Transition Delay Using Biomimetic Fish Scale Arrays

Aquatic animals have developed effective strategies to reduce their body drag over a long period of time. In this work, the influence of the scales of fish on the laminar-to-turbulent transition in the boundary layer is investigated. Arrays of biomimetic fish scales in typical overlapping arrangements are placed on a flat plate in a low-turbulence laminar water channel. Transition to turbulence is triggered by controlled excitation of a Tollmien-Schlichting (TS) wave. It was found that the TS wave can be attenuated with scales on the plate which generate streamwise streaks. As a consequence, the transition location was substantially delayed in the downstream direction by 55% with respect to the uncontrolled reference case. This corresponds to a theoretical drag reduction of about 27%. We thus hypothesize that fish scales can stabilize the laminar boundary layer and prevent it from early transition, reducing friction drag. This technique can possibly be used for bio-inspired surfaces as a laminar flow control means

Surface charge mediated cell-surface interaction on piezoelectric materials

Cell–material interactions play an essential role in the development of scaffold-based tissue engineering strategies. Cell therapies are still limited in treating injuries when severe damage causes irreversible loss of muscle cells. Electroactive biomaterials and, in particular, piezoelectric materials offer new opportunities for skeletal muscle tissue engineering since these materials have demonstrated suitable electroactive microenvironments for tissue development. In this study, the influence of the surface charge of piezoelectric poly(vinylidene fluoride) (PVDF) on cell adhesion was investigated. The cytoskeletal organization of C2C12 myoblast cells grown on different PVDF samples was studied by immunofluorescence staining, and the interactions between single live cells and PVDF were analyzed using an atomic force microscopy (AFM) technique termed single-cell force spectroscopy. It was demonstrated that C2C12 myoblast cells seeded on samples with net surface charge present a more elongated morphology, this effect being dependent on the surface charge but independent of the poling direction (negative or positive surface charge). It was further shown that the cell deadhesion forces of individual C2C12 cells were higher on PVDF samples with an overall negative surface charge (8.92 ± 0.45 nN) compared to those on nonpoled substrates (zero overall surface charge) (4.06 ± 0.20 nN). These findings explicitly demonstrate that the polarization/surface charge is an important parameter to determine cell fate as it affects C2C12 cell adhesion, which in turn will influence cell behavior, namely, cell proliferation and differentiationPortuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019, UID/BIA/04050/2013, UID/BIO/04469, project POCI-01-0145-FEDER-028237 and under BioTecNorte operation (NORTE-01-0145-FEDER-000004). The authors also thank the FCT for the SFRH/BD/111478/2015 (S.R.) and SFRH/BPD/90870/2012 (C.R.) grants. Funds provided by FCT in the framework of EuroNanoMed 2016 call, Project LungChek ENMed/0049/2016 are also gratefully acknowledged. The authors acknowledge funding by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-3-R (AEI/FEDER, UE) and from the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06

Roughness-induced transition by quasi-resonance of a varicose global mode

The onset of unsteadiness in a boundary-layer flow past a cylindrical roughness element is investigated for three flow configurations at subcritical Reynolds numbers, both experimentally and numerically. On the one hand, a quasi-periodic shedding of hairpin vortices is observed for all configurations in the experiment. On the other hand, global stability analyses have revealed the existence of a varicose isolated mode, as well as of a sinuous one, both being linearly stable. Nonetheless, the isolated stable varicose modes are highly sensitive, as ascertained by pseudospectrum analysis. To investigate how these modes might influence the dynamics of the flow, an optimal forcing analysis is performed. The optimal response consists of a varicose perturbation closely related to the least stable varicose isolated eigenmode and induces dynamics similar to that observed experimentally. The quasi-resonance of such a global mode to external forcing might thus be responsible for the onset of unsteadiness at subcritical Reynolds numbers, hence providing a simple explanation for the experimental observations

Optimisation of conductive polymer biomaterials for cardiac progenitor cells

The characterisation of biomaterials for cardiac tissue engineering applications is vital for the development of effective treatments for the repair of cardiac function. New smart materials developed from conductive polymers can provide dynamic benefits in supporting and stimulating stem cells via controlled surface properties, electrical and electromechanical stimulation. In this study we investigate the control of surface properties of conductive polymers through a systematic approach to variable synthesis parameters, and how the resulting surface properties influence the viability of cardiac progenitor cells. A thorough analysis investigating the effect of electropolymerisation parameters, such as current density and growth, and reagent variation on physical properties provides a fundamental understanding of how to optimise conductive polymer biomaterials for cardiac progenitor cells.Funding Agencies|Linkoping University; IGEN (post-doc grant); COST-Action [MP1003]; Knut och Alice Wallenberg Commemorative Fund; European Research Agency</p