Hemocompatible and Bioactive Heparin‐Loaded PCL‐α‐TCP Fibrous Membranes for Bone Tissue Engineering

The combination of bioactive components such as calcium phosphates and fibrous structures are encouraging niche‐mimetic keys for restoring bone defects. However, the importance of hemocompatibility of the membranes is widely ignored. Heparin‐loaded nanocomposite poly(ε‐caprolactone) (PCL)‐α‐tricalcium phosphate (α‐TCP) fibrous membranes are developed to provide bioactive and hemocompatible constructs for bone tissue engineering. Nanocomposite membranes are optimized based on bioactivity, mechanical properties, and cell interaction. Consequently, various concentrations of heparin molecules are loaded within nanocomposite fibrous membranes. In vitro heparin release profiles reveal a sustained release of heparin over the period of 14 days without an initial burst. Moreover, heparin encapsulation enhances mesenchymal stem cell (MSC) attachment and proliferation, depending on the heparin content. It is concluded that the incorporation of heparin within TCP–PCL fibrous membranes provides the most effective cellular interactions through synergistic physical and chemical cues.     

Synergistic Effects of Beta Tri‐Calcium Phosphate and Porcine‐Derived Decellularized Bone Extracellular Matrix in 3D‐Printed Polycaprolactone Scaffold on Bone Regeneration

Bone‐derived extracellular matrix (ECM) is widely used in studies on bone regeneration because of its ability to provide a microenvironment of native bone tissue. However, a hydrogel, which is a main type of ECM application, is limited to use for bone graft substitutes due to relative lack of mechanical properties. The present study aims to fabricate a scaffold for guiding effective bone regeneration. A polycaprolactone (PCL)/beta‐tricalcium phosphate (β‐TCP)/bone decellularized extracellular matrix (dECM) scaffold capable of providing physical and physiological environment are fabricated using 3D printing technology and decoration method. PCL/β‐TCP/bone dECM scaffolds exhibit excellent cell seeding efficiency, proliferation, and early and late osteogenic differentiation capacity in vitro. In addition, outstanding results of bone regeneration are observed in PCL/β‐TCP/bone dECM scaffold group in the rabbit calvarial defect model in vivo. These results indicate that PCL/β‐TCP/bone dECM scaffolds have an outstanding potential as bone graft substitutes for effective bone regeneration.     

Release of prostaglandin E(1) from N-(2-hydroxypropyl)methacrylamide copolymer conjugates by bone cells

Bone-targeting N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-PGE(1) conjugates, containing cathepsin K sensitive spacers, were incubated with induced osteoclasts and osteoblasts, their precursors, and control non-skeletal cells. The release of PGE(1) was monitored by an HPLC assay. In both murine and human cell lines, osteoclasts appeared to be the most active cells in the cleavage (PGE(1) release). Incubation with osteoblasts also resulted in fast PGE(1) release, whereas precursor and control cells released PGE(1) with a substantially slower rate than bone cells (apparently through ester bond cleavage). Experiments in the presence of inhibitors revealed that other enzymes, in addition to cathepsin K, were participating in the cleavage of the conjugate. Confocal fluorescence studies exposed internalization of the conjugate by endocytosis with ultimate localization in the lysosomal/endosomal compartment.     

Liquid and gas chromatography coupled to isotope ratio mass spectrometry for the determination of 13C-valine isotopic ratios in complex biological samples

On-line gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) is commonly used to measure isotopic ratios at natural abundance as well as for tracer studies in nutritional and medical research. However, high-precision (13)C isotopic enrichment can also be measured by liquid chromatography-isotope ratio mass spectrometry (LC-IRMS). Indeed, LC-IRMS can be used, as shown by the new method reported here, to obtain a baseline separation and to measure (13)C isotopic enrichment of underivatised amino acids (Asp, Thr-Ser, Glu, Pro, Gly, Ala, Cys and Val). In case of Val, at natural abundance, the SD(delta(13)C) reported with this method was found to be below 1 per thousand . Another key feature of the new LC-IRMS method reported in this paper is the comparison of the LC-IRMS approach with the conventional GC-C-IRMS determination. To perform this comparative study, isotopic enrichments were measured from underivatised Val and its N(O, S)-ethoxycarbonyl ethyl ester derivative. Between 0.0 and 1.0 molar percent excess (MPE) (delta(13)C= -12.3 to 150.8 per thousand), the calculated root-mean-square (rms) of SD was 0.38 and 0.46 per thousand and the calculated rms of accuracy was 0.023 and 0.005 MPE, respectively, for GC-C-IRMS and LC-IRMS. Both systems measured accurately low isotopic enrichments (0.002 atom percent excess (APE)) with an SD (APE) of 0.0004. To correlate the relative (delta(13)C) and absolute (atom%, APE and MPE) isotopic enrichment of Val measured by the GC-C-IRMS and LC-IRMS devices, mathematical equations showing the slope and intercept of the curves were established and validated with experimental data between 0.0 to 2.3 MPE. Finally, both GC-C-IRMS and LC-IRMS instruments were also used to assess isotopic enrichment of protein-bound (13)C-Val in tibial epiphysis in a tracer study performed in rats. Isotopic enrichments measured by LC-IRMS and GC-C-IRMS were not statistically different (p>0.05). The results of this work indicate that the LC-IRMS was successful for high-precision (13)C isotopic measurements in tracer studies giving (13)C isotopic enrichment similar to the GC-C-IRMS but without the step of GC derivatisation. Therefore, for clinical studies requiring high-precision isotopic measurement, the LC-IRMS is the method of choice to measure the isotopic ratio.     

Propagation of time-reversed Lamb waves in acrylic cylindrical tubes as cortical-bone-mimicking phantoms

The present study aims to investigate the propagation of time-reversed Lamb waves in acrylic cylindrical tubes as cortical-bone-mimicking phantoms. Time-reversed Lamb waves could be successfully launched in 6 acrylic tubes with wall thicknesses from 2 to 12 mm by using a modified time reversal method. The group velocities of the time-reversed Lamb waves in the acrylic tubes were measured by using the axial transmission technique. They decreased very slightly with increasing wall thickness, showing good agreement with the theoretical group velocity of the A0 Lamb wave in the acrylic plate. These results suggest that the time-reversed Lamb waves in the acrylic tubes would essentially behave as the A0 Lamb wave, consistent with the behavior of the slow guided wave in long cortical bones. It is expected that the application of the time-reversed Lamb waves in long bones would enhance clinical potential of ultrasonic technologies for the diagnosis of osteoporosis.     

Towards the development of a fossil bone geochemical standard: an inter-laboratory study

Ten international laboratories participated in an inter-laboratory comparison of a fossil bone composite with the objective of producing a matrix and structure-matched reference material for studies of the bio-mineralization of ancient fossil bone. We report the major and trace element compositions of the fossil bone composite, using in-situ method as well as various wet chemical digestion techniques.For major element concentrations, the intra-laboratory analytical precision (%RSD_r) ranges from 7 to 18%, with higher percentages for Ti and K. The %RSD_r are smaller than the inter-laboratory analytical precision (%RSD_R; <15-30%). Trace element concentrations vary by ∼5 orders of magnitude (0.1 mg kg⁻¹ for Th to 10,000 mg kg⁻¹ for Ba). The intra-laboratory analytical precision %RSD_r varies between 8 and 45%. The reproducibility values (%RSD_R) range from 13 to <50%, although extreme value >100% was found for the high field strength elements (Hf, Th, Zr, Nb). The rare earth element (REE) concentrations, which vary over 3 orders of magnitude, have %RSD_r and %RSD_R values at 8-15% and 20-32%, respectively. However, the REE patterns (which are very important for paleo-environmental, taphonomic and paleo-oceanographic analyses) are much more consistent.These data suggest that the complex and unpredictable nature of the mineralogical and chemical composition of fossil bone makes it difficult to set-up and calibrate analytical instruments using conventional standards, and may result in non-spectral matrix effects. We propose an analytical protocol that can be employed in future inter-laboratory studies to produce a certified fossil bone geochemical standard.     

Laser polarimetry of the orientation structure of bone tissue osteons

A matrix method is proposed for describing polarization properties of biological tissues as an aggregate of uniaxial crystal structures. We investigated 25 μm-thick histological sections of compact bone tissue which provided single light scattering. It is shown that in this case there exists a unique relationship between the polarization parameters of the boundary laser field and the parameters of anisotropy and orientation of the structural elements of biological tissue. On this basis, contactless methods of laser polarimetry of histological sections of bone tissue have been proposed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 52–55, January–February, 2000.     

反演在骨生长方程参数识别中的应用

基于BFGS算法,根据自行设计的动物实验,得到在不同应力环境中,快速生长期大鼠股骨生 长与重建过程中骨密度实测数据,采用反演数值方法,获取了骨生长方程中随时间变化的 生物参数B和K. 通过正演验证,表明所建立的基于BFGS算法的参数识别方法具有较好的 稳定性和较高的识别精度,能够反演出比较切合实际的生物参数数值. 研究表明,反问 题方法是解决生命现象不可测性和未知性问题的有效手段,把反演方法应用到骨生长与重建 等生命现象的研究中,可确定、修正预设的数学模式,为数值量化骨适应生物模型的建立提 供了一条可行的途径.     

Hydrostatic extrusion of polyethylene filled with hydroxyapatite

The hydrostatic extrusion of polyethylene filled with hydroxyapatite has been studied. It is shown that the extrusion behavior is qualitatively similar to that of unfilled polymer. Extruded products with flexural moduli of at least 10 GPa and flexural strengths of 90 MPa have been produced, which can be considered as candidates for load-bearing bone substitute materials. © 1997 John Wiley & Sons, Ltd.