Materials and Orthopedic Applications for Bioresorbable Inductively Coupled Resonance Sensors.

Bioresorbable passive resonance sensors based on inductor-capacitor (LC) circuits provide an auspicious sensing technology for temporary battery-free implant applications due to their simplicity, wireless readout, and the ability to be eventually metabolized by the body. In this study, the fabrication and performance of various LC circuit-based sensors are investigated to provide a comprehensive view on different material options and fabrication methods. The study is divided into sections that address different sensor constituents, including bioresorbable polymer and bioactive glass substrates, dissolvable metallic conductors, and atomic layer deposited (ALD) water barrier films on polymeric substrates. The manufactured devices included a polymer-based pressure sensor that remained pressure responsive for 10 days in aqueous conditions, the first wirelessly readable bioactive glass-based resonance sensor for monitoring the complex permittivity of its surroundings, and a solenoidal coil-based compression sensor built onto a polymeric bone fixation screw. The findings together with the envisioned orthopedic applications provide a reference point for future studies related to bioresorbable passive resonance sensors.

Bioresorbable Conductive Wire with Minimal Metal Content.

The emergence of transient electronics has created the need for bioresorbable conductive wires for signal and energy transfer. We present a fully bioresorbable wire design where the conductivity is provided by only a few micrometers thick electron-beam evaporated magnesium layer on the surface of a polymer fiber. The structure is electrically insulated with an extrusion coated polymer sheath, which simultaneously serves as a water barrier for the dissolvable magnesium conductor. The resistance of the wires was approximately 1 Ω cm-1 and their functional lifetime in buffer solution was more than 1 week. These properties could be modified by using different conductor materials and film thicknesses. Furthermore, the flexibility of the wires enabled the fabrication of planar radio frequency (RF) coils, which were wirelessly measured. Such coils have the potential to be used as wireless sensors. The wire design provides a basis for bioresorbable wires in applications where only a minimal amount of metal is desired, for example, to avoid toxicity.

Nanocellulose and chitosan based films as low cost, green piezoelectric materials.

Nanocellulose and chitosan have recently started to get attention as environmentally friendly piezoelectric materials for sensor and energy harvesting applications. Conversely, current commercially available flexible piezoelectric films made of for example polyvinylidene difluoride (PVDF) are relatively expensive and made from non-renewable materials. We measured the piezoelectric responses (2-8 pC/N) for solvent casted films based on nanocellulose, microcrystalline chitosan and their blends. In addition, the tensile properties of the piezoelectric films were characterized to find out if chitosan could be used to enhance the flexibility of the brittle nanocellulose films. Based on the results, plain chitosan is an interesting piezoelectric material itself. In addition, blending nanocellulose and chitosan could be a potential method for tailoring the properties of solvent casted low cost, green piezoelectric films.

Testing and comparing of film-type sensor materials in measurement of plantar pressure distribution.

Simple in-shoe sensors based on film-type sensor materials were developed in this study. Three sensor materials were tested: polyvinylidenefluoride (PVDF), cellulose nanofibrils (CNF) and ElectroMechanical Film (EMFi). Plantar pressure distributions of a subject were measured with the developed in-shoe sensors; each consisting of three sensor channels (lateral and medial metatarsal heads and heel). In addition, piezoelectric sensor sensitivities and crosstalk between the sensor channels were determined. Differences between the tested film-type materials and measured plantar pressure distribution signals were studied.

Novel wireless electroencephalography system with a minimal preparation time for use in emergencies and prehospital care.

BACKGROUND: Although clinical applications such as emergency medicine and prehospital care could benefit from a fast-mounting electroencephalography (EEG) recording system, the lack of specifically designed equipment restricts the use of EEG in these environments. METHODS: This paper describes the design and testing of a six-channel emergency EEG (emEEG) system with a rapid preparation time intended for use in emergency medicine and prehospital care. The novel system comprises a quick-application cap, a device for recording and transmitting the EEG wirelessly to a computer, and custom software for displaying and streaming the data in real-time to a hospital. Bench testing was conducted, as well as healthy volunteer and patient measurements in three different environments: a hospital EEG laboratory, an intensive care unit, and an ambulance. The EEG data was evaluated by two experienced clinical neurophysiologists and compared with recordings from a commercial system. RESULTS: The bench tests demonstrated that the emEEG system's performance is comparable to that of a commercial system while the healthy volunteer and patient measurements confirmed that the system can be applied quickly and that it records quality EEG data in a variety of environments. Furthermore, the recorded data was judged to be of diagnostic quality by two experienced clinical neurophysiologists. CONCLUSIONS: In the future, the emEEG system may be used to record high-quality EEG data in emergency medicine and during ambulance transportation. Its use could lead to a faster diagnostic, a more accurate treatment, and a shorter recovery time for patients with neurological brain disorders.

Embedded capacitive sensor system for hip surgery rehabilitation: online measurements and long-term stability.

We are developing an embedded system that measures the force between foot and insole with a low-cost laminated capacitive sensor matrix. The system is intended to guide a hip surgery patient to train the operated leg with a suitable force. In this paper, we present an embedded measurement system, which is able to estimate the total plantar force in real-time and to give instant feedback to a user. We also present a method for compensating the drift of capacitive sensors. A 5-hour long test measurement was made in order to validate the system. According to the preliminary test, the compensation method effectively prevents the drift of the baseline of the force reading.