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Mechanically tunable, human mesenchymal stem cell viable poly(ethylene glycol)-oxime hydrogels with invariant precursor composition, concentration, and stoichiometry.

ABSTRACT: Hydrogels are used widely for exploratory tissue engineering studies. However, currently no hydrogel systems have been reported that exhibit a wide range of elastic modulus without changing precursor concentration, identity, or stoichiometry. Herein, ester and amide-based PEG-oxime hydrogels with tunable moduli (~5-30 kPa) were synthesized with identical precursor mass fraction, stoichiometry, and concentration by varying the pH and buffer concentration of the gelation solution, exploiting the kinetics of oxime bond formation. The observed modulus range can be attributed to increasing amounts of network defects in slower forming gels, as confirmed by equilibrium swelling and small angle neutron scattering (SANS) experiments. Finally, hMSC viability was confirmed in these materials in a 24 h assay. While only an initial demonstration of the potential utility, the controlled variation in defect density and modulus is an important step forward in isolating system variables for hypothesis-driven biological investigations.

SUBMITTER: Dilla RA

PROVIDER: S-EPMC6820350 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Project description:Valve interstitial cells (VIC) are the primary cell type residing within heart valve tissues. In many valve pathologies, VICs become activated and will subsequently profoundly remodel the valve tissue extracellular matrix (ECM). A primary indicator of VIC activation is the upregulation of ?-smooth muscle actin (?SMA) stress fibers, which in turn increase VIC contractility. Thus, contractile state reflects VIC activation and ECM biosynthesis levels. In general, cell contraction studies have largely utilized two-dimensional substrates, which are a vastly different micro mechanical environment than 3D native leaflet tissue. To address this limitation, hydrogels have been a popular choice for studying cells in a three-dimensional environment due to their tunable properties and optical transparency, which allows for direct cell visualization. In the present study, we extended the use of hydrogels to study the active contractile behavior of VICs. Aortic VICs (AVIC) were encapsulated within poly(ethylene glycol) (PEG) hydrogels and were subjected to flexural-deformation tests to assess the state of AVIC contraction. Using a finite element model of the experimental setup, we determined the effective shear modulus ? of the constructs. An increase in ? resulting from AVIC active contraction was observed. Results further indicated that AVIC contraction had a more pronounced effect on ? in softer gels (72?±?21% increase in ? within 2.5?kPa gels) and was dependent upon the availability of adhesion sites (0.5-1?mM CRGDS). The transparency of the gel allowed us to image AVICs directly within the hydrogel, where we observed a time-dependent decrease in volume (time constant ?=3.04 min) when the AVICs were induced into a hypertensive state. Our results indicated that AVIC contraction was regulated by both the intrinsic (unseeded) gel stiffness and the CRGDS peptide concentrations. This finding suggests that AVIC contractile state can be profoundly modulated through their local micro environment using modifiable PEG gels in a 3D micromechanical-emulating environment. Moving forward, this approach has the potential to be used towards delineating normal and diseased VIC biomechanical properties using highly tunable PEG biomaterials. STATEMENT OF SIGNIFICANCE.

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Mechanically tunable, human mesenchymal stem cell viable poly(ethylene glycol)-oxime hydrogels with invariant precursor composition, concentration, and stoichiometry.

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