University of Delaware

Doctoral Dissertation Defense – Zheng Cao

BME PhD Candidate Zheng Cao will be defending their dissertation:


A Dynamic Tunable Platform To Manipulate Fibroblast Activation


  • Location: BPI 140 AB
  • Zoom Link:
  • Password: ZhengC
  • Date: Thursday, September 7, 2023
  • Time: 9:30 am
  • Committee: Elise Corbin, Kristi Kiick, Charles Dhong, Velia Fowler, April Kloxin


Adverse remodeling of the heart after myocardial infarction (MI), also known as cardiac fibrosis, will lead to the stiffening and anisotropic conversion of myocardium tissue and stoppage of blood throughout the body, which will eventually cause death. The annual cost for treatment of MI causes a heavy burden to patients. However, most current treatments are limited to implantation of cardiac patch, cardiac stent, and bypass surgery, which are the non-targeted therapies. Moderate myocardial fibrosis contributes to the positive regeneration of heart after MI, whereas the excessive fibrosis can lead to irreversible and malfunctional infarcted heart. Thus, a systematic investigation on the cardiac fibrosis development and myocardium remodeling after MI is in urgent need in order to unveil the mechanism of cardiac fibrosis development and translate into the targeted therapeutic strategies.

In vitro substrates have been broadly applied in biomedical field as the disease model platforms for the physiological and pathological process. Creating an in vitro model for post-MI tissue study that can mimic the physical properties of infarcted heart with spatial-temporal variation is critical as the building block, yet there has been an effective device used to recapitulate the dynamic nature of the infarcted heart tissue. The recent emergence of novel material with stiffness-tunability in response to an external magnetic field, magnetorheological elastomers (MREs), reveals an excellent in-situ modulation of stiffness with a wide range which provides a promising tool for biomedical applications. However, widening of hysteresis loop observed in MREs is not identical to characteristic hysteresis loop of the soft ferromagnetic material, which was previously attributed to the particle motion. Thus, unravelling particle motion within the matrix is an urgent need and a critical step to explain the magnetic hysteresis loop widening of MREs, which will facilitate and expand its biomedical applications.

Ultrasoft MREs made by incorporating carbonyl iron particles into soft Sylgard 527 polydimethylsiloxane (PDMS) showed a large magnetic-field dependent changes in their stiffness changes. Our recent studies exhibited the widening of the magnetic hysteresis loop in these soft MREs compared to the relatively pinched loop observed for the stiffer MREs. This interesting behavior made us hypothesize that iron particles displacement in response to external magnetic field within the soft PDMS matrix contributes to the magnetic hysteresis loop widening. We experimentally validated our hypothesis by tracking fluorescently labelled carbonyl iron particles motion in the MREs responding to various magnetic field strengths. Particle coating and bioconjugation of fluorophores were also characterized to validate the success of modification and retain of the magnetic properties of modified carbonyl iron particles. Our findings for the first time demonstrate successful modification of carbonyl iron particles and observe that particles primarily move along the external magnetic field direction within the MREs material, and such particles displacement results in the magnetic hysteresis loop widening.

One of the physical cues after MI is cardiac tissue stiffness with spatial-temporal variation. Infarct border zone, a tissue region laying between infarcted tissue and adjacent healthy tissue, exhibits gradient stiffness change. The border region is of great importance and interest in the inflammatory and remodeling after MI involving infarction expansion, fibrosis formation, and reparative process. The efforts researchers been putting together have advanced the development of a variety of in vitro platforms to mimic microenvironment of infarct border region that allows us to have a more controllable and cost-effective approach to characterize the microenvironment features. Whereas the dynamic nature of gradient stiffness of infarct border zone have not yet been achieved. In this work, we use MREs as our base material to fabricate an innovative 2D in vitro platform with capability of in-situ modulation on the stiffness gradient mimicking continuously changing micro-environment of infarcted myocardium. This allows us to examine the inflammatory response of primary cardiac fibroblasts (NHCF-V) in a spatiotemporal manner regarding the different biomarkers’ expression, including αSMA, TGF-β, ACTA2, COLI/III, and MMP1. We found that cardiac fibroblasts exhibit spatially different activation and cytokine secretion in the infarcted and remote regions within the same model and presented a phenotypic conversion as time proceeded. COL1A1/3A1 and MMP1 exhibits a more robust regulation at 24 h. Additionally, the tunability of such gradient stiffness model allows us to modulate the stiffness gradient on demand, either increase or decrease stiffness gradient, to mimic different stage during remodeling process. Recognizing that remodeling is guided by many different types of cues that co-exist in vivo, it is also important to recognize that these cues may cooperate or compete to ultimately direct remodeling. Specifically, we examine the competition and cooperation of a chemical cue (anti-fibrotic drug, A 83-01) and mechanical cue (substrate softening) in tandem to attenuate fibrotic biomarker responses of cardiac fibroblasts. Individual intervention by drug and softening exhibited a competitive or/and cooperative effect to the combined intervention in order to regulate fibrosis. This work reveals the spatiotemporal variation of fibrotic response in cardiac fibroblasts as well as the complexity of anti-fibrotic drug dosing and stiffness-varying interactions on cardiac fibroblasts. This platform with a more realistic microenvironment will not only provide us a unique in vitro tool to study disease progression mechanisms, such as cardiac fibrosis, but also serve as a cost-effective, pathophysiological relevant model for potential therapeutics screening.

Topography, particularly anisotropic structure of heart tissue, is another important physical cue in the in vivo cellular microenvironment after MI. Integrating anisotropic features with stiffness-tunable materials not only allow us to construct a both physiological and pathological relevant building block, but also enable us to probe interactions between topography and stiffness cues. In this study, we introduced an alternative MREs as our in vitro substrate, EcoGel MREs, which retains higher anisotropic patterns fidelity than conventional MREs. Our results indicate that the combination of dynamic changes in stiffness with and without topographic cues induces different effects on the alignment and activation or deactivation of myofibroblasts. Specifically, cells cultured on patterned substrates exhibited a more aligned morphology than cells cultured on flat material; moreover, cell alignment was not dependent on substrate stiffness. On a patterned substrate, there was no significant change in the number of activated myofibroblasts when the material was temporally stiffened, but temporal softening caused a significant decrease in myofibroblast activation, indicating a competing interaction of these characteristics on cell behavior.