Ultrasensitive capacitive sensing system for smart medical devices with ability to monitor fracture healing stages

Impact of transforaminal lumbar interbody fusion on rod load: a comparative biomechanical analysis between a cadaveric instrumentation and simulated bone fusion

BACKGROUND

Recent research has demonstrated the potential of implant load monitoring to assess posterolateral spinal fusion in a sheep model. This study investigated whether such a system could monitor bone fusion after interbody fusion surgery by biomechanically testing of human cadaveric lumbar spines in two states: following a transforaminal lumbar interbody fusion (TLIF) procedure and after simulating bone fusion.

METHODS

Eight human cadaveric spines underwent a TLIF procedure at L4-L5. An implantable sensor system was attached to one rod, while two strain gauges were attached to the contralateral rod (dorsally and ventrally) to derive implant load changes during unconstrained flexion-extension (FE), lateral bending (LB) and axial rotation (AR) motion. The specimens were retested after simulating bone fusion at L4-L5. Range of motion (ROM) of L4-L5 was measured during each loading mode.

RESULTS

ROM decreased in the simulated bone fusion state in all loading directions (p ≤ 0.002). Compared to the TLIF motion, the remnant motion after simulated fusion was 53 ± 21 % in FE, 40 ± 12 % in LB, and 49 ± 16 % in AR. In both states, measured strain on the posterior instrumentation was highest during LB motion. All sensors detected a significant decrease in load-induced rod strain after simulated bone fusion in LB (p ≤ 0.002). The strain measured by the implantable strain sensor, the dorsal strain gauge, and the ventral strain gauge decreased to 49 ± 12 %, 49 ± 17 %, and 54 ± 17 %, respectively.

CONCLUSION

Rod load measured via strain sensors can monitor fusion progression after a TLIF procedure when measured during isolated LB of the lumbar spine. This study provides the basis for further development and understanding of in vivo implant load data.

Bioelectronic osteosynthesis plate to monitor the fracture bone healing using electric capacitive variations

BACKGROUND

Bone fractures represent a global public health issue. Over the past few decades, a sustained increase in the number of incidents and prevalent cases have been reported, as well as in the years lived with disability. Current monitoring techniques predominantly rely on imaging methods, which can result in subjective assessments, and expose patients to unnecessary cumulative doses of radiation. Besides, they are costly and incapable of providing continuous daily detection of fracture healing stages. Technological advances are still required to design fixation systems with the ability to minimize the risk of delayed healing and nonunion conditions for timely medical intervention, such that preventive procedures can be provided. This work proposes.

METHODS

An innovative bioelectronic osteosynthesis plate, minimally customized from a fixation device used in clinical practice, was developed to monitor the bone-implant interface to effectively detect the progression of bone fractures stages. Our technology includes a network-architectured capacitive interdigitated system, a Bluetooth module, an analog-to-digital converter, a multiplexer, a microcontroller, and a miniaturized battery.

RESULTS

Both experimental tests with biological tissues and numerical simulations show strong evidence that this bioelectronic implant is able: (i) to detect the four distinct bone healing stages, with capacitance decreases throughout the healing process; and (ii) to monitor the callus formation across multiple target regions.

CONCLUSIONS

This work provides a significant contribution to the design of bioelectronic implant technologies for highly personalized sensing of biointerfaces. Our bioelectronic fixation implant supports faster fracture healing, mainly for delayed healing and non-union conditions.

A millimetre-scale capacitive biosensing and biophysical stimulation system for emerging bioelectronic bone implants

Bioelectronic bone implants are being widely recognized as a promising technology for highly personalized bone/implant interface sensing and biophysical therapeutic stimulation. Such bioelectronic devices are based on an innovative concept with the ability to be applied to a wide range of implants, including in fixation and prosthetic systems. Recently, biointerface sensing using capacitive patterns was proposed to overcome the limitations of standard imaging technologies and other non-imaging technologies; moreover, electric stimulation using capacitive patterns was proposed to overcome the limitations of non-instrumented implants. We here provide an innovative low-power miniaturized electronic system with ability to provide both therapeutic stimulation and bone/implant interface monitoring using network-architectured capacitive interdigitated patterns. It comprises five modules: sensing, electric stimulation, processing, communication and power management. This technology was validated using in vitro tests: concerning the sensing system, its ability to detect biointerface changes ranging from tiny to severe bone-implant interface changes in target regions was validated; concerning the stimulation system, its ability to significantly enhance bone cells' full differentiation, including matrix maturation and mineralization, was also confirmed. This work provides an impactful contribution and paves the way for the development of the new generation of orthopaedic biodevices.

The application of impantable sensors in the musculoskeletal system: a review

As the population ages and the incidence of traumatic events rises, there is a growing trend toward the implantation of devices to replace damaged or degenerated tissues in the body. In orthopedic applications, some implants are equipped with sensors to measure internal data and monitor the status of the implant. In recent years, several multi-functional implants have been developed that the clinician can externally control using a smart device. Experts anticipate that these versatile implants could pave the way for the next-generation of technological advancements. This paper provides an introduction to implantable sensors and is structured into three parts. The first section categorizes existing implantable sensors based on their working principles and provides detailed illustrations with examples. The second section introduces the most common materials used in implantable sensors, divided into rigid and flexible materials according to their properties. The third section is the focal point of this article, with implantable orthopedic sensors being classified as joint, spine, or fracture, based on different practical scenarios. The aim of this review is to introduce various implantable orthopedic sensors, compare their different characteristics, and outline the future direction of their development and application.