currently lacking but will be critical to engineer improved cryomedicine procedures. This dissertation addresses this problem by presenting three separate but related studies of freezing-induced deformation at multiple length scales including nanometer-scale protein fibrils, single cells and whole tissues. A combination of rigorous experimentation and computational modeling is used to characterize post-thaw biomaterial structure and properties, predict biomaterial behavior and assess its post-thaw biological functionality. Firstly, freezing-induced damage on hierarchical extracellular matrix structure of collagen is investigated at molecular, fibril and matrix levels. Results indicate to a specific kind of fibril damage due to freezing-induced expansion of intrafibrillar fluid. This is followed by a study of freezing-induced cell and tissue deformation coupled to osmotically driven cellular water transport. Computational and semi empirical modeling of these processes indicate that intracellular deformation of the cell during freezing is heterogeneous and can interfere with cellular water transport, thereby leading to previously unconsidered mechanisms of cell freezing response. In addition, cellular water transport is identified as the critical limiting factor on the amount of freezing-induced tissue deformation, particularly in native tissues with high cell densities. Finally, effects of cryopreservation on post-thaw biological functionality of collagen engineered tissue constructs is investigated where cell-matrix interactions during fibroblast migration are considered as the functional response. Simultaneous cell migration and extracellular matrix deformation are characterized. Results show diminished cell-matrix coupling by freeze/thaw accompanied by a subtle decrease in cell migration. A connection between these results and freezing-induced collagen fibril damage is also suggested. Overall, this dissertation provides new fundamental knowledge on cryodamage mechanisms and a collection of novel multi-purpose engineering tools that will open the way for rational design of cryomedicine technologies

Cell-matrix Interactions During En Masse Cell Migration

Extended wound care, including prolonged treatment of burn injuries, acute and chronic wounds, is a significant source of patient discomfort and financial burden to public healthcare programs. Both accelerated healing and prevention of scar formation are highly desired but remain to be challenging to achieve. This is primary due to limited understanding of interactions between cells and the surrounding extracellular matrix (ECM) during wound healing. Particularly, collective migration of fibroblasts through provisional matrix, so called en masse migration, is one of these interactions that play a critical role in later stages of granulation tissue formation and wound closure. In addition to biochemical cues, mechanical properties of the tissue are recently being considered to play a significant role during these processes. In particular, both stiffness of ECM is suggested as important factors for single cell migration. However, it is still not clear how these mechanical factors affect bi-directional interactions between a group of fibroblasts and the ECM. In order to address this question, we performed measurements of fibroblast migration on collagen matrices where matrix stiffness was independently varied by controlling collagen concentrations. (Expected results) It was found that the extent of fibroblast migration increased as stiffness of substrate increased. The results of this study are useful to understand the mechanical interactions between cells and ECM during wound healing and have implications to development of new wound dressings for improved wound healing outcomes

Tumor-microenvironment-on-chip to Mimic Tumor Heterogeneity

Ductal Carcinoma In Situ (DCIS) is a non-invasive cancer that forms around breast milk ducts that can potentially progress into invasive breast cancer if untreated. Lack of models to study its diverse pathophysiology and differential response to treatments poses a challenge to develop standard treatment modalities with improved therapeutic outcomes. The traditional in vitro models such as cell monolayer are convenient but insufficient to represent the physiological characteristics of DCIS tumor microenvironment and often fail to predict clinical outcomes. The animal models effectively simulate the in vivo environment but also lack the ability to control the environmental parameters to match specific conditions making it difficult to address the heterogeneities in disease state and patient-to-patient variations. It is critical to develop a new DCIS model system that offers physiologically relevant features with high degree of control. In order to address this need, a novel microfluidic in vitro model was developed. A lumen structure to represent the milk duct in breast was generated along the microfluidic channel using a fluid dynamic phenomenon called viscous finger patterning in which as the less viscous fluid passes through, it leaves a continuous trail that makes a hollow tubular structure in the collagen hydrogel. Consequently, MCF-7 breast cancer cell lines were cultured along the lumen surface with BR5 stromal fibroblast in collagen hydrogel. A relatively straight, smooth lumen was achieved at a higher concentration of collagen gel by viscous finger patterning with an optimal flow rate. The interaction between a non-invasive breast cancer cell line, MCF-7 and stromal fibroblast most likely remain unchanged, thus mimicking the DCIS. This new model system is a potential tool to study DCIS progression and treatment response by offering physiologically relevant features that can be tailored to match disease state and patient specific conditions

Análisis y valoración del capital intelectual desarrollado por las maquiladoras del norte de Tamaulipas, México: el caso de Nuevo Laredo

Conocer la contribución que las Empresas extranjeras maquiladoras, ahora Industria Manufacturera, Maquiladora y de Servicios de Exportación (IMMEX) aportan a México. En la actualidad hay más de 5,000 empresas, generan 2´300,000 fuentes de trabajo directo, INEGI (2015). Aprovechando la integración económica y su situación geográfica del país continúan instalándose más. La IMMEX tiene su twin en el extranjero, por tal, un alto porcentaje de su producción se exporta. Son empresas globalizadas, favorecen así al país ingresando divisas. Para el caso de Nuevo Laredo, identificar el sector IMMEX que prodiga conocimiento, capacita y adiestramiento al personal, permitiendo así, conocer y manipular tecnología de última generación. La investigación y desarrollo propicia valor agregado, induce a innovar productos, las twins transfieren esa tecnología a su IMMEX. La competitiva y desarrollo se sustenta implantando procesos productivos y normas medio ambientales, ofreciendo seguridad dentro y fuera de la empresa, para identificase como Empresa Socialmente Responsable

[2]共同利用研究(平成10年度)

Contains supplementary text, figures and movie description

Least-squares spectral element solution of incompressible Navier-Stokes equations with adaptive refinement

Least-squares spectral element solution of steady, two-dimensional, incompressible flows are obtained by approximating velocity, pressure and vorticity variable set on GaussLobatto-Legendre nodes. Constrained Approximation Method is used for h- and p-type nonconforming interfaces of quadrilateral elements. Adaptive solutions are obtained using a posteriori error estimates based on least squares functional and spectral coefficient. Effective use of p-refinement to overcome poor mass conservation drawback of leastsquares formulation and successful use of h- and p-refinement together to solve problems with geometric singularities are demonstrated. Capabilities and limitations of the developed code are presented using Kovasznay flow, flow past a circular cylinder in a channel and backward facing step flow

Effects of F/T conditions on post-thaw denaturation temperature.

<p>‘*’ indicates significant difference (<i>p</i> < 0.05).</p

Recovery of collagen post-thaw thermal stability by use of cryoprotectant, DMSO.

<p>Recovery of collagen post-thaw thermal stability by use of cryoprotectant, DMSO.</p

Prediction of denaturation temperature decrease upon F/T by computational modeling.

<p>(A) The change in denaturation temperature upon hypothetical expansion of a tightly packed fibril (minimum porosity). (B) The amount of freezing-induced fibril expansion and change in denaturation temperature as a function of unfrozen fibril porosity.</p