A Passive Biodegradable Implant for Subcutaneous Soft Tissue Trauma Monitoring

Abstract

In-body medical devices can play an important role in clinical monitoring and diagnosis of diseases. Wireless devices implanted within a patient have to be physically small, and must overcome the challenges of having a little or no onboard electrical power and the highly attenuating electromagnetic propagation environment which is the human body. In this paper, we investigate the use of biodegradable implant to monitor the healing of soft-tissue trauma and to allow early stage diagnosis of infection. The implantable tag is designed to degrade in a predetermined and controlled method, the stage of which can be measured from outside the body without the need for further surgical intervention. The speed of degradation of the tag depends on the temperature and acidity of the subcutaneous tissue in which the tag is implanted. We show that as the electrical length of the tag pattern increases due to degradation, the resonant frequency changes significantly, and this change in resonant frequency can be detected from outside the patient. Results are presented showing the tag's performance at normal and oblique incidence, and techniques for miniaturizing and enhancing the tag's response sensitivity are given. As the entire tag is biodegradable, there is no need for further postoperative surgery to remove it from the patient at the end of its useful life.

Biodegradable Implantable Sensors: Materials Design, Fabrication, and Applications

“…A biodegradable and implantable RF identification tag has been created as another wireless operation mode. [89] The device can be implanted to observe tissue healing and to permit early i) The layers of resistive sensors. ii) Image of the sensing element with serpentine traces.…”

Investigations into improving the detectability of self‐resonant RFID tags

“…Information is, therefore, stored in their forward and reflected frequency response and communication between the tag and the interrogator takes place using the backscattering mechanism [5,15]. A single uniform cross-shaped resonator similar to the one presented in [8] and used in the literature for FSS applications [16] has been designed. Fig.…”

“…Despite the growing interests in RFID technology in various sectors of industry, few attempts have been made to use selfresonant tags as an implantable device. It has been suggested in [8,9] that backscattering tags could be employed as a biodegradable subcutaneous implant for early-stage diagnoses of post-surgical infection. Nevertheless, it has been shown that the backscattered signal was highly attenuated by the biological medium and some signal detectability issues have been encountered.…”

“…In fact, the human body consists of various layers with different electrical properties; therefore, it is not a favourable medium for electromagnetic waves [10]. For the subcutaneous implant in [8], the communication medium of the human body was found to lower the resonance frequency of the tag and to cause signal power loss, when these dielectric losses increase beyond a certain limit it may lead to flattening the response of the tag; therefore, a tag design with strong resonance characteristics needs to be adopted.…”

“…Two self-resonant tags are studied, a uniform cross and gammadion cross-shaped resonators, to highlight the possibility of using miniaturised tag without affecting the RF signature. Both resonators can be reconfigured by applying some switching techniques (such as optical switches or by using biodegradable materials as suggested in [8]) to alter their electrical lengths to embed different information in their frequency response. However, switching mechanisms are not considered in this work, and discrete physical states of these two resonators have been evaluated.…”