A systematic review of vitamin D status in populations worldwide.

Vitamin D deficiency is associated with osteoporosis and is thought to increase the risk of cancer and CVD. Despite these numerous potential health effects, data on vitamin D status at the population level and within key subgroups are limited. The aims of the present study were to examine patterns of 25-hydroxyvitamin D (25(OH)D) levels worldwide and to assess differences by age, sex and region. In a systematic literature review using the Medline and EMBASE databases, we identified 195 studies conducted in forty-four countries involving more than 168 000 participants. Mean population-level 25(OH)D values varied considerably across the studies (range 4·9-136·2 nmol/l), with 37·3 % of the studies reporting mean values below 50 nmol/l. The highest 25(OH)D values were observed in North America. Although age-related differences were observed in the Asia/Pacific and Middle East/Africa regions, they were not observed elsewhere and sex-related differences were not observed in any region. Substantial heterogeneity between the studies precluded drawing conclusions on overall vitamin D status at the population level. Exploratory analyses, however, suggested that newborns and institutionalised elderly from several regions worldwide appeared to be at a generally higher risk of exhibiting lower 25(OH)D values. Substantial details on worldwide patterns of vitamin D status at the population level and within key subgroups are needed to inform public health policy development to reduce risk for potential health consequences of an inadequate vitamin D status.

Development of specific collagen scaffolds to support the osteogenic and chondrogenic differentiation of human bone marrow stromal cells.

Type I Collagen matrices of defined porosity, incorporating carbonate substituted hydroxyapatite (HA) crystals, were assessed for their ability to support osteo- and chondrogenic differentiation of human bone marrow stromal cells (HBMSCs). Collagen-HA composite scaffolds supported the osteogenic differentiation of HBMSCs both in vitro and in vivo as demonstrated by histological and micro-CT analyses indicating the extensive penetration of alkaline phosphatase expressing cells and new matrix synthesis with localised areas immunologically positive for osteocalcin. In vivo, extensive new osteoid formation of implant origin was observed in the areas of vasculature. Chondrogenic matrix synthesis was evidenced in the peripheral regions of pure collagen systems by an abundance of Sox9 expressing chondrocytes embedded within a proteoglycan and collagen II rich ECM. The introduction of microchannels to the scaffold architecture was seen to enhance chondrogenesis. Tissue specific gene expression and corresponding matrix synthesis indicate that collagen matrices support the growth and differentiation of HBMSCs and suggest the potential of this platform for understanding the ECM cues necessary for osteogenesis and chondrogenesis.

The impact of critical point drying with liquid carbon dioxide on collagen-hydroxyapatite composite scaffolds.

Collagen-hydroxyapatite composites for bone tissue engineering are usually made by freezing an aqueous dispersion of these components and then freeze-drying. This method creates a foamed matrix which may not be optimum for growing cell colonies larger than a few hundred micrometres due to the limited diffusion of nutrients and oxygen, and the limited removal of waste metabolites. Incorporating a network of microchannels in the interior of the scaffold which may permit the flow of nutrient-rich media has been proposed as a method to overcome these diffusion constraints. A novel three-dimensional printing and critical point drying technique previously used to make collagen scaffolds has been modified to create collagen-hydroxyapatite scaffolds. This study investigates the properties of collagen and collagen-hydroxyapatite scaffolds and whether subjecting collagen and hydroxyapatite to critical point drying with liquid carbon dioxide results in any changes to the individual components. Specifically, the hydroxyapatite component was characterized before and after processing using wavelength-dispersive X-ray spectroscopy, X-ray diffraction and infrared spectroscopy. Critical point drying did not induce elemental, crystallographic or molecular changes in the hydroxyapatite. The quaternary structure of collagen was characterized using transmission electron microscopy and the quarter-staggered array characteristic of native collagen remained after processing. Microstructural characterization of the composites using scanning electron microscopy showed the hydroxyapatite particles were mechanically interlocked in the collagen matrix. The in vitro biological response of MG63 osteogenic cells to the composite scaffolds were characterized using the Alamar Blue, PicoGreen, alkaline phosphate and Live/Dead assays, and revealed that the critical point dried scaffolds were non-cytotoxic.

Controlling the processing of collagen-hydroxyapatite scaffolds for bone tissue engineering.

Scaffolds are an important aspect of the tissue engineering approach to tissue regeneration. This study shows that it is possible to manufacture scaffolds from type I collagen with or without hydroxyapatite (HA) by critical point drying. The mean pore sizes of the scaffolds can be altered from 44 to 135 microm depending on the precise processing conditions. Such pore sizes span the range that is likely to be required for specific cells. The mechanical properties of the scaffolds have been measured and behave as expected of foam structures. The degradation rate of the scaffolds by collagenase is independent of pore size. Dehydrothermal treatment (DHT), a common method of physically crosslinking collagen, was found to denature the collagen at a temperature of 120 degrees C resulting in a decrease in the scaffold's resistance to collagenase. Hybrid scaffold structures have also been manufactured, which have the potential to be used in the generation of multi-tissue interfaces. Microchannels are neatly incorporated via an indirect solid freeform fabrication (SFF) process, which could aid in reducing the different constraints commonly observed with other scaffolds.