Porosity and surface curvature effects on the permeability and wall shear stress of trabecular bone: Guidelines for biomimetic scaffolds for bone repair.

Scaffolds are an essential component of bone tissue engineering to provide support and create a physiological environment for cells. Biomimetic scaffolds are a promising approach to fulfill the requirements. Bone allografts are widely used scaffolds due to their mechanical and structural characteristics. The scaffold geometry is well known to be an important determinant of induced mechanical stimulation felt by the cells. However, the impact of allograft geometry on permeability and wall shear stress distribution is not well understood. This information is essential for designing biomimetic scaffolds that provide a suitable environment for cells to proliferate and differentiate. The present study investigates the effect of geometry on the permeability and wall shear stress of bone allografts at both macroscopic and microscopic scales. Our results concluded that the wall shear stress was strongly correlated with the porosity of the allograft. The level of wall shear stress at a local scale was also determined by the surface curvature characteristics. The results of this study can serve as a guideline for future biomimetic scaffold designs that provide a mechanical environment favorable for osteogenesis and bone repair.

A New Microarchitecture-Based Parameter to Predict the Micromechanical Properties of Bone Allografts.

Scaffolds are an essential component of bone tissue engineering. They provide support and create a physiological environment for cells to proliferate and differentiate. Bone allografts extracted from human donors are promising scaffolds due to their mechanical and structural characteristics. Bone microarchitecture is well known to be an important determinant of macroscopic mechanical properties, but its role at the microscopic, i.e., the trabeculae level is still poorly understood. The present study investigated linear correlations between microarchitectural parameters obtained from X-ray computed tomography (micro-CT) images of bone allografts, such as bone volume fraction (BV/TV), degree of anisotropy (DA), or ellipsoid factor (EF), and micromechanical parameters derived from micro-finite element calculations, such as mean axial strain (εz) and strain energy density (We). DAEF, a new parameter based on a linear combination of the two microarchitectural parameters DA and EF, showed a strong linear correlation with the bone mechanical characteristics at the microscopic scale. Our results concluded that the spatial distribution and the plate-and-rod structure of trabecular bone are the main determinants of the mechanical properties of bone at the microscopic level. The DAEF parameter could, therefore, be used as a tool to predict the level of mechanical stimulation at the local scale, a key parameter to better understand and optimize the mechanism of osteogenesis in bone tissue engineering.

One-Pot Derivatization for Wide-Scope Detection of Nucleobases and Deoxyribosides in Natural Medicinal Foods with Liquid Chromatography-Tandem Mass Spectrometry.

A new chemical labeling-based LC-MS/MS approach was developed for quantitative profiling of nine canonical bases and deoxynucleosides (dNs) in natural products. Using 2-bromo-1-(4-dimethylamino-phenyl)-ethaone (BrDPE) as the tagging reagent, a previously unexploited N-alkylpyrimidine derivative (Nad) was created for one-pot labeling of widescope nucleobases via a flexible bromophilic substitution under mild conditions. The derivatization notably improved the LC-MS detection sensitivity by 31-107 fold, enabling a fast dilute-and-shoot analysis of highly diluted samples. The optimized and validated method demonstrated satisfactory accuracy (87-107%), precision (RSDs < 7.5%), and recovery (89-105%) for matrix-matched standard addition. The method was applied to simultaneously determine all target analytes and four uncanonical analogues and base-modified species in seven traditional health foods, which differ in contents by up to 600-fold for discrimination among samples. Further, the base-labeled Nads exhibit a unique fragmentation signature that could be used for untargeted screening of nucleobase-containing metabolites by simplified LC-MS/MS workflow to improve quality evaluation of natural medicinal products.

Structure-Dependent Modulation of Substrate Binding and Biodegradation Activity of Pirin Proteins toward Plant Flavonols.

Pirin is a nonheme metalloprotein that occurs widely in human tissues and is highly conserved across all taxa. Pirin proteins typically function as nuclear transcription regulators, but two Pirin orthologs, YhhW (from Escherichia coli) and hPirin (from humans) were revealed to possess enzymatic activity of degrading quercetin. The exact role of Pirin homologues and their catalytic specificity remain poorly understood. In this work, by screening against a panel of plant flavonoids, we found that both Pirins catalyze the oxidative degradation of a wide spectrum of flavonol analogues and release carbon monoxide (CO) in the process. This shows that Pirin acts on a broad range of substrates and could represent a novel dietary source of CO in vivo. Although the kinetic profiles differ substantially between two Pirins, the identified substrate structures all share a 2,3-double bond and 3-hydroxyl and 4-oxo groups on their "flavonol backbone," which contribute to the specific enzyme-substrate interaction. While hPirin is iron-dependent, YhhW is identified as a novel nickel-containing dioxygenase member of the bicupin family. Besides the expanded Pirin activity, we present the crystal structures of the native Ni-YhhW and tag-free Fe-hPirin, revealing the distinctive differences occurring at the metal-binding site. In addition, YhhW features a flexible Ω-loop near the catalytic cavity, which may help stabilize the reaction intermediates via a Ni-flavonol complex. The structure-dependent modulation of substrate binding to the catalytic cavity adds to understanding the differential dispositions of natural flavonols by human and bacterial Pirins.