Mode & mechanism of low intensity pulsed ultrasound (LIPUS) in fracture repair

Effects of Low-Intensity Pulsed Ultrasound on the Regulation of Free Fatty Acid Release in 3T3-L1 Cells

OBJECTIVES

To investigate the effects of low-intensity pulsed ultrasound (LIPUS) on the proliferation, differentiation, and tumor necrosis factor-α (TNF-α)-induced lipolysis of 3T3-L1 cells, and to explore the feasibility of regulating the release of free fatty acids (FFA) to prevent lipotoxicity.

METHODS

Different intensities (30, 60, 90, and 120 mW/cm2) of LIPUS were applied to 3T3-L1 preadipocytes for different durations (5, 10, 15, 20, 25, and 30 minutes). Appropriate parameters for subsequent experiments were selected by assessing cell viability. The effect of LIPUS on the proliferation and differentiation of 3T3-L1 cells was evaluated by microscope observation, flow cytometry, and lipid content determination. After treated with LIPUS and TNF-α (50 ng/mL), the degree of lipolysis was assessed by measuring the extracellular FFA content. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the mRNA expression of relevant genes.

RESULTS

Different parameters of LIPUS significantly enhance the viability of 3T3-L1 cells (P < .05), with 20 minutes and 30 mW/cm2 as the most suitable settings. After LIPUS treatment, 3T3-L1 cell proliferation accelerated, apoptosis rate and G1 phase cell proportion decreased, the content of lipid droplets and TG was increased in differentiated cells, while FFA release decreased (P < .05). The expression of PCNA, PPARγ, C/EBPα, Perilipin A mRNA increased, and the expression of TNF-α, ATGL, HSL mRNA decreased (P < .05).

CONCLUSIONS

LIPUS could promote the proliferation and differentiation of 3T3-L1 cells and inhibit TNF-α-induced lipolysis, indicating its potential as a therapy for mitigating lipotoxicity caused by decompensated adipocytes.

[Effectiveness of low-intensity pulsed ultrasound in patients after osteotomy: A systematic review]

The use of low intensity pulsed ultrasound (LIPUS) therapy for bone healing and fracture treatment is increasingly considered as a therapeutic alternative with moderate economic cost and none or minimal adverse effects (e.g., low reaction to the conductive gel). However, there is some controversy regarding its scientific evidence. The present review seeks to shed some light on this controversy and to cover an area of study not occupied by previous or current work on ultrasound therapy. It is necessary to know the real impact of the treatment with low intensity pulsed ultrasound in patients with osteotomy, as well as its applicability as a post-surgery protocol to improve the recovery and rehabilitation processes and, at the end of the day, to reduce the time of disability.

Latest Progress of LIPUS in Fracture Healing: A Mini-Review

The use of low-intensity pulsed ultrasound (LIPUS) for promoting fracture healing has been Food and Drug Administration (FDA)-approved since 1994 due to largely its non-thermal effects of sound flow sound radiation force and so on. Numerous clinical and animal studies have shown that LIPUS can accelerate the healing of fresh fractures, nonunions, and delayed unions in pulse mode regardless of LIPUS devices or circumstantial factors. Rare clinical studies show limitations of LIPUS for treating fractures with intramedullary nail fixation or low patient compliance. The biological effect is achieved by regulating various cellular behaviors involving mesenchymal stem/stromal cells (MSCs), osteoblasts, chondrocytes, and osteoclasts and with dose dependency on LIPUS intensity and time. Specifically, LIPUS promotes the osteogenic differentiation of MSCs through the ROCK-Cot/Tpl2-MEK-ERK signaling. Osteoblasts, in turn, respond to the mechanical signal of LIPUS through integrin, angiotensin type 1 (AT1), and PIEZO1 mechano-receptors, leading to the production of inflammatory factors such as COX-2, MCP-1, and MIP-1β fracture repair. LIPUS also induces CCN2 expression in chondrocytes thereby coordinating bone regeneration. Finally, LIPUS suppresses osteoclast differentiation and gene expression by interfering with the ERK/c-Fos/NFATc1 cascade. This mini-review revisits the known effects and mechanisms of LIPUS on bone fracture healing and strengthens the need for further investigation into the underlying mechanisms.

The Effect of Low-Intensity Pulsed Ultrasound on Bone Regeneration and the Expression of Osterix and Cyclooxygenase-2 during Critical-Size Bone Defect Repair

Low-intensity pulsed ultrasound (LIPUS) is a form of ultrasound that utilizes low-intensity pulsed waves. Its effect on bones that heal by intramembranous ossification has not been sufficiently investigated. In this study, we examined LIPUS and the autologous bone, to determine their effect on the healing of the critical-size bone defect (CSBD) of the rat calvaria. The bone samples underwent histological, histomorphometric and immunohistochemical analyses. Both LIPUS and autologous bone promoted osteogenesis, leading to almost complete closure of the bone defect. On day 30, the bone volume was the highest in the autologous bone group (20.35%), followed by the LIPUS group (19.12%), and the lowest value was in the control group (5.11%). The autologous bone group exhibited the highest intensities of COX-2 (167.7 ± 1.1) and Osx (177.1 ± 0.9) expression on day 30. In the LIPUS group, the highest intensity of COX-2 expression was found on day 7 (169.7 ±1.6) and day 15 (92.7 ± 2.2), while the highest Osx expression was on day 7 (131.9 ± 0.9). In conclusion, this study suggests that LIPUS could represent a viable alternative to autologous bone grafts in repairing bone defects that are ossified by intramembranous ossification.

L-Type Calcium Channel Modulates Low-Intensity Pulsed Ultrasound-Induced Excitation in Cultured Hippocampal Neurons

As a noninvasive technique, ultrasound stimulation is known to modulate neuronal activity both in vitro and in vivo. The latest explanation of this phenomenon is that the acoustic wave can activate the ion channels and further impact the electrophysiological properties of targeted neurons. However, the underlying mechanism of low-intensity pulsed ultrasound (LIPUS)-induced neuro-modulation effects is still unclear. Here, we characterize the excitatory effects of LIPUS on spontaneous activity and the intracellular Ca2+ homeostasis in cultured hippocampal neurons. By whole-cell patch clamp recording, we found that 15 min of 1-MHz LIPUS boosts the frequency of both spontaneous action potentials and spontaneous excitatory synaptic currents (sEPSCs) and also increases the amplitude of sEPSCs in hippocampal neurons. This phenomenon lasts for > 10 min after LIPUS exposure. Together with Ca2+ imaging, we clarified that LIPUS increases the [Ca2+]cyto level by facilitating L-type Ca2+ channels (LTCCs). In addition, due to the [Ca2+]cyto elevation by LIPUS exposure, the Ca2+-dependent CaMKII-CREB pathway can be activated within 30 min to further regulate the gene transcription and protein expression. Our work suggests that LIPUS regulates neuronal activity in a Ca2+-dependent manner via LTCCs. This may also explain the multi-activation effects of LIPUS beyond neurons. LIPUS stimulation potentiates spontaneous neuronal activity by increasing Ca2+ influx.

Ultrasound-dependent kinetics of bone mineralization

Bone Mineral Density (BMD) is an important parameter in the development of orthopedic fracture-healing methods. A recent article (Inoue, S., et al. Bone. 2023, 177, 116916) investigated the use of higher intensity ultrasound to promote murine bone formation by measuring BMD levels. In this work, we present the numerical values of BMD, which show sigmoid kinetics and hyperbolic asymptotic increase with the application of higher intensity ultrasound. Our analysis may provide a foundation for the understanding and application of ultrasound to the human body.

Physical Stimulation Methods Developed for In Vitro Neuronal Differentiation Studies of PC12 Cells: A Comprehensive Review

PC12 cells, which are derived from rat adrenal pheochromocytoma cells, are widely used for the study of neuronal differentiation. NGF induces neuronal differentiation in PC12 cells by activating intracellular pathways via the TrkA receptor, which results in elongated neurites and neuron-like characteristics. Moreover, the differentiation requires both the ERK1/2 and p38 MAPK pathways. In addition to NGF, BMPs can also induce neuronal differentiation in PC12 cells. BMPs are part of the TGF-β cytokine superfamily and activate signaling pathways such as p38 MAPK and Smad. However, the brief lifespan of NGF and BMPs may limit their effectiveness in living organisms. Although PC12 cells are used to study the effects of various physical stimuli on neuronal differentiation, the development of new methods and an understanding of the molecular mechanisms are ongoing. In this comprehensive review, we discuss the induction of neuronal differentiation in PC12 cells without relying on NGF, which is already established for electrical, electromagnetic, and thermal stimulation but poses a challenge for mechanical, ultrasound, and light stimulation. Furthermore, the mechanisms underlying neuronal differentiation induced by physical stimuli remain largely unknown. Elucidating these mechanisms holds promise for developing new methods for neural regeneration and advancing neuroregenerative medical technologies using neural stem cells.

The potential role of mechanotransduction in the management of pediatric calvarial bone flap repair

Pediatric patients suffering traumatic brain injuries may require a decompressive craniectomy to accommodate brain swelling by removing a portion of the skull. Once the brain swelling subsides, the preserved calvarial bone flap is ideally replaced as an autograft during a cranioplasty to restore protection of the brain, as it can reintegrate and grow with the patient during immature skeletal development. However, pediatric patients exhibit a high prevalence of calvarial bone flap resorption post-cranioplasty, causing functional and cosmetic morbidity. This review examines possible solutions for mitigating pediatric calvarial bone flap resorption by delineating methods of stimulating mechanosensitive cell populations with mechanical forces. Mechanotransduction plays a critical role in three main cell types involved with calvarial bone repair, including mesenchymal stem cells, osteoblasts, and dural cells, through mechanisms that could be exploited to promote osteogenesis. In particular, physiologically relevant mechanical forces, including substrate deformation, external forces, and ultrasound, can be used as tools to stimulate bone repair in both in vitro and in vivo systems. Ultimately, combating pediatric calvarial flap resorption may require a combinatorial approach using both cell therapy and bioengineering strategies.

Higher-intensity ultrasound accelerates fracture healing via mechanosensitive ion channel Piezo1

Osteoporosis-related fractures are a major public health problem. Mechanobiological stimulation utilizing low-intensity pulsed ultrasound (LIPUS) is the most widely accepted modality for accelerating fracture healing. However, recent evidence has demonstrated the ineffectiveness of LIPUS, and the biophysical mechanisms of ultrasound-induced bone formation also remain elusive. Here, we demonstrate that ultrasound at a higher intensity than LIPUS effectively accelerates fracture healing in a mouse osteoporotic fracture model. Higher-intensity ultrasound promoted chondrogenesis and hypertrophic differentiation of chondrocytes in the fracture callus. Higher-intensity ultrasound also increased osteoblasts and newly formed bone in the callus, resulting in accelerated endochondral ossification during fracture healing. In addition, we found that accelerated fracture healing by ultrasound exposure was attenuated when the mechanosensitive ion channel Piezo1 was inhibited by GsMTx4. Ultrasound-induced new bone formation in the callus was attenuated in fractured mice treated with GsMTx4. Similar results were also confirmed in a 3D osteocyte-osteoblast co-culture system, where osteocytic Piezo1 knockdown attenuated the expression of osteoblastic genes after ultrasound exposure. Together these results demonstrate that higher-intensity ultrasound than clinically used LIPUS can accelerate endochondral ossification after fractures. Furthermore, our results suggest that mechanotransduction via Piezo1 mediates ultrasound-stimulated fracture healing and bone formation.

Low-Intensity Pulsed Ultrasound Promotes BMP9 Induced Osteoblastic Differentiation in Rat Dedifferentiated Fat Cells

Dedifferentiated fat cells (DFATs) isolated from mature adipocytes have a multilineage differentiation capacity similar to mesenchymal stem cells and are considered as promising source of cells for tissue engineering. Bone morphogenetic protein 9 (BMP9) and low-intensity pulsed ultrasound (LIPUS) have been reported to stimulate bone formation both in vitro and in vivo. However, the combined effect of BMP9 and LIPUS on osteoblastic differentiation of DFATs has not been studied. After preparing DFATs from mature adipose tissue from rats, DFATs were treated with different doses of BMP9 and/or LIPUS. The effects on osteoblastic differentiation were assessed by changes in alkaline phosphatase (ALP) activity, mineralization/calcium deposition, and expression of bone related genes; Runx2, osterix, osteopontin. No significant differences for ALP activity, mineralization deposition, as well as expression for bone related genes were observed by LIPUS treatment alone while treatment with BMP9 induced osteoblastic differentiation of DFATs in a dose dependent manner. Further, co-treatment with BMP9 and LIPUS significantly increased osteoblastic differentiation of DFATs compared to those treated with BMP9 alone. In addition, upregulation for BMP9-receptor genes was observed by LIPUS treatment. Indomethacin, an inhibitor of prostaglandin synthesis, significantly inhibited the synergistic effect of BMP9 and LIPUS co-stimulation on osteoblastic differentiation of DFATs. LIPUS promotes BMP9 induced osteoblastic differentiation of DFATs in vitro and prostaglandins may be involved in this mechanism.

Multicenter consensus statements on the use of low-intensity pulsed ultrasound (LIPUS) in Hand Surgery

OBJECTIVE

The purpose of this agreement was to establish consensus statements on the use of low-intensity pulsed ultrasound (LIPUS) in hand surgery.

METHODS

Based on Delphi consensus methodology, a preliminary list of questions on the use of LIPUS in hand surgery was developed by an interdisciplinary team of hand and plastic surgeons as well as psychologists and experts from communications science. Based on these, questionnaires were invented and a total of three Delphi rounds have been conducted. Delphi panelists consisted of 11 German hand surgeons with a mean experience in hand surgery of 15 years (7-23 years). Questions and statements were revised during this process, resulting in a consensus at the end of round three.

RESULTS

After three Delphi rounds, the following recommendations could be derived. LIPUS can be applied for impaired fracture healing of the digits, metacarpals, carpal bones as well as a prophylactic procedure in order to avoid further revision surgery. LIPUS therapy can be useful in addition to revision surgery for delayed union and non-unions. In the case of certain risk factors (replantation, revascularization, osteoporosis, smoking), it can be applied directly postoperatively in order to prevent impaired fracture healing. It should be applied for 90-120 days.

CONCLUSION

There is a consensus among German hand surgeons, when and how LIPUS can be applied for improving fracture healing of the hand. Randomized controlled trials with direct comparison of fracture treatment with and without LIPUS are needed to support these statements with objective data.

Increased intracellular diffusivity of macromolecules within a mammalian cell by low-intensity pulsed ultrasound

Whilst a number of studies have demonstrated that low-intensity pulsed ultrasound (LIPUS) is a promising therapeutic ultrasound technique that can be used for delivering mild mechanical stimuli to target tissue non-invasively, the underlying biophysical mechanisms still remain unclear. Most mechanism studies have focused explicitly on the effects of LIPUS on the cell membrane and mechanosensitive receptors. In the present study, we propose an additional mechanism by which LIPUS propagation through living cells may directly impact intracellular dynamics, particularly the diffusion transport of biomolecules. To support our hypothesis, human epithelial-like cells (SaOS-2 and HeLa) seeded on a confocal dish placed on a microscope stage were exposed to LIPUS with various exposure conditions (ultrasound frequencies of 0.5, 1 and 3 MHz, peak acoustic pressure of 200 and 400 kPa, a pulse repetition frequency of 1 kHz and a 20 % duty cycle), and the diffusivities of various sizes of biomolecules in the cytoplasm area were measured using fluorescence recovery after photobleaching (FRAP). Furthermore, giant unilamellar vesicles (GUVs) filled with macromolecules were used to examine the physical causal relationship between LIPUS and molecular diffusion changes. Nucleocytoplasmic transport coefficients were also measured by modified FRAP that bleaches the whole cell nuclear region. Extracellular signal-regulated kinases (ERK) activity (the phosphorylation dynamics) was monitored using fluorescence resonance energy transfer (FRET) microscopy. All the measurements were taken during, before and after the LIPUS exposure. Our experimental results clearly showed that the diffusion coefficients of macromolecules within the cell increased with acoustic pressure by 12.1 to 33.5 % during the sonication, and the increments were proportional to their molecular sizes regardless of the ultrasound frequency used. This observation in living cells was consistent with the GUVs exposed to the LIPUS, which indicated that the diffusivity increase was a passive physical response to the acoustic energy of LIPUS. Under the 1 MHz LIPUS exposure with 400 kPa, the passive nucleocytoplasmic transport of enhanced green fluorescent protein (EGFP) was accelerated by 21.4 %. With the same LIPUS exposure condition, both the diffusivity and phosphorylation of ERK induced by EGF treatment were significantly elevated simultaneously, which implied that LIPUS could also modify the kinase kinetics in the signal transduction process. Taken together, this study is the first attempt to uncover the physical link between LIPUS and the dynamics of intracellular macromolecules and related biological processes that LIPUS can possibly increase the diffusivity of intracellular macromolecules, leading to the changes in the basic cellular processes: passive nucleocytoplasmic transport and ERK. Our findings can provide a novel perspective that the mechanotransduction process that the intracellular region, in addition to the cell membrane, can convert the acoustic stimuli of LIPUS to biochemical signals.

Ultrasound-Driven Healing: Unleashing the Potential of Chondrocyte-Derived Extracellular Vesicles for Chondrogenesis in Adipose-Derived Stem Cells

Repairing cartilage defects represents a significant clinical challenge. While adipose-derived stem cell (ADSC)-based strategies hold promise for cartilage regeneration, their inherent chondrogenic potential is limited. Extracellular vesicles (EVs) derived from chondrocytes (CC-EVs) have shown potential in enhancing chondrogenesis, but their role in promoting chondrogenic differentiation of ADSCs remains poorly understood. Moreover, the clinical application of EVs faces limitations due to insufficient quantities for in vivo use, necessitating the development of effective methods for extracting significant amounts of CC-EVs. Our previous study demonstrated that low-intensity ultrasound (LIUS) stimulation enhances EV secretion from mesenchymal stem cells. Here, we identified a specific LIUS parameter for chondrocytes that increased EV secretion by 16-fold. CC-EVs were found to enhance cell activity, proliferation, migration, and 21-day chondrogenic differentiation of ADSCs in vitro, while EVs secreted by chondrocytes following LIUS stimulation (US-CC-EVs) exhibited superior efficacy. miRNA-seq revealed that US-CC-EVs were enriched in cartilage-regeneration-related miRNAs, contributing to chondrogenesis in various biological processes. In conclusion, we found that CC-EVs can enhance the chondrogenesis of ADSCs in vitro. In addition, our study introduces ultrasound-driven healing as an innovative method to enhance the quantity and quality of CC-EVs, meeting clinical demand and addressing the limited chondrogenic potential of ADSCs. The ultrasound-driven healing unleashes the potential of CC-EVs for chondrogenesis possibly through the enrichment of cartilage-regeneration-associated miRNAs in EVs, suggesting their potential role in cartilage reconstruction. These findings hold promise for advancing cartilage regeneration strategies and may pave the way for novel therapeutic interventions in regenerative medicine.

Musculoskeletal Biomaterials: Stimulated and Synergized with Low Intensity Pulsed Ultrasound

Clinical biophysical stimulating strategies, which have significant effects on improving the function of organs or treating diseases by causing the salutary response of body, have shown many advantages, such as non-invasiveness, few side effects, and controllable treatment process. As a critical technique for stimulation, the low intensity pulsed ultrasound (LIPUS) has been explored in regulating osteogenesis, which has presented great promise in bone repair by delivering a combined effect with biomaterials. This review summarizes the musculoskeletal biomaterials that can be synergized with LIPUS for enhanced biomedical application, including bone regeneration, spinal fusion, osteonecrosis/osteolysis, cartilage repair, and nerve regeneration. Different types of biomaterials are categorized for summary and evaluation. In each subtype, the verified biological mechanisms are listed in a table or graphs to prove how LIPUS was effective in improving musculoskeletal tissue regeneration. Meanwhile, the acoustic excitation parameters of LIPUS that were promising to be effective for further musculoskeletal tissue engineering are discussed, as well as their limitations and some perspectives for future research. Overall, coupled with biomimetic scaffolds and platforms, LIPUS may be a powerful therapeutic approach to accelerate musculoskeletal tissue repair and even in other regenerative medicine applications.

A Bibliometric Analysis for Low-Intensity Ultrasound Study Over the Past Three Decades

Low-intensity ultrasound (LI-US) is a non-invasive stimulation technique that has emerged in recent years and has been shown to have positive effects on neuromodulation, fracture healing, inflammation improvement, and metabolic regulation. This study reports the conclusions of a bibliometric analysis of LI-US. Input data for the period between 1995 and 2022, including 7209 related articles in the field of LI-US, were collected from the core library of the Web of Science (WOS) database. Using these data, a set of bibliometric indicators was obtained to gain knowledge on different aspects: global production, research areas, and sources analysis, contributions of countries and institutions, author analysis, citation analysis, and keyword analysis. This study combined the data analysis capabilities provided by the WOS database, making use of two bibliometric software tools: R software and VOS viewer to achieve analysis and data exploration visualization, and predicted the further development trends of LI-US. It turns out that the United States and China are co-leaders while Zhang ZG is the most significant author in LI-US. In the future, the hot spots of LI-US will continue to focus on parameter research, mechanism discussion, safety regulations, and neuromodulation applications.

Knowledge mapping and global trends in the field of low-intensity pulsed ultrasound and endocrine and metabolic diseases: a bibliometric and visual analysis from 2012 to 2022

Background

Low-intensity pulsed ultrasound (LIPUS) is a highly promising therapeutic method that has been widely used in rehabilitation, orthopedics, dentistry, urology, gynecology, and other multidisciplinary disease diagnoses and treatments. It has attracted extensive attention worldwide. However, there is currently a lack of comprehensive and systematic research on the current status and future development direction of the LIPUS field. Therefore, this study comprehensively analyzed LIPUS-related reports from the past decade using bibliometrics methods, and further conducted research specifically focusing on its application in endocrine and metabolic diseases.

Methods

We downloaded LIPUS literature from 2012 to 2022 reported in the Web of Science Core Collection Science Citation Index-Expanded and Social Sciences Citation Index, and used bibliometric analysis software such as VOSviewer and CiteSpace to execute the analysis and visualize the results.

Results

We searched for 655 English articles published on LIPUS from 2012 to 2022. China had the highest number of published articles and collaborations between China and the United States were the closest in this field. Chongqing Medical University was the institution with the highest output, and ULTRASOUND IN MEDICINE AND BIOLOGY was the journal with the most related publications. In recent years, research on the molecular mechanisms of LIPUS has continued to deepen, and its clinical applications have also continued to expand. The application of LIPUS in major diseases such as oxidative stress, regeneration mechanism, and cancer is considered to be a future research direction, especially in the field of endocrinology and metabolism, where it has broad application value.

Conclusion

Global research on LIPUS is expected to continue to increase, and future research will focus on its mechanisms of action and clinical applications. This study comprehensively summarizes the current development status and global trends in the field of LIPUS, and its research progress in the field of endocrine and metabolic diseases, providing valuable reference for future research in this field.

Influence of Low-Intensity Pulsed Ultrasound Parameters on the Bone Mineral Density in Rat Model: A Systematic Review

OBJECTIVE

Bone recovery typically depends on the age of organisms or the prevalence of metabolic disorders such as osteoporosis, which is a metabolic condition characterized by decreased bone strength and bone mineral density (BMD). Therefore, low-intensity pulsed ultrasound (LIPUS), a non-invasive method for osteogenic stimulation, presents promising results. However, heterogeneity in animal study designs is a typical characteristic. Hence, we conducted a systematic review to evaluate the effectiveness of LIPUS in the recovery of experimental bone defects using rat models. We examined the areal and volumetric BMD to identify LIPUS doses to be applied and evaluated the accuracy reported by previous studies.

METHODS

The Virtual Health Library regional portal, PubMed, Embase, EBSCOhost, Scopus and CAPES were reviewed for animal studies that compared fracture treatments based on LIPUS with sham or no treatments using rat models and reported BMD as an outcome. The tool provided by the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) and the Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies (CAMARADES) checklist were used to assess the bias and quality of such studies.

RESULTS

Of the six studies reviewed, the most frequently used LIPUS dose had an ultrasonic frequency of 1.0 MHz, repetition rate of 0.1 kHz and pulse duration of 2000 μs. An intensity (ISATA) of 30 mW/cm2 was the most preferred for bone recovery. However, the BMD could not solely irrefutably evaluate the effectiveness of LIPUS in bone recovery as the results were discordant with each other. The discrepancies in experimental methodologies, low-quality classifications and high risk of bias in the selected studies, however, did not validate the undertaking of a meta-analysis.

CONCLUSION

On the basis of the BMD results, no sufficient evidence was found to recommend the use of LIPUS for bone recovery in rat models. Thus, this systematic review indicates that the accuracy of such reports must be improved to improve their scientific quality to facilitate a transition of LIPUS applications from pre-clinical research to clinic use.

Low-intensity pulsed ultrasound in obstetrics and gynecology: advances in clinical application and research progress

In the past decade, research on ultrasound therapy in obstetrics and gynecology has rapidly developed. Currently, high-intensity ultrasound has been widely used in clinical practice, while low-intensity ultrasound has gradually emerged as a new trend of transitioning from pre-clinical research to clinical applications. Low-intensity pulsed ultrasound (LIPUS), characterized by a non-invasive low-intensity pulse wave stimulation method, employs its non-thermal effects to achieve safe, economical, and convenient therapeutic outcomes. LIPUS converts into biochemical signals within cells through pathways such as cavitation, acoustic flow, and mechanical stimulation, regulating molecular biological mechanisms and exerting various biological effects. The molecular biology mechanisms underlying the application of LIPUS in obstetrics and gynecology mainly include signaling pathways, key gene expression, angiogenesis, inflammation inhibition, and stem cell differentiation. LIPUS plays a positive role in promoting soft tissue regeneration, bone regeneration, nerve regulation, and changes in cell membrane permeability. LIPUS can improve the treatment benefit of premature ovarian failure, pelvic floor dysfunction, nerve damage caused by intrauterine growth restriction, ovariectomized osteoporosis, and incomplete uterine involution through the above biological effects, and it also has application value in the adjuvant treatment of malignant tumors such as ovarian cancer and cervical cancer. This study outlines the biological mechanisms and applications of LIPUS in treating various obstetric and gynecologic diseases, aiming to promote its precise application and provide a theoretical basis for its use in the field.

Ultrasound therapy for a week promotes regeneration and reduces pro-inflammatory macrophages in a rat sciatic nerve autograft model

Peripheral nerve injury causes long-term motor dysfunction. Ultrasound (US) therapy is expected to accelerate peripheral nerve regeneration. However, its optimal usage and effects on macrophage phenotypes during peripheral nerve regeneration remain unknown. In this study, we investigated the optimal duration of US therapy and its effects on macrophage phenotype. Twenty-seven rats with autologous sciatic nerve grafting were divided into three groups: two received US therapy (1 MHz frequency, intensity of 140 mW/cm², 20% duty cycle, 5 min/day) for one (US1) or 4 weeks (US4), and one group received sham stimulation. Immunohistochemistry was performed 3 and 7 days after injury in another set of 12 rats. Eight weeks after the injury, the compound muscle action potential amplitude of the gastrocnemius in the US1 and US4 groups was significantly higher than that in the sham group. The toe-spreading test showed functional recovery, whereas the gait pattern during treadmill walking did not recover. There were no significant differences in motor function, histomorphometry, or muscle weight between groups. Immunohistochemistry showed that US therapy decreased the number of pro-inflammatory macrophages seven days after injury. Therefore, US therapy for both one or 4 weeks can similarly promote reinnervation and reduce proinflammatory macrophages in autograft model rats.

Effect of low-intensity pulsed ultrasound on osteogenic differentiation of human induced membrane-derived cells in Masquelet technique

INTRODUCTION

The Masquelet technique is a relatively new method for large bone defect treatment. In this technique, grafted bone tissue is used, and after the cement is removed, the induced membrane (IM; that form around the cement spacers placed in the bone defect region) is thought to play an important role in promoting bone formation. On the other hand, low-intensity pulsed ultrasound (LIPUS) is known to promote fracture healing and angiogenesis through mechanical stimulation. This study aimed to investigate the in vitro effects of LIPUS on the osteogenic differentiation of human induced membrane-derived cells (IMCs).

METHODS

Seven patients who had been treated using the Masquelet technique were enrolled. The IM was harvested during the second stage of the technique. IMCs were isolated, cultured in growth medium, and then divided into two groups: (1) control group, IMCs cultured in osteogenic medium without LIPUS, and (2) LIPUS group, IMCs cultured in osteogenic medium with LIPUS treatment. Adherent cells from the IM samples were harvested after the first passage and evaluated for cell surface protein expression using immunostaining. A cell proliferation assay was used to count the number of IMCs using a hemocytometer. Osteogenic differentiation capability was assessed using an alkaline phosphatase (ALP) activity assay, Alizarin Red S staining, and real-time reverse transcription-polymerase chain reaction.

RESULTS

Cell surface antigen profiling revealed that the IMCs contained cells positive for the mesenchymal stem cell-related markers CD73, CD90, and CD105. No significant difference in cell numbers was found between the control and LIPUS groups. The ALP activity of IMCs in the LIPUS group was significantly higher than that in the control group on days 7 and 14. Alizarin red S staining intensity was significantly higher in the LIPUS group than in the control group on day 21. Runx2 and VEGF expression was significantly upregulated on days 7 and 14, respectively, compared with levels in the control group.

CONCLUSION

We demonstrated the significant effect of LIPUS on the osteogenic differentiation of human IMCs. This study indicates that LIPUS can be used as an additional tool for the enhancement of the healing process of the Masquelet technique.

Gene expression changes in therapeutic ultrasound-treated venous leg ulcers

Introduction

Low-frequency, low-intensity ultrasound has been previously shown to promote healing of chronic wounds in humans, but mechanisms behind these effects are poorly understood. The purpose of this study was to evaluate gene expression differences in debrided human venous ulcer tissue from patients treated with low-frequency (20 kHz), low-intensity (100 mW/cm2) ultrasound compared to a sham treatment in an effort to better understand the potential biological mechanisms.

Methods

Debrided venous ulcer tissue was collected from 32 subjects one week after sham treatment or low-frequency, low-intensity ultrasound treatment. Of these samples, 7 samples (3 ultrasound treated and 4 sham treated) yielded sufficient quality total RNA for analysis by ultra-high multiplexed PCR (Ampliseq) and expression of more than 24,000 genes was analyzed. 477 genes were found to be significantly differentially expressed between the ultrasound and sham groups using cut-off values of p < 0.05 and fold change of 2.

Results and Discussion

The top differentially expressed genes included those involved in regulation of cell metabolism, proliferation, and immune cell signaling. Gene set enrichment analysis identified 20 significantly enriched gene sets from upregulated genes and 4 significantly enriched gene sets from downregulated genes. Most of the enriched gene sets from upregulated genes were related to cell-cell signaling pathways. The most significantly enriched gene set from downregulated genes was the inflammatory response gene set. These findings show that therapeutic ultrasound influences cellular behavior in chronic wounds as early as 1 week after application. Considering the well-known role of chronic inflammation in impairing wound healing in chronic wounds, these results suggest that a downregulation of inflammatory genes is a possible biological mechanism of ultrasound-mediated venous chronic wound healing. Such increased understanding may ultimately lead to the enhancement of ultrasound devices to accelerate chronic wound healing and increase patient quality of life.

Low-intensity pulsed ultrasound promotes proliferation and myelinating genes expression of Schwann cells through NRG1/ErbB signaling pathway

Schwann cells (SCs) are the major component of myelin sheath in the peripheral nervous system, which are necessary in the development, function maintenance, and repair of peripheral nerves. This study aimed to investigate the potential mechanism of low-intensity pulsed ultrasound (LIPUS) affecting the proliferation and myelinating activity of SCs. Rat Schwann cell line RSC96 were cultured and exposed to LIPUS of different duty ratios (control, 20 %, 50 %, 80 %). Results demonstrated that LIPUS with a duty ratio of 50 % showing the maximal effect in facilitating proliferation of SCs. The expressions of Krox20 and myelin basic protein (MBP), the key molecules of SC myelination, and the potent inducer of myelination neuregulin 1 (NRG1) and its receptors ErbB2 and ErbB3 increased significantly by LIPUS. The reaction of these factors to LIPUS were both time- and duty ratio-dependent: namely LIPUS with higher duty ratios took effects when applied repeatedly over more consecutive days. These observations indicated that NRG1/ErbB signaling pathway might contribute to the effects of LIPUS on the proliferation and myelinating status of SCs, which could be one of the mechanisms in the protective role of LIPUS in nerve repair and regeneration. Our work provided novel insights for promising strategies of nerve repair therapy.

Bone Healing Gone Wrong: Pathological Fracture Healing and Non-Unions-Overview of Basic and Clinical Aspects and Systematic Review of Risk Factors

Bone healing is a multifarious process involving mesenchymal stem cells, osteoprogenitor cells, macrophages, osteoblasts and -clasts, and chondrocytes to restore the osseous tissue. Particularly in long bones including the tibia, clavicle, humerus and femur, this process fails in 2-10% of all fractures, with devastating effects for the patient and the healthcare system. Underlying reasons for this failure are manifold, from lack of biomechanical stability to impaired biological host conditions and wound-immanent intricacies. In this review, we describe the cellular components involved in impaired bone healing and how they interfere with the delicately orchestrated processes of bone repair and formation. We subsequently outline and weigh the risk factors for the development of non-unions that have been established in the literature. Therapeutic prospects are illustrated and put into clinical perspective, before the applicability of biomarkers is finally discussed.

Application of low-intensity pulsed ultrasound on tissue resident stem cells: Potential for ophthalmic diseases

INTRODUCTION

Tissue-resident stem cells (TRSCs) have the ability to self-renew and differentiate throughout an individual's lifespan, and they utilize both mechanisms to maintain homeostasis and regenerate damaged tissues. Several studies suggest that these stem cells can serve as a potential source for cell-replacement-based therapy by promoting differentiation or expansion. In recent years, low-intensity pulsed ultrasound (LIPUS) has been demonstrated to effectively stimulate stem cell proliferation and differentiation, promote tissue regeneration, and inhibit inflammatory responses.

AIMS

To present a comprehensive overview of current application and mechanism of LIPUS on tissue resident stem cells.

METHODS

We searched PubMed, Web of Science for articles on the effects of LIPUS on tissue resident stem cells and its application.

RESULTS

The LIPUS could modulate cellular activities such as cell viability, proliferation and differentiation of tissue resident stem cells and related cells through various cellular signaling pathways. Currently, LIPUS, as the main therapeutic ultrasound, is being widely used in the treatment of preclinical and clinical diseases.

CONCLUSION

The stem cell research is the hot topic in the biological science, while in recent years, increasing evidence has shown that TRSCs are good targets for LIPUS-regulated regenerative medicine. LIPUS may be a novel and valuable therapeutic approach for the treatment of ophthalmic diseases. How to further improve its efficiency and accuracy, as well as the biological mechanism therein, will be the focus of future research.

LIPUS as a potential strategy for periodontitis treatment: A review of the mechanisms

Periodontitis is a chronic inflammatory condition triggered by oral bacteria. A sustained inflammatory state in periodontitis could eventually destroy the alveolar bone. The key objective of periodontal therapy is to terminate the inflammatory process and reconstruct the periodontal tissues. The traditional Guided tissue regeneration (GTR) procedure has unstable results due to multiple factors such as the inflammatory environment, the immune response caused by the implant, and the operator's technique. Low-intensity pulsed ultrasound (LIPUS), as acoustic energy, transmits the mechanical signals to the target tissue to provide non-invasive physical stimulation. LIPUS has positive effects in promoting bone regeneration, soft-tissue regeneration, inflammation inhibition, and neuromodulation. LIPUS can maintain and regenerate alveolar bone during an inflammatory state by suppressing the expression of inflammatory factors. LIPUS also affects the cellular behavior of periodontal ligament cells (PDLCs), thereby protecting the regenerative potential of bone tissue in an inflammatory state. However, the underlying mechanisms of the LIPUS therapy are still yet to be summarized. The goal of this review is to outline the potential cellular and molecular mechanisms of periodontitis-related LIPUS therapy, as well as to explain how LIPUS manages to transmit mechanical stimulation into the signaling pathway to achieve inflammatory control and periodontal bone regeneration.

Low-Intensity Pulsed Ultrasound Treatment for Non-unions of Long Bone Fractures in a Scottish District General Hospital

OBJECTIVE

Despite advances in treatment, the management of fracture non-union remains a challenging and complex problem in orthopaedics. Low-intensity pulsed ultrasound (LIPUS) treatment has been shown to be an effective, non-invasive, affordable treatment option. This treatment was evaluated in a Scottish district hospital over a nine-year period, which included the COVID-19 pandemic.

MATERIALS AND METHODS

This submission describes a case series at Dr Gray's Hospital in Scotland, 18 patients in whom fracture non-union was treated using LIPUS.

RESULTS

An overall healing rate of 94% was achieved. Exogen™ (Bioventus LLC, NC, USA) proved to be most successful in oligotrophic non-union. No observed patient demographic appeared predictive of outcome. LIPUS treatment failed in one case. No significant adverse effects of LIPUS were detected.

CONCLUSION

LIPUS represents a useful, cost-effective potential alternative to revision surgery. LIPUS may therefore be the preferred treatment when surgical intervention and face-to-face interactions are to be minimised, as during the COVID-19 pandemic.

The Evaluation of Meniscus Regenerative Effects of LIPUS-Induced CCN Proteins: Induction by LIPUS of CCN2 and Meniscus-Related Genes in Cultured Meniscus Cells and Meniscus Tissues

Menisci are a pair of crescent-shaped fibrocartilages and composed primarily of type I collagen. Inner region of the meniscus has similar characteristics to articular cartilage. Low-intensity pulsed ultrasound (LIPUS) has been reported to have chondroprotective effects on chondrocytes by inducing the expression of chondrocyte differentiation markers and CCN2/CTGF production. Here, we describe an experimental approach that investigates the distinct cellular behavior of human inner and outer meniscus cells in response to LIPUS stimulation. Our experimental model can analyze the relationships between LIPUS-induced CCN2 and its repairing role in the meniscus.

Instructional review of key factors to achieve successful outcomes when using low-intensity pulsed ultrasound in fracture repair

Low-intensity pulsed ultrasound (LIPUS) treatment of fractures has been available to the orthopaedic community for nearly three decades; however, it is still considered an experimental treatment by some clinicians, even though there is a wealth of clinical data. Based on the evaluation of clinical trial data, we have established key criteria which can lead to LIPUS success and avoid failure. These are fracture gap size and stability, accurate transducer placement and minimum treatment number. However, from a clinician's view, the correct attitude to treatment must be observed, and this has also been discussed. It is hoped, armed with this new evaluation of the clinical data, that clinicians can treat patients with LIPUS more effectively, resulting in fewer failures of treatment.

The therapeutic effects of low-intensity pulsed ultrasound in musculoskeletal soft tissue injuries: Focusing on the molecular mechanism

Musculoskeletal soft tissue injuries are very common and usually occur during both sporting and everyday activities. The intervention of adjuvant therapies to promote tissue regeneration is of great importance to improving people's quality of life and extending their productive lives. Though many studies have focused on the positive results and effectiveness of the LIPUS on soft tissue, the molecular mechanisms standing behind LIPUS effects are much less explored and reported, especially the intracellular signaling pathways. We incorporated all research on LIPUS in soft tissue diseases since 2005 and summarized studies that uncovered the intracellular molecular mechanism. This review will also provide the latest evidence-based research progress in this field and suggest research directions for future experiments.

Biochemical and Physiological Events Involved in Responses to the Ultrasound Used in Physiotherapy: A Review

Therapeutic ultrasound (TUS) is the ultrasound modality widely used in physical therapy for the treatment of acute and chronic injuries of various biological tissues. Its thermal and mechanical effects modify the permeability of the plasma membrane, the flow of ions and molecules and cell signaling and, in this way, promote the cascade of physiological events that culminate in the repair of injuries. This article is a review of the biochemical and physiological effects of TUS with parameters commonly used by physical therapists. Integrins can translate the mechanical signal of the TUS into a cellular biochemical signal for protein synthesis and modification of the active site of enzymes, so cell function and metabolism are modified. TUS also alters the permeability of the plasma membrane, allowing the influx of ions and molecules that modulate the cellular electrochemical signaling pathways. With biochemical and electrochemical signals tampered with, the cellular response to damage is then modified or enhanced. Greater release of pro-inflammatory factors, cytokines and growth factors, increased blood flow and activation of protein kinases also seem to be involved in the therapeutic response of TUS. Although a vast number of publications describe the mechanisms by which TUS can interact with the biological system, little is known about the metabolic possibilities of TUS because of the lack of standardization in its application.

Effects of Low-Intensity Pulsed Ultrasound on the Migration and Homing of Human Amnion-Derived Mesenchymal Stem Cells to Ovaries in Rats With Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI) can cause multiple sequelae and is currently incurable. Mesenchymal stem cell (MSC) transplantation might provide an effective treatment method for POI. However, the clinical application of systemic MSC transplantation is limited by the low efficiency of cell homing to target tissue in vivo, including systemic MSC transplantation for POI treatment. Thus, exploration of methods to promote MSC homing is necessary. This study was to investigate the effects of low-intensity pulsed ultrasound (LIPUS) on the migration and homing of transplanted human amnion–derived MSCs (hAD-MSCs) to ovaries in rats with chemotherapy-induced POI. For LIPUS treatment, hAD-MSCs were exposed to LIPUS or sham irradiation. Chemokine receptor expressions in hAD-MSCs were detected by polymerase chain reaction (PCR), Western blot, and immunofluorescence assays. hAD-MSC migration was detected by wound healing and transwell migration assays. Cyclophosphamide-induced POI rat models were established to evaluate the effects of LIPUS on the homing of systemically transplanted hAD-MSCs to chemotherapy-induced POI ovaries in vivo. We found that hAD-MSCs expressed chemokine receptors. The LIPUS promoted the expression of chemokine receptors, especially CXCR4, in hAD-MSCs. SDF-1 induced hAD-MSC migration. The LIPUS promoted hAD-MSC migration induced by SDF-1 through SDF-1/CXCR4 axis. SDF-1 levels significantly increased in ovaries induced by chemotherapy in POI rats. Pretreating hAD-MSCs with LIPUS increased the number of hAD-MSCs homing to ovaries in rats with chemotherapy-induced POI to some extent. However, the difference was not significant. Both hAD-MSC and LIPUS-pretreated hAD-MSC transplantation reduced ovarian injuries and improved ovarian function in rats with chemotherapy-induced POI. CXCR4 antagonist significantly reduced the number of hAD-MSCs- and LIPUS-pretreated hAD-MSCs homing to POI ovaries, and further reduced their efficacy in POI treatment. According to these findings, pretreating MSCs with LIPUS before transplantation might provide a novel, convenient, and safe technique to explore for improving the homing of systemically transplanted MSCs to target tissue.

Mechanosensitive Piezo1 and Piezo2 ion channels in craniofacial development and dentistry: Recent advances and prospects

Mechanical forces play important roles in many biological processes and there is increasing interest and understanding of these roles. Mechanotransduction is the process by which mechanical stimuli are converted to biochemical signals through specific mechanisms, and this results in the activation of downstream signaling pathways with specific effects on cell behaviors. This review systematically summarizes the current understanding of the mechanosensitive Piezo1 and Piezo2 ion channels in craniofacial bone, tooth, and periodontal tissue, presenting the latest relevant evidence with implications for potential treatments and managements of dental and orofacial diseases and deformities. The mechanosensitive ion channels Piezo1 and Piezo2 are widely expressed in various cells and tissues and have essential functions in mechanosensation and mechanotransduction. These channels play an active role in many physiological and pathological processes, such as growth and development, mechano-stimulated bone homeostasis and the mediation of inflammatory responses. Emerging evidence indicates the expression of Piezo1 and Piezo2 in bone, dental tissues and dental tissue-derived stem cells and suggests that they function in dental sensation transduction, dentin mineralization and periodontal bone remodeling and modulate orthodontic tooth movement.

Role of low-intensity pulsed ultrasound in regulating macrophage polarization to accelerate tendon-bone interface repair

Low-intensity pulsed ultrasound (LIPUS) has been proven to accelerate the healing of the tendon-bone interface (TBI), and macrophages are considered to play an important regulatory role. This study was designed to explore the polarization of macrophages during treatment of TBI injury with LIPUS. In a rat model of rotator cuff tear, LIPUS or mock sonication (controls) was administered from 1 week postoperatively. The supraspinatus-supraspinatus tendon-humerus complexes were harvested for further evaluation at different time points for measures such as new bone formation, TBI maturity, ultimate failure load and stiffness, and types of macrophages. In vitro, bone marrow-derived macrophages were cultured, and polarization was identified after stimulation with or without LIPUS (the LIPUS or control groups, respectively). Two weeks posttreatment, the LIPUS group showed higher bone volume/total volume ratios and better TBI maturity scores. Six weeks posttreatment, the failure load of the LIPUS group was significantly higher than that of the control group. LIPUS also accelerated initial inflammatory macrophage accumulation and facilitated anti-inflammatory macrophage polarization (M2) in the late period. In the in vitro macrophage polarization model, the LIPUS group showed a higher proportion of M2 macrophages and mRNA expression of anti-inflammatory genes than the control group, while there was no significant difference in the proinflammatory macrophages between the two groups. Our observations revealed that macrophage polarization may be a potential mechanism of LIPUS treatment for TBI repair.

The perceptions of clinicians using low-intensity pulsed ultrasound (LIPUS) for orthopaedic pathology: A national qualitative study

INTRODUCTION

Low-intensity pulsed ultrasound (LIPUS) is a non-invasive treatment modality for delayed union or non-union of acute fractures. We aimed to assess the current use of LIPUS at a national level in the United Kingdom, why and how clinicians use it, what treatment protocols are followed, and what the current perceptions are on this technology.

METHODOLOGY

Using a detailed online survey compromised of 20 questions delivered to known LIPUS users, we were able to collect qualitative data on indication of use, type of machine used, personal views on the technology, frequency of usage, and treatment protocols. Each question was peer-reviewed to exclude bias.

RESULTS

A total of 70 respondents completed the survey. LIPUS was used by most clinicians for cases of non-union (N = 55, 78.5%) and delayed union (N = 51, 72.8%). The majority of respondents personally used a LIPUS device between 1 and 5 times in 12 months (N = 38, 54.3%). Most considered LIPUS a failure after three to six months of treatment without clinical improvement (N = 39, 55.7%). A total of 32 respondents (45.7%) mentioned the need for funding approval before accessing LIPUS technology. Poor revision surgery candidates (N = 48, 68.6%) and atrophic non-union (N = 46, 65.7%) were the most frequently cited reasons for using LIPUS technology as treatment. Most participants (N = 48, 68.6%) considered LIPUS to be cost-effective. Despite most clinicians being comfortable with the use of LIPUS, some respondents did not understand the basic science underpinning the technology nor could explain the need for LIPUS to patients comfortably.

CONCLUSION

LIPUS technology may have a significant role to play in the treatment of orthopaedic fracture related pathology. Regular users perceived the technology to be cost-effective and efficacious. Further research should standardize treatment protocols and aim to establish a national LIPUS registry.

Low-intensity pulsed ultrasound promotes periodontal regeneration in a beagle model of furcation involvement

Objective: To evaluate the regeneration potential of periodontitis tissue treated by low-intensity pulsed ultrasound (LIPUS) combined with the guided tissue regeneration (GTR) technique in a beagle model of furcation involvement (FI).

Background: Achieving predictable regeneration remains a clinical challenge for periodontitis tissue due to the compromised regenerative potential caused by chronic inflammation stimulation. LIPUS, an FDA-approved therapy for long bone fracture and non-unions, has been demonstrated effective in the in vitro attenuation of inflammation-induced dysfunction of periodontal ligament stem cells (PDLSCs), the key cells contributing to periodontal regeneration. However, the in vivo effect of LIPUS on periodontitis tissue is rarely reported.

Methods: A beagle model of FI was established, and the experimental teeth were randomly assigned into three groups: control group, GTR group, and GTR+LIPUS group. Radiographic examinations were performed, and clinical periodontal parameters were recorded to reflect the periodontal condition of different groups. Histological analyses using H&amp;E and Masson’s staining were conducted to evaluate the periodontal tissue regeneration.

Results: LIPUS could enhance new periodontal bone formation and bone matrix maturity in FI after GTR treatment. Moreover, clinical assessment and histomorphometric analyses revealed less inflammatory infiltration and superior vascularization within bone grafts in the LIPUS treatment group, indicating the anti-inflammatory and pro-angiogenic effects of LIPUS in FI.

Conclusion: Our investigation on a large animal model demonstrated that LIPUS is a promising adjunctive approach for the regeneration of periodontitis tissue, paving a new avenue for LIPUS application in the field of periodontal regenerative medicine.

A randomized comparative study between high-intensity laser vs low-intensity pulsed ultrasound both combined with exercises for the treatment of knee osteoarthritis

OBJECTIVE

To compare the effects of high-intensity laser therapy (HILT) plus exercise therapy (ET) vs low-intensity pulsed ultrasound (LIPUS) plus ET in knee osteoarthritis (KOA).

METHODS

A single blinded randomized controlled trial in an outpatient setting. There were 60 participants with grades II and III KOA based on the radiological findings in Kellgren and Lawrence grading scale. Participants were allocated randomly into three groups, study group I (HILT+ET), study group II (LIPUS+ET), and control (ET) group. Participants in the three groups received active range of motion (ROM) exercises, muscle strengthening, and flexibility exercises. Treatment was administered 5 times/wk for two successive weeks. Primary outcomes involved visual analog scale (VAS), secondary outcomes involved knee ROM, proprioceptive accuracy and Western Ontario and McMaster Universities Arthritis Index scale. All outcomes were measured pre- and post-treatment.

RESULTS

The mean age of participants was 55.4 ± 6.34, 55.2 ± 4.77 and 57 ± 6.39 years in HILT+ET, LIPUS+ET and control group respectively. There were statistically significant time-by-group effects (mixed-design multivariate analysis of variance) on all measured outcomes for all groups (P < .0001). However, HILT+ET yielded better improvement than the other groups (P < .0001). Between-group comparison revealed a significant difference in all measured outcomes between study group 1 vs study group 2, and between each study group vs the control group (P = .0001).

CONCLUSION

The effect of HILT combined with exercises achieved better results in pain, knee ROM, proprioceptive accuracy and functional disability than LIPUS combined with exercises and both are better than exercises only.

Advances in the application of low-intensity pulsed ultrasound to mesenchymal stem cells

Mesenchymal stem cells (MSCs) are stem cells that exhibit self-renewal capacity and multi-directional differentiation potential. They can be extracted from the bone marrow and umbilical cord, as well as adipose, amnion, and other tissues. They are widely used in tissue engineering and are currently considered an important source of cells in the field of regenerative medicine. Since certain limitations, such as an insufficient cell source, mature differentiation, and low transplantation efficiency, are still associated with MSCs, researchers have currently focused on improving the efficacy of MSCs. Low-intensity pulsed ultrasound (LIPUS) has mechanical, cavitation, and thermal effects that can produce different biological effects on organs, tissues, and cells. It can be used for fracture treatment, cartilage repair, and stem cell applications. An in-depth study of the role and mechanism of action of LIPUS in MSC treatment would promote our understanding of LIPUS and promote research in this field. In this article, we have reviewed the progress in research on the use of LIPUS with various MSCs and comprehensively discussed the progress in the use of LIPUS for promoting the proliferation, differentiation, and migration of MSCs, as well as its future prospects.

Low-Intensity Pulsed Ultrasound Promotes Osteogenic Potential of iPSC-Derived MSCs but Fails to Simplify the iPSC-EB-MSC Differentiation Process

Induced pluripotent stem cell (iPSC)-derived mesenchymal stem cells (iMSCs) are a promising cell source for bone tissue engineering. However, iMSCs have less osteogenic potential than BMSCs, and the classical iPSC-EB-iMSC process to derive iMSCs from iPSCs is too laborious as it involves multiple in vitro steps. Low-intensity pulsed ultrasound (LIPUS) is a safe therapeutic modality used to promote osteogenic differentiation of stem cells. Whether LIPUS can facilitate osteogenic differentiation of iMSCs and simplify the iPSC-EB-iMSC process is unknown. We stimulated iMSCs with LIPUS at different output intensities (20, 40, and 60 mW/cm²) and duty cycles (20, 50, and 80%). Results of ALP activity assay, osteogenic gene expression, and mineralization quantification demonstrated that LIPUS was able to promote osteogenic differentiation of iMSCs, and it worked best at the intensity of 40 mW/cm² and the duty cycle of 50% (LIPUS40/50). The Wnt/β-catenin signaling pathway was involved in LIPUS40/50-mediated osteogenesis. When cranial bone defects were implanted with iMSCs, LIPUS40/50 stimulation resulted in a significant higher new bone filling rate (72.63 ± 17.04)% than the non-stimulated ones (34.85 ± 4.53)%. Daily exposure to LIPUS40/50 may accelerate embryoid body (EB)-MSC transition, but it failed to drive iPSCs or EB cells to an osteogenic lineage directly. This study is the first to demonstrate the pro-osteogenic effect of LIPUS on iMSCs. Although LIPUS40/50 failed to simplify the classical iPSC-EB-MSC differentiation process, our preliminary results suggest that LIPUS with a more suitable parameter set may achieve the goal. LIPUS is a promising method to establish an efficient model for iPSC application.

Development of a Novel Perfusion Rotating Wall Vessel Bioreactor with Ultrasound Stimulation for Mass-Production of Mineralized Tissue Constructs

BACKGROUND

As stem cells are considered a promising cell source for tissue engineering, many culture strategies have been extensively studied to generate in vitro stem cell-based tissue constructs. However, most approaches using conventional tissue culture plates are limited by the lack of biological relevance in stem cell microenvironments required for neotissue formation. In this study, a novel perfusion rotating wall vessel (RWV) bioreactor was developed for mass-production of stem cell-based 3D tissue constructs.

METHODS

An automated RWV bioreactor was fabricated, which is capable of controlling continuous medium perfusion, highly efficient gas exchange with surrounding air, as well as low-intensity pulsed ultrasound (LIPUS) stimulation. Embryonic stem cells encapsulated in alginate/gelatin hydrogel were cultured in the osteogenic medium by using our bioreactor system. Cellular viability, growth kinetics, and osteogenesis/mineralization were thoroughly evaluated, and culture media were profiled at real time. The in vivo efficacy was examined by a rabbit cranial defect model.

RESULTS

Our bioreactor successfully maintained the optimal culture environments for stem cell proliferation, osteogenic differentiation, and mineralized tissue formation during the culture period. The mineralized tissue constructs produced by our bioreactor demonstrated higher void filling efficacy in the large bone defects compared to the group implanted with hydrogel beads only. In addition, the LIPUS modules mounted on our bioreactor successfully reached higher mineralization of the tissue constructs compared to the groups without LIPUS stimulation.

CONCLUSION

This study suggests an effective biomanufacturing strategy for mass-production of implantable mineralized tissue constructs from stem cells that could be applicable to future clinical practice.

Pitfalls preventing bone union with EXOGEN Low-Intensity Pulsed Ultrasound

OBJECTIVES

To evaluate the efficacy of EXOGEN in achieving union and common pitfalls in its use within the Manchester Foundation Trust (MFT) and Salford Royal Foundation Trust (SRFT).

METHOD

Patients receiving EXOGEN therapy between 01/01/2017 and 31/12/2019 at hospitals within MFT and SRFT were identified using EXOGEN logbooks and hospital IT systems. An equal number of patients were included from both sites. Data were retrospectively collected from clinical documents detailing clinical presentation comorbidities, and radiographic images, determining the radiological union post EXOGEN therapy. In addition, local practices were observed and compared to EXOGEN's standardized guidance for clinicians.

RESULTS

Fifty-eight patients were included in the primary review, with 9 subsequently excluded based on insufficient clinical data. 47% of patients achieved radiological union following completion of EXOGEN therapy. Outcomes of the 23 patients with persistent non-union were as follows - 18 were referred for revision surgery, 5 were prescribed further EXOGEN therapy, 2 refused or were unfit for further intervention, and 1 did not have a plan documented. No significant baseline differences were present in both outcome groups. However, at MFT and SRFT, rates of union with EXOGEN are below that previously published in the literature.

CONCLUSION

EXOGEN has proven successful in facilitating union in established cases of non-union without the risk and cost associated with revision surgery. Centre outcome differences may be explained by failure to educate clinicians and patients on the correct use of the EXOGEN device, failure to standardize follow-up or monitor compliance, and must be addressed to improve current services.

Low-Intensity Pulsed Ultrasound Stimulation for Bone Fractures Healing: A Review

Low-intensity pulsed ultrasound (LIPUS) is a developing technology, which has been proven to improve fracture healing process with minimal thermal effects. This noninvasive treatment accelerates bone formation through various molecular, biological, and biomechanical interactions with tissues and cells. Although LIPUS treatment has shown beneficial effects on different bone fracture locations, only very few studies have examined its effects on deeper bones. This study provides an overview on therapeutic ultrasound for fractured bones, possible mechanisms of action, clinical evidences, current limitations, and its future prospects.

Effect of Low-Intensity Pulsed Ultrasound on the Graft-Bone Healing of Artificial Ligaments: An In Vitro and In Vivo Study

BACKGROUND

As many researchers have focused on promoting the graft-bone healing of artificial ligaments, even with numerous chemical coatings, identifying a biosafe, effective, and immediately usable method is still important clinically.

PURPOSE

(1) To determine whether a low-intensity pulsed ultrasound system (LIPUS) promotes in vitro cell viability and osteogenic differentiation and (2) to assess the applicability and effectiveness of LIPUS in promoting the graft-bone healing of artificial ligaments in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

Polyethylene terephthalate (PET) sheets and grafts were randomly assigned to control and LIPUS groups. MC3T3-E1 preosteoblasts were cultured on PET sheets. Cell viability and morphology were evaluated using a live/dead viability assay and scanning electron microscopy. Alkaline phosphatase activity, calcium nodule formation, and Western blot were evaluated for osteogenic differentiation. For in vivo experiments, the effect of LIPUS was evaluated via an extra-articular graft-bone healing model in 48 rabbits: the osteointegration and new bone formation were tested by micro-computed tomography and histological staining, and the graft-bone bonding was tested by biomechanical testing.

RESULTS

Cell viability was significantly higher in the LIPUS group as compared with control (living and dead compared between control and LIPUS groups, P = .0489 vs P = .0489). Better adherence of cells and greater development of extracellular matrix were observed in the LIPUS group. Furthermore, LIPUS promoted alkaline phosphatase activity, calcium nodule formation, and the protein expression of collagen 1 (P = .0002) and osteocalcin (P = .0006) in vitro. Micro-computed tomography revealed higher surrounding bone mass at 4 weeks and newly formed bone mass at 8 weeks in the LIPUS group (P = .0014 and P = .0018). Histological analysis showed a narrower interface and direct graft-bone contact in the LIPUS group; the surrounding bone area at 4 weeks and the mass of newly formed bone at 4 and 8 weeks in the LIPUS group were also significantly higher as compared with control (surrounding bone, P < .0001; newly formed bone, P = .0016 at 4 weeks and P = .005 at 8 weeks). The ultimate failure load in the LIPUS group was significantly higher than in the control group (P < .0001 at 4 weeks; P = .0008 at 8 weeks).

CONCLUSION

LIPUS promoted the viability and osteogenic differentiation of MC3T3-E1 preosteoblasts in vitro and enhanced the graft-bone healing of PET artificial ligament in vivo.

CLINICAL RELEVANCE

LIPUS is an effective physical stimulation to enhance graft-bone healing after artificial ligament implantation.

Low-Intensity Pulsed Ultrasound Promotes Repair of 4-Vinylcyclohexene Diepoxide-Induced Premature Ovarian Insufficiency in SD Rats

Women with premature ovarian insufficiency (POI) may be more vulnerable to a variety of health risks. To seek a new method to treat the disease, the effects of low-intensity pulsed ultrasound (LIPUS) on promoting repair of ovarian injury in female SD rats induced by 4-vinylcyclohexene diepoxide (VCD) were explored in this research. A total of 24 female SD rats were subjected to intraperitoneal injection of VCD to induce POI. Successful modeling was achieved in 22 rats, which were then randomized into VCD + LIPUS group (n = 13) and VCD group (n = 9). The control group (n = 5) was injected with equal normal saline. Hematoxylin and eosin staining, enzyme-linked immunosorbent assay, Western blot analysis, scanning electron microscope, immunohistochemistry, and terminal deoxynucleotidyl transferase-mediated nick end labeling assay were applied to detect the results. The results indicated that rats in the VCD group showed disorder in the estrous cycle, the number of atresia follicles and apoptosis granulosa cells increased (p < .05). After the LIPUS treatment, the estrous cycle recovered, the number of follicles increased (p < .05), the level of E2 and anti-Müllerian hormone enhanced (p < .05), and the follicle-stimulating hormone decreased (p < .05). The expression of NF-κB p65, TNFα, Bax, ATF4, and caspase-3 in ovarian tissue was significantly decreased (p < .05). These findings showed that LIPUS could promote the repair of the VCD-induced ovarian damage in SD rats, which has the potential to be further applied in the clinic.

Investigating the Optimal Initiation Time of Ultrasound Therapy for Peripheral Nerve Regeneration after Axonotmesis in Rats

This study was aimed at identifying the optimal initiation time of ultrasound (US) therapy for peripheral nerve regeneration after axonotmesis. Thirty-six rats with sciatic nerve crush injury were divided into four groups that received US irradiation initiated 1, 7 or 14 d after injury, or sham stimulation for 4 wk. Motor function analysis was conducted weekly; however, there was no significant improvement attributed to US treatment. Four weeks after injury, compound muscle action potential amplitude values of the group in which US irradiation was initiated 1 d after the injury exhibited significant improvement compared with the sham stimulation group. In addition, myelin sheath thickness was significantly greater in the 1-d group than in other groups. These results indicate that US treatment initiated 1 d after peripheral nerve injury promotes maximum regeneration.

Low-Intensity Pulsed Ultrasound Promotes Osteogenic Differentiation of Reamer-Irrigator-Aspirator Graft-Derived Cells in Vitro

Recently, reamer-irrigator-aspirator (RIA) systems have been increasingly used to harvest autologous bone grafts. RIA graft materials contain bone marrow, which provides a viable source to derive large numbers of mesenchymal stem cells. Low-intensity pulsed ultrasound (LIPUS) significantly accelerates the differentiation of stem cells derived from bone marrow. This in vitro study investigated the effect of LIPUS on the osteogenic activity and differentiation of RIA graft-derived cells. A small amount of RIA graft was obtained from seven patients. After the cells derived from RIA grafts were cultured, they were divided into two groups: the LIPUS and control groups. LIPUS was applied once daily for 20 min (1.5 MHz, pulse duration: 200 µs, pulse repetition rate: 1 kHz, spatial average-temporal average intensity: 30 mW/cm²). Alkaline phosphatase activity (113.4% and 130.1% on days 7 and 14), expression of osteoblast-related genes (ALP, Runx2) and mineralization (135.2% on day 21) of the RIA graft-derived cells were significantly higher in the LIPUS group than in the control group. However, LIPUS did not affect the cell proliferation of RIA graft-derived cells. This study indicates that LIPUS may enhance the healing of non-union and critical bone defects treated by autologous bone grafting using the RIA system.

Comparison Between Clinically Available Low-Intensity Pulsed Ultrasound (LIPUS) and a Novel Bimodal Acoustic Signal System for Accelerating Fracture Healing

Low-intensity pulsed ultrasound (LIPUS) accelerates fracture healing by stimulating the production of bone callus and the mineralization process. This study compared a novel bimodal acoustic signal (BMAS) device for bone fracture healing to a clinical LIPUS system (EXOGEN; Bioventus, Durham, NC, USA). Thirty rabbits underwent a bilateral fibular osteotomy. Each rabbits' legs were randomized to receive 20-min treatment daily for 18 days with BMAS or LIPUS. The latter utilizes a longitudinal ultrasonic mode only, while the former employs ultrasound-induced shear stress to promote bone formation. Power Doppler imaging (PDI) was acquired days 0, 2, 4, 7, 11, 14, and 18 post-surgery to monitor treatment response and quantified off-line. X-rays were acquired to evaluate fractures on days 0, 14, 18, and 21. Seventeen rabbits completed the study and were euthanized day 21 post-surgery. The fibulae were analyzed to determine maximum torque, initial torsional stiffness, and angular displacement at failure. ANOVAs and paired t-tests were used to compare pair-wise outcome variables for the two treatment modes on a per rabbit basis. The BMAS system induced better fracture healing with greater stiffness (BMAS 0.21 ± 0.19 versus LIPUS 0.16 ± 0.19 [Formula: see text]cm/°, p = 0.050 ) and maximum torque (BMAS 7.84 ± 5.55 versus LIPUS 6.26 ± 3.46 [Formula: see text]cm, p = 0.022 ) than the LIPUS system. Quantitative PDI assessments showed a higher amount of vascularity with LIPUS than BMAS on days 4 and 18 ( ). In conclusion, the novel BMAS technique achieved better bone fracture healing response than the current Food and Drug Administration (FDA)-approved LIPUS system.

Low-intensity pulsed ultrasound-generated singlet oxygen induces telomere damage leading to glioma stem cell awakening from quiescence

Cancer stem cells, quiescent and drug resistant, have become a therapeutic target. Unlike high-intensity focused ultrasound directly killing tumor, low-intensity pulsed ultrasound (LIPUS), a new noninvasive physical device, promotes pluripotent stem cell differentiation and is primarily applied in tissue engineering but rarely in oncotherapy. We explored the effect and mechanism of LIPUS on glioma stem cell (GSC) expulsion from quiescence. Here, we observed that LIPUS led to attenuated expression of GSC biomarkers, promoted GSC escape from G0 quiescence, and significantly weakened the Wnt and Hh pathways. Of note, LIPUS transferred sonomechanical energy into cytochrome c and B5 proteins, which converted oxygen molecules into singlet oxygen, triggering telomere crisis. The in vivo and in vitro results confirmed that LIPUS enhanced the GSC sensitivity to temozolomide. These results demonstrated that LIPUS "waked up" GSCs to improve their sensitivity to chemotherapy, and importantly, we confirmed the direct targeted proteins of LIPUS in GSCs.