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

Structural and chemical features of xenograft bone substitutes: A systematic review of in vitro studies

Xenograft bone substitutes are obtained from different species and prepared by various procedures including heat treatment, hydrazine, and chemical and hydrothermal methods. These grafts are utilized widely because of similar structure and properties to human bone, proper bone formation, and biocompatibility. The aim of this systematic review was to evaluate different xenografts from structural and chemical aspects. In vitro studies published in English language, which assessed xenografts' features, met the inclusion criteria. Electronic search of four databases including PubMed, Google Scholar, Scopus, and Web of Science and a hand search until September 2020 were performed. The irrelevant studies were the ones which focused on cell adhesion and effect of growth factors. Finally, 25 studies were included in the review. Nineteen studies used bovine xenografts, and 12 studies applied heat treatment as their preparation method. Particles showed various morphologies, and their largest size was observed at 5 mm. From 18 studies, it is found that the smallest pore size was 1.3 µm and the highest pore size was 1000 µm. There is large heterogeneity of porosity, crystallinity, Ca/P ratio, and osteogenesis based on the preparation method. Proper porosity and the connection between pores affect bone regeneration. Therefore, biomaterial selection and outcomes evaluation should be interpreted separately.

Interfacial bonding between mineral platelets in bone and its effect on mechanical properties of bone

Bone is a composite material consisting principally of apatite mineral, collagen fibrils, non-collagenous proteins, and other organic species. Recent electron microscopy studies have shown that the mineral in bone occurs as stacks of thin polycrystalline sheets ("mineral lamellae," MLs) which surround and lie between the collagen fibrils. We focus on the effect of the interface between these mineral lamellae on the mechanical properties of bone. Previous studies on bone treated with sodium hypochlorite (NaClO) to remove all organic material showed a greatly weakened mineral framework. Here, we treated femoral cortical bone with ethylenediamine (EDA), which only removes collagen, to study the effect of its removal on bone properties. We tested the degree of completion of the treatment by Raman spectroscopy and thermogravimetric analysis. When only collagen is removed, a continuous mineral structure remains and is less weakened than by NaClO treatment. Transmission electron microscopy study of finely ground particles of the EDA treated bone shows that stacks of MLs remain joined, whereas in NaClO treated bone, only isolated crystals are present. Thus, we infer that the MLs in bone are held together in stacks by an organic glue, which is destroyed by NaClO, but which survives the EDA treatment. We show that this glue may contribute to the stiffness, strength, and energy absorption of bone. Further studies are needed to discover the chemical nature of this glue. This study provides a starting point for such investigations.

Deproteinization of Cortical Bone: Effects of Different Treatments

Bone is a biological composite material having collagen and mineral as its main constituents. In order to better understand the arrangement of the mineral phase in bone, porcine cortical bone was deproteinized using different chemical treatments. This study aims to determine the best method to remove the protein constituent while preserving the mineral component. Chemicals used were H₂O₂, NaOCl, NaOH, and KOH, and the efficacy of deproteinization treatments was determined by thermogravimetric analysis and Raman spectroscopy. The structure of the residual mineral parts was examined using scanning electron microscopy. X-ray diffraction was used to confirm that the mineral component was not altered by the chemical treatments. NaOCl was found to be the most effective method for deproteinization and the mineral phase was self-standing, supporting the hypothesis that bone is an interpenetrating composite. Thermogravimetric analyses and Raman spectroscopy results showed the preservation of mineral crystallinity and presence of residual organic material after all chemical treatments. A defatting step, which has not previously been used in conjunction with deproteinization to isolate the mineral phase, was also used. Finally, Raman spectroscopy demonstrated that the inclusion of a defatting procedure resulted in the removal of some but not all residual protein in the bone.

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.

The effect of enamel proteins on erosion

Enamel proteins form a scaffold for growing hydroxyapatite crystals during enamel formation. They are then almost completely degraded during enamel maturation, resulting in a protein content of only 1% (w/v) in mature enamel. Nevertheless, this small amount of remaining proteins has important effects on the mechanical and structural properties of enamel and on the electrostatic properties of its surface. To analyze how enamel proteins affect tooth erosion, human enamel specimens were deproteinated. Surface microhardness (SMH), surface reflection intensity (SRI) and calcium release of both deproteinated and control specimens were monitored while continuously eroding them. The deproteination itself already reduced the initial SMH and SRI of the enamel significantly (p < 0.001 and p < 0.01). During the course of erosion, the progression of all three evaluated parameters differed significantly between the two groups (p < 0.001 for each). The deproteinated enamel lost its SMH and SRI faster, and released more calcium than the control group, but these differences were only significant at later stages of erosion, where not only surface softening but surface loss can be observed. We conclude that enamel proteins have a significant effect on erosion, protecting the enamel and slowing down the progression of erosion when irreversible surface loss starts to occur.

Fibres and cellular structures preserved in 75-million-year-old dinosaur specimens

Exceptionally preserved organic remains are known throughout the vertebrate fossil record, and recently, evidence has emerged that such soft tissue might contain original components. We examined samples from eight Cretaceous dinosaur bones using nano-analytical techniques; the bones are not exceptionally preserved and show no external indication of soft tissue. In one sample, we observe structures consistent with endogenous collagen fibre remains displaying ∼ 67 nm banding, indicating the possible preservation of the original quaternary structure. Using ToF-SIMS, we identify amino-acid fragments typical of collagen fibrils. Furthermore, we observe structures consistent with putative erythrocyte remains that exhibit mass spectra similar to emu whole blood. Using advanced material characterization approaches, we find that these putative biological structures can be well preserved over geological timescales, and their preservation is more common than previously thought. The preservation of protein over geological timescales offers the opportunity to investigate relationships, physiology and behaviour of long extinct animals.

Kinome profiling of osteoblasts on hydroxyapatite opens new avenues on biomaterial cell signaling

In degenerative diseases or lesions, bone tissue replacement and regeneration are important clinical goals. The most used bone substitutes today are hydroxyapatite (HA) scaffolds. These scaffolds, developed over the last few decades, present high porosity and good osteointegration, but haven't completely solved issues related to bone defects. Moreover, the exact intracellular mechanisms involved in the response to HA have yet to be addressed. This prompted us to investigate the protein networks responsible for signal transduction during early osteoblast adhesion on synthetic HA scaffolds. By performing a global kinase activity assay, we showed that there is a specific molecular machinery responding to HA contact, immediately triggering pathways leading to cytoskeleton rearrangement due to activation of Adducin 1 (ADD1), protein kinase A (PKA), protein kinase C (PKC), and vascular endothelial growth factor (VEGF). Moreover, we found a significantly increased phosphorylation of the activating site Ser-421 in histone deacetylase 1 (HDAC1), a substrate of Cyclin-Dependent Kinase 5 (CDK5). These phosphorylation events are hallmarks of osteoblast differentiation, pointing to HA surfaces ability to promote differentiation. We also found that AKT was kept active, suggesting the maintenance of survival pathways. Interestingly, though, the substrate sequence of CDK5 also presented higher phosphorylation levels when compared to control conditions. To our knowledge, this kinase has never before been related to osteoblast biology, opening a new avenue of investigation for novel pathways involved in this matter. These results suggest that HA triggers a specific intracellular signal transduction cascade during early osteoblast adhesion, activating proteins involved with cytoskeleton rearrangement, and induction of osteoblast differentiation.

Effect of hydrazine based deproteination protocol on bone mineral crystal structure

In several bone deproteination protocols the chemical agent used for protein cleavage is hydrazine. The effect of hydrazine deproteination method on the crystal size and crystallinity of the bone mineral was studied. Bovine bones were subjected to this protocol and the crystal size and crystallinity of the remaining bone mineral were determined by X-ray Diffraction (XRD), by measuring the width at the half of the maximum intensity of the (002) reflection. It was found that hydrazine deproteination induces noteworthy increase of crystal size and crystallinity. The effect was enhanced by increasing hydrazine temperature from 25 to 55°C. Furthermore, infrared spectroscopy revealed that hydrazine facilitates the removal of carbonate and acid phosphate ions from bone mineral. It is proposed that the mechanism of modification of crystal size and crystallinity lies on the removal of these ions thus, resulting in crystal re-organization.

The role of enamel proteins in protecting mature human enamel against acidic environments: a double layer force spectroscopy study

Characterisation of the electrostatic properties of dental enamel is important for understanding the interfacial processes that occur on a tooth surface and how these relate to the natural ability of our teeth to withstand chemical attack from the acids in many soft drinks. Whereas, the role of the mineral component of the tooth enamel in providing this resistance to acid erosion has been studied extensively, the influence of proteins that are also present within the structure is not well understood. In this paper, we report for the first time the use of double-layer force spectroscopy to directly measure electrostatic forces on as received and hydrazine-treated (deproteinated) enamel surfaces in solutions with different pH to determine how the enamel proteins influence acid erosion surface potential and surface charge of human dental enamel. The deproteination of the treated samples was confirmed by the loss of the amide bands (~1,300-1,700 cm(-1)) in the FTIR spectrum of the sample. The force characteristics observed were found to agree with the theory of electrical double layer interaction under the assumption of constant potential and allowed the surface charge per unit area to be determined for the two enamel surfaces. The values and, importantly, the sign of these adsorbed surface charges indicates that the protein content of dental enamel contributes significantly to the electrostatic double layer formation near the tooth surface and in doing so can buffer the apatite crystals against acid attack. Moreover, the electrostatic interactions within this layer are a driving factor for the mineral transfer from the tooth surface and the initial salivary pellicle formation.

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.

Hydroxyapatite surface solubility and effect on cell adhesion

In living organisms the biological hydroxyapatite is in constant contact with body fluids, such as blood serum and saliva. Thus, dissolution, solubility and precipitation take place as part of the interaction of this material with biological fluids in tissues. In this work we have obtained the solubility constant for the system formed from aqueous solutions in equilibrium with hydroxyapatite and thus indirectly obtained the composition of the modified hydroxyapatite surface. In order to check the effects of this equilibrium and of the modification that the surface of hydroxyapatite suffers in aqueous solutions, we cultured pre-osteoblasts onto hydroxyapatite discs before and after equilibrium. The results revealed key steps of the mechanism for the bioactivity of hydroxyapatite, which are the solubilization of hydroxyapatite and the equilibrium that is formed on the surface. These processes modify the hydroxyapatite surface, whose composition is changed to a new calcium phosphate compound with the chemical formula of CaHPO4. A clear description of the transformations that occur on the surface of hydroxyapatite and of the interplay between these transformations and cell activity are two fundamental aspects of processes in which hydroxyapatite takes part, such as bone substitution, bone remodeling, osteoporosis and caries.

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.