Modeling of a New Percutaneous Orthopedic Implant System to Control the Post-surgery Osseointegration Process

This study presents a mechanical model of a novel medical device designed to optimize the osseointegration process in upper and lower limb amputees, leading to the promotion of optimal rehabilitation. The medical device is developed to reduce the risk of implant failure, leading to re-amputation above the implant. The proposed model serves several purposes: 1) to guide the osseointegration process by providing electrical endo-stimulation directly to the bone-implant contact site, using an invasive electrical stimulation system, which is implanted in the bone permanently, 2) to locally transmit stem cells after implantation, without the need for opening the skin or perforating the bone, which is particularly useful for regenerative medicine after partial healing of the implant, 3) to transmit necessary nutrients from the bone, also without opening the skin or puncturing the bone, and 4) to combat infections by locally administering drugs after implantation.

Active osseointegration in an ex vivo porcine bone model

Achieving osseointegration is a fundamental requirement for many orthopaedic, oral, and craniofacial implants. Osseointegration typically takes three to 6 months, during which time implants are at risk of loosening. The aim of this study was to investigate whether osseointegration could be actively enhanced by delivering controllable electromechanical stimuli to the periprosthetic bone. First, the osteoconductivity of the implant surface was confirmed using an in vitro culture with murine preosteoblasts. The effects of active treatment on osseointegration were then investigated in a 21-day ex vivo model with freshly harvested cancellous bone cylinders (n = 24; Ø10 mm × 5 mm) from distal porcine femora, with comparisons to specimens treated by a distant ultrasound source and static controls. Cell viability, proliferation and distribution was evident throughout culture. Superior ongrowth of tissue onto the titanium discs during culture was observed in the actively stimulated specimens, with evidence of ten-times increased mineralisation after 7 and 14 days of culture (p < 0.05) and 2.5 times increased expression of osteopontin (p < 0.005), an adhesive protein, at 21 days. Moreover, histological analyses revealed increased bone remodelling at the implant-bone interface in the actively stimulated specimens compared to the passive controls. Active osseointegration is an exciting new approach for accelerating bone growth into and around implants.

Bioelectricity in dental medicine: a narrative review

BACKGROUND

Bioelectric signals, whether exogenous or endogenous, play crucial roles in the life processes of organisms. Recently, the significance of bioelectricity in the field of dentistry is steadily gaining greater attention.

OBJECTIVE

This narrative review aims to comprehensively outline the theory, physiological effects, and practical applications of bioelectricity in dental medicine and to offer insights into its potential future direction. It attempts to provide dental clinicians and researchers with an electrophysiological perspective to enhance their clinical practice or fundamental research endeavors.

METHODS

An online computer search for relevant literature was performed in PubMed, Web of Science and Cochrane Library, with the keywords "bioelectricity, endogenous electric signal, electric stimulation, dental medicine."

RESULTS

Eventually, 288 documents were included for review. The variance in ion concentration between the interior and exterior of the cell membrane, referred to as transmembrane potential, forms the fundamental basis of bioelectricity. Transmembrane potential has been established as an essential regulator of intercellular communication, mechanotransduction, migration, proliferation, and immune responses. Thus, exogenous electric stimulation can significantly alter cellular action by affecting transmembrane potential. In the field of dental medicine, electric stimulation has proven useful for assessing pulp condition, locating root apices, improving the properties of dental biomaterials, expediting orthodontic tooth movement, facilitating implant osteointegration, addressing maxillofacial malignancies, and managing neuromuscular dysfunction. Furthermore, the reprogramming of bioelectric signals holds promise as a means to guide organism development and intervene in disease processes. Besides, the development of high-throughput electrophysiological tools will be imperative for identifying ion channel targets and precisely modulating bioelectricity in the future.

CONCLUSIONS

Bioelectricity has found application in various concepts of dental medicine but large-scale, standardized, randomized controlled clinical trials are still necessary in the future. In addition, the precise, repeatable and predictable measurement and modulation methods of bioelectric signal patterns are essential research direction.

Bio-Piezoelectric Ceramic Composites for Electroactive Implants-Biological Performance

Barium titanate (BaTiO3) piezoelectric ceramic may be a potential alternative for promoting osseointegration due to its piezoelectric properties similar to bone electric potentials generated in loading function. In this sense, the aim of this in vitro study was to evaluate the cellular response of human osteoblasts and gingival fibroblasts as well as the impact on S. oralis when in contact with BaTiO3 functionalized zirconia implant surfaces with piezoelectric properties. Zirconia discs with BaTiO3 were produced and contact poling (piezo activation) was performed. Osteoblasts (hFOB 1.19), fibroblasts (HGF hTERT) and S. oralis were culture on discs. Cell viability and morphology, cell differentiation markers, bacterial adhesion and growth were evaluated. The present study suggests that zirconia composite surfaces with the addition of piezoelectric BaTiO3 are not cytotoxic to peri-implant cells. Also, they seem to promote a faster initial osteoblast differentiation. Moreover, these surfaces may inhibit the growth of S. oralis by acting as a bacteriostatic agent over time. Although the piezoelectric properties do not affect the cellular inflammatory profile, they appear to enable the initial adhesion of bacteria, however this is not significant over the entire testing period. Furthermore, the addition of non-poled BaTiO3 to zirconia may have a potential reduction effect on IL-6 mediated-inflammatory activity in fibroblasts.

The Sympathetic Nervous System in Dental Implantology

The sympathetic nervous system plays a vital role in various regulatory mechanisms. These include the well-known fight-or-flight response but also, for example, the processing of external stressors. In addition to many other tissues, the sympathetic nervous system influences bone metabolism. This effect could be highly relevant concerning osseointegration, which is responsible for the long-term success of dental implants. Accordingly, this review aims to summarize the current literature on this topic and to reveal future research perspectives. One in vitro study showed differences in mRNA expression of adrenoceptors cultured on implant surfaces. In vivo, sympathectomy impaired osseointegration in mice, while electrical stimulation of the sympathetic nerves promoted it. As expected, the beta-blocker propranolol improves histological implant parameters and micro-CT measurements. Overall, the present data are considered heterogeneous. However, the available publications reveal the potential for future research and development in dental implantology, which helps to introduce new therapeutic strategies and identify risk factors for dental implant failure.

Electrical stimulation to promote osseointegration of bone anchoring implants: a topical review

Electrical stimulation has shown to be a promising approach for promoting osseointegration in bone anchoring implants, where osseointegration defines the biological bonding between the implant surface and bone tissue. Bone-anchored implants are used in the rehabilitation of hearing and limb loss, and extensively in edentulous patients. Inadequate osseointegration is one of the major factors of implant failure that could be prevented by accelerating or enhancing the osseointegration process by artificial means. In this article, we reviewed the efforts to enhance the biofunctionality at the bone-implant interface with electrical stimulation using the implant as an electrode. We reviewed articles describing different electrode configurations, power sources, and waveform-dependent stimulation parameters tested in various in vitro and in vivo models. In total 55 English-language and peer-reviewed publications were identified until April 2020 using PubMed, Google Scholar, and the Chalmers University of Technology Library discovery system using the keywords: osseointegration, electrical stimulation, direct current and titanium implant. Thirteen of those publications were within the scope of this review. We reviewed and compared studies from the last 45 years and found nonuniform protocols with disparities in cell type and animal model, implant location, experimental timeline, implant material, evaluation assays, and type of electrical stimulation. The reporting of stimulation parameters was also found to be inconsistent and incomplete throughout the literature. Studies using in vitro models showed that osteoblasts were sensitive to the magnitude of the electric field and duration of exposure, and such variables similarly affected bone quantity around implants in in vivo investigations. Most studies showed benefits of electrical stimulation in the underlying processes leading to osseointegration, and therefore we found the idea of promoting osseointegration by using electric fields to be supported by the available evidence. However, such an effect has not been demonstrated conclusively nor optimally in humans. We found that optimal stimulation parameters have not been thoroughly investigated and this remains an important step towards the clinical translation of this concept. In addition, there is a need for reporting standards to enable meta-analysis for evidence-based treatments.

Enhancing osteoblast survival through pulsed electrical stimulation and implications for osseointegration

Electrical stimulation has been suggested as a means for promoting the direct structural and functional bonding of bone tissue to an artificial implant, known as osseointegration. Previous work has investigated the impact of electrical stimulation in different models, both in vitro and in vivo, using various electrode configurations for inducing an electric field with a wide range of stimulation parameters. However, there is no consensus on optimal electrode configuration nor stimulation parameters. Here, we investigated a novel approach of delivering electrical stimulation to a titanium implant using parameters clinically tested in a different application, namely peripheral nerve stimulation. We propose an in vitro model comprising of Ti6Al4V implants precultured with MC3T3-E1 preosteoblasts, stimulated for 72 h at two different pulse amplitudes (10 µA and 20 µA) and at two different frequencies (50 Hz and 100 Hz). We found that asymmetric charge-balanced pulsed electrical stimulation improved cell survival and collagen production in a dose-dependent manner. Our findings suggest that pulsed electrical stimulation with characteristics similar to peripheral nerve stimulation has the potential to improve cell survival and may provide a promising approach to improve peri-implant bone healing, particularly to neuromusculoskeletal interfaces in which implanted electrodes are readily available.

Continuous Electrical Stimulation Affects Initial Growth and Proliferation of Adipose-Derived Stem Cells

The aim of the study was to establish electrical stimulation parameters in order to improve cell growth and viability of human adipose-derived stem cells (hADSC) when compared to non-stimulated cells in vitro. hADSC were exposed to continuous electrical stimulation with 1.7 V AC/20 Hz. After 24, 72 h and 7 days, cell number, cellular surface coverage and cell proliferation were assessed. In addition, cell cycle analysis was carried out after 3 and 7 days. After 24 h, no significant alterations were observed for stimulated cells. At day 3, stimulated cells showed a 4.5-fold increase in cell numbers, a 2.7-fold increase in cellular surface coverage and a significantly increased proliferation. Via cell cycle analysis, a significant increase in the G2/M phase was monitored for stimulated cells. Contrastingly, after 7 days, the non-stimulated group exhibited a 11-fold increase in cell numbers and a 4-fold increase in cellular surface coverage as well as a significant increase in cell proliferation. Moreover, the stimulated cells displayed a shift to the G1 and sub-G1 phase, indicating for metabolic arrest and apoptosis initiation. In accordance, continuous electrical stimulation of hADSC led to a significantly increased cell growth and proliferation after 3 days. However, longer stimulation periods such as 7 days caused an opposite result indicating initiation of apoptosis.

Electrochemical methods to enhance osseointegrated prostheses

Osseointegrated (OI) prosthetic limbs have been shown to provide an advantageous treatment option for amputees. In order for the OI prosthesis to be successful, the titanium implant must rapidly achieve and maintain proper integration with the bone tissue and remain free of infection. Electrochemical methods can be utilized to control and/or monitor the interfacial microenvironment where the titanium implant interacts with the biological system (host bone tissue or bacteria). This review will summarize the current understanding of how electrochemical modalities can influence bone tissue and bacteria with specific emphasis on applications where the metallic prosthesis itself can be utilized directly as a stimulating electrode for enhanced osseointegration and infection control. In addition, a summary of electrochemical impedance sensing techniques that could be used to potentially assess osseointegration and infection status of the metallic prosthesis is presented.

Biocompatibility of (Ba,Ca)(Zr,Ti)O3 piezoelectric ceramics for bone replacement materials

Total joint replacement implants are generally designed to physically mimic the biological environment to ensure compatibility with the host tissue. However, implant instability exposes patients to long recovery periods, high risk for revision surgeries, and high expenses. Introducing electrical stimulation to the implant site to accelerate healing is promising, but the cumbersome nature of wired devices is detrimental to the implant design. We propose a novel strategy to stimulate cells at the implant site by utilizing piezoelectric ceramics as electrical stimulation sources. The inherent ability of these materials to form electric surface potentials under mechanical load allows them to act as internal power sources. This characteristic is commonly exploited in non-biomedical applications such as transducers or sensors. We investigate calcium/zirconium-doped barium titanate (BCZT) ceramics in an in vitro environment to determine their potential as implant materials. BCZT exhibits low cytotoxicity with human osteoblast and endothelial cells as well as high piezoelectric responses. Microstructural adaptation was identified as a route for optimizing piezoelectric behavior. Our results show that BCZT is a promising system for biomedical applications. Its characteristic ability to autonomously generate electric surface potentials opens the possibility to functionalize existing bone replacement implant designs to improve implant ingrowth and long-term stability.

Electrical stimulation-based bone fracture treatment, if it works so well why do not more surgeons use it?

BACKGROUND

Electrical stimulation (EStim) has been proven to promote bone healing in experimental settings and has been used clinically for many years and yet it has not become a mainstream clinical treatment.

METHODS

To better understand this discrepancy we reviewed 72 animal and 69 clinical studies published between 1978 and 2017, and separately asked 161 orthopedic surgeons worldwide about their awareness, experience, and acceptance of EStim for treating fracture patients.

RESULTS

Of the 72 animal studies, 77% reported positive outcomes, and the most common model, bone, fracture type, and method of administering EStim were dog, tibia, large bone defects, and DC, respectively. Of the 69 clinical studies, 73% reported positive outcomes, and the most common bone treated, fracture type, and method of administration were tibia, delayed/non-unions, and PEMF, respectively. Of the 161 survey respondents, most (73%) were aware of the positive outcomes reported in the literature, yet only 32% used EStim in their patients. The most common fracture they treated was delayed/non-unions, and the greatest problems with EStim were high costs and inconsistent results.

CONCLUSION

Despite their awareness of EStim's pro-fracture healing effects few orthopedic surgeons use it in their patients. Our review of the literature and survey indicate that this is due to confusion in the literature due to the great variation in methods reported, and the inconsistent results associated with this treatment approach. In spite of this surgeons seem to be open to using this treatment if advancements in the technology were able to provide an easy to use, cost-effective method to deliver EStim in their fracture patients.

Nerve electrical stimulation enhances osseointegration of implants in the beagle

Dental implantation has been the primary method for the treatment of tooth loss, but longer than 3 months healing times are generally required. Because immediate load implants are suitable only for certain categories of implant patients, it has value to develop a novel method to facilitate the implant-bone osseointegration process. Cylindrical titanium implants were implanted in the tooth sockets of beagles, and microelectrode stimulation of the sympathetic nerves in the infraorbital nerve was performed after implantation for 1 week. The authors found that one-sided nerve stimulation was shown to evoke consistent electric potential changes in both sides of the infraorbital nerves. Moreover, after 4 weeks of implantation, more new bone was clearly observed around the implants in the beagles that received electrical stimulation treatment than was observed in the control animals. Furthermore, a higher mineralization density was measured in the new peri-implant bone tissues of the stimulated beagles when compared to controls. These results demonstrate that the simple and safe physical method of microelectrode stimulation to sympathetic nerves can promote the formation of new bone and the osseointegration of implants. This technique is worth promoting and has the potential to reduce the healing time of dental implantation in future clinical cases.