Long-term stimulation with alternating electric fields modulates the differentiation and mineralization of human pre-osteoblasts

Role of low-level alternating current and impedance for enhancing microalgae biomass and lipid production

Microalgae hold significant potential for producing value-added bioproducts in pharmaceutical, cosmetic, food, and biofuel industries, with a global market value estimated at US$ 11.8 billion in 2023. Innovations in culturing systems, such as electric stimulation, aim to enhance growth performance, as it can improve cellular processes, including nutrient uptake and lipid accumulation. This study investigates the effect of low alternating electrical currents (μA) on the growth and lipid production of the halotolerant microalga Dunaliella salina across varying salt concentrations (3.5 % and 8.5 % Conway medium). Applying electric stimulation at 50, 750, and 990 μA for 30 min daily over 15 days resulted in significant enhancements, particularly at 3.5 % salinity, where lipid content increased by 144 %. The findings indicate that electrical stimulation notably reduced the lag phase and increased exponential growth rates, with superior growth coefficients correlating with higher medium impedance rather than direct current levels.

Enhancing Bone Health with Conjugated Linoleic Acid: Mechanisms, Challenges, and Innovative Strategies

Conjugated linoleic acid (CLA) is a bioactive compound known for its anti-inflammatory, anti-carcinogenic, and metabolic effects, with growing interest in its role in supporting bone health. Preclinical studies, particularly those involving the t10c12 isomer, have shown that CLA can enhance bone mineral density (BMD) by enhancing bone formation and reducing bone resorption, indicating its potential as a therapeutic agent to improve bone health. However, clinical trials have yielded inconsistent results, underscoring the difficulty in translating animal model successes to human applications. A major challenge is CLA's low water solubility, poor absorption, and limited bioavailability, which restrict its therapeutic effectiveness. To address these issues, nanoparticle-based delivery systems have been proposed to improve its solubility, stability, and resistance to oxidative damage, thereby enhancing its bioactivity. Recent studies also suggest that electrical stimulation can stimulate bone regeneration by promoting bone cell proliferation, differentiation, and adherence to scaffolds. This review explores the combined use of CLA supplementation and electrical stimulation as a novel approach to improving bone health, particularly in osteoporosis management. By integrating CLA's biological effects with the regenerative potential of electrical stimulation, this multimodal strategy offers a promising method for enhancing bone restoration, with significant implications for clinical applications in bone health.

Safety and preliminary efficacy of an electrically stimulated implant for mandibular bone regeneration: a pilot study in a large animal model

OBJECTIVES

Large mandibular defects present challenges for bone regeneration. This pilot study evaluates the safety and preliminary efficacy of direct electrical stimulation (ES) on tissue healing in a preclinical model, testing whether ES can enhance bone formation in critical-size mandibular defects.

MATERIALS AND METHODS

Six adult mini pigs with critical-size mandibular defects were used in a split-mouth design. The test group (n = 6) received 0.5 V AC/20 Hz ES for 3 × 45 min daily over three weeks, while the control group (n = 6) had no stimulation. Safety, early bone growth, and soft tissue effects were assessed at three locations: S1 (cancellous bone interface), S2 (middle of the defect), and S3 (pristine dense bone).

RESULTS

The ES group showed no adverse effects, confirming implant safety. The ES group exhibited significantly higher bone formation, particularly in S2 and S3. Enhanced vascularization and immune response, in terms of increased mast cells, were also observed in S2.

CONCLUSIONS

The implant device with ES is safe and promotes bone formation and vascularization in select sub-regions (S2 and S3). However, ES alone may not suffice for complete bone regeneration in critical-sized defects, and further optimization is needed.

CLINICAL RELEVANCE

This study demonstrates the potential of ES to improve bone healing in large mandibular defects, offering insights for clinical use in maxillofacial reconstruction.

Alternating electrical fields to stimulate osteogenic cells and biomimetic calcium phosphate-coated titanium substrates-A combinatorial approach to bone regeneration

Biophysical stimuli such as alternating electrical fields can mimic endogenous electrical potentials and currents in natural bone. This can help to improve the healing and reconstruction of bone tissue. However, little is known about the combined influence of biomaterials and alternating electric fields on bone cells. Therefore, this study aimed to investigate the impact of both, biomaterials and alternating electric fields, on osteoblast as well as osteoclast differentiation. Initially, either RAW 264.7 or MC3T3-E1 cells were seeded on Ti6Al4V substrates as a load-bearing implant material, modified with biomimetic calcium phosphate (BCP), or uncoated as a reference. The cells were stimulated towards osteoclastic and osteoblastic differentiation via respective growth factors. The effects of BCP substrate modification on cell differentiation were examined after 7 days for RAW 264.7 and after 14 days for MC3T3-E1 cells. In a further series of tests, either RAW 264.7 or MC3T3-E1 cells were seeded on BCP-modified Ti6Al4V substrates, stimulated towards differentiation using growth factors, and further electrically stimulated via alternating electric fields of different voltages and frequencies. In parallel to the first test series RAW 264.7 and MC3T3-E1 cells were stimulated for 7 and 14 days, respectively. Cell morphology was examined via scanning electron microscopy. Cell viabilities were assessed via WST-8 assay. Electrically stimulated MC3T3-E1 cell orientation was evaluated based on fluorescence microscopy images. Marker genes were examined via qPCR. While BCP increased osteoclast-specific gene expression, it had the opposite effect on osteoblast-related genes compared to respective cells seeded on uncoated Ti6Al4V substrates. ES with different parameters showed a broad cellular response due to electrocoupling. While cell viability assessments and gene expression analyses showed clear differences between ES samples and unstimulated controls, only minor cell morphology and orientation differences were observed. Furthermore, there was no clear trend towards a dominant influence of either voltage or frequency as control parameters. Further studies were initiated to investigate the underlying intracellular mechanisms targeted by ES. This work provides an introduction to the targeted control of cellular processes using defined electric fields. The optimization of voltage and frequency could provide therapeutic windows to control specific cellular functions and potentially improve bone regeneration and remodeling processes.

Exploring the role of directly coupled alternating electric fields on chondrocyte morphology and redifferentiation capacity with a focus on sex differences

Purpose

In cell-based therapies addressing articular cartilage lesions, a central challenge is to avoid the formation of fibrous cartilage resulting from dedifferentiation processes. Electrical stimulation emerges as a promising approach for promoting chondrocytic redifferentiation. This study investigated the effects of varying electric fields on morphological changes and the redifferentiation capacity of human chondrocytes with regard to alterations in sex.

Methods

Chondrocytes, isolated from the articular cartilage of male and female patients undergoing total knee replacement, were exposed to alternating electric fields of varying strengths ranging from 0.8 to 1.2, 15 to 20 and 100 to 140 V/m. Afterwards, cell morphology and viability, as well as the deposition of collagen (Col) 1 and 2, were evaluated.

Results

Following electrical stimulation, in particular at 15-20 V/m, an increase in the Col2/Col1 ratio and an elevated proportion of rounded, chondrocyte-like cell morphology were observed, indicating a promoting effect on the redifferentiation of chondrocytes. Comparative analysis between both sexes revealed that chondrocytes from female donors exhibit higher Col1 synthesis rates, a decreased Col2/Col1 ratio, and a higher proportion of elongated, fibroblast-like cells compared to chondrocytes derived from male donors.

Conclusion

Our in vitro study suggests that chondrocytes from male donors are more prone to re-differentiate after electrical stimulation.

Level of Evidence

N/A.

Effects of electrical stimulation with alternating fields on the osseointegration of titanium implants in the rabbit tibia - a pilot study

Introduction: Electrical stimulation has been used as a promising approach in bone repair for several decades. However, the therapeutic use is hampered by inconsistent results due to a lack of standardized application protocols. Recently, electrical stimulation has been considered for the improvement of the osseointegration of dental and endoprosthetic implants. Methods: In a pilot study, the suitability of a specifically developed device for electrical stimulation in situ was assessed. Here, the impact of alternating electric fields on implant osseointegration was tested in a gap model using New Zealand White Rabbits. Stimulation parameters were transmitted to the device via a radio transceiver, thus allowing for real-time monitoring and, if required, variations of stimulation parameters. The effect of electrical stimulation on implant osseointegration was quantified by the bone-implant contact (BIC) assessed by histomorphometric (2D) and µCT (3D) analysis. Results: Direct stimulation with an alternating electric potential of 150 mV and 20 Hz for three times a day (45 min per unit) resulted in improved osseointegration of the triangular titanium implants in the tibiae of the rabbits. The ratio of bone area in histomorphometry (2D analysis) and bone volume (3D analysis) around the implant were significantly increased after stimulation compared to the untreated controls at sacrifice 84 days after implantation. Conclusion: The developed experimental design of an electrical stimulation system, which was directly located in the defect zone of rabbit tibiae, provided feedback regarding the integrity of the stimulation device throughout an experiment and would allow variations in the stimulation parameters in future studies. Within this study, electrical stimulation resulted in enhanced implant osseointegration. However, direct electrical stimulation of bone tissue requires the definition of dose-response curves and optimal duration of treatment, which should be the subject of subsequent studies.

Advances in electroactive biomaterials: Through the lens of electrical stimulation promoting bone regeneration strategy

The regenerative capacity of bone is indispensable for growth, given that accidental injury is almost inevitable. Bone regenerative capacity is relevant for the aging population globally and for the repair of large bone defects after osteotomy (e.g., following removal of malignant bone tumours). Among the many therapeutic modalities proposed to bone regeneration, electrical stimulation has attracted significant attention owing to its economic convenience and exceptional curative effects, and various electroactive biomaterials have emerged. This review summarizes the current knowledge and progress regarding electrical stimulation strategies for improving bone repair. Such strategies range from traditional methods of delivering electrical stimulation via electroconductive materials using external power sources to self-powered biomaterials, such as piezoelectric materials and nanogenerators. Electrical stimulation and osteogenesis are related via bone piezoelectricity. This review examines cell behaviour and the potential mechanisms of electrostimulation via electroactive biomaterials in bone healing, aiming to provide new insights regarding the mechanisms of bone regeneration using electroactive biomaterials.

The translational potential of this article

This review examines the roles of electroactive biomaterials in rehabilitating the electrical microenvironment to facilitate bone regeneration, addressing current progress in electrical biomaterials and the mechanisms whereby electrical cues mediate bone regeneration. Interactions between osteogenesis-related cells and electroactive biomaterials are summarized, leading to proposals regarding the use of electrical stimulation-based therapies to accelerate bone healing.

Synergy between 3D-extruded electroconductive scaffolds and electrical stimulation to improve bone tissue engineering strategies

In this work, we propose a simple, reliable, and versatile strategy to create 3D electroconductive scaffolds suitable for bone tissue engineering (TE) applications with electrical stimulation (ES). The proposed scaffolds are made of 3D-extruded poly(ε-caprolactone) (PCL), subjected to alkaline treatment, and of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), anchored to PCL with one of two different crosslinkers: (3-glycidyloxypropyl)trimethoxysilane (GOPS) and divinyl sulfone (DVS). Both cross-linkers allowed the formation of a homogenous and continuous coating of PEDOT:PSS to PCL. We show that these PEDOT:PSS coatings are electroconductive (11.3-20.1 S cm-1), stable (up to 21 days in saline solution), and allow the immobilization of gelatin (Gel) to further improve bioactivity. In vitro mineralization of the corresponding 3D conductive scaffolds was greatly enhanced (GOPS(NaOH)-Gel - 3.1 fold, DVS(NaOH)-Gel - 2.0 fold) and cell colonization and proliferation were the highest for the DVS(NaOH)-Gel scaffold. In silico modelling of ES application in DVS(NaOH)-Gel scaffolds indicates that the electrical field distribution is homogeneous, which reduces the probability of formation of faradaic products. Osteogenic differentiation of human bone marrow derived mesenchymal stem/stromal cells (hBM-MSCs) was performed under ES. Importantly, our results clearly demonstrated a synergistic effect of scaffold electroconductivity and ES on the enhancement of MSC osteogenic differentiation, particularly on cell-secreted calcium deposition and the upregulation of osteogenic gene markers such as COL I, OC and CACNA1C. These scaffolds hold promise for future clinical applications, including manufacturing of personalized bone TE grafts for transplantation with enhanced maturation/functionality or bioelectronic devices.

Discrimination between the effects of pulsed electrical stimulation and electrochemically conditioned medium on human osteoblasts

BACKGROUND

Electrical stimulation is used for enhanced bone fracture healing. Electrochemical processes occur during the electrical stimulation at the electrodes and influence cellular reactions. Our approach aimed to distinguish between electrochemical and electric field effects on osteoblast-like MG-63 cells. We applied 20 Hz biphasic pulses via platinum electrodes for 2 h. The electrical stimulation of the cell culture medium and subsequent application to cells was compared to directly stimulated cells. The electric field distribution was predicted using a digital twin.

RESULTS

Cyclic voltammetry and electrochemical impedance spectroscopy revealed partial electrolysis at the electrodes, which was confirmed by increased concentrations of hydrogen peroxide in the medium. While both direct stimulation and AC-conditioned medium decreased cell adhesion and spreading, only the direct stimulation enhanced the intracellular calcium ions and reactive oxygen species.

CONCLUSION

The electrochemical by-product hydrogen peroxide is not the main contributor to the cellular effects of electrical stimulation. However, undesired effects like decreased adhesion are mediated through electrochemical products in stimulated medium. Detailed characterisation and monitoring of the stimulation set up and electrochemical reactions are necessary to find safe electrical stimulation protocols.