The potential of pulsed low intensity ultrasound to stimulate chondrocytes matrix synthesis in agarose and monolayer cultures

Metabolomic Profiling and Characterization of a Novel 3D Culture System for Studying Chondrocyte Mechanotransduction

Background/Objective

Articular chondrocytes synthesize and maintain the avascular and aneural articular cartilage. In vivo these cells are surrounded by a 3D pericellular matrix (PCM) containing predominantly collagen VI. The PCM protects chondrocytes and facilitates mechanotransduction. PCM stiffness is critical in transmitting biomechanical signals to chondrocytes. Various culture systems with different hydrogels are used to encapsulate chondrocytes for 3D culture, but many lack either the PCM or the in vivo stiffness of the cartilage matrix. This study aimed at establishing a culture system to investigate a) if chondrocytes cultured in alginate will develop a PCM and b) study mechanotransduction via metabolic changes induced in 3D agarose-embedded chondrocytes upon mechanical stimulation.

Methods

We cultured primary human and bovine chondrocytes in monolayers or as alginate encapsulated cells in media containing sodium L-ascorbate. PCM expression was analyzed by immunofluorescence and western blots. We further characterized the response of chondrocytes embedded in physiologically stiff agarose to dynamic compression through metabolomic profiling.

Results

We found that primary human and bovine chondrocytes, when cultured in alginate beads with addition of sodium L-ascorbate for 7 days, had a pronounced PCM, retained their phenotype, and synthesized both collagens VI and II. This novel culture system enables alginate-encapsulated chondrocytes to develop a robust PCM thereby creating a model system to study mechanotransduction in the presence of an endogenous PCM. We also observed distinct compression-induced changes in metabolomic profiles between the monolayer-agarose and alginate-released agarose-embedded chondrocytes indicating physiological changes in cell metabolism.

Conclusion/Significance

These data show that 3D preculture of chondrocytes in alginate before encapsulation in physiologically stiff agarose leads to pronounced development of pericellular matrix that is sustained in the presence of ascorbate. This model can be useful in studying the mechanism by which chondrocytes respond to cyclical compression and other types of loading simulating in vivo physiological conditions.

Effectiveness of low-intensity pulsed ultrasound on osteoarthritis: molecular mechanism and tissue engineering

Osteoarthritis (OA) is distinguished by pathological alterations in the synovial membrane, articular cartilage, and subchondral bone, resulting in physical symptoms such as pain, deformity, and impaired mobility. Numerous research studies have validated the effectiveness of low-intensity pulsed ultrasound (LIPUS) in OA treatment. The periodic mechanical waves generated by LIPUS can mitigate cellular ischemia and hypoxia, induce vibration and collision, produce notable thermal and non-thermal effects, alter cellular metabolism, expedite tissue repair, improve nutrient delivery, and accelerate the healing process of damaged tissues. The efficacy and specific mechanism of LIPUS is currently under investigation. This review provides an overview of LIPUS's potential role in the treatment of OA, considering various perspectives such as the synovial membrane, cartilage, subchondral bone, and tissue engineering. It aims to facilitate interdisciplinary scientific research and further exploration of LIPUS as a complementary technique to existing methods or surgery. Ongoing research is focused on determining the optimal dosage, frequency, timing, and treatment strategy of LIPUS for OA. Additional research is required to clarify the precise mechanism of action and potential impacts on cellular, animal, and human systems prior to its integration into therapeutic applications.

The effectiveness of therapeutic ultrasound to the mechanically damaged chondrocyte culture

OBJECTIVE

This study aimed to evaluate the efficacy of low intensity (0.1-0.8 Watt/cm2) pulsed ultrasound on chondrocyte cell proliferation and migration.

METHODS

Low-intensity pulsed ultrasound (frequency 3 MHz, duty cycle 25%, and pulse repetition frequency 150 Hz) for 5 minutes at different spatial average intensities was applied on chondrocyte cells. First, the optimum dose with significantly increased proliferation was determined to be 0.5 W/cm2 for 5 minutes of duration. Then, 0.5 W/cm2 ultrasound intensity was applied for durations of 2.5, 5, 7.5, and 10 minutes, and healing was assessed by monitoring cell migration and proliferation.

RESULTS

At the intensity of 0.5 W/cm2 48 hours after the application, a statistically significant increase in proliferation (p = .0089) was observed in chondrocyte cells compared to the control group. Proliferation was analyzed at 4, 8, 24, and 48 hours after applying 0.5 W/cm2 ultrasound for durations of 2.5, 5, 7.5, and 10 minutes. Statistically significant increases were observed at 4 hours (p = .009), 8 hours (p = .032), 24 hours (p = .0084), and 48 hours (p = .00098) with 10 minutes of exposure. For 7.5 min of exposure duration, significant increases were observed at 48 hours (p = .045). In migration for all parameters, no statistically significant improvement (p > .05) was observed.

CONCLUSION

It was shown that low intensity pulsed ultrasound induces cartilage cell proliferation; therefore, it may have a disease-modifying effect in the treatment of osteoarthritis. However, no positive effect was observed on cartilage cell migration.

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.

Effects and mechanotransduction pathways of therapeutic ultrasound on healthy and osteoarthritic chondrocytes: a systematic review of in vitro studies

OBJECTIVE

To investigate the effects and mechanotransduction pathways of therapeutic ultrasound on chondrocytes.

METHOD

PubMed, EMBASE and Web of Science databases were searched up to 19^th September 2021 to identify in vitro studies exploring ultrasound to stimulate chondrocytes for osteoarthritis (OA) treatment. Study characteristics, ultrasound parameters, in vitro setup, and mechanotransduction pathways were collected. Risk of bias was judged using the Risk of Bias Assessment for Non-randomized Studies (RoBANS) tool.

RESULTS

Thirty-one studies were included comprising healthy and OA chondrocytes and explants. Most studies had high risk of performance, detection and pseudoreplication bias due to lack of temperature control, setup calibration, inadequate semi-quantitatively analyzes and independent experiments. Ultrasound was applied to the culture plate via acoustic gel, water bath or culture media. Regardless of the setup used, ultrasound stimulated the cartilage production and suppressed its degradation, although the effect size was nonsignificant. Ultrasound inhibited p38, c-Jun N-terminal kinases (JNK) and factor nuclear kappa B (NFκB) pathways in OA chondrocytes to reduce apoptosis, inflammation and matrix degradation, while triggered phosphoinositide-3-kinase/akt (PI3K/Akt), extracellular signal-regulated kinase (ERK), p38 and JNK pathways in healthy chondrocytes to promote matrix synthesis.

CONCLUSION

The included studies suggest that ultrasound application induces therapeutic effects on chondrocytes. However, these results should be interpreted with caution because high risk of performance, detection and pseudoreplication bias were identified. Future studies should explore the application of ultrasound on human OA chondrocytes cultures to potentiate the applicability of ultrasound towards cartilage regeneration of knee with OA.

A Combinational Therapy of Articular Cartilage Defects: Rapid and Effective Regeneration by Using Low-Intensity Focused Ultrasound After Adipose Tissue-Derived Stem Cell Transplantation

BACKGROUND

Although low-intensity pulsed ultrasound has been reported to be potential cartilage regeneration, there still unresolved treatment due to cartilage fibrosis and degeneration by a lack of rapid and high-efficiency treatment. The purpose of this study was to investigate the effect of a combination therapy of focused acoustic force and stem cells at site for fast and efficient healing on cartilage regeneration.

METHODS

Using a rat articular cartilage defects model, one million adipose tissue-derived stem cells (ASCs) were injected into the defect site, and low-intensity focused ultrasound (LOFUS) in the range of 100-600 mV was used for 20 min/day for 2 weeks. All experimental groups were sacrificed after 4 weeks in total. The gross appearance score and hematoxylin and eosin (H&E), Alcian blue, and Safranin O staining were used for measuring the chondrogenic potential. The cartilage characteristics were observed, and type II collagen, Sox 9, aggrecan, and type X collagen were stained with immunofluorescence. The results of the comprehensive analysis were calculated using the Mankin scoring method.

RESULTS

The gross appearance scores of regenerated cartilage and chondrocyte-like cells in H&E images were higher in LOFUS-treated groups compared to those in negative control or ASC-treated groups. Safranin O and Alcian blue staining demonstrated that the 100 and 300 mV LOFUS groups showed greater synthesis of glycosaminoglycan and proteoglycan. The ASC + LOFUS 300 mV group showed positive regulation of type II collagen, Sox 9 and aggrecan and negative regulation of type X collagen, which indicated the occurrence of cartilage regeneration based on the Mankin score result.

CONCLUSION

The combination therapy, which involved treatment with ASC and 300 mV LOFUS, quickly and effectively reduced articular cartilage defects.

Low-Intensity Pulsed Ultrasound Alleviates Hypoxia-Induced Chondrocyte Damage in Temporomandibular Disorders by Modulating the Hypoxia-Inducible Factor Pathway

Temporomandibular disorders are a common cause of chronic pain in the orofacial region and have a complex and multi-factorial pathophysiology. Mechanical loading or inflammatory conditions have been shown to decrease oxygen tension within the joint cartilage and activate the hypoxia-inducible factor (HIF) pathway, which in turn aggravates the pathological processes underlying temporomandibular joint (TMJ) disorders. We previously showed that low-intensity pulsed ultrasound (LIPUS) treatment effectively repairs TMJ injury induced by chronic sleep deprivation (CSD). Here, we explored the effects of LIPUS treatment on hypoxia-induced chondrocyte injury. We found that it effectively restored the proliferation capacity of mandibular chondrocytes under hypoxic conditions and lowered their rate of apoptosis. Chondrogenic capacity, as assessed by type II collagen levels, and mucin-positive areas were also significantly increased after LIPUS treatment. Levels of matrix metalloprotein-3 and interleukin-6 decreased in mandibular chondrocytes following this treatment, whereas the expression of tissue inhibitor of metalloproteinase-1 increased. We also found that HIF-1α expression was upregulated in mandibular chondrocytes under hypoxic conditions and was further enhanced by LIPUS treatment. Similarly, HIF-2α levels increased in mandibular chondrocytes under hypoxic conditions but decreased following LIPUS treatment. Subsequently, we established a CSD-induced TMJ injury model and found that LIPUS increased mucin-positive areas as well as HIF-1α expression and decreased HIF-2 level in the chondrocyte layer. Together, our results indicate that the protective effect of LIPUS on chondrocyte is partly associated with the HIF pathway.

Degenerate intervertebral disc-like pH induces a catabolic mechanoresponse in human nucleus pulposus cells

Mechanical stimulation is known to influence intervertebral disc (IVD) cell behavior and function, but the effect on disc cells is routinely considered in isolation from other microenvironmental factors. Acidic pH has been shown to be a prominent and detrimental microenvironmental factor present in degenerate IVDs, but its influence on the human disc cell mechanoresponse has never been studied. We investigated the response of agarose-encapsulated human nucleus pulposus (NP) cells to 0.004 MPa, 1.0 Hz and 1 hour of compression (Flexcell FX4000 Compression System) under pH conditions representative of nondegenerate (pH 7.1) and degenerate (pH 6.5) IVDs. Cell viability, extracellular matrix production, and expression of anabolic/anti-catabolic and catabolic genes were assessed. We report that preculture of NP cells in agarose gels was required in order for cells to be mechanoresponsive, and this correlated with increased type VI collagen, α5β1 integrin, and fibronectin expression. Furthermore, the matrix homeostatic response observed at pH 7.1 (representative of nondegenerate IVDs; increased aggrecan [AGC], tissue inhibitor of metalloproteinases-1 [TIMP1], matrix metalloproteinase-3 [MMP3], a disintegrin and metalloproteinase with thrombospondin motif-5 [ADAMTS5] gene expression) was RGD-integrin dependent, whereas only MMP3 remained mechanoresponsive at pH 6.5, and this was independent of RGD-integrins. Our findings suggest differential mechanotransduction pathways operating for specific genes, with RGD-integrin dependent AGC expression, but not RGD-independent MMP3 expression, inhibited at pH representative of degenerate IVDs (pH 6.5), which could contribute to the catabolic phenotype observed during IVD degeneration.

CLINICAL SIGNIFICANCE

Characterizing the influence of the mechanical and chemical intervertebral disc microenvironment on disc cells, particularly in disc degeneration, could help develop future therapeutic strategies for the treatment of discogenic back pain.

TGF-β1-induced chondrogenesis of bone marrow mesenchymal stem cells is promoted by low-intensity pulsed ultrasound through the integrin-mTOR signaling pathway

Background

Low-intensity pulsed ultrasound (LIPUS) is a mechanical stimulus that plays a key role in regulating the differentiation of bone marrow mesenchymal stem cells (BMSCs). However, the way in which it affects the chondrogenic differentiation of BMSCs remains unknown. In this study, we aimed to investigate whether LIPUS is able to influence TGF-β1-induced chondrogenesis of BMSCs through the integrin-mechanistic target of the Rapamycin (mTOR) signaling pathway.

Methods

BMSCs were isolated from rat bone marrow and cultured in either standard or TGF-β1-treated culture medium. BMSCs were then subjected to LIPUS at a frequency of 3 MHz and a duty cycle of 20%, and integrin and mTOR inhibitors added in order to analyze their influence on cell differentiation. BMSCs were phenotypically analyzed by flow cytometry and the degree of chondrogenesis evaluated through toluidine blue staining, immunofluorescence, and immunocytochemistry. Furthermore, expression of COL2, aggrecan, SOX9, and COL1 was assessed by qRT-PCR and western blot analysis.

Results

We found that LIPUS promoted TGF-β1-induced chondrogenesis of BMSCs, represented by increased expression of COL2, aggrecan and SOX9 genes, and decreased expression of COL1. Notably, these effects were prevented following addition of integrin and mTOR inhibitors.

Conclusions

Taken together, these results indicate that mechanical stimulation combined with LIPUS promotes TGF-β1-induced chondrogenesis of BMSCs through the integrin-mTOR signaling pathway.

Comparative assessment of intrinsic mechanical stimuli on knee cartilage and compressed agarose constructs

A well-established cue for improving the properties of tissue-engineered cartilage is mechanical stimulation. However, the explicit ranges of mechanical stimuli that correspond to favorable metabolic outcomes are elusive. Usually, these outcomes have only been associated with the applied strain and frequency, an oversimplification that can hide the fundamental relationship between the intrinsic mechanical stimuli and the metabolic outcomes. This highlights two important key issues: the firstly is related to the evaluation of the intrinsic mechanical stimuli of native cartilage; the second, assuming that the intrinsic mechanical stimuli will be important, deals with the ability to replicate them on the tissue-engineered constructs. This study quantifies and compares the volume of cartilage and agarose subjected to a given magnitude range of each intrinsic mechanical stimulus, through a numerical simulation of a patient-specific knee model coupled with experimental data of contact during the stance phase of gait, and agarose constructs under direct-dynamic compression. The results suggest that direct compression loading needs to be parameterized with time-dependence during the initial culture period in order to better reproduce each one of the intrinsic mechanical stimuli developed in the patient-specific cartilage. A loading regime which combines time periods of low compressive strain (5%) and frequency (0.5Hz), in order to approach the maximal principal strain and fluid velocity stimulus of the patient-specific cartilage, with time periods of high compressive strain (20%) and frequency (3Hz), in order to approach the pore pressure values, may be advantageous relatively to a single loading regime throughout the full culture period.

Clinical applications of low-intensity pulsed ultrasound and its potential role in urology

Low-intensity pulsed ultrasound (LIPUS) is a form of ultrasound that delivered at a much lower intensity (<3 W/cm²) than traditional ultrasound energy and output in the mode of pulse wave, and it is typically used for therapeutic purpose in rehabilitation medicine. LIPUS has minimal thermal effects due to its low intensity and pulsed output mode, and its non-thermal effects which is normally claimed to induce therapeutic changes in tissues attract most researchers’ attentions. LIPUS have been demonstrated to have a rage of biological effects on tissues, including promoting bone-fracture healing, accelerating soft-tissue regeneration, inhibiting inflammatory responses and so on. Recent studies showed that biological effects of LIPUS in healing morbid body tissues may be mainly associated with the upregulation of cell proliferation through activation of integrin receptors and Rho/ROCK/Src/ERK signaling pathway, and with promoting multilineage differentiation of mesenchyme stem/progenitor cell lines through ROCK-Cot/Tpl2-MEK-ERK signaling pathway. Hopefully, LIPUS may become an effective clinical procedure for the treatment of urological diseases, such as chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), erectile dysfunction (ED), and stress urinary incontinence (SUI) in the field of urology. It still needs an intense effort for basic-science and clinical investigators to explore the biomedical applications of ultrasound.

Low Intensity Pulsed Ultrasound Promotes the Extracellular Matrix Synthesis of Degenerative Human Nucleus Pulposus Cells Through FAK/PI3K/Akt Pathway

STUDY DESIGN

In vitro experimental study.

OBJECTIVE

To investigate the effect of low-intensity pulsed ultrasound (LIPUS) on the extracellular matrix (ECM) synthesis of degenerative human nucleus pulposus cells and explore the molecular mechanism.

SUMMARY OF BACKGROUND DATA

LIPUS has been used successfully for bone fracture healing and been proved to be effective in stimulating ECM metabolism in animal intervertebral disc cells. However, whether LIPUS also exerts an anabolic effect on degenerative human nucleus pulposus cells and the possible molecular mechanism is still unclear.

METHODS

The degenerative human nucleus pulposus cells were cultured in calcium alginate beads. In the LIPUS group, cells were exposed to an average temporal intensity of 30  mW/cm2 and a frequency of 1.5  MHz of LIPUS 20 minutes daily for 1 week. The control group was cultured in the same way but without LIPUS stimulation. The LY294002 group was stimulated by LIPUS and treated with LY294002 simultaneously. The expression of aggrecan, collagen-II, Sox9, tissue inhibitor of metalloproteinase-,1 and matrix metalloproteinase-3 were evaluated by Enzyme-Linked Immunosorbent Assay, Western blot or RT-PCR. Expression of signaling proteins involved in FAK/PI3K/Akt pathway was studied by Western blot analysis.

RESULTS

LIPUS significantly upregulated expression of aggrecan, collagen-II, Sox9, and tissue inhibitor of metalloproteinase-1 compared with control group, but inhibited secretion of matrix metalloproteinase-3. The study further demonstrated that the upregulation of aggrecan, collagen-II, and Sox9 was related to the activation of focal adhesion kinase (FAK)//PI3K/Akt pathway caused by LIPUS. Moreover, inhibition of PI3K/Akt significantly suppressed the special biological effect activated by LIPUS.

CONCLUSION

LIPUS promotes the ECM synthesis of degenerative human nucleus pulposus cells through activation of FAK/PI3K/Akt pathway.

LEVEL OF EVIDENCE

N/A.

Pulsed low-intensity ultrasound increases proliferation and extracelluar matrix production by human dermal fibroblasts in three-dimensional culture

This study evaluated the effect of pulsed low-intensity ultrasound on cell proliferation, collagen production and glycosaminoglycan deposition by human dermal fibroblasts encapsulated in alginate. Hoechst 33258 assay for cell number, hydroxyproline assay for collagen content, dimethylmethylene blue assay for glycosaminoglycan content and scanning electron microscopy were performed on the encapsulated cells treated with pulsed low-intensity ultrasound and a control group that remained untreated. Pulsed low-intensity ultrasound showed a significant effect on cell proliferation and collagen deposition but no consistent pattern for glycosaminoglycan content. Alcian blue staining showed that glycosaminoglycans were deposited around the cells in both treated and control groups. These results suggest that pulsed low-intensity ultrasound alone shows a positive effect on cell proliferation and collagen deposition even without growth factor supplements.

Effect of low-intensity pulsed ultrasound on posterolateral lumbar fusion of rabbit

OBJECTIVE

To observe the effect of low-intensity pulsed ultrasound in the posterolateral lumbar fusion of rabbit.

METHODS

A total of 48 New Zealand white rabbits were randomly divided into the observation group and control group, including the autogenous iliac observation group, artificial bone observation group, artificial bone control group and autogenous iliac control group according to the different bone grafting. The posterolateral lumbar fusion of rabbits in each group was analyzed and compared.

RESULTS

After 4 weeks of treatment using the low-intensity pulsed ultrasound, the fusion in the bone grafting area of observation group was good. There was the relatively dense fusion area between the right transverse process and artificial bone. The left transverse process had been completely fused, with the clear bone trabecula through the fusion area. There was no significant fusion sign in the control group. According to the fusion comparison between two groups, the fusion rate of the observation group was 83.3% and it was significantly higher than the one of the control group (37.5%). Results of the comparison were statistically significant (P<0.05). The number of chondrocytes and the increase in the relative gray-scale in the fusion area of the iliac observation group were significantly higher than ones of the iliac control group (P<0.05). The number of chondrocytes and the increase in the relative gray-scale in the fusion area of the artificial bone observation group were significantly higher than ones of the artificial bone control group (P<0.05). The expression of IL-1, IL-6 and IL-17 4 weeks after the treatment of the observation group was significantly lower than the one of the control group, with the statistical significance (P<0.05). It indicated that the treatment of low-intensity pulsed ultrasound could reduce the expression level of inflammatory factors.

CONCLUSIONS

The low-intensity pulsed ultrasound can significantly increase the bone grafting fusion rate of the rabbit's posterolateral lumbar fusion. The possible mechanism is that it promotes the lumbar posterolateral endochondral ossification and reduces the inflammatory reaction.

Dependence of light attenuation and backscattering on collagen concentration and chondrocyte density in agarose scaffolds

Optical coherence tomography (OCT) has been applied for high resolution imaging of articular cartilage. However, the contribution of individual structural elements of cartilage on OCT signal has not been thoroughly studied. We hypothesize that both collagen and chondrocytes, essential structural components of cartilage, act as important light scatterers and that variation in their concentrations can be detected by OCT through changes in backscattering and attenuation. To evaluate this hypothesis, we established a controlled model system using agarose scaffolds embedded with variable collagen concentrations and chondrocyte densities. Using OCT, we measured the backscattering coefficient (µb) and total attenuation coefficient (µt) in these scaffolds. Along our hypothesis, light backscattering and attenuation in agarose were dependent on collagen concentration and chondrocyte density. Significant correlations were found between µt and chondrocyte density (ρ = 0.853, p < 0.001) and between µt and collagen concentration (ρ = 0.694, p < 0.001). µb correlated significantly with chondrocyte density (ρ = 0.504, p < 0.001) but not with collagen concentration (ρ = 0.103, p = 0.422) of the scaffold. Thus, quantitation of light backscattering and, especially, attenuation could be valuable when evaluating the integrity of soft tissues, such as articular cartilage with OCT.

Candidate mediators of chondrocyte mechanotransduction via targeted and untargeted metabolomic measurements

Chondrocyte mechanotransduction is the process by which cartilage cells transduce mechanical loads into biochemical and biological signals. Previous studies have identified several pathways by which chondrocytes transduce mechanical loads, yet a general understanding of which signals are activated and in what order remains elusive. This study was performed to identify candidate mediators of chondrocyte mechanotransduction using SW1353 chondrocytes embedded in physiologically stiff agarose. Dynamic compression was applied to cell-seeded constructs for 0-30min, followed immediately by whole-cell metabolite extraction. Metabolites were detected via LC-MS, and compounds of interest were identified via database searches. We found several metabolites which were statistically different between the experimental groups, and we report the detection of 5 molecules which are not found in metabolite databases of known compounds indicating potential novel molecules. Targeted studies to quantify the response of central energy metabolites to compression found a transient increase in the ratio of NADP+ to NADPH and a continual decrease in the ratio of GDP to GTP, suggesting a flux of energy into the TCA cycle. These data are consistent with the remodeling of cytoskeletal components by mechanically induced signaling, and add substantial new data to a complex picture of how chondrocytes transduce mechanical loads.

The mechanical microenvironment of high concentration agarose for applying deformation to primary chondrocytes

Cartilage and chondrocytes experience loading that causes alterations in chondrocyte biological activity. In vivo chondrocytes are surrounded by a pericellular matrix with a stiffness of ~25-200kPa. Understanding the mechanical loading environment of the chondrocyte is of substantial interest for understanding chondrocyte mechanotransduction. The first objective of this study was to analyze the spatial variability of applied mechanical deformations in physiologically stiff agarose on cellular and sub-cellular length scales. Fluorescent microspheres were embedded in physiologically stiff agarose hydrogels. Microsphere positions were measured via confocal microscopy and used to calculate displacement and strain fields as a function of spatial position. The second objective was to assess the feasibility of encapsulating primary human chondrocytes in physiologically stiff agarose. The third objective was to determine if primary human chondrocytes could deform in high-stiffness agarose gels. Primary human chondrocyte viability was assessed using live-dead imaging following 24 and 72h in tissue culture. Chondrocyte shape was measured before and after application of 10% compression. These data indicate that (1) displacement and strain precision are ~1% and 6.5% respectively, (2) high-stiffness agarose gels can maintain primary human chondrocyte viability of >95%, and (3) compression of chondrocytes in 4.5% agarose can induce shape changes indicative of cellular compression. Overall, these results demonstrate the feasibility of using high-concentration agarose for applying in vitro compression to chondrocytes as a model for understanding how chondrocytes respond to in vivo loading.

Low-intensity pulsed ultrasound inhibits messenger RNA expression of matrix metalloproteinase-13 induced by interleukin-1β in chondrocytes in an intensity-dependent manner

The effect of low-intensity pulsed ultrasound (LIPUS) on articular cartilage metabolism has been characterized. However, the effect of LIPUS intensity on articular cartilage degradation factors remains unknown. This study aimed to investigate the immediate effect of LIPUS at several intensities on cultured chondrocytes treated with interleukin-1β (IL-1β) to induce an inflammatory response and on articular cartilage explants. Cultured chondrocytes and articular cartilage explants were treated by LIPUS at intensities of 0, 7.5, 30 and 120 mW/cm(2) or 0, 27 and 67 mW/cm(2), respectively. mRNA analysis revealed that LIPUS inhibited induction of MMP13 mRNA expression by 100 pg/mL IL-1β in cultured chondrocytes in an intensity-dependent manner. LIPUS also inhibited MMP13 and MMP1 mRNA expression in articular cartilage explants. Our results indicate that LIPUS may potentially protect articular cartilage by inhibiting MMP mRNA expression in an intensity-dependent manner and should thus be considered a useful candidate for daily treatment of OA.

Pulsed-low intensity ultrasound enhances extracellular matrix production by fibroblasts encapsulated in alginate

In this study, the effect of pulsed-low intensity ultrasound on cell proliferation, collagen production and glycosaminoglycan deposition by 3T3 fibroblasts encapsulated in alginate was evaluated. Hoechst 33258 assay for cell number, hydroxyproline assay for collagen content and dimethylamine blue assay for glycosaminoglycan content were performed on samples from cell cultures treated with pulsed-low intensity ultrasound and a control group. Pulsed-low intensity ultrasound shows no effect on cell proliferation, while collagen and glycosaminoglycan contents were consistently higher in the samples treated with pulsed-low intensity ultrasound, showing a statistically significant difference (p < 0.05) on day 10. Alcian blue staining showed that glycosaminoglycans were deposited around the cells in both groups. These results suggest that pulsed-low intensity ultrasound shows no effect on cell proliferation but has potential for inducing collagen and glycosaminoglycan production in cells cultured in alginate gels.

Study of factors affecting the magnitude and nature of ultrasound exposure with in vitro set-ups

Therapeutic ultrasound is a clinically applied method to improve fracture healing and holds great potential as a manipulator of biologic material relevant to tissue engineering approaches. Unfortunately, the cell stimulating property of ultrasound is not known, which inhibits the optimal use of this technique. Additionally, many in vitro studies in this field use ultrasound configurations that are vulnerable to errors during calibration and use. These errors arise from the structural simplicity and incomplete characterization of these configurations. In this study, pulse-echo ultrasound, laser Doppler vibrometry and Schlieren imaging were applied to noninvasively characterize common in vitro experimental configurations. Fine wire thermocouple measurements were conducted to characterize any possible temperature rise during the ultrasound exposures. The results quantified the frequency dependent sound transmission through culture wells and the standing wave effect within the cell volume. These effects can cause uncertainty of up to 700% in the actual ultrasound exposure experienced by the cell. A temperature rise of 2.7°C was measured from an ultrasound configuration commonly used in vitro ultrasound studies. Furthermore, wave mode conversion in culture wells was observed, emphasizing the complexity of these sonications. Similar type Lamb waves have been observed in bone in vivo. Thus, Lamb waves may be a mechanism for stimulating the cells.