Fibrous sensors

Fibrous sensor for compression and traction detection in laminated composites... 

Fibrous sensors to help the monitoring of weaving process... 

The transport of information from sensors to the central nervous system and of instructions from the central nervous system to the various organs occurs through electric impulses transported by nerve cells (see Fig. 6.17). These cells consist of a body with star-like projections and a long fibrous tail called an axon. While in some molluscs the whole membrane is in contact with the intercellular liquid, in other animals it is covered with a multiple myeline layer which is interrupted in definite segments (nodes of Ranvier). The Na+,K+-ATPase located in the membrane maintains marked ionic concentration differences in the nerve cell and in the intercellular liquid. For example, the squid axon contains 0.05 MNa+, 0.4 mK+, 0.04-0.1 m Cl-, 0.27 m isethionate anion and 0.075 m aspartic acid anion, while the intercellular liquid contains 0.46 m Na+, 0.01 m K+ and 0.054 m Cl-. 

The first sensor proposed for detecting gastric and oesophageal pH24, made use of two fluorophores, fluorescein and eosin, immobilised onto fibrous particles of amino-ethyl cellulose, fixed on polyester foils. Only tested in vitro, the sensor reveals a satisfactory response time of around 20 seconds. 

Addition of potassium ions to the fibers leaves the fibrous structure intact but destroys the helicity [128]. Sandwich complexes between the cation and 114d are observed. With higher concentrations of potassium, the sandwich complexes break down and isolated 4K+114d are observed (Scheme 61). In both complexed forms the salt blocks the chirality transfer from the side chains to the supramolecular assemblies. Such fibers with controllable chirality can be interesting materials for molecular switches or in sensors devices. 

The major factors impacting sensor performance, whatever the physiological basis, are the degree of local vascularity and the loss of functional microvessels, together with the eventual presence and thickness of a fibrous capsule. Continued inflammation and collagen deposition eventually reach an equilibrium state, and the thickness of the fibrous capsule has been proposed as an index of biocompatibility.32 The thickness and vascularity of the capsule depend on the size, surface texture, and porosity of the implant.33-35... 

Polyurethanes have also been employed as outer sensor membranes. Yu et al. evaluated the biocompatibility and analytical performance of a subcutaneous glucose sensor with an epoxy-enhanced polyurethane outer membrane.15 The membrane was mechanically durable and the resulting sensors were functional for up to 56 days when implanted in the subcutaneous tissue of rats. Despite the improved sensor lifetime, all of the polyurethane-coated sensors were surrounded by a fibrous capsule, indicating an enduring inflammatory response that is undesirable due to the aforementioned effects on analytical sensor performance. To date, the clinical success of most passive approaches has been rather limited. It is doubtful that one passive material alone will be capable of imparting long-term (i.e., weeks to months) biocompatibility for in vivo use due to the extremely dynamic nature of the wound environment. 

The sensor substrates can easily be incorporated into pre-existing deposition equipment (Fig. 13.15a). This technique has led to the production of fibrous growth and high surface area morphologies (Fig. 13.15b). This... 

The packaging of the pressure transducer is also a problem that needs to be addressed, especially when the transducer is in contact with blood for long periods of time. Not only must the package be biocompatible, but it also must allow the appropriate pressure to be transmitted from the biological fluid to the diaphragm. Thus, a material that is mechanically stable under corrosive and aqueous environments in the body is needed. Chronically implanted objects are usually coated with a fibrous capsule by the body as a part of the foreign body response, and this capsule can exert a force on the pressure sensor that will affect its baseline pressure. Thus, it is important to package pressure sensors with materials that will minimize this encapsulation. 

G Langereis, L de Voogd-Claessen, A SipilS, H Illing-Guntfaer, A Spaepen, T Linz, CONTEXT Contactless sensors for body monitoring incorporated in textiles , FiberMed06 Fibrous Products in Medical and Health Care, Tampere Hall, Finland, 2006. 

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