Premature Rupture of the Fetal Membrane

Preterm labor is one of the leading and rising causes of infant mortality, and nearly 40% of these cases are linked with preterm premature rupture of membrane (pPROM). This is a debilitating condition that can sometimes be reversed by spontaneous sealing of the membrane which has been shown to be mediated by fetal macrophage recruitment and polarization. However, the role of mesenchymal cells in the recruitment and polarization of macrophages is not well understood, nor are the mechanical property changes the fetal membrane undergoes that may make it susceptible to rupture. Amnion-derived mesenchymal stem cells (MSCs) are a major constituent of the most loadbearing part of the fetal membrane, and understanding their differentiation, migration, and the soluble factors they release in response to the viscoplastic properties of their niche could be key to therapeutically addressing and perhaps preventing pPROM. Recent advances in biomaterial science have shown that specific mechanical properties of the extracellular matrix (ECM) can drive stem cell differentiation, signaling pathways, and remodeling of their environment. It has also been shown that the mechanical properties of the ECM change significantly in diseased versus normal states, independent of soluble signaling factors. The overarching hypothesis is that the viscoplastic properties of the ECM drive secretion of proteins from MSCs, which in turn affect recruitment of macrophages and in turn affects pPROM healing. Therefore, the specific aims of this project are to (1) investigate the viscoplastic property changes in the fetal membrane, (2) mimic those properties in RGD-functionalized alginate hydrogels to optimize wound healing, and then (3) assess the therapeutic effect of encapsulated MSCs on fetal membrane healing in vivo.

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Measuring Dynamic Nanoscale Forces in the Cellular Environment

Cellular mechanics play a major role in countless biological processes such as cell differentiation, cell migration, and immune cell programming, and yet, the techniques currently available to measure force vectors in biological materials and timescales are inadequate. Current methods rely on 2D-limited measurements such as atomic force microscopy (AFM) and nanoindentation, or measurements in 3D that incorrectly assume perfect material elasticity such as microrheology or traction force microscopy (TFM). However, for live cell imaging in 3D, these restrictions may obfuscate results as the environments are either biologically irrelevant or they do not directly measure the material mechanics in a quantitative manner. Most biological materials exhibit dissipation and rearrangement of polymeric architecture in response to forces in a time-dependent manner, and precise measurement of this process is of key importance as the degree of a tissue remodelability has been linked to various diseases, including migratory metastatic cancers as well as those originating from the bone marrrow. If we can precisely measure mechanical forces and quantify the remodeling, the complex interplay between cell phenotype and tissue mechanics will allow the development of methods for detection and treatment of disease.

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Keratinocyte Stem Cell Differentiation and Callus Formation as a Function of ECM Plasticity

Skin is the largest organ of the body and an incredibly complex material consisting of cells like keratinocyte stem cells differentiating and extruding adhesive proteins that form the composite enabling our existence. Without properly functioning skin, fetuses are often nonviable or development into adulthood is highly limited. Wound healing from even the most minor of injuries could be life-threatening. Callus formation is an accelerated case of keratinocyte differentiation, and several fatal disease states can be attributed to suboptimal expression of various ECM-associated proteins such as collagen and keratin. Though keratinocyte differentiation and callus formation has been previously investigated on the molecular biology level, little has been done to investigate both the ECM changes through the lens of materials science. Previous work with MSCs has shown ECM plasticity to have significant long-term effects on cell phenotype in the absence of induced shear forces, long after cells have started to remodel and extrude their own matrix. Using an alginate hydrogel system, we will encapsulate keratinocyte stem cells and independently control the stiffness, mesh size, and plasticity. The hypothesis being that layers of the skin present different viscoplastic properties, which would influence how repeated frictional forces exerted on skin can cause network rearrangement, driving keratinocyte differentiation. This project consists of three parts: mechanically characterizing the cellular/ECM composites, investigating how network plasticity affects the differentiation of keratinocytes, and adapting callus network architecture to improve the toughness of synthetic polymer materials.

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