Our laboratory developed an electrochemical method which transforms collagen solutions to solid state material by densification and unidirectional alignment of molecules [1] based on the principles of isoelectric focusing (IEF). Randomly oriented molecules at the onset migrate to the isoelectic plane when current is applied to the solution. However, the driving forces behind the focusing phenomena are not fully understood.

The forces exerted on the flagellum of the swimming alga Chlamydomonas reinhardtii by surrounding fluid are estimated from video data. “Wild-type” cells, as well as cells lacking inner dynein arms ( ida3 ) and cells lacking outer dynein arms ( oda2 ) were imaged (350 fps; 125 nm). Digital image registration and sorting algorithms provide high-resolution descriptions of the kinematics of the cell body and flagellum. The swimming cell is then modeled as an ellipsoid in Stokes flow, propelled by viscous forces that depend linearly on the velocity of the flagellum. The coefficients ( C N and C T ) that related normal and tangent forces on the flagellum to corresponding velocity components are estimated from equilibrium requirements. Their values are consistent among all three genotypes and similar to theoretical predictions.

The response of neural cells to mechanical cues is a critical component of the innate neuroprotective cascade aimed at minimizing the consequences of traumatic brain injury (TBI). Reactive gliosis and the formation of glial scars around the lesion site are among the processes triggered by TBI where mechanical stimuli play a central role. It is well established that the mechanical properties of the microenvironment influence phenotype and morphology in most cell types. It has been shown that astrocytes change morphology [1] and cytoskeletal content [2] when grown on substrates of varying stiffness, and that mechanically injured astrocyte cultures show alterations in cell stiffness [3]. Accurate estimates of the mechanical properties of central nervous system (CNS) cells in their in-vivo conditions are needed to develop multiscale models of TBI. Lu et al found astrocytes to be softer than neurons under small deformations [4]. In recent studies, we investigated the response of neurons to large strains and at different loading rates in order to develop single cell models capable of simulating cell deformations in regimes relevant for TBI conditions [5]. However, these studies have been conducted on cells cultured on hard substrates, and the measured cell properties might differ from their in-vivo counterparts due to the aforementioned effects. Here, in order to investigate the effects of substrate stiffness on the cell mechanical properties, we used atomic force microscopy (AFM) and confocal imaging techniques to characterize the response of primary neurons and astrocytes cultured on polyacrylamide (PAA) gels of varying composition. The use of artificial gels minimizes confounding effects associated with biopolymer gels (both protein-based and polysaccharide-based) where specific receptor bindings may trigger additional biochemical responses [1].

Finite element analysis of single cells embedded in an extracellular matrix have been used widely to provide new insights into the cellular loading in cartilage [1] and meniscus [2]. Deformations derived from a homogeneous tissue model are generally used to drive simulations using microstructural representations. Implicit in this setup is the assumption of the equivalence of macrostructural (tissue) constitutive response and average stress-strain response of the microstructural (cellular) model. Higher cell densities within tissue volume [3] may increase the uncertainty introduced by this assumption and may also influence how macroscopic loads are transferred to the cells. We have previously shown, albeit with a two-dimensional simulation, the potential mismatches in such variables for increasing strain level and cell density, specifically for no cell, one, and three cell representations [4]. Hence, the objective of this study was to quantify the differences between the overall response and cellular deformation in three-dimensional nonlinearly elastic microstructural cartilage models embedded with either one or three cells. Multiscale coupling approaches targeting prediction of cell deformations from tissue and/or organ level loading will likely benefit from this investigation while balancing computational demand with accuracy requirements.

Iron oxide nanoparticles are of particular interest for drug delivery applications, since they can be targeted to a specific location using a magnetic field. We are interested in delivering drugs to atherosclerotic plaques via these nanoparticles. However, prior to using nanoparticles in vivo , they must be shown as relatively non-toxic to cells. We and others have shown that bare iron oxide nanoparticles are readily taken up by cells, where they catalyze production of highly toxic reactive oxygen species [1]. This oxidative stress disrupts the cell cytoskeleton, alters cell mechanics, and may change other critical cell functions. Iron oxide nanoparticles for in vivo biomedical applications are often coated with a polysaccharide (eg. dextran) or a polymer (eg. polyethylene glycol, PEG). Both the size and the surface coating of the nanoparticle play an important role in cell toxicity.