Computational and clinical investigation on the role of mechanical vibration on orthodontic tooth movement

The aim of this study is to investigate the biomechanics for orthodontic tooth movement (OTM) subjected to concurrent single-tooth vibration (50 Hz) with conventional orthodontic force application, via a clinical study and computational simulation. Thirteen patients were recruited in the clinical study, which involved distal retraction of maxillary canines with 1.5 N (150 g) force for 12 weeks. In a split mouth study, vibration and non-vibration sides were randomly assigned to each subject. Vibration of 50 Hz, of approximately 0.2 N (20 g) of magnitude, was applied on the buccal surface of maxillary canine for the vibration group. A mode-based steady-state dynamic finite element analysis (FEA) was conducted based on an anatomically detailed model, complying with the clinical protocol. Both the amounts of space closure and canine distalization of the vibration group were significantly higher than those of the control group, as measured intra-orally or on models (p < 0.05). Therefore it is indicated that a 50 Hz and 20 g single-tooth vibration can accelerate maxillary canine retraction. The volume-average hydrostatic stress (VHS) in the periodontal ligament (PDL) was computationally calculated to be higher with vibration compared with the control group for maxillary teeth and for both linguo-buccal and mesial-distal directions. An increase in vibratory frequency further amplified the PDL response before reaching a local natural frequency. An amplification of PDL response was also shown to be induced by vibration based on computational simulation. The vibration-enhanced OTM can be described by mild, vigorous and diminishing zones among which the mild zone is considered to be clinically beneficial.     

Atomistic simulation of nanomechanical properties of Alzheimer’s Aβ(1–40) amyloid fibrils under compressive and tensile loading

In addition to being associated with severe degenerative diseases, amyloids show exceptional mechanical properties including great strength, sturdiness and elasticity. However, thus far physical models that explain these properties remain elusive, and our understanding of molecular deformation and failure mechanisms of individual amyloid fibrils is limited. Here we report a series of molecular dynamics simulations, carried out to analyze the mechanical response of two-fold symmetric Aβ(1–40) amyloid fibrils, twisted protein nanofilaments consisting of a H-bonded layered structure. We find a correlation of the mechanical behavior with chemical and nanostructural rearrangements of the fibril during compressive and tensile deformation, showing that the density of H-bonds varies linearly with the measured strain. Further, we find that both compressive and tensile deformation is coupled with torsional deformation, which is manifested in a strong variation of the interlayer twist angle that is found to be proportional to both the applied stress and measured strain. In both compression and tension we observe an increase of the Young's modulus from 2.34 GPa (for less than 0.1% strain in compression and 0.2% strain in tension), to 12.43 GPa for compression and 18.05 GPa for tension. The moduli at larger deformation are in good agreement with experimental data, where values in the range of 10–20 GPa have been reported. Our studies confirm that amyloids feature a very high stiffness, and elucidate the importance of the chemical and structural rearrangements of the fibrils during deformation.     

The region-dependent biphasic viscoelastic properties of human temporomandibular joint discs under confined compression

The objective of this study was to determine the biphasic viscoelastic properties of human temporomandibular joint (TMJ) discs, correlate these properties with disc biochemical composition, and examine the relationship between these properties and disc dynamic behavior in confined compression. The equilibrium aggregate modulus (H_A), hydraulic permeability (k), and dynamic modulus were examined between five disc regions. Biochemical assays were conducted to quantify the amount of water, collagen, and glycosaminoglycan (GAG) content in each region. The creep tests showed that the average equilibrium moduli of the intermediate, lateral, and medial regions were significantly higher than for the anterior and posterior regions (69.75±11.47 kPa compared to 22.0±5.15 kPa). Permeability showed the inverse trend with the largest values in the anterior and posterior regions (8.51±1.36×10^?15 m⁴/Ns compared with 3.75±0.72×10^?15 m⁴/Ns). Discs were 74.5% water by wet weight, 62% collagen, and 3.2% GAG by dry weight. Regional variations were only observed for water content which likely results in the regional variation in biphasic mechanical properties. The dynamic modulus of samples during confined compression is related to the aggregate modulus and hydraulic permeability of the tissue. The anterior and posterior regions displayed lower complex moduli over all frequencies (0.01–3 Hz) with average moduli of 171.8–609.3 kPa compared with 454.6–1613.0 kPa for the 3 central regions. The region of the TMJ disc with higher aggregate modulus and lower permeability had higher dynamic modulus. Our results suggested that fluid pressurization plays a significant role in the load support of the TMJ disc under dynamic loading conditions.     

Oscillatory fluid flow induces the osteogenic lineage commitment of mesenchymal stem cells: The effect of shear stress magnitude,frequency, and duration

A potent regulator of bone anabolism is physical loading. However, it is currently unclear whether physical stimuli such as fluid shear within the marrow cavity is sufficient to directly drive the osteogenic lineage commitment of resident mesenchymal stem cells (MSC). Therefore, the objective of the study is to employ a systematic analysis of oscillatory fluid flow (OFF) parameters predicted to occur in vivo on early MSC osteogenic responses and late stage lineage commitment. MSCs were exposed to OFF of 1 Pa, 2 Pa and 5 Pa magnitudes at frequencies of 0.5 Hz, 1 Hz and 2 Hz for 1 h, 2 h and 4 h of stimulation. Our findings demonstrate that OFF elicits a positive osteogenic response in MSCs in a shear stress magnitude, frequency, and duration dependent manner that is gene specific. Based on the mRNA expression of osteogenic markers Cox2, Runx2 and Opn after short-term fluid flow stimulation, we identified that a regime of 2 Pa shear magnitude and 2 Hz frequency induces the most robust and reliable upregulation in osteogenic gene expression. Furthermore, long-term mechanical stimulation utilising this regime, elicits a significant increase in collagen and mineral deposition when compared to static control demonstrating that mechanical stimuli predicted within the marrow is sufficient to directly drive osteogenesis.     

Dynamic mechanical properties of the tissue-engineered matrix associated with individual chondrocytes

The success of cell-based tissue engineering approaches in restoring biological function will be facilitated by a comprehensive fundamental knowledge of the temporal evolution of the structure and properties of the newly synthesized matrix. Here, we quantify the dynamic oscillatory mechanical behavior of the engineered matrix associated with individual chondrocytes cultured in vitro for up to 28 days in alginate scaffolds. The magnitude of the complex modulus (|E*|) and phase shift (δ) were measured in culture medium using Atomic Force Microscopy (AFM)-based nanoindentation in response to an imposed oscillatory deformation (amplitude ～5 nm) as a function of frequency (f=1–316 Hz), probe tip geometry (2.5 μm radius sphere and 50 nm radius square pyramid), and in the absence and presence of growth factors (GF, insulin growth factor-1, IGF-1, and osteogenic protein-1, OP-1). |E*| for all conditions increased nonlinearly with frequency dependence approximately f^1/2 and ranged between ～1 and 25 kPa. This result, along with theoretical calculations of the characteristic poroelastic relaxation frequency, f_p, (～50–90 Hz) suggested that this time-dependent behavior was governed primarily by fluid flow-dependent poroelasticity, rather than flow-independent viscoelastic processes associated with the solid matrix. |E*(f)| increased, (f) decreased, and the hydraulic permeability, k, decreased with time in culture and with growth factor treatment. This trend of a more elastic-like response was thought to be associated with increased macromolecular biosynthesis, density, and a more mature matrix structure/organization.     

RGD-dependent integrins are mechanotransducers in dynamically compressed tissue-engineered cartilage constructs

Recent studies have shown that integrins act as mechanoreceptors in articular cartilage. In this study, we examined the effect of blocking RGD-dependent integrins on both ECM gene expression and ECM protein synthesis.Chondrocytes were isolated from full-depth porcine articular cartilage and seeded in 3% agarose constructs. These constructs were loaded in compression with 15% strain at 0.33 and 1 Hz for 12 h, in the presence or absence of GRGDSP, which blocks RGD-dependent integrin receptors. The levels of mRNA for aggrecan, collagen II and MMP-3 were determined by semi-quantitative PCR at several time points up to 24 h post-stimulation. DNA and sGAG content were determined at several time points up to 28 days post-stimulation.At 0.33 Hz, the mRNA levels for aggrecan and MMP-3 were increased after loading, but the mRNA levels for collagen II remained unchanged. Incubation with GRGDSP counteracted these effects. Loading at 1 Hz led to increased mRNA levels for all three molecules directly after loading and these effects were counteracted by incubation with GRGDSP. The constructs that were loaded at 0.33 Hz showed a lower amount of sGAG, compared to the unstrained control. In contrast, loading at 1 Hz caused an increase in sGAG deposition over the culture period. Blocking integrins had only a counteracting effect on the long-term biosynthetic response of constructs that were compressed at 1 Hz.The results confirmed the role of RGD-dependent integrins as mechanotransducers in the regulation of both ECM gene expression and matrix biosynthesis for chondrocytes seeded in agarose under the applied loading regime. Interestingly, this role seems to be dependent on the applied loading frequency.     

In situ deformation of growth plate chondrocytes in stress-controlled static vs dynamic compression

Longitudinal bone growth in children/adolescents occurs through endochondral ossification at growth plates and is influenced by mechanical loading, where increased compression decreases growth (i.e., Hueter-Volkmann Law). Past in vivo studies on static vs dynamic compression of growth plates indicate that factors modulating growth rate might lie at the cellular level. Here, in situ viscoelastic deformation of hypertrophic chondrocytes in growth plate explants undergoing stress-controlled static vs dynamic loading conditions was investigated. Growth plate explants from the proximal tibia of pre-pubertal rats were subjected to static vs dynamic stress-controlled mechanical tests. Stained hypertrophic chondrocytes were tracked before and after mechanical testing with a confocal microscope to derive volumetric, axial and lateral cellular strains. Axial strain in hypertrophic chondrocytes was similar for all groups, supporting the mean applied compressive stress’s correlation with bone growth rate and hypertrophic chondrocyte height in past studies. However, static conditions resulted in significantly higher lateral (p < 0.001) and volumetric cellular strains (p ≤ 0.015) than dynamic conditions, presumably due to the growth plate’s viscoelastic nature. Sustained compression in stress-controlled static loading results in continued time-dependent cellular deformation; conversely, dynamic groups have less volumetric strain because the cyclically varying stress limits time-dependent deformation. Furthermore, high frequency dynamic tests showed significantly lower volumetric strain (p = 0.002) than low frequency conditions. Mechanical loading protocols could be translated into treatments to correct or halt progression of bone deformities in children/adolescents. Mimicking physiological stress-controlled dynamic conditions may have beneficial effects at the cellular level as dynamic tests are associated with limited lateral and volumetric cellular deformation.     

Lamellar lubrication in vivo and vitro: Friction testing of hexagonal boron nitride

Phospholipid molecules (PLs) in vivo and graphite, molybdenum disulfide, tungsten disulfide and hexagonal boron nitride (h-BN) in vitro are good examples of frictionless lubricants. PLs and solid materials have the ability to form multi-bilayer or layered structures similar to lamellate solid. It has been confirmed experimentally that PLs as lamellar lubricants protect the surface of joints against wear while acting as frictionless lubricant. An experimental study has been conducted on the friction properties of h-boron nitride on porous non-full journal bearings. The porous non-full journal bearings were a mixture of 97.5 wt.% Fe and 2.5 wt.% Cu powder, and compressed to a density of 5.9 g/cm³. The porosity of non-full journal bearings were15.5 and 27.8 wt.% and were impregnated with vaseline and vaseline + 5 wt.% h-BN. Additionally, the two additives SFR NLGI #2 (or SFR 2522) grease and graphite grease were used for comparison to h-BN. The tribological tests were performed on a four-ball machine under load of 49 daN, and a friction tribotester. The above experiment strongly suggested that h-BN has the ability to lubricate under load with very low friction coefficient comparable to phospholipids. Relatively low surface energy and low adhesion between the crystallites are giving the additives low friction coefficient. The results of the experimental studies showed that h-BN as an additive in vaseline possesses friction reducing properties, and excellent anti-wear properties.     

Comparison of neoadjuvant oral chemotherapy with UFT plus Folinic acid or Capecitabine concomitant with radiotherapy on locally advanced rectal cancer

AimTo evaluate the differences in treatment response and the impact on survival with both oral agents (UFT and Capecitabine) as neoadjuvant chemotherapy administered concomitantly with radiotherapy.BackgroundThere are still no studies comparing the use of neoadjuvant oral chemotherapy either with UFT plus Folinic acid or Capecitabine concomitant with radiotherapy in locally advanced rectal cancer (LARC).Materials and methodsA set of 112 patients with LARC were treated preoperatively. GROUP 1 – 61 patients underwent concomitant oral chemotherapy with Capecitabine (825 mg/m² twice daily). GROUP 2 – 51 patients submitted to concomitant oral chemotherapy with UFT (300 mg/m²/d) + Folinic acid (90 mg/d) and radiotherapy. 57.1% of patients were submitted to adjuvant chemotherapy.ResultsGROUP 1: acute toxicity – 80.3%; pathological complete response (pCR) – 10.5%; tumor downstaging (TD) – 49.1%; nodal downstaging (ND) – 76.5%; loco-regional response (LRR) – 71.9%; toxicity to adjuvant chemotherapy – 75%. GROUP 2: acute toxicity – 80.4%; pCR – 28%; TD – 62%; ND – 75.6%; LRR – 78%; toxicity to adjuvant chemotherapy – 56%. There was no difference in survival nor loco-regional control between the groups.ConclusionsPatients treated with neoadjuvant oral UFT + Folinic acid had a higher rate of pathologic complete response than patients treated with Capecitabine concomitant with radiotherapy. There were no differences in downstaging, LRR, toxicity, survival or loco-regional control between both groups. There was a trend to a higher rate of toxicity to adjuvant chemotherapy in the Capecitabine group.     

In vitro bone growth responds to local mechanical strain in three-dimensional polymer scaffolds

Mechanical stimulation plays a key role in healing and remodelling of bone tissue in vivo, and is used in bone tissue regeneration strategies in vitro. Although macroscopic compression of three-dimensional (3-D) seeded constructs can increase bone formation, it is not yet reported how this response is related to differences in local mechanical strains inside the scaffolds. In this study, we experimentally test the hypothesis that differences in local average of heterogeneous strains in a polymer scaffold will correlate with induced differences in the local biological response.Twenty-four poly(l-lactic acid) porous scaffolds seeded with rat bone cells were cultured first for 2 and 3 weeks under static conditions, respectively. Then for 1 week, half of the scaffolds were cyclically compressed (1.5%, 1 Hz), 1 h daily, with continuous perfusion (0.1 ml/min). The remaining half was kept under static conditions. The pore-surface strains in the scaffolds at the start of culture were calculated with micro-finite element modelling based on micro-Computed Tomography (μCT) images. The locations of mineralized nodules were determined from μCT images and coupled to the calculated strains.Detectable mineralized nodules (>10³ μm³) were only present in the loaded samples. Averages of absolute principal strains at the start of culture were significantly higher at nodule sites than at sites without a nodule.The results support the hypothesis that regenerating bone tissue in a 3-D porous scaffold responds to local mechanical strain. The methodology presented in this study can contribute design optimisation of tissue regeneration strategies relying on mechanical stimulation.     

Tibial nerve somatosensory evoked response detection using uni and multivariate coherence

This work aims at comparing the capability of two Objective Response Detection techniques, the Magnitude-Squared Coherence (MSC or Ordinary Coherence) and its multivariate extension, the Multiple Coherence (MC), of detecting the somatosensory evoked response. Electroencephalographic (EEG) signals were collected during somatosensory stimulation from forty adult volunteers without history of neurological disease and with normal somatosensory evoked potential (SEP), using the 10-20 International System. All leads were referenced to the earlobe average. Current pulses with 200 μs of duration were applied to the right posterior tibial nerve at the motor threshold intensity level (the lowest intensity able to produce hallux oscillations) at the rate of 5 Hz. The MSC was applied to the derivations [Cz], [Fz], [C3] and [C4] – commonly used for tibial nerve SEP recordings with bipolar derivations – and the MC was applied to the pairs [Cz][Fz] and [C3][C4]. Both estimates (MC and MSC) were calculated with M = 100 and 500 epochs and the response detection was based on rejecting the null hypothesis of response absence, which is achieved when the estimates exceed the critical value (detection threshold) calculated for a given significance level (α = 0.05). The results showed that if two leads are available, the application of the MC is better than the MSC applied to each lead individually.     

Behaviour and welfare of veal calves fed different amounts of solid feed supplemented to a milk replacer ration adjusted for similar growth

Veal calves in Europe are typically fed large quantities of milk replacer and small amounts of solid feed, a diet known to lead to the development of abnormal oral behaviours in these animals. These abnormal oral behaviours are thought to be an indication of frustration, chronic stress, and hence poor welfare. The present study investigated how different feeding strategies, differing in solid feed and milk replacer provision, affected the behaviour and welfare of veal calves across time. Four treatment groups (A–D) comprising of 12 Holstein–Friesian bull calves each (7.6 ± 0.1 weeks old and 54.7 ± 0.3 kg at arrival), penned in groups of three, were fed one of four amounts of a solid feed mixture, i.e. 50% concentrates, 25% fresh maize silage, and 25% wheat straw (on dry matter [DM] basis): A = 0, B = 9, C = 18, and D = 27 g DM/kg^0.75/d. Provision of milk replacer was adjusted to achieve similar average daily gain across treatments. Behaviour was recorded around feeding (10 min continuous focal observations of individual calves) and throughout the day (7 sessions of 30 min scan sampling at 5 min interval every 2 h from 06:30 h) every week for four months. In an attempt to find an easy practical method to measure behavioural response to feeding strategy, two 3-min behavioural tests were carried out: (1) in months 1 and 3, calves were presented with a ball and latency to make oral contact with it was recorded; and (2) in month 1, calves were presented with an overall and time spent orally manipulating (i.e. chewing or licking) it was recorded using scan sampling every 10 s. Calves in treatment D displayed less abnormal oral behaviours around feeding, less tongue playing throughout the day, and more chewing in the first two months, compared to treatment A. Treatment B only led to lower tongue playing levels compared to A and treatment C had no benefit in terms of reducing abnormal oral behaviours. Although a solid feed dose–response was expected on the display of abnormal behaviours in veal calves, treatment C did not fit within this expectation. These findings point to a more complex relationship between solid feed and abnormal oral behaviour frequency in veal calves. The two behavioural tests distinguished the different treatments as expected, and thus showed a solid feed dose–response. Because of an increase in chewing and ruminating efficiency over time, amounts of solid feed should be increased with age to maintain high levels of chewing and ruminating. Moreover, high levels of chewing and ruminating may have to be maintained long enough at the beginning of the fattening period to lead to a reduction in abnormal oral behaviours.     

Ciliogenesis in cryopreserved mammalian tracheal epithelial cells cultured at the air–liquid interface

To determine air–liquid interface (ALI) culture derived from cryopreserved mammalian tracheal ciliated cells is a viable ciliated cell model for the investigations of regulatory mechanisms of ciliary beat frequency (CBF), two studies were performed using ovine and porcine tracheae obtained from local slaughterhouses. The protease-digested tracheal ciliated cells were harvested and cultured at the ALI using collagen-coated, porous membrane inserts. In study 1, the ALI culturing protocols were established using non-cryopreserved ovine tracheal ciliated cells. Ciliogenesis was documented with immuno-histology and electron micrographs. Vigorous beating cilia were video-recorded. CBF was measured by laser light scattering. The functional integrity of the autonomic receptors of the ciliated cells was confirmed with the stimulatory responses of CBF using luminal methacholine and basolateral terbutaline. In study 2, porcine tracheal ciliated cells stored in liquid nitrogen for a minimum of 4 weeks were used. The cryopreserved cells were thawed and cultured using the ALI protocol established in study 1. After two months, cilia outgrowths were confirmed using video microscopy and scanning electron micrograph (SEM). The trans-epithelial resistances were 28.5 kΩ (n = 4). Luminal applications of 1 μM and 10 μM methacholine stimulated CBF from a baseline of 7.4 ± 0.2 Hz to 8.4 ± 0.8 Hz and 7.7 ± 0.4 Hz, respectively (n = 5). Basolateral applications of 1 μM and 10 μM terbutaline stimulated CBF from a baseline of 7.5 ± 0.3 Hz to 8.2 ± 0.4 Hz and 8.0 ± 0.4 Hz, respectively (n = 5). These data demonstrated that a ciliated cell bank can be established using cryopreserved ciliated cells for pulmonary drug discovery and toxicological screening.     

Real-time observation of fluid flows in tissue during stress relaxation using Raman spectroscopy

This paper outlines a technique to measure fluid levels in articular cartilage tissue during an unconfined stress relaxation test. A time series of Raman spectrum were recorded during relaxation and the changes in the specific Raman spectral bands assigned to water and protein were monitored to determine the fluid content of the tissue. After 1000 s unconfined compression the fluid content of the tissue is reduced by an average of 3.9% ± 1.7%. The reduction in fluid content during compression varies between samples but does not significantly increase with increasing strain. Further development of this technique will allow mapping of fluid distribution and flows during dynamic testing making it a powerful tool to understand the role of interstitial fluid in the functional performance of cartilage.     

A novel fluorescence-based cellular permeability assay

Vascular permeability is a pathologic process in many disease states ranging from metastatic progression of malignancies to ischemia–reperfusion injury. In order to more precisely study tissue, and more specifically cell layer permeability, our goal was to create a fluorescence-based assay which could quantify permeability without radioactivity or electrical impedance measurements. Human aortic endothelial cells were grown in monolayer culture on Costar®-Transwell® clear polyester membrane 6-well cell culture inserts. After monolayer integrity was confirmed, vascular endothelial growth factor (VEGF₁₆₅) at varying concentrations with a fixed concentration of yellow-green fluorescent 0.04 μm carboxylate-modified FluoSpheres® microspheres were placed in the luminal chamber and incubated for 24 h. When stimulated with VEGF₁₆₅ at 20, 40, 80, and 100 ng/ml, this assay system was able to detect increases in trans-layer flux of 8.2 ± 2.4%, 16.0 ± 3.7%, 41.5 ± 4.9%, and 58.6 ± 10.1% for each concentration, respectively. This represents the first fluorescence-based permeability assay with the sensitivity to detect changes in the permeability of a cell layer to fluid flux independent of protein flux; as well as being simpler and safer than previous radioactive-and impedance-based permeability assays. With the application of this in vitro assay to a variety of pathologic conditions, both the dynamics and physiology relating to cellular permeability can be more fully investigated.     

Micropipette aspiration of the Pacinian corpuscle

The Pacinian corpuscle (PC) is a cutaneous mechanoreceptor sensitive to high-frequency vibrations (20–1000 Hz). The PC is of importance due to its integral role in somatosensation and the critical need to understand PC function for haptic feedback system development. Previous theoretical and computational studies have modeled the physiological response of the PC to sustained or vibrating mechanical stimuli, but they have used estimates of the receptor’s mechanical properties, which remain largely unmeasured. In this study, we used micropipette aspiration (MPA) to determine an apparent Young’s modulus for PCs isolated from a cadaveric human hand. MPA was applied in increments of 5 mm H₂O (49 Pa), and the change in protrusion length of the PC into the pipette was recorded. The protrusion length vs. suction pressure data were used to calculate the apparent Young’s modulus. Using 10 PCs with long-axis lengths of 2.99 ± 0.41 mm and short-axis lengths of 1.45 ± 0.22 mm, we calculated a Young’s modulus of 1.40 ± 0.86 kPa. Our measurement is on the same order of magnitude as those approximated in previous models, which estimated the PC to be on the same order of magnitude as skin or isolated cells, so we recommend that a modulus in the kPa range be used in future studies.     

Dynamic loading stimulates chondrocyte biosynthesis when encapsulated in charged hydrogels prepared from poly(ethylene glycol) and chondroitin sulfate

This study aimed to elucidate the role of charge in mediating chondrocyte response to loading by employing synthetic 3D hydrogels. Specifically, neutral poly(ethylene glycol) (PEG) hydrogels were employed where negatively charged chondroitin sulfate (ChS), one of the main extracellular matrix components of cartilage, was systematically incorporated into the PEG network at 0%, 20% or 40% to control the fixed charge density. PEG hydrogels were employed as a control environment for extracellular events which occur as a result of loading, but which are not associated with a charged matrix (e.g., cell deformation and fluid flow). Freshly isolated bovine articular chondrocytes were embedded in the hydrogels and subject to dynamic mechanical stimulation (0.3 Hz, 15% amplitude strains, 6 h) and assayed for nitric oxide production, cell proliferation, proteoglycan synthesis, and collagen deposition. In the absence of loading, incorporation of charge inhibited cell proliferation by ~ 75%, proteoglycan synthesis by ~ 22–50% depending on ChS content, but had no affect on collagen deposition. Dynamic loading had no effect on cellular responses in PEG hydrogels. However, dynamically loading 20% ChS gels inhibited nitrite production by 50%, cell proliferation by 40%, but stimulated proteoglycan and collagen deposition by 162% and 565%, respectively. Dynamic loading of 40% ChS hydrogels stimulated nitrite production by 62% and proteoglycan synthesis by 123%, but inhibited cell proliferation by 54% and collagen deposition by 52%. Upon removing the load and culturing under free-swelling conditions for 36 h, the enhanced matrix synthesis observed in the 20% ChS gels was not maintained suggesting that loading is necessary to stimulate matrix production. In conclusion, extracellular events associated with a charged matrix have a dramatic affect on how chondrocytes respond to mechanical stimulation within these artificial 3D matrices suggesting that streaming potentials and/or dynamic changes in osmolarity may be important regulators of chondrocytes while cell deformation and fluid flow appear to have less of an effect.     

Intramedullary pressure and matrix strain induced by oscillatory skeletal muscle stimulation and its potential in adaptation

Intramedullary pressure (ImP) and low-level bone strain induced by oscillatory muscle stimulation (MS) has the potential to mitigate bone loss induced by disuse osteopenia, i.e., hindlimb suspension (HLS). To test this hypothesis, we evaluated (a) MS-induced ImP and bone strain as function of stimulation frequency and (b) the adaptive responses to functional disuse, and disuse plus 1 and 20 Hz stimulation in vivo. Femoral ImP and bone strain generated by MS were measured in the frequencies of 1–100 Hz in four rats. Forty retired breeder rats were used for the in vivo HLS study. The quadriceps muscle was stimulated at frequencies of 1 and 20 Hz, 10 min/d for four weeks. The metaphyseal trabecular bone quantity and microstructure at the distal femur were evaluated using μCT, while bone formation indices were analyzed using histomorphometric technique. Oscillatory MS generated a maximum ImP of 45±9 mmHg at 20 Hz and produced a maximum matrix strain of 128±19 με at 10 Hz. Our analyses from the in vivo study showed that MS at 20 Hz was able to attenuate trabecular bone loss and partially maintain the microstructure induced by HLS. Conversely, there was no evidence of an adaptive effect of stimulation at 1 Hz on disused skeleton. The results suggested that oscillatory MS regulates fluid dynamics and mechanical strain in bone, which serves as a critical mediator of adaptation. These results clearly demonstrated the ability of MS in attenuating bone loss from the disuse osteopenia, which may hold potential in mitigating skeletal degradation imposed by conditions of disuse, and may serve as a biomechanical intervention in clinic application.     

Wire tension versus wire frequency: An experimental Ilizarov frame study

Stability of an Ilizarov frame highly depends on maintenance of adequate tension in the wires. Wire tension should be measured accurately in experimental laboratory studies when new types of wire fixators are tested. In this study, 20 wires were tested using two different wire fixators. The wires were sequentially tensioned from 0 to 1275 N in 50 N intervals. For each tension value, corresponding vibration frequency was recorded. We then described the relationship between wire tension and wire vibration frequency in an empirical equation (R²=99.8). Wire vibration frequency can also be described theoretically by the Euler–Bernoulli equation for a thin beam. Theoretical frequencies were calculated and compared with corresponding experimental frequencies. A close agreement was found (95% limits of agreement, ±3.2 Hz). This empirical equation represents a simple tool, applicable when investigating the effect of new wire fixators, pre-tensioning and frame constructions on wire tension.