Control of Fibroblast Differentiation in Acoustically-Responsive Scaffolds using Ultrasound-Induced Matrix Stiffening

Abstract

Cells respond to biochemical and biomechanical cues (e.g., stiffness) from the surrounding extracellular matrix (ECM). Cellular differentiation into more specialized cell types is a common cellular response intimately related to these cues. Regenerative medicine often employs implantable hydrogel scaffolds as surrogates of the native ECM and as carriers of biomolecules and cells. The mechanical properties of hydrogels are conventionally designed a priori and are often static and uniform. That is to say, the mechanical properties cannot be dynamically controlled following implantation in a user-defined, on demand manner. The Fabiilli lab utilizes specialized composite hydrogel scaffolds that have mechanical characteristics that can be modulated when focused ultrasound (FUS) is applied. These scaffolds, termed acoustically-responsive scaffolds (ARSs), consist of a phase-shift emulsions (PSE) embedded within a polymerized fibrin matrix. PSE is non-thermally vaporized when FUS is applied, and expands into a gas bubble, thereby causing localized compaction and significant increases in stiffness of the matrix surrounding the bubble.1 In this in vitro study, we investigate how these localized increases in matrix stiffness can be used to control the differentiation of fibroblasts into myofibroblasts, a transition which occurs at high stiffnesses.2 Findings indicated that vaporized PSE generated stable bubbles as well as bubbles that recondensed within the ARS, and that ɑSMA intensity was qualitatively higher at locations proximal to vaporized PSE compared to distal locations. Quantitatively, the normalized aSMA signal intensity was significantly increased in regions proximal to the vaporized PSE (p = 0.0007 and p = 0.0478).