The Advantages of Flexibility: The Role of Entropy in Crystal Structures Containing C-H···F Interactions.

Molecular crystal structures are often interpreted in terms of strong, structure directing, intermolecular interactions, especially those with distinct geometric signatures such as H-bonds or π-stacking interactions. Other interactions can be overlooked, perhaps because they are weak or lack a characteristic geometry. We show that although the cumulative effect of weak interactions is significant, their deformability also leads to occupation of low energy vibrational energy levels, which provides an additional stabilizing entropic contribution. The entropies of five fluorobenzene derivatives have been calculated by periodic DFT calculations to assess the entropic influence of C-H···F interactions in stabilizing their crystal structures. Calculations reproduce inelastic neutron scattering data and experimental entropies from heat capacity measurements. C-H···F contacts are shown to have force constants which are around half of those of more familiar interactions such as hydrogen bonds, halogen bonds, and C-H···π interactions. This feature, in combination with the relatively high mass of F, means that the lowest energy vibrations in crystalline fluorobenzenes are dominated by C-H···F contributions. C-H···F contacts occur much more frequently than would be expected from their enthalpic contributions alone, but at 150 K, the stabilizing contribution of entropy provides, at -10 to -15 kJ mol-1, a similar level of stabilization to the N-H···N hydrogen bond in ammonia and O-H···O hydrogen bond in water.

The Effect of High Pressure on Polymorphs of a Derivative of Blatter's Radical: Identification of the Structural Signatures of Subtle Phase Transitions.

The effect of pressure on the α and ß polymorphs of a derivative of Blatter's radical, 3-phenyl-1-(pyrid-2-yl)-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl, has been investigated using single-crystal X-ray diffraction to maximum pressures of 5.76 and 7.42 GPa, respectively. The most compressible crystallographic direction in both structures lies parallel to π-stacking interactions, which semiempirical Pixel calculations indicate are also the strongest interactions present. The mechanism of compression in perpendicular directions is determined by void distributions. Discontinuities in the vibrational frequencies observed in Raman spectra measured between ambient pressure and ∼5.5 GPa show that both polymorphs undergo phase transitions, the α phase at 0.8 GPa and the ß phase at 2.1 GPa. The structural signatures of the transitions, which signal the onset of compression of initially more rigid intermolecular contacts, were identified from the trends in the occupied and unoccupied volumes of the unit cell with pressure and in the case of the ß phase by deviations from an ideal model of compression defined by Birch-Murnaghan equations of state.

Experimental and Computational Studies of Ruthenium Complexes Bearing Z-Acceptor Aluminum-Based Phosphine Pincer Ligands.

Reaction of [Ru(C6H4PPh2)2(Ph2PC6H4AlMe(THF))H] with CO results in clean conversion to the Ru-Al heterobimetallic complex [Ru(AlMePhos)(CO)3] (1), where AlMePhos is the novel P-Al(Me)-P pincer ligand (o-Ph2PC6H4)2AlMe. Under photolytic conditions, 1 reacts with H2 to give [Ru(AlMePhos)(CO)2(µ-H)H] (2) that is characterized by multinuclear NMR and IR spectroscopies. DFT calculations indicate that 2 features one terminal and one bridging hydride that are respectively anti and syn to the AlMe group. Calculations also define a mechanism for H2 addition to 1 and predict facile hydride exchange in 2 that is also observed experimentally. Reaction of 1 with B(C6F5)3 results in Me abstraction to form the ion pair [Ru(AlPhos)(CO)3][MeB(C6F5)3] (4) featuring a cationic [(o-Ph2PC6H4)2Al]+ ligand, [AlPhos]+. The Ru-Al distance in 4 (2.5334(16) Å) is significantly shorter than that in 1 (2.6578(6) Å), consistent with an enhanced Lewis acidity of the [AlPhos]+ ligand. This is corroborated by a blue shift in both the observed and computed νCO stretching frequencies upon Me abstraction. Electronic structure analyses (QTAIM and EDA-ETS) comparing 1, 4, and the previously reported [Ru(ZnPhos)(CO)3] analogue (ZnPhos = (o-Ph2PC6H4)2Zn) indicate that the Lewis acidity of these pincer ligands increases along the series ZnPhos < AlMePhos < [AlPhos]+.

Behavior of Occupied and Void Space in Molecular Crystal Structures at High Pressure.

We report a Monte Carlo algorithm for calculation of occupied ("network") and unoccupied ("void") space in crystal structures. The variation of the volumes of the voids and the network of intermolecular contacts with pressure sensitively reveals discontinuities associated with first- and second-order phase transitions, providing insights into the effect of compression (and, in principle, other external stimuli) at a level between those observed in individual contact distances and the overall unit cell dimensions. The method is shown to be especially useful for the correlation of high-pressure crystallographic and spectroscopic data, illustrated for naphthalene, where a phase transition previously detected by vibrational spectroscopy, and debated in the literature for over 80 years, has been revealed unambiguously in crystallographic data for the first time. Premonitory behavior before a phase transition and crystal collapse at the end of a compression series has also been detected. The network and void volumes for 129 high-pressure studies taken from the Cambridge Structural Database (CSD) were fitted to equation of state to show that networks typically have bulk moduli between 40 and 150 GPa, while those of voids fall into a much smaller range, 2-5 GPa. These figures are shown to reproduce the narrow range of overall bulk moduli of molecular solids (ca. 5-20 GPa). The program, called CellVol, has been written in Python using the CSD Python API and can be run through the command line or through the Cambridge Crystallographic Data Centre's Mercury interface.

A first-order phase transition in Blatter's radical at high pressure.

The crystal structure of Blatter's radical (1,3-diphenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl) has been investigated between ambient pressure and 6.07 GPa. The sample remains in a compressed form of the ambient-pressure phase up to 5.34 GPa, the largest direction of strain being parallel to the direction of π-stacking interactions. The bulk modulus is 7.4 (6) GPa, with a pressure derivative equal to 9.33 (11). As pressure increases, the phenyl groups attached to the N1 and C3 positions of the triazinyl moieties of neighbouring pairs of molecules approach each other, causing the former to begin to rotate between 3.42 to 5.34 GPa. The onset of this phenyl rotation may be interpreted as a second-order phase transition which introduces a new mode for accommodating pressure. It is premonitory to a first-order isosymmetric phase transition which occurs on increasing pressure from 5.34 to 5.54 GPa. Although the phase transition is driven by volume minimization, rather than relief of unfavourable contacts, it is accompanied by a sharp jump in the orientation of the rotation angle of the phenyl group. DFT calculations suggest that the adoption of a more planar conformation by the triazinyl moiety at the phase transition can be attributed to relief of intramolecular H...H contacts at the transition. Although no dimerization of the radicals occurs, the π-stacking interactions are compressed by 0.341 (3) Šbetween ambient pressure and 6.07 GPa.

Morphology of bony callus growth in healing of a sheep tibial osteotomy.

Long bone fractures typically heal via formation of an external callus, which helps stabilise the bone fragments. Callus composition and morphology influence the mechanical environment, which in turn regulates the progression of healing. Therefore characterising callus development over time is crucial in understanding this mechanobiological regulation. Although bony callus is often assumed to grow towards the fracture from either side, this is not consistent with observations from large animal studies and clinical cases. Therefore, we sought to quantify the morphology of bony callus over time in a large animal model. Sheep tibiae were x-rayed weekly over eight weeks following an osteotomy (n=5), with fixation allowing up to 10% axial displacement under normal weight-bearing. After scaling radiographs by known landmarks and normalising greyscales, bony callus boundaries were defined by manual segmentation. The lateral callus area and coordinates of its centroid were calculated from each image. The external callus initially formed adjacent to the osteotomy site. Over the first four weeks, callus growth from its outer surfaces was characterised by its centre of area moving outwards and away from the osteotomy, on both proximal and distal fragments. Subsequent weeks showed consolidation and resorption from the outer surface of the callus. Our approach allowed bony callus development to be tracked in individuals throughout healing. Contrary to the view that periosteal bone formation originates distant from the fracture, our data showed bony callus adjacent to the defect from early stages, followed by approximately concentric growth. This discrepancy highlights the need for data specific to experimental conditions, and particularly early stages of healing, for evaluating theoretical models of mechanical regulation.

Measuring, evaluating and improving the effectiveness of invasive predator control programs: Feral cat baiting as a case study.

Reducing the impacts of invasive predators is a key objective for conservation managers, livestock producers and human health agencies globally. The efficacy of invasive predator control programs, however, is highly variable. To improve control efficacy, managers require a fundamental understanding of the factors that contribute to the success or failure of a control program. Using a predator baiting program as a case study, we measured the efficacy of baiting as a control tool to significantly reduce feral cat (Felis catus) populations. We used camera traps and cat-borne GPS collars to monitor changes in feral cat populations at a baited site and an unbaited site, using a Before-After, Control-Impact (BACI) design. We also identified five key elements required for a successful baiting program (bait encounter rate, availability, attractiveness, palatability and lethality) and simultaneously measured these to identify areas for potential improvement. Baiting was ineffective at reducing feral cat populations; collared cat mortality was only 11% (1/9), with camera traps revealing negligible reductions in the number of cat detection events (9%), naïve occupancy (15%), and no significant change in the relative abundance of feral cats (F1,54 = 0.8641, P = 0.357). Several factors contributed to the poor control efficacy. Bait encounter rates were low, with cats active along tracks (where baits were laid) < 4% of the time. Cats encountered only 14% (7/50) of monitored baits, but none were eaten. Initially, baits appeared attractive to cats; however meat ants and desiccation rapidly decreased bait palatability. Bait availability to cats declined rapidly, with 36% of monitored baits (18/50) removed by non-target species within the first 48 h. The mortality of one collared cat and chemical assays confirmed that, on average, each bait contained sufficient 1080 to kill a large (>5 kg) feral cat. Our findings suggest that altering bait deployment patterns, increasing bait densities and improving bait palatability could potentially improve the efficacy of baiting programs to reduce feral cat populations. Our study provides a framework to measure and evaluate the key elements that contribute to efficacy of pest control programs, and to identify opportunities for improving outcomes of future control programs.

External kinetics of the kettlebell snatch in amateur lifters.

BACKGROUND: Kettlebell lifting has gained increased popularity as both a form of resistance training and as a sport, despite the paucity of literature validating its use as a training tool. Kettlebell sport requires participants to complete the kettlebell snatch continuously over prolonged periods of time. Kettlebell sport and weightlifting involve similar exercises, however, their traditional uses suggest they are better suited to training different fitness qualities. This study examined the three-dimensional ground reaction force (GRF) and force applied to the kettlebell over a 6 min kettlebell snatch set in 12 kettlebell-trained males. METHODS: During this set, VICON was used to record the kettlebell trajectory with nine infrared cameras while the GRF of each leg was recorded with a separate AMTI force plate. Over the course of the set, an average of 13.9 ± 3.3 repetitions per minute were performed with a 24 kg kettlebell. Significance was evaluated with a two-way ANOVA and paired t-tests, whilst Cohen's F (ESF) and Cohen's D (ESD) were used to determine the magnitude. RESULTS: The applied force at the point of maximum acceleration was 814 ± 75 N and 885 ± 86 N for the downwards and upwards phases, respectively. The absolute peak resultant bilateral GRF was 1,746 ± 217 N and 1,768 ± 242 N for the downwards and upwards phases, respectively. Bilateral GRF of the first and last 14 repetitions was found to be similar, however there was a significant difference in the peak applied force (F (1.11) = 7.42, p = 0.02, ESF = 0.45). Unilateral GRF was found have a significant difference for the absolute anterior-posterior (F (1.11) = 885.15, p < 0.0001, ESF = 7) and medio-lateral force vectors (F (1.11) = 5.31, p = 0.042, ESF = 0.67). DISCUSSION: Over the course of a single repetition there were significant differences in the GRF and applied force at multiple points of the kettlebells trajectory. The kettlebell snatch loads each leg differently throughout a repetition and performing the kettlebell snatch for 6 min will result in a reduction in peak applied force.

Computational simulation of bone fracture healing under inverse dynamisation.

Adaptive finite element models have allowed researchers to test hypothetical relationships between the local mechanical environment and the healing of bone fractures. However, their predictive power has not yet been demonstrated by testing hypotheses ahead of experimental testing. In this study, an established mechano-biological scheme was used in an iterative finite element simulation of sheep tibial osteotomy healing under a hypothetical fixation regime, "inverse dynamisation". Tissue distributions, interfragmentary movement and stiffness across the fracture site were compared between stiff and flexible fixation conditions and scenarios in which fixation stiffness was increased at a discrete time-point. The modelling work was conducted blind to the experimental study to be published subsequently. The simulations predicted the fastest and most direct healing under constant stiff fixation, and the slowest healing under flexible fixation. Although low fixation stiffness promoted more callus formation prior to bridging, this conferred little additional stiffness to the fracture in the first 5 weeks. Thus, while switching to stiffer fixation facilitated rapid subsequent bridging of the fracture, no advantage of inverse dynamisation could be demonstrated. In vivo data remains necessary to conclusively test this treatment protocol and this will, in turn, provide an evaluation of the model's performance. The publication of both hypotheses and their computational simulation, prior to experimental testing, offers an appealing means to test the predictive power of mechano-biological models.

Parasite stress and pathogen avoidance relate to distinct dimensions of political ideology across 30 nations.

People who are more avoidant of pathogens are more politically conservative, as are nations with greater parasite stress. In the current research, we test two prominent hypotheses that have been proposed as explanations for these relationships. The first, which is an intragroup account, holds that these relationships between pathogens and politics are based on motivations to adhere to local norms, which are sometimes shaped by cultural evolution to have pathogen-neutralizing properties. The second, which is an intergroup account, holds that these same relationships are based on motivations to avoid contact with outgroups, who might pose greater infectious disease threats than ingroup members. Results from a study surveying 11,501 participants across 30 nations are more consistent with the intragroup account than with the intergroup account. National parasite stress relates to traditionalism (an aspect of conservatism especially related to adherence to group norms) but not to social dominance orientation (SDO; an aspect of conservatism especially related to endorsements of intergroup barriers and negativity toward ethnic and racial outgroups). Further, individual differences in pathogen-avoidance motives (i.e., disgust sensitivity) relate more strongly to traditionalism than to SDO within the 30 nations.

Effects of strain artefacts arising from a pre-defined callus domain in models of bone healing mechanobiology.

Iterative computational models have been used to investigate the regulation of bone fracture healing by local mechanical conditions. Although their predictions replicate some mechanical responses and histological features, they do not typically reproduce the predominantly radial hard callus growth pattern observed in larger mammals. We hypothesised that this discrepancy results from an artefact of the models' initial geometry. Using axisymmetric finite element models, we demonstrated that pre-defining a field of soft tissue in which callus may develop introduces high deviatoric strains in the periosteal region adjacent to the fracture. These bone-inhibiting strains are not present when the initial soft tissue is confined to a thin periosteal layer. As observed in previous healing models, tissue differentiation algorithms regulated by deviatoric strain predicted hard callus forming remotely and growing towards the fracture. While dilatational strain regulation allowed early bone formation closer to the fracture, hard callus still formed initially over a broad area, rather than expanding over time. Modelling callus growth from a thin periosteal layer successfully predicted the initiation of hard callus growth close to the fracture site. However, these models were still susceptible to elevated deviatoric strains in the soft tissues at the edge of the hard callus. Our study highlights the importance of the initial soft tissue geometry used for finite element models of fracture healing. If this cannot be defined accurately, alternative mechanisms for the prediction of early callus development should be investigated.

Is starting with the feet out of the water faster in backstroke swimming?

This study aimed to determine if starting with the feet above the water (FAW) in male backstroke swimming resulted in faster start times (15-m time) than when the feet were underwater (FUW). It was hypothesised that setting higher on the wall would generate increased horizontal force and velocity, resulting in quicker starts. Twelve high-level male backstrokers performed three trials of the FAW and FUW techniques. A biomechanical swimming testing system comprising one force plate (1,000 Hz), four lateral-view (100Hz), and five overhead (50Hz) video cameras captured the swimmers' performance. Data for each participant's fastest trial for each technique were collated, grouped, and statistically analysed. Analysis included Wilcoxon, Spearman Rho correlation, and regression analysis. Wilcoxon results revealed a significantly faster start time for the FAW technique (p < 0.01). Peak horizontal force was significantly smaller for FAW (p = 0.02), while take-off horizontal velocity was significantly greater (p = 0.01). Regression analysis indicated take-off horizontal velocity to be a good predictor of start time for both techniques, and the horizontal displacement of the centre of mass for the FAW start.

Mechanical tension as a driver of connective tissue growth in vitro.

We propose the progressive mechanical expansion of cell-derived tissue analogues as a novel, growth-based approach to in vitro tissue engineering. The prevailing approach to producing tissue in vitro is to culture cells in an exogenous "scaffold" that provides a basic structure and mechanical support. This necessarily pre-defines the final size of the implantable material, and specific signals must be provided to stimulate appropriate cell growth, differentiation and matrix formation. In contrast, surgical skin expansion, driven by increments of stretch, produces increasing quantities of tissue without trauma or inflammation. This suggests that connective tissue cells have the innate ability to produce growth in response to elevated tension. We posit that this capacity is maintained in vitro, and that order-of-magnitude growth may be similarly attained in self-assembling cultures of cells and their own extracellular matrix. The hypothesis that growth of connective tissue analogues can be induced by mechanical expansion in vitro may be divided into three components: (1) tension stimulates cell proliferation and extracellular matrix synthesis; (2) the corresponding volume increase will relax the tension imparted by a fixed displacement; (3) the repeated application of static stretch will produce sustained growth and a tissue structure adapted to the tensile loading. Connective tissues exist in a state of residual tension, which is actively maintained by resident cells such as fibroblasts. Studies in vitro and in vivo have demonstrated that cellular survival, reproduction, and matrix synthesis and degradation are regulated by the mechanical environment. Order-of-magnitude increases in both bone and skin volume have been achieved clinically through staged expansion protocols, demonstrating that tension-driven growth can be sustained over prolonged periods. Furthermore, cell-derived tissue analogues have demonstrated mechanically advantageous structural adaptation in response to applied loading. Together, these data suggest that a program of incremental stretch constitutes an appealing way to replicate tissue growth in cell culture, by harnessing the constituent cells' innate mechanical responsiveness. In addition to offering a platform to study the growth and structural adaptation of connective tissues, tension-driven growth presents a novel approach to in vitro tissue engineering. Because the supporting structure is secreted and organised by the cells themselves, growth is not restricted by a "scaffold" of fixed size. This also minimises potential adverse reactions to exogenous materials upon implantation. Most importantly, we posit that the growth induced by progressive stretch will allow substantial volumes of connective tissue to be produced from relatively small initial cell numbers.

Reviewing current knowledge in snatch performance and technique: the need for future directions in applied research.

This is a review of current research trends in weightlifting literature relating to the understanding of technique and its role in successful snatch performance. Reference to the world records in the snatch from the 1960s onwards indicates little progress across all weight categories. With such mediocre advances in performance at the International level, there is a need to better understand how snatch technique can improve performance even if only by a small margin. Methods of data acquisition for technical analysis of the snatch have involved mostly 2-dimensional barbell and joint kinematics. Although key variables which play a role in the successful outcome of a snatch lift have been heavily investigated, few studies have combined variables relating both the barbell and the weightlifter in their analyses. This suggests the need for a more detailed approach integrating both barbell-related and weightlifter-related data to enhance understanding of the mechanics of a successful lift. Currently, with the aid of technical advances in motion analysis, data acquisition, and methods of analysis, a more accurate representation of the movement can be provided. Better ways of understanding the key characteristics of technique in the snatch could provide the opportunity for more effective individualized feedback from the coach to the athlete, which should in turn lead to improved performance in competition.

Carbachol-induced volume adaptation in mouse bladder and length adaptation via rhythmic contraction in rabbit detrusor.

The length-tension (L-T) relationships in rabbit detrusor smooth muscle (DSM) are similar to those in vascular and airway smooth muscles and exhibit short-term length adaptation characterized by L-T curves that shift along the length axis as a function of activation and strain history. In contrast to skeletal muscle, the length-active tension (L-T(a)) curve for rabbit DSM strips does not have a unique peak tension value with a single ascending and descending limb. Instead, DSM can exhibit multiple ascending and descending limbs, and repeated KCl-induced contractions at a particular muscle length on an ascending or descending limb display increasingly greater tension. In the present study, mouse bladder strips with and without urothelium exhibited KCl-induced and carbachol-induced length adaptation, and the pressure-volume relationship in mouse whole bladder displayed short-term volume adaptation. Finally, prostaglandin-E(2)-induced low-level rhythmic contraction produced length adaptation in rabbit DSM strips. A likely role of length adaptation during bladder filling is to prepare DSM cells to contract efficiently over a broad range of volumes. Mammalian bladders exhibit spontaneous rhythmic contraction (SRC) during the filling phase and SRC is elevated in humans with overactive bladder (OAB). The present data identify a potential physiological role for SRC in bladder adaptation and motivate the investigation of a potential link between short-term volume adaptation and OAB with impaired contractility.

Adjustable passive stiffness in mouse bladder: regulated by Rho kinase and elevated following partial bladder outlet obstruction.

Detrusor smooth muscle (DSM) contributes to bladder wall tension during filling, and bladder wall deformation affects the signaling system that leads to urgency. The length-passive tension (L-T(p)) relationship in rabbit DSM can adapt with length changes over time and exhibits adjustable passive stiffness (APS) characterized by a L-T(p) curve that is a function of both activation and strain history. Muscle activation with KCl, carbachol (CCh), or prostaglandin E(2) at short muscle lengths can increase APS that is revealed by elevated pseudo-steady-state T(p) at longer lengths compared with prior T(p) measurements at those lengths, and APS generation is inhibited by the Rho Kinase (ROCK) inhibitor H-1152. In the current study, mouse bladder strips exhibited both KCl- and CCh-induced APS. Whole mouse bladders demonstrated APS which was measured as an increase in pressure during passive filling in calcium-free solution following CCh precontraction compared with pressure during filling without precontraction. In addition, CCh-induced APS in whole mouse bladder was inhibited by H-1152, indicating that ROCK activity may regulate bladder compliance during filling. Furthermore, APS in whole mouse bladder was elevated 2 wk after partial bladder outlet obstruction, suggesting that APS may be relevant in diseases affecting bladder mechanics. The presence of APS in mouse bladder will permit future studies of APS regulatory pathways and potential alterations of APS in disease models using knockout transgenetic mice.

Using three-dimensional kinematics to identify feedback for the Snatch: a case study.

This case study evaluated the importance of peak bar velocity and starting posture adopted by a novice weightlifter to the outcome of a Snatch lift. Multiple observations of both successful and unsuccessful attempts were captured using 3D motion analysis (VICON MX: 500 Hz). The following data analysis was then used to derive feedback. In total, 133 attempts of loads ranging from 75 to 100% of 1 repetition maximum (1RM) were performed by the subject (age = 25 years, stature = 171 cm, mass = 74.8 kg, Snatch 1RM = 80 kg). Variables included peak bar velocity, pelvis, hip, knee and ankle joint angles at the starting position for the right side and the difference between (left minus right) sides. No main effects for load, success, or their interactions were found for peak bar velocity. Starting position kinematics were mostly nonsignificant between the outcome of Snatch attempts. Right ankle joint angle was the only exception, where unsuccessful attempts displayed greater (p = 0.0228) dorsiflexion. A more comprehensive finding was achieved through the partition modeling; this analysis provided valuable insight and coaching feedback for the subject in relation to his lower body kinematics at the starting position. Furthermore, the accuracy of this feedback was verified using a holdback data set. Specifically, anterior pelvic tilt (>17.6°) and hip joint (<89.6°) angle were identified as the key features to increasing the likelihood of success. In conclusion, this case study outlines a method of data collection and analysis to assist coaching feedback for an individual.

Basic gait and symmetry measures for primary school-aged children and young adults. II: walking at slow, free and fast speed.

This study recorded basic gait data from 656 healthy primary school-aged children (5-13 years) and 81 young adults (18-27 years) whilst walking over-ground across a level walkway at varying speed. It investigated the effect of gait speed and re-examined the issue of gait maturation. Participants completed 6-8 walks at self-selected slow, free and fast speed along a GAITRite walkway whilst wearing athletic shoes. Outcome measures (non-normalized and normalized) were gait speed, cadence, step and stride length, step and stride time, support base, single and double support (%), stance duration (%), foot angle and associated symmetry measures. Compared to free speed, participants walked 24% slower for the slow speed and 30% faster for the fast speed (p<0.0001). Both normalized and non-normalized measures of cadence, step and stride length increased with speed (p<0.001) whereas step and stride time reduced (p<0.001). As a percentage of the gait cycle, single support and stance duration increased with speed (p<0.001) whereas double support reduced (p<0.001). Foot angle was significantly less (less toe-out) for the fast speed than the free and slow speeds (p<0.001) whereas support base was unaffected by speed. Symmetry measures were unaffected by age or speed. Step and stride symmetry differentials (combining conditions) fell around 0.8 cm, whereas symmetry differentials for step and stance time, single and double support fell around 0.7%. This information can be used by clinicians and researchers to assess the gait of children.

Toward biomimetic materials in bone regeneration: functional behavior of mesenchymal stem cells on a broad spectrum of extracellular matrix components.

Bone defect treatments can be augmented by mesenchymal stem cell (MSC) based therapies. MSC interaction with the extracellular matrix (ECM) of the surrounding tissue regulates their functional behavior. Understanding of these specific regulatory mechanisms is essential for the therapeutic stimulation of MSC in vivo. However, these interactions are presently only partially understood. This study examined in parallel, for the first time, the effects on the functional behavior of MSCs of 13 ECM components from bone, cartilage and hematoma compared to a control protein, and hence draws conclusions for rational biomaterial design. ECM components specifically modulated MSC adhesion, migration, proliferation, and osteogenic differentiation, for example, fibronectin facilitated migration, adhesion, and proliferation, but not osteogenic differentiation, whereas fibrinogen enhanced adhesion and proliferation, but not migration. Subsequently, the integrin expression pattern of MSCs was determined and related to the cell behavior on specific ECM components. Finally, on this basis, peptide sequences are reported for the potential stimulation of MSC functions. Based on the results of this study, ECM component coatings could be designed to specifically guide cell functions.

Mechanical stimulation of the pro-angiogenic capacity of human fracture haematoma: involvement of VEGF mechano-regulation.

Compromised angiogenesis appears to be a major limitation in various suboptimal bone healing situations. Appropriate mechanical stimuli support blood vessel formation in vivo and improve healing outcomes. However, the mechanisms responsible for this association are unclear. To address this question, the paracrine angiogenic potential of early human fracture haematoma and its responsiveness to mechanical loading, as well as angiogenic growth factors involved, were investigated in vitro. Human haematomas were collected from healthy patients undergoing surgery within 72 h after bone fracture. The haematomas were embedded in a fibrin matrix, and cultured in a bioreactor resembling the in vivo conditions of the early phase of bone healing (20% compression, 1 Hz) over 3 days. Conditioned medium (CM) from the bioreactor was then analyzed. The matrices were also incubated in fresh medium for a further 24 h to evaluate the persistence of the effects. Growth factor (GF) concentrations were measured in the CM by ELISAs. In vitro tube formation assays were conducted on Matrigel with the HMEC-1 cell line, with or without inhibition of vascular endothelial growth factor receptor 2 (VEGFR2). Cell numbers were quantified using an MTS test. In vitro endothelial tube formation was enhanced by CM from haematomas, compared to fibrin controls. The angiogenesis regulators, vascular endothelial growth factor (VEGF) and transforming growth factor beta1 (TGF-beta1), were released into the haematoma CM, but not angiopoietins 1 or 2 (Ang1, 2), basic fibroblast growth factor (bFGF) or platelet-derived growth factor (PDGF). Mechanical stimulation of haematomas, but not fibrin controls, further increased the induction of tube formation by their CM. The mechanically stimulated haematoma matrices retained their elevated pro-angiogenic capacity for 24 h. The pro-angiogenic effect was cancelled by inhibition of VEGFR2 signalling. VEGF concentrations in CM tended to be elevated by mechanical stimulation; this was significant in haematomas from younger, but not from older patients. Other GFs were not mechanically regulated. In conclusion, the paracrine pro-angiogenic capacity of early human haematomas is enhanced by mechanical stimulation. This effect lasts even after removing the mechanical stimulus and appears to be VEGFR2-dependent.