Quantifying the correlation between spatially defined oxygen gradients and cell fate in an engineered three-dimensional culture model

A challenge in three-dimensional tissue culture remains the lack of quantitative information linking nutrient delivery and cellular distribution. Both in vivo and in vitro, oxygen is delivered by diffusion from its source (blood vessel or the construct margins). The oxygen level at a defined distance from its source depends critically on the balance of diffusion and cellular metabolism. Cells may respond to this oxygen environment through proliferation, death and chemotaxis, resulting in spatially resolved gradients in cellular density. This study extracts novel spatially resolved and simultaneous data on tissue oxygenation, cellular proliferation, viability and chemotaxis in three-dimensional spiralled, cellular collagen constructs. Oxygen concentration gradients drove preferential cellular proliferation rates and viability in the higher oxygen zones and induced chemotaxis along the spiral of the collagen construct; an oxygen gradient of 1.03 mmHg mm(-1) in the spiral direction induced a mean migratory speed of 1015 μm day(-1). Although this movement was modest, it was effective in balancing the system to a stable cell density distribution, and provided insights into the natural cell mechanism for adapting cell number and activity to a prevailing oxygen regime

Engineering angiogenesis by hypoxia-induced signaling: Adopting a physiological approach

Successful engineering of tissues with clinically relevant size and complexity critically depends on their in vitro pre-vascularization which can promote cell survival, differentiation and rapid vascularization post-implantation. However, mimicking in vitro the physiological complexity of a vascular network currently presents major obstacles1. In this study we tested the hypothesis that a hypoxia-induced signaling (HIS) - cell population can generate the complete angiogenic cascade necessary for inducing endothelial cell sprouting and tubule formation within a 3D construct

Perfusion of oxygen in 3D plastic compressed collagen constructs

The development of 3D connective tissues in vitro is heavily dependent upon remodelling of the matrix, in particular collagen, by resident cells. We have developed a novel plastic compression (PC) technique, for the fabrication of dense cell-collagen based bio-mimetic tissues (Brown et al. 2005). Cell survival in these PC collagen constructs is critical for successful tissue modelling and so the aim here is to understand, quantitatively their dynamic perfusion. This is important for the development of tissue bioreactors for the culture of PC constructs. We have used a fibre-optic oxygen sensor to measure changing oxygen levels in the core of such constructs. This effectively measures O2 consumption by cells, and by extrapolation, gradients and diffusion properties in the model tissues, which can be correlated with cell death

Enhancing the mechanical properties of collagen by photo-chemical cross-linking

Cell survival within mechanically strong scaffolds is critical in the design of tissue engineered constructs. Collagen type I gels tend to be mechanically weak due to the low percentage of collagen with limited orientation and crosslinking. To enhance the properties of collagen type I gels we used the following approaches: a) plastically compress the collagen gel to increase the density and b) photochemically crosslink the gel using riboflavin as a photoinitiator and high intensity blue light. Following plastic compression both the collagen density and cell number increase 58-fold1. This study aims to assess mechanical properties and the degree of cell viability in different areas of the compressed gel following cross-linking. Patterns of cross-linking were also applied to induce anisotropic features to the gel

Mechanical loading of 3-D muscle constructs

Mechanical conditioning of many tissue engineered construct will be critical, particularly mechano-responsive tissues such as skeletal muscle. It has been shown that application of defined uniaxial loads to 3D constructs through the tensioning- culture force monitor (t-CFM), has been shown to regulate protease expression in fibroblasts (Prajapati et al. 2000). Insulin-like growth factor (IGF-1) is an important growth factor in proliferation and differentiation of skeletal myoblasts (Florini et al. 1996), along with it a recently isolated isoform, mechano-growth factor (MGF) is found to be upregulated in skeletal muscle in vivo following exercise (Yang et al. 1996)

Endothelial cell migration and aggregation in response to hypoxia-induced signalling

The vascularisation of any graft, engineered implant or injury site is a key factor for optimal repair and regeneration. New blood vessel formation is a physiological response to tissue hypoxia, through upregulation of angiogenic factor signalling. We engineered cell-mediated hypoxia in a convenient cell type, human dermal fibroblasts (HDFs), to form a population of Hypoxia-Induced Signalling (HIS) cells and showed that HIS responses by HDFs induce endothelial cell (EC) migration and tubule formation both in vitro and in viv

Energy allocation and behaviour in the growing broiler chicken

Broiler chickens are increasingly at the forefront of global meat production but the consequences of fast growth and selection for an increase in body mass on bird health are an ongoing concern for industry and consumers. To better understand the implications of selection we evaluated energetics and behaviour over the 6-week hatch-to-slaughter developmental period in a commercial broiler. The effect of posture on resting metabolic rate becomes increasingly significant as broilers grow, as standing became more energetically expensive than sitting. The proportion of overall metabolic rate accounted for by locomotor behaviour decreased over development, corresponding to declining activity levels, mean and peak walking speeds. These data are consistent with the inference that broilers allocate energy to activity within a constrained metabolic budget and that there is a reducing metabolic scope for exercise throughout their development. Comparison with similarly sized galliforms reveals that locomotion is relatively energetically expensive in broilers

2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus statement on catheter and surgical ablation of atrial fibrillation: executive summary.

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Suboptimal management of severe menopausal symptoms by Nigerian Gynaecologists: a call for mandatory continuing medical education for physicians

<p>Abstract</p> <p>Background</p> <p>Effective management of menopause is an important way to improve the quality of life of the increasing number of older women. The study sought to find out if Nigerian Gynaecologists offer effective treatment for severe menopausal symptoms.</p> <p>Methods</p> <p>126 Nigerian Gynaecologists representing the six health zones of Nigeria were interviewed to determine the menopausal symptoms they had ever encountered in their practices, frequency of the symptoms, treatments ever offered for severe symptoms including their attitude to, and practice of hormone replacement therapy.</p> <p>Results</p> <p>A Nigerian Gynaecologist encountered an average of one patient with menopausal symptoms every three months (range: 0-3 patients per month). The commoner symptoms they encountered were hot flushes (88%), insomnia (75.4%), depression (58.0%), irritability (56.3%), night sweats (55.6%) and muscle pains (54.8%) while urinary symptoms (16.7%) and fracture (1.6%) were less common. Treatments ever offered for severe symptoms were reassurance (90.5%), anxiolytics (68.3%), analgesics (14.3), HRT (7.9%), Vitamins (4%), Beta-blockers (3.2%) and Danazol (2.4%). These treatments were offered as a matter of institutional traditions rather than being based on any evidence of their efficacy.</p> <p>Conclusion</p> <p>The result revealed that most Nigerian Gynaecologists prefer reassurance and anxiolytics for managing severe menopausal symptoms instead of evidence-based effective therapies. A policy of mandatory continuing medical education for Nigerian physicians is recommended to ensure evidence-based management of gynaecological problems, including menopause.</p