Low‐intensity pulsed ultrasound stimulation promotes osteoblast differentiation through hedgehog signaling

Developing and Investigating a Nanovibration Intervention for the Prevention/Reversal of Bone Loss Following Spinal Cord Injury

Osteoporosis disrupts the fine-tuned balance between bone formation and resorption, leading to reductions in bone quantity and quality and ultimately increasing fracture risk. Prevention and treatment of osteoporotic fractures is essential for reductions in mortality, morbidity, and the economic burden, particularly considering the aging global population. Extreme bone loss that mimics time-accelerated osteoporosis develops in the paralyzed limbs following complete spinal cord injury (SCI). In vitro nanoscale vibration (1 kHz, 30 or 90 nm amplitude) has been shown to drive differentiation of mesenchymal stem cells toward osteoblast-like phenotypes, enhancing osteogenesis and inhibiting osteoclastogenesis simultaneously. Here, we develop and characterize a wearable device designed to deliver and monitor continuous nanoamplitude vibration to the hindlimb long bones of rats with complete SCI. We investigate whether a clinically feasible dose of nanovibration (two 2 h/day, 5 days/week for 6 weeks) is effective at reversing the established SCI-induced osteoporosis. Laser interferometry and finite element analysis confirmed transmission of nanovibration into the bone, and microcomputed tomography and serum bone formation and resorption markers assessed effectiveness. The intervention did not reverse SCI-induced osteoporosis. However, serum analysis indicated an elevated concentration of the bone formation marker procollagen type 1 N-terminal propeptide (P1NP) in rats receiving 40 nm amplitude nanovibration, suggesting increased synthesis of type 1 collagen, the major organic component of bone. Therefore, enhanced doses of nanovibrational stimulus may yet prove beneficial in attenuating/reversing osteoporosis, particularly in less severe forms of osteoporosis.

LIPUS regulates the progression of knee osteoarthritis in mice through primary cilia-mediated TRPV4 channels

Osteoarthritis (OA) is a common disease in middle-aged and elderly people. An imbalance in calcium ion homeostasis will contribute to chondrocyte apoptosis and ultimately lead to the progression of OA. Transient receptor potential channel 4 (TRPV4) is involved in the regulation of intracellular calcium homeostasis. TRPV4 is expressed in primary cilia, which can sense mechanical stimuli from outside the cell, and its abnormal expression is closely related to the development of OA. Low-intensity pulsed ultrasound (LIPUS) can alleviate chondrocyte apoptosis while the exact mechanism is unclear. In this project, with the aim of revealing the mechanism of action of LIPUS, we proposed to use OA chondrocytes and animal models, LIPUS intervention, inhibition of primary cilia, use TRPV4 inhibitors or TRPV4 agonist, and use Immunofluorescence (IF), Immunohistochemistry (IHC), Western Blot (WB), Quantitative Real-time PCR (QP) to detect the expression of cartilage synthetic matrix and endoplasmic reticulum stress markers. The results revealed that LIPUS altered primary cilia expression, promoted synthetic matrix metabolism in articular chondrocytes and was associated with primary cilia. In addition, LIPUS exerted a active effect on OA by activating TRPV4, inducing calcium inward flow, and facilitating the entry of NF-κB into the nucleus to regulate synthetic matrix gene transcription. Inhibition of TRPV4 altered primary cilia expression in response to LIPUS stimulation, and knockdown of primary cilia similarly inhibited TRPV4 function. These results suggest that LIPUS mediates TRPV4 channels through primary cilia to regulate the process of knee osteoarthritis in mice.

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.

Low-intensity pulsed ultrasound reduces alveolar bone resorption during orthodontic treatment via Lamin A/C-Yes-associated protein axis in stem cells

BACKGROUND

The bone remodeling during orthodontic treatment for malocclusion often requires a long duration of around two to three years, which also may lead to some complications such as alveolar bone resorption or tooth root resorption. Low-intensity pulsed ultrasound (LIPUS), a noninvasive physical therapy, has been shown to promote bone fracture healing. It is also reported that LIPUS could reduce the duration of orthodontic treatment; however, how LIPUS regulates the bone metabolism during the orthodontic treatment process is still unclear.

AIM

To investigate the effects of LIPUS on bone remodeling in an orthodontic tooth movement (OTM) model and explore the underlying mechanisms.

METHODS

A rat model of OTM was established, and alveolar bone remodeling and tooth movement rate were evaluated via micro-computed tomography and staining of tissue sections. In vitro, human bone marrow mesenchymal stem cells (hBMSCs) were isolated to detect their osteogenic differentiation potential under compression and LIPUS stimulation by quantitative reverse transcription-polymerase chain reaction, Western blot, alkaline phosphatase (ALP) staining, and Alizarin red staining. The expression of Yes-associated protein (YAP1), the actin cytoskeleton, and the Lamin A/C nucleoskeleton were detected with or without YAP1 small interfering RNA (siRNA) application via immunofluorescence.

RESULTS

The force treatment inhibited the osteogenic differentiation potential of hBMSCs; moreover, the expression of osteogenesis markers, such as type 1 collagen (COL1), runt-related transcription factor 2, ALP, and osteocalcin (OCN), decreased. LIPUS could rescue the osteogenic differentiation of hBMSCs with increased expression of osteogenic marker inhibited by force. Mechanically, the expression of LaminA/C, F-actin, and YAP1 was downregulated after force treatment, which could be rescued by LIPUS. Moreover, the osteogenic differentiation of hBMSCs increased by LIPUS could be attenuated by YAP siRNA treatment. Consistently, LIPUS increased alveolar bone density and decreased vertical bone absorption in vivo. The decreased expression of COL1, OCN, and YAP1 on the compression side of the alveolar bone was partially rescued by LIPUS.

CONCLUSION

LIPUS can accelerate tooth movement and reduce alveolar bone resorption by modulating the cytoskeleton-Lamin A/C-YAP axis, which may be a promising strategy to reduce the orthodontic treatment process.

Application of Ultrasound to Enhancing Stem Cells Associated Therapies

Pluripotent stem cell therapy exhibits self-renewal capacity and multi-directional differentiation potential and is considered an important regenerative approach for the treatment of several diseases. However, insufficient cell transplantation efficiency, uncontrollable differentiation, low cell viability, and difficult tracing limit its clinical applications and treatment outcome. Ultrasound (US) has mechanical, cavitation, and thermal effects that can produce different biological effects on organs, tissues, and cells. US can be combined with different US-responsive particles for enhanced physical-chemical stimulation and drug delivery. In the meantime, US also can provide a noninvasive and harmless imaging modality for deep tissue in vivo. An in-depth evaluation of the role and mechanism of action of US in stem cell therapy would enhance understanding of US and encourage research in this field. In this article, we comprehensively review progress in the application of US alone and combined with US-responsive particles for the promotion of proliferation, differentiation, migration, and in vivo detection of stem cells and the potential clinical applications.

LIPUS accelerates bone regeneration via HDAC6-mediated ciliogenesis

Delayed fracture union and nonunion are common complications of fracture encountered, while Low-intensity pulsed ultrasound (LIPUS) can stimulate bone regeneration. Still, the underlying mechanism of LIPUS on bone regeneration has been poorly understood, which resulted in varied outcomes in the clinic. Therefore, figuring out the mechanism of LIPUS on bone regeneration can lay the foundation for better use of LIPUS in clinical bone regenerative therapies. In this study, we created transgenic mice to reveal the relationship between the periosteal cells' fate and the number of ciliated cells under the LIPUS stimulation. In vitro, we isolated the periosteal cell and aim to figure out the relationship between LIPUS and HDAC6-mediated ciliogenesis and find out a potential target for LIPUS-based bone regeneration strategies. The results showed that LIPUS promoted femoral bone defect regeneration and enhanced osteogenic differentiation of Prrx1⁺ cells. However, these pro-effects were significantly weakened when the Prrx1⁺ cell's primary cilia were knocked down. Besides, LIPUS stimulated the formation of Prrx1⁺ cells' primary cilia in the bone defect microenvironment. In vitro, the results supported that LIPUS enhanced the osteogenic differentiation of Prrx1⁺ cells through HDAC6-mediated ciliogenesis. In conclusion, λ LIPUS could promote the osteogenic differentiation of Prrx1⁺ cells to stimulate bone regeneration and inhibit the expression of HDAC6 to increase the prevalence of primary cilia in Prrx1⁺ cells. LIPUS could enhance the osteogenic differentiation of Prrx1⁺ cells mainly through HDAC6-mediated ciliogenesis.

The role of hypertrophic chondrocytes in regulation of the cartilage-to-bone transition in fracture healing

Endochondral bone formation is an important pathway in fracture healing, involving the formation of a cartilaginous soft callus and the process of cartilage-to-bone transition. Failure or delay in the cartilage-to-bone transition causes an impaired bony union such as nonunion or delayed union. During the healing process, multiple types of cells including chondrocytes, osteoprogenitors, osteoblasts, and endothelial cells coexist in the callus, and inevitably crosstalk with each other. Hypertrophic chondrocytes located between soft cartilaginous callus and bony hard callus mediate the crosstalk regulating cell-matrix degradation, vascularization, osteoclast recruitment, and osteoblast differentiation in autocrine and paracrine manners. Furthermore, hypertrophic chondrocytes can become osteoprogenitors and osteoblasts, and directly contribute to woven bone formation. In this review, we focus on the roles of hypertrophic chondrocytes in fracture healing and dissect the intermingled crosstalk in fracture callus during the cartilage-to-bone transition.

Effectiveness and Mechanisms of Low-Intensity Pulsed Ultrasound on Osseointegration of Dental Implants and Biological Functions of Bone Marrow Mesenchymal Stem Cells

Dental implant restoration is the preferred choice for patients with dentition defects or edentulous patients, and obtaining stable osseointegration is the determining factor for successful implant healing. The risk of implant failure during the healing stage is still an urgent problem in clinical practice due to differences in bone quality at different implant sites and the impact of some systemic diseases on bone tissue metabolism. Low-intensity pulsed ultrasound (LIPUS) is a noninvasive physical intervention method widely recognized in the treatment of bone fracture and joint damage repair. Moreover, many studies indicated that LIPUS could effectively promote the osseointegration of dental implants and improve the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). This review is aimed at investigating the research progress on the use of LIPUS in dental implant medicine from three aspects: (1) discuss the promoting effects of LIPUS on osseointegration and peri-implant bone regeneration, (2) summarize the effects and associated mechanisms of LIPUS on the biological functions of BMSCs, and (3) introduce the application and prospects of LIPUS in the clinical work of dental implantation. Although many challenges need to be overcome in the future, LIPUS is bound to be an efficient and convenient therapeutic method to improve the dental implantation success rate and expand clinical implant indications.

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&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.

Primary cilia and PTH1R interplay in the regulation of osteogenic actions

Primary cilia are subcellular structures specialized in sensing different stimuli in a diversity of cell types. In bone, the primary cilium is involved in mechanical sensing and transduction of signals that regulate the behavior of mesenchymal osteoprogenitors, osteoblasts and osteocytes. To perform its functions, the primary cilium modulates a plethora of molecules including those stimulated by the parathyroid hormone (PTH) receptor type I (PTH1R), a master regulator of osteogenesis. Binding of the agonists PTH or PTH-related protein (PTHrP) to the PTH1R or direct agonist-independent stimulation of the receptor activate PTH1R signaling pathways. In turn, activation of PTH1R leads to regulation of bone formation and remodeling. Herein, we describe the structure, function and molecular partners of primary cilia in the context of bone, playing special attention to those signaling pathways that are mediated directly or indirectly by PTH1R in association with primary cilia during the process of osteogenesis.

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.

LIPUS inhibits inflammation and catabolism through the NF-κB pathway in human degenerative nucleus pulposus cells

Background

Low-intensity pulsed ultrasound (LIPUS) is a safe and noninvasive rehabilitative physical therapy with anti-inflammatory effects. The current study investigated the effect of LIPUS on the inflammation of nucleus pulposus (NP) cells and its underlying mechanism.

Methods

Human NP cells were acquired from lumbar disc herniation tissue samples and cultured for experiments. Human NP cells were treated with LPS and then exposed to LIPUS (15 mW/cm², 30 mW/cm² and 60 mW/cm²) for 20 min daily for 3 days to determine the appropriate intensity to inhibit the expression of the inflammatory factors TNF-α and IL-1β. The gene and protein expression of aggrecan, collagen II, MMP-3 and MMP-9 was measured by real‐time PCR and western blotting, respectively. The activity of the nuclear factor‐kappa B (NF‐κB) pathway was examined by western blotting and immunofluorescence. After pretreatment with the NF-κB inhibitor PDTC, the expression of TNF-α, IL-1β, MMP-3 and MMP-9 was measured by real‐time PCR.

Results

LIPUS at intensities of 15 mW/cm², 30 mW/cm² and 60 mW/cm² inhibited LPS-induced NP cell expression of the inflammatory factors TNF-α and IL-1β, especially at 30 mW/cm². LIPUS significantly upregulated the gene and protein expression of aggrecan and collagen II and downregulated the gene and protein expression of MMP-3 and MMP-9 in LPS-induced NP cells. The NF‐κB signaling pathway was inhibited by LIPUS through inhibiting the protein expression of p-P65 and the translocation of P65 into the nucleus in LPS-induced NP cells. In addition, LIPUS had similar effects as the NF-κB inhibitor PDTC by inhibiting the NF-κB signaling pathway, inflammation and catabolism in LPS-induced human degenerative nucleus pulposus cells.

Conclusion

LIPUS inhibited inflammation and catabolism through the NF‐κB pathway in human degenerative nucleus pulposus cells.

Longitudinal effects of low-intensity pulsed ultrasound on osteoporosis and osteoporotic bone defect in ovariectomized rats

Low-intensity pulsed ultrasound (LIPUS) with an intensity (spatial average temporal average, I_SATA) of 30 mW/cm² has been widely proved to be effective on impaired bone healing, but showing little effectiveness in the treatment of osteoporosis. We hypothesized that the intensity of LIPUS may be a key factor in explaining this difference, thus two intensity levels, the widely used 30 mW/cm² and a higher 150 mW/cm², were used to simultaneously treat osteoporosis and osteoporotic bone defect in ovariectomized (OVX) rats with a 1-mm drill hole on their left femurs.Results showed that 150 mW/cm² LIPUS augmented the healing rate of the drill hole than 30 mW/cm² after 3-week LIPUS treatment, although did not further enhance the healing rate after 6-week LIPUS treatment. For ameliorating osteoporosis, 150 mW/cm² LIPUS achieved more advantages over 30 mW/cm² in improving bone density, microstructure and biomechanics 6 weeks after LIPUS intervention. In conclusion, LIPUS with an intensity of 30 mW/cm² was sufficient to facilitate bone defect healing, but a higher intensity can be considered as a rapid trigger for osteoporotic bone repair. In addition, improving the intensity of LIPUS may be a potentially effective consideration for alleviation of osteoporosis, and the LIPUS regimen in the treatment of osteoporosis remains to be optimized.

Low-intensity pulsed ultrasound protects subchondral bone in rabbit temporomandibular joint osteoarthritis by suppressing TGF-β1/Smad3 pathway

Transforming growth factor β1(TGF-β1)/Smad3 pathway promotes the pathological progression of subchondral bone in osteoarthritis. The aim of this study is to determine the effect of low-intensity pulsed ultrasound (LIPUS) on the pathological progression and TGF-β1/Smad3 pathway of subchondral bone in temporomandibular joint osteoarthritis (TMJOA). Rabbit TMJOA model was established by type II collagenase induction. The left joint in this model was continuously stimulated with LIPUS for 3 and 6 weeks (1 MHz; 30 mW/cm² ) for 20 min/day. The morphological and histological features of subchondral bone were respectively examined by microcomputed tomography and Safranin-O staining. The number of osteoclasts was quantitatively assessed by tartrate-resistant acid phosphatase staining. Immunohistochemistry and Western blot analysis were conducted to evaluate the protein expression of Cathepsin K and TGF-β1/Smad3 pathway. The results indicated that LIPUS could improve the trabecular microstructure and histological characteristics of subchondral bone in rabbit TMJOA. It also suppressed abnormal subchondral bone resorption and activation of TGF-β1/Smad3 pathway, characterized by the number of osteoclasts, protein expression levels of Cathepsin K, TGF-β1, type II TGFβ receptor, and phosphorylated Smad3 (pSmad3) were decreased. In conclusion, LIPUS promoted the quality of subchondral bone by suppressing osteoclast activity and TGF-β1/Smad3 pathway in rabbit TMJOA.

[A review of mechanisms by which low-intensity pulsed ultrasound affects bone regeneration]

Low-intensity pulsed ultrasound (LIPUS) is a common physical therapy to accelerate the healing of bone fracture and treat delayed union of bone fracture. Vessels, nerves, and bone tissue are essential constituents of bone system. Recently, increasing evidence has been revealed that LIPUS can not only promote bone regeneration by directly regulating osteoblasts, osteoblasts, mesenchymal stem cells, but also have a positive impact on the repair of bone healing through vessels and nerves. Thus, we reviewed and summarized the latest published literature about the molecular mechanism for the effects of LIPUS on bone regeneration, which might offer a promising therapy for bone-related diseases.

Ultrasound Therapy: Experiences and Perspectives for Regenerative Medicine

Ultrasound has emerged as a novel tool for clinical applications, particularly in the context of regenerative medicine. Due to its unique physico-mechanical properties, low-intensity ultrasound (LIUS) has been approved for accelerated fracture healing and for the treatment of established non-union, but its utility has extended beyond tissue engineering to other fields, including cell regeneration. Cells and tissues respond to acoustic ultrasound by switching on genetic repair circuits, triggering a cascade of molecular signals that promote cell proliferation, adhesion, migration, differentiation, and extracellular matrix production. LIUS also induces angiogenesis and tissue regeneration and has anti-inflammatory and anti-degenerative effects. Accordingly, the potential application of ultrasound for tissue repair/regeneration has been tested in several studies as a stand-alone treatment and, more recently, as an adjunct to cell-based therapies. For example, ultrasound has been proposed to improve stem cell homing to target tissues due to its ability to create a transitional and local gradient of cytokines and chemokines. In this review, we provide an overview of the many applications of ultrasound in clinical medicine, with a focus on its value as an adjunct to cell-based interventions. Finally, we discuss the various preclinical and clinical studies that have investigated the potential of ultrasound for regenerative medicine.

Characterization of primary cilia features reveal cell-type specific variability in in vitro models of osteogenic and chondrogenic differentiation

Primary cilia are non-motile sensory antennae present on most vertebrate cell surfaces. They serve to transduce and integrate diverse external stimuli into functional cellular responses vital for development, differentiation and homeostasis. Ciliary characteristics, such as length, structure and frequency are often tailored to distinct differentiated cell states. Primary cilia are present on a variety of skeletal cell-types and facilitate the assimilation of sensory cues to direct skeletal development and repair. However, there is limited knowledge of ciliary variation in response to the activation of distinct differentiation cascades in different skeletal cell-types. C3H10T1/2, MC3T3-E1 and ATDC5 cells are mesenchymal stem cells, preosteoblast and prechondrocyte cell-lines, respectively. They are commonly employed in numerous in vitro studies, investigating the molecular mechanisms underlying osteoblast and chondrocyte differentiation, skeletal disease and repair. Here we sought to evaluate the primary cilia length and frequencies during osteogenic differentiation in C3H10T1/2 and MC3T3-E1 and chondrogenic differentiation in ATDC5 cells, over a period of 21 days. Our data inform on the presence of stable cilia to orchestrate signaling and dynamic alterations in their features during extended periods of differentiation. Taken together with existing literature these findings reflect the occurrence of not only lineage but cell-type specific variation in ciliary attributes during differentiation. These results extend our current knowledge, shining light on the variabilities in primary cilia features correlated with distinct differentiated cell phenotypes. It may have broader implications in studies using these cell-lines to explore cilia dependent cellular processes and treatment modalities for skeletal disorders centered on cilia modulation.

Impact of low-intensity pulsed ultrasound on transcription and metabolite compositions in proliferation and functionalization of human adipose-derived mesenchymal stromal cells

To investigate the effect of low-intensity pulsed ultrasound (LIPUS) on the proliferation of human adipose-derived mesenchymal stromal cells (hASCs) and uncovered its stimulation mechanism. LIPUS at 30 mW/cm² was applied for 5 min/day to promote the proliferation of hASCs. Flow cytometry was used to study the cell surface markers, cell cycle, and apoptosis of hASCs. The proliferation of hASCs was detected by cell counting kit-8, cell cycle assay, and RT-PCR. The expression of hASCs cytokines was determined by ELISA. The differences between transcriptional genes and metabolites were analyzed by transcript analysis and metabolomic profiling experiments. The number of cells increased after LIPUS stimulation, but there was no significant difference in cell surface markers. The results of flow cytometry, RT-PCR, and ELISA after LIPUS was administered showed that the G₁ and S phases of the cell cycle were prolonged. The expression of cell proliferation related genes (CyclinD1 and c-myc) and the paracrine function related gene (SDF-1α) were up-regulated. The expression of cytokines was increased, while the apoptosis rate was decreased. The results of transcriptome experiments showed that there were significant differences in 27 genes;15 genes were up-regulated, while 12 genes were down-regulated. The results of metabolomics experiments showed significant differences in 30 metabolites; 7 metabolites were up-regulated, and 23 metabolites were down-regulated. LIPUS at 30 mW/cm² intensity can promote the proliferation of hASCs cells in an undifferentiating state, and the stem-cell property of hASCs was maintained. CyclinD1 gene, c-myc gene, and various genes of transcription and products of metabolism play an essential role in cell proliferation. This study provides an important experimental and theoretical basis for the clinical application of LIPUS in promoting the proliferation of hASCs cells.

Shortening of Overall Orthodontic Treatment Duration with Low-Intensity Pulsed Ultrasound (LIPUS)

The aim of this retrospective clinical study was to determine if there is a reduction in the overall treatment duration in orthodontic patients using low-intensity pulsed ultrasound (LIPUS) and Invisalign SmartTrack® clear aligners. Data were collected from the first thirty-four patients (9 males, 25 females; average age 41.37 ± 15.02) who finished their orthodontic treatment using an intraoral LIPUS device and Invisalign clear aligners in a private clinic. The LIPUS parameters used by patients at home for 20 min/day were: ultrasonic frequency 1.5 MHz, pulse duration 200µs, pulse repetition rate 1 kHz, and spatial average-temporal average intensity 30mW/cm². A control group (11 males, 23 females; average age 31.36 ± 14.41) matching for the same malocclusions was randomly selected from finished treatment cases of the same clinician. The date of first Invisalign attachment placement and first use of LIPUS application was recorded as T0, and the date of retainer delivery was recorded as T1. The treatment duration (T1–T0) and treatment reduction percentage with LIPUS device were collected and analyzed using two-sample t-test in Microsoft Excel. Treatment duration was significantly reduced in the LIPUS group (541.44 ± 192.23 days) compared to control group (1061.05 ± 455.64 days) (p < 0.05). The LIPUS group showed on average 49% reduction in the overall treatment time as compared to the control group. The average compliance of the patients using LIPUS was 66.02%. Patients who used LIPUS showed a clinically significant reduction in the overall orthodontic treatment duration compared to the control group who used Invisalign clear aligners only.

Low-intensity pulsed ultrasound improves osseointegration of dental implant in mice by inducing local neuronal production of αCGRP

OBJECTIVE

This study aimed to explore the effect of Low-intensity pulsed ultrasound (LIPUS) on implant osseointegration and elucidate the role of α-calcitonin gene-related peptide (αCGRP) in this process.

DESIGN

In vivo, αCGRP^+/+ (Wild-type model) mice and αCGRP^-/- (Knock-out model) mice with implants immediately placed in the maxillary first molars extraction sockets were treated with LIPUS. We detected details of peri-implant bone tissues by micro-CT, real-time PCR and histological analysis. In vitro, αCGRP^+/+ and αCGRP^-/- dorsal root ganglia (DRG) neurons were cultured and exposed to LIPUS. Then conditioned media from these neurons were collected and added to osteoblasts to analyze cell differentiation, mineralization and proliferation by real-time PCR, alkaline phosphatase (ALP) and cell counting kit-8 (CCK-8) assay. Besides, ELISA was performed to determine the effect of LIPUS on the αCGRP secretion in neurons.

RESULTS

In vivo tests revealed that αCGRP^-/- mice displayed worse osseointegration when compared to αCGRP^+/+ mice. LIPUS could enhance implant osseointegration in αCGRP+/+ mice but had little effect on αCGRP^-/- mice. Meanwhile, αCGRP was elevated during the osseointegration with LIPUS treatment. In vitro, LIPUS promoted αCGRP secretion in DRG neurons, thereby enhanced osteogenic differentiation and mineralization of osteoblasts. Also we proved that the effects of LIPUS was duty cycle-related and LIPUS of 80% duty cycle had the strongest impacts.

CONCLUSIONS

Our findings demonstrated that LIPUS could enhance osseointegration of dental implant by inducing local neuronal production of αCGRP, providing a new idea to promote peri-implant osseointegration and bone regeneration.

Impact of Ultrasound Therapy on Stem Cell Differentiation - A Systematic Review

OBJECTIVE

This is a systematic review of the effects of low-intensity pulsed ultrasound (LIPUS) on stem cell differentiation.

BACKGROUND DATA

Recent studies have investigated several types of stem cells from different sources in the body. These stem cells should strictly be certified and promoted for cell therapies before being used in medical applications. LIPUS has been used extensively in treatment centers and in research to promote stem cell differentiation, function, and proliferation.

MATERIALS AND METHODS

The databases of PubMed, Google Scholar, and Scopus were searched for abstracts and full-text scientific papers published from 1989-2019 that reported the application of LIPUS on stem cell differentiation. Related English language articles were found using the following defined keywords: low-intensity pulsed ultrasound, stem cell, differentiation. Criteria for inclusion in the review were: LIPUS with frequencies of 1-3 MHz and pulsed ultrasound intensity of <500 mW/cm2. Duration, exposure time, and cell sources were taken into consideration.

RESULTS

Fifty-two articles were selected based on the inclusion criteria. Most articles demonstrated that the application of LIPUS had positive effects on stem cell differentiation. However, some authors recommended that LIPUS combined with other physical therapy aides was more effective in stem cell differentiation.

CONCLUSION

LIPUS significantly increases the level of stem cell differentiation in cells derived mainly from bone marrow mesenchymal stem cells. There is a need for further studies to analyze the effect of LIPUS on cells derived from other sources, particularly adipose tissue-derived mesenchymal stem cells, for treating hard diseases, such as osteoporosis and diabetic foot ulcer. Due to a lack of reporting on standard LIPUS parameters in the field, more experiments comparing the protocols for standardization of LIPUS parameters are needed to establish the best protocol, which would allow for the best results.

Effects of low-intensity pulsed ultrasound exposure on rats tibia periosteum

The periosteum is a rich source of osteoprogenitor cells and periosteal grafts can be used as an alternative method to replace bone grafts. The low-intensity pulsed ultrasound (LIPUS) has often been used as a noninvasive method to stimulate osteogenesis and reduce the fracture healing time. The aim of this study was to evaluate the effects of the ultrasound exposure on the rat tibia periosteum. Group I (7 animals) received LIPUS therapy on the left tibia for 7 days and group II (7 animals) on the left tibia for 14 days. After euthanasia, the tibias were processed. Number of periosteal cells and vessels and thickness of the periosteum were analyzed. The number of periosteal cells was higher in stimulated periosteum compared to controls at 7 and 14 days, but the number of vessels and the thickness only were higher in the group stimulated at 14 days. Furthermore, the ultrasound treatment for 14 days was more effective than 7 days. The ultrasound stimulation of the periosteum prior to grafting procedure can be advantageous, since it increases periosteal activity, and LIPUS may be an alternative method for stimulating the periosteum when the use of periosteal grafts in bone repair is needed.

Current State of Bone Adhesives-Necessities and Hurdles

The vision of gluing two bone fragments with biodegradable and biocompatible adhesives remains highly fascinating and attractive to orthopedic surgeons. Possibly shorter operation times, better stabilization, lower infection rates, and unnecessary removal make this approach very appealing. After 30 years of research in this field, the first adhesive systems are now appearing in scientific reports that may fulfill the comprehensive requirements of bioadhesives for bone. For a successful introduction into clinical application, special requirements of the musculoskeletal system, challenges in the production of a bone adhesive, as well as regulatory hurdles still need to be overcome. In this article, we will give an overview of existing synthetic polymers, biomimetic, and bio-based adhesive approaches, review the regulatory hurdles they face, and discuss perspectives of how bone adhesives could be efficiently introduced into clinical application, including legal regulations.

Low-intensity pulsed ultrasound promotes proliferation and migration of HaCaT keratinocytes through the PI3K/AKT and JNK pathways

Although the effects of low-intensity pulsed ultrasound (LIPUS) on diverse cell types have been fully studied, the functional role of LIPUS in keratinocytes remains poorly understood. This study aimed to investigate the effects of LIPUS on proliferation and migration of HaCaT cells as well as the regulatory mechanisms associated with signaling pathways. Human HaCaT cells were exposed or not to LIPUS, and cell proliferation and migration were measured by BrdU incorporation assay and Transwell assay, respectively. Expression of proteins associated with proliferation and migration was evaluated by western blot analysis. Expression of key kinases in the PI3K/AKT and JNK pathways was also evaluated by western blot analysis. Effects of LIPUS on the PI3K/AKT and JNK pathways, and whether LIPUS affected HaCaT cells via these two pathways were finally explored. When the parameter of LIPUS (number of cycles) was set at 300, cell viability was the highest after LIPUS stimulation. We then found that the percentage of BrdU positive cells was enhanced by LIPUS, along with up-regulation of cyclinD1, CDK6, CDK4, and VEGF. LIPUS promoted migration, as well as up-regulation of MMP-2 and MMP-9. Phosphorylation levels of key kinases in the PI3K/AKT and JNK pathways were increased by LIPUS. Inhibition of either PI3K/AKT pathway or JNK pathway attenuated effects of LIPUS on HaCaT cells, and co-inhibition of these two pathways showed augmented effects. LIPUS promoted proliferation and migration of HaCaT cells through activating the PI3K/AKT and JNK pathways.