Suzanne Ferreri

Mitigation of Bone Loss with Ultrasound Induced Dynamic Mechanical Signals in an OVX Induced Rat Model of Osteopenia

This study tests the hypothesis that an ultrasound generated dynamic mechanical signal can attenuate bone loss in an estrogen deficient model of osteopenia. Eighty-four 16-week-old Sprague-Dawley rats were divided into six groups: baseline control, age-matched control, ovariectomy (OVX) control, OVX+5mW/cm(2) ultrasound (US), OVX+30mW/cm(2) US and OVX+100mW/cm(2) US. Low intensity pulsed ultrasound (LIPUS) was delivered transdermally at the L4/L5 vertebrae, using gel-coupled plane wave US transducers. The signal, characterized by 200μs pulses of 1.5MHz sine waves repeating at 1kHz with spatial-averaged temporal-averaged (SATA) intensities of 5, 30 or 100mW/cm(2), was applied 20 min/day, 5 days/week for 4 weeks. OVX treatment reduced bone volume fraction 40% and compromised microstructure at 4 weeks. LIPUS treatment, however, significantly increased BV/TV (+33%) compared to OVX controls for the 100mW/cm(2) treated group. SMI and Tb.N showed significant improvements compared with OVX for the 100mW/cm(2) treated group and Tb.Th was significantly improved in the 30 and 100mW/cm(2) treated groups. Improvements in bones microstructural characteristics with 100mW/cm(2) US treatment translated into improved load bearing characteristics, including a significant 42% increase in apparent level elastic modulus compared to OVX controls. Significant improvement of trabecular mechanical strength was also observed in the treated animals, e.g., principal compressive stress (represent bones ability to resist loads) was significantly higher compared to OVX controls. Histomorphometric analysis also showed that treatment with 100mW/cm(2) US resulted in a 76% improvement in MS/BS. In addition, measures of bone quantity and quality at the femoral metaphysis suggest that LIPUS is site specific. This study indicates that localized ultrasound treatment, delivered at specific intensities, has beneficial effects on intact bone and may represent a novel intervention for bone loss.

Determination of bone's mechanical matrix properties by nanoindentation.

Osteoporosis is a devastating disease that is characterized not only by a reduction in bone quantity but also by deterioration in bone quality. The quality of bone tissue is greatly influenced by its mechanical properties and, therefore, investigations into the etiology and enhanced detection of osteoporosis, or the efficacy of interventions, may require the assessment of bones mechanical properties at the level of the tissue. Nanoindentation is a relatively new technique that is capable of evaluating bones quasi-static and dynamic mechanical properties on extremely small volumes of tissue. These data can be used directly to describe the pre-yield properties of the matrix, but can also be combined with imaging techniques and mechanical models to extrapolate the mechanical properties from the level of the tissue to that of the organ.

Dynamic hydraulic fluid stimulation regulated intramedullary pressure.

Physical signals within the bone, i.e. generated from mechanical loading, have the potential to initiate skeletal adaptation. Strong evidence has pointed to bone fluid flow (BFF) as a media between an external load and the bone cells, in which altered velocity and pressure can ultimately initiate the mechanotransduction and the remodeling process within the bone. Load-induced BFF can be altered by factors such as intramedullary pressure (ImP) and/or bone matrix strain, mediating bone adaptation. Previous studies have shown that BFF induced by ImP alone, with minimum bone strain, can initiate bone remodeling. However, identifying induced ImP dynamics and bone strain factor in vivo using a non-invasive method still remains challenging. To apply ImP as a means for alteration of BFF, it was hypothesized that non-invasive dynamic hydraulic stimulation (DHS) can induce local ImP with minimal bone strain to potentially elicit osteogenic adaptive responses via bone-muscle coupling. The goal of this study was to evaluate the immediate effects on local and distant ImP and strain in response to a range of loading frequencies using DHS. Simultaneous femoral and tibial ImP and bone strain values were measured in three 15-month-old female Sprague Dawley rats during DHS loading on the tibia with frequencies of 1Hz to 10Hz. DHS showed noticeable effects on ImP induction in the stimulated tibia in a nonlinear fashion in response to DHS over the range of loading frequencies, where they peaked at 2Hz. DHS at various loading frequencies generated minimal bone strain in the tibiae. Maximal bone strain measured at all loading frequencies was less than 8με. No detectable induction of ImP or bone strain was observed in the femur. This study suggested that oscillatory DHS may regulate the local fluid dynamics with minimal mechanical strain in the bone, which serves critically in bone adaptation. These results clearly implied DHSs potential as an effective, non-invasive intervention for osteopenia and osteoporosis treatments.

Interrelation between external oscillatory muscle coupling amplitude and in vivo intramedullary pressure related bone adaptation

Interstitial bone fluid flow (IBFF) is suggested as a communication medium that bridges external physical signals and internal cellular activities in the bone, which thus regulates bone remodeling. Intramedullary pressure (ImP) is one main regulatory factor of IBFF and bone adaptation related mechanotransduction. Our group has recently observed that dynamic hydraulic stimulation (DHS), as an external oscillatory muscle coupling, was able to induce local ImP with minimal bone strain as well as to mitigate disuse bone loss. The current study aimed to evaluate the dose dependent relationship between DHSs amplitude, i.e., 15 and 30mmHg, and in vivo ImP induction, as well as this correlation on bones phenotypic change. Simultaneous measurements of ImP and DHS cuff pressures were obtained from rats under DHS with various magnitudes and a constant frequency of 2Hz. ImP inductions and cuff pressures upon DHS loading showed a positively proportional response over the amplitude sweep. The relationship between ImP and DHS cuff pressure was evaluated and shown to be proportional, in which ImP was raised with increases of DHS cuff pressure amplitudes (R(2)=0.98). A 4-week in vivo experiment using a rat hindlimb suspension model demonstrated that the mitigation effect of DHS on disuse trabecular bone was highly dose dependent and related to DHSs amplitude, where a higher ImP led to a higher bone volume. This study suggested that sufficient physiological DHS is needed to generate ImP. Oscillatory DHS, potentially induces local fluid flow, has shown dose dependence in attenuation of disuse osteopenia.

Improved Prediction of Local Trabecular Strain Enhances Non-Invasive Assessment of Micro Bone Strength Using a Surface Smoothing Technique in FEA

One key issue in clinical, non-invasive assessment of bone quality and fracture risk is the accurate prediction of localized trabecular strength through the determination of peak stress values and locations. Additionally, it has been suggested that peak stress/strain concentrations may play an important role in driving the bone remodeling process. Micro-CT based voxel finite element (FE) meshes have been widely used in nondestructive evaluation of global stiffness. Subsequently, this technique has been advantageous in studies addressing changes in bone volume and microstructure.Copyright

Nanoindentation measurements of viscoelastic material properties are sensitive to preparation techniques

This study tests the hypothesis that bones tissue level elastic and viscoelastic mechanical properties are altered by dehydration and that rehydration can be used to recover changes to bones mechanical properties. When samples were exposed to short periods of dehydration(24 hours) during sample preparation trabecular bone elastic modulus increased 36%(p<0.05) and tan δ decreased 33%(p<0.05). However, following rehydration both elastic modulus and tan δ were restored such that there were no differences between rehydrated samples and fresh controls. Similar results were found in cortical bone. When samples were exposed to long periods of dehydration(30 days) in sample preparation cortical bone elastic modulus increased 28%(p<0.05) and tan δ decreased 30%(p<0.05). Following rehydration, elastic modulus increased such that there was no difference between rehydrated and fresh controls. However, while tan δ increased following rehydration(12%, p<0.05), it was significantly lower than fresh controls (21%, p<0.05). Interestingly, cortical bone exposed to long term dehydration recovered tan δ such that there were no differences between rehydrated samples and fresh controls. Viscoelastic material properties most strongly reflect the mechanical contributions of collagen; therefore, one possible explanation could be that long term dehydration alters collagen organization, potentially through cross-linking.

Therapeutic ultrasound on bone cellular and in vivo adaptation

Objective: It is well documented that ultrasound, as a mechanical signal, can produce a wide variety of biological effects in vitro and in vivo. The purpose of the current study was to (1) develop a methodology to allow for in-vitro manipulating osteoblastic cells using acoustic radiation force generated by ultrasound, (2) use this methodology to determine the morphological and biological responses of bone cells to ultrasound, and (3) mitigate bone loss under estrogen deficient osteopenia. Methods: In Vitro Cellular Manipulation: We used a therapy focused transducer, which has spherical cap with 64 mm diameter and 62.64 mm focal length. A laser guide MC3T3-E1 osteoblastic cells were cultured in α-MEM containing 1% penicillin-streptomycin and 10% decomplemented newborn calf serum. In Vivo OVX Model: 72, 16 w.o. Sprague-Dawley rats were divided into six groups; baseline control, age-matched control, OVX control, OVX + 5 mW/cm2 ultrasound (US), OVX + 30 mW/cm2 US and OVX + 100 mW/cm2 US. Low intensity pulsed...

Mechanobiologic acoustics on bone cellular and in vivo adaptation

It is well documented that ultrasound, as a mechanical signal, can produce a wide variety of biological effects in vitro and in vivo. The purpose of the current study was to evaluate acoustics on both in vivo and in vitro adaptation of bone cells and tissue. The results indicated that focused ultrasound can create local fluid flow nearby cells. In vivo results suggest that low-intensity pulse ultrasound can induced mechanical wave in tissue and initiate bone adaptation. Thus, dynamic ultrasound can inhibit bone loss and preserve bone strength under conditions of estrogen deficient osteopenia.

Local and Distant Intramedullary Pressure and Bone Strain by Dynamic Hydraulic Stimulation

Osteoporosis gives rise to fragile bones that have higher fracture risks due to diminished bone mass and altered bone microarchitecture [1]. Mechanical loading mediated bone adaptation has demonstrated promising potentials as a non-pharmacological alteration for both osteogenic response and attenuation of osteopenia [2]. Intramedullary pressure (ImP) has been proposed as a key factor for fluid flow initiation and mechanotransductive signal inductions in bone. It is also suggested that integration of strain signals over time allows low-level mechanical strain in the skeleton to trigger osteogenic activities. The potential bone fluid flow induced by strain and ImP mediates adaptive responses in the skeleton [3]. Previous in vivo studies using oscillatory electrical stimulations showed that dynamic muscle contractions can generate ImP and bone strain to mitigate disuse osteopenia in a frequency-dependent manner. To apply ImP alteration as a means for bone fluid flow regulation, it may be necessary to develop a new method that could couple external loading with internal bone fluid flow. In order to further study the direct effect of ImP on bone adaptation, it was hypothesized that external dynamic hydraulic stimulation (DHS) can generate ImP with minimal strain in a frequency-dependent manner. The aim of this study was to evaluate the immediate effects on local and distant ImP and bone strain induced by a novel, non-invasive dynamic external pressure stimulus in response to a range of loading frequencies.Copyright

Induced Intramedullary Pressure by Dynamic Hydraulic Stimulation and Its Potential in Attenuation of Bone Loss

Bone loss is a critical health problem of astronauts in long-term space missions. A growing number of evidence has pointed out bone fluid flow as a critical regulator in mechanotransductive signaling and bone adaptation. Intramedullary pressure (ImP) is a key mediator for bone fluid flow initiation and it influences the osteogenic signals within the skeleton. The potential ImP-induced bone fluid flow then triggers bone adaptation [1]. Previous in vivo study has demonstrated that ImP induced by oscillatory electrical stimulations can effectively mitigate disuse osteopenia in a frequency-dependent manner in a disuse rat model [2, 3]. In order to develop the translational potentials of ImP, a non-invasive intervention with direct fluid flow coupling is necessary to develop new treatments for microgravity-induced osteopenia/osteoporosis.© 2011 ASME