Differential and synergistic effects of mechanical stimulation and growth factor presentation on vascular wall function

Abstract

We investigated the hypothesis that immobilizing TGF-β1 within fibrin hydrogels may act in synergy with cyclic mechanical stimulation to enhance the properties of vascular grafts. To this end, we engineered a fusion TGF-β1 protein that can covalently anchor to fibrin during polymerization upon the action of factor XIII. We also developed a 24-well based bioreactor in which vascular constructs can be mechanically stimulated by distending the silastic mandrel in the middle of each well. TGF-β1 was either conjugated to fibrin or supplied in the culture medium and the fibrin based constructs were cultured statically for a week followed by cyclic distention for another week. The tissues were examined for myogenic differentiation, vascular reactivity, mechanical properties and ECM content. Our results showed that some aspects of vascular function were differentially affected by growth factor presentation vs. pulsatile force application, while others were synergistically enhanced by both. Overall, this two-prong biomimetic approach improved ECM secretion, vascular reactivity and mechanical properties of vascular constructs. These findings may be applied in other tissue engineering applications such as cartilage, tendon or cardiac regeneration where growth factors TGF-β1 and mechano-stimulation play critical roles.

Hybrid Biomaterial with Conjugated Growth Factors and Mesenchymal Stem Cells for Ectopic Bone Formation

“…Previous work in our laboratory has shown that fibrin immobilized TGF-b1-promoted MSC differentiation to SMCs uniformly throughout fibrin rings, eliminating growth factor diffusion limitations. 33,42 VEGF has been used to promote angiogenesis in many previous studies, however, neovessels formed only in the presence of VEGF have been shown to be unstable and degrade rapidly in vitro, and at a slower extent in vivo. This is likely due to the lack of pericytes and SMCs, which typically enwrap neovessels within the body.…”

“…Fibrin has been extensively studied as a scaffold and a number of studies have shown that fibrin is a growth factor carrier for tissue regeneration. 33,42 In addition, fibrin has also been used to deliver stem cells for bone tissue engineering. 43,44 Ideally, incorporation of a vascularized network into engineered bone substitutes to mimic the structure of natural bone tissue is necessary to promote rapid bone regeneration.…”

Cadherin-11 is a novel regulator of extracellular matrix synthesis and tissue mechanics

“…Furthermore, the initial rate of compaction was ∼2.38% per hour for WT cells but less than half of that at ∼1.01% per hour for Cdh11 −/− cells. We also measured the mechanical properties and collagen content of tissue constructs prepared from Cdh11 −/− or WT mouse dermal fibroblasts, as we described in previous publications (DiazChavez et al, 2008;Liang et al, 2013;Koobatian et al, 2016). To this end, we prepared cylindrical tissue equivalents by embedding cells in fibrin hydrogels that were polymerized around cylindrical mandrels and cultured in the presence of TGF-β1 for 2 weeks.…”

“…Experimental triplicates or quadruplicates with each group were used to measure area of fibrin gel as a fraction of total area (A/A 0 ) of a standard 24-well plate (A 0 =2 cm 2 ). These gels were further cultured in vessel medium (Liang et al, 2013) in the same plates for 14 days, to allow for collagen deposition and remodeling.…”

Differential Effects of Culture Senescence and Mechanical Stimulation on the Proliferation and Leiomyogenic Differentiation of MSC from Different Sources: Implications for Engineering Vascular Grafts

“…The medium was changed the following day after gel polymerization, and every other day thereafter. TEV constructs on the 24-PP were kept under static conditions for 1 week, and then pulsed for 1 week periodically (0.3 s/1.7 s distended/rested as reported previously 21,30,31 ).…”