When pressure is applied to a localized area of the body for an extended time, the resulting loss of blood flow and subsequent reperfusion to the tissue causes cell death and a pressure ulcer develops. Preventing pressure ulcers is challenging because the combination of pressure and time that results in tissue damage varies widely between patients, and the underlying damage is often severe by the time a surface wound becomes visible. Currently, no method exists to detect early tissue damage and enable intervention. Here we demonstrate a flexible, electronic device that non-invasively maps pressure-induced tissue damage, even when such damage cannot be visually observed. Using impedance spectroscopy across flexible electrode arrays in vivo on a rat model, we find that impedance is robustly correlated with tissue health across multiple animals and wound types. Our results demonstrate the feasibility of an automated, non-invasive 'smart bandage' for early detection of pressure ulcers.

In this paper we employed phospholipid Langmuir monolayers as membrane models to probe interactions with chitosan. Using a combination of surface pressure--area and surface potential--area isotherms and rheological measurements with the pendent drop technique, we observed that chitosan interacts with phospholipid molecules at the air-water interface. We propose a model in which chitosan interacts with the phospholipids mainly through electrostatic interactions, but also including H-bonding and hydrophobic forces, depending on the phospholipid packing density. At large areas per molecule, chitosan in the subphase adsorbs onto the monolayer, expanding it. At small areas per molecule, chitosan is located in the subsurface. Indeed, a mixed chitosan-phospholipid monolayer can be transferred onto solid supports, even at high surface pressures. The effects of chitosan on the viscoelastic properties of phospholipid monolayers may be taken as evidence for the ability of chitosan to disrupt cell membranes.

The interaction between chitosan and Langmuir and Langmuir-Blodgett (LB) films of dimyristoyl phosphatidic acid (DMPA) is investigated, with the films serving as simplified cell membrane models. At the air-water interface, chitosan modulates the structural properties of DMPA monolayers, causing expansion and decreasing the monolayer elasticity. As the surface pressure increased, some chitosan molecules remained at the interface, but others were expelled. Chitosan could be transferred onto solid supports alongside DMPA using the LB technique, as confirmed by infrared spectroscopy and quartz crystal microbalance measurements. The analysis of sum-frequency vibration spectroscopy data for the LB films combined with surface potential measurements for the monolayers pointed to chitosan inducing the ordering of the DMPA alkyl chains. Furthermore, the morphology of DMPA LB films, studied with atomic force microscopy, was affected significantly by the incorporation of chitosan, with the mixed chitosan-DMPA films displaying considerably higher thickness and roughness, in addition to chitosan aggregates. Because chitosan affected DMPA films even at pressures characteristic of cell membranes, we believe this study may help elucidate the role of chitosan in biological systems.

. Utilizing the versatility of printing and plastic electronic processes, electrode arrays consisting of 31 electrodes with electrode-to-electrode spacing ranging from 2 to 7 mm are fabricated and used for impedance mapping of conformal surfaces at 15 kHz. Overall, the fabrication process of an inkjet-printed gold electrode array that is electrically reproducible, mechanically robust, and promising for bioimpedance and biopotential measurements is demonstrated.

This review paper brings an overview of the use of chitosans in nanostructured films produced with the Langmuir-Blodgett (LB) or the electrostatic layer-by-layer (LbL) techniques, with emphasis on their possible applications. From a survey in the literature one may identify three main types of study with chitosan in nanostructured films. First, the interaction between chitosans and phospholipid Langmuir monolayers has been investigated for probing the mechanisms of chitosan action in their biological applications, with the monolayers serving as cell membrane models. In the second type, chitosan serves as a matrix for immobilization of biomolecules in LB as well as in LbL films, for which chitosan is suitable to help preserve the bioactivity of such biomolecules for long periods of time even in dry, solid films. An important application of these chitosan-containing films is in sensing and biosensing. The third type of study involves exploiting the mechanical and biocompatibility properties of chitosan in producing films with enhanced properties, for example, for tissue engineering. It is emphasized that chitosans have been proven excellent building blocks to produce films with controlled molecular architecture, allowing for synergy between distinct materials. We also discuss the prospects of the field, following a critical review of the latest developments in nanostructured chitosan films.

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The polysaccharide chitosan has been largely used in many biological applications as a fat and cholesterol reducer, bactericide agent, and wound healing material. While the efficacy for some of such uses is proven, little is known about the molecular-level interactions involved in these applications. In this study, we employ mixed Langmuir and Langmuir-Blodgett (LB) films of negatively charged dimyristoyl phosphatidic acid (DMPA) and cholesterol as cell membrane models to investigate the role of cholesterol in the molecular-level action of chitosan. Chitosan does not remove cholesterol from the monolayer. The interaction with chitosan tends to expand the DMPA monolayer due to its interpenetration within the film. On the other hand, cholesterol induces condensation of the DMPA monolayer. The competing effects cause the surface pressure isotherms of mixed DMPA-cholesterol films on a chitosan subphase to be unaffected by the cholesterol mole fraction, due to distinct degrees of chitosan penetration into the film in the presence of cholesterol. By combining polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation spectroscopy (SFG), we showed that chitosan induces order into negatively charged phospholipid layers, whereas the opposite occurs for cholesterol. In conclusion, chitosan has its penetration in the film modulated by cholesterol, and electrostatic interactions with negatively charged phospholipids, such as DMPA, are crucial for the action of chitosan.