Two fluorescent quantum clusters of gold, namely Au₂₅ and Au₈, have been synthesized from mercaptosuccinic acid-protected gold nanoparticles of 4–5 nm core diameter by etching with excess glutathione. While etching at pH ∼3 yielded Au₂₅, that at pH 7–8 yielded Au₈. This is the first report of the synthesis of two quantum clusters starting from a single precursor. This simple method makes it possible to synthesize well-defined clusters in gram quantities. Since these clusters are highly fluorescent and are highly biocompatible due to their low metallic content, they can be used for diagnostic applications.

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. Tissue Engineering involves the combination of cells, growth factors and biomaterials into artificial constructs which, upon implantation, can improve the healing capacity of the human body. A remaining challenge involves providing physical stimuli to individual cells, thereby guiding them towards the properties of the desired tissue type. Perfusion bioreactors try to control the local concentration of oxygen, nutrients and growth factors and mechanical stresses by varying the fluid flow. In this work, we predict the shear stress that individual cells experience at the microscopic scale, as a function of the bioreactor inlet flow velocity, by making use of the immersed boundary method. This method combines an Eulerian grid (fixed in space) with a Lagrangian grid (moving with the flow) to model the deformation of cells due to flow inside a scaffold pore. Our simulations show that the local shear stress levels on specific, realistic cell geometries are different from the shear stress levels on empty scaffolds, which are often still used as a reference. Finally, we predict and discuss the additional effect of realistic flow on other mechanical cell properties, such as its deformation and its cortical tension.