Assessment of human bones encompassing physiological decay and damage using piezo sensors in non-bonded configuration

Abstract

In the recent years, several biomedical applications of lead zirconate titanate piezo-electric ceramic patches based on the electro-mechanical impedance technique have been reported in the literature. However, practical application of the technique on live subjects is severely hampered due to the requirement of bonding the patch with bone or cartilage with an adhesive. In addition, live subjects have skin cover over the bone. This article proposes and evaluates the feasibility of employing lead zirconate titanate patches as biomedical sensors in non-bonded configuration for assessing the physiological conditions of bones. For this purpose, a special design is proposed where the lead zirconate titanate patch is first bonded on a thin aluminum strip, which is in turn clamped securely on the biomedical subject. The proposed configuration is investigated both in vitro and in vivo. The non-bonded piezo sensors are first investigated to identify dynamic parameters of the bone through lab-based experimental study involving artificial bones. Thereafter, physiological damage and decay conditions are artificially simulated in the experimental bones and the same are correlated with changes in conductance signatures from the non-bonded piezo sensor as well as the lead zirconate titanate patch in the conventional adhesively bonded (direct bonding to the subject) configuration. The trend of the conductance signatures in the healthy and the damaged conditions from the non-bonded piezo sensor is found to correlate well with the corresponding signatures from the directly bonded piezo sensor. At the same time, the repeatability of the signatures is also found to be satisfactory. After success in bare bones, the non-bonded piezo sensor configuration is extended to monitor the condition of bones covered with skin and tissue, simulated in the lab with the aid of silicone-based coating. Finally, a proof-of-concept experiment on a live human subject is successfully demonstrated. The overall results of the study demonstrate very good prospects of employing lead zirconate titanate patches in non-bonded piezo sensor mode for monitoring the condition of human bones and other related biomedical subjects.

Numerical evaluation of nonbonded piezo sensor for biomedical diagnostics using electromechanical impedance technique

“…The influence of skin on the conductance signature was additionally investigated using additional modeling. Although quite cumbersome, best efforts were made to generate 3D model of the bones accurately with the primary dimensions similar to the real bones investigated by the authors . For simplicity, minor details like exact shape of bone and unevenness of bone surface were omitted.…”

“…Meshing was done for all the components involved, which are aluminum strip, epoxy adhesive, bone, and the PZT patch. In the actual experiment, this aluminum strip was secured to the bone using jubilee clamps at the ends of the aluminum strip . In numerical analysis, the same was simulated by sticking the ends of the aluminum strip to the bone through epoxy bond.…”

“…For the experimental bone model, jubilee clamps were employed for tightening the NBPS. By varying the level of tightening, three levels of clamping, namely, open, partial, and fully tightened configurations, were achieved.…”

“…In the related experimental study by the authors, the physiological one time decay (like that in osteomalacia) was achieved by dipping the bone in a chemical solution (methyl ethyl ketone) over a time period. The corresponding condition was simulated in the numerical model by removing a reasonable portion of the bone, as shown in Figure , equivalent to the bone material lost to the chemical leaching in the actual experiment.…”

“…However, in most of the diagnostic cases of live human or animal subjects, the DBPS poses not only a health hazard but could also be an irritant for the subject. In order to develop a practical substitute of the DBPS configuration while maintaining the effectiveness of measurement well within discernible limits, proof‐of‐concept experiments with a nonbonded piezo sensor (NBPS) have been successfully performed by the authors . Both NBPS and DBPS, illustrated in Figure , are based on the EMI technique, where high‐frequency (typically >30 kHz) vibrations generated by the surface bonded PZT patch are used to detect changes in structural drive point impedance caused by cracks or any other type of damage.…”