A Quantitative Approach for the Bone-implant Osseointegration Assessment Based on Ultrasonic Elastic Guided Waves

Advanced Piezoelectric Materials, Devices, and Systems for Orthopedic Medicine

Harnessing the robust electromechanical couplings, piezoelectric materials not only enable efficient bio-energy harvesting, physiological sensing and actuating but also open enormous opportunities for therapeutic treatments through surface polarization directly interacting with electroactive cells, tissues, and organs. Known for its highly oriented and hierarchical structure, collagen in natural bones produces local electrical signals to stimulate osteoblasts and promote bone formation, inspiring the application of piezoelectric materials in orthopedic medicine. Recent studies showed that piezoelectricity can impact microenvironments by regulating molecular sensors including ion channels, cytoskeletal elements, cell adhesion proteins, and other signaling pathways. This review thus focuses on discussing the pioneering applications of piezoelectricity in the diagnosis and treatment of orthopedic diseases, aiming to offer valuable insights for advancing next-generation medical technologies. Beginning with an introduction to the principles of piezoelectricity and various piezoelectric materials, this review paper delves into the mechanisms through which piezoelectric materials accelerated osteogenesis. A comprehensive overview of piezoelectric materials, devices, and systems enhancing bone tissue repair, alleviating inflammation at infection sites, and monitoring bone health is then provided, respectively. Finally, the major challenges faced by applications of piezoelectricity in orthopedic conditions are thoroughly discussed, along with a critical outlook on future development trends.

Evaluation of a vibration modeling technique for the in-vitro measurement of dental implant stability

The Advanced System for Implant Stability Testing (ASIST) is a device currently being developed to noninvasively measure implant stability by estimating the mechanical stiffness of the bone-implant interface, which is reported as the ASIST Stability Coefficient (ASC). This study's purpose was to determine whether changes in density, bonding, and drilling technique affect the measured vibration of a dental implant, and whether they can be quantified as a change in the estimated BII stiffness. Stability was also measured using RFA, insertion torque (IT) and the pullout test. Bone-level tapered implants (4.1 mm diameter, 10 mm length) were inserted in polyurethane foam as an artificial bone substitute. Samples were prepared using different bone densities (20, 30, 40 PCF), drilling sequences, and superglue to simulate a bonded implant. Measurements were compared across groups at a significance level of 0.05. The ASC was able to indicate changes in each factor as a change in the interfacial stiffness. IT and pullout force values also showed comparable increases. Furthermore, the relative difference in ISQ values between experimental groups was considerably smaller than the ASC. While future work should be done using biological bone and in-vivo systems, the results of this in-vitro study suggest that modelling of the implant system with a vibration-based approach may provide a noninvasive method of assessing the mechanical stability of the implant.

Monitoring Osseointegration Process Using Vibration Analysis

Osseointegration implant has attracted significant attention as an alternative treatment for transfemoral amputees. It has been shown to improve patients' sitting and walking comfort and control of the artificial limb, compared to the conventional socket device. However, the patients treated with osseointegration implants require a long rehabilitation period to establish sufficient femur-implant connection, allowing the full body weight on the prosthesis stem. Hence, a robust assessment method on the osseointegration process is essential to shorten the rehabilitation period and identify the degree of osseointegration prior to the connection of an artificial limb. This paper investigates the capability of a vibration-related index (E-index) on detecting the degree of simulated osseointegration process with three lengths of the residual femur (152, 190 and 228 mm). The adhesive epoxy with a setting time of 5 min was applied at the femur-implant interface to represent the stiffness change during the osseointegration process. The cross-spectrum and colormap of the normalised magnitude demonstrated significant changes during the cure time, showing that application of these plots could improve the accuracy of the currently available diagnostic techniques. Furthermore, the E-index exhibited a clear trend with a noticeable average increase of 53% against the cure time for all three residual length conditions. These findings highlight that the E-index can be employed as a quantitative justification to assess the degree of osseointegration process without selecting and tracing the resonant frequency based on the geometry of the residual femur.

Implants with Sensing Capabilities

Because of the aging human population and increased numbers of surgical procedures being performed, there is a growing number of biomedical devices being implanted each year. Although the benefits of implants are significant, there are risks to having foreign materials in the body that may lead to complications that may remain undetectable until a time at which the damage done becomes irreversible. To address this challenge, advances in implantable sensors may enable early detection of even minor changes in the implants or the surrounding tissues and provide early cues for intervention. Therefore, integrating sensors with implants will enable real-time monitoring and lead to improvements in implant function. Sensor integration has been mostly applied to cardiovascular, neural, and orthopedic implants, and advances in combined implant-sensor devices have been significant, yet there are needs still to be addressed. Sensor-integrating implants are still in their infancy; however, some have already made it to the clinic. With an interdisciplinary approach, these sensor-integrating devices will become more efficient, providing clear paths to clinical translation in the future.

Experimental Investigation of Vibration Analysis on Implant Stability for a Novel Implant Design

Osseointegrated prostheses are widely used following transfemoral amputation. However, this technique requires sufficient implant stability before and during the rehabilitation period to mitigate the risk of implant breakage and loosening. Hence, reliable assessment methods for the osseointegration process are essential to ensure initial and long–term implant stability. This paper researches the feasibility of a vibration analysis technique for the osseointegration (OI) process by investigating the change in the dynamic response of the residual femur with a novel implant design during a simulated OI process. The paper also proposes a concept of an energy index (the E–index), which is formulated based on the normalized magnitude. To illustrate the potential of the E–index, this paper reports on changes in the vibrational behaviors of a 133 mm long amputated artificial femur model and implant system, with epoxy adhesives applied at the interface to simulate the OI process. The results show a significant variation in the magnitude of the colormap against curing time. The study also shows that the E–index was sensitive to the interface stiffness change, especially during the early curing process. These findings highlight the feasibility of using the vibration analysis technique and the E–index to quantitatively monitor the osseointegration process for future improvement on the efficiency of human health monitoring and patient rehabilitation.

Detection and Imaging of Damages and Defects in Fibre-Reinforced Composites by Magnetic Resonance Technique

Defectively manufactured and deliberately damaged composite laminates fabricated with different continuous reinforcing fibres (respectively, carbon and glass) and polymer matrices (respectively, thermoset and thermoplastic) were inspected in magnetic resonance imaging equipment. Two pulse sequences were evaluated during non-destructive examination conducted in saline solution-immersed samples to simulate load-bearing orthopaedic implants permanently in contact with biofluids. The orientation, positioning, shape, and especially the size of translaminar and delamination fractures were determined according to stringent structural assessment criteria. The spatial distribution, shape, and contours of water-filled voids were sufficiently delineated to infer the amount of absorbed water if thinner image slices than this study were used. The surface texture of composite specimens featuring roughness, waviness, indentation, crushing, and scratches was outlined, with fortuitous artefacts not impairing the image quality and interpretation. Low electromagnetic shielding glass fibres delivered the highest, while electrically conductive carbon fibres produced the poorest quality images, particularly when blended with thermoplastic polymer, though reliable image interpretation was still attainable.

The state of the art of osseointegration for limb prosthesis

Osseointegration (OI) is the direct attachment of bone onto a titanium implant. Recently, the term is used to describe "transdermal" implants that allow an external prosthesis to be connected directly to the skeleton. This technology eliminates the challenges of conventional socket-based prostheses, such as skin breakdown and poor fit, which are common in patients with major extremity amputations. Osseointegration patients demonstrate encouraging improvements in quality of life and function. Patients report improvement in prosthetic use, prosthetic mobility, global health, and pain reduction on a variety of clinical assessment tools. Various implants have been developed for osseointegration for amputees. These implants use a variety of fixation strategies and surface augments to allow for successful integration into the host bone. Regardless of design, all OI implants face similar challenges, particularly infections. Other challenges include the inability to determine when integration has occurred and the inability to detect loss of integration. These challenges may be met by incorporating sensing systems into the implants. The percutaneous nature of the metal devices can be leveraged so that internal sensors need not be wireless, and can be interrogated by external monitoring systems, thus providing crucial, real-time information about the state of the implant. The purpose of this review is to (1) review the basic science behind osseointegration, (2) provide an overview of current implants, practice patterns, and clinical outcomes, and (3) preview sensor technologies which may prove useful in future generations of transdermal orthopaedic implants.

Quantitative assessment of compress-type osseointegrated prosthetic implants in human bone using electromechanical impedance spectroscopic methods

Osseointegrated (OI) prostheses are a promising alternative to traditional socket prostheses. They can enhance the quality of life of amputees by avoiding fit and comfort issues commonly associated with sockets. The main structural element of the OI prosthesis is a biocompatible metallic implant that is surgically implanted into the bone of the residual limb. The implant is designed to provide a conducive surface for the host bone to osseointegrate with. The osseointegration process of the implant is difficult to clinically evaluate, leading to conservative postoperative rehabilitation approaches. Elastic stress waves generated in an OI prosthesis have been previously proposed to interrogate the implant-bone interface for quantitative assessment of the osseointegration process. This paper provides a detailed overview of the various elastic stress wave methods previously explored for in situ characterization of OI implants. Specifically, the paper explores the use of electromechanical impedance spectroscopy (EIS) to assess the OI process in compress-type OI prostheses. The EIS approach measures the electrical impedance spectrum of lead zirconate titanate elements bonded to the free end of the implant. The research utilizes both numerical simulation and experimental verification to establish that the electromechanical impedance spectrum is sensitive (between 400 and 460 kHz) to both the degree and location of osseointegration. A baseline-free OI index is proposed to quantify the degree of osseointegration at the implant-bone interface and to assess the stability of the OI implant for clinical decision making.

Non-radiative healing assessment techniques for fractured long bones and osseointegrated implant

The paper provides an overview of the fracture healing process of long bones, a review of work that proposed appropriate physical parameters for the assessment of healing and highlights some recent work that reported on the development of non-radiative technique for healing assessment. An overview of the development and monitoring of osseointegration for trans-femoral osseointegrated implant is also presented. The state of healing of a fractured long bone and the stability of osseointegrated implants can be seen as engineering structural components where the mechanical properties are restored to facilitate their desired function. To this end, this paper describes non-radiative techniques that are useful for healing assessment and the stability assessment of osseointegrated implants. The achievement of non-radiative quantitative assessment methodologies to determine the state of healing of fractured long bones and to assess the stability of osseointegrated implant will shorten the patient's rehabilitation time, allowing earlier mobility and return to normal activities. Recent work on the development of assessment techniques supported by the Office of Naval Research as part of the Monitoring of Osseointegrated Implant Prosthesis program is highlighted.