Department of Food Processing Technology and Management

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Author: search.filters.author.Herman, RamonEnd date: 2019

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    THE INFLUENCE OF SWELLING ON LOCAL ELASTIC PROPERTIES OF POLYACRYLAMIDE HYDROGELS
    (Open Science Framework, 2017) Ramesh, Subramani; Alicia, Izquierdo-Alvarez; Pinaki, Bhattacharya; Mathieu, Meerts; Paula, Moldenaers; Herman, Ramon; Hans Van, Oosterwyck
    Polyacrylamide (PAM)hydrogelsarecommonly usedas soft cell culture substrates for cell mechanical and mechanobiological studiesbecause oftheir tunable stiffness,easeof handling, transparent natureand surface functionalization to promote cell adhesion. The dependence of bulk rheological and local elastic properties (for example, as assessed by means of Atomic Force Microscopyor AFM) of PAM hydrogels onmonomer and cross-linkerconcentrationsand on polymerization temperature havebeen extensively investigated.PAM hydrogels are known to swell, which may affect their elastic properties and therefore may complicate the interpretation ofcell culturingexperiments because of a lack of control of substrate stiffness. Direct measurements of the effect of swelling on PAM elastic properties are scarce. We report here, for the first time, the direct observation of swelling (by measuring the volumetric swelling ratio) and its influence onlocal elastic properties, as measuredby AFM. Bulk rheological measurements were performed as well to enable the comparison between local and global elastic properties during and after hydrogel polymerization. Four PAM hydrogel compositions were considered,with corresponding storage shear moduliof 4530 Pa(termed stiffest), 2900 Pa(stiff), 538 Pa(soft)and 260 Pa(softest) as measured immediately after polymerization. These values as well as values obtained during hydrogel polymerization were found to be in good agreement with the local elastic moduli derived from AFM and assuming hydrogel incompressibility. After polymerization, the hydrogels were subjected to swelling conditions over six days in phosphate buffered salineand swelling ratios and local elastic moduli were measured each day.Additional short term measurements (at 0, 3, 6, 9, 12 and 24 hours) were performed for the soft and softest gelsto study their swelling kinetics in more detail. Swelling ratio and local elastic modulus did not change with time for the stiffest and stiff gels, while for the soft and softest gels substantialchanges between Day 0 and Day 1were found for both swelling ratio (21.6%and 133% increase for soft and softest gel respectively) and local elastic modulus (33.7%and 33.3% decrease for soft and softest gel respectively). Experimental data werefurther analysed theoretically by combining models of ideal elastomeric gels with a poroelastic swelling kinetics model, which confirmed the validity of observed trends with respect to literature data. The results demonstrate that swelling can have an important effect on PAM elastic properties and must be taken into account when using PAM as a cell culture substrate, particularly for PAM gels with low monomer and cross-linker concentrations
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    IMMERSED BOUNDARY MODELS FOR QUANTIFYING FLOW-INDUCED MECHANICAL STIMULI ON STEM CELLS SEEDED ON 3D SCAFFOLDS IN PERFUSION BIOREACTORS
    (PLOS Computational Biology, 2016-09-22) Yann, Guyot; Bart, Smeets; Tim, Odenthal; Ramesh, Subramani; Frank P, Luyten; Herman, Ramon; Ioannis, Papantoniou; Liesbet, Geris
    Perfusion bioreactors regulate flow conditions in order to provide cells with oxygen, nutrients and flow-associated mechanical stimuli. Locally, these flow conditions can vary depending on the scaffold geometry, cellular confluency and amount of extra cellular matrix deposition. In this study, a novel application of the immersed boundary method was introduced in order to represent a detailed deformable cell attached to a 3D scaffold inside a perfusion bioreactor and exposed to microscopic flow. The immersed boundary model permits the prediction of mechanical effects of the local flow conditions on the cell. Incorporating stiffness values measured with atomic force microscopy and micro-flow boundary conditions obtained from computational fluid dynamics simulations on the entire scaffold, we compared cell deformation, cortical tension, normal and shear pressure between different cell shapes and locations. We observed a large effect of the precise cell location on the local shear stress and we predicted flow-induced cortical tensions in the order of 5 pN/μm, at the lower end of the range reported in literature. The proposed method provides an interesting tool to study perfusion bioreactors processes down to the level of the individual cell’s micro-environment, which can further aid in the achievement of robust bioprocess control for regenerative medicine applications.
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    ROBUST SCALABLE SYNTHESIS OF A BIS-UREA DERIVATIVE FORMING THIXOTROPIC AND CYTOCOMPATIBLE SUPRAMOLECULAR HYDROGELS
    (Royal Society of Chemistry, 2019-06-06) Laurens A J, Rutgeerts; Al, Halifa Soulta; Ramesh, Subramani; Burak, Toprakhisar; Herman, Ramon; Monissa C, Paderes; Wim M, De Borggraeve; Jennifer, Patterson
    Synthetic hydrogels address a need for affordable, industrially scalable scaffolds for tissue engineering. Herein, a novel low molecular weight gelator is reported that forms self-healing supramolecular hydrogels. Its robust synthesis can be performed in a solvent-free manner using ball milling. Strikingly, encapsulated cells spread and proliferate without specific cell adhesion ligands in the nanofibrous material.
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    IMMERSED BOUNDARY MODELSFOR QUANTIFYING FLOW-INDUCED MECHANICAL STIMULI ON STEM CELLS SEEDED ON 3D SCAFFOLDS IN PERFUSION BIOREACTORS
    (PLOS Computational Biology, 2016-09-22) Yann, Guyot; Bart, Smeets; Tim, Odentha; Ramesh, Subramani; Frank P, Luyten; Herman, Ramon; Ioannis, Papantoniou; Liesbet, Geris
    Perfusion bioreactors regulate flow conditions in order to provide cells with oxygen, nutrients and flow-associated mechanical stimuli. Locally, these flow conditions can vary depending on the scaffold geometry, cellular confluency and amount of extra cellular matrix deposition. In this study, a novel application of the immersed boundary method was introduced in order to represent a detailed deformable cell attached to a 3D scaffold inside a perfusion bioreactor and exposed to microscopic flow. The immersed boundary model permits the prediction of mechanical effects of the local flow conditions on the cell. Incorporating stiffness values measured with atomic force microscopy and micro-flow boundary conditions obtained from computational fluid dynamics simulations on the entire scaffold, we compared cell deformation, cortical tension, normal and shear pressure between different cell shapes and locations. We observed a large effect of the precise cell location on the local shear stress and we predicted flow-induced cortical tensions in the order of 5 pN/μm, at the lower end of the range reportedin literature. The proposed method provides an interesting tool to study perfusion bioreactors processes down to the level of the individual cell’s micro-environment, which can furtheraid in the achievement of robust bioprocess control for regenerative medicine applications.