Interplay between long- and short-range interactions drives neuritogenesis on stiff surfaces

Dynamically Mapping the Topography and Stiffness of the Leading Edge of Migrating Cells Using AFM in Fast-QI Mode

Cell migration profoundly influences cellular function, often resulting in adverse effects in various pathologies including cancer metastasis. Directly assessing and quantifying the nanoscale dynamics of living cell structure and mechanics has remained a challenge. At the forefront of cell movement, the flat actin modules─the lamellipodium and the lamellum─interact to propel cell migration. The lamellipodium extends from the lamellum and undergoes rapid changes within seconds, making measurement of its stiffness a persistent hurdle. In this study, we introduce the fast-quantitative imaging (fast-QI) mode, demonstrating its capability to simultaneously map both the lamellipodium and the lamellum with enhanced spatiotemporal resolution compared with the classic quantitative imaging (QI) mode. Specifically, our findings reveal nanoscale stiffness gradients in the lamellipodium at the leading edge, where it appears to be slightly thinner and significantly softer than the lamellum. Additionally, we illustrate the fast-QI mode's accuracy in generating maps of height and effective stiffness through a streamlined and efficient processing of force-distance curves. These results underscore the potential of the fast-QI mode for investigating the role of motile cell structures in mechanosensing.

High intrinsic mechanical flexibility of mouse prion nanofibrils revealed by measurements of axial and radial Young's moduli

Self-templated protein aggregation and intracerebral deposition of aggregates, sometimes in the form of amyloid fibrils, is a hallmark of mammalian prion diseases. What distinguishes amyloid fibrils formed by prions from those formed by other proteins is not clear. On the basis of previous studies on yeast prions that correlated high intrinsic fragmentation rates of fibrils with prion propagation efficiency, it has been hypothesized that the nanomechanical properties of prion amyloid such as strength and elastic modulus may be the distinguishing feature. Here, we reveal that fibrils formed by mammalian prions are relatively soft and clearly in a different class of rigidities when compared to nanofibrils formed by nonprions. We found that amyloid fibrils made of both wild-type and mutant mouse recombinant PrP(23-231) have remarkably low axial elastic moduli of 0.1-1.4 GPa. We demonstrate that even the proteinase K resistant core of these fibrils has similarly low intrinsic rigidities. Using a new mode of atomic force microscopy called AM-FM mode, we estimated the radial modulus of PrP fibrils at ∼0.6 GPa, consistent with the axial moduli derived by using an ensemble method. Our results have far-reaching implications for the understanding of protein-based infectivity and the design of amyloid biomaterials.

Protocol and cell responses in three-dimensional conductive collagen gel scaffolds with conductive polymer nanofibres for tissue regeneration

It has been established that nerves and skeletal muscles respond and communicate via electrical signals. In regenerative medicine, there is current emphasis on using conductive nanomaterials to enhance electrical conduction through tissue-engineered scaffolds to increase cell differentiation and tissue regeneration. We investigated the role of chemically synthesized polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) conductive polymer nanofibres for conductive gels. To mimic a naturally derived extracellular matrix for cell growth, type I collagen gels were reconstituted with conductive polymer nanofibres and cells. Cell viability and proliferation of PC-12 cells and human skeletal muscle cells on these three-dimensional conductive collagen gels were evaluated in vitro. PANI and PEDOT nanofibres were found to be cytocompatible with both cell types and the best results (i.e. cell growth and gel electrical conductivity) were obtained with a low concentration (0.5 wt%) of PANI. After 7 days of culture in the conductive gels, the densities of both cell types were similar and comparable to collagen positive controls. Moreover, PC-12 cells were found to differentiate in the conductive hydrogels without the addition of nerve growth factor or electrical stimulation better than collagen control. Importantly, electrical conductivity of the three-dimensional gel scaffolds increased by more than 400% compared with control. The increased conductivity and injectability of the cell-laden collagen gels to injury sites in order to create an electrically conductive extracellular matrix makes these biomaterials very conducive for the regeneration of tissues.