Chiara Spagnoli

Poly(vinyl alcohol) as versatile biomaterial for potential biomedical applications

In this paper, we present some new case examples where the chemical versatility of poly (vinyl alcohol) (PVA) can be used for potential biomedical applications. PVA, the polymeric material used for designing new nanostructured devices, is water soluble, biocompatible and has excellent physical properties. We point out the possibility of obtaining wall-to-wall chemical hydrogels as well as microgels without diminishing the biocompatibility available in the starting PVA material. Injectability is another important factor to take into account in controlled drug delivery for gene therapy. In this respect, in this paper, established and more innovative methods are prospected in order to obtain particles with dimensions suitable for these applications.

Reducing probe dependent drift in atomic force microscope with symmetrically supported torsion levers

Drift and thermal instability present significant limitations to atomic force microscopy and other cantilever-based sensor measurements. Most drift has been attributed to the asymmetric geometry of the cantilever, which acts as a chemical and thermal bimorphs. For example, cantilevers drift hundreds of nanometers upon immersion in water. The time course of drift is roughly exponential with a time constant of ∼70min. Symmetrically supported torsion cantilevers significantly reduce this drift. Prototypical torsion levers have long-term drift of 1.0±0.36A∕min, more than an order of magnitude smaller than commercial cantilevers. These torsion levers also have extraordinarily high thermal stability. In response to a 20°C change in bath temperature, they move an average of 15±11nm, whereas traditional levers deflect by >1μm.

Drift-free atomic force microscopy measurements of cell height and mechanical properties

Atomic force microscopy (AFM) is used to study the morphological and mechanical properties of living cells. However, experiments performed over minutes to hours are subject to significant instrumental drift. The main sources of drift are the cantilevers geometrical asymmetry and bimorphic construction. We developed a simple software Stick-and-Move (SaM) routine for AFM that eliminates drift by continuously referencing the sample position to the substrate while acquiring force-distance curves. Control experiments show no drift over 15 min at an acquisition rate of 0.1 Hz. As a proof of concept, we applied the SaM to study the response of rat astrocytes to osmotic stress, observing dimensional and constitutive changes during volume regulation.

Hydrodynamics of torsional probes for atomic force microscopy in liquids

Improving the force resolution of atomic force microscopy for soft samples in liquid requires soft cantilevers with reduced hydrodynamic cross section. Single and dual axis torsion levers [Beyder and Sachs, 2006] are an attractive technology. They have reduced area and reduced drift due to the symmetric support [Beyder et al., 2006] can add a second dimension using two independent axes. Here we investigate the hydrodynamics of these probes using three-dimensional transient fluid-structure interaction models with comparison to the experimental data. The computed Q factors and wet/dry resonance frequencies of different modes compare well with experimental measurements indicating that continuum viscous hydrodynamics can be used effectively to predict probe performance. The modeling further explores cross-axis hydrodynamic coupling and the influence of a nearby sample plane to provide guidance on approach algorithms and the possibilities of parametric detection.