Effect of deproteination on bone mineral morphology: implications for biomaterials and aging

Biomaterials from human bone – probing organic fraction removal by chemical and enzymatic methods

Two different deproteination and defatting processes of human bone were investigated, by combined infrared and neutron techniques: a previously reported hydrazine extraction and a newly developed multi-enzymatic treatment. Complementary Fourier transform infrared total attenuated reflectance and inelastic neutron scattering spectroscopies were applied, allowing access to all vibrational modes of the samples. The effectiveness of the different experimental protocols for removing the organic constituents of bone (lipids and protein) was probed, as well as their effect on bone's structural and crystallinity features. The results thus gathered are expected to have an impact on bioanthropological, archaeological and medical sciences, namely regarding the development of novel biocompatible materials for orthopaedic xenografts.

The effectiveness of two defatting & deproteination processes of human bone were assessed by combined infrared and inelastic neutron scattering spectroscopies.

Effect of strontium ranelate on bone mineral: Analysis of nanoscale compositional changes

Strontium ranelate has been used to prevent bone loss and stimulate bone regeneration. Although strontium may integrate into the bone crystal lattice, the chemical and structural modifications of the bone when strontium interacts with the mineral phase are not completely understood. The objective of this study was to evaluate apatite from the mandibles of rats treated with strontium ranelate in the drinking water and compare its characteristics with those from untreated rats and synthetic apatites with and without strontium. Electron energy loss near edge structures from phosphorus, carbon, calcium and strontium were obtained by electron energy loss spectroscopy in a transmission electron microscope. The strontium signal was detected in the biological and synthetic samples containing strontium. The relative quantification of carbon by analyzing the CK edge at an energy loss of ΔE = 284 eV showed an increase in the number of carbonate groups in the bone mineral of treated rats. A synthetic strontium-containing sample used as control did not exhibit a carbon signal. This study showed physicochemical modifications in the bone mineral at the nanoscale caused by the systemic administration of strontium ranelate.

A silicon cell cycle in a bacterial model of calcium phosphate mineralogenesis

The prokaryote Corynebacterium matruchotii produces calcium phosphate (bone salt) and may serve as a convenient model for examining individual factors relevant to vertebrate calcification. A factor of current clinical uncertainty is silicon. To investigate its possible role in biomineralisation advanced optical (digital deconvolution and 3D fluorescent image rendering) and electron microscopy (EDX microanalysis and elemental mapping) were applied to calcifying microbial colonies grown in graded Si concentrations (0-60mM). Cell viability was confirmed throughout by TO-PRO-3-iodide and SYTO-9 nucleic acid staining. It was observed that calcium accumulated in dense intracellular microspherical objects (types i-iii) as nanoparticles (5 nm, type i), nanospheres (30-50 nm, type ii) and filamentous clusters (0.1-0.5 μm, type iii), with a regular transitory Si content evident. With bacterial colony development (7-28 days) the P content increased from 5 to 60%, while Si was displaced from 60 to 5%, distinguishing the phenomenon from random contamination, and with a significant relationship (p<0.001) found between calcified object number and Si supplementation (optimum 0.01mM). The Si-containing, intracellular calcified objects (also positive for Mg and negative with Lysensor blue DND-167 for acidocalcisomes) were extruded naturally in bubble-like chains to complete the cycle by coating the cell surface with discrete mineral particles. These could be harvested by lysis, French press and density fractionation when Si was confirmed in a proportion. It was concluded that the unexplained orthopaedic activity of Si may derive from its special property to facilitate calcium phosphorylation in biological systems, thereby recapitulating an ancient and conserved bacterial cycle of calcification via silicification.

Minerals form a continuum phase in mature cancellous bone

Bone is a hierarchically structured composite consisting of a protein phase (type I collagen) and a mineral phase (carbonated apatite). The objective of this study was to investigate the hierarchical structure of mineral in mature bone. A method to completely deproteinize bone without altering the original structure is developed, and the completion is confirmed by protein analysis techniques. Stereoscopy and field emission electron microscopy are used to examine the structural features from submillimeter- to micrometer- to nanometer-length scales of bovine femur cancellous bone. Stereoscopic images of fully deproteinized and demineralized bovine femur cancellous bone samples show that fine trabecular architecture is unaltered and the microstructural features are preserved, indicating the structural integrity of mineral and protein constituents. SEM revealed that bone minerals are fused together and form a sheet-like structure in a coherent manner with collagen fibrils. Well-organized pore systems are observed at varying hierarchical levels. Mineral sheets are peeled off and folded after compressive deformation, implying strong connection between individual crystallites. Results were compared with commercially available heat-deproteinized bone (Bio-Oss(®)), and evidence showed consistency in bone mineral structure. A two-phase interpenetrating composite model of mature bone is proposed and discussed.

N-acetyl cysteine alleviates cytotoxicity of bone substitute

Lack of cytocompatibility in bone substitutes impairs healing in surrounding bone. Adverse biological events around biomaterials may be associated with oxidative stress. We hypothesized that a clinically used inorganic bone substitute is cytotoxic to osteoblasts due to oxidative stress and that N-acetyl cysteine (NAC), an antioxidant amino acid derivative, would detoxify such material. Only 20% of rat calvaria osteoblasts were viable when cultured on commercial deproteinized bovine bone particles for 24 hr, whereas this percentage doubled on bone substitute containing NAC. Intracellular ROS levels markedly increased on and under bone substitutes, which were reduced by prior addition of NAC to materials. NAC restored suppressed alkaline phosphatase activity in the bone substitute. Proinflammatory cytokine levels from human osteoblasts on the bone substitute decreased by one-third or more with addition of NAC. NAC alleviated cytotoxicity of the bone substitute to osteoblastic viability and function, implying enhanced bone regeneration around NAC-treated inorganic biomaterials.

A new tool to assess the mechanical properties of bone due to collagen degradation

Current clinical tools for evaluating fracture risk focus only on the mineral phase of bone. However, changes in the collagen matrix may affect bone mechanical properties, increasing fracture risk while remaining undetected by conventional screening methods such as dual energy x-ray absorptiometry (DXA) and quantitative ultrasound (QUS). The mechanical response tissue analyzer (MRTA) is a non-invasive, radiation-free potential clinical tool for evaluating fracture risk. The objectives of this study were two-fold: to investigate the ability of the MRTA to detect changes in mechanical properties of bone as a result of treatment with 1 M potassium hydroxide (KOH) and to evaluate the differences between male and female bone in an emu model. DXA, QUS, MRTA and three-point bending measurements were performed on ex vivo emu tibiae before and after KOH treatment. Male and female emu tibiae were endocortically treated with 1 M KOH solution for 1-14 days, resulting in negligible collagen loss (0.05%; by hydroxyproline assay) and overall mass loss (0.5%). Three-point bending and MRTA detected significant changes in modulus between days 1 and 14 of KOH treatment (-18%) while all values measured by DXA and QUS varied by less than 2%. This close correlation between MRTA and three-point bending results support the utility of the MRTA as a clinical tool to predict fracture risk. In addition, the significant reduction in modulus contrasted with the negligible amount of collagen removal from the bone after KOH exposure. As such, the significant changes in bone mechanical properties may be due to partial debonding between the mineral and organic matrix or in situ collagen degradation rather than collagen removal. In terms of sex differences, male emu tibiae had significantly decreased failure stress and increased failure strain and toughness compared to female tibiae with increasing KOH treatment time.

Effect of hydrazine deproteination on bone mineral phase: A critical view

Over the last 30 years several techniques have been developed to separate bone matrix and bone mineral, in order to allow for a study of each component independently of the other. Preservation of original characteristics of the phase studied after isolation has always been a great challenge for all such techniques. The hydrazine deproteination procedure, first proposed by Termine, has been one of the processes most widely used for studying bone mineral. It is found to be one of the most effective, notwithstanding controversy over its efficiency in bone deproteination and criticism regarding possible changes it could make to the characteristics of bone mineral. In this work, we have studied the possible chemical and physical alterations caused by the hydrazine deproteination process to bone mineral from rats and to other materials of biological interest. Materials were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffractometry (XRD), inductive coupled plasma-optical emission spectroscopy (ICP-OES), C-H-N analysis and infrared spectroscopy (FTIR), before and after hydrazine deproteination. Finally, here we present a comprehensive discussion on the criticism of hydrazine deproteination. The experimental results obtained in this work, even when compared to the results in the literature, show that most widespread criticism to the hydrazine deproteination process is not completely justified.

Scanning and transmission electron microscopy for evaluation of order/disorder in bone structure

A comparative characterization of the structure of normal and abnormal (osteoporotic) human lumbar and thoracic vertebrae samples was carried out to reveal the type of possible disorder. Samples from the bone fragments extracted during the surgery due to vertebra fractures were examined by scanning electron microscopy (SEM), conventional and high resolution transmission electron microscopy (TEM and HRTEM), and X-ray energy dispersive spectroscopy (EDS). Contrary to what might be expected in accordance with possible processes of dissolution, formation and remineralization of hard tissues, no changes in phase composition of mineral part, crystal sizes (length, width, and thickness), and arrangement of crystals on collagen fibers were detected in abnormal bones compared to the normal ones. The following sizes were determined by HRTEM for all bone samples: <or= 20 nm in length, 3-15 nm in width, and 0.8 nm in thickness (the height of hexagonal HAP unit cell along the [2110] direction. Significant overgrowth of organic fibers filled up the former paths for blood vessels and nerves together with organic films covering the mineral part was revealed by SEM only in osteoporotic bones. EDS showed that this organic tissue was not mineralized. Penetration of such organic fibers inside bones can result in bone dilatation and lower the mineral density, deteriorating the mechanical properties and finally terminating in fracture.