Friday, 01 October 2021 12:00
VIRTUAL PRESENTATION BY
Professor Jacques Huyghe and Dr Kyriaki Koupepidou
ABSTRACT – Presentation 1
Biomedical engineers face porous media with very low stiffness, high osmolarity and extremely large deformations. Examples are superabsorbent hydrogels and living cells. Volume strains above 1000% strain are commonplace in diapers, female pads and growth plates. The strong nonlinearities of large deformation formulations of poromechanics hamper the use of analytical solutions. Large deformation u-p formulations fail in this regime. This means that simulation tools of poromechanics are inapt to a great deal of biology, which typically unfolds in the intracellular space. Local mass balance violation is the culprit under extremely large deformations. In order to address this issue, a mixed hybrid formulation of poromechanics of swelling gel based on a Raiviart-Thomas finite element was developed. This formulation strictly complies with local mass balance. Swelling computations are possible down to a shear modulus of 10 kPa. Surface instabilities easily develop as osmotic forces overtake the stabilising effect of the elasticity. Fracture simulation using large deformation XFEM including flow within the crack, between the crack and the formation and within the crack, allows for initiation, coalescence and bifurcation of cracks. XFEM computations predict experimentally observed staccato propagation of cracks in hydrogels. Constitutive modelling of swelling requires the concurrent use of elastic, mixing and ionic energies in Flory-Rehner swelling model. Interaction terms between elastic and ionic energies occur because the stiffness of gels directly depends on ionic concentrations Future perspectives on constitutive modelling of swelling and fracturing gels include herniation of intervertebral disc, mechanotransduction of extracelluar matrix and design of biomimetic hydrogels. Hydraulic fracturing of shale is an important geotechnical application.
ABSTRACT – Presentation 2
Stimuli-responsive metal-organic materials (MOMs) exhibit structural flexibility when exposed to different guest molecules. In particular, when this flexibility involves a structural transformation from a nonporous (closed) to a highly porous (open) phase, the material offers great potential utility in gas storage and separation. Such materials are often described as “switching”, a term which refers to a reversible closed-to-open transition at a certain “gate-opening” pressure. Despite the substantial technological applicability, examples of switching materials still remain extremely scarce, with a recent survey classifying them in the 0.07% of all reported MOMs. The aim of the presented study is to synthesize new switching MOMs, and control their gate-opening pressures through ligand substitution. Two new platforms of switching MOMs are presented: (i) the X-ddi and (ii) the X-dia platform. Structural transformations are triggered by common organic liquids, gases and heat. Systematic investigation of closed-phase and guest-loaded single crystals by X-ray diffraction revealed that the transitions are enabled by the rotational flexibility of the ligand and the ability of the molecular building block (MBB) to contort. Ligand substitution induces changes in both the gate-opening pressures and the isotherm shapes. These promising results provide mechanistic insights on closed-to-open phase transitions and make valuable contributions to the library of switching MOMs.
ABOUT THE PRESENTERS
Jacques Huyghe is the Bernal Chair of Biomedical Engineering at the University of Limerick. He holds a Master’s Degree in Civil Engineering from Ghent University Belgium (1979) and a Ph.D from Eindhoven University of Technology, The Netherlands. He has a unique signature in that he has been working at the interface between biomedical and petroleum engineering. He had repeatedly promoted the close analogies between biological tissues and geomaterials and the urgent need to exploit these analogies in developing numerical models and industrial/clinical technologies. He has authored more than 125 full-size SCI-publications, is the recipient of many awards including a Royal Dutch Shell donation (1995-1998), a fellowship of the Royal Netherlands Academy of Arts and Sciences (1996-2001), a swelling materials Interpore Award (2013) and the Kimberly-Clark Distinguished Lectureship Award 2022. He has collaborated with many industrial partners including Philips Research, Shell Research and Procter & Gamble. His present interest is in mechanotransduction through voltage gated ion channels in intervertebral disc, swelling and fracture of superabsorbents and poromechanical modelling of coronary blood low and microvascular flow of red blood cells.
Kyriaki Koupepidou is a first year Masters Student in Michael J. Zaworotko’s group at the Bernal Institute. She received her BSc in Materials Chemistry from the University of Cyprus, where she completed her undergraduate research thesis under the supervision of Anastasios J. Tasiopoulos. Her main research interests involve the synthesis of flexible metal-organic materials and the employment of crystal engineering strategies to fine-tune their properties.
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