Bio-compatible wireless inductive thin-film strain sensor for monitoring the growth and strain response of bone in osseointegrated prostheses

Abstract

Many benefits can be derived from in situ monitoring of the growth, load response, and condition of human bone. In particular, bone monitoring offers opportunity to advance understanding and designing of osseointegrated mechanical components fixated into bones such as artificial joints and more recently osseointegrated prosthetic limbs. In this study, a bio-compatible wireless inductive strain-sensing system is proposed, which is designed to monitor the growth and strain response of bone-hosting implants. Thin-film circuit fabrication methods based on lithography are adopted to develop a conformable wireless strain sensor designed as a passive resistive-inductive-capacitive circuit. Two forms of strain sensing are designed into the thin-film sensor. First, parallel-plate capacitors fabricated from metal electrodes and a polyimide dielectric layer are introduced to modulate bone strain onto a resonant frequency of the thin-film sensor. A second resonant frequency is introduced in the sensor design to measure circumferential bone growth using a highly nonlinear titanium-resistive element, whose resistance exponentially increases well after 1000 me under monotonic increasing hoop strain. To ensure the possibility for implantation in animal subjects in future study, the thin-film sensing system is fabricated using mainly bio-compatible polymers (e.g. polyimide) and metals (e.g. titanium and gold). Fabricated prototypes inductively coupled using an impedance analyzer are experimentally tested. Results reveal linear response of the first resonant frequency to low levels of strain with a sensitivity of 4.555 Hz per unit microstrain. The second resonant frequency is sensitive to the resistive fuse with nonlinear fuse behavior initiated above 1000 me and impedance phase increasing exponentially thereafter.

Novel magnetic stimulation methodology for low-current implantable medical devices

“…However, current small-scale (up to micro-scale) implantable magnetic devices require that high electrical currents (usually exceeding 1 A) must flow in the stimulation coils to ensure the delivery of therapeutic efficient magnetic flux densities [1,2,25,[29][30][31]. This problem has been addressed by using extracorporeal wireless powering [32]; however, this approach presents significant limitations, as it is uncomfortable for patients, it troubles their routine activities and it strongly reduces the periodicity of operation of bioelectronic medical devices [33]. Therefore, as future personalized medicine will demand autonomous stand-alone biomagnetic stimulators with self-powering ability for long-term personalized therapeutic operation [16,17,21,25,34], a new methodology is demanded to simultaneously require low electric current excitations and ensure the delivery of suitable magnetic field stimuli.…”

Altering the Course of Technologies to Monitor Loosening States of Endoprosthetic Implants

“…(T1-L1) Burton, Sun, and Lynch [72] developed a strain sensor to measure bone growth. The technology comprises two cosurface circuits: one for measuring the axial strain, and the other for the radial strain (Figure 16 a).…”

Surface textures for stretchable capacitive strain sensors

“…For instance, flexible resistancebased sensors have been developed using carbon nanotubes Srivastava et al (2011) and graphene nanosheets Manna et al (2019). Capacitance-based sensors have been proposed from bio-compatible polymers Burton et al (2019) and nanocomposite thin films Lee et al (2016). Research examples targeting biological skin mimicry for SHM applications include strain sensing sheets based on large area electronics and integrated circuits Tung et al (2014); Zhang et al (2014); Zhou et al (2010), electrical impedance tomography Hallaji et al (2014); Gupta et al (2016), and multifunctional materials Downey et al (2018); Yan et al (2019).…”